Publications

 

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2017

309) Ultralight, thermally insulating, compressible polyimide fiber assembled sponges

Author(s): Jiang, S.; Uch, B.; Agarwal, S.; Greiner, A. Source: ACS Appl. Mater. Interfaces Volume: 9 Pages: 32308-32315 Published: 2017

Abstract: Tunable density, thermally and mechanically stable, elastic, and thermally insulating sponges are required for demanding applications. Hierarchically structured sponges with bimodal interconnected pores, porosity more than 99%, and tunable densities (between 7.6 and 10.1 mg/cm3) are reported using polyimide (PI) as high temperature stable polymer. The sponges are made by freeze-drying a dispersion of short PI fibers and precursor polymer, poly(amic acid) (PAA). The concept of “self-gluing” the fibrous network skeleton of PI during sponge formation was applied to achieve mechanical stability without sacrificing the thermal properties. The sponges showed initial degradation above 400 and 500 °C in air and nitrogen, respectively. They have low thermal conductivity of 0.026 W/mK and thermal diffusivity of 1.009 mm2/s for a density of 10.1 mg/cm3. The sponges are compressible for at least 10 000 cycles and good thermal insulators even at high compressions. These fibrous PI sponges are promising candidates for potential applications in thermal insulation, lightweight construction, high-temperature filtration, sensors, and catalyst carrier for high-temperature reactions.

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308) Exploration of macroporous polymeric sponges as drug carriers

Author(s): Duan, G.; Bagheri, A.; Jiang, S.; Golenser, J.; Agarwal, S.; Greiner, A. Source: Biomacromolecules DOI: 10.1021/acs.biomac.7b00852

Abstract: Achieving high drug loading capacity and controlling drug delivery are two main challenges related to drug carriers. In this study, polymeric macroporous sponges with very high pore volume and large porosity are introduced as a new-type of drug carrier. Due to the high pore volume (285 and 166 cm3/g for the sponges with densities of 3.5 and 6.0 mg/cm3, respectively), the sponges exhibit very high drug loading capacities with average values of 1870 ± 114 and 2697 ± 73 mg/g in the present study, which is much higher than the meso and microporous drug carriers (<1500 mg/g). In order to control the release profiles, an additional poly(p-xylylene) (PPX) coating was deposited by chemical vapor deposition on the drug loaded sponge. Consequently, Artemisone (ART) release in the aqueous medium could be retarded, depending on the density of the sponge and the thickness of the coating. In future, the new 3D polymeric sponges would be highly beneficial as drug carriers for the programmed release of drugs for treatment of chronic diseases.

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307) Fate of so-called biodegradable polymers in seawater and freshwater

Author(s): Bagheri, A.; Laforsch, C.; Greiner, A.; Agarwal, S. Source: Global Challenges Vol. 1 Issue 4 DOI: 10.1002/gch2.201700048 Published: 23. June 2017

Abstract:  The stability of polymers with C[BOND]C and stable C[BOND]heteroatom backbones against chemicals, hydrolysis, temperature, light, and microbes has challenged society with the problem of accumulation of plastic waste and its management worldwide. Given careless disposal of plastic waste, large amounts of plastic litter accumulate in the environment and disintegrate into microplastics. One of the questions frequently raised in the recent times is if so-called biodegradable polymers can substitute conventional polymers for several applications and help to tackle this challenge. The answer is not so simple as biodegradability is a certified property occurring only under certain environmental conditions and therefore requires systematic study. As a first step, this study focusses on comparative degradation studies of six polymers (five taken from the so-called biodegradable polyesters, including poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), polylactic acid (PLA), poly(3-hydroxybutyrate) (PHB), Ecoflex, and one well-known non-degradable polymer poly(ethylene terephthalate) (PET) in artificial seawater and freshwater under controlled conditions for 1 year. Only amorphous PLGA shows 100% degradation as determined by weight loss, change in molar mass with time, NMR, electron microscopy, and high-performance liquid chromatography. This is a step forward in understanding the degradability of polyesters required for the design of environmentally friendly novel polymers for future use.

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306) Low-density open cellular sponges as functional materials

Author(s): Jiang, S.; Agarwal, S.; Greiner, A. Source: Angew. Chem. Int. Ed. DOI: 10.1002/anie.201700684 Published: 2017

Abstract: Low density macroporous sponges with densities less than 100 mg cm-3 are a challenge and an opportunity in advanced chemistry and material science. The challenge lies in the precise preparation of the sponges with property combinations that lead to novel applications. Bottom-up and top-down chemical and engineering methods for preparation are a major focus of this review, with an emphasis on carbon and polymer materials. Light weight, sustainability, breathability, special wetting characteristics, large mass transfer, mechanical stability, and large pore volume are typical characteristics of sponges made of advanced materials and could lead to novel applications. Some selected sponge properties and potential applications are discussed.

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305) Elimination of Schistosoma mansoni in infected mice by slow release of artemisone

Author(s): Gold, D.; Alian, M.; Domb, A.; Karawani, Y.; Jbarien, M.; Chollet, J.; Haynes, R. K.; Wong, H. N.; Buchholz, V.; Greiner, A. Source: International Journal for Parasitology: Drugs and Drug Resistance Volume: 7 Pages: 241-247 DOI: 10.1016/j.ijpddr.2017.05.002 Published: 2017

Abstract: The current treatment of schistosomiasis is based on the anti-helminthic drug praziquantel (PZQ). PZQ affects only the adult stages of schistosomes. In addition, resistance to PZQ is emerging. We suggest a drug, which could serve as a potential alternative or complement to PZQ, and as a means of treating infections at earlier, pre-granuloma stage. Derivatives of the peroxidic antimalarial drug artemisinin have been indicated as alternatives, because both plasmodia and schistosomes are blood-feeding parasites. The mechanism of action of artemisinins is related to oxidative effects of the artemisinins on intracellular reductants leading to formation of cytotoxic reactive oxygen species. We used artemisone, which has improved pharmacokinetics and anti-plasmodial activity, and reduced toxicity compared to other artemisinins in clinical use against malaria. We infected adult mice by subcutaneous injection of S. mansoni cercariae (about 200) and treated them at various times post infection by the following methods: i. artemisone suspension administered by gavage (400–450 mg/kg); ii. subcutaneous injection of a gel containing a known concentration of artemisone (115–120 mg/kg); iii. subcutaneous insertion of the drug incorporated in a solid polymer (56–60 mg/kg); iv. intraperitoneal injection of the drug solubilized in DMSO (115–120 mg/kg). Drug administration in polymers was performed to enable slow release of the artemisone that was verified in vivo and in vitro bioassays using drug-sensitive malaria parasites. We found superior strong anti-schistosome effects up to a total reduction of worm number, mainly following repetitive treatments with the drug absorbed in the polymers (73.1% and 95.9% reduction in mice treated with artemisone in gel 7 and 14, and 21, 28 and 35 days post infection, respectively). The results indicate that artemisone has a potent anti-schistosome activity. Its main importance in this context is its effectiveness in treating hosts harboring juvenile schistosomes, before egg-deposition and induction of deleterious immune responses.

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304) Electrogenic single-species biocomposites as anodes for microbial fuel cells

Author(s): Kaiser, P.; Reich, S.; Leykam, D.; Willert-Porada, M.; Greiner, A.; Freitag, R. Source: Macromol. Biosci. Vol. 17 Issue 7 DOI: 10.1002/mabi.201600442 Published: 2017

Abstract: Integration of electrogenic microorganisms remains a challenge in biofuel cell technology. Here, synthetic biocomposites (“artificial biofilms”) are proposed. Bacteria (Shewanella oneidensis) are embedded in a hydrogel matrix (poly(vinyl alcohol)) via wet- and electrospinning, creating fibers and nonwoven gauzes. The bacteria remain viable and metabolically active. The performance is compared to S. oneidensis suspension cultures and “natural” biofilms. While lower than with the suspension cultures, the power output from the fuel cells with the artificial biofilms is higher than with the natural one. Handling, reproducibility, and stability are also better. Artificial biofilms can therefore contribute to resolving fundamental issues of design, scale up, and monosepsis in biofuel cell technology. 

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303) Biobased polycarbonate as a gas separation membrane and "breathing glass" for energy saving applications

Author(s): Hauenstein, O.; Rahman, Md. M.; Elsayed, M.; Krause-Rehberg, R.; Agarwal, S.; Abetz, V.; Greiner, A. Source: Adv. Mater. Technol. Vol. 2 Issue 5 DOI: 10.1002/admt.201700026 Published: 2017

Abstract: The biobased poly(limonene carbonate) (PLimC) synthesized by catalytic copolymerization of trans-limonene oxide and CO2 unifies sustainability, carbon capture and utilization of CO2 in one material. Films of PLimC show surprisingly high gas permeation and good selectivity. Additionally, it is not only very permeable to gases, but also to light, while simultaneously being a good heat insulator and mechanically strong, representing a novel type of material that is defined here as “breathing glass.” Hence, this study investigates the gas permeation and the selectivity in detail. The selectivity of PLimC for CO2 can be understood by its high fractional free volume, which is determined by positron annihilation lifetime spectroscopy supported by simulations. The CO2 permeability of PLimC at 30 °C is 68 barrer, while the CO2/N2 selectivity is ≈19, which places PLimC in a promising position in the Robeson plot and makes it unique due to its excellent transparency and processability under ambient conditions. Based on the high permeability of PLimC to gases and light, this study discusses here a completely new potential application of light transparent, gas-permeable polymer films as “breathing glass.”

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302) Ultralight sponges of poly(para-xylylene) by template-assisted chemical vapour deposition

Author(s): Moss, T.; Paulus, I. E.; Raps, D.; Altstädt, V.; Greiner, A. Source: e-polymers DOI: https://doi.org/10.1515/epoly-2016-0329 Published: 2017

Abstract: Particle foams and open cell sponges play nowadays an important role in academia and industrial research. The fabrication of new high-performance foams is one of the challenges. Until now, it is impossible to visualise the quality of particle foams, and the quantification is only possible with expensive analytical methods like scanning electron microscopy. In this work, we demonstrate a simple method for the visualisation of void sizes and defects inside particle foams on the basis of expanded polystyrene. The concept was transferred to porous materials, which work as templates for the formation of ultralight poly(para-xylylene) foams with stunning properties.

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301) Spongy gels by a top-down approach from polymer fibrous sponges

Author(s): Jiang, S.; Duan, G.; Kuhn, U.; Mörl, M.; Altstädt, V.; Yarin, A. L.; Greiner, A. Source: Angew. Chem. Int. Ed. Volume: 56 Pages: 3285-3288 DOI: 10.1002/anie.201611787 Published: 2017

Abstract: Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge.

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300) Controlled release of artemisone for the treatment of experimental cerebral malaria

Author(s): Golenser, J.; Buchholz, V.; Bagheri, A.; Nasereddin, A.; Dzikowski, R.; Guo, J.; Hunt, N.; Eyal, S.; Vakruk, N.; Greiner, A. Source: Parasites & Vectors Volume: 10:117 DOI: 10.1186/s13071-017-2018-7 Published: MAR 2017

Abstract: Cerebral malaria (CM) is a leading cause of malarial mortality resulting from infection by Plasmodium falciparum. Treatment commonly involves adjunctive care and injections or transfusion of artemisinins. All artemisinins that are in current use are metabolized to dihydroxyartemisinin (DHA), to which there is already some parasite resistance. We used artemisone, a derivative that does not convert to DHA, has improved pharmacokinetics and anti-plasmodial activity and is also anti-inflammatory (an advantage given the immunopathological nature of CM). We examined controlled artemisone release from biodegradable polymers in a mouse CM model. This would improve treatment by exposing the parasites for a longer period to a non-toxic drug concentration, high enough to eliminate the pathogen and prevent CM. The preparations were inserted into mice as prophylaxis, early or late treatment in the disease course. The most efficient formulation was a rigid polymer, containing 80 mg/kg artemisone, which cured all of the mice when used as early treatment and 60% of the mice when used as a very late treatment (at which stage all control mice would die of CM within 24 h). In those mice that were not completely cured, relapse followed a latent period of more than seven days. Prophylactic treatment four days prior to the infection prevented CM. We also measured the amount of artemisone released from the rigid polymers using a bioassay with cultured P. falciparum. Significant amounts of artemisone were released throughout at least ten days, in line with the in vivo prophylactic results. Overall, we demonstrate, as a proof-of-concept, a controlled-sustained release system of artemisone for treatment of CM. Mice were cured or if treated at a very late stage of the disease, depicted a delay of a week before death. This delay would enable a considerable time window for exact diagnosis and appropriate additional treatment. Identical methods could be used for other parasites that are sensitive to artemisinins (e.g. Toxoplasma gondii and Neospora caninum).
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299) Unlocking nanocarriers for the programmed release of antimalarial drugs

Author(s): Bagheri, A.; Agarwal, S.; Golenser, J.; Greiner, A.; Source: Global Challenges Volume: 1 Issue: 2 DOI: 10.1002/gch2.201600011 Published: FEB 2017

Abstract: A programmable release system with wide range of release profiles of the antimalarial artemisone (ART) from fibrous nanocarriers (NFN) is presented. This is achieved following a new paradigm of using ART-loaded NFN in infusion system of hydrophobic drug eluting nanocarriers, adapted to clinical applications. Very importantly, under these conditions ART did not degrade as it was observed in solution.  

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298) Biosorption of copper from aqueous environments by micrococcus luteus in cell suspension and when encapsulated

Author(s): Letnik, I.; Avrahami, R.; Port, R.; Greiner, A.; Zussman, E.; Rokem, J. S.; Greenblatt, C. Source: International Biodeterioration & Biodegradation Volume: 116 Pages: 64-72 DOI: 10.1016/j.ibiod.2016.09.029

Abstract: The ability to sequester or tolerate copper has been described for a number of bacteria. It was shown that
Micrococcus luteus tolerates copper, and possible mechanisms of uptake for this bacterium have been
proposed. Using a count live of M. luteus (CFU), 10% survived a copper concentration of 370 ppm.
Maximum sorption capacity was 59 mg of Cu2þ/g of dry cells at pH 6. Several proteins of M. luteus with
copper affinity were identified by enrichment on a metal-chelating resin followed by LC-MS/MS to
identify the metallome. Use of SEM/EDX showed how copper concentrated on the bacterial surface,
whereas TEM indicated that copper was found also inside the cells. The enhanced capability of M. luteus
to bind copper was tested using three configurations: free cells on an agar surface and cells encapsulated
in alginate or in electrospun polymer composites. The latter showed the highest capability to bind copper
(~76 mg Cu2þ/g dry cells). Such polymer composites may potentially be used in various water-based
applications such as treatment of wastewater with a high concentration of copper or other heavy metals.

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297) Bottom-up meets top-down: Patchy hybrid nonwovens as an efficient catalysis platform

Author(s): Schöbel, J.; Burgard, M.; Hills, C.; Dersch, R.; Dulle, M.; Volk, K.; Karg, M.; Greiner, A.; Schmalz, H. Source: Angewandte Chemie Volume: 56 Issue: 1 Pages 405-408 DOI: 10.1002/anie.201609819

Abstract: Heterogeneous catalysis with supported nanoparticles (NPs) is a highly active field of research. However, the efficient stabilization of NPs without deteriorating their catalytic activity is challenging. By combining top-down (coaxial electrospinning) and bottom-up (crystallization-driven self-assembly) approaches, we prepared patchy nonwovens with functional, nanometer-sized patches on the surface. These patches can selectively bind and efficiently stabilize gold nanoparticles (AuNPs). The use of these AuNP-loaded patchy nonwovens in the alcoholysis of dimethylphenylsilane led to full conversion under comparably mild conditions and in short reaction times. The absence of gold leaching or a slowing down of the reaction even after ten subsequent cycles manifests the excellent reusability of this catalyst system. The flexibility of the presented approach allows for easy transfer to other nonwoven supports and catalytically active NPs, which promises broad applicability.

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2016

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296) Tensile versus AFM testing of electrospun PVA nanofibers: bridging the gap from microscale to nanoscale

Author(s): Neugirg, BR (Neugirg, Benedikt R.); Burgard, M (Burgard, Matthias); Greiner, A (Greiner, Andreas); Fery, A (Fery, Andreas)
Source: JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS  Volume: 54  Issue: 23  Pages: 2418-2424  DOI: 10.1002/polb.24225  Published: DEC 2016

Abstract: Design and application of mechanically extraordinary nanofibers requires their full comprehension, based on conclusive testing methods. Electrospun polymer nanofibers, for instance, show a progressive and pronounced increase in their Young's moduli when diameters decrease below the µm scale. Measurement of mechanical properties in this diameter range is challenging and in the vast majority of reports, two classes of methods are commonly used: highly sensitive tensile testing and atomic force microscopy three-point deformation testing. Despite the methods' inherent dissimilarity, we resolve their conformity for the first time, with respect to the determination of Young's moduli. Here, we benchmark them against each other for electrospun polyvinyl-alcohol nanofibers, a well-defined model system. Our results provide an experimental basis for a comprehensive understanding of nanofiber structures and its implications on their mechanical properties.

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295) Polyimide nanofibers by „green“ electrospinning via aqueous solution for filtration applications

Author(s): Jiang, SH (Jiang, Shaohua); Hou, HQ (Hou, Haoqing); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas) Source: ACS SUSTAINABLE CHEMISTRY & ENGINEERING Volume: 4  Issue: 9  Pages: 4797-4804  DOI: 10.1021/acssuschemeng.6b01031  Published: SEP 2016 
Abstract: The use of large amounts of environmentally unfriendly, toxic, and flammable organic solvents in electrospinning of polymers puts demand on the development of new methods and formulations for making water stable hydrophobic nanofibers from water-soluble precursor solution. Electrospun polyimide (PI) nanofibers are of particular interest for a variety of applications due to their extraordinary thermal and chemical stability. However, the intermediate precursor of polyimide, the polyamic acid (PAA) has to be electrospun from harmful solvents like dimethylformamide (DMF) which is a serious obstacle for technical applications of electrospun PI. This work highlights the formation of PI nanofibers by "green" electrospinning of ammonium salts of PAA from water. The high temperature used for imidization in the second step also removed ammonia and the template polymer by sintering giving PI nanofibers with diameter 295 +/- 58 nm. The thus obtained PI nanofibers by "green" electrospinning were defined as "green" PI nanofibers. Aerosol filtration of "green" PI nanofibers showed a performance that was very similar to PI nanofibers obtained by electrospinning of PAA from DMF. Additionally, it has been shown that the "green" PI nanofibers were suitable for the filtration of hot oil as well.

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294) Wie Mikroorganismen und Elektroden interagieren

Author(s): Schröder, U.; Greiner, A.; Rosenbaum, M. A.; Harnisch, F. Source: Nachrichten aus der Chemie Volume: 64 Pages: 732-737 2016 DOI: DOI: 10.1002/nadc.20164044968

Die Verknüpfung von Elektrochemie und Mikrobiologie ist Forschung mit Anwendungspotenzial: von der Energiegewinnung aus Abwasser bis zur Synthese von Chemikalien. Wichtige Rollen spielen Elektrochemie, Mikrobiologie und Materialwissenschaften.

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293) Hierarchically Structured Poly(alkyl-p-xylylene) Nonwovens with Superhydrophobic Properties

Author(s): Paulus, IE (Paulus, Ilka E.); Moss, T (Moss, Tobias); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 301  Issue: 10  Pages: 1225-1231  DOI: 10.1002/mame.201600140  Published: OCT 2016  
Abstract: Hierarchically structured poly(alkyl-p-xylylene) (alkyl-PPX) nonwovens are prepared by specific parameter variation during the electrospinning process. The investigated parameters are changes in solutions properties and ambient humidity level, which lead to the formation of different fiber architectures and surface morphologies. The characterization of the nonwovens by scanning electron microscopy confirms the formation of hierarchically structured fibers, comprising bead-on-string architecture if spun from tetra hydrofuran (THF) solutions, and porous surfaces at relative humidity (RH) levels > 30% for both chloroform and THF solutions. The wetting properties of nonwovens spun from THF and chloroform solutions are analyzed by water contact angle (CA) measurements, roll-angle determination, and high speed imaging. PPX-heptyl and PPX-butyl fiber mats spun from 2.5 wt% THF and PPX-heptyl spun from 3 wt% chloroform solutions at RH > 75% show superhydrophobic and self-cleaning properties with CA > 153 and roll-off angles of 10-15 degrees. The nonwovens maintain their fiber morphology and water-repellent properties after thermal and mechanical stress.

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292) Assembly of gold nanoparticles on gold nanorods using functionalized poly(n-isopropylacrylamide) as polymeric “glue”

Author(s): Fan, ZY (Fan, Ziyin); Tebbe, M (Tebbe, Moritz); Fery, A (Fery, Andreas); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas) Source: PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION Volume: 33  Issue: 9  Pages: 698-702  DOI: 10.1002/ppsc.201600081  Published: SEP 2016

Abstract: A telechelic thermoresponsive polymer, α-amino-ω-thiol-poly(N-isopropylacrylamide) (H2N-PNiPAM-SH), is used as the polymeric glue to assemble gold nanoparticles (AuNPs) around gold nanorods (AuNRs) into a satellite structure. Prepared by reversible addition-fragmentation chain transfer polymerization followed by hydrazinolysis, H2N-PNiPAM-SH is able to interlink the two types of the gold building blocks with the thiol-end grafting on AuNRs and the amine-end coordinating on the AuNP surface. The density of the grafted AuNPs on AuNRs can be tuned by adjusting the molar ratio between AuNPs and AuNRs in the feed. The resulted satellite-like assembly exhibits unique optical property that was responsive to temperature change.

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291) Bio-based polycarbonate as synthetic toolbox

Author(s): Hauenstein, O; Agarwal, S; Greiner, A Source: Nature communications Volume: 7 Pages: 11862
DOI: 10.1038/ncomms11862 Published: 2016 Jun 15
Abstract: Completely bio-based poly(limonene carbonate) is a thermoplastic polymer, which can be synthesized by copolymerization of limonene oxide (derived from limonene, which is found in orange peel) and CO2. Poly(limonene carbonate) has one double bond per repeating unit that can be exploited for further chemical modifications. These chemical modifications allow the tuning of the properties of the aliphatic polycarbonate in nearly any direction. Here we show synthetic routes to demonstrate that poly(limonene carbonate) is the perfect green platform polymer, from which many functional materials can be derived. The relevant examples presented in this study are the transformation from an engineering thermoplastic into a rubber, addition of permanent antibacterial activity, hydrophilization and even pH-dependent water solubility of the polycarbonate. Finally, we show a synthetic route to yield the completely saturated counterpart that exhibits improved heat processability due to lower reactivity. 

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290) Protection of vine plants against Esca disease by breathable electrospun antifungal nonwovens

Author(s): Buchholz, V (Buchholz, Viola); Molnar, M (Molnar, Melanie); Wang, H (Wang, Hui); Reich, S (Reich, Steffen); Agarwal, S (Agarwal, Seema); Fischer, M (Fischer, Michael); Greiner, A (Greiner, Andreas) Source: MACROMOLECULAR BIOSCIENCE  Volume: 16  Issue: 9  Pages: 1391-1397  DOI: 10.1002/mabi.201600118  Published: SEP 2016

Abstract: The harmful Esca disease in vine plants caused by wood-inhabiting fungi including Phaeomoniella chlamydospora (Pch) is spreading all across the world. This disease leads to poor vine crops and a slow decline or to a sudden dieback of the vine plants. The pruning wounds of vine plants are the main entry point for Pch. While model experiments with aerosol particles recommend electrospun nonwovens as a suitable barrier to block Pch, tests with living spores show clearly that only electrospun fibrous nonwovens do not prevent Pch invasion. However it is found, that with antifungal additives electrospun nonwovens could be applied successfully for blocking of Pch to infect the substrate. Thereby, a highly useful concept for the protection of vine plants against Esca disease is provided which could also serve as a concept for related plant diseases. 

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289) Ultralight open cell polymer sponges with advanced properties by PPX CVD coating

Author(s): Duan, GG (Duan, Gaigai); Jiang, SH (Jiang, Shaohua); Moss, T (Moss, Tobias); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas) Source: POLYMER CHEMISTRY  Volume: 7  Issue: 15  Pages: 2759-2764  DOI: 10.1039/c6py00339g  Published: 2016  
Abstract: Ultralight polyacrylate sponges were prepared from dispersions of short electrospun polymer fibres by freeze drying and coated with poly(p-xylylene) (PPX) by chemical vapour deposition (CVD). The PPX coating of the sponges increased the compression strength, the water contact angle, and the solvent resistance significantly without significant alteration of the sponge morphology.
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288) Patchy Wormlike Micelles with Tailored Functionality by Crystallization-Driven Self-Assembly: A Versatile Platform for Mesostructured Hybrid Materials

Author(s): Schobel, J (Schoebel, Judith); Karg, M (Karg, Matthias); Rosenbach, D (Rosenbach, Dominic); Krauss, G (Krauss, Gert); Greiner, A (Greiner, Andreas); Schmalz, H (Schmalz, Holger) Source: MACROMOLECULES  Volume: 49  Issue: 7  Pages: 2761-2771  DOI: 10.1021/acs.macromol.6b00330  Published: APR 12 2016  
Abstract: One-dimensional patchy nanostructures are interesting materials due to their excellent interfacial activity and their potential use as carrier for functional nanoparticles. Up to now only wormlike crystalline-core micelles (wCCMs) with a nonfunctional patchy PS/PMMA corona were accessible using crystallization-driven self-assembly (CDSA) of polystyrene-block-polyethylene-block-poly(methyl methacrylate) (SEM) triblock terpolymers. Here, we present a facile approach toward functional, patchy wCCMs, bearing tertiary amino groups in one of the surface patches. The corona forming PM1VLA. block of a SEM triblock terpolymer was functionalized by amidation with different N,N-dialkylethylenediamines in a polymer analogous fashion. The CDSA of the functionalized triblock terpolymers in THE was found to strongly depend on the polarity/solubility of the amidated PMMA block. The lower the polarity of the amidated PMMA block (increased solubility), the higher is the accessible degree of functionalization upon which defined, well-dispersed wCCMs are formed. Interestingly, also the structure of the patchy corona can be tuned by the composition/chemistry of the functional patch, giving rise to spherical patches for R = methyl, ethyl and rectangular patches for R = isopropyl. Patchy wCCMs were successfully used as template for the selective incorporation of Au nanoparticles within the amidated corona patches, showing their potential as versatile platform for the construction of functional, mesostructured hybrid materials.

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287) Quantitative comparison of the antimicrobial efficiency of leaching versus nonleaching polymer materials                                                                                                                                                                                                   By: Bruenke, J (Bruenke, Joerg); Roschke, I (Roschke, Ingolf); Agarwal, S (Agarwal, Seema); Riemann, T (Riemann, Thomas); Greiner, A (Greiner, Andreas) Source: MACROMOLECULAR BIOSCIENCE Volume: 16 Issue: 5 Pages: 647-654 DOI: 10.1002/mabi.201500266 Published: MAY 2016
Abstract: New antimicrobial materials will be more and more in the focus for hygienic and clinical disease control. Antimicrobial materials have to be distinguished in leaching and nonleaching materials. For many applications of antimicrobial materials on implants the use of nonleaching materials is essential. Therefore, the antimicrobial efficiency of leaching and nonleaching polymers has been investigated quantitatively in vitro in direct comparison on a highly relevant implant of central venous catheters (CVCs) using a well-established called Certika test. This test is especially designed to test antimicrobial properties of leachable and nonleachable materials. This contribution demonstrates that newly developed nonleaching antimicrobial CVCs are equivalent to conventional leaching CVC systems in their antimicrobial performance against gram-positive and gram-negative bacteria, as well as Candida species. The use of new nonleaching antimicrobial polymers as shown here for CVCs represents a different mode of action with the aim to prevent infections also with antibiotic-resistant strains and reduced side effects.
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286) Supramolecular Nanocomposites: Dual-Functional Cholesteric Hydroxypropyl Cellulose Esters Chemically Linked to Gold Nanoparticles
Author(s): Ohlendorf, P (Ohlendorf, Peter); Dulle, M (Dulle, Martin); Forster, S (Foerster, Stephan); Greiner, A (Greiner, Andreas)
Source: CHEMNANOMAT  Volume: 2  Issue: 4  Pages: 290-296  DOI: 10.1002/cnma.201600042 Published: APR 2016  
Abstract: Functionalization of metal nanoparticles with liquid crystal polymers (LCP) is attractive for the formation of supramolecular structures with unique physical properties. We discovered that the chemical linkage of a liquid crystalline thiolated cellulose ester (HPC-MTP_80) to gold nanoparticles (AuNP) leads, by control of the supramolecular structure, to a novel concept for functional materials with practical applications. At a critical concentration ratio of only 1.7 mol% HPC-MTP_80, on average, only single HPC-MTP_80 functionalized AuNP exist, forming a LC phase. Pure HPC-MTP_80 forms a cholesteric phase with a pitch in the range of visible light. The slow pitch formation enables usage as a protective sealing material. This property in combination with the temperature dependence of the pitch makes HPC-MTP_80 a perfect sensor for temperature monitoring of sensitive products like valuable pharmaceutics. Even the presence of very small amounts of functionalized AuNP in the nanocomposite suppress the pitch formation in the range of visible light, providing access for a possible application as a sensitive AuNP detector.

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285) Wet-Laid Meets Electrospinning: Nonwovens for Filtration Applications from Short Electrospun Polymer Nanofiber Dispersions
Author(s): Langner, M (Langner, Markus); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS Volume: 37 Issue: 4 Pages: 351-355 DOI: 10.1002/marc.201500514 Published: FEB 2016
Abstract: Dispersions of short electrospun fibers are utilized for the preparation of nanofiber nonwovens with different weight area on filter substrates. The aerosol filtration efficiencies of suspension-borne nanofiber nonwovens are compared to nanofiber nonwovens prepared directly by electrospinning with similar weight area. The filtration
efficiencies are found to be similar for both types of nonwovens. With this, a large potential opens for processing, design, and application of new nanofiber nonwovens obtained by wet-laying of short electrospun nanofiber suspensions.

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284) Synthesis and Enzymatic Degradation of Soft Aliphatic Polyesters
Author(s): Buchholz, V (Buchholz, Viola); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR BIOSCIENCE Volume: 16 Issue: 2 Pages: 207-213 DOI: 10.1002/mabi.201500279 Published: FEB 2016
Abstract: Novel aliphatic enzymatically degradable polyesters with short alkyl side chains for tuning crystallinity are presented in this work. The intrinsic problem of aliphatic polyesters is their brittleness and tendency to crystallize. This was modulated by the synthesis of random copolyesters based on aliphatic linear monomers, adipic acid, 1,5-pentanediol and monomers with aliphatic branches, such as 2-butyl-2-ethyl-1,3-propanediol by polycondensation. The resulting copolyesters were crystalline, wax-like or had liquid texture with varied mechanical properties and enzymatic degradability depending upon the copolymer composition. Such polyesters are of significant interest for a wide range of possible applications such as controlled drug delivery, agricultural applications and as packing materials.

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283) Self-Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness
Author(s): Serrano, MSK (Serrano, Melissa S. Koehn); Konig, TAF (Koenig, Tobias A. F.); Haataja, JS (Haataja, Johannes S.); Lobling, TI (Lobling, Tina I.); Schmalz, H
(Schmalz, Holger); Agarwal, S (Agarwal, Seema); Fery, A (Fery, Andreas); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS Volume: 37 Issue: 3 Pages: 215-220 DOI: 10.1002/marc.201500509 Published: FEB 2016
Abstract: Gold nanoparticles (AuNP) with pyridyl end-capped polystyrenes (PS-4VP) as quasi-monodentate ligands self-assemble into ordered PS-4VP/AuNP nanostructures with 3D hexagonal spatial order in the dried solid state. The key for the formation of these ordered structures is the modulation of the ratio AuNP versus ligands, which proves the importance of ligand design and quantity for the preparation of novel ordered polymer/metal nanoparticle conjugates. Although the assemblies of PS-4VP/AuNP in dispersion lack in high dimensional order, strong plasmonic interactions are observed due to close contact of AuNP. Applying temperature as an external stimulus allows the reversible distortion of plasmonic interactions within the AuNP nanocomposite structures, which can be observed directly by naked eye. The modulation of the macroscopic optical properties accompanied by this structural distortion of plasmonic interaction opens up very interesting sensoric applications.
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282) Bio-based polycarbonate from limonene oxide and CO2 with high molecular weight, excellent thermal resistance, hardness and transparency
Author(s): Hauenstein, O (Hauenstein, O.); Reiter, M (Reiter, M.); Agarwal, S (Agarwal, S.); Rieger, B (Rieger, B.); Greiner, A (Greiner, A.)
Source: GREEN CHEMISTRY Volume: 18 Issue: 3 Pages: 760-770 DOI: 10.1039/c5gc01694k Published: 2016
Abstract: Completely bio-based, high molecular weight (>100 kDa) poly(limonene carbonate) (PLimC) with attractive thermal (glass transition temperature, T-g = 130 degrees C) and optical properties (transmission 94%, haze 0.75%) was prepared by coupling bio-based limonene oxide (LO) and carbon dioxide (CO2) using a beta-diiminate zinc catalyst (bdi)Zn(OAc). The molar mass of the polymer could be controlled by changing the ratio of catalyst and monomer, keeping molar mass dispersities low. The synthesis of the LO with very high content (> 85%) of trans-isomer and absence of impurities with hydroxyl functionality was also established, which was necessary to obtain a high molar mass of polymer and almost quantitative conversion of epoxide during polymerisation. The upscaled syntheses of both the monomer and the polymer (>1 kg per batch) were readily realised, suggesting an easy transfer to pilot plant scale. The polymerisation kinetics were studied suggesting a second order dependence on LO concentration, wherefrom a mechanism is proposed with an alternating insertion of LO and CO2. The effect of chain-ends on the thermal stability of PLimC was studied with a thermal desorption unit coupled with gas chromatography-mass spectrometry (GC-MS) experiments. PLimC with thermal stability as high as 240 degrees C could be achieved using appropriate end-capping agents. PLimC is characterised by excellent transparency and hardness.

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281) Chemical vapour deposition of soluble poly(p-xylylene) copolymers with tuneable properties
Author(s): Paulus, IE (Paulus, Ilka E.); Heiny, M (Heiny, Markus); Shastri, VP (Shastri, V. Prasad); Greiner, A (Greiner, Andreas)
Source: POLYMER CHEMISTRY Volume: 7 Issue: 1 Pages: 54-62 DOI: 10.1039/c5py01343g Published: 2016
Abstract: Chemical vapour deposition (CVD) is a technique widely applied for the synthesis of thin and highly conformal polymer coatings. The copolymerization of poly(1,4-xylylene)s (PPX), with 2-hydroxyethyl methacrylate (HEMA) via CVD revives a hardly investigated field of PPX chemistry. The use of alkyl substituted [2.2]paracyclophanes leads to soluble PPX-copolymers. Proof of copolymerization was obtained by correlation of both monomer units in H-1, C-13-HMBC 2D-NMR spectra. Next, insoluble p(PX-N-co-HEMA) copolymers were synthesized in a modified commercially available SCS Labcoater. The availability of the hydroxy ester functionality of HEMA on the film surface was indirectly confirmed by the reduction of water contact angles down to 65 degrees. Preliminary studies using human umbilical vein endothelial cells (HUVEC) indicate the cytocompatibility of as deposited p(PX-N-co-HEMA) films.

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2015

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280) Polymer cages as universal tools for the precise bottom-up synthesis of metal nanoparticles
Author(s): Fan, Z (Fan, Ziyin); Chen, X (Chen, Xuelian); Serrano, MK (Serrano, Melissa Kohn); Schmalz, H (Schmalz, Holger); Rosenfeldt, S (Rosenfeldt, Sabine); Forster, S (Foerster, Stephan); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 54  Issue: 48  Pages: 14539-14544  DOI: 10.1002/ange.201506415  Published: NOV 23 2015  
Abstract: A template synthesis allows the preparation of monodisperse nanoparticles with high reproducibility and independent from self-assembly requirements. Tailor-made polymer cages were used for the preparation of nanoparticles, which were made of cross-linked macromolecules with pendant thiol groups. Gold nanoparticles (AuNPs) were prepared in the polymer cages in situ, by using different amounts of cages versus gold. The polymer cages exhibited a certain capacity, below which the AuNPs could be grown with excellent control over the size and shape. Control experiments with a linear diblock copolymer showed a continuous increase in the AuNP size as the gold feed increased. This completely different behavior regarding the AuNP size evolution was attributed to the flexibility of the polymer chain depending on cross-linking. Moreover, the polymer cages were suitable for the encapsulation of AgNPs, PdNPs, and PtNPs by the in situ method.
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279) Large multipurpose exceptionally conductive polymer sponges obtained by efficient wet-chemical metallization
Author(s): Langner, M; Agarwal, S; Baudler, A; Schroder, U; Greiner, A
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 25  Issue: 39  Pages: 6182-6188  DOI: 10.1002/adfm.201502636  Published: OCT 21 2015  
Abstract: Exceptionally conductive (250 S cm(-1)), very fast electrically heatable, thermally insulating, antimicrobial 3D polymeric sponges with very low density (approximate to 30 mg cm(-3)), superhydrophobicity, and high porosity, their method of preparation, and manifold examples for applications are presented here. The electrical heatability is reversible, reaching 90 degrees C with 4.4 W in about 19-20 s and cooling immediately on switching off the voltage. The sponges show high contact angles >150 degrees against water on the sponge surface as well as inside the sponge. Water droplets injected into the sponges are ejected. A facile wet-chemical method established for macroscopic melamine-formaldehyde sponges is the key for the thorough in-depth surface metallization of the sponges. The coating thickness and uniformity depend on the metallization formulation, conditions of metallization, and the type of metal used. A scanning electron microscope is used for morphology characterization. A reduced metallization rate in air is highly critical for the in-depth uniform coating of metals. The resulting metallized sponges could be highly interesting for heating as well as insulation devices in addition to oil/water separation membranes.
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278) Living composites of electrospun yeast cells for bioremediation and ethanol production
Author(s): Letnik, I; Avrahami, R; Rokem, JS; Greiner, A; Zussman, E; Greenblatt, C
Source: BIOMACROMOLECULES  Volume: 16  Issue: 10  Pages: 3322-3328  DOI: 10.1021/acs.biomac.5b00970  Published: OCT 2015  
Abstract: The preparation of composites of living functional cells and polymers is a major challenge. We have fabricated such "living composites" by preparation of polymeric microtubes that entrap yeast cells. Our approach was the process of coaxial electrospinning in which a core containing the yeast was "spun" within a shell of non-biodegradable polymer. We utilized the yeast Candida tropicalis, which was isolated from olive water waste. It is particularly useful since it degrades phenol and other natural polyphenols, and it is capable of accumulating ethanol. The electrospun yeast cells showed significant activity of bioremediation of phenol and produced ethanol, and, in addition, the metabolic processes remained active for a prolonged period. Comparison of electrospun cells to planktonic cells showed decreased cell activity; however, the olive water waste after treatment by the yeast was no longer toxic for Escherichia coli, suggesting that detoxification and prolonged viability and activity may outweigh the reduction of efficiency.
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277) Living composites of bacteria and polymers as biomimetic films for metal sequestration and bioremediation
Author(s): Knierim, C (Knierim, Christian); Enzeroth, M (Enzeroth, Michaela); Kaiser, P (Kaiser, Patrick); Dams, C (Dams, Christian); Nette, D (Nette, David); Seubert, A (Seubert, Andreas); Klingl, A (Klingl, Andreas); Greenblatt, CL (Greenblatt, Charles L.); Jerome, V (Jerome, Valerie); Agarwal, S (Agarwal, Seema); Freitag, R (Freitag, Ruth); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR BIOSCIENCE Volume: 15  Issue: 8  Pages: 1052-1059  DOI: 10.1002/mabi.201400538  Published: AUG 2015  
Abstract: Herein, we report on composite materials of biologically active microorganisms placed in a synthetic polymer matrix. These so-called "living composites" were utilized for gold sequestration (Micrococcus luteus) and bioremediation of nitrite (Nitrobacter winogradskyi) to demonstrate functionality. For the preparation of the living composites the bacteria were first encased in a water-soluble polymer fiber (poly(vinyl alcohol), PVA) followed by coating the fibers with a shell of hydrophobic poly(p-xylylene) (PPX) by chemical vapor deposition (CVD). The combination of bacteria with polymer materials assured the stability and biologically activity of the bacteria in an aqueous environment for several weeks.
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276) Highways for ions in polymers-3D-imaging of electrochemical interphase formation
Author(s): Wesp, V (Wesp, Veronika); Zakel, J (Zakel, Julia); Schafer, M (Schaefer, Martin); Paulus, I (Paulus, Ilka); Greiner, A (Greiner, Andreas); Weitzel, KM (Weitzel, Karl-Michael)
Source: ELECTROCHIMICA ACTA  Volume: 170  Pages: 122-130  DOI: 10.1016/j.electacta.2015.04.117  Published: JUL 10 2015  
Abstract: The formation of a cesium interphase in-between a polymer film and a platinum electrode has been initiated by low energy bombardment induced ion transport. To this end two different samples of a poly (p-xylylene)(PPX) film, deposited on a platinum electrode have been bombarded by a low energy cesium ion beam. Ions are transported through the film according to the laws of electro-diffusion. They are neutralized at the interface between the PPX film and the metal electrode. Consequently, a cesium interphase is formed. 3D imaging of the interphase by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) reveals a correlation between structural characteristics of the interphase and conduction properties of the PPX film. The bombardment of PPX films consisting of a homogenous network leads to the formation of a uniform interphase. The bombardment of PPX films with nonintermittent pathways (NIPs) for the transport of ions leads to the formation of cesium islands which ultimately spread out laterally leading to a non-uniform interphase behind the PPX film. This picture is supported by measurements of the ionic conductivity which differs characteristically for the two kinds of PPX films. (C) 2015 Elsevier Ltd. All rights reserved.
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275) Polymer/Nanoparticle Hybrid Materials of Precise Dimensions by Size-Exclusive Fishing of Metal Nanoparticles
Author(s): Fan, ZY (Fan, Ziyin); Serrano, MK (Serrano, Melissa Koehn); Schaper, A (Schaper, Andreas); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ADVANCED MATERIALS  Volume: 27  Issue: 26  Pages: 3888-+  DOI: 10.1002/adma.201501306  Published: JUL 8 2015  
Abstract: Polymer cages prepared by etching of gold nanoparticles from polymer templates by the "grafting around" method are designed for selective separation of metal nanoparticles. The separation process is demonstrated as a fast biphasic ligand exchange reaction. The high separation efficiency and size selectivity of the polymer cage is verified by comparison with the linear block copolymer.
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274) Reversible gold nanorod alignment in mechano-responsive elastomers
Author(s): Pletsch, H (Pletsch, Holger); Tebbe, M (Tebbe, Moritz); Dulle, M (Dulle, Martin); Forster, B (Foerster, Beate); Fery, A (Fery, Andreas); Forster, S (Foerster, Stephan); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: POLYMER  Volume: 66  Pages: 167-172  DOI: 10.1016/j.polymer.2015.04.037  Published: JUN 1 2015  
Abstract: Inspired by an increasing demand for stimuli-controlled assembly of nanostructures, mechano-responsive nanocomposites are designed with tremendous scope in material applications. Providing switchable properties by means of mechanical stimulation, elastomer-incorporated gold nanorods (AuNR) are presented herein. Stepless and reversible control over the orientational AuNR alignment and therefore over macroscopic anisotropy - is exerted by uniaxial film elongation. In context of optical applications, substantial impact on the plasmonic properties within adjustable spectral ranges is demonstrated. Mechano-responsive nanocomposites with high thermal colloidal stability are prepared via a facile hetero-phase ligand exchange procedure where complete coverage of the AuNR surface with hydrophobic ligands is achieved. (C) 2015 Elsevier Ltd. All rights reserved.
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273) Ultralight, Soft Polymer Sponges by Self-Assembly of Short Electrospun Fibers in Colloidal Dispersions
Author(s): Duan, GG (Duan, Gaigai); Jiang, SH (Jiang, Shaohua); Jerome, V (Jerome, Valerie); Wendorff, JH (Wendorff, Joachim H.); Fathi, A (Fathi, Amir); Uhm, J (Uhm, Jaqueline); Altstadt, V (Altstaedt, Volker); Herling, M (Herling, Markus); Breu, J (Breu, Josef); Freitag, R (Freitag, Ruth); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 25  Issue: 19  Pages: 2850-2856  DOI: 10.1002/adfm.201500001  Published: MAY 20 2015  
Abstract: Ultralight polymer sponges are prepared by freeze-drying of dispersions of short electrospun fibers. In contrast to many other highly porous materials, these sponges show extremely low densities (<3 mg cm(-3)) in combination with low specific surface areas. The resulting hierarchical pore structure of the sponges gives basis for soft and reversibly compressible materials and to hydrophobic behavior in combination with excellent uptake for hydrophobic liquids. Owing to their large porosity, cell culturing is successful after hydrophilic modification of the sponges.
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272) Modified vibrating-mesh nozzles for advanced spray-drying applications
Author(s): Beck-Broichsitter, M (Beck-Broichsitter, Moritz); Paulus, IE (Paulus, Ilka E.); Greiner, A (Greiner, Andreas); Kissel, T (Kissel, Thomas)
Source: EUROPEAN JOURNAL OF PHARMACEUTICS AND BIOPHARMACEUTICS  Volume: 92  Pages: 96-101  DOI: 10.1016/j.ejpb.2015.03.001  Published: MAY 2015  
Abstract: This work describes uniform polymer coatings allowing for an adjustment of the orifice dimension of vibrating-mesh nozzles and therefore, size of emerging formulation droplets and dried particles, which is of general interest for diverse spray-drying applications.
Chemical vapor deposition of poly(p-xylylene) (PPXN) on aperture templates of the B-90 spray-dryer (orifice diameters: similar to 4.0 mu m) caused a reduction of the opening cross-sections of similar to 50%. Thus, a more efficient formulation atomization was observed (finer droplets). Likewise, application of PPXN-coated, rather than plain nozzles, resulted in significantly smaller (particle diameter: 1.3 vs. 3.6 mu m) and narrower distributed (span: similar to 1.4 vs. similar to 1.8) sildenafil-loaded poly(lactide-co-glycolide) microparticles. Prediction of the size of spray-dried microparticles using the size results of atomized droplets ("residual core method") was shown to be in agreement with the observed values. Formulations prepared with plain and PPXN-coated nozzles exhibited a sustained sildenafil release profile with mean dissolution times of similar to 1.5 and similar to 4.0 h, respectively.
Regardless of the starting aperture template, any desired orifice dimension and therefore, dried particle size could be achieved by generating adequate polymer deposits. (C) 2015 Elsevier B.V. All rights reserved.
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271) Preparation of Conductive Gold Nanowires in Confined Environment of Gold-Filled Polymer Nanotubes
Author(s): Mitschang, F (Mitschang, Fabian); Langner, M (Langner, Markus); Vieker, H (Vieker, Henning); Beyer, A (Beyer, Andre); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 36  Issue: 3  Pages: 304-310  DOI: 10.1002/marc.201400485  Published: FEB 12 2015  
Abstract: Continuous conductive gold nanofibers are prepared via the tubes by fiber templates process. First, poly(l-lactide) (PLLA)-stabilized gold nanoparticles (AuNP) with over 60 wt% gold are synthesized and characterized, including gel permeation chromatography coupled with a diode array detector. Subsequent electrospinning of these AuNP with template PLLA results in composite nanofibers featuring a high gold content of 57 wt%. Highly homogeneous gold nanowires are obtained after chemical vapor deposition of 345 nm of poly(p-xylylene) (PPX) onto the composite fibers followed by pyrolysis of the polymers at 1050 degrees C. The corresponding heat-induced transition from continuous gold-loaded polymer tubes to smooth gold nanofibers is studied by transmission electron microscopy and helium ion microscopy using both secondary electrons and Rutherford backscattered ions.
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270) Does it have to be carbon? Metal anodes in microbial fuel cells and related bioelectrochemical systems
Author(s): Baudler, A (Baudler, Andre); Schmidt, I (Schmidt, Igor); Langner, M (Langner, Markus); Greiner, A (Greiner, Andreas); Schroder, U (Schroeder, Uwe)
Source: ENERGY & ENVIRONMENTAL SCIENCE  Volume: 8  Issue: 7  Pages: 2048-2055  DOI: 10.1039/c5ee00866b  Published: 2015  
Abstract: Copper and silver are antimicrobial metals, on whose surface bacteria do not grow. As our paper demonstrates, this commonly reported antimicrobial property does not apply to electrochemically active, electrode respiring bacteria. These bacteria readily colonize the surface of these metals, forming a highly active biofilm. Average anodic current densities of 1.1 mA cm(-2) (silver) and 1.5 mA cm(-2) (copper) are achieved data that are comparable to that of the benchmark material, graphite (1.0 mA cm(-2)). Beside the above metals, nickel, cobalt, titanium and stainless steel (SUS 304) were systematically studied towards their suitability as anode materials for microbial fuel cells and related bioelectrochemical systems. The bioelectrochemical data are put in relation to physical data of the materials (specific conductivity, standard potential) and to basic economic considerations. It is concluded that especially copper represents a highly promising anode material, suitable for application in high-performance bioelectrochemical systems.
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269) Synthesis of liquid crystalline thioether-functionalized hydroxypropyl cellulose esters
Author(s): Ohlendorf, P (Ohlendorf, Peter); Greiner, A (Greiner, Andreas)
Source: POLYMER CHEMISTRY  Volume: 6  Issue: 14  Pages: 2734-2739  DOI: 10.1039/c4py01709a  Published: 2015  
Abstract: The successful synthesis of novel cholesteric hydroxypropyl cellulose (HPC) ester derivatives with pitch heights in the visible range and with functional thioether groups is reported here. The new methylthio-propionated HPC (HPC-MTP) was synthesized by the esterification of hydroxypropyl cellulose with 3-methylthiopropionyl chloride (MTP). Chain degradation and cross-linking of cellulose chains during esterification were avoided and complete esterification of all OH groups was achieved by the use of N,N-dimethylacetamide (DMAc) as the solvent. The structure of HPC-MTP was analyzed by NMR- and IR-spectroscopy and SEC. The physical properties of this new material were measured by TGA, DSC, wide angle X-ray scattering, polarization microscopy and UV/Vis spectroscopy. HPC-MTP products were found to be thermotropic liquid crystalline and formed cholesteric and nematic phases. The formation of lyotropic phases was observed with triglyme as the solvent.
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268) Preparing a pseudo-solid by the reinforcement of a polydentate thioether using silver nanoparticles
Author(s): Pletsch, H (Pletsch, Holger); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: NANOSCALE  Volume: 7  Issue: 5  Pages: 1977-1983  DOI: 10.1039/c4nr06834c  Published: 2015  
Abstract: The design of networks from polymers and noble metal nanoparticles requires thorough control over topological polymer-particle arrangements. This study explores the interaction between a linear polydentate poly(propylene sulfide) (PPrS) ligand and silver nanoparticles (AgNPs) with an aim to study its effect on mechanical and viscoelastic properties. Very low amounts (0.30 vol%) of silver nanoparticles lead to significant mechanical reinforcement of PPrS, yielding viscoelastic properties of an unfastened network with solid-like elastic responses on mechanical stimulation. The materials are made by ring-opening anionic polymerization of propylene sulfide to yield high molar mass PPrS with a total of 593 thioether functionalities per chain, followed by a simple in situ "grafting to" method to homogeneously incorporate AgNPs into the polymer matrix. From investigations on the chain dynamics using dynamic rheology it is concluded that well-dispersed AgNPs impose additional topological constraints on the polymer chains. Calculations of the statistical interparticle distances support a tele-bridging polymer-particle arrangement.
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2014

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267) Solvent-Free Aqueous Dispersions of Block Copolyesters for Electrospinning of Biodegradable Nonwoven Mats for Biomedical Applications
Author(s): Bubel, K (Bubel, Kathrin); Grunenberg, D (Grunenberg, Daniel); Vasilyev, G (Vasilyev, Gleb); Zussman, E (Zussman, Eyal); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 299  Issue: 12  Pages: 1445-1454  DOI: 10.1002/mame.201400116  Published: DEC 2014  
Abstract: Biodegradable block copolyesters are processed from water to water-stable electrospun fibers without use of any organic solvent, which is of major importance for a variety of applications. The copolyesters (poly(epsilon-caprolactone-b-methoxypolyethylene glycol)) (PCL-b-MPEG)) are emulsified in water at 90 degrees C in presence of poly(ethylene oxide) (PEO) using melt dispersion method. Dramatic increase in viscosity is observed upon addition of PEO to aqueous dispersions of copolyesters. Evidence of structure formation in aqueous PCL-b-MPEG/PEO dispersions is adduced using rheological studies. PCL block length dependent water stable nanofiber non-wovens are obtained upon electrospinning of the dispersions.
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266) Tea- Bag- Like Polymer Nanoreactors Filled with Gold Nanoparticles
Author(s): Mitschang, F (Mitschang, Fabian); Schmalz, H (Schmalz, Holger); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 53  Issue: 19  Pages: 4972-4975  DOI: 10.1002/anie.201402212  Published: MAY 5 2014  
Abstract: Gold-containing polymer nanotubes, which showed both catalytic activity and resistance to leaching, were prepared by the tubes by fiber templates (TUFT) process. For this purpose, electrospun polymer nonwovens with incorporated poly(L-lactide)-stabilized gold nanoparticles were coated with poly(p-xylylene) by the chemical vapor deposition process, and then the inner fiber templates were removed. The resulting polymer tubes carried encapsulated gold nanoparticles which were shown to be immobilized and featured pronounced catalytic activity towards the hydrolytic oxidation of dimethylphenylsilane and the alcoholysis of dimethylphenylsilane with n-butanol. The macroscopic nonwovens could be used as tea-bag-like catalyst systems and showed excellent reusability.
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265) Highly Flexible and Tough Concentric Triaxial Polystyrene Fibers
Author(s): Jiang, SH (Jiang, Shaohua); Duan, GG (Duan, Gaigai); Zussman, E (Zussman, Eyal); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: ACS APPLIED MATERIALS & INTERFACES  Volume: 6  Issue: 8  Pages: 5918-5923  DOI: 10.1021/am500837s  Published: APR 23 2014  
Abstract: A combination of appropriate reinforcing material and morphology led to the highly tough, flexible, and strong polystyrene fibers by electrospinning. Concentric fiber morphology with reinforcing elastomeric thermoplastic polyurethane (TPU) sandwiched between the two layers of polystyrene made by a special nozzle (triaxial) showed toughness of >270 J g(-1) and 300% elongation without any cracks in comparison to toughness of <0.5 J g(-1) and elongation at break of <5% of polystyrene single fibers. The concentric triaxial morphology showed great advantage in comparison to the coaxial structure. Toughness and elongation at break were 1376 and 628% higher, respectively, for triaxial morphology in comparison to the from the sandwich structure.
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264) Blocked Bacteria Escape by ATRP Grafting of a PMMA Shell on PVA Microparticles
Author(s): Knierim, C (Knierim, Christian); Greenblatt, CL (Greenblatt, Charles L.); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR BIOSCIENCE  Volume: 14  Issue: 4  Pages: 537-545  DOI: 10.1002/mabi.201300398  Published: APR 2014  
Abstract: This paper reports on the preparation and characterization of living composites consisting of poly(vinylalcohol) (PVA) hydrogel microparticles with living bacteria and a shell of poly(methyl methacrylate) (PMMA). The grafting of the PMMA shell is accomplished in the presence of living bacteria by surface polymerization of PMMA using atom transfer radical polymerization (ATRP). The PMMA shell prevents the uncontrolled bacterial escape from the hydrogel microparticles, which otherwise marks a major problem of these composites. The encapsulation of microparticles with living bacteria by PMMA retards bacteria escape upon contact to water for >20 d. The functionality of the PMMA shell is proven both by the release of fluorescein in buffer and an altered release time of bacteria in buffer solution.
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263) Ultrasound-Mediated Synthesis of High-Molecular Weight Polystyrene-Grafted Silver Nanoparticles by Facile Ligand Exchange Reactions in Suspension
Author(s): Pletsch, H (Pletsch, Holger); Peng, L (Peng, Ling); Mitschang, F (Mitschang, Fabian); Schaper, A (Schaper, Andreas); Hellwig, M (Hellwig, Michael); Nette, D (Nette, David); Seubert, A (Seubert, Andreas); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: SMALL  Volume: 10  Issue: 1  Pages: 201-208  DOI: 10.1002/smll.201300594  Published: JAN 15 2014  
Abstract: Ultrasound mediated facile ligand exchange method in suspension for the formation of polystyrenegrafted silver nanoparticles is reported. Amazingly, this method allows even grafting of very high molecular weight polystyrenes (up to 217 200 g mol(-1)) having a single terminal thiol group at the chain end. Detailed studies are carried out to gain insights in the role of molecular weight of the ligands and the mechanism of the ligand exchange reactions. Key factors are determined to be the droplet formation by ultrasonification and low silver content, which enhances the availability of the terminal thiol end group significantly. The extraordinary compatibility of the ligand exchange method in particular regarding high molecular weights is attributed to hydrophilic orientation of the terminal thiol groups at the liquidliquid interphase. This is proved conclusively by using an in situ method as a reference approach in which agglomeration occurs at considerably lower molecular weights due to the absence of preferred end group orientation within the polymer coil. In homogeneous phase only the chain length is found to be the crucial factor in stabilization of silver nanoparticles.
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2013

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262) Smart secondary polyurethane dispersions
Author(s): Chen, F (Chen, Fei); Hehl, J (Hehl, Judith); Su, Y (Su, Yu); Mattheis, C (Mattheis, Claudia); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: POLYMER INTERNATIONAL  Volume: 62  Issue: 12  Pages: 1750-1757  DOI: 10.1002/pi.4481  Published: DEC 2013  
Abstract: Secondary dispersions of cationic segmented polyurethanes (PUs) with thermoresponsivity (upper critical solution temperature (UCST) in water), high solid contents and antibacterial properties are highlighted in this paper. PUs were prepared by polyaddition reactions and subsequent quaternization with methyl iodide. No additional stabilizers, organic solvents or special procedures were required to obtain stable aqueous dispersions containing up to 10wt% PU; in contrast, stable dispersions were straightforwardly accessed by a combination of UCST behavior and repulsive electrostatic forces among the positively charged segments, which meets the requirements of a green chemistry process. Particle size and UCST strongly depended on the solid content of the dispersions and the content of poly(ethylene glycol) segments in the copolymers. The dispersions exhibited fast-acting antibacterial properties against Escherichia coli. (c) 2013 Society of Chemical Industry
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261) Transition-Metal-Functionalized PAMAM Dendrimers Encapsulated in PPX Tubes as Reusable Catalysts
Author(s): Mitschang, F (Mitschang, Fabian); Dettlaff, BK (Dettlaff, Barbara K.); Lindner, JP (Lindner, Jean-Pierre); Studer, A (Studer, Armido); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULES  Volume: 46  Issue: 22  Pages: 8784-8789  DOI: 10.1021/ma401815x  Published: NOV 26 2013  
Abstract: Composite nanofibers of polyurethane and catalytically active Pd- or Cu-functionalized poly(amido amine) dendrimers were electrospun and subsequently coated with poly(p-xylylene) by the chemical vapor deposition. After removal of the inner polyurethane template matrix, the dendrimers remained encapsulated inside the confinement and the leaching behavior of the caged dendritic catalysts was studied. The tube system was successfully used as a readily reusable tea bag type catalyst for Suzuki Miyaura couplings and alkyne/azide click reactions.
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260) Short electrospun polymeric nanofibers reinforced polyimide nanocomposites
Author(s): Jiang, SH (Jiang, Shaohua); Duan, GG (Duan, Gaigai); Schobel, J (Schoebel, Judith); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: COMPOSITES SCIENCE AND TECHNOLOGY  Volume: 88  Pages: 57-61  DOI: 10.1016/j.compscitech.2013.08.031  Published: NOV 14 2013  
Abstract: This work highlights the usage of short electrospun fibers for the first time for the preparation of homogeneous polymer nanofiber/polymer composites and the improvement in mechanical properties by an order to magnitude compared to as-electrospun long and continuous nanofibers. Dispersions of short electrospun nanofibers can be processed by liquid processing techniques resulting in nanofiber nonwoyens similar to electrospun nonwovens but is independent from the demands of the electrospinning process is one of the emphasis of this work. The re-formation of electrospun fiber nonwovens by dispersion casting of short electrospun polyimide (PI) nanofibers and the preparation of homogeneous polymer/polymer nanofiber composite films were selected as representative examples for showing the versatility of short electrospun fibers. The self-reinforced PI/PI-short nanofiber composite films were obtained from mixtures of short electrospun PI nanofibers and polyamic acid after imidization. Significant improvement of 53% and 87% in mechanical properties like tensile strength and modulus, respectively in comparison to the neat PI film was observed by using just 2 wt% of short fibers. Parallel experiments were also carried out with long and continuous electrospun PI fibers and amazingly a huge difference was observed. The amount of continuously long fibers required for achieving almost the same strength was much higher i.e. 38 wt% in comparison to the 2 wt% required of short fibers. (C) 2013 Elsevier Ltd. All rights reserved.
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259) Short nylon-6 nanofiber reinforced transparent and high modulus thermoplastic polymeric composites
Author(s): Jiang, S (Jiang, Shaohua); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: COMPOSITES SCIENCE AND TECHNOLOGY  Volume: 87  Pages: 164-169  DOI: 10.1016/j.compscitech.2013.08.011  Published: OCT 18 2013  
Abstract: The use of small amounts (<5 wt%) of short nylon-6 nanofibers (diameter less than 200 nm) for reinforcing mechanical properties of TPU without losing its optical properties is highlighted in this work. The interaction of H-bonding type between the reinforcing fibers and the matrix polymer could provide a homogenous distribution of fibers and a strong interface leading to significant enhancement in mechanical properties (185% increase in E modulus) as shown by comparative use of TPU and PMMA as matrix polymers. The reinforcing effect of short fibers was attained without sacrificing transparency (>90% transparency in 400-800 nm range) of TPU. The effective use of short nylon-6 fibers in comparison to the long and continuous fibers is also discussed. (C) 2013 Elsevier Ltd. All rights reserved.
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258) Tenside-Free Biodegradable Polymer Nanofiber Nonwovens by "Green Electrospinning"
Author(s): Bubel, K (Bubel, Kathrin); Zhang, Y (Zhang, Yi); Assem, Y (Assem, Yasser); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULES  Volume: 46  Issue: 17  Pages: 7034-7042  DOI: 10.1021/ma401044s  Published: SEP 10 2013  
Abstract: This work highlights the formation and use of tenside-free biodegradable polyester dispersions in water for making water stable nanofibers in accordance with the method of "Green Electrospinning". The concept was to use the amphiphilic block copolyesters poly[(hexamethylene adipate)-block-(methoxypolyethylene glycol)] (PHA-b-MPEG) and poly[(epsilon-caprolactone)-block-(methoxypolyethylene glycol)] (PCL-b-MPEG) for making tenside-free water dispersions. Different copolymers with varied block lengths were synthesized and converted to high-concentration aqueous dispersions by the solvent displacement method followed by dialysis. The dispersions were electrospun with solid contents of up to 28 wt %. Via addition of small amounts of a high-molecular weight poly(ethylene oxide) as a template polymer, the dispersions were processed to nanofiber nonwovens by electrospinning. Water stable PHA-b-MPEG and PCL-b-MPEG nanofibers were obtained by aqueous extraction of the nanofibers.
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257) Chameleon Nonwovens by Green Electrospinning
Author(s): Giebel, E (Giebel, Elisabeth); Mattheis, C (Mattheis, Claudia); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 23  Issue: 25  Pages: 3156-3163  DOI: 10.1002/adfm.201201873  Published: JUL 5 2013  
Abstract: Electrospun ionic nonwovens are obtained by green electrospinning of aqueous dispersions. The resulting nonwovens are termed as chameleon nonwovens since their surface properties can be tailored in a large variety by coating of different functionalities following the protocol of the layer-by-layer process (LBL). The dimensional stability of the electrospun fibers in the chameleon nonwovens is achieved by photo-cross-linking after electrospinning and thereby overcoming the repulsive forces of the ionic moieties in the fibers. Depending on the nature of the ionic moieties different materials are coated by LBL including dyes, antibacterial materials, silver, and gold nanoparticles. Enhanced coating efficiency for coating of metal nanoparticles is observed when the chameleon nonwovens were precoated by a polyelectrolyte.
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256) Functional materials by electrospinning of polymers
Author(s): Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: PROGRESS IN POLYMER SCIENCE  Volume: 38  Issue: 6  Pages: 963-991  DOI: 10.1016/j.progpolymsci.2013.02.001  Published: JUN 2013  
Abstract: About a decade ago electrospinning was primarily concerned with the preparation of nanofibers from synthetic polymers and to a lower degree from natural polymers targeting predominantly technical applications areas such as textiles and filters as well as medical areas such as tissue engineering and drug delivery. Since then strong progress has been made not only in the understanding and theoretical modeling of the complex processes governing electrospinning and in the strict control of fiber formation by material and operating parameters but also in the design of a broad range of technical spinning devices. These achievements have in turn allowed for an extension of electrospinning towards fiber formation based not only on polymers of synthetic, biological nature but also on metals, metal oxides, ceramics, organic/organic, organic/inorganic as well as inorganic/inorganic composite systems. Here not only preparation schemes were investigated but properties and functions of the nanofibers were analyzed and potential applications were evaluated. As far as technical applications are concerned nanofibers composed of such materials can today be designed in a highly controlled way to display specific structural features. They include phase morphology and surface topology as well as unique functions including in particular magnetic, optical, electronic, sensoric, catalytic functions specific for one-dimensional architectures. Significant developments have also been achieved towards the exploitation of such functional nanofibers in applications involving among others fuel cells, lithium ion batteries, solar cell, electronic sensors as well as photocatalysts. One major target is currently the incorporation of such functional nanofibers in micrometer-sized electronic devices or even the construction of such devices purely from nanofibers. (C) 2013 Elsevier Ltd. All rights reserved.
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255) Controlled antibody/(bio-) conjugation of inorganic nanoparticles for targeted delivery
Author(s): Montenegro, JM (Montenegro, Jose-Maria); Grazu, V (Grazu, Valeria); Sukhanova, A (Sukhanova, Alyona); Agarwal, S (Agarwal, Seema); de la Fuente, JM (de la Fuente, Jesus M.); Nabiev, I (Nabiev, Igor); Greiner, A (Greiner, Andreas); Parak, WJ (Parak, Wolfgang J.)
Source: ADVANCED DRUG DELIVERY REVIEWS  Volume: 65  Issue: 5  Pages: 677-688  DOI: 10.1016/j.addr.2012.12.003  Published: MAY 2013  
Abstract: Arguably targeting is one of the biggest problems for controlled drug delivery. In the case that drugs can be directed with high efficiency to the target tissue, side effects of medication are drastically reduced. Colloidal inorganic nanoparticles (NPs) have been proposed and described in the last 10 years as new platforms for in vivo delivery. However, though NPs can introduce plentiful functional properties (such as controlled destruction of tissue by local heating or local generation of free radicals), targeting remains an issue of intense research efforts. While passive targeting of NPs has been reported (the so-called enhanced permeation and retention, EPR effect), still improved active targeting would be highly desirable. One classical approach for active targeting is mediated by molecular recognition via capture molecules, i.e. antibodies (Abs) specific for the target. In order to apply this strategy for NPs, they need to be conjugated with Abs against specific biomarkers. Though many approaches have been reported in this direction, the controlled bioconjugation of NPs is still a challenge. In this article the strategies of controlled bioconjugation of NPs will be reviewed giving. particular emphasis to the following questions: 1) how can the number of capture molecules per NP be precisely adjusted, and 2) how can the Abs be attached to NP surfaces in an oriented way. Solution of both questions is a cornerstone in controlled targeting of the inorganic NPs bioconjugates. (C) 2013 Elsevier B.V. All rights reserved.
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254) The Importance of Crosslinking and Glass Transition Temperature for the Mechanical Strength of Nanofibers Obtained by Green Electrospinning
Author(s): Giebel, E (Giebel, Elisabeth); Getze, J (Getze, Julia); Rocker, T (Roecker, Thorsten); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 298  Issue: 4  Pages: 439-446  DOI: 10.1002/mame.201200080  Published: APR 2013  
Abstract: Crosslinked particles containing butyl acrylate, methyl methacrylate, and allyl methacrylate are prepared by free-radical emulsion polymerization. The glass transition temperatures of the polymers are varied by the crosslinking densities in the latex particles. Aqueous acrylate dispersions with polymers of different glass transition temperatures are electrospun with PVA as the matrix polymer. The effects of crosslinking density and Tg on the structure and mechanical properties of the fibers are studied. Crosslinking of unreacted allyl groups is induced by UV irradiation to stabilize the fibers by interparticle crosslinking. Both the ability to undergo interparticle crosslinking and the E modulus depend on the merging of the particles during the electrospinning process.
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253) Immobilization of catalysts in poly(p-xylylene) nanotubes
Author(s): Hepperle, JAM (Hepperle, Johannes A. M.); Mitschang, F (Mitschang, Fabian); Bier, AK (Bier, Anna K.); Dettlaff, BK (Dettlaff, Barbara K.); Greiner, A (Greiner, Andreas); Studer, A (Studer, Armido)
Source: RSC ADVANCES  Volume: 3  Issue: 48  Pages: 25976-25981  DOI: 10.1039/c3ra43647k  Published: 2013  
Abstract: This paper describes the immobilization of a TEMPO-derivative and a copper catalyst in ethinyl-functionalized poly(p-xylylene) nanotubes which are readily prepared by the Tubes by Fiber Templates (TUFT) process. Catalyst conjugation to the nanotubes is achieved via the Cu-catalyzed azide alkyne cycloaddition (CuAAC). The TEMPO-functionalized nanotubes are successfully used as recyclable catalysts for oxidation of benzyl alcohol. Recycling studies show that the TEMPO-modified nanotubes can be reused 20 times without loss of catalytic activity. Conjugation of the nanotubes with a bipyridine moiety provides a material that allows for immobilization of metal catalysts. Treatment with a Cu(I)-salt leads to a hybrid material, which shows high activity as a recyclable catalyst in the CuAAC. Recycling experiments reveal that these Cu-nanotubes can be reused for 18 runs.
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252) Bombardment induced ion transport - Part III: Experimental potassium ion conductivities in poly(para-xylylene)
Author(s): Schulze, S (Schulze, S.); Schafer, M (Schaefer, M.); Greiner, A (Greiner, A.); Weitzel, KM (Weitzel, K-M.)
Source: PHYSICAL CHEMISTRY CHEMICAL PHYSICS  Volume: 15  Issue: 5  Pages: 1481-1487  DOI: 10.1039/c2cp43144k  Published: 2013  
Abstract: The bombardment induced ion transport (BIIT) technique has been employed for studying the ionic conductivity of thin poly(p-xylylene) (PPX) films. The experiment is based on bombarding a PPX film with a c.w. potassium ion beam. The transport of ions through the film - which follows the laws of electrodiffusion - is detected as a neutralization current on the backside electrode on which the film has been deposited. This backside current scales quadratically with the acceleration potential of the ion beam and inversely cubically with the thickness of the film. This confirms theoretical predictions made in part I of this mini-series (Phys. Chem. Chem. Phys., 2011, 13, 20112-20122). This characteristic is markedly different from the Ohm-like current-voltage properties of a solid electrolyte, e. g. an ion conducting glass. The diffusion coefficient for K+ in PPX is determined to be 8.528 x 10(-16) cm(2) s(-1) at 333 K. From the temperature dependence of the diffusion coefficient we conclude that a hopping mechanism with an activation energy of 2.74 eV +/- 0.18 eV is operative.
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2012

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251) PDMAEMA based gene delivery materials
Author(s): Agarwal, S (Agarwal, Seema); Zhang, Y (Zhang, Yi); Maji, S (Maji, Samarendra); Greiner, A (Greiner, Andreas)
Source: MATERIALS TODAY  Volume: 15  Issue: 9  Pages: 388-393  Published: SEP 2012  
Abstract: Gene transfection is the transfer of genetic material like DNA into cells. Cationic polymers which form nanocomplexes with DNA, so-called non-viral gene vectors, are a highly promising platform for efficient gene transfection. Despite intensive research efforts and some of the on-going clinical trials on gene transfection, none of the existing cationic polymer systems are generally acceptable for human gene therapy. Since the process of gene transfection is complex and puts different challenges and demands on the delivery system, there is a strong requirement for the design and development of a multifunctional system in a simple way. This review will discuss recent efforts in design, synthesis, and performance of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) nanocomplexes with DNA.
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250) Novel Layer-by-Layer Procedure for Making Nylon-6 Nanofiber Reinforced High Strength, Tough, and Transparent Thermoplastic Polyurethane Composites
Author(s): Jiang, SH (Jiang, Shaohua); Duan, GG (Duan, Gaigai); Hou, HQ (Hou, Haoqing); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: ACS APPLIED MATERIALS & INTERFACES  Volume: 4  Issue: 8  Pages: 4366-4372  DOI: 10.1021/am3010225  Published: AUG 2012  
Abstract: We highlight a novel composite fabrication method based on solution casting, electrospinning, and film stacking for preparing highly transparent nylon-6 nanofiber reinforced thermoplastic polyurethane (TPU) composite films. The procedure is simple and can be extended to the other thermoplastics. The morphology of fiber/matrix interface and the properties of composite films were also investigated. The method led to a significant reinforcement in mechanical properties of TPU like tensile strength, E modulus, strain, and toughness just using very small amounts of nylon fibers (about 0.4-1.7 wt %; 150-300 nm diameter). The enhanced mechanical properties were achieved without sacrificing optical properties like transparency of TPU.
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249) Antimicrobial Hydantoin-Containing Polyesters
Author(s): Tan, LC (Tan, Licheng); Maji, S (Maji, Samarendra); Mattheis, C (Mattheis, Claudia); Zheng, MY (Zheng, Mengyao); Chen, YW (Chen, Yiwang); Caballero-Diaz, E (Caballero-Diaz, E.); Gil, PR (Gil, Pilar Rivera); Parak, WJ (Parak, Wolfgang J.); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR BIOSCIENCE  Volume: 12  Issue: 8  Pages: 1068-1076  DOI: 10.1002/mabi.201100520  Published: AUG 2012  
Abstract: A new N-hydantoin-containing biocompatible and enzymatically degradable polyester with antibacterial properties is presented. Different polyesters of dimethyl succinate, 1,4-butanediol, and 3-[N,N-di(beta-hydroxyethyl)aminoethyl]-5,5- dimethylhydantoin in varying molar ratios are prepared via two-step melt polycondensation. The antibacterially active N-halamine form is obtained by subsequent chlorination of the polyesters with sodium hypochlorite. Chemical structures, thermal properties, and spherulitic morphologies of the copolymers are studied adopting FT-IR, NMR, TGA, DSC, WAXD, and POM. The polyesters exhibit antibacterial activity against Escherichia coli. The adopted synthetic approach can be transferred to other polyesters in a straightforward manner.
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248) Ultra-long palladium nanoworms by polymer grafts
Author(s): Bokern, S (Bokern, Stefan); Volz, K (Volz, Kerstin); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: JOURNAL OF NANOPARTICLE RESEARCH  Volume: 14  Issue: 8  Article Number: 1041  DOI: 10.1007/s11051-012-1041-z  Published: AUG 2012  
Abstract: Chemically and morphologically stable, non-aggregating palladium nanoworms with diameters of 2 nm and lengths of up to 10 nm with a graft-to polystyrene shell were synthesized in a straight-forward one-phase system, and proof for the mechanism of formation is presented. The synthesis has been achieved by the application of omega-2,2'-bipyridyl-polystyrene as stabilizer, which led to a "graft-to'' structure of palladium nanoworms with polystyrene shell. The nanoworms have been characterized by TEM, XRD, and coupled GPC-UV/Vis measurement. It was possible to show that the formation of nanoworms proceeds by agglomeration of spherical palladium nanoparticles. This mechanism was transferred to omega-thiol-polystyrene as stabilizer, which results in either spherical nanoparticles (low ratio Pd:Polymer, <2 nm diameter) or high aspect ratio nanoworms (high ratio Pd: Polymer, up to 10 x 120 nm), proving that the formation of palladium nanoworms was not exclusive for pyridine/amine-based ligands.
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247) Water-Stable Nonwovens Composed of Electrospun Fibers from Aqueous Dispersions by Photo-Cross-Linking
Author(s): Giebel, E (Giebel, Elisabeth); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 297  Issue: 6  Special Issue: SI  Pages: 532-539  DOI: 10.1002/mame.201100401  Published: JUN 2012  
Abstract: Copolymers of MMA, BA, and MABP are prepared by radical emulsion polymerization in water. As a result aqueous dispersions of these copolymers are obtained with particle sizes around 60120?nm. After addition of some PVA the dispersions are electrospun. The resulting fibers display different morphologies depending on the copolymer composition. Inter- and intra-particle cross-linking is achieved by photo-cross-linking induced by the MABP moieties yielding fibers with good thermomechanical properties depending on the content of MABP. With this approach, thermomechanically stable electrospun fibers with smooth surface structure can be obtained by electrospinning from water.
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246) Preparation of Continuous Gold Nanowires by Electrospinning of High-Concentration Aqueous Dispersions of Gold Nanoparticles
Author(s): Gries, K (Gries, Katharina); Vieker, H (Vieker, Henning); Golzhauser, A (Goelzhaeuser, Armin); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: SMALL  Volume: 8  Issue: 9  Pages: 1436-1441  DOI: 10.1002/smll.201102308  Published: MAY 7 2012  
Abstract: Gold nanowires are prepared by the electrospinning of highly concentrated aqueous dispersions of gold nanoparticles (AuNPs) in the presence of poly(vinyl alcohol) and subsequent annealing at higher temperatures. Continuous wires of sintered AuNPs are obtained as a result of this process. The Au wires are characterized by transmission electron microscopy, helium ion microscopy, optical microscopy, and X-ray diffractometry.
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245) Tough and Transparent Nylon-6 Electrospun Nanofiber Reinforced Melamine-Formaldehyde Composites
Author(s): Jiang, SH (Jiang, Shaohua); Hou, HQ (Hou, Haoqing); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: ACS APPLIED MATERIALS & INTERFACES  Volume: 4  Issue: 5  Pages: 2597-2603  DOI: 10.1021/am300286m  Published: MAY 2012  
Abstract: The use of nylon-6 electrospun nanofiber mats as reinforcement with synergistic effect in tensile strength and toughness for melamine-formaldehyde (MF) resin is highlighted in this article. Interestingly, there was a drastic effect of the wetting procedure of reinforcing fiber mat by the MF resin on the morphology and mechanical properties of the composites. The wetting of nylon fibers by passing through a solution of MF resin showed a core-shell morphology and a significant improvement in properties as compared to the dip-coating procedure for wetting of the fibers. Depending on the wt% of reinforcing nylon fiber mats, the composites could be considered as either fiber reinforced MF composites or MF glued nylon fibers.
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244) Electrospun copper oxide nanofibers for H2S dosimetry
Author(s): Hennemann, J (Hennemann, Joerg); Sauerwald, T (Sauerwald, Tilman); Kohl, CD (Kohl, Claus-Dieter); Wagner, T (Wagner, Thorsten); Bognitzki, M (Bognitzki, Michael); Greiner, A (Greiner, Andreas)
Source: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE  Volume: 209  Issue: 5  Pages: 911-916  DOI: 10.1002/pssa.201100588  Published: MAY 2012  
Abstract: We present the preparation and characterization of a novel copper(II)oxide (CuO) nanofiber based sensor with very high sensitivity and selectivity to hydrogen sulfide (H2S). The working principle is based on the phase transition of semi-conducting p-type CuO to strongly degenerated p-type copper sulfide (CuS) with metallic conductivity. Electrospun polymer fiber networks of polyvinyl butyrate (PVB) and Cu(NO3)(2) were attached on standard gas sensing substrates and calcined to CuO at 600 degrees C in ambient air for 24 h. Continuous exposure to H2S (0.1-5 ppm) as well as a sequence of 1 ppm H2S pulses result in a dosimeter type behavior of the nanofiber sensors. Triggered by a certain dose (gas concentration multiplied by time) a steep conductance increase of the sensitive layer over several orders of magnitude is observed. After reaching this percolation threshold only small conductance changes were observed. These fiber based sensors show a remarkably high specificity, there is no response to carbon monoxide, hydrogen, and methane at 160 degrees C. The fiber network can be regenerated by raising the operating temperature to 350 degrees C for 30 min in absence of H2S.
[GRAPHICS]
(c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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243) Thermally Cross-Linkable Poly(p-xylylene)s for Advanced Low-Dielectric Applications
Author(s): Mulpuri, SV (Mulpuri, Syamkumar V.); Shin, BG (Shin, Boo-Gyo); Bognitzki, M (Bognitzki, Michael); Greiner, A (Greiner, Andreas); Yoon, DY (Yoon, Do Y.)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 213  Issue: 7  Pages: 705-712  DOI: 10.1002/macp.201100558  Published: APR 13 2012  
Abstract: A novel series of poly(p-xylylene) homopolymer and copolymers containing thermally cross-linkable cyclohexenyl moiety are prepared via base-catalyzed Gilch route to yield high-molecular-weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 degrees C and the glass transition temperature (Tg) is in the range of 136 - 250 degrees C. They undergo thermal cross-linking via the cyclohexenyl moiety. The cross-linked polymer exhibits a high Tg of 294 degrees C, a low coefficient of thermal expansion (CTE) of 45 ppm K-1. A low dielectric constant of 2.5 and a very low dielectric loss tan d of 0.0004 at 1 GHz are obtained, which are superior to conventional interconnect polymers.
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242) Vinyl-functionalized gold nanoparticles as artificial monomers for the free radical copolymerization with methyl methacrylate
Author(s): Gries, K (Gries, Katharina); El Helou, M (El Helou, Mira); Witte, G (Witte, Gregor); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: POLYMER  Volume: 53  Issue: 8  Pages: 1632-1639  DOI: 10.1016/j.polymer.2012.02.008  Published: APR 3 2012  
Abstract: Vinyl-functionalized gold nanoparticles (AuNP) were prepared by surface polymerization of vinyl-functionalized ligands induced by carboxy-functionalized radical initiators followed by vinyl-transformation of the carboxy-group. These AuNP were regarded as artificial molecules as they were used as comonomers for the free radical copolymerization with methyl methacrylate (MMA). Successful copolymerization was proven by gel permeation chromatography (GPC) and by thermogravimetrical analysis (TGA). Further analysis of the novel hybrid material was carried out by transmission electron microscopy (TEM) and by atomic force microscopy (AFM) to proof the presence of AuNP and their arrangement. (C) 2012 Elsevier Ltd. All rights reserved.
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241) Synthesis, Structure, and Properties of Alkyl-Substituted PPXs by Chemical Vapor Deposition for Stent Coatings
Author(s): Bier, AK (Bier, Anna K.); Bognitzki, M (Bognitzki, Michael); Mogk, J (Mogk, Jochen); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULES  Volume: 45  Issue: 3  Pages: 1151-1157  DOI: 10.1021/ma202270w  Published: FEB 14 2012  
Abstract: High-molecular-weight un-cross-linked poly(p-xylylene) (PPX) derivatives (3) with one lateral linear alkyl substituent (methyl octyl) on each phenylene moiety were prepared by pyrolysis of corresponding paracyclophanes followed by chemical vapor deposition (CVD). Most of these PPX derivatives showed good solubility in organic solvents which allowed purification by reprecipitation, structural analysis by solution NMR techniques, and molecular weight analysis by gel permeation chromatography. High thermal stability of 3 was found by thermogravimetric analysis. The glass transition temperatures decreased systematically with increasing alkyl chain length from 53 to -23 degrees C. Increased elongation to break up to 380% was analyzed by stress-strain experiments for as-deposited films indicating excellent coating properties, which were proven by initial coating tests on stents.
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240) Water-Stable All-Biodegradable Microparticles in Nanofibers by Electrospinning of Aqueous Dispersions for Biotechnical Plant Protection
Author(s): Bansal, P (Bansal, Priyanka); Bubel, K (Bubel, Kathrin); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: BIOMACROMOLECULES  Volume: 13  Issue: 2  Pages: 439-444  DOI: 10.1021/bm2014679  Published: FEB 2012  
Abstract: Pheromone eluting oligolactide (OLA) microcapsules immobilized in electrospun biodegradable polyester nanofibers were obtained by electrospinning of; aqueous dispersions of the microcapsules. OLA was prepared by conventional melt polycondensation of lactic acid. Following the protocol of the solvent displacement method, OLA was dissolved in acetone and mixed with Brij S20 and the pheromone of the European grape vine moth, Lobesia Botrana, (E,Z)-7,9-dodecadien-l-yl acetate (DA). Up to 32 wt % of this mixture could, be dispersed in water with colloidal stability of several weeks without any sedimentation. Without DA as well as OLA, no stable dispersions of OLA in water, were obtained. Replacement of DA by classical hydrophobes typically used for miniemulsions did not yield stable dispersions, but the addition of octyl acetate, which shows structural similarity to DA, yielded stable dispersions in water up to 10 wt 96. Dispersions of OLA/DA were successfully electrospun in combination with an aqueous dispersion of a biodegradable block copolyester resulting in water-stable nanofibers containing OLA/DA microcapsules. Release of DA from microcapsules and fibers was retarded in comparison with non encapsulated DA, as shown by model studies.
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239) Synthesis, Properties, and Processing of New Siloxane-Substituted Poly(p-xylylene) via CVD
Author(s): Bier, AK (Bier, Anna K.); Bognitzki, M (Bognitzki, Michael); Schmidt, A (Schmidt, Alexander); Greiner, A (Greiner, Andreas); Gallo, E (Gallo, Emanuela); Klack, P (Klack, Patrick); Schartel, B (Schartel, Bernhard)
Source: MACROMOLECULES  Volume: 45  Issue: 2  Pages: 633-639  DOI: 10.1021/ma2021369  Published: JAN 24 2012  
Abstract: The synthesis of a disiloxane-functionalized [2.2]paracyclophane and its polymerization to the corresponding siloxane-substituted poly(p-xylylene) via chemical vapor deposition (CVD) has been described. Because of the enhanced solubility of the siloxane substituted poly(p-xylylene) analysis of the molecular structure by NMR, molecular weight, and polydispersity by gel permeation chromatography (GPC), and processing by film casting as well as nanofiber formation by electrospinning was possible. Structural isomers were found by NMR which was expected due to the isomeric mixture of the precursor. High molecular weights at moderate polydispersities were found by GPC which was unexpected for a vapor phase deposition polymerization. The amorphous morphology in combination with a low glass transition temperature led to high elongation at break for the siloxane substituted poly(p-xylylene). Significant difference for the wetting versus water was found for as-deposited films,.solution cast films, and nanofibers obtained by electrospinning with contact angles up to 135 degrees close to superhydrophobic behavior.
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2011

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238) Preparation of Gold Nanoparticle-Poly(L-menthyl methacrylate) Conjugates via ATRP Polymerization
Author(s): Gries, K (Gries, Katharina); Bubel, K (Bubel, Kathrin); Wohlfahrt, M (Wohlfahrt, Malte); Agarwal, S (Agarwal, Seema); Koert, U (Koert, Ulrich); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 212  Issue: 23  Pages: 2551-2557  DOI: 10.1002/macp.201100449  Published: DEC 1 2011  
Abstract: Poly(L-menthyl methacrylate) (PMenMA) is synthesized by atom transfer radical polymerization (ATRP) of methyl L-mentholacrylate using bis[2-(2-bromoisobutyrooxy)ethyl]disulfide] ((BiBOE)(2))S(2)) as the ATRP coinitiator. Reduction of hydrogen tetrachloroaureate(III) (HAuCl(4) center dot 3 H(2)O) by Super-Hydride in the presence of PMenMA yields gold nanoparticles (AuNP)-PMenMA conjugates in the size range of 220 nm, depending on the ratio of PMenMA and HAuCl(4). AuNP-PMenMA is characterized by TEM, NMR, IR-, and UV-spectroscopy. The correlation of the ratio of (AuNP)-PMenMA conjugates and free PMenMA is analyzed by gel permeation chromatography (GPC).
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237) Precisely Designed Gold Nanoparticles by Surface Polymerization - Artificial Molecules as Building Blocks for Novel Materials
Author(s): Bokern, S (Bokern, Stefan); Gries, K (Gries, Katharina); Gortz, HH (Goertz, Hans-Helmut); Warzelhan, V (Warzelhan, Volker); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 21  Issue: 19  Pages: 3753-3759  DOI: 10.1002/adfm.201100590  Published: OCT 7 2011  
Abstract: The synthesis of gold nanoparticles (2-4 nm) carrying a single functional polystyrene chain and its characterization by gel permeation chromatography are reported. This has been achieved by a new type of macromolecular azo-initiator based on telechelic polystyrene with containing alpha,omega-methylcoumarin endgroups and an azo group in the middle of the polystyrene. The structure and the near-quantitative functionality of the initiator have been verified by performing NMR, GPC, and UV-vis measurements. This macroinitiator has been used to initiate a surface polymerization of 4-vinylthiophenol molecules immobilized on the surface of gold nanoparticles. As a product, gold nanoparticles carrying exactly one polystyrene chain have been synthesized with functionalization degrees of up to 90% (crude yield). Proof and quantification of the functionalization degree have been demonstrated by application of a GPC setup with a diode array detector for online UV-vis spectra.
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236) Electrospun carbon fiber mat with layered architecture for anode in microbial fuel cells
Author(s): Chen, SL (Chen, Shuiliang); He, GH (He, Guanghua); Carmona-Martinez, AA (Carmona-Martinez, Alessandro Alfredo); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas); Hou, HQ (Hou, Haoqing); Schroder, U (Schroeder, Uwe)
Source: ELECTROCHEMISTRY COMMUNICATIONS  Volume: 13  Issue: 10  Pages: 1026-1029  DOI: 10.1016/j.elecom.2011.06.009  Published: OCT 2011  
Abstract: Layered carbon fiber mats have been prepared by layer-by-layer (LBL) electrospinning of polyacrylonitrile onto thin natural cellulose paper and subsequent carbonization. The layered carbon fiber mat has been proved to be a promising microbial fuel cell anode for high density layered biofilm propagation and high bioelectrocatalytic anodic current density. (C) 2011 Elsevier B.V. All rights reserved.
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235) Quick Polymerization from Electrospun Macroinitiators for Making Thermoresponsive Nanofibers
Author(s): Brandl, C (Brandl, Christian); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 296  Issue: 9  Pages: 858-864  DOI: 10.1002/mame.201100031  Published: SEP 14 2011  
Abstract: Thermoresponsive nanofibers by very fast grafting of N,N-isopropylacrylamide (NIPAAm) from electrospun atom transfer radical polymerization (ATRP) macroinitiator are presented in this work. The heterogenous grafting of NIPAAm onto macroinitiator fibers could be done in few minutes, i.e., in less than 5 min. The procedure involved electrospinning of an ATRP macroinitiator and subsequent PNIPAAm grafting using "grafting from" technique. The ATRP Macroinitiator was based on a copolymer of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA). The growth of the PNIPAAm layer on electrospun fibers was followed by IR-spectroscopy and SEM analysis. The temperature-dependent-phase transition was proven by contact angle measurements and could be shown on the same surface for many cycles.
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234) Synthesis and characterization of substituted polynorbornene derivatives
Author(s): Mulpuri, SV (Mulpuri, Syamkumar V.); Shin, J (Shin, Jinbok); Shin, BG (Shin, Boo-Gyo); Greiner, A (Greiner, Andreas); Yoon, DY (Yoon, Do Y.)
Source: POLYMER  Volume: 52  Issue: 19  Pages: 4377-4386  DOI: 10.1016/j.polymer.2011.07.019  Published: SEP 1 2011  
Abstract: This paper describes palladium (II) catalyst based synthesis and detailed characterization of vinyl-type polynorbornenes (PNBs) with bulky phenyl, adamantane, or norbornane substituents linked by ester, ether, or alkyl bridges. The structure-property relationships of the substituted PNBs were investigated concerning the thermal stability, glass transition temperature, wide-angle X-ray scattering (WAXS) patterns, mechanical properties, and dielectric characteristics. PNBs with phenyl substituted pendant groups improved the solubility and film forming properties due to aromatic aromatic interactions. The substituted PNBs exhibited good thermal and thermo-mechanical properties with thermal decomposition temperature (T(d,5%)) above 300 degrees C and glass transition temperature in the range of 134-325 degrees C. WAXS studies revealed the presence of local nano-scale order in the noncrystalline state, especially in ester bridged adamantane and norbornane substituted polymers, probably due to the steric packing requirements of bulky side groups coupled with dipolar interactions. Nanoindentation results showed high modulus (6.5-7.9 GPa) and hardness (0.11-0.38 GPa) for PNBs with diester adamantane and norbornane substituted polymers. Excellent dielectric properties with a dielectric constant (e.) of 2.5 and a dielectric loss tangent (tan delta) of 0.0005 were measured for poly [2-(4-phenylbutyl)-5-norbornene] at 1 GHz, rendering it very attractive for interconnect dielectric films in high-frequency electronic devices. (C) 2011 Elsevier Ltd. All rights reserved.
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233) Electrospinning and cutting of ultrafine bioerodible poly(lactide-co-ethylene oxide) tri- and multiblock copolymer fibers for inhalation applications
Author(s): Thieme, M (Thieme, Marcel); Agarwal, S (Agarwal, Seema); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 22  Issue: 9  Pages: 1335-1344  DOI: 10.1002/pat.1617  Published: SEP 2011  
Abstract: Triblock copolymers made up of poly(ethylene oxide) (PEO) and polylactide (PLA) were synthesized and converted to fibers by the electrospinning process. A two-step in situ-synthesis in bulk was applied to extend PLA-PEO-PLA triblock copolymers with relatively short block length and low molecular weight in order to obtain electrospinnable materials. DL-lactide was polymerized to the hydroxyl chain ends of PEO via the stannous octoate route. Hexamethylene diisocyanate (HDI) was added as chain extender in the second step, leading to poly(ether-ester-urethane) multiblock copolymers. The materials were electrospun from solutions in chloroform. Different concentrations and voltages were analyzed. The ether and ester blocks were varied in their block length and their effects on the fiber morphology was studied. Variations in the electrical conductivity of the chloroform solutions were investigated by adding triethyl benzyl ammonium chloride (TEBAC) in different amounts. Finally, with high quality electrospun PLA-PEO-PEO triblock copolymer fibers mechanical cutting was possible. Copyright (C) 2009 John Wiley & Sons, Ltd.
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232) Electrospun nanofiber mats coating-new route to flame retardancy
Author(s): Gallo, E (Gallo, E.); Fan, Z (Fan, Z.); Schartel, B (Schartel, B.); Greiner, A (Greiner, A.)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 22  Issue: 7  Special Issue: SI  Pages: 1205-1210  DOI: 10.1002/pat.1994  Published: JUL 2011  
Abstract: A novel route toward halogen-free fire retardancy of polymers through innovative surface coating is described. Nanofiber mats based on polyimide are deposited on PA66 through electrospinning. Scanning electron microscopy is used to characterize the nanofibers. Cone calorimeter tests were performed to evaluate the fire performance. Because of their low thermal conductivity, electrospun nanofiber mats act not only as sacrificial layers but also as a protective surface that delays ignition. The effect is influenced by the fiber diameters and the imidization. Copyright (C) 2011 John Wiley & Sons, Ltd.
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231) Synthesis of new thermoplastic elastomers by silver nanoparticles as cross-linker
Author(s): Bokern, S (Bokern, Stefan); Fan, ZY (Fan, Ziyin); Mattheis, C (Mattheis, Claudia); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULES  Volume: 44  Issue: 12  Pages: 5036-5042  DOI: 10.1021/ma200738b  Published: JUN 28 2011  
Abstract: A novel type of elastomers with silver nanoparticles (AgNP) as cross-linkers has been obtained by a quantitative one-phase bottom-up procedure based on alpha,omega-dimercapto-poly(cis-1,4-isoprene) (PIP). This telechelic polymer with high cis-content of >80% and near-quantitative fiinctionalization degree has been synthesized in a one-pot procedure by anionic polymerization. It was cross-linked by coordination of the thiol groups to in-situ synthesized AgNP to yield a repeatedly melt-processable elastomer. It was found that the E-modulus increased up to an ideal ratio of AgNP to PIP and decreases drastically with AgNP oversaturation due to decreasing cross-linking density. Swelling experiments were in agreement with these results. The cross-linking of telechelic polymers with metal nanoparticles has been applied to other metals and polymers, leading to cross-linked materials in all cases. Antibacterial properties of the silver-containing elastomers were found by the Kirby-Bauer test.
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230) Stimuli-Responsive Elastic Polyurethane-Based Superabsorber Nanomat Composites
Author(s): Chen, F (Chen, Fei); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 296  Issue: 6  Pages: 517-523  DOI: 10.1002/mame.201000387  Published: JUN 16 2011  
Abstract: Photoresponsive superabsorber particles containing a crosslinked hydrophilic core and a hydrophobic azobenzene-containing shell were used to prepare photoresponsive polymeric nanomats, thus combining photoresponsivity with high porosity, toughness, and hydrophilicity. The properties of the nanomat composites were highly dependent upon the amount of the superabsorber photochromic particles added. Stable, highly elastic composite nanomats with very high loading (up to approximate to 50 wt.-%), good water absorption capacity (4000%) and relatively good tensile strength (3 MPa) were obtained. The photoresponsive behavior of the composites is demonstrated, which leads to relatively fast water desorption.
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229) Electrospun and solution blown three-dimensional carbon fiber nonwovens for application as electrodes in microbial fuel cells
Author(s): Chen, SL (Chen, Shuiliang); Hou, HQ (Hou, Haoqing); Harnisch, F (Harnisch, Falk); Patil, SA (Patil, Sunil A.); Carmona-Martinez, AA (Carmona-Martinez, Alessandro A.); Agarwal, S (Agarwal, Seema); Zhang, YY (Zhang, Yiyun); Sinha-Ray, S (Sinha-Ray, Suman); Yarin, AL (Yarin, Alexander L.); Greiner, A (Greiner, Andreas); Schroder, U (Schroeder, Uwe)
Source: ENERGY & ENVIRONMENTAL SCIENCE  Volume: 4  Issue: 4  Pages: 1417-1421  DOI: 10.1039/c0ee00446d  Published: APR 2011  
Abstract: Three-dimensional carbon fiber electrodes prepared by electrospinning and solution blowing are shown to be excellent electrode materials for bioelectrochemical systems such as microbial fuel cells or microbial electrolysis cells. The bioelectrocatalytic anode current density is shown to reach values of up to 30 A m(-2), which represents the highest reported values for electroactive microbial biofilms.
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228) Design of pheromone releasing nanofibers for plant protection
Author(s): Hellmann, C (Hellmann, Christoph); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 22  Issue: 4  Pages: 407-413  DOI: 10.1002/pat.1532  Published: APR 2011  
Abstract: Plants tend to attract diseases quite similar to human beings. Pesticides tend to be used to control such diseases. An alternative route, at least as far as damages from insects is concerned, envisions the application of pheromones. These cause a disorientation of male insects so that they are no longer able to locate the females, which finally gives rise to suppression of reproduction. The approach considered in this paper is based on the release of pheromones from polymer carriers, in particular, from nanofibers webs as obtained by electrospinning. These may be distributed across the field quite similar to spider webs. The pheromones are required to be incorporated in sufficiently high concentrations in the nanofibers via electrospinning and to be released from the nanofibers for a sufficiently long time expanding over several weeks to months. Polyamide 6 as well as cellulose acetate was used as a polymer carrier in the investigations reported in this contribution. Studies reveal that fluid pheromones can, in fact, be incorporated in the nanofibers to more than 33 wt%. They may undergo a nanoscalar phase separation within the fibers during electrospinning. Furthermore, thermogravimetric studies revealed via in vitro release studies that the pheromones are released from the nanofibers in a nearly linear fashion over a period covering many weeks. Copyright (C) 2009 John Wiley & Sons, Ltd.
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227) Polymer/Bacteria Composite Nanofiber Nonwovens by Electrospinning of Living Bacteria Protected by Hydrogel Microparticles
Author(s): Gensheimer, M (Gensheimer, Marco); Brandis-Heep, A (Brandis-Heep, Astrid); Agarwal, S (Agarwal, Seema); Thauer, RK (Thauer, Rudolf K.); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR BIOSCIENCE  Volume: 11  Issue: 3  Pages: 333-337  DOI: 10.1002/mabi.201000310  Published: MAR 10 2011  
Abstract: Physically crosslinked PVA-hydrogel microparticles are utilized for encapsulation of E. coli and M. luteus. The bacteria survive dry storage or treatment with bacteria-hostile organic solvents significantly better than unprotected bacteria as proven by culture-test experiments. The bacteria-protecting PVA microparticles are available for standard polymer-solution-processing techniques, as exemplarily shown by co-electrospinning of living bacteria encapsulated in dry PVA-hydrogel microparticles together with PVB-, PLLA-, and PCL-form organic solvents.
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226) On the way to clean and safe electrospinning-green electrospinning: emulsion and suspension electrospinning
Author(s): Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 22  Issue: 3  Special Issue: SI  Pages: 372-378  DOI: 10.1002/pat.1883  Published: MAR 2011  
Abstract: For the process of electrospinning, either water or organic solvents are used as solvents depending upon the solubility of the materials to be spun. For many applications, such as tissue engineering, biomedical, agricultural, etc., the toxicity of the organic solvent used could be highly critical. Besides this, the high viscosities of such polymer solutions even for low weight per cent (wt%) polymer solutions (generally for conventional electrospinning a maximum of 10-15wt% polymer solution can be used) prevent high polymer concentrations and thereby reduces the productivity of the electrospinning process. This justifies the need for an approach which would alleviate concerns regarding safety, toxicology, and environmental problems, in addition, would also overcome the restrictions of too high polymer concentrations of polymer solutions. The answer could be suspension electrospinning. The term suspension electrospinning is referred to the electrospinning of aqueous dispersions (lattices) of water insoluble polymers and is defined in this article as Green Electrospinning. The present mini review highlights the efforts in this promising area of Emulsion and Suspension Electrospinning including their chances and limitations. Copyright (C) 2011 John Wiley & Sons, Ltd.
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225) Polymer grafted silver and copper nanoparticles with exceptional stability against aggregation by a high yield one-pot synthesis
Author(s): Bokern, S (Bokern, Stefan); Getze, J (Getze, Julia); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: POLYMER  Volume: 52  Issue: 4  Pages: 912-920  DOI: 10.1016/j.polymer.2010.12.031  Published: FEB 17 2011  
Abstract: A straightforward synthesis of silver nanoparticles (mean diameters well below 4 nm) with a "graft-to" polystyrene shell (PS@Ag) is described and different synthesis routes are compared. In addition to standard methods like TEM, XRD, UV/Vis and DSC the hybrid material has also been characterized by gel permeation chromatography (GPC).
Long-term stable hybrid materials with silver contents up to 18 wt-% have been realized. The exceptional stability allows industrial-scale processing by melt extrusion. No aggregation or agglomeration of silver nanoparticles is observed after melt co-extrusion with conventional polystyrene at 190 C. The co-extruded blends with silver nanoparticle contents up to 1 wt-% show a homogenous dispersion of nanoparticles in the polystyrene matrix. The synthesis route has also been applied to PS-block-PMMA stabilized silver nanoparticles and to copper to yield polystyrene-stabilized copper nanoparticles with diameters well below 3 nm. (C) 2011 Elsevier Ltd. All rights reserved.
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224) Polymer-bound 4-methylcoumarin/1-heptanoyl-5-fluorouracil photodimers: NMR elucidation of dimer structure
Author(s): Sinkel, C (Sinkel, Carsten); Schwarzer, MC (Schwarzer, Martin C.); Frenking, G (Frenking, Gernot); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MAGNETIC RESONANCE IN CHEMISTRY  Volume: 49  Issue: 2  Pages: 70-75  DOI: 10.1002/mrc.2711  Published: FEB 2011  
Abstract: Heterodimers based on the polymer-bound chromophore 4-methylcoumarin and the prodrug 1-heptanoyl-5-fluorouracil, synthesized by photochemical [2 + 2]-cycloaddition are promising photoresponsive drug depots. Drug release experiments are one possibility to deliver proof of a successful reversible drug immobilization, whereas NMR spectroscopy is a potent tool for further structural characterization of these polymer-bound heterodimers. In case of the random copolymer poly(methyl methacrylate-co-7-(2'-methacryloyloxyethoxy)-4-methylcoumarin) three dimers have been identified of which the syn head-to-tail was the predominant one. In contrast, only the syn head-to-head dimer was formed in reasonable yield when the 4-methylcoumarin monofunctionalized pMMA was used as the base polymer. 1D and 2D NMR spectroscopic techniques combined with some theoretical calculations helped in successfully closing one major gap concerning polymer bound 4-methylcoumarin/1-heptanoyl-5-fluorouracil heterodimers that are of potential use in photoresponsive drug delivery devices. Copyright (C) 2011 John Wiley & Sons, Ltd.
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223) Living characteristics of the free-radical ring-closing polymerization of diallyldimethylammonium chloride
Author(s): Blinco, JP (Blinco, James P.); Greiner, A (Greiner, Andreas); Barner-Kowollik, C (Barner-Kowollik, Christopher); Agarwal, S (Agarwal, Seema)
Source: EUROPEAN POLYMER JOURNAL  Volume: 47  Issue: 1  Pages: 111-114  DOI: 10.1016/j.eurpolymj.2010.10.025  Published: JAN 2011  
Abstract: In this communication we provide the most recent results on RAFT-mediated ring-closing polymerization of diallyldimethylammonium chloride (DADMAC) The polymerization was carried out in aqueous solution employing 2 2`-azobis(2-methylpropionamidine)-dihydrochloride as the free radical initiator and trithiocarbonate RAFI' agent (2-{[(dodecylsulfanyl)carbonothioyl sulfanyl]}propanoic acid DoPAT) as the controlling RAFT agent The results show that - while the system is not as completely controlled as previously described - it is nevertheless possible to mediate the polymerization of DADMAC and impart some living characteristics onto the system The initial study on the RAFT-mediated polymerization of DADMAC may have overestimated the degree of livingness within this reaction However it is possible - at low conversions - for some living characteristics to be observed as the evolution of molecular weight with conversion is linear In addition polymers with a reasonably narrow polydispersity can be Isolated (c) 2010 Elsevier Ltd All rights reserved
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222) Vielseitige Nanofaserstrukturen durch Elektrospinnen.
Author(s): WENDORFF, J. H.; AGARWAL, S.; GREINER, A.
Source: Nachrichten aus der Chemie  Volume: 59  Pages: 714-718 DOI: 10.1002/nadc.201180495 Published: 2011  
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221) Organic electrospun nanofibers as vehicles toward intelligent pheromone dispensers: characterization by laboratory investigations.
Author(s): LINDNER, I.; HEIN, D. F.; BREUER, M.; HUMMEL, H. E.; DEUKER, A.; VILCINSKAS, A.; LEITHOLD, G.; HELLMANN, CH.; DERSCH, R.; WENDORFF, J. H.; GREINER, A.
Source: Common. Appl. Biol. Sci.  Volume: 76  Pages: 1-9  Published: 2011  
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2010

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220) Highly Oriented Crystalline PE Nanofibrils Produced by Electric-Field-Induced Stretching of Electrospun Wet Fibers
Author(s): Yoshioka, T (Yoshioka, Taiyo); Dersch, R (Dersch, Roland); Greiner, A (Greiner, Andreas); Tsuji, M (Tsuji, Masaki); Schaper, AK (Schaper, Andreas K.)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 295  Issue: 12  Pages: 1082-1089  DOI: 10.1002/mame.201000207  Published: DEC 10 2010  
Abstract: In order to enhance the molecular orientation of electrospun nanofibers, a novel collection technique is proposed and applied to the spinning of polyethylene from high temperature solution. The technique makes use of a parallel-electrode collector that acts before solidification of the fiber occurs. The resulting multiple-necking morphology is composed of fine nanofibrils with very small diameter and narrow size distribution. The crystalline orientation of the nanofibrils was analyzed by TED. The formation mechanism of the nanofibrils is discussed. The strong elongational effect of the electric-field-induced stretching force in the parallel-electrode collector is demonstrated by the orientational analysis and by observation of the multiple-necking morphology.
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219) Novel 'Nano in Nano' Composites for Sustained Drug Delivery: Biodegradable Nanoparticles Encapsulated into Nanofiber Non-Wovens
Author(s): Beck-Broichsitter, M (Beck-Broichsitter, Moritz); Thieme, M (Thieme, Marcel); Nguyen, J (Nguyen, Juliane); Schmehl, T (Schmehl, Thomas); Gessler, T (Gessler, Tobias); Seeger, W (Seeger, Werner); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas); Kissel, T (Kissel, Thomas)
Source: MACROMOLECULAR BIOSCIENCE  Volume: 10  Issue: 12  Pages: 1527-1535  DOI: 10.1002/mabi.201000100  Published: DEC 8 2010  
Abstract: Novel 'nano in nano' composites consisting of biodegradable polymer nanoparticles incorporated into polymer nanofibers may efficiently modulate drug delivery. This is shown here using a combination of model compound-loaded biodegradable nanoparticles encapsulated in electrospun fibers. The dye coumarin 6 is used as model compound for a drug in order to simulate drug release from loaded poly(lactide-co-glycolide) nanoparticles. Dye release from the nanoparticles occurs immediately in aqueous solution. Dye-loaded nanoparticles which are encapsulated by electrospun polymer nanofibers display a significantly retarded release.
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218) Nanofibers by Green Electrospinning of Aqueous Suspensions of Biodegradable Block Copolyesters for Applications in Medicine, Pharmacy and Agriculture
Author(s): Sun, JY (Sun, Jinyuan); Bubel, K (Bubel, Kathrin); Chen, F (Chen, Fei); Kissel, T (Kissel, Thomas); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 31  Issue: 23  Pages: 2077-2083  DOI: 10.1002/marc.201000379  Published: DEC 1 2010  
Abstract: Poly(hexamethylene adipate)-PEO block copolymers (PHA-b-PEO) with different PEO contents were synthesized and processed to aqueous suspensions with high solid contents by a solvent displacement method followed by dialysis. The best suspension displayed a solid content of 16 wt.-% and an average particle size of 108 nm. This suspension was mixed with a small amount of high molecular weight PEO and Brij78 and electrospun into corresponding nanofibers. After extraction with water, nanofibers of PHA-b-PEO were obtained. Electrospinning of aqueous suspensions of biodegradable polyesters alleviates concerns regarding safety, toxicology and environmental problems, which are associated with spinning of such polyesters from harmful organic solvents and thereby offers novel perspectives for applications in medicine, pharmacy and agriculture. Electrospinning of polymers from aqueous suspensions avoiding harmful organic solvents is suggested to be "green electrospinning''.
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217) Gradient nanowires and nanotubes
Author(s): Agarwal, S (Agarwal, S.); Eckhardt, B (Eckhardt, B.); Grossmann, F (Grossmann, F.); Greiner, A (Greiner, A.); Goring, P (Goering, P.); Wehrspohn, RB (Wehrspohn, R. B.); Wendorff, J (Wendorff, J.)
Source: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS  Volume: 247  Issue: 10  Pages: 2451-2457  DOI: 10.1002/pssb.201046240  Published: OCT 2010  
Abstract: Different routes to prepare gradient nanowire and nanotubes are presented including the use of polymeric and metal nanoparticles. In the case of electrospinning, latex particles have been added to electrospinning solution. The properties of the fibres have been studied theoretically and experimentally. In the case of face-to-face-wetting of porous templates, solution as well as melt wetting for different polymeric composition from both sides of the template is carried out. It turned out that solution wetting leads to an intermixing of the compounds whereas as melt wetting leads to sharp compositional interfaces. The method has been extended to include plasmonic and magnetic nanoparticles for nanophotonic applications.
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(C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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216) A Polymeric Drug Depot Based on 7-(2 '-Methacryloyloxyethoxy)-4-methylcoumarin Copolymers for Photoinduced Release of 5-Fluorouracil Designed for the Treatment of Secondary Cataracts
Author(s): Sinkel, C (Sinkel, Carsten); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 211  Issue: 17  Pages: 1857-1867  DOI: 10.1002/macp.201000206  Published: SEP 1 2010  
Abstract: The synthesis of a polymeric, photoresponsive drug-delivery system on the basis of 4-methylcoumarin-side-chain-functionalized methacrylic copolymers with different degrees of functionalization is reported. Drug-release experiments in solution indicated a maximum release of 22 mu g of 5-fluorouracil per 1 mg of polymer. Polymer analogous photochemical drug immobilization does not lead to observable intermolecular cross-linking. Miscibility experiments with PMMA suggest that the bulk polymerization of homogeneous, transparent polymer sheets for intraocular lens fabrication, using MMA as the matrix monomer and incorporating the polymer-drug conjugates as a functional component, is possible.
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215) Structure property correlations for electrospun nanofiber nonwovens
Author(s): Hussain, D (Hussain, D.); Loyal, F (Loyal, F.); Greiner, A (Greiner, A.); Wendorff, JH (Wendorff, J. H.)
Source: POLYMER  Volume: 51  Issue: 17  Pages: 3989-3997  DOI: 10.1016/j.polymer.2010.06.036  Published: AUG 4 2010  
Abstract: Highly porous nonwovens composed of nanofibers and produced by electrospinning are key elements in a broad range in technical but also in Life Science areas. Applications for gas or fluid filtration, textile applications, carriers for catalysts and scaffolds for tissue engineering are selected examples. These applications require well defined nonwoven parameters such as in particular pore diameters, internal surfaces as well as permeation properties. Electrospinning, on the other hand, allows to control structural parameters such as fiber diameter, nonwoven architecture as well as in certain limits the total porosity. It is thus highly important to know as much as possible about the correlations between the structural parameters controlled by electrospinning and the parameters controlling the performance of the nonwovens composed of the electrospun nanofibers. In the present contribution we analyze these correlations for different types of electrospun nonwovens for a broad range of fiber diameters on an experimental scale The nonwoven considered are composed of polyacrylonitrile (PAN) and polyamide 6 (PA 6) fibers. Results are that pore diameters, specific surface area and permeation coefficients scale in a transparent way with fiber diameters. Finally we briefly compare these experimental results with corresponding predictions gained for ideal nonwovens predominantly from Monte Carlo simulations. The results suggest that one is able to design electrospun nanofiber based nonwovens with predetermined properties and functions in a highly controlled way. (C) 2010 Elsevier Ltd. All rights reserved.
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214) Chemistry on Electrospun Polymeric Nanofibers: Merely Routine Chemistry or a Real Challenge?
Author(s): Agarwal, S (Agarwal, Seema); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 31  Issue: 15  Pages: 1317-1331  DOI: 10.1002/marc.201000021  Published: AUG 3 2010  
Abstract: Nanofiber-based non-wovens can be prepared by electrospinning. The chemical modification of such nanofibers or chemistry using nanofibers opens a multitude of application areas and challenges. A wealth of chemistry has been elaborated in recent years on and with electrospun nanofibers. Known methods as well as new methods have been applied to modify the electrospun nanofibers and thereby generate new materials and new functionalities. This Review summarizes and sorts the chemistry that has been reported in conjunction with electrospun nanofibers. The major focus is on catalysis and nanofibers, enzymes and nanofibers, surface modification for biomedical and specialty applications, coatings of fibers, crosslinking, and bulk modifications. A critical focus is on the question: what could make chemistry on or with nanofibers different from bulk chemistry?
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213) Vinyl-Type Polymerization of Alkylester-Substituted Norbornenes Without Endo/Exo Separation
Author(s): Muller, K (Mueller, Kerstin); Jung, Y (Jung, Youngsuk); Yoon, DY (Yoon, Do Y.); Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 211  Issue: 14  Pages: 1595-1601  DOI: 10.1002/macp.200900647  Published: JUL 15 2010  
Abstract: The vinyl-type homo- and copolymerization of 9-norborn-5-en-2yl-nonane acid ethyl ester and 2-hexyl-5-norbornen was investigated. Both monomers were polymerized using di-mu-chlorobis(6-methoxybicyclo[2.2.1]hept-2-ene-endo-5 sigma,2 pi)palladium(II) and AgSbF(6) as catalysts. Poly(2-hexyl-5-norbornene) is soluble in common organic solvents and has a T(g) of 252 degrees C. Poly(9-norborn-5-en-2yl-nonane acid ethyl ester) shows swelling in solvents like THF, chlorobenzene or chloroform and has a T(g) of 136 degrees C. The solubility of the copolymers depends on the amount of 9-norborn-5-en-2yl-nonane acid ethyl ester. E-modulus measurements of copolymers with different amounts of ester showed an increase of flexibility when increasing the content of 9-norborn-5-en-2yl-nonane acid ethyl ester in the copolymer.
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212) Thermomorphological study of the terahertz lattice modes in polyvinylidene fluoride and high-density polyethylene
Author(s): Wietzke, S (Wietzke, Steffen); Jansen, C (Jansen, Christian); Reuter, M (Reuter, Marco); Jung, T (Jung, Tilmann); Hehl, J (Hehl, Judith); Kraft, D (Kraft, Dietmar); Chatterjee, S (Chatterjee, Sangam); Greiner, A (Greiner, Andreas); Koch, M (Koch, Martin)
Source: APPLIED PHYSICS LETTERS  Volume: 97  Issue: 2  Article Number: 022901  DOI: 10.1063/1.3462312  Published: JUL 12 2010  
Abstract: Semicrystalline polymers possess a complex morphology comprising both crystalline and amorphous domains. We investigate two representatives from this group, polyvinylidene fluoride and high-density polyethylene, with terahertz time-domain spectroscopy. Intriguingly, the thermal gradient of lattice modes arising from the crystalline phase changes at the glass transition. Thus, terahertz spectroscopy can identify the glass transition temperature T(g) even in highly crystalline polymers, where conventional methods such as differential scanning calorimetry fail. Furthermore, these findings provide experimental evidence of the strong interactions between the amorphous and the crystalline domains, as the glass transition is an exclusive feature of the mobile amorphous fraction. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3462312]
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211) RGD-functionalisation of PLLA nanofibers by surface coupling using plasma treatment: influence on stem cell differentiation
Author(s): Paletta, JRJ (Paletta, Jurgen Rudolf Josef); Bockelmann, S (Bockelmann, Sarah); Walz, A (Walz, Andreas); Theisen, C (Theisen, Christina); Wendorff, JH (Wendorff, Joachim Heinz); Greiner, A (Greiner, Andreas); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne); Schofer, MD (Schofer, Markus Dietmar)
Source: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE  Volume: 21  Issue: 4  Pages: 1363-1369  DOI: 10.1007/s10856-009-3947-2  Published: APR 2010  
Abstract: The aim of this study was to functionalize the surface of synthetic poly-(l-lactic) (PLLA) nanofibers with RGD peptide, in order to promote growth and osteogenic differentiation of human mesenchymal stem cells (hMSC) in vitro. The cRGD was coupled onto PLLA nanofibers using oxygen plasma combined with EDC/sulfo-NHS activation. Matrices were seeded with hMSC and cultivated over a period of 22 days under growth conditions and analyzed during the course of cultivation. The plasma activation of PLLA nanofibers resulted in a reduction of hydrophobicity as well as a formation of carboxyl groups on the surface of the fibers. Furthermore, maximum load, but not young's modulus was influenced by the treatment with oxygen plasma. When hMSC were cultured onto the cRGD functionalized scaffolds, cells showed no increased proliferation or cell density but an induction of genes associated with the osteoblast lineage. In brief, this study indicates that functional peptides of the extracellular matrix can be coupled onto PLLA nanofibers using plasma treatment in combination with EDC/sulfo-NHS treatment. These groups are accessible for the growing cell and mediate probably some osteoinductive properties of collagen nanofibers.
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210) In Vitro Study of Dexamethasone Release From Poly(p-xylylene) Films
Author(s): Hanefeld, P (Hanefeld, Phillip); Agarwal, S (Agarwal, Seema); Kumar, R (Kumar, Rakesh); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 211  Issue: 2  Pages: 265-269  DOI: 10.1002/macp.200900537  Published: JAN 19 2010  
Abstract: Stents or metal endoprotheses are currently used to prevent restenosis after percutaneous transluminal angioplasty (PTA). Recently multi-component systems comprising implant applications, e. g., stents, protective and/or a drug containing layers, have found wide-spread application. Permanent and biocompatible stent coatings based on polyp-xylylene) (PPX) films were investigated for their potential to form drug containing reservoirs. The model drug dexamethasone was loaded into films of PPX by solvent treatment. Loading efficiency and in vitro drug release profiles were studied under physiological conditions. Linear release of dexamethasone was observed when PPX/dexamethasone films were coated by an additional PPX film as cover layer.
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2009

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209) Effect of Different Bicomponent Electrospinning Techniques on the Formation of Polymeric Nanosprings
Author(s): Chen, SL (Chen, Shuiliang); Hou, HQ (Hou, Haoqing); Hu, P (Hu, Ping); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 294  Issue: 11  Pages: 781-786  DOI: 10.1002/mame.200900139  Published: NOV 12 2009  
Abstract: The effect of different bicomponent electrospinning techniques i.e., off-centered coaxial electrospinning and side-by-side electrospinning, on the formation of tight nanocoils (nanosprings) was studied. Since right balance between the longitudinal compressive forces arising from the shrinking thermoelastic components and the rigidity emerging from the stiff component and conductivity is required for nanospring formation, conductive solutions of flexible and rigid components were used for the electrospinning. Under optimum conditions, nanofiber mats with almost 100% nanospring morphology were generated using off-centered and side-by-side electrospinning techniques. Mechanical properties of aligned nanomats with and without nanosprings, produced at different collecting speeds are provided.
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208) Electrospinning of Manmade and Biopolymer Nanofibers-Progress in Techniques, Materials, and Applications
Author(s): Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachin H.)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 19  Issue: 18  Pages: 2863-2879  DOI: 10.1002/adfm.200900591  Published: SEP 23 2009  
Abstract: Electrospinning of nanofibers has developed quickly from a laboratory curiosity to a highly versatile method for the preparation of a wide variety of nanofibers, which are of interest from a fundamental as well as a technical point of view. A wide variety of materials has been processed into individual nanofibers or nanofiber mats with very different morphologies. The diverse properties of these nanofibers, based on different physical, chemical, or biological behavior, mean they are of interest for different applications ranging from filtration, antibacterial coatings, drug release formulations, tissue engineering, living membranes, sensors, and so on. A particular advantage of electrospinning is that numerous non-fiber forming materials can be immobilized by electrospinning in nanofiber nonwovens, even very sensitive biological objects such as virus, bacteria, and cells. The progress made during the last few years in the field of electrospinning is fascinating and is highlighted in this Feature Article, with particular emphasis on results obtained in the authors' research units. Specific areas of importance for the future of electrospinning, and which may open up novel applications, are also highlighted.
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207) Progress in the Field of Electrospinning for Tissue Engineering Applications
Author(s): Agarwal, S (Agarwal, Seema); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: ADVANCED MATERIALS  Volume: 21  Issue: 32-33  Pages: 3343-3351  DOI: 10.1002/adma.200803092  Published: SEP 4 2009  
Abstract: Electrospinning is an extremely promising method for the prevention of tissue engineering (TE) scaffolds. This technique provides nonwovens resembling in their fibrillar structures those of the extracellular matrix (ECM), and offering large surface areas, ease of functionalization for various purposes, and controllable mechanical properties. The recent developments toward large-scale productions combined with the simplicity of the process render this technique very attractive. Progress concerning the use of electrospinning for TE applications has advanced impressively. Different groups have tackled the problem of electrospinning for TE applications from different angles. Nowadays, electrospinning of the majority of biodegradable and biocompatible polymers, either synthetic or natural, for TE applications is straightforward. Different issues, such as cell penetration, incorporation of growth and differentiating factors, toxicity or solvents used, productivity, functional gradient, etc. are main points of current considerations. The progress in the use of electrospinning of TE applications is highlighted in this article with focus on major problems encountered and on various solutions available until now.
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206) Poly(styrene-co-n-butyl acrylate) Nanofibers with Excellent Stability against Water by Electrospinning from Aqueous Colloidal Dispersions
Author(s): Stoiljkovic, A (Stoiljkovic, Aleksandar); Venkatesh, R (Venkatesh, Rajan); Klimov, E (Klimov, Evgueni); Raman, V (Raman, Vijay); Wendorff, JH (Wendorff, J. H.); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULES  Volume: 42  Issue: 16  Pages: 6147-6151  DOI: 10.1021/ma900354u  Published: AUG 25 2009  
Abstract: Less brittle nanofibers with excellent stability against water can be prepared via electrospinning of dispersions of styrene-acrylate copolymers from an aqueous environment. The versatility of emulsion polymerization technique allows us to tailor a wide range of properties of the dispersed polymer and the subsequent nanofibers. It was shown that the minimum film formation temperature (MFFT) and correspondingly the glass transition temperature (T(g)) of the colloidal polymer, which can be varied by changing the composition of the monomers,have to be in the range of processing temperature, resulting in formation of the fibers with homogeneous morphology and good dimensional stability.
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205) Effect of direct RGD incorporation in PLLA nanofibers on growth and osteogenic differentiation of human mesenchymal stem cells
Author(s): Schofer, MD (Schofer, Markus Dietmar); Boudriot, U (Boudriot, Ulrich); Bockelmann, S (Bockelmann, Sarah); Walz, A (Walz, Andreas); Wendorff, JH (Wendorff, Joachim Heinz); Greiner, A (Greiner, Andreas); Paletta, JRJ (Paletta, Juergen Rudolf Josef); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne)
Source: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE  Volume: 20  Issue: 7  Pages: 1535-1540  DOI: 10.1007/s10856-009-3719-z  Published: JUL 2009  
Abstract: The aim of this study was to functionalize synthetic poly-(L-lactic) (PLLA) nanofibers by direct incorporation of cRGD, in order to promote adhesion, growth and osteogenic differentiation of human mesenchymal stem cells (hMSC) in vitro. The cRGD was incorporated into PLLA nanofibers either by emulsion [PLLA-cRGD (d)] or suspension [PLLA-cRGD (s)]. Matrices were seeded with hMSC and cultivated over a period of 28 days under growth conditions and analyzed during the course. Although the mode of incorporation resulted in different distributions of the RGD peptide, it had no impact on the fiber characteristics when compared to corresponding unblended PLLA control fibers. However, hMSC showed better adherence on PLLA-cRGD (d). Nevertheless, this advantage was not reflected during the course of cultivation. Furthermore, the PLLA-cRGD (s) fibers mediated the osteogenic potential of collagen (determined as the expression and deposition of collagen and osteocalcin) to some extent. Further studies are needed in order to optimize the RGD distribution and concentration.
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204) Polymeric Nanosprings by Bicomponent Electrospinning
Author(s): Chen, SL (Chen, Shuiliang); Hou, HQ (Hou, Haoqing); Hu, P (Hu, Ping); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 294  Issue: 4  Pages: 265-271  DOI: 10.1002/mame.200800342  Published: APR 14 2009  
Abstract: An enhanced elasticity of electrospun fibers while retaining their strength would be of great benefit for a set of applications (including tissue engineering). One route toward enhanced elasticity may be based on the introduction of curvature, i.e., of buckled or tight nanocoil (nanospring) configurations. The concept investigated in this contribution is to introduce such configurations via a differential shrinkage of a parallel arrangement of a flexible thermoplastic elastomer (polyurethane) component and a rigid thermoplastic component. Core-shell fibers are produced for this purpose by coaxial electrospinning. It is observed that buckling-nanospring formation can be achieved in this way. The morphology of such fibers and also modifications in the conductivity of the spinning solutions have a considerable effect on details of buckling and nanospring formation.
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203) Influence of nanofibers on the growth and osteogenic differentiation of stem cells: a comparison of biological collagen nanofibers and synthetic PLLA fibers
Author(s): Schofer, MD (Schofer, Markus Dietmar); Boudriot, U (Boudriot, Ulrich); Wack, C (Wack, Christina); Leifeld, I (Leifeld, Irini); Grabedunkel, C (Graebeduenkel, Christian); Dersch, R (Dersch, Roland); Rudisile, M (Rudisile, Markus); Wendorff, JH (Wendorff, Joachim Heinz); Greiner, A (Greiner, Andreas); Paletta, JRJ (Paletta, Jurgen Rudolf Josef); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne)
Source: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE  Volume: 20  Issue: 3  Pages: 767-774  DOI: 10.1007/s10856-008-3634-8  Published: MAR 2009  
Abstract: The aim of this study was to compare biological collagen I (ColI) and synthetic poly-(l-lactide) (PLLA) nanofibers concerning their stability and ability to promote growth and osteogenic differentiation of human mesenchymal stem cells in vitro. Matrices were seeded with human stem cells and cultivated over a period of 28 days under growth and osteoinductive conditions and analyzed during the course. During this time the PLLA nanofibers remained stable while the presence of cells resulted in an attenuation of the ColI nanofiber mesh. Although there was a tendency for better growth and osteoprotegerin production of stem cells when cultured on collagen nanofibers, there was no significant difference compared to PLLA nanofibers or controls. The gene expression of alkaline phosphate, osteocalcin and collagen I diminished in the initial phase of cultivation independent of the polymer used. In the case of PLLA fibers, this gene expression normalized during the course of cultivation, whereas the presence of collagen nanofibers resulted in an increased gene expression of osteocalcin and collagen during the course of the experiment. Taken together the PLLA fibers were easier to produce, more stable and did not compromise growth and differentiation of stem cells over the course of experiment. On the other hand, collagen nanofibers supported the differentiation process to some extent. Nevertheless, the need for fixation as well as the missing stability during cell culture requires further work.
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202) High Precision Deposition Electrospinning of nanofibers and nanofiber nonwovens
Author(s): Hellmann, C (Hellmann, Ch.); Belardi, J (Belardi, J.); Dersch, R (Dersch, R.); Greiner, A (Greiner, A.); Wendorff, JH (Wendorff, J. H.); Bahnmueller, S (Bahnmueller, S.)
Source: POLYMER  Volume: 50  Issue: 5  Pages: 1197-1205  DOI: 10.1016/j.polymer.2009.01.029  Published: FEB 23 2009  
Abstract: Electrospinning is known to produce nanofiber nonwovens with lateral dimensions in 10 cm up to the meter range meeting thus requirements characteristic of filter, textile or even tissue engineering applications. For particular applications other types of deposition pattern are of benefit (i) in which the deposition area is strongly limited in the lateral dimension, (ii) in which a linear deposition path is oriented along a specified direction or (iii) in which the nonwovens are deposited following a predesigned pattern. This paper reports experimental results for the High Precision Deposition Electrospinning (HPDE) approach introduced by us earlier. It is based on a syringe type die-counter electrode set-up used for conventional continuous electrospinning, the key feature being a reduction of the distance between the spinning die and the substrate from the conventional value of 10-50 cm down to the millimeter and below mm range in order to suppress the onset of bending instabilities and the corresponding spread of the deposition area. The architecture of the nonwovens is controlled in this case by buckling processes and deflections of the jet by transiently charged nanofibers on the substrate. A second important feature of the set-up is a counter electrode/substrate which can be subjected to precise motions in the deposition plane. Based on a careful optimization of the spinning parameters and a tight online control of the spinning process a deposition of individual nanofibers or nonwovens is achieved which meets all deposition requirements specified above. This opens the route towards novel applications among others in areas relying on specific surface architectures such as sensorics, microfluidics and possibly also surfaces of implants. (c) 2009 Elsevier Ltd. All rights reserved.
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201) Reusable Catalysts Based on Dendrimers Trapped in Poly(p-xylylene) Nanotubes
Author(s): Lindner, JP (Lindner, Jean-Pierre); Roben, C (Roeben, Caren); Studer, A (Studer, Armido); Stasiak, M (Stasiak, Michael); Ronge, R (Ronge, Ramona); Greiner, A (Greiner, Andreas); Wendorff, HJ (Wendorff, Hans-Joachim)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 48  Issue: 47  Pages: 8874-8877  DOI: 10.1002/anie.200903448  Published: 2009  
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200) Supercapacitors based on hybrid carbon nanofibers containing multiwalled carbon nanotubes
Author(s): Guo, QH (Guo, Qiaohui); Zhou, XP (Zhou, Xiaoping); Li, XY (Li, Xiaoyan); Chen, SL (Chen, Shuiliang); Seema, A (Seema, Agarwal); Greiner, A (Greiner, Andreas); Hou, HQ (Hou, Haoqing)
Source: JOURNAL OF MATERIALS CHEMISTRY  Volume: 19  Issue: 18  Pages: 2810-2816  DOI: 10.1039/b820170f  Published: 2009  
Abstract: Hybrid carbon nanofibers containing multiwalled carbon nanotubes (CNTs) were produced by electrospinning CNTs suspended in a solution of polyacrylonitrile in N,N-dimethylformamide, followed by carbonization and activation using a hydroperoxide-water steam mixture at 650 degrees C. Transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the CNT-embedded carbon nanofibers. The specific surface area of the nanofibers was measured using the Brunauer-Emmett-Teller method. The electrochemical properties of the nanofibers were characterized by cyclic voltammetry and galvanotactic charge/discharge in 1MH(2)SO(4) electrolyte. The specific capacitance of electric double-layer capacitors containing CNT-embedded carbon nanofibers as electrodes reached 310 F g(-1), which is almost double that obtained for capacitors containing virgin carbon nanofibers as electrodes. The CNTs embedded in the carbonized electrospun nanofibers provide improved conductive pathways for charge transfer in the electrodes and therefore lead to a significantly enhanced specific capacitance.
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199) "Barbed Nanowires" From Polymers via Electrospinning
Author(s): Holzmeister, A (Holzmeister, Andreas); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: POLYMER ENGINEERING AND SCIENCE  Volume: 49  Issue: 1  Pages: 148-153  DOI: 10.1002/pen.21233  Published: JAN 2009  
Abstract: Electrospinning is a highly versatile technique that allows producing fibers with diameters down to a few nanometers not only from polymers but also from metals, metal oxides, or ceramics. Fiber formation in electrospinning differs strongly from other fiber producing methods such as extrusion in that it is basically governed by self-assembly processes induced by specific electrostatic interactions following the Earnshaw theorem of electrostatics. This allows the production of nanofibers with very peculiar shapes. Here, we report the one step fabrication of barbed nanofibers due to a particular choice of the spinning conditions. Such barbed fibers allow, among others, to control the total porosity of nanofiber nonwovens and to reduce the tendency of linear nano-objects towards aggregation. POLYM. ENG. SCI., 49:148-153, 2009. (C) 2008 Society of Plastics Engineers
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198) Characterization of a PLLA-Collagen I Blend Nanofiber Scaffold with Respect to Growth and Osteogenic Differentiation of Human Mesenchymal Stem Cells
Author(s): Schofer, MD (Schofer, Markus Dietmar); Boudriot, U (Boudriot, Ulrich); Leifeld, I (Leifeld, Irini); Sutterlin, RI (Suetterlin, Romina Isolde); Rudisile, M (Rudisile, Markus); Wendorff, JH (Wendorff, Joachim Heinz); Greiner, A (Greiner, Andreas); Paletta, JRJ (Paletta, Juergen Rudolf Josef); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne)
Source: THESCIENTIFICWORLDJOURNAL  Volume: 9  Pages: 118-129  DOI: 10.1100/tsw.2009.13  Published: 2009  
Abstract: The aim of this study was to enhance synthetic poly(L-lactic acid) (PLLA) nanofibers by blending with collagen I (COLI) in order to improve their ability to promote growth and osteogenic differentiation of stem cells in vitro. Fiber matrices composed of PLLA and COLI in different ratios were characterized with respect to their morphology, as well as their ability to promote growth of human mesenchymal stem cells (hMSC) over a period of 22 days. Furthermore, the course of differentiation was analyzed by gene expression of alkaline phosphatase (ALP), osteocalcin (OC), and COLI. The PLLA-COLI blend nanofibers presented themselves with a relatively smooth surface. They were more hydrophilic as compared to PLLA nanofibers alone and formed a gel-like structure with a stable nanofiber backbone when incubated in aqueous solutions. We examined nanofibers composed of different PLLA and COLI ratios. A composition of 4: 1 ratio of PLLA: COLI showed the best results. When hMSC were cultured on the PLLA-COLI nanofiber blend, growth as well as osteoblast differentiation (determined as gene expression of ALP, OC, and COLI) was enhanced when compared to PLLA nanofibers alone. Therefore, the blending of PLLA with COLI might be a suitable tool to enhance PLLA nanofibers with respect to bone tissue engineering.
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197) Lack of Obvious Influence of PLLA Nanofibers on the Gene Expression of BMP-2 and VEGF during Growth and Differentiation of Human Mesenchymal Stem Cells
Author(s): Schofer, MD (Schofer, M. D.); Fuchs-Winkelmann, S (Fuchs-Winkelmann, S.); Wack, C (Wack, C.); Rudisile, M (Rudisile, M.); Dersch, R (Dersch, R.); Leifeld, I (Leifeld, I.); Wendorff, J (Wendorff, J.); Greiner, A (Greiner, A.); Paletta, JRJ (Paletta, J. R. J.); Boudriot, U (Boudriot, U.)
Source: THESCIENTIFICWORLDJOURNAL  Volume: 9  Pages: 313-319  DOI: 10.1100/tsw.2009.36  Published: 2009  
Abstract: Growth factors like bone morphogenetic protein 2 (BMP-2) and vascular endothelial growth factor (VEGF) play an important role in bone remodeling and fracture repair. Therefore, with respect to tissue engineering, an artificial graft should have no negative impact on the expression of these factors. In this context, the aim of this study was to analyze the impact of poly(L-lactic acid) (PLLA) nanofibers on VEGF and BMP-2 gene expression during the time course of human mesenchymal stem cell (hMSC) differentiation towards osteoblasts. PLLA matrices were seeded with hMSCs and cultivated over a period of 22 days under growth and osteoinductive conditions, and analyzed during the course of culture, with respect to gene expression of VEGF and BMP-2. Furthermore, BMP-2-enwoven PLLA nanofibers were used in order to elucidate whether initial down-regulation of growth factor expression could be compensated. Although there was a great interpatient variability with respect to the expression of VEGF and BMP-2, PLLA nanofibers tend to result in a down-regulation in BMP-2 expression during the early phase of cultivation. This effect was diminished in the case of VEGF gene expression. The initial down-regulation was overcome when BMP-2 was directly incorporated into the PLLA nanofibers by electrospinning. Furthermore, the incorporation of BMP-2 into the PLLA nanofibers resulted in an increase in VEGF gene expression. Summarized, the results indicate that the PLLA nanofibers have little effect on growth factor production. An enhancement in gene expression of BMP-2 and VEGF can be achieved by an incorporation of BMP-2 into the PLLA nanofibers.
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196) Influence of Poly-(L-Lactic Acid) Nanofiber Functionalization on Maximum Load, Young's Modulus, and Strain of Nanofiber Scaffolds Before and After Cultivation of Osteoblasts: An In Vitro Study
Author(s): Paletta, JRJ (Paletta, Juergen R. J.); Erffmeier, K (Erffmeier, Karla); Theisen, C (Theisen, Christina); Hussain, D (Hussain, Daniel); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne); Schofer, MD (Schofer, Markus D.)
Source: THESCIENTIFICWORLDJOURNAL  Volume: 9  Pages: 1382-1393  DOI: 10.1100/tsw.2009.149  Published: 2009  
Abstract: The aim of this study was to characterize the influence of functionalization of synthetic poly-(L-lactic acid) (PLLA) nanofibers on mechanical properties such as maximum load, elongation, and Young's modulus. Furthermore, the impact of osteoblast growth on the various nanofiber scaffolds stability was determined. Nanofiber matrices composed of PLLA, PLLA-collagen, or BMP-2-incorporated PLLA were produced from different solvents by electrospinning. Standardized test samples of each nanofiber scaffold were subjected to failure protocol before or after incubation in the presence of osteoblasts over a period of 22 days under osteoinductive conditions. PLLA nanofibers electrospun from hexafluoroisopropanol (HFIP) showed a higher strain and tended to have increased maximum loads and Young's modulus compared to PLLA fibers spun from dichloromethane. In addition, they had a higher resistance during incubation in the presence of cells. Functionalization by incorporation of growth factors increased Young's modulus, independent of the solvent used. However, the incorporation of growth factors using the HFIP system resulted in a loss of strain. Similar results were observed when PLLA was blended with different ratios of collagen. Summarizing the results, this study indicates that different functionalization strategies influence the mechanical stability of PLLA nanofibers. Therefore, an optimization of nanofibers should not only account for the optimization of biological effects on cells, but also has to consider the stability of the scaffold.
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2008

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195) Use of electrospinning technique for biomedical applications
Author(s): Agarwal, S (Agarwal, Seema); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: POLYMER  Volume: 49  Issue: 26  Pages: 5603-5621  DOI: 10.1016/j.polymer.2008.09.014  Published: DEC 8 2008  
Abstract: The electrospinning technique provides non-wovens to the order of few nanometers with large surface areas, ease of functionalisation for various purposes and superior mechanical properties. Also, the possibility of large scale productions combined with the simplicity of the process makes this technique very attractive for many different applications. Biomedical field is one of the important application areas among others utilising the technique of electrospinning like filtration and protective material, electrical and optical applications, sensors, nanofiber reinforced composites etc. Electrospinning assembly can be modified in different ways for combining materials properties with different morphological structures for these applications. The importance of electrospinning, in general, for biomedical applications like tissue engineering drug release, wound dressing, enzyme immobilization etc. is highlighted in this feature article. The focus is also on the types of materials that have been electrospun and the modifications that have been carried Out in conventional electrospinning apparatus keeping in view the specific needs for various biomedical applications. (c) 2008 Elsevier Ltd. All rights reserved.
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194) Polymer nanophase by use of electrospinning
Author(s): Agarwal, S (Agarwal, Seema); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: CHEMIE INGENIEUR TECHNIK  Volume: 80  Issue: 11  Pages: 1671-1676  DOI: 10.1002/cite.200800117  Published: NOV 2008  
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193) Electrospun Silica-Polybenzimidazole Nanocomposite Fibers
Author(s): von Graberg, T (von Graberg, Till); Thomas, A (Thomas, Arne); Greiner, A (Greiner, Andreas); Antonietti, M (Antonietti, Markus); Weber, J (Weber, Jens)
Source: MACROMOLECULAR MATERIALS AND ENGINEERING  Volume: 293  Issue: 10  Pages: 815-819  DOI: 10.1002/mame.200800183  Published: OCT 10 2008  
Abstract: A new route for the manufacturing of silica/poly(benzimidazole) (PBI) nanocomposites fibers is described. PBI was synthesized via melt polycondensation and polycondensation in poly(phosphoric acid). Solutions of PBI and silica nanoparticles in N,N-dimethylacetamide (DMAc) were electrospun to fibers and non-wovens. The resulting materials were analyzed by ATR-IR spectroscopy, small-angle X-ray scattering (SAXS) and nitrogen sorption measurements. The non-wovens could be processed towards dense, cross-linked membranes by hot pressing and treatment with p-xylylene dichloride.
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192) Electrospinning of poly-L-lactide nanofibers on liquid reservoir collectors
Author(s): Rocker, T (Roecker, Thorsten); Greiner, A (Greiner, Andreas)
Source: E-POLYMERS  Article Number: 111  Published: AUG 27 2008  
Abstract: The electrospinning process of Poly-L-lactide (PLA) solutions using liquid reservoir collectors was studied. As collector liquids, distilled water and sodium chloride solutions of different concentrations were used. A new, non-linear correlation of the fiber diameter and the filling of the collector was found. It was also proved, that the electrical conductivity of the substrate has a strong influence on the electrospinning process and the nanofibers obtained therein, both in diameter and in morphology.
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191) Immobilization of oligostyrene-prolinol conjugates into polystyrene via electrospinning and applications of these fibers in catalysis
Author(s): Roben, C (Roeben, Caren); Stasiak, M (Stasiak, Michael); Janza, B (Janza, Birgit); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.); Studer, A (Studer, Armido)
Source: SYNTHESIS-STUTTGART  Issue: 14  Pages: 2163-2168  DOI: 10.1055/s-2008-1067146  Published: JUL 16 2008  
Abstract: This paper reports the synthesis of prolinol-oligostytrene conjugates and their immobilization into a polystyrene matrix by using the electrospinning process. Via this approach fibers with a large surface area (fiber diameter of 1.2 mu m) containing the prolinol conjugate are readily obtained. The fibers are shown to be catalytically active in a test Michael reaction. The fibrous catalyst system can readily be removed from the reaction mixture and be reused. However, a decrease of the catalyst activity was noticed upon recycling the fibrous catalyst systems.
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190) Synthesis, characterization, and properties evaluation of methylcoumarin end-functionalized poly(methyl methacrylate) for photoinduced drug release
Author(s): Sinkel, C (Sinkel, Carsten); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULES  Volume: 41  Issue: 10  Pages: 3460-3467  DOI: 10.1021/ma702622p  Published: MAY 27 2008  
Abstract: The synthesis of novel methylcoumarin end-functionalized poly(methyl methacrylate) of different molecular weights using atom transfer radical polymerization (ATRP) is reported. 7-(2'-Bromoisobutyryloxy)4-methylcoumarin was used as the ATRP initiator at 70 degrees C using copper(I) bromide/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The theoretical and experimental number-average molecular weights M-n with narrow polydispersities (M-w/M-n = 1.1-1.4) agreed very well. Photochemical drug loading of the methylcoumarin end-functionalized polymer was performed in solution (chloroform/acetone 1:2) with benzophenone as additional photosensitizer using a 50-fold excess of the pro-drug 1-heptanoyl-5-fluorouracil (H5FU). UV/vis and NMR spectroscopy were used for the characterization of the polymer drug conjugate and indicated an almost quantitative conversion of coumarin moieties into photodimers. The change of polymer properties like thermal stability, glass transition, and molecular weight after photochemical drug immobilization was also studied. The glass transition temperature increased only negligibly, whereas the thermal decomposition commenced at considerably lower temperature for the polymer drug conjugate. The molecular weight distribution of the H5FU-loaded polymer showed no detectable chain degradation due to the applied UV irradiation. The characterization of the photoinduced drug release was investigated for a single photon absorption (SPA) process. The polymer drug conjugate was irradiated at lambda = 266 nm to cleave the cyclobutane linker between the methylcoumarin moiety and the pro-drug H5FU. The drug release was monitored and quantified using high-performance liquid chromatography (HPLC). Assuming quantitative hydrolysis of H5FU, 4.76 mu g of 5-fluorouracil (5FU) per 1 mg of polymer drug conjugate was released on irradiation.
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189) Cylindrical polymer nanostructures by solution template wetting
Author(s): Schlitt, S (Schlitt, Stefanie); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: MACROMOLECULES  Volume: 41  Issue: 9  Pages: 3228-3234  DOI: 10.1021/ma071822k  Published: MAY 13 2008  
Abstract: Wetting of porous templates, e.g., porous aluminum oxide with pore diameters in the range from 25 up to several 100 nm, by polymer melts has been demonstrated previously to be a highly effective way toward the preparation of polymer nanotubes. The concept evaluated in this contribution is to perform wetting from polymer solutions rather than from melts with particular emphasis on the influence of the molecular weight of the polymer used for wetting. Narrow molecular weight fractions were used for this purpose. The aim is to extend the nature of nanostructures which become available by wetting and to allow functionalization of the nanostructures by additives such as drugs or biological objects which decompose at elevated temperatures. Polystyrene was used as model polymer. Results are first of all that the quality of the solvent-good, Theta, or poor-and the polymer concentration are important wetting parameters as far as the preparation of stable cylindrical structures is concerned and second that nanowires, nanotubes, or cylindrical structures with a regular arrangement of voids can be prepared reproducibly by a proper variation of the molecular weight of the polymer used.
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188) Electrospun biodegradable nanofiber nonwovens for controlled release of proteins
Author(s): Maretschek, S (Maretschek, Sascha); Greiner, A (Greiner, Andreas); Kissel, T (Kissel, Thomas)
Source: JOURNAL OF CONTROLLED RELEASE  Volume: 127  Issue: 2  Pages: 180-187  DOI: 10.1016/j.jconrel.2008.01.011  Published: APR 21 2008  
Abstract: Electrospinning of emulsions composed of an organic poly(L-lactide) solution and an aqueous protein solution yielded protein containing nanofiber nonwovens (NNs) having a mean fiber diameter of approximately 350 nm. Cytochrome C was chosen as a hydrophilic model protein for encapsulation. SEM imaging and gas adsorption measurements were carried out to determine morphology and surface characteristics of the different nanofiber nonwovens. Transmission electron microscopy was used to clarify the localization of the protein within the NN. PLLA NNs exhibited a highly hydrophobic surface which led to a slow wetting. It was shown that the protein release was dependent on the surface tension of the release medium. Electrospinning of emulsions consisting of an organic solution of PLLA and an aqueous solution of hydrophilic polymers yielded fibers composed of a polymer blend. The resulting NNs exhibited a less hydrophobic surface, which gave us the opportunity to tailor the release profile via this technology. Furthermore it was investigated how the addition of different amounts of hydrophilic polymer to the aqueous phase influenced the morphology of the resulting NNs. (c) 2008 Elsevier B.V. All rights reserved.
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187) Stoichiometric functionalization of gold nanoparticles in solution through a free radical polymerization approach
Author(s): Kruger, C (Krueger, Christian); Agarwal, S (Agarwal, Seerna); Greiner, A (Greiner, Andreas)
Source: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  Volume: 130  Issue: 9  Pages: 2710-+  DOI: 10.1021/ja0763495  Published: MAR 5 2008  
Abstract: A new simple concept for the stoichiametrical funclionalization of nanoparticles based on free radical polymerization of vinyl protected nanoparticles is presented. To demonstrate this concept 2-bis(4-vinylphenyl)disulfane was synthesized and used in the synthesis of gold nanoparticles leading to 4-vinylthiophenol functionalized nanoparticles. Simple free radical polymerization of these particles initiated by 4,4'-azobis-(4-cyanopentanoic acid) delivered nanoparticles with a single carboxyl group. These monofunctionalized gold nanoparticles were utilized for chemical preparation of gold nanoparticle dippers as well as for construction of gold nanoparticle arrays via binding to polyallylamine.
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186) Polymer tubes with longitudinal composition gradient by face-to-face wetting
Author(s): Kriha, O (Kriha, Olaf); Gring, P (Gring, Petra); Milbradt, M (Milbradt, Marc); Azgarwal, S (Azgarwal, Seema); Steinhart, M (Steinhart, Martin); Wehrspohn, R (Wehrspohn, Ralf); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: CHEMISTRY OF MATERIALS  Volume: 20  Issue: 3  Pages: 1076-1081  DOI: 10.1021/cm702088v  Published: FEB 12 2008  
Abstract: Nanoporous and macroporous templates were simultaneously infiltrated from both of their opposite surfaces using model polymers labeled with fluorescent probes or bearing probe molecules detectable by energy-dispersive X-ray spectroscopy by precursor wetting. Face-to-face wetting with polymeric solutions resulted in partial mixing of both components, leading to tubular nanostructures characterized by a longitudinal composition gradient. Mixing of the components infiltrated from the opposite surfaces could be prevented by face-to-face wetting with polymeric melts, leading to the formation of tubular components predominantly consisting of the pure components that were separated by sharp interfaces.
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185) Electrospun nanofiber belts made from high performance copolyimide
Author(s): Chen, SL (Chen, Shuiliang); Hu, P (Hu, Ping); Greiner, A (Greiner, Andreas); Cheng, CY (Cheng, Chuyun); Cheng, HF (Cheng, Haofang); Chen, FF (Chen, Fangfang); Hou, HQ (Hou, Haoqing)
Source: NANOTECHNOLOGY  Volume: 19  Issue: 1  Article Number: 015604  DOI: 10.1088/0957-4484/19/01/015604  Published: JAN 9 2008  
Abstract: Electrospun nanofibers based on copolyimides were made, aiming at finding a promising method for improving the mechanical properties of electrospun polyimide nanofibers. The copolyimide had a backbone consisting of 3,3', 4,4'-biphenyl-tetracarboxylic dianhydride (BPDA), biphenylamide (BPA) and 4,4'-oxydianiline (ODA) residues. The structure and composition of the copolyimide was controlled by the ratio of rigid BPA and flexible ODA moieties. The electrospun copolyimide nanofibers were collected in the form of a belt using a rotating disc with a rim of 8 mm width. Scanning electron microscopy (SEM), infrared (IR) spectroscopy, x-ray scattering and tensile testing, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were used to characterize the nanofiber belts. The nanofibers had a diameter range from 80 to 300 nm and were well aligned in the belts. The thermal stability of the nanofiber belts was over 460 degrees C. The tensile test showed that the copolyimide nanofiber belts had much better mechanical properties than either of the flexible and rigid homo-polyimide (homo-PI) nanofiber belts. The tensile strength, modulus and elongation to break of the copolyimide nanofiber belt with BPA/ODA ratio of 40/60 are respectively 1.1 +/- 0.1 GPa, 6.2 +/- 0.7 GPa and 20.8 +/- 1.2%, compared to 459 +/- 36 MPa, 2.1 +/- 0.3 GPa and 41.3 +/- 2.2% for BPDA/ODA homo-PI as well as 384 +/- 18 MPa, 11.5 +/- 0.6 GPa and 3.9 +/- 0.1% for BPDA/BPA homo-PI. The important feature is that the electrospun polymer nanofibers can be made very strong by using copolyimides as spinning materials.
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184) Functional Self-Assembled Nanofibers by Electrospinning
Author(s): Greiner, A (Greiner, A.); Wendorff, JH (Wendorff, J. H.)
Edited by: Shimizu T
Source: SELF-ASSEMBLED NANOMATERIALS I: NANOFIBERS  Book Series: Advances in Polymer Science  Volume: 219  Pages: 107-171  DOI: 10.1007/12_2008_146  Published: 2008  
Abstract: Electrospinning constitutes a unique technique for the production of nanofibers with diameters down to the range of a few nanometers. In strong contrast to conventional fiber producing techniques, it relies on self-assembly processes driven by the Coulomb interactions between charged elements of the fluids to be spun to nanofibers. The transition from a macroscopic fluid object such as a droplet emerging from a die to solid nanofibers is controlled by a set of complex physical instability processes. They give rise to extremely high extensional deformations and strain rates during fiber formation causing among others a high orientational order in the nanofibers as well as enhanced mechanical properties. Electrospinning is predominantly applied to polymer based materials including natural and synthetic polymers, but, more recently, its use has been extended towards the production of metal, ceramic and glass nanofibers exploiting precursor routes. The nanofibers can be functionalized during electrospinning by introducing pores, fractal surfaces, by incorporating functional elements such as catalysts, quantum dots, drugs, enzymes or even bacteria. The production of individual fibers, random nonwovens, or orientationally highly ordered nonwovens is achieved by an appropriate selection of electrode configurations. Broad areas of application exist in Material and Life Sciences for such nanofibers, including not only optoelectronics, sensorics, catalysis, textiles, high efficiency filters, fiber reinforcement but also tissue engineering, drug delivery, and wound healing. The basic electrospinning process has more recently been extended towards compound co-electrospinning and precision deposition electrospinning to further broaden accessible fiber architectures and potential areas of application.
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183) Influence of Poly(L-Lactic Acid) Nanofibers and BMP-2-Containing Poly(L-Lactic Acid) Nanofibers on Growth and Osteogenic Differentiation of Human Mesenchymal Stem Cells
Author(s): Schofer, MD (Schofer, Markus D.); Fuchs-Winkelmann, S (Fuchs-Winkelmann, Susanne); Grabedunkel, C (Graebeduenkel, Christian); Wack, C (Wack, Christina); Dersch, R (Dersch, Roland); Rudisile, M (Rudisile, Markus); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas); Paletta, JRJ (Paletta, Juergen R. J.); Boudriot, U (Boudriot, Ulrich)
Source: THESCIENTIFICWORLDJOURNAL  Volume: 8  Pages: 1269-1279  DOI: 10.1100/tsw.2008.163  Published: 2008  
Abstract: The aim of this study was to characterize synthetic poly-(L-lactic acid) (PLLA) nanofibers concerning their ability to promote growth and osteogenic differentiation of stem cells in vitro, as well as to test their suitability as a carrier system for growth factors. Fiber matrices composed of PLLA or BMP-2-incorporated PLLA were seeded with human mesenchymal stem cells and cultivated over a period of 22 days under growth and osteoinductive conditions, and analyzed during the course of culture, with respect to gene expression of alkaline phosphatase (ALP), osteocalcin (OC), and collagen I (COL-I). Furthermore, COL-I and OC deposition, as well as cell densities and proliferation, were analyzed using fluorescence microscopy. Although the presence of nanofibers diminished the dexamethasone-induced proliferation, there were no differences in cell densities or deposition of either COL-I or OC after 22 days of culture. The gene expression of ALP, OC, and COL-I decreased in the initial phase of cell cultivation on PLLA nanofibers as compared to cover slip control, but normalized during the course of cultivation. The initial down-regulation was not observed when BMP-2 was directly incorporated into PLLA nanofibers by electrospinning, indicating that growth factors like BMP-2 might survive the spinning process in a bioactive form.
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182) State-of-the-art of polymer nanofibers.
Author(s): AGARWAL, S.; GREINER, A.
Source: Man-Made Fiber Year Book  Volume: 10  Pages: 1  Published: 2008  
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181) An introduction to electrospinning and nanofibers (book review).
Author(s): GREINER, A.
Source: Journal of Engineered Fibers. And Fabrics  Volume: 3  Pages: 46-47  Published: 2008  
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2007

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180) Magnetically anisotropic cobalt and iron nanofibers via electrospinning
Author(s): Graeser, M (Graeser, Martin); Bognitzki, M (Bognitzki, Michael); Massa, W (Massa, Werner); Pietzonka, C (Pietzonka, Clemens); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: ADVANCED MATERIALS  Volume: 19  Issue: 23  Pages: 4244-+  DOI: 10.1002/adma.200700849  Published: DEC 3 2007  
Abstract: Magnetically anisotropic cobalt and iron nanofibers (see figure) are obtained via oriented polymer-supported electrospinning and subsequent reduction and thermal treatment. The cobalt and iron nature of the fibers is confirmed by XRD analysis. Fibers of both metals show ferromagnetic behavior. Parallel aligned iron nanofibers revealed anisotropic hysteresis loops depending on field-fiber orientation.
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179) Structurally and chemically heterogeneous nanofibrous nonwovens via electrospinning
Author(s): Holzmelster, A (Holzmelster, Andreas); Rudisile, M (Rudisile, Markus); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: EUROPEAN POLYMER JOURNAL  Volume: 43  Issue: 12  Pages: 4859-4867  DOI: 10.1016/j.eurpolymj.2007.09.014  Published: DEC 2007  
Abstract: Homogeneous nonwovens composed of polymer nanofibers of a given diameter are characterized by structural parameters such as the average pore sizes and internal surfaces as well as by transport properties, which are strongly correlated to the fiber diameter Lit a given porosity. Such nonwovens are used among others for filter applications, protective clothing or as scaffolds for tissue engineering. A frequent requirement is that, to be able to prepare nonwovens optimised for the specific application, one has to find ways to disrupt this strong correlation allowing independent modification of pore diameter, transport properties and internal Surface or to induce local chemical and Structural heterogeneities within the nonwoven. The route explored in this paper is based on the electrospinning of heterogeneous nonwovens composed of nanofibers with two different average diameters (by a ratio of up to 10 and more) on the one hand and/or different chemical nature on the other hand. Spinning parameters have been optimised to achieve this goal. In addition, nonwovens composed of fibers with circular cross-section and with ribbon-like cross-section have been prepared. (c) 2007 Elsevier Ltd. All right reserved.
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178) Micrcowave-assisted controlled ring-closing cyclopolymerization of diallyldimethylammonium chloride via the RAFT process
Author(s): Assem, Y (Assem, Yasser); Greiner, A (Greiner, Andreas); Agarwal, S (Agarwal, Seema)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 28  Issue: 18-19  Pages: 1923-1928  DOI: 10.1002/marc.200700377  Published: SEP 18 2007  
Abstract: The present studies provide the first example of controlled free radical polymerization of a cyclopolymerizing monomer, i.e. diallyldimethylammonium chloride (DADMAC) via reversible addition fragmentation chain transfer (RAFT) chemistry in the presence of trithiocarbonate agent in aqueous solution at 60 degrees C under microwave irradiation. The polymers [poly(diallyldimethylammonium chloride), PDADMAC] were soluble in water characterization of the polymers was achieved via NMR spectroscopy. The cyclization reactions during DADMAC polymerization under microwave! irradiation attained higher conversions at each time interval as compared to thermal heating. The rate enhancements till around 520% were seen for some reactions. High molecular weight PDADMAC with narrow poly-dispersities (approaching PDI approximate to 1.05) could be made using microwave irradiation.
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177) Novel biohybrid materials by electrospinning: Nanofibers of poly(ethylene oxide) and living bacteria
Author(s): Gensheimer, M (Gensheimer, Marco); Becker, M (Becker, Mathias); Brandis-Heep, A (Brandis-Heep, Astrid); Wendorff, JH (Wendorff, Joachim H.); Thauer, RK (Thauer, Rudolf K.); Greiner, A (Greiner, Andreas)
Source: ADVANCED MATERIALS  Volume: 19  Issue: 18  Pages: 2480-+  DOI: 10.1002/adma.200602936  Published: SEP 17 2007  
Abstract: Poly(ethylene oxide) (PEO) fibers with living bacteria were obtained by electrospinning of aqueous dispersions of E. coli and Microccus luteus bacteria with PEO. E. coli as well as Micrococcus luteus bacteria survived electrospin ning process. However, E. coli did not survive dry storage in PEO nonwovens at 20 degrees C for more than one hour. In contrast, Micrococcus luteus survived at least 250 h dry storage at 20 degrees C in eletrospun PEO nonwovens.
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176) Connection of hippocampal neurons by magnetically controlled movement of short electrospun polymer fibers - A route to magnetic micromanipulators
Author(s): Kriha, O (Kriha, Olaf); Becker, M (Becker, Mathias); Lehmann, M (Lehmann, Martina); Kriha, D (Kriha, Dorothee); Krieglstein, J (Krieglstein, Josef); Yosef, M (Yosef, Maekele); Schlecht, S (Schlecht, Sabine); Wehrspohn, RB (Wehrspohn, Ralf B.); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: ADVANCED MATERIALS  Volume: 19  Issue: 18  Pages: 2483-+  DOI: 10.1002/adma.200601937  Published: SEP 17 2007  
Abstract: Controlled movement of short electrospun fluorescent fibers has been accomplished by electrospinning of anthracene-modified PMMA loaded with superparamagnetic cobalt nanoparticles. Subsequently, composite fibers were mechanically cut, dispersed in water and moved under the influence of an external ferromagnet.
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175) Design of polymer nanofiber systems for the immobilization of homogeneous catalysts - Preparation and leaching studies
Author(s): Stasiak, M (Stasiak, Michael); Roben, C (Roeben, Caren); Rosenberger, N (Rosenberger, Nadine); Schleth, F (Schleth, Florian); Studer, A (Studer, Armido); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: POLYMER  Volume: 48  Issue: 18  Pages: 5208-5218  DOI: 10.1016/j.polymer.2007.07.006  Published: AUG 24 2007  
Abstract: In this paper a novel general concept for the immobilization of catalysts is presented. It will be shown that catalysts covalently bound to low-molecular weight polystyrene (M-n > 4000 g/mol) can be immobilized into high molecular weight polystyrene nanofibers using the electro-spinning process. The immobilized catalyst-oligostyrene conjugates are well dispersed within the fibers as shown by DSC and X-ray studies. In DMSO, the oligostyrene tails of the catalysts suppress the leaching of the catalysts out of the fibers into the solution for thermodynamic reasons. Leaching studies are conducted using naphthalene-conjugated oligostyrenes using fluorescence spectroscopy. The naphthalene-polystyrene conjugates with defined molecular weight are readily prepared using nitroxide-mediated radical polymerization (NMP). As a model catalyst system, proline-poly styrene conjugates are synthesized by NMP to study catalyst leaching out of the polystyrene nanofibers used as a catalyst matrix. (c) 2007 Elsevier Ltd. All rights reserved.
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174) Polymer core-shell fibers with metal nanoparticles as nanoreactor for catalysis
Author(s): Graeser, M (Graeser, Martin); Pippel, E (Pippel, Eckhard); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: MACROMOLECULES  Volume: 40  Issue: 17  Pages: 6032-6039  DOI: 10.1021/ma070898d  Published: AUG 21 2007  
Abstract: We have prepared polymer core-shell fibers containing salts of palladium, rhodium, and platinum. These salts were reduced within the core of the fibers by thermal decomposition at elevated temperatures and by using hydrogen as reduction medium. Monometal nanoparticles as well as mixed bimetal nanoparticles were produced in this way. The resulting fibers consisted either of a hollow core carrying the nanoparticles or a polymer core in which the nanoparticles were distributed. Both systems were successfully applied to specific hydrogenation reactions in which the shell served the purpose of immobilizing the catalyst nanoparticles, controlling the access to them, and allowing their recovery after the reaction whereas the core acted as the confined reaction site with an easy access of the reactants to the catalytic sites.
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173) Preparation of water-stable submicron fibers from aqueous latex dispersion of water-insoluble polymers by electrospinning
Author(s): Stoiljkovic, A (Stoiljkovic, Aleksandar); Ishaque, M (Ishaque, Michael); Justus, U (Justus, Uwe); Hamel, L (Hamel, Lisa); Klimov, E (Klimov, Evgeni); Heckmann, W (Heckmann, Walter); Eckhardt, B (Eckhardt, Bruno); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: POLYMER  Volume: 48  Issue: 14  Pages: 3974-3981  DOI: 10.1016/j.polymer.2007.04.050  Published: JUN 29 2007  
Abstract: Submicron polystyrene (PS) fibers were prepared by electrospinning of an aqueous dispersion of PS latex and a small amount of poly(vinyl alcohol) (PVA) and subsequent extraction by water. Depending on particle size, surfactant, ratio of PS:PVA, and applied voltage fibers of different morphology and water stability were obtained. Analysis of latex fibers by TEM revealed hexagonal packaging of particles within the fibers. (c) 2007 Elsevier Ltd. All rights reserved.
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172) Nondestructive mechanical release of ordered polymer microfiber arrays from porous templates
Author(s): Grimm, S (Grimm, Silko); Schwirn, K (Schwirn, Kathrin); Goring, P (Goering, Petra); Knoll, H (Knoll, Heiko); Miclea, PT (Miclea, Paul T.); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.); Wehrspohn, RB (Wehrspohn, Ralf B.); Gosele, U (Goesele, Ulrich); Steinhart, M (Steinhart, Martin)
Source: SMALL  Volume: 3  Issue: 6  Special Issue: SI  Pages: 993-1000  DOI: 10.1002/smll.200600544  Published: JUN 2007  
Abstract: The fabrication of one-dimensional (1D) nanostructures and microstructures inside the pores of porous templates is intensively investigated. The release of these structures is commonly accomplished by etching and destroying the templates. The 1D nanostructures and microstructures tend to condense because of the occurrence of capillary forces during drying of the specimens. It is shown that highly ordered arrays of polymer microfibers can be easily detached from silanized porous templates by mechanical lift-off. This procedure leaves the templates intact, thus allowing their recycling, and does not involve the use of solutions or solvents, thus circumventing condensation. Therefore, mechanical lift-off may enable the up-scaling of template-based approaches to the fabrication of highly ordered assemblies of 1D nanostructures and microstructures.
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171) One-step production of polymeric microtubes by co-electrospinning
Author(s): Dror, Y (Dror, Y.); Salalha, W (Salalha, W.); Avrahami, R (Avrahami, R.); Zussman, E (Zussman, E.); Yarin, AL (Yarin, A. L.); Dersch, R (Dersch, R.); Greiner, A (Greiner, A.); Wendorff, JH (Wendorff, J. H.)
Source: SMALL  Volume: 3  Issue: 6  Special Issue: SI  Pages: 1064-1073  DOI: 10.1002/smll.200600536  Published: JUN 2007  
Abstract: Herein we demonstrate the ability to fabricate polymeric microtubes with an inner diameter of approximately 3 mu m through co-electrospinning of core and shell polymeric solutions. The mechanism by which the core/shell structure is transformed into hollow fibers (microtubes) is primarily based on the evaporation of the core solution through the shell and is described here in detail. Additionally, we present the filling of these microtubes, thus demonstrating their possible use in microfluidics. We also report the incorporation of a protein (green fluorescent protein) within such fibers, which is of interest for sensorics.
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170) Organic tube/rod hybrid nanofibers with adjustable segment lengths by bidirectional template wetting
Author(s): Kriha, O (Kriha, Olaf); Zhao, LL (Zhao, Lili); Pippel, E (Pippel, Eckhard); Gosele, U (Goesele, Ulrich); Wehrspohn, RB (Wehrspohn, Ralf B.); Wendorff, JH (Wendorff, Joachim H.); Steinhart, M (Steinhart, Martin); Greiner, A (Greiner, Andreas)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 17  Issue: 8  Pages: 1327-1332  DOI: 10.1002/adfm.200601021  Published: MAY 21 2007  
Abstract: Segmented nanotubes and nanorods exhibiting a variation in their composition along their long axes represent a new and exciting class of nanomaterials. It is shown that bidirectional template wetting enables the integration of functional and complex polymeric materials into segmented nanofibers. First, a template is wetted under conditions in which a solid polymeric thread with adjustable length fills a pore segment starting from one template surface. Subsequently, a second wetting step starting from the opposite template surface yields segmented nanofibers. ne exploitation of different wetting mechanisms results in the formation of tube/rod hybrid nanofibers.
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169) Poly(ethylene carbonate): A thermoelastic and biodegradable biomaterial for drug eluting stent coatings?
Author(s): Unger, F (Unger, F.); Westedt, U (Westedt, U.); Hanefeld, P (Hanefeld, P.); Wombacher, R (Wombacher, R.); Zimmermann, S (Zimmermann, S.); Greiner, A (Greiner, A.); Ausborn, M (Ausborn, M.); Kissel, T (Kissel, T.)
Source: JOURNAL OF CONTROLLED RELEASE  Volume: 117  Issue: 3  Pages: 312-321  DOI: 10.1016/j.jconrel.2006.11.003  Published: FEB 26 2007  
Abstract: A first feasibility study exploring the utility of poly(ethylene carbonate) (PEC) as coating material for drug eluting stents under in vitro conditions is reported. PEC (Mw 242 kDa, Mw/Mn=1.90) was found to be an amorphous polymer with thermoelastic properties. Tensile testing revealed a stress to strain failure of more than 600%. These properties are thought to be advantageous for expanding coated stents. In vitro cytotoxicity tests showed excellent cytocompatibility of PEC. Based on these findings, a new stenting concept was suggested, pre-coating a bare-metal stent with PPX-N as non-biodegradable basis and applying a secondary PEC coating using an airbrush method. After manual expansion, no delamination or destruction of the coating could be observed using scanning electron microscopy.
The surface degradation-controlled release mechanism of PEC may provide the basis for "on demand" drug eluting stent coatings, releasing an incorporated drug predominantly at an inflamed implantation site upon direct contact with superoxide-releasing macrophages. As a release model, metal plates of a defined size and area were coated under the same conditions as the stents with PEC containing radiolabelled paclitaxel. An alkaline KO2- solution served as a superoxide source. Within 12 h, 100% of the incorporated paclitaxel was released, while only 20% of the drug was released in non-superoxide releasing control buffer within 3 weeks. (c) 2006 Elsevier B.V. All rights reserved.
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168) Microwave-assisted free radical copolymerizations of styrene and methyl methacrylate
Author(s): Stange, H (Stange, Heiner); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 28  Issue: 4  Pages: 504-508  DOI: 10.1002/marc.200600841  Published: FEB 19 2007  
Abstract: Free radical copolymerizations of styrene and MMA were performed in toluene and DMF as solvents using different peroxide initiators with and without microwave irradiation. A general trend showed significant solvent dependence of monomer conversion rate only for copolymerizations initiated by tert-butyl perbenzoate in DMF compared to toluene but nearly no impact for copolymerizations initiated by dicumyl peroxide and dibenzoyl peroxide. Significant variations in copolymer composition were not observed for reactions under conventional heating compared to microwave irradiation. It was concluded that enhanced initiator decomposition under microwave irradiation in DMF accelerate polymerization of styrene and MMA by formation of larger amount of initiator radicals.
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167) Electrospinning: A fascinating method for the preparation of ultrathin fibres
Author(s): Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 46  Issue: 30  Pages: 5670-5703  DOI: 10.1002/anie.200604646  Published: 2007  
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166) Electrospinning of nanofibres: Towards new techniques, functions, and applications
Author(s): Dersch, R (Dersch, Roland); Graeser, M (Graeser, Martin); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: AUSTRALIAN JOURNAL OF CHEMISTRY  Volume: 60  Issue: 10  Pages: 719-728  DOI: 10.1071/CH07082  Published: 2007  
Abstract: Nanofibres, core-shell nanofibres, as well as hollow nanofibres and nanotubes based on polymers, serve as a platform for a broad range of applications as filters, textiles, in photonics, sensors, catalysis, or in medicine and pharmacy. Such nanoobjects become available by techniques such as the well-known electrospinning and the more recently developed co-electrospinning of nanofibres. Electrospinning takes place in the latter case by two or more concentrically arranged dies that yield core-shell fibres or fibres with droplet-like inclusions arranged along the centre of the fibres, where the inclusions are composed of polymers, low-molar-mass synthetic functional units, or molecules of biological origins such as proteins. Furthermore, template methods have been developed using electrospun nanofibres or a porous substrate, which yield core-shell fibres of complex architectures, with or without gradient structures or hollow nanofibres and nanotubes. These techniques are not restricted to polymers of synthetic and natural origin, but are able-based on precursor substances-to deliver nanofibres and nanotubes also composed of metals, glasses, and ceramics. Furthermore, these preparation techniques allow the direct introduction into these nanostructures of specific functional compounds such as semiconductor or catalytic nanoparticles and chromophores, in addition to enzymes, proteins, microorganisms, etc. during the preparation process in a very gentle way. Of particular interest are such nanostructures in medicine and pharmacy, for instance, as scaffolds for tissue engineering or as drug-delivery systems for tumour therapy.
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165) Polymer fibers as carriers for homogeneous catalysts
Author(s): Stasiak, M (Stasiak, Michael); Studer, A (Studer, Armido); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: CHEMISTRY-A EUROPEAN JOURNAL  Volume: 13  Issue: 21  Pages: 6150-6156  DOI: 10.1002/chem.200601555  Published: 2007  
Abstract: This paper describes a polymer fiber-based approach for the immobilization of homogeneous catalysts. The goal is to generate products that are free of catalysts which would be of great importance for the development of optoelectronic or pharmaceutical compounds. Electrospinning was employed to prepare the non-woven fiber assembly composed of polystyrene. The homogeneous catalyst scandium triflate was immobilized on the polystyrene fibers during electrospinning and on corresponding core shell fibers using a fiber template approach. An imino aldol and an aza-Diels-Alder model reaction were carried out with each fibrous catalytic system. This resulted in the immobilization of homogeneous catalysts in a polymer environment without loss of their catalytic activity and may even be enhanced when compared with reactions carried out in homogeneous solutions.
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164) Material encapsulation and transport in core-shell micro/nanofibers, polymer and carbon nanotubes and micro/nanochannels
Author(s): Yarin, AL (Yarin, A. L.); Zussman, E (Zussman, E.); Wendorff, JH (Wendorff, J. H.); Greiner, A (Greiner, A.)
Source: JOURNAL OF MATERIALS CHEMISTRY  Volume: 17  Issue: 25  Pages: 2585-2599  DOI: 10.1039/b618508h  Published: 2007  
Abstract: In this article, we review recent work on the co-electrospinning of polymer core-shell nanofibers and the manufacture of hollow nanotubes. The encapsulation and release of bioactive compounds from co-electrospun core-shell fibers is considered next, bearing in mind such applications as sensors and drug release. Then, nanofluidic phenomena in nanotubes made via co-electrospinning (as well as via the other processes) are discussed. We also consider dielectrophoresis in microchannels as a possible tool for the separation of viruses, nanoparticles and macromolecules.
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163) Elektrospinnen: eine faszinierende Methode zur Präparation ultradünner Fasern.
Author(s): GREINER, A.; WENDORFF, J. H.
Source: Angew. Chemie  Volume: 119  Pages: 5770-5805  Published: 2007  
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2006

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162) Nonflexible coils in solution: A neutron spin-echo investigation of alkyl-substituted polynorbornenes in tetrahydrofuran
Author(s): Monkenbusch, M (Monkenbusch, Michael); Allgaier, J (Allgaier, Juergen); Richter, D (Richter, Dieter); Stellbrink, J (Stellbrink, Joerg); Fetters, LJ (Fetters, Lewis J.); Greiner, A (Greiner, Andreas)
Source: MACROMOLECULES  Volume: 39  Issue: 26  Pages: 9473-9479  DOI: 10.1021/ma0618979  Published: DEC 26 2006  
Abstract: The dynamics of rigid random polymer coils in dilute solution has been investigated by neutron spin-echo (NSE) spectroscopy. The polymers used were polynorbornenes that consist of chains of the bridged norbornene rings with hexyl (PNBH) or propyl (PNBP) side groups. These polymer molecules have large internal rotation barriers that hinder conformational changes and give each chain a kind of individual shape memory. Thereby the chains exhibit a dynamical stiffness that leads to a significantly retarded relaxation as compared to flexible polyisoprene chains (PI). While the latter perfectly match the prediction of the Zimm model, the polynorbornene spectra display the signature of a dynamical stiffness due to the "frozen" coil conformation of the PNBH or PNBP chains.
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161) Electrospinning approaches toward scaffold engineering - A brief overview
Author(s): Boudriot, U (Boudriot, Ulrich); Dersch, R (Dersch, Roland); Greiner, A (Greiner, Andreas); Wendorff, JH (Wendorff, Joachim H.)
Source: ARTIFICIAL ORGANS  Volume: 30  Issue: 10  Pages: 785-792  DOI: 10.1111/j.1525-1594.2006.00301.x  Published: OCT 2006  
Abstract: Tissue engineering involves the in vitro seeding of cells onto scaffolds which assume the role of supporting cell adhesion, migration, proliferation, and differentiation, and which define the three-dimensional shape of the tissue to be engineered. Among the various types of scaffold architectures available, scaffolds based on nanofibers mimicking to a certain extent the structure of the extracellular matrix offer great advantages. Electrospinning is the technique of choice for the preparation of such scaffolds. Investigations have revealed that the nanofibrous structure promotes cell adhesion, proliferation, and differentiation. Parameters relevant for these processes such as fiber diameters, surface topology, porosity, mechanical properties, and the fibrous architecture of the scaffold can be controlled by electrospinning in a broad range.
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160) Preparation of sub-micrometer copper fibers via electrospinning
Author(s): Bognitzki, M (Bognitzki, Michael); Becker, M (Becker, Mathias); Graeser, M (Graeser, Martin); Massa, W (Massa, Werner); Wendorff, JH (Wendorff, Joachim H.); Schaper, A (Schaper, Andreas); Weber, D (Weber, Dirk); Beyer, A (Beyer, Andre); Golzhauser, A (Goelzhaeuser, Armin); Greiner, A (Greiner, Andreas)
Source: ADVANCED MATERIALS  Volume: 18  Issue: 18  Pages: 2384-+  DOI: 10.1002/adma.200600103  Published: SEP 18 2006  
Abstract: Sub-micrometer length copper fibers are obtained via polymer supported electrospinning and subsequent thermal treatment. The copper nature of the fibers is confirmed by using energy- dispersive X-ray analysis and wide- angle X-ray analysis (see figure). The copper fibers show metallic conductivity as confirmed by conductance measurements in a low-energy electron point source microscope.
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159) Coating of poly(p-xylylene) by PLA-PEO-PLA triblock copolymers with excellent polymer-polymer adhesion for stent applications
Author(s): Hanefeld, P (Hanefeld, Phillip); Westedt, U (Westedt, Ullrich); Wombacher, R (Wombacher, Ralf); Kissel, T (Kissel, Thomas); Schaper, A (Schaper, Andreas); Wendorff, JH (Wendorff, Joachim H.); Greiner, A (Greiner, Andreas)
Source: BIOMACROMOLECULES  Volume: 7  Issue: 7  Pages: 2086-2090  DOI: 10.1021/bm050642k  Published: JUL 10 2006  
Abstract: Poly(p-xylylene) (PPX) was deposited by chemical vapor deposition (CVD) on stainless steel substrates. These PPX films were coated by solution casting of poly( lactide)-poly(ethylene oxide)-poly(lactide) triblock copolymers (PLA-PEO-PLA) loaded with C-14-labeled paclitaxel. Adhesion of PLA-PEO-PLA on PPX substrate coatings was measured using the blister test method. Excellent adhesion of the block copolymers on PPX substrates was found. Stress behavior and film integrity of PLA-PEO-PLA was compared to pure PLA on unexpanded and expanded stent bodies and was found to be superior for the block copolymers. The release of paclitaxel from the biodegradable coatings was studied under physiological conditions using the scintillation counter method. Burst release of paclitaxel was observed from PLA-PEO-PLA layers regardless of composition, but an increase in paclitaxal loading was observed with increasing content of PEO.
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158) Biohybrid nanosystems with polymer nanofibers and nanotubes
Author(s): Greiner, A (Greiner, A.); Wendorff, JH (Wendorff, J. H.); Yarin, AL (Yarin, A. L.); Zussman, E (Zussman, E.)
Source: APPLIED MICROBIOLOGY AND BIOTECHNOLOGY  Volume: 71  Issue: 4  Pages: 387-393  DOI: 10.1007/s00253-006-0356-z  Published: JUL 2006  
Abstract: Advanced techniques for the preparation of nanofibers, core shell fibers, hollow fibers, and rods and tubes from natural and synthetic polymers with diameters down to a few nanometers have recently been established. These techniques, among them electro- and co-electrospinning and specific template methods, allow the incorporation not only of semiconductor or catalytic nanoparticles or chromophores but also enzymes, proteins, microorganism, etc., directly during the preparation process into these nanostructures in a very gentle way. One particular advantage is that biological objects such as, for instance, proteins can be immobilized in a fluid environment within these polymer-based nano-objects in such a way that they keep their native conformation and the corresponding functions. The range of applications of such biohybrid nanosystems is extremely broad, for instance, in the areas of biosensorics, catalysis, drug delivery, or optoelectronics.
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157) Investigation of the ion permeability of poly(p-xylylene) films
Author(s): Hanefeld, P (Hanefeld, P); Sittner, F (Sittner, F); Ensinger, W (Ensinger, W); Greiner, A (Greiner, A)
Source: E-POLYMERS  Article Number: 026  Published: JUN 2 2006  
Abstract: The ion permeability of poly(p-xylylene) (PPX, parylene-N(R)) thin films was investigated using a cyclovoltammetric setup. Iron rods of different surface roughness were coated with PPX films of different thickness (140-700 nm) by vapour phase deposition (Gorham process). The presence of pinholes in PPX films deposited as described was analyzed by ion permeability according to cyclovoltammetric measurements. Current densities were directly related to the area of iron not covered by the polymer. It was found that films deposited on iron surfaces by the Gorham process showed significant ion permeability for film thicknesses below 500 nm and no permeability at all for films equal to or thicker than 700 nm, which indicated the absence of pinholes of PPX films of 700 nm thickness. Furthermore, films of 140 nm were deposited on iron surfaces of different roughness (the mean roughness was measured to be 10(2) nm, 10(3) nm and 10(5) nm). Current density increased by the increase in roughness, which confirmed that pinhole formation correlated with surface roughness.
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156) Polyelectrolyte functionalization of electrospun fibers
Author(s): Muller, K (Muller, K); Quinn, JF (Quinn, JF); Johnston, APR (Johnston, APR); Becker, M (Becker, M); Greiner, A (Greiner, A); Caruso, F (Caruso, F)
Source: CHEMISTRY OF MATERIALS  Volume: 18  Issue: 9  Pages: 2397-2403  DOI: 10.1021/cm0527060k  Published: MAY 2 2006  
Abstract: We report the layer-by-layer (LbL) surface functionalization of high aspect ratio (> 100000: 1) polystyrene (PS) electrospun fibers (ESFs) of various diameters (400 nm or 1.5 mu(M)) with polyelectrolytes (PEs), deoxyribonucleic acid (DNA) oligonucleotides, and PE/gold nanoparticle (AU(NP)) composite layers. ESFs were coated with poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) multilayers, the thickness of which was controlled by adjusting the number of PE layers deposited. PAH/PSS multilayer buildup was demonstrated by dissolving the inner PS fibers with tetrahydrofuran, resulting in the formation of hollow PAH/PSS fibers. DNA inultilayer coated ESFs were also prepared using oligonucleotides with repeating blocks of adenosine and guanosine (polyA(15)G(15)) and thymidine and cytidine (polyT(15)C(15)). The polyT(15)C(15) was labeled with tetramethylrhodamine. Linear DNA multilayer buildup on the ESFs was observed through an increase in fluorescence intensity using confocal laser scanning microscopy. Finally, nanocomposite PE/gold fibers were prepared by immersing the PA-H/PSS-coated PS fibers into a dispersion of 4-(dimethylamino)pyridine-stabilized Au-NP. This resulted in a dense packing of AUNP in the PE film localized on the PS fiber surface. These fibers have potential application in sensing, filtration, and catalysis and as release materials in medicine and agriculture.
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155) Paclitaxel releasing films consisting of poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) and their potential as biodegradable stent coatings
Author(s): Westedt, U (Westedt, U); Wittmar, M (Wittmar, M); Hellwig, M (Hellwig, M); Hanefeld, P (Hanefeld, P); Greiner, A (Greiner, A); Schaper, AK (Schaper, AK); Kissel, T (Kissel, T)
Source: JOURNAL OF CONTROLLED RELEASE  Volume: 111  Issue: 1-2  Pages: 235-246  DOI: 10.1016/j.jconrel.2005.12.012  Published: MAR 10 2006  
Abstract: Although substantial progress in catheter and stent design has contributed to the success of percutaneous transluminal angioplasty (PTA) of atherosclerotic disease, the incidence of restenosis caused by in-stent neointimal hyperplasia remains a serious problem. Therefore, stents with a non-degradable polymer coating showing controlled release of active ingredients have become ail attractive option for the site-specific delivery of anti-restenotic agents. Biodegradable coatings using polyesters, namely poly(lactic-co-glycolic acid) (PLGA) and different poly(vinyl alcohol)graft-poly(lactic-co-glycolic acid) (PVA-g-PLGA) as paclitaxel-eluting stent coating materials were investigated here to evaluate their influence on the release kinetic. Whereas PLGA showed sigmoid release behavior, the paclitaxel release from PVA-g-PLGA films was continuous over 40 days without initial drug burst. Wide angle X-ray diffraction confirmed that paclitaxel is dissolved in the polymer matrix. Paclitaxel crystallization can be observed at a drug load of >= 10%. The effect of drug loading oil polymer degradation was Studied in films prepared from PVA(300)-g-PLGA(30) with paclitaxel loadings of 5% and 15% over a time period of 6 weeks. The results suggest a surface-like erosion mechanism in films. A model stent (Jostent peripheral) coated with Parylene N, a poly(p-xylylene) (PPX) derivate, was covered with a second layer of PVA(300)-9-PLGA(15), and PVA(300)-g-PLGA(30) by using airbrush method. Morphology of coated stents, and film integrity after expansion from 3.12 to 5 mm was investigated by scanning electron microscopy (SEM). The devices resisted mechanical stress during stent expansion and merit further investigation under in vivo conditions. (c) 2006 Elsevier B.V. All rights reserved.
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154) Synthesis and rheological properties of poly(5-n-hexylnorbornene)
Author(s): Muller, K (Muller, K); Kreiling, S (Kreiling, S); Dehnicke, K (Dehnicke, K); Allgaier, J (Allgaier, J); Richter, D (Richter, D); Fetters, LJ (Fetters, LJ); Jung, Y (Jung, Y); Yoon, DY (Yoon, DY); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 207  Issue: 2  Pages: 193-200  DOI: 10.1002/macp.200500228  Published: JAN 23 2006  
Abstract: Poly(5-n-hexylnorbornene) (PHNB) was obtained in high molecular weight and high yields by vinyl-type polymerization of 5-n-hexyl-2-norbornene (endo/exo = 77/23) with [NiBr(NPMe(3))](4)/B(C(6)F(5))(3) as catalyst precursor. The combination of size exclusion chromatography with online light scattering and intrinsic viscosity measurements allowed the Mark-Houwink expressions to be evaluated in tetrahydrofuran. The unperturbed chain dimensions for poly(5-n-hexylnorbornene) were estimated via the extrapolation procedure of Burchard-Stockmayer-Fixman. This evaluation of the unperturbed chain dimension in turn permits the calculation of the entanglement molecular weight and the plateau modulus via the packing length model. This allows the determination of rheological properties for these materials where conventional rheology measurements are difficult, or impossible.
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153) Microwave-assisted free radical polymerizations and copolymerizations of styrene and methyl methacrylate
Author(s): Stange, H (Stange, H); Ishaque, M (Ishaque, M); Niessner, N (Niessner, N); Pepers, M (Pepers, M); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 27  Issue: 2  Pages: 156-161  DOI: 10.1002/marc.200500640  Published: JAN 23 2006  
Abstract: Radical homopolymerizations and copolymerizations of styrene were performed in toluene and N,N-dimethylformamide (DMF) as solvents using different initiators with and without microwave irradiation. Only the homopolyrnerization of styrene under microwave irradiation in DMF with DtBP showed significantly enhanced styrene conversion whereas other initiators resulted in no or only slight increase of styrene conversion under microwave irradiation. In any case. DMF was required to gain in styrene conversion under microwave irradiation. Significantly higher monomer conversions were observed under otherwise comparable conditions in the copolymerization of styrene and methyl methacrylate (MMA) in DMF Microwave-induced selectivity of monomers was not observed in copolymerizations.
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152) Synthesis and characterisation of graft co-polymers of derivatives of poly(p-xylylene)
Author(s): Madan, R (Madan, R); Greiner, A (Greiner, A)
Source: DESIGNED MONOMERS AND POLYMERS  Volume: 9  Issue: 1  Pages: 81-87  DOI: 10.1163/156855506775526214  Published: 2006  
Abstract: Soluble derivatives of poly(p-xylylene) (PPX) were obtained by chemical vapour deposition polymerization and by Gilch-type polymerization. These PPX derivatives were chloromethylated by treatment with paraform aldehyde in the presence of trichloromethyl silane and stannic chloride. The chloromethylated PPX derivatives were reacted with anionic living poly(E-caprolactone) to form corresponding graft co-polymers.
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151) Functional polymer nanofibers and nanotubes via electrospinning
Author(s): Zeng, J (Zeng, J.); Sun, Z (Sun, Z.); Hou, H (Hou, H.); Dersch, R (Dersch, R.); Wickel, H (Wickel, H.); Wendorff, JH (Wendorff, J. H.); Greiner, A (Greiner, A.)
Edited by: Reneker DH; Fong H
Source: POLYMERIC NANOFIBERS  Book Series: ACS SYMPOSIUM SERIES  Volume: 918  Pages: 163-+  Published: 2006  
Abstract: Functional polymer nanofibers were prepared by electrospinning of ternary polymer solutions (e. g. poly-L-lactide (PLA)) and low molecular weight metal compounds. These functionalized fibers were further modified by coating with poly(p-xylylene) (PPX) via chemical vapor deposition (CVD). Removal of PLA by decomposition or selective solvent extraction resulted in the formation of nanotubes with e. g. Pd-nanoparticles on the inside or outside of the tubes depending on the reaction conditions. Functional nanotubes available for numerous chemical modifications were obtained by the TUFT-process (Tubes by Fiber Templates). According to this process by PLA template fibers were coated with a mixture of poly(vinylalcohol) (PVA) and poly(acrylic acid) (PAA) followed by CVD of PPX as a protective coating. Heating of these composite fibers resulted in decomposition of PLA and chemical crosslinking PVA/PAA. Residual OH-groups were used as reactive sites for immobilization of functional small molecules such as anthracene derivatives. Co-electrospinning by coaxial jets of different materials resulted in fibers with concentric variation of materials concentration. For example, fibers with PLA shell and Pd core where obtained after co-electrospinning of PLA-chloroform and palladium diacetate - THF solutions followed by heating to 170 degrees C.
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150) Das Reich der Nanotechnologie am Beispiel von Nanofasern und Nanoröhren
Author(s): GREINER, A.
Source: Europäischer Wirtschaftsverlag  Published: 2006  
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2005

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149) Photo-induced solid-state crosslinking of electrospun poly(vinyl alcohol) fibers
Author(s): Zeng, J (Zeng, J); Hou, HQ (Hou, HQ); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 26  Issue: 19  Pages: 1557-1562  DOI: 10.1002/marc.200500545  Published: OCT 6 2005  
Abstract: Poly(vinyl alcohol) (PVA) was derivatized by polymer analogous reaction with thienyl acryloyl chloride and processed to submicrometer fibers by electrospinning from aqueous solution. Water solubility of otherwise water-soluble PVA fibers was reduced considerably by UV cross-linking of thienyl acrylate modified PVA fibers in the solid state. Water stability of these crosslinked fibers was proven by water steam test at 95 degrees C.
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148) Synthesis and microstructural characterisation of copolymers of L-lactide and trimethylene carbonate prepared using the SmI2/Sm initiator system
Author(s): Agarwal, S (Agarwal, S); Puchner, M (Puchner, M); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH)
Source: POLYMER INTERNATIONAL  Volume: 54  Issue: 10  Pages: 1422-1428  DOI: 10.1002/pi.1865  Published: OCT 2005  
Abstract: Polymerisation of trimethylene carbonate (TMC) and its copolymerisation with L-lactide (LA) using the SmI2/Sm initiator system is reported. The reactions were carried out at different temperatures to optimize the reaction conditions. Reactivity ratio values evaluated using the Kelen-Tiidos method were 7.24 and 0.25 for LA and TMC, respectively. Microstructure of the copolymers and its change with the reaction time is reported using 1D (H-1 and C-13) and 2D heteronuclear multiple-bond correlation NMR spectroscopic techniques. Electrospinning of the resulting copolymers was tried for the generation of fibres. Drastic deviations of the thermodynamic state from equilibrium were seen in the first heating cycle of the DSC trace of the electrospun fibres and are also reported here. (c) 2005 Society of Chemical Industry.
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147) A Commentary on "Polyarylenes and poly(arylenevinylenes), 7. A soluble ladder polymer via bridging of functionalized polyp-phenylene)-precursors"
Author(s): Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 26  Issue: 17  Pages: 1361-1361  DOI: 10.1002/marc.200500486  Published: SEP 5 2005  
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146) Poly(vinyl alcohol) nanofibres by electrospinning: influence of molecular weight on fibre shape
Author(s): Jun, Z (Jun, Z); Hou, HQ (Hou, HQ); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: E-POLYMERS  Article Number: 038  Published: JUN 4 2005  
Abstract: Poly(vinyl alcohol) (PVA) nanofibres were obtained by electrospinning of PVA/water solutions. Formation of beaded fibres combined with decreased fibre diameters was observed for low PVA concentrations. Electrospinning of blends of PVA of different molecular weight resulted in less bead formation and smaller fibre diameters as compared to corresponding homopolymers of similar viscosity.
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145) Poly(vinyl alcohol) nanofibers by electrospinning as a protein delivery system and the retardation of enzyme release by additional polymer coatings
Author(s): Zeng, J (Zeng, J); Aigner, A (Aigner, A); Czubayko, F (Czubayko, F); Kissel, T (Kissel, T); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: BIOMACROMOLECULES  Volume: 6  Issue: 3  Pages: 1484-1488  DOI: 10.1021/bm0492576  Published: MAY-JUN 2005  
Abstract: Protein-loaded (bovine serum albumin (BSA) or luciferase) poly(vinyl alcohol) (PVA) nanofibers were obtained by electrospinning. Poly(p-xylylene) (PPX, also coined as parylene) coated PVA/BSA nanofibers were prepared by chemical vapor deposition (CVD). The release of BSA from PVA nanofibers under physiological conditions was monitored by absorption spectroscopy. Burst release of BSA was noted with uncoated PVA nanofibers. In contrast, PPX-coated nanofibers exhibited a significantly retarded release of BSA depending on the coating thickness of PPX (ranging from 40 to 300 nm). Luciferase was used here as model enzyme, which after electrospinning retained its enzyme activity. This preservation of enzyme activity and the continuous release of the intact enzyme from the immersed fibers meets a fundamental prerequisite for the application of enzymes or other sensitive agents released from electrospun nanofibers under physiological conditions.
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144) Synthesis of methyl methacrylate and N-aryl itaconimide block copolymers via atom-transfer radical polymerization
Author(s): Anand, V (Anand, V); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A); Choudhary, V (Choudhary, V)
Source: POLYMER INTERNATIONAL  Volume: 54  Issue: 5  Pages: 823-828  DOI: 10.1002/pi.1776  Published: MAY 2005  
Abstract: The paper describes the synthesis of block copolymers of methyl methacrylate (MMA) and N-aryl itaconimides using atom-transfer radical polymerization (ATRP) via a poly(methyl methacrylate)-Cl/CuBr/bipyridine initiating system or a reverse ATRP AIBN/FeCl(3)center dot 6H(2)O/PPh3 initiating system. Poly(methyl methacrylatc) (PMMA) macroinitiator, ie with a chlorine chain-end (PMMA-Cl), having a predetermined molecular weight (M-n = 1.27 x 10(4) gmol(-1)) and narrow polydispersity index (PDI = 1.29) was prepared using AIBN/FeCl(3)center dot 6H(2)O/PPh3, which was then used to polymerize Naryl itaconimides. Increase in molecular weight with little effect on polydispersity was observed on polymerization of N-aryl itaconimides using the PMMA-Cl/CuBr/Bpy initiating system. Only oligomeric blocks of N-aryl itaconimides could be incorporated in the PMMA backbone. High molecular weight copolymer with a narrow PDI (1.43) could be prepared using tosyl chloride (TsCl) as an initiator and CuBr/bipyridine as catalyst when a mixture of MMA and N-(P-chlorophenyl) itaconimide in the molar ratio of 0.83:0.17 was used. Thermal characterization was performed using differential scanning calorimetry (DSC) and dynamic thermogravimetry. DSC traces of the block copolymers showed two shifts in base-line in some of the block copolymers; the first transition corresponds to the glass transition temperature of PMMA and second transition corresponds to the glass transition temperature of poly(N-aryl itaconimides). A copolymer obtained by taking a mixture of monomers ie MMA:N-(p-chlorophenyl) itaconimide in the molar ratio of 0.83:0.17 showed a single glass transition temperature. (c) 2005 Society of Chemical Industry.
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143) Electrospun polyacrylonitrile nanofibers containing a high concentration of well-aligned multiwall carbon nanotubes
Author(s): Hou, HQ (Hou, HQ); Ge, JJ (Ge, JJ); Zeng, J (Zeng, J); Li, Q (Li, Q); Reneker, DH (Reneker, DH); Greiner, A (Greiner, A); Cheng, SZD (Cheng, SZD)
Source: CHEMISTRY OF MATERIALS  Volume: 17  Issue: 5  Pages: 967-973  DOI: 10.1021/cm0484955  Published: MAR 8 2005  
Abstract: Composite nanofiber sheets of well-aligned polyacrylonitrile nanofibers (PAN) containing multiwall carbon nanotubes (MWCNTs) were prepared by electrospinning a MWCNT-suspended Solution of PAN in dimethyl formamide using a moving collector. Scanning electron microscopy, atomic force microscopy, transmission electron microscopy (TEM), IR spectroscopy, Raman spectroscopy, X-ray scattering, and the Instron test were used to characterize the nanofiber sheets. TEM observation showed the MWCNTs were parallel and oriented along the axes of the nanofibers. The mechanical properties of the composite nanofibers were reinforced by MWCNT fillers. Carbonization processes showed that a higher concentration of MWCNTs effectively resisted heat shrinkage of the composite nanofiber sheet.
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142) Polymer components - Nanofibers and nanorubes
Author(s): Dersch, R (Dersch, R); Greiner, A (Greiner, A); Steinhart, M (Steinhart, M); Wendorff, JH (Wendorff, JH)
Source: CHEMIE IN UNSERER ZEIT  Volume: 39  Issue: 1  Pages: 26-35  DOI: 10.1002/ciuz.200400321  Published: FEB 2005  
Abstract: The nanotechnology, a cross-sectional technology par excellence, stimulates G broad spectrum of fields of applications extending from optoelectronics, sensorics, ecology, chemistry and biotechnology to medicine and pharmacy. Nonofibers and nonotubes ore a highly versatile platform for such applications. To produce these nonoobjects a set of novel preparation techniques such as electrospinning and specific template approaches based on nanofibers and mesoporous substrates has been developed. Nonofibers and nonotubes consisting of polymers, metals, ceramics, glasses or combinations of such materials have thus become accessible. The integration of such nonoobjects in larger devices is the next challenge.
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141) Nanoprocessing of polymers: applications in medicine, sensors, catalysis, photonics
Author(s): Dersch, R (Dersch, R); Steinhart, M (Steinhart, M); Boudriot, U (Boudriot, U); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 16  Issue: 2-3  Special Issue: SI  Pages: 276-282  DOI: 10.1002/pat.568  Published: FEB-MAR 2005  
Abstract: Nanofibers and nanotubes based on polymers offer a broad range of applications in areas such as photonics, sensorics, catalysis or medicine and pharmacy. A set of preparation techniques which allow to introduce simultaneous specific functions into such nanoobjects has been developed recently. These include electrospinning and co-electrospinning of nanofibers as well as template methods utilizing eletrospun nanofibers or porous substrates. These techniques yield infinitively long nanofibers and nanotubes with well defined aspect ratios respectively with diameters down to a few ten nanometers. These nanofibers and nanotubes can be functionalised, among others by using biodegradable materials or via the incorporation of nanoparticles or precursor molecules, in such a way that applications for tissue engineering, for catalysis, photonics and sensorics become available. Copyright (c) 2005 John Wiley N Sons, Ltd.
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140) Preparation of hollow silica nanospheres by surface-initiated atom transfer radical polymerization on polymer latex templates
Author(s): Chen, YW (Chen, YW); Kang, ET (Kang, ET); Neoh, KG (Neoh, KG); Greiner, A (Greiner, A)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 15  Issue: 1  Pages: 113-117  DOI: 10.1002/adfm.200400179  Published: JAN 2005  
Abstract: Poly(vinylbenzyl chloride), (PVBC) latex particles of about 100 nm in size are prepared by emulsion polymerization. Silyl functional groups are introduced onto the PVBC-nanoparticle templates via surface-initiated atom transfer radical polymerization of 3-(trimethoxysilyl)propyl methacrylate. The silyl groups are then converted into a silica shell, approximately 20 nm thick, via a reaction with tetraethoxysilane in ethanolic ammonia. Hollow silica nanospheres are finally generated by thermal decomposition of the PVBC template cores. Field-emission scanning electron microscopy and field-emission transmission electron microscopy are used to characterize the intermediate products and the hollow nanospheres. Fourier-transform infrared spectroscopy results indicate that the polymer cores are completely decomposed.
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139) 2D NMR characterisation of 5-norbornene-2-nonaneacidethylester and 5-norbornene-2-hexane
Author(s): Mueller, K (Mueller, K); Chun, SH (Chun, SH); Greiner, A (Greiner, A); Agarwal, S (Agarwal, S)
Source: DESIGNED MONOMERS AND POLYMERS  Volume: 8  Issue: 3  Pages: 237-248  Published: 2005  
Abstract: 5-Norbornene-2-nonaneacidethylester and 5-norbomene-2-hexane were synthesised by Diels-Alder reaction of cyclopentadiene and corresponding olefins. Diels-Aider reaction usually results in a mixture of endo and exo isomers. The monomers were obtained in an approximate ratio of 75:25 (endo/exo), which was determined by GC-MS and H-1-NMR-spectroscopy. Both monomers were detailed characterized using ID H-1-NMR, ID C-13-NMR, 2D (1)HJH COSY, 2D H-1-C-13 HMQC and 2D H-1-C-13 HMBC techniques.
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138) Quick atom transfer radical polymerization of N,N-diisopropyl ammonium acrylate in the presence of air
Author(s): Kazemi, A (Kazemi, A); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A)
Source: DESIGNED MONOMERS AND POLYMERS  Volume: 8  Issue: 6  Pages: 673-678  DOI: 10.1163/156855505774597731  Published: 2005  
Abstract: The atom transfer radical polymerization of N,N-diisopropyl ammonium acrylate was successfully carried out, either with continuous exposure to air or in the presence of small amounts of air, which were introduced to the reaction mixture during the polymerization. A linear growth of molecular weight as a function of conversion and low polydispersities of the polymers synthesised here were consistent with the controlled polymerization. Since the polymerization was carried out in the presence of air, oxygen may act as co-catalyst or can be an initiator in a CuBr/bipy/O-2 complex.
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137) Preparation of poly(p-xylylene) TUFT-tubes containing palladium, silver, or copper nanoparticles.
Author(s): SUN, Z.; ZENG, J.; HOU, H.; WICKEL, H.; WENDORFF, J. H.; GREINER, A.
Source: Progr. Colloid Polym. Sci.  Volume: 130  Pages: 15-19  Published: 2005  
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136) Electrospun poly(vinyl alcohol)/poly(acrylic acid) fibres with excellent water-stability
Author(s): Zeng, J (Zeng, J); Hou, HQ (Hou, HQ); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: E-POLYMERS  Article Number: 078  Published: DEC 9 2004  
Abstract: The water stability of electrospun poly(vinyl alcohol) (PVA) nanofibres was improved significantly by annealing with poly(acrylic acid) (PAA). Effects of annealing were tested on solution-cast PVA/PAA films by measurement of the swelling degree. The influence of PVA/PAA ratio, annealing temperature and period, molecular weight of PAA, and addition of esterification catalyst was investigated. The results were verified by a significant improvement of the water-stability of electrospun PVA/PAA composite nanofibres.
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135) Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: Electrospun composite nanofiber sheets
Author(s): Ge, JJ (Ge, JJ); Hou, HQ (Hou, HQ); Li, Q (Li, Q); Graham, MJ (Graham, MJ); Greiner, A (Greiner, A); Reneker, DH (Reneker, DH); Harris, FW (Harris, FW); Cheng, SZD (Cheng, SZD)
Source: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  Volume: 126  Issue: 48  Pages: 15754-15761  DOI: 10.1021/ja048648p  Published: DEC 8 2004  
Abstract: Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers; were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CdropN:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to similar to1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 X 10(-6)/degreesC along the axis of aligned nanofibers containing 20 wt % MWNTs.
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134) Electrospun poly-l-lacticle nanofibres as scaffolds for tissue engineering
Author(s): Boudriot, U (Boudriot, U); Dersch, R (Dersch, R); Goetz, B (Goetz, B); Griss, P (Griss, P); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH)
Source: BIOMEDIZINISCHE TECHNIK  Volume: 49  Issue: 9  Pages: 242-247  DOI: 10.1515/BMT.2004.046  Published: SEP 2004  
Abstract: Tissue engineering is a promising tool for treating structural and functional defects in bone and cartilage. To provide optimal conditions for three-dimensional cell growth the use of a scaffold is necessary. The aim of the study was to test the potential application of an electrospun poly (I-lactide)-nanostructured scaffold as a matrix for tissue engineering. Matrices were seeded with human osteosarcoma MG-63 cells and cultivated for 14 days. Cells showed a clear preference for growth along the nanofibres, and demonstrated no signs of degeneration or apoptosis. The fine structure of electrospun nanofibres makes them an ideal scaffold for tissue engineering, in particular for cartilage repair. They can be "doped" with growth factors, medications, etc., and are both biocompatible and biodegradable.
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133) Nanoporous low-kappa polyimide films via poly(amic acid)s with grafted poly(ethylene glycol) side chains from a reversible addition-fragmentation chain-transfer-mediated process
Author(s): Chen, YW (Chen, YW); Wang, W (Wang, W); Yu, WH (Yu, WH); Yuan, ZL (Yuan, ZL); Kang, ET (Kang, ET); Neoh, KG (Neoh, KG); Krauter, B (Krauter, B); Greiner, A (Greiner, A)
Source: ADVANCED FUNCTIONAL MATERIALS  Volume: 14  Issue: 5  Pages: 471-478  DOI: 10.1002/adfm.200305050  Published: MAY 2004  
Abstract: Thermally-initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone-pretreated poly[N,N'-(1,4-phenylene)-3,3',4,4'-benzophenonetetra-carboxylic amic acid] (PAmA) via a reversible addition-fragmentation chain-transfer (RAFT)-mediated process was carried out. The chemical compositions and structures of the copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and molecular weight measurements. The "living" character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous low-dielectric-constant (IOW-K) polyimide (PI) films were prepared by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films obtained from the RAFT-mediated graft copolymers had well-preserved PI backbones, porosity in the range of 5-17%, and pore size in the range of 30-50 nm. The pores were smaller and the pore-size distribution more uniform than those of the corresponding nanoporous PI films obtained via graft copolymers from conventional free-radical processes. Dielectric constants approaching 2 were obtained for the nanoporous PI films prepared from the RAFT-mediated graft copolymers.
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132) Nanowires and nanotubes with polymers
Author(s): Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A); Steinhart, M (Steinhart, M)
Source: NACHRICHTEN AUS DER CHEMIE  Volume: 52  Issue: 4  Pages: 426-431  Published: APR 2004  
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131) The role of iron carbide in multiwalled carbon nanotube growth
Author(s): Schaper, AK (Schaper, AK); Hou, HQ (Hou, HQ); Greiner, A (Greiner, A); Phillipp, F (Phillipp, F)
Source: JOURNAL OF CATALYSIS  Volume: 222  Issue: 1  Pages: 250-254  DOI: 10.1016/j.jcat.2003.11.011  Published: FEB 15 2004  
Abstract: The pyrolysis of organometallic precursors followed by a catalyst-assisted transformation of carbon into graphite is one successful route toward the high-yield production of aligned carbon nanotubes (CNTs) with well-defined dimensions and structure. In this work we have studied the particular growth mechanisms of multiwalled CNTs synthesized from FePc and FeCp2 as precursors in the pyrolysis process. TEM investigations including in situ heating experiments enabled us to directly observe the surface segregation of graphite at the expense of the encapsulated catalyst material. The observations suggest that the structural growth process is determined by the dissolution of carbon in the quasi-liquid catalyst particle, its diffusion through the particle, and its segregation in the form of graphene layers in the case of supersaturation. These processes were proved to occur via the formation of an intermediate iron carbide phase. The results also demonstrated how the increasing expulsory forces may cause the gradual displacement of the fluid catalyst during nanotube growth. (C) 2003 Elsevier Inc. All rights reserved.
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130) Copper nanoparticles encapsulated in multi-shell carbon cages
Author(s): Schaper, AK (Schaper, AK); Hou, H (Hou, H); Greiner, A (Greiner, A); Schneider, R (Schneider, R); Phillipp, F (Phillipp, F)
Source: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING  Volume: 78  Issue: 1  Pages: 73-77  DOI: 10.1007/s00339-003-2199-0  Published: JAN 2004  
Abstract: Nanoparticles are attracting increasing interest because of their high potential for a great number of practical applications, such as optical and electronic devices, nanoscale storage, and delivery systems. Using Cu-phthalocyanine as precursor material, we have synthesized multi-shell graphitic carbon nanospheres without and with metal encapsulation, depending on the pyrolysis conditions. The encapsulated elemental copper nanocrystals achieved using that route were of the order of 50 nm in size. The particles were characterized in detail by high-resolution transmission electron microscopy (HRTEM) and by energy filtering microscopy (EFTEM). The concentric graphitic carbon shells of the as-grown particles were clearly discernable. After in situ high-temperature annealing, an increase in the degree of order was observed. Under high-voltage electron irradiation and heating, a melting point reduction of the enclosed nanosized copper of more than 200 K could be detected, as compared to the melting point 1083degreesC of bulk copper. Time-resolved imaging revealed the displacement of the melting copper by migration through the carbon shells, leaving intact carbon cages with a central hole. At intermediate stages of this process the transformation into a hexagonal morphology of the copper nanocrystals was observed.
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129) Hydrolytic and enzymatic degradation of liquid-crystalline aromatic/aliphatic copolyesters
Author(s): Chen, YW (Chen, YW); Jia, ZH (Jia, ZH); Schaper, A (Schaper, A); Kristiansen, M (Kristiansen, M); Smith, P (Smith, P); Wombacher, R (Wombacher, R); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: BIOMACROMOLECULES  Volume: 5  Issue: 1  Pages: 11-16  DOI: 10.1021/bm034388c  Published: JAN-FEB 2004  
Abstract: Aromatic/aliphatic copolyesters containing hydrophilic moieties in the main chain or side chain were synthesized by bulk polycondensation of aromatic monomers without or with solubilizing substituents and aliphatic monomers. Hydrolytic and enzymatic degradation studies were carried out in vitro at 37degreesC in pH 7.4 phosphate buffer and in Tris-HCl buffer containing proteinase K. The results indicate that liquid-crystalline aromatic/aliphatic copolyesters are degradable hydrolytically as well as enzymatically. The change in composition and morphology of the polyester films were monitored by nuclear magnetic resonance and scanning electron microscopy. The results suggested that aromatic species and aliphatic moieties could be released into aqueous solution during hydrolytic degradation of aromatic/aliphatic copolyesters with ethyleneoxy groups on the side chain. Modifying aromatic species with hydrophilic groups in aromatic/aliphatic copolyesters was an efficient method to improve degradability and biocompatibility due to improved solubility of degradation products in aqueous solution. Mechanical tests indicated that the copolyesters exhibited good mechanical properties prior to degradation, which can be of relevance for bone tissue engineering.
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128) Polymer nanofibers prepared by electrospinning.
Author(s): DERSCH, R.; GREINER, A.; WENDORFF, J. H.
Source: In: Dekker Encyclopedia of Nanoscience and Nanotechnology; 293; Eds. Schwartz, J. A., Contesen, C. J.; Putgern, K.; Marcel Dekker New York  Published: 2004  
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127) Compound core-shell polymer nanofibers by co-electrospinning
Author(s): Sun, ZC (Sun, ZC); Zussman, E (Zussman, E); Yarin, AL (Yarin, AL); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: ADVANCED MATERIALS  Volume: 15  Issue: 22  Pages: 1929-+  DOI: 10.1002/adma.200305136  Published: NOV 17 2003  
Abstract: Co-electrospinning of core-shell polymer nanofibers (see Figure) is introduced. This process can be used for manufacturing of coaxial nanofibers made of pairs of different materials. Non-spinnable materials can be forced into 1D arrangements by co-electrospinning using a spinnable shell polymer. The method results in a novel two-stage approach for fabrication of nanotubes instead of the previously used three-stage process.
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126) Thermotropic aromatic/lactide copolyesters with solubilizing side chains on aromatic rings
Author(s): Chen, YW (Chen, YW); Wombacher, R (Wombacher, R); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: POLYMER  Volume: 44  Issue: 19  Pages: 5513-5520  DOI: 10.1016/S0032-3861(03)00571-8  Published: SEP 2003  
Abstract: Liquid-crystalline polyesters with solubilizing side chains on aromatic rings have been synthesized by melt polycondensation of diacid dichlorides and silylated hydroquinones. Corresponding copolyesters incorporated with lactide units were obtained by addition of oligolactides. The molecular structures of these polymers were verified by spectroscopy techniques. Molecular weights were characterized by gel permeation chromatography. X-ray diffraction studies confirmed that all polyesters are partially crystalline and have self-organized ordered stacking structures. The polyesters can form smectic melts upon heating above the melting temperature. Contact angle measurements and water absorption data of solution cast films showed that the polyesters have relatively high hydrophilicity and decreasing contact angle with increasing amount of lactide moieties. (C) 2003 Elsevier Ltd. All rights reserved.
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125) Large-scale synthesis and characterization of helically coiled carbon nanotubes by use of Fe(CO)(5) as floating catalyst precursor
Author(s): Hou, HQ (Hou, HQ); Jun, Z (Jun, Z); Weller, F (Weller, F); Greiner, A (Greiner, A)
Source: CHEMISTRY OF MATERIALS  Volume: 15  Issue: 16  Pages: 3170-3175  DOI: 10.1021/cm021290g  Published: AUG 12 2003  
Abstract: Helically shaped multiwalled carbon nanotubes (HCNTs) (diameter 30-80 nm) were obtained as main products in large quantities by co-pyrolysis of Fe(CO)(5) as floating catalyst precursor and pyridine or toluene as carbon source at temperatures above 1000 degreesC under flow of hydrogen. In contrast, pyrolysis at 700-800 degreesC yielded only carbon-coated Fe nanoparticles. The HCNTs were characterized by electron microscopy, Raman spectroscopy, and wide-angle X-ray diffraction. The growth mechanism of the HCNTs was discussed on the basis of previously reported models.
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124) Design, synthesis, and properties of new biodegradable aromatic/aliphatic liquid crystalline copolyesters
Author(s): Chen, YW (Chen, YW); Wombacher, R (Wombacher, R); Wendorff, JH (Wendorff, JH); Visjager, J (Visjager, J); Smith, P (Smith, P); Greiner, A (Greiner, A)
Source: BIOMACROMOLECULES  Volume: 4  Issue: 4  Pages: 974-980  DOI: 10.1021/bm0340164  Published: JUL-AUG 2003  
Abstract: Liquid crystalline copolyesters of high molecular weight were obtained by polycondensation of aromatic diols, diacyl dichlorides, oligolactides, and poly(ethylene glycol)s. Hydrophilicity of the copolyesters was controlled by the content of ethyleneoxy moieties as verified by contact angle measurements. Copolyesters with ethyleneoxy moieties showed significant enhancement of degradability under physiological conditions in comparison to copolyester without ethyleneoxy moieties, which makes these copolyesters promising materials for bone tissue engineering as also verified by hardness testing and mechanical testing.
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123) Insertion of chalcogen atoms into the gallium-gallium bonds of acetato-bridged digallanes
Author(s): Uhl, W (Uhl, W); Cuypers, L (Cuypers, L); Spies, T (Spies, T); Weller, F (Weller, F); Harbrecht, B (Harbrecht, B); Conrad, M (Conrad, M); Greiner, A (Greiner, A); Puchner, M (Puchner, M); Wendorff, JH (Wendorff, JH)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 629  Issue: 7-8  Pages: 1124-1130  DOI: 10.1002/zaac.200300443  Published: JUL 2003  
Abstract: The digallium(II) compound R2Ga2(mu-OOCCH3)(2) 2 [R = CH(SiMe3)(2)] has a short Ga-Ga single bond, which is bridged by two acetato ligands. Owing to the chelating coordination by both carboxylato groups the gallium atoms are coordinatively saturated and have coordination numbers of four. Treatment of 2 with chalcogen atom donors such as propylene sulfide, triethylphosphonium selenide and telluride gave the insertion of sulfur, selenium and tellurium atoms into the Ga-Ga bond. By the oxidation of the gallium atoms products resulted which have angled Ga-S-Ga-(3), Ga-Se-Ga- (4) and Ga-Te-Ga units (5) in their molecular cores. In all cases, the carboxylato ligands remain in their bridging positions between two gallium atoms. The tellurium compound 5 shows a phase transition in the solid state, which was investigated by X-ray powder diffraction and DSC methods.
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122) Two-photon-induced cycloreversion reaction of coumarin photodimers
Author(s): Kim, HC (Kim, HC); Kreiling, S (Kreiling, S); Greiner, A (Greiner, A); Hampp, N (Hampp, N)
Source: CHEMICAL PHYSICS LETTERS  Volume: 372  Issue: 5-6  Pages: 899-903  DOI: 10.1016/S0009-2614(03)00535-9  Published: MAY 6 2003  
Abstract: Photochemical reactions induced by two-photon-absorption processes offer several advantages over common one-photon initiated photoreactions, e.g., three-dimensional spatial control. We present the photocleavage reaction of coumarin photodimers via a two-photon process using pulsed frequency-doubled Nd:YAG-laser light. The two-photon-induced cycloreversion reaction leads selectively to the cleavage of the coumarin photodimers resulting in the formation of monomeric coumarin molecules. The two-photon cross section of the coumarin photodimer was determined to be of 1.6 x 10(-52) cm(4) s photon(-1). The presented reaction is of interest, e.g., for the photo-triggered release of chemicals in areas which cannot be directly optically addressed due to cover layers which have a high absorption at the single-photon-absorption wavelength. (C) 2003 Elsevier Science B.V. All rights reserved.
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121) Homopolymers and random copolymers of 5,6-benzo-2-methylene-1,3-dioxepane and methyl methacrylate: Structural characterization using 1D and 2D NMR
Author(s): Wickel, H (Wickel, H); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 36  Issue: 7  Pages: 2397-2403  DOI: 10.1021/ma025983u  Published: APR 8 2003  
Abstract: Complete structural characterization of 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) monomer and its homopolymer is carried out using 1D and 2D NMR techniques. Copolymers of BMDO were made with MMA under ATRP reaction conditions. The copolymer compositions were obtained from H-1 NMR spectroscopy. The reactivity ratios for the copolymerization of BMDO with MMA were determined using the Kelen-Tud (o) over bars method and was found to be r(BMDO) = 0.53 and r(MMA) = 1.96. Compositional and configurational sequence analysis of copolymers is also done.
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120) Poly-L-lactide nanofibers by electrospinning - Influence of solution viscosity and electrical conductivity on fiber diameter and fiber morphology
Author(s): Jun, Z (Jun, Z); Hou, HQ (Hou, HQ); Schaper, A (Schaper, A); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: E-POLYMERS  Article Number: 009  Published: MAR 8 2003  
Abstract: Poly-L-lactide (PLA) fibers were obtained by electrospinning of PLA / dichloromethane solutions. Formation of beaded fibers combined with decreased fiber diameters were observed for low PLA concentrations in solution. Increase of the electrical conductivity by addition of pyridinium formiate (PF) caused a significant reduction of bead formation. The electrospinning of dilute PLA / PF / dichloromethane solutions resulted in PLA nanofibers. Systematic variations clearly identified the solution viscosity and the electrical conductivity at otherwise fixed parameters (surface tension, molecular weight, electrode geometry, electrical field, etc.) as crucial parameters for the formation of beads upon electrospinning of PLA dichloromethane solutions.
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119) Synthesis and opto-electronic properties of cholesteric cellulose esters
Author(s): Greiner, A (Greiner, A); Hou, H (Hou, H); Reuning, A (Reuning, A); Thomas, A (Thomas, A); Wendorff, JH (Wendorff, JH); Zimmermann, S (Zimmermann, S)
Source: CELLULOSE  Volume: 10  Issue: 1  Pages: 37-52  DOI: 10.1023/A:1023038303103  Published: MAR 2003  
Abstract: Cholesteric materials display unique optical properties which can be exploited in opto-electronic applications such as light emitting diodes. The key feature is the position of the wavelength of the emitted light relative to the one of the selective reflection band. We have synthesized a set of cellulose derivatives displaying the cholesteric phase with the aim to investigate the correlation between chemical structure and properties. Phase transition temperatures, the chain packing, the wavelength of selective reflection but also absorption and fluorescence spectra were investigated as a function of the degree of substitution (DS), the nature of lateral substituents, the composition of doped systems and blends of different cellulose derivatives. Investigated were furthermore the degree of circular polarization of the emitted light for guest-host systems and for cellulose systems with chromophores linked by covalent bonds to the cellulose backbone as well as their performance in light emitting diodes. The conclusion is that the optical properties can be accounted for on the basis of the model of a one-dimensional photonic crystal. The limiting factor with respect to opto-electronic applications is the poor control of the uniformity of the helix formation and orientation.
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118) Electrospun nanofibers: Internal structure and intrinsic orientation
Author(s): Dersch, R (Dersch, R); Liu, TQ (Liu, TQ); Schaper, AK (Schaper, AK); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH)
Source: JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY  Volume: 41  Issue: 4  Pages: 545-553  DOI: 10.1002/pola.10609  Published: FEB 15 2003  
Abstract: Electrospinning gives rise to polymer nanofibers. The spinning process is characterized by strong deformations of the polymer material taking place during the spinning process and a very rapid structure formation process happening within milliseconds. We were interested in the influence of the peculiar spinning process on the structures of nanofibers. For this purpose, we analyzed the internal structures of nanofibers spun from polyamide-6 and polylactide with an average diameter of about 50 nm. The fibers were partially crystalline, with degrees of crystallinity not significantly smaller than those found for less rapidly quenched and much thicker melt-extruded fibers. The annealing of polyamide fibers at elevated temperatures resulted in a transformation from the disordered T modification to the more highly ordered a modification, and this again was in close agreement with the response of melt-extruded fibers. The orientation of the crystals along the fiber axis was strongly inhomogeneous: it was, on average, very weak, yet it could be quite pronounced locally. Small elongations of approximately 10% resulted in well-developed homogeneous crystal orientations. (C) 2003 Wiley Periodicals, Inc.
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117) Thermotropic aromatic/lactide copolyesters with lateral methoxyethyleneoxy substituents
Author(s): Chen, YW (Chen, YW); Wombacher, R (Wombacher, R); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: CHEMISTRY OF MATERIALS  Volume: 15  Issue: 3  Pages: 694-698  DOI: 10.1021/cm0213016  Published: FEB 11 2003  
Abstract: Liquid-crystalline polyesters with lateral methoxyethyleneoxy substituents and phenyl substituents were obtained by melt polycondensation of diacid dichlorides and silylated hydroquinones. Corresponding copolyesters were obtained by addition of oligolactides. The molecular structures of these polymers were verified by IR and NMR spectroscopy. Molecular weights obtained by GPC and end-group analysis proved enhanced molecular weights. All copolyesters were partially crystalline according to WAXS analysis and formed smectic melts upon heating above the melting temperature. Contact angle measurements of solution cast films showed relatively high hydrophilicity and decreasing contact angle with increasing amounts of oligolactide moieties.
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116) Large-scale synthesis of aligned carbon nanotubes using FeCl3 as floating catalyst precursor
Author(s): Hou, HQ (Hou, HQ); Schaper, AK (Schaper, AK); Jun, Z (Jun, Z); Weller, F (Weller, F); Greiner, A (Greiner, A)
Source: CHEMISTRY OF MATERIALS  Volume: 15  Issue: 2  Pages: 580-585  DOI: 10.1021/cm020970g  Published: JAN 28 2003  
Abstract: The continuous interest in carbon nanotubes (CNTs) and nanotube arrays has led us to discover new routes of high-yield and low-cost synthesis of CNTs with controlled tube structure. Here we show that a dilute solution of FeCl3 in toluene and N,N'-dimethylaminoacetate is a high-efficiency floating catalyst precursor in a chemical vapor deposition process. The growth structure and the self-assembling behavior of the resulting multiwall tubes was characterized using scanning and transmission electron microscopy. Clear indications are provided of the participation of iron carbide in the tube formation at higher temperatures. The characteristic cone-shaped morphology of the tubes is described in detail and discussed in terms of its interesting practical implications.
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115) Unusual complex chemistry of rare-earth elements: Large ionic radii-small coordination numbers
Author(s): Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 42  Issue: 12  Pages: 1340-1354  DOI: 10.1002/anie.200390346  Published: 2003  
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114) Multi-wall carbon nanotubes with uniform chirality: evidence for scroll structures
Author(s): Ruland, W (Ruland, W); Schaper, AK (Schaper, AK); Hou, H (Hou, H); Greiner, A (Greiner, A)
Source: CARBON  Volume: 41  Issue: 3  Pages: 423-427  Article Number: PII S0008-6223(02)00342-1  DOI: 10.1016/S0008-6223(02)00342-1  Published: 2003  
Abstract: Multi-wall carbon nanotubes (MWCNT) obtained by catalytic decomposition of iron phthalocyanine are investigated by high resolution electron microscopy and electron diffraction (ED). The evaluation of the ED patterns shows that all MWCNTs studied have a uniform chirality, i.e. all tubes of a given MWCNT show the same chiral angle. The conditions for the formation of nested tubes are discussed. A comparison of the values of the chiral angles with those of the corresponding interwall spacings, both obtained from the ED patterns, leads to the conclusion that these MWCNTs have a scroll structure, very probably consisting of one single rolled-up graphene sheet. (C) 2002 Elsevier Science Ltd. All rights reserved.
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113) Two-photon induced drug delivery from polymeric intraocular lenses.
Author(s): HAMPP, N.; KIM, H. C.; KREILING, S.; HESSE, L.; GREINER, A.
Source: In: R. W. Steiner (ed), Therapeutic Laser Applications and Laser Tissue Interactions  Pages: 161-168  Published: 2003  
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112) Grafting of vinyl-type polynorbornene on polybutadiene and polyisoprene
Author(s): Schroers, M (Schroers, M); Demeter, J (Demeter, J); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 203  Issue: 18  Pages: 2658-2664  DOI: 10.1002/macp.200290046  Published: DEC 30 2002  
Abstract: High molecular weight vinyl-type polynorborene was obtained by polymerization of norborene initiated by [NiBr)MPMe3)](4)/B(C6F5)(3). Polymerization in the presence of olefins resulted in termination of polynorborene chains by olefins moieties. Molecular weight of polynorborenes terminated by vinylidene compounds are lower than those terminated by vinyl and vinylene compounds. Corresponding polymerizations with polybutadiene and polyisoprene yielded graft copolymers with polynorbornene as grafts without contamination by homopolymerized polynorbornene. Crafting reactions were proved by spectroscopy, GPC, and degradation experiments using OsO4.
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111) Homoleptic lanthanide complexes of chelating bis(phosphanyl)amides: Synthesis, structure, and ring-opening polymerization of lactones
Author(s): Roesky, PW (Roesky, PW); Gamer, MT (Gamer, MT); Puchner, M (Puchner, M); Greiner, A (Greiner, A)
Source: CHEMISTRY-A EUROPEAN JOURNAL  Volume: 8  Issue: 22  Pages: 5265-5271  DOI: 10.1002/1521-3765(20021115)8:22<5265::AID-CHEM5265>3.0.CO;2-V  Published: NOV 15 2002  
Abstract: Treatment of the bis(phosphanyl)amide (Ph2P)(2)NH with KH in boiling THF followed by crystallization from THF/n-pentane leads to [K(thf)n][N(PPh2)(2)] (n=1.25, 1.5). Reaction of [K(thf)(n)][N(PPh2)(2)] with anhydrous yttrium or lanthanide trichlorides in a 3:1 molar ratio afforded homoleptic bis(phosphanyl)amide complexes [Ln{N(PPh2)(2)}(3)] (Ln=Y, Er) as large crystals in good yields. [Ln{N(PPh2)(2)}(3)] can also be obtained by reaction of the homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides [Ln{N(SiMe3)(2)}(3)] (Ln = Y, La, Nd) with three equivalents of (Ph2P)(2)NH in boiling toluene. The single-crystal X-ray structures of these complexes always show eta(2) coordination of the ligand. Dynamic behavior of the ligand is observed in solution and is caused by rapid exchange of the two different phosphorus atoms. [Ln{N(PPh2)(2)}(3)] was used as catalyst for the polymerization of epsilon-caprolactone. Significant differences in terms of correlation of theoretical and experimental molecular weights as well as polydispersities were observed depending on the nature of Ln. On the basis of the crystal structure of the heteroleptic complex [Lu{N(PPh2)(2)}(3)- (thf)], we suggest that in the initiation step of e-caprolactone polymerization the lactone adds to the lanthanide atom to form a sevenfold coordination sphere around the central atom.
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110) Carbon nanotubes and spheres produced by modified ferrocene pyrolysis
Author(s): Hou, HQ (Hou, HQ); Schaper, AK (Schaper, AK); Weller, F (Weller, F); Greiner, A (Greiner, A)
Source: CHEMISTRY OF MATERIALS  Volume: 14  Issue: 9  Pages: 3990-3994  DOI: 10.1021/cm021206x  Published: SEP 2002  
Abstract: Single-wall carbon nanotubes (SWCNTs) and well-aligned thin multiwall carbon nanotubes (MWCNTs) were successfully synthesized via pyrolysis of a powder mixture of ferrocene and anthracene or 9,10-dibromoanthracene. It is shown that the size of the MWCNTs can be tuned just by changing the ratio of ferrocene/anthracene in the mixture. A lower ratio resulted in low-diameter MWCNTs containing up to five graphene layers only; a high ratio has led to thick MWCNTs with more than 25 layers. Furthermore, there are two extreme cases, the pyrolysis of powders at a low ratio of 1:7 that gives rise to carbon nanospheres and the pyrolysis of pure ferrocene in a H-2 flow that mainly gives rise to metal nanoparticles. When powder mixtures of ferrocene and 9,10-dibromoanthracene are pyrolyzed, both SWCNTs and spherical carbon-coated iron nanoparticles are obtained.
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109) Trend report macromolecular chemistry 2001
Author(s): Mayer, S (Mayer, S); Zentel, R (Zentel, R); Wilhelm, M (Wilhelm, M); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 203  Issue: 12  Pages: 1743-1753  DOI: 10.1002/1521-3935(200208)203:12<1743::AID-MACP1743>3.0.CO;2-7  Published: AUG 30 2002  
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108) Synthesis and properties of novel poly(p-xylylene)s with aliphatic substituents
Author(s): Ishaque, M (Ishaque, M); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A)
Source: E-POLYMERS  Article Number: 031  Published: JUL 3 2002  
Abstract: Poly(p-xylylene)s (PPX) with aliphatic substituents at the alpha position were synthesized by chemical vapor deposition (CVD) via vapor phase pyrolysis of alpha-chloro-1,4-xylenes, or by base-induced dehydrohalogenation of alpha-chloro-1,4-xylenes (Gilch route). These PPXs are soluble under ambient conditions in organic solvents. The glass transition temperature of the tert-butyl substituted PPX is remarkably high. Good thermal stability under nitrogen was observed for the trifluoromethyl substituted PPX. A functionalized compound suitable for polymer analogous reactions is the norbornenyl substituted PPX.
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107) Crystal structures of the phosphoraneiminato complex [INi(NPMe3)](4)center dot C4H8O center dot C7H8 and of the phosphanimine complex [INi{Me2Si(NPMe3)(2)}(HNPMe3)]I-+(-)
Author(s): Muller, U (Muller, U); Bock, O (Bock, O); Sippel, H (Sippel, H); Grob, T (Grob, T); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 628  Issue: 7  Pages: 1703-1707  DOI: 10.1002/1521-3749(200207)628:7<1703::AID-ZAAC1703>3.0.CO;2-3  Published: JUL 2002  
Abstract: The phosphoraneiminato complex [1Ni(NPMe3)](4) was obtained by reaction of NiI2 in molten Me3SiNPMe3 in the presence of potassium fluoride at 200degreesC. Dark-green single crystals of [INi(NPMe3)](4) (.) C4H8O (.) C7H8 were formed from THF-toluene solution. According to the X-ray crystal structure determination the complex has a Ni4N4 heterocubane core and its symmetry deviates only marginally from T-d (space group Pca2(1), Z = 4, a = 3160.7(6), b = 1001.5(1), c = 1422.6(8) pm). The [INi(NPMe3)](4) molecules are stacked to columns parallel to b, with a nearly tetragonal pattern in projection on (010). The solvent molecules reside in channels between the columns. A side product of the synthesis were blue single crystals of the phosphanimine complex [INi{Me2Si(NPMe3)(2)}(HNPMe3)]I-+(-). The crystal structure determination (space group Pca2(1), Z = 4, a = 1213.3(4) b - 1582.7(6), c = 1339.7(4) pm) revealed a distorted tetrahedral coordination of the Ni atom in the cation; the coordinated atoms are the two N atoms of the chelating bis(phosphane)imine molecule, the N atom of the phosphaneimine molecule HNPMe3 and one iodo ligand.
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106) Polymer nanotubes by wetting of ordered porous templates
Author(s): Steinhart, M (Steinhart, M); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A); Wehrspohn, RB (Wehrspohn, RB); Nielsch, K (Nielsch, K); Schilling, J (Schilling, J); Choi, J (Choi, J); Gosele, U (Gosele, U)
Source: SCIENCE  Volume: 296  Issue: 5575  Pages: 1997-1997  DOI: 10.1126/science.1071210  Published: JUN 14 2002  
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105) Efficient control on molecular weight in the synthesis of poly (p-xylylene)s via Gilch polymerization
Author(s): Brink-Spalink, F (Brink-Spalink, F); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 35  Issue: 9  Pages: 3315-3317  DOI: 10.1021/ma010623c  Published: APR 23 2002  
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104) Macromolecular chemistry 2001
Author(s): Mayer, S (Mayer, S); Zentel, R (Zentel, R); Wilhelm, M (Wilhelm, M); Greiner, A (Greiner, A)
Source: NACHRICHTEN AUS DER CHEMIE  Volume: 50  Issue: 4  Pages: 442-+  Published: APR 2002  
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103) Poly(p-xylylene) nanotubes by coating and removal of ultrathin polymer template fibers
Author(s): Hou, HQ (Hou, HQ); Jun, Z (Jun, Z); Reuning, A (Reuning, A); Schaper, A (Schaper, A); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 35  Issue: 7  Pages: 2429-2431  DOI: 10.1021/ma011607i  Published: MAR 26 2002  
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102) Macromolecular chemistry 2001
Author(s): Mayer, S (Mayer, S); Zentel, R (Zentel, R); Wilhelm, M (Wilhelm, M); Greiner, A (Greiner, A); Ulbrich, D (Ulbrich, D); Vollmer, M (Vollmer, M)
Source: NACHRICHTEN AUS DER CHEMIE  Volume: 50  Issue: 3  Pages: 346-357  Published: MAR 2002  
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101) Diiodosamarium based polymerisations
Author(s): Agarwal, S (Agarwal, S); Greiner, A (Greiner, A)
Source: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1  Issue: 18  Pages: 2033-2042  DOI: 10.1039/b203903f  Published: 2002  
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100) Phosphoraneiminato complexes of zirconium: Crystal structures of [ZrCl3(NPPh3)(HNPPh3)(2)] and [ZrCl2(NPPh3)(2)(HNPPh3)(2)]
Author(s): Grob, (Grob,); Geiseler, G (Geiseler, G); Harms, K (Harms, K); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 628  Issue: 1  Pages: 217-221  Published: JAN 2002  
Abstract: The phosphoraneiminato complexes [ZrCl3-(NPPh3)(HNPPh3)(2)] (1) and [ZrCl2(NPPh3)(2)(HNPPh3)(2)] (2) have been obtained by reaction of [ZrCl4(THF)(2)] with [CsNPPh3](4) in THF solution to give colourless moisture sensitive crystals which are characterized by X-ray structure de-terminations. [ZrCl3(NPPh3)(HNPPh3)(2)] (1): Space group P(1) over bar, Z = 2, lattice dimensions at 193 K: a = 1209.4(2); b = 1480.8(2), c =: 1814.2(2) pm; alpha = 71.203(13)degrees, beta = 71.216(13)degrees, gamma = 74.401(13)degrees; R = 0.0476. The zirconium atom of 1 is oktahedrally coordinated by the three chlorine atoms in meridional arrangement and by the three nitrogen atoms of the (NPPh3-) ligand and of the two phosphane imine molecules HNPPh3. The ZrN bond distance of the (NPPh3-) group (193.5 pm) corresponds with a double bond. [ZrCl2(NPPh3)(2)(HNPPh3)(2)] (2): Space group P(1) over bar, Z = 4, lattice dimensions at 193 K: a = 1447.6(2); b = 1925.7(2), c = 2457.0(2) pm, alpha = 67.317(12)degrees, beta = 87.376(12)degrees, gamma = 87.103(13)degrees; R = 0.0408. The zirconium atom in 2 is octahedrally coordinated by the two chlorine atoms in trans position, and by the nitrogen atoms of the two (NPPh3-) groups as well as by the two HNPPh3 molecules. The ZrN distance of the (NPPh3-) ligands (198.9 and 202.0 pm) suggest some pi-interaction between the zirconium and the nitrogen atoms.
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2001

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99) Novel [Sm2I(NPPh3)(5)(DME)] initiator for the living ring-opening polymerization of epsilon-caprolactone and delta-valerolactone
Author(s): Ravi, P (Ravi, P); Grob, T (Grob, T); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 34  Issue: 25  Pages: 8649-8653  DOI: 10.1021/ma010496k  Published: DEC 4 2001  
Abstract: Ring-opening polymerization of epsilon -caprolactone (CL) and delta -valerolactone (VL) was carried out using the initiator system [Sm2I(NPPh3)(5)(DME)] in the presence of toluene. Experimental molecular weights were in good agreement with the theoretical molecular weights for [CL](0)/[1](0) up to 350. Polydispersities are low at 0-20 degreesC but increase at higher temperatures. Addition of small amounts of coordinating solvents such as THF and DME decreased the rate of polymerization and thereby reduced the polydispersity. The active polymer chain ends have been shown by sequential copolymerization of CL and VL, resulting in block copolymers.
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98) Titanium dioxide tubes from sol-gel coating of electrospun polymer fibers
Author(s): Caruso, RA (Caruso, RA); Schattka, JH (Schattka, JH); Greiner, A (Greiner, A)
Source: ADVANCED MATERIALS  Volume: 13  Issue: 20  Pages: 1577-+  DOI: 10.1002/1521-4095(200110)13:20<1577::AID-ADMA1577>3.0.CO;2-S  Published: OCT 16 2001  
Abstract: Electrospun polymer fibers can be coated with amorphous titanium dioxide using a sol-gel coating technique. After removal of the organic material by thermal treatment hollow titania fibers are produced. The sol-gel coating is able to reproduce the finer details of the fiber, e.g., the Figure shows how oval nodules that were indentations on the initial polymer are mimicked in the final inorganic structure of the titania fibers (see also images on the front cover).
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97) Ring-opening polymerization of epsilon-caprolactone by phosphorane iminato and cyclopentadienyl complexes of rare earth elements
Author(s): Ravi, P (Ravi, P); Grob, T (Grob, T); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 202  Issue: 12  Pages: 2641-2647  DOI: 10.1002/1521-3935(20010801)202:12<2641::AID-MACP2641>3.0.CO;2-Q  Published: AUG 30 2001  
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96) Crystal structures of trans-[NiBr2(pyridine)(4)] and [Ni(HNPEt3)(4)]I-2
Author(s): Grob, T (Grob, T); Neumuller, B (Neumuller, B); Harms, K (Harms, K); Schmock, F (Schmock, F); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 627  Issue: 8  Pages: 1928-1931  DOI: 10.1002/1521-3749(200108)627:8<1928::AID-ZAAC1928>3.0.CO;2-V  Published: AUG 2001  
Abstract: Turquoise single crystals of trans-[NiBr2(pyridine)(4)] have been obtained by the reaction of excess pyridine with nickel(II) bromide/diacetonealcohol. According to the crystal structure determination the nickel atom is octahedrally coordinated by the two bromine atoms in trans-position and by the nitrogen atoms of the pyridine molecules. Space group Pna2(1), Z = 4, lattice dimensions at 20 degreesC: a = 1592.9(2) b = 943.8(1), c = 1413.0(2) pm, R-1 = 0.0492. Dark blue single crystals of the phosphoraneimine complex [Ni(HNPEt3)(4)]I-2 have been obtained from NiI2/H2O with excess Me3SiNPEt3 and subsequent re crystallization from acetonitrile. According to the crystal structure determination the nickel atom is tetrahedrally coordinated by the nitrogen atoms of the HNPEt3 molecules. The iodide ions are connected via N-H (. . .) I contacts with the cation to form an ion triple. Space group P2(1)/c, Z = 4, lattice dimensions at -80 degreesC: a = 1934.9(2), b = 1078.3(1), c = 1966.3(2)pm, beta = 111.040(8)degrees; R-1 = 0.043.
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95) Preparation of fibers with nanoscaled morphologies: Electrospinning of polymer blends
Author(s): Bognitzki, M (Bognitzki, M); Frese, T (Frese, T); Steinhart, M (Steinhart, M); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH); Schaper, A (Schaper, A); Hellwig, M (Hellwig, M)
Source: POLYMER ENGINEERING AND SCIENCE  Volume: 41  Issue: 6  Pages: 982-989  DOI: 10.1002/pen.10799  Published: JUN 2001  
Abstract: The aim was to prepare fibers with diameters below the micrometer range characterized by specific bulk morphologies and surface topologies. Such materials are of interest for various applications including reinforcement, sensors or filtration as well as the formation of functional tubes by the use of fiber templates. We were able to manufacture highly structured submicrometer fibers by electrospinning from ternary solutions using polylactide (PLA) and polyvinylpyrrolidone (PVP) as polymer model components. Co-continuous phase morphologies resulted from phase separation processes taking place during fiber formation. In a subsequent step, specific surface topologies or fine pores were generated by selective removal of one of the components.
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94) Phosphoraneiminato- and phosphaneimine complexes of Nickel(II). Crystal structures of [Ni(O3SCF3) (NPMe3)] (4) [Ni4Br5{NP(NMe2)(3)}(3)], [NiBr2{HNP(NMe2)(3)}(2)], and [Ni(PMePh2)(4)]
Author(s): Krieger, M (Krieger, M); Gould, RO (Gould, RO); Harms, K (Harms, K); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 627  Issue: 4  Pages: 747-754  DOI: 10.1002/1521-3749(200104)627:4<747::AID-ZAAC747>3.0.CO;2-H  Published: MAR 2001  
Abstract: Black-violet single crystals of [Ni(O3SCF3)(NPMe3)](4) (1) have been prepared from [NiBr(NPMe3)], and copper(l)triflate by metathesis reaction. The nickel atoms are associated via mu (3)-N bridges of the (NPMe3-) groups to form a heterocubane. The triflate ions are bonded to the Ni atoms in a chelate fashion. Blue single crystals of [Ni4Br5{NP(NMe2)(3)}(3)] (2) are obtained by the reaction of NiBr2 with Me3SiNP(NMe2)(3) in boiling toluene in the presence of sodium fluoride. The Ni atoms in 2 are associated with three mu (3)-bridged nitrogen atoms of the (NP(NMe2)(3)(-)) groups as well as by a mu (3)-Br atom to give a distorted heterocubane. Deep blue single crystals of the phosphaneimine complex [NiBr2{HNP(NMe2)(3)}(2)] (3) are formed from Me3SiNP(NMe2)(3) and NiBr2 in boiling dichloromethane. In 3 the Ni atom is tetrahedrally coordinated by the bromine atoms and by the nitrogen atoms of the phosphane imine molecules. Pale red crystals of [Ni(PMePh2)(4)] (4) have been obtained by the reaction of [NiBr(NPMe3)](4) with lithium phenylacetilyde in the presence of PMePh2. In 4 the Ni atom is distorted tetrahedrally coordinated by the phosphorus atoms of the phosphane molecules with Ni-P distances of 219.9 pm in average. 1-4 have been characterized by crystallographic X-ray analyses.
1: Space group P2(1)/n, Z = 4, lattice dimensions at 193 K: a = 1566.7(2): b = 1479.9(1); c = 1960,6(2) pmt beta = 105.908(9)degrees; R = 0.0443.
2 3CH(2)Cl(2): Space group P2(1)/c, Z = 4. lattice dimensions at 293 K: a = 1226.0(3); b = 1614.0(3); c = 2406.0(5) pm; beta = 92.33(3)degrees; R=0.0703.
3: Space group C2/c, Z = 4, latttice dimensions at 203 K: a = 1840.7(1); b = 810,1(1); c = 1607.2(2)pml beta = 94.74(1)degrees, R = 0.0340.
4: Space group P (1) over bar, Z = 2, lattice dimensions at 223 K: a = 1053.1(2); b = 1315.0(3); c = 1674.5(3) pm: alpha = 81.55(1)degrees; p = 79.15(2)degrees; gamma = 84.91(2)degrees; R = 0.0497. 

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93) Effect of blending of cholesteric cellulose esters on the pitch height
Author(s): Hou, HQ (Hou, HQ); Reuning, A (Reuning, A); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULAR BIOSCIENCE  Volume: 1  Issue: 1  Pages: 45-48  DOI: 10.1002/1616-5195(200101)1:1<45::AID-MABI45>3.3.CO;2-R  Published: FEB 8 2001  
Abstract: Butyric esters (BuPC) of hydroxypropylcellulose (HPC) with different degrees of substitution (DS) were obtained by the reaction of (2-hydroxypropyl)cellulose with butyryl chloride. Blends of these BuPCs were obtained from ternary solutions by removal of the common solvent. The blends displayed thermotropic cholesteric mesophases and showed iridescent colors at ambient temperatures depending on the blend composition. The spectroscopic analysis of the blends showed systematic variations of the reflection colors with variations of the ratio of the blend components between the reflection colors of the pure blend components to pitch heights from 308-640 nm.
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92) Nanostructured fibers via electrospinning
Author(s): Bognitzki, M (Bognitzki, M); Czado, W (Czado, W); Frese, T (Frese, T); Schaper, A (Schaper, A); Hellwig, M (Hellwig, M); Steinhart, M (Steinhart, M); Greiner, A (Greiner, A); Wendorff, JH (Wendorff, JH)
Source: ADVANCED MATERIALS  Volume: 13  Issue: 1  Pages: 70-+  DOI: 10.1002/1521-4095(200101)13:1<70::AID-ADMA70>3.3.CO;2-8  Published: JAN 5 2001  
Abstract: Structured polymer fibers with diameters down to tens of nanometers are of interest for applications in filters, in composite reinforcement, or as templates for the preparation of functional nanotubes. The Figure shows fibers of poly-L-lactide produced by electrospinning from a dichloromethane solution exhibiting regular pores or pits in the 100 nm range.
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91) Crystal structure of potassium triflate-butyrolactone, [K-3(O3SCF3)(3)(O2C4H6)(2)]
Author(s): Grob, T (Grob, T); Seybert, G (Seybert, G); Massa, W (Massa, W); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 627  Issue: 1  Pages: 1-3  DOI: 10.1002/1521-3749(200101)627:1<1::AID-ZAAC1>3.0.CO;2-H  Published: JAN 2001  
Abstract: Single Crystals of [K-3(O3SCF3)(3)(O2C4H6)(2)] (1) have been obtained as a by-product from the reaction of KNPPh3 with Yb(O3SCF3)(3) in THF with subsequent addition of butyrolactone, The structure of 1 consists of three symmetry-independent potassium ions which are linked by the oxygen atoms of the triflate ions and the butyrolactone molecules to give a supramolecular structure with layers normal to the crystallographic b-axis. The carbonyl oxygen atoms of both butyrolactone molecules show a mu (3)-bridging function between three K+ ions, one of them is, in addition, coordinated by the ring O-atom in a chelate manner, 1: Space group P2(1)/c, Z = 4, lattice dimensions at 193 K: a = 1155,0(1), b=1537.2(1), c= 1531.1(1) pm, beta = 100.623(7)degrees. R=0.0484.
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90) Synthesis and structure-property relationships of novel poly(p-xylylene)s with aromatic substituents.
Author(s): ISHAQUE, M.; WOMBACHER, R.; WENDORFF, J. H.; GREINER, A.
Source: e-Polymers  Volume: 5  Published: 2001  
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89) Sm based initiators for the ring-opening polymerization of L-lactide.
Author(s): AGARWAL, S.; KARL, M.; DEHNICKE, K.; GREINER, A.
Source: e-Polymers  Volume: 12  Published: 2001  
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88) Molecular weight control and end group functionalization of polynorbornene
By Ni(II)-initiated polymerization of norbornene in the presence of ethylene and α-olefins.

Author(s): MAST, C.; KRIEGER, M.; DEHNICKE, K.; GREINER, A.
Source: e-Polymers  Volume: 16  Published: 2001  
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2000

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87) Tuning of the pitch height of thermotropic cellulose esters
Author(s): Hou, HQ (Hou, HQ); Reuning, A (Reuning, A); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 201  Issue: 15  Pages: 2050-2054  DOI: 10.1002/1521-3935(20001001)201:15<2050::AID-MACP2050>3.0.CO;2-I  Published: OCT 23 2000  
Abstract: Butyric esters of (2-hydroxypropyl) cellulose (BuPC) with different degree of substitution(DS) were synthesized via control of the esterification time of butyryl chloride and (2-hydroxypropyl) cellulose. These BuPCs are thermotropic and displayed different colors at ambient temperature due to the formation of a cholesteric structure and the occurrence of a corresponding cholesteric reflection. The pitch height was found to increase significantly with a decrease of the degree of substitution. Both the glass transition temperature and the melting temperature are not affected by variation of the DS. The BuPC samples displayed a banded texture or focal-conic texture, respectively. The X-ray diffraction studies revealed the presence of a layer structure. The cl-spacing between two adjacent layers in the cholesteric structure displayed no significant dependence on the DS in the range from 2 to 3.
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86) Optical properties of guest host systems based on cellulose derivatives
Author(s): Arici, E (Arici, E); Greiner, A (Greiner, A); Hou, HQ (Hou, HQ); Reuning, A (Reuning, A); Wendorff, JH (Wendorff, JH)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 201  Issue: 15  Pages: 2083-2090  DOI: 10.1002/1521-3935(20001001)201:15<2083::AID-MACP2083>3.0.CO;2-V  Published: OCT 23 2000  
Abstract: Guest host systems composed of various types of esters of (2-hydroxypropyl) cellulose and the chromophore coumarin 334 were characterized with respect to the absorption and emission properties as a function of the concentration of the chromophore and the nature of the esters. The results were compared with the ones obtained for solutions of the chromophore with low molar mass solvents. The cellulose derivatives are characterized by good film forming capabilities, a high solubility for the chromophores, by significant solvatochromic effects both in absorption and emission and by the formation of excimers at elevated concentration of the chromophores. These features make such cellulose derivatives interesting candidates as matrix materials for host-guest systems in areas such as organic light emitting devices pr sensors. Their tendency to display a cholesteric super-structure is of particular interest.
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85) Time dependence of the steady state fluorescence in polymer guest-host systems
Author(s): Arici, E (Arici, E); Greiner, A (Greiner, A); Raubacher, F (Raubacher, F); Wendorff, JH (Wendorff, JH)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 201  Issue: 14  Pages: 1679-1686  DOI: 10.1002/1521-3935(20000901)201:14<1679::AID-MACP1679>3.0.CO;2-C  Published: SEP 28 2000  
Abstract: The fluorescence of guest-hot systems composed of an amorphous polymer matrix and various concentrations of selected chromophores is considered. Such systems are of interest for applications in organic light emitting diodes. The observation is that the fluorescence results predominantly from excimers and that the excimer emission is strongly reduced as a function of irradiation time in the polymer matrix while no such effects were found for solutions of the chromophore in low molar mass solvents. The rate of change of steady state fluorescence depends on the polymer matric and the process is partially reversible in some guest-host systems. We tentatively attribute the effect to time dependent configurational changes taking place within the chromophore-polymer matrix due to irradiation.
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84) Polarized electroluminescence from liquid crystalline polymers
Author(s): Clauswitz, KUW (Clauswitz, KUW); Geffarth, F (Geffarth, F); Greiner, A (Greiner, A); Lussem, G (Lussem, G); Wendorff, JH (Wendorff, JH)
Source: SYNTHETIC METALS  Volume: 111  Pages: 169-171  DOI: 10.1016/S0379-6779(99)00339-2  Published: JUN 1 2000  
Abstract: Polymer liquid crystalline materials display unique properties that can be exploited in organic light-emitting diodes (LEDs). Characteristic features are the anisotropy of electronic properties as well as a tendency to form spontaneously homogeneous monodomain films. It is found that liquid crystalline polymers can be used in LEDs to control the state of polarization of the emitted light. A linearly polarized or circularly polarized emission can be achieved depending on the intrinsic structure of the liquid crystalline material and on the corresponding optical properties. (C) 2000 Elsevier Science S.A. All rights reserved.
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83) Polymer, metal, and hybrid nano- and mesotubes by coating degradable polymer template fibers (TUFT process)
Author(s): Bognitzki, M (Bognitzki, M); Hou, HQ (Hou, HQ); Ishaque, M (Ishaque, M); Frese, T (Frese, T); Hellwig, M (Hellwig, M); Schwarte, C (Schwarte, C); Schaper, A (Schaper, A); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: ADVANCED MATERIALS  Volume: 12  Issue: 9  Pages: 637-+  DOI: 10.1002/(SICI)1521-4095(200005)12:9<637::AID-ADMA637>3.0.CO;2-W  Published: MAY 3 2000  
Abstract: Communication: Coating extremely thin degradable template polymer fibers with the desired wall materials forms the basis of the straightforward and highly versatile method described here for the production of polymer, metal, and hybrid nano- and mesotubes. Tubes with highly structured inner surfaces (see Figure) may be fabricated, which is of great interest for applications requiring large surface/volume ratios (see also cover).
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82) Rare earth metal initiated ring-opening polymerization of lactones
Author(s): Agarwal, S (Agarwal, S); Mast, C (Mast, C); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 21  Issue: 5  Pages: 195-212  DOI: 10.1002/(SICI)1521-3927(20000301)21:5<195::AID-MARC195>3.0.CO;2-4  Published: MAR 24 2000  
Abstract: The progress in the synthesis of organolanthanide complexes supports the exploration of these compounds as initiators for ring-opening polymerization (ROP) of lactones. The performance of these initiators in terms of yield, molecular weight, polydispersity, stereoregularity is affected by the ligands and by the oxidation state of the respective rare earth metals. Several initiators are known to initiate living polymerization of lactones with excellent polydispersities of the thus obtained polymers. Differences in the performance of the initiators are caused by differences in the initiation mechanism, chain growth mechanism, or side reactions. ROP of lactones was extended to block- and graft copolymerization with polylactones, polylactides, and polyolefins either by simply utilizing living polymer chain ends, by transformation of living polymer chain ends, or by usage of polyinitiators.
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81) Homoleptic phosphoraneiminato complexes of rare earth elements as initiators for ring-opening polymerization of lactones
Author(s): Grob, T (Grob, T); Seybert, G (Seybert, G); Massa, W (Massa, W); Weller, F (Weller, F); Palaniswami, R (Palaniswami, R); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  Volume: 39  Issue: 23  Pages: 4373-+  DOI: 10.1002/1521-3773(20001201)39:23<4373::AID-ANIE4373>3.0.CO;2-K  Published: 2000  
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80) Homoleptische Phosphaniminato-Komplexe von Seltenerdelementen als Initiatoren für die ringöffnende Polymerisation von Lactonen.
Author(s): GROEB, T.; SEYBERT, G.; MASSA, W.; WELLER, F.; PALANISWAMI, R.; GREINER, A.; DEHNICKE, K.
Source: Angew. Chem.  Volume: 112  Pages: 4542-4544  Published: 2000  
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1999

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79) Investigations on the morphology of poly-1,4-(phenylethyl xylylene) in solution
Author(s): Schnablegger, H (Schnablegger, H); Antonietti, M (Antonietti, M); Goltner, C (Goltner, C); Stapff, IH (Stapff, IH); Brink-Spalink, F (Brink-Spalink, F); Greiner, A (Greiner, A)
Source: ACTA POLYMERICA  Volume: 50  Issue: 11-12  Pages: 391-398  DOI: 10.1002/(SICI)1521-4044(19991201)50:11/12<391::AID-APOL391>3.0.CO;2-2  Published: DEC 1999  
Abstract: Several poly-1,4-(phenylethyl xylylene)s of varying molecular weight were investigated with a combination of X-ray and light scattering techniques as well as with scanning force and transmission electron microscopy to elucidate their aggregation behavior in solution. It turns out that this polymer aggregates into ribbon-like supermolecular structures. Aggregation is the more pronounced the higher the concentration and the molecular weight of the polymer. Switching the solvent from tetrahydrofuran to chloroform only weakly diminishes the ability to form aggregates. The stiff aggregate ribbons in solution are 30-40 nm broad, about 5 MI high and several micrometers long. The cross-section of the ribbons is inhomogeneous and presumably consists of 0.5 nm thick layers.
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78) Phosphoraneiminato complexes of rare-earth elements. Crystal structures of [Yb2Cp3(NPPh3)(3)], [YCp(NPPh3)(mu-OSiMe2NPPh3)](2), and [M(NPPh3)(2)(mu-OSiMe2NPPh3)](2) with M = Y and Sm
Author(s): Anfang, S (Anfang, S); Grob, T (Grob, T); Harms, K (Harms, K); Seybert, G (Seybert, G); Massa, W (Massa, W); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 625  Issue: 11  Pages: 1853-1859  DOI: 10.1002/(SICI)1521-3749(199911)625:11<1853::AID-ZAAC1853>3.0.CO;2-4  Published: NOV 1999  
Abstract: The ytterbium complex [Yb2Cp3(NPPh3)(3)] with sesqui distribution of cyclopentadienide and phosphoraneiminato ligands is made from YbCp2Cl and LiNPPh3 in boiling toluene and isolated as yellow, moisture sensitive crystals, which enclose three molecules of toluene per unit cell. [Yb2Cp3(NPPh3)]. 3C(7)H(8) (1): Space group Pbca, Z = 8, lattice dimensions at -80 degrees C: a = 2727.6(2), b = 1977.5(1), c = 2848.9(2) pm; R = 0.0541. Two of the (NPPh3)(-)-groups link the ytterbium atoms to a nonplanar Yb2N2 four-membered ring with a folding angle of 17.1 degrees along the Yb...Yb connecting line. The third (NPPh3)(-) group is terminally bonded with a short Yb-N distance of 214.2 pm.
[YCp(NPPh3) (mu-OSiMe2NPPh3)](2). 4C(7)H(8) (2) originates from YCpCl2 and LiNPPh3 in boiling toluene with Baysilon-paste participating forming colourless, moisture sensitive crystals. Space group P2(1)/c, Z = 2, lattice dimensions at -80 degrees C: a = 1469.0(1), b = 1234.1(1), c = 2761.5(2)pm, beta = 93.196(10)degrees; R = 0.0518. In 2 the yttrium atoms are linked via the oxygen atoms of the (OSiMe2NPPh3)(-) groups to form a centrosymmetric Y2O2 four-membered ring with Y-O bonds of different lengths. Together with the terminally bonded (NPPh3)(-)-ligand, the eta(5)-C5H5- group, and the N atom of the siloxyphosphaneimine group, which functions as a donor atom, the Y atoms achieve coordination number five. [Y(NPPh3)(2)(mu-OSiMe2NPPh3)](2). 2C(7)H(8) (3) and [Sm(NPPh3)(2)(mu-OSiMe2NPPh3)](2) (4) originate from the metal trichlorides with KNPPh3 in THF with Baysilon paste participating and subsequent crystallization from toluene as colourless, moisture sensitive crystal needles. 3: Space group P2(1)/n, Z = 2, lattice dimensions at -80 degrees C: a = 1804.1(2), b = 1401.8(1), c = 2221.6(2) pm, beta = 98.716(9)degrees; R = 0.0537.
4: Space group <P(1)over bar >, Z = 1, lattice dimensions at -80 degrees C: a = 1363.4(1), b = 1364.9(1), c = 1650.6(1) pm; alpha = 112.457(8)degrees beta = 91.948(9)degrees, gamma = 114.974(8)degrees; R = 0.0308.
3 and 4 form centrosymmetric dimeric molecules in which the metal atoms are linked via the oxygen atoms of the (OSiMe2NPPh3)(-) groups to form M2O2 four-membered rings with M-O bonds of varying length. Together with the terminally bonded (NPPh3)(-) ligands and the N atom of the siloxyphosphaneimine ligand, which functions as a donor atom, the metal atoms achieve coordination number five.
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77) Synthesis and properties of liquid crystalline aromatic copolyesters with lactide moieties
Author(s): Haderlein, G (Haderlein, G); Petersen, H (Petersen, H); Schmidt, C (Schmidt, C); Wendorff, JH (Wendorff, JH); Schaper, A (Schaper, A); Jones, DB (Jones, DB); Visjager, J (Visjager, J); Smith, P (Smith, P); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 200  Issue: 9  Pages: 2080-2087  DOI: 10.1002/(SICI)1521-3935(19990901)200:9<2080::AID-MACP2080>3.0.CO;2-Y  Published: SEP 1999  
Abstract: High molecular weight liquid crystalline copolyesters were obtained by copolycondensation of aromatic diols and diacyl chlorides with oligolactides. The molecular structure of these copolyesters was verified by NMR studies. The copolyesters form nematic melts, which can be frozen in into a nematic glass. Unexpectedly, a fibrillar structure was observed exclusively on the surface of solution cast films. In spite of a significant content of lactide moieties of the copolyesters their films and fibers are characterized by exceptional mechanical properties. Initial experiments indicated excellent biocompatibility based on cell seeding experiments and microscopic evidence.
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76) Samarium(III)-mediated graft polymerization of epsilon-caprolactone and L-lactide on functionalized poly(p-xylylene)s: Model studies and polymerizations
Author(s): Agarwal, S (Agarwal, S); Brandukova-Szmikowski, NE (Brandukova-Szmikowski, NE); Greiner, A (Greiner, A)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 10  Issue: 9  Pages: 528-534  DOI: 10.1002/(SICI)1099-1581(199909)10:9<528::AID-PAT905>3.0.CO;2-3  Published: SEP 1999  
Abstract: The reductive coupling of ar aromatic monocarbonyl compounds in the presence of SmI2 results in the formation of Samarium(lll) dialkoxides. These Sm(III) dialkoxides have been utilized as initiators fbr ring opening polymerization (ROP) of lactones and lactides. The reductive coupling of aromatic dicarbonyl compounds results in the formation of Sm(III) polyalkoxides which have been used as polyinitiator for (ROP) of lactones and lactides. The products of this process are poly(p-xylylene)s grafted by polylactones or polylactides. Grafting efficiency depends significantly on reaction conditions and is currently limited to 28%. Copyright (C) 1999 John Wiley & Sons, Ltd.
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75) Crystal structures of the samarium amido complexes [Sm(mu-X){N(SiMe3)(2)}(2)(THF)](2) with X = Cl, Br
Author(s): Karl, M (Karl, M); Seybert, G (Seybert, G); Massa, W (Massa, W); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 625  Issue: 9  Pages: 1405-1407  DOI: 10.1002/(SICI)1521-3749(199909)625:9<1405::AID-ZAAC1405>3.0.CO;2-5  Published: SEP 1999  
Abstract: The crystal structures of the title compounds have been determined by X-ray methods. [Sm(mu-Cl) . {N(SiMe3)(2)}(2)(THF)](2) (1): Space group P2(1)/n, Z = 2, lattice dimensions at 223 K: a = 1429.5(2), b = 1302.3(3), c = 1658.6(3) pm, beta = 114.212(10)degrees, R = 0.0561. [Sm(mu-Br) . {N(SiMe3)(2)}(2)(THF)](2) (2): Space group Pbca, Z = 4, lattice dimensions at 223 K: a = 1850.0(7), b = 1611.0(9), c = 1888.1(6) pm, R = 0.0497.
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74) Ring-opening polymerization of epsilon-caprolactone and delta-valerolactone using new Sm(III) mu-Halo-bis(trimethylsilyl)amido complexes
Author(s): Agarwal, S (Agarwal, S); Karl, M (Karl, M); Dehnicke, K (Dehnicke, K); Seybert, G (Seybert, G); Massa, W (Massa, W); Greiner, A (Greiner, A)
Source: JOURNAL OF APPLIED POLYMER SCIENCE  Volume: 73  Issue: 9  Pages: 1669-1674  DOI: 10.1002/(SICI)1097-4628(19990829)73:9<1669::AID-APP7>3.0.CO;2-1  Published: AUG 29 1999  
Abstract: New Sm(III) mu-halo-bis(trimethylsilyl)amido complexes [Sm(mu-X) {N(SiMe3)(2)}(2)(THF)](2) (X = Cl, Br) were synthesized and their crystal structures were analyzed. These complexes were used as catalysts for the homopolymerization of epsilon-caprolactone and delta-valerolactone and found to initiate ring-opening polymerization (ROP) of these monomers in high conversion over a short period, giving homopolymers with a moderate polydispersity index (similar to 2.0). The effect of temperature and the catalyst amount on the molecular weight distribution was also studied. Mechanistic studies were conducted using 1 : 1 and 1 : 6 molar ratios of mu-halo-bis-(trimethylsilyl)amido complexes and epsilon-caprolactone by H-1-NMR and C-13-NMR spectroscopic techniques and revealed the presence of more than one initiating species. (C) 1999 John Wiley & Sons, Inc.
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73) Synthesis and properties of omega-phenylalkyl-substituted poly(p-xylylene)s prepared by base-induced 1,6-dehydrohalogenation
Author(s): Schafer, O (Schafer, O); Brink-Spalink, F (Brink-Spalink, F); Smarsly, B (Smarsly, B); Schmidt, C (Schmidt, C); Wendorff, JH (Wendorff, JH); Witt, C (Witt, C); Kissel, T (Kissel, T); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 200  Issue: 8  Pages: 1942-1949  DOI: 10.1002/(SICI)1521-3935(19990801)200:8<1942::AID-MACP1942>3.0.CO;2-H  Published: AUG 1999  
Abstract: Reaction parameters were optimized for the synthesis of high molecular weight omega-phenylalkyl-substituted derivatives of poly(p-xylylene) (PPX) by base-induced 1,6-dehydrohalogenation of corresponding 4-halogenomethyltoluenes. Class transition temperatures decreased systematically with increasing alkyl spacer of the lateral substituent. The highest elongation at break was observed for the 4-phenylbutyl-substituted PPX. Level I tests on the biocompatibility of 4-phenylbutyl-substituted PPX indicated low toxicity.
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72) Amido metalates of rare earth elements. Syntheses and crystal structures of [Na(12-clown-4)(2)][M{N(SiMe3)(2)}(3)(OSiMe3)] (M = Sm, Yb), [Na(THF)(3)Sm(N(SiMe3)(2)}(3)(C C-Ph)], [Na(THF)(6)][Lu-2(mu-NH2)(mu-NSiMe3){N(SiMe3)(2)}(4)], and of [NaN(SiMe3)(2)(THF)](2). Applications of rare earth metal complexes as polymerization catalysts
Author(s): Karl, M (Karl, M); Seybert, G (Seybert, G); Massa, W (Massa, W); Harms, K (Harms, K); Agarwal, S (Agarwal, S); Maleika, R (Maleika, R); Stelter, W (Stelter, W); Greiner, A (Greiner, A); Heitz, W (Heitz, W); Neumuller, B (Neumuller, B); Dehnicke, K (Dehnicke, K)
Source: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE  Volume: 625  Issue: 8  Pages: 1301-1309  DOI: 10.1002/(SICI)1521-3749(199908)625:8<1301::AID-ZAAC1301>3.0.CO;2-0  Published: AUG 1999  
Abstract: The amido silyloxy complexes [Na(12-crown-4)(2)][M{N(SiMe3)(2)}(3)(OSiMe3)] with M = Sm (la), Eu (Ib), To (Ic), and Lu (Id) were obtained from the trisamides M[N(SiMe3)(3)](3) and NaOSiMe3 in n-hexane in the presence of 12-crown-4; they form yellow to orange-red crystals, of which la and Ic were characterized crystallographically. The complexes crystallize isotypically with one another in the monoclinic space group I2/a with eight formula units per unit cell. The metal atoms of the complex anions are tetra-hedrally coordinated by the three nitrogen atoms of the N(SiMe3)(2)(-) ligands and by the oxygen atom of the OSiMe3- ligand. With 172.4 degrees for la and 179.3 degrees for Ic the bond angles M-O-Si are practically linear.
With ethynylbenzene in the presence of NaN(SiMe3)(2) in tetrahydrofuran the trisamides M[N(SiMe3)2]3 react under formation of the complexes [Na(THF)(3)M{N(SiMe3)(2)}(3).(C = C-Ph)] with M = Ce (2a), Sm (2b), and Eu (2c), of which 2b was characterized crystallographically (monoclinic, space group P2(1)/n, Z = 4). 2b forms an ion pair in which the terminal carbon atom of the C = C-Ph- ligand is connected with the samarium atom of the Sm[N(SiMe3)(2)](3) group and the sodium ion is side-on connected with the acetylido group. According to the crystal structure determination (space group P2(1)2(1)2(1), Z = 4) [Na(THF)(6)] [Lu-2(mu-NH2) (mu-NSiMe3).{N(SiMe3)(2)}(4)] (3), which is formed as a by-product, consists of [Na(THF)6](+) ions and dimeric anions, in which the lutetium atoms are connected to form a planar Lu2N2 four-membered ring via a mu-NH2 bridge with average Lu-N distances of 227.2 pm and via a mu-NSiMe3 bridge of average Lu-N distances of 218.5 pm. According to the crystal structure determination (space group P (1) over bar, Z = 1) [NaN(SiMe3)(2)(THF)](2) (4) forms centrosymmetric dimeric molecules with Na-N distances of the Na2N2 four-membered ring of 239.9 pm and distances Na-O of the terminally bonded THF molecules which are 226.7 pm.
The vinylic polymerization of methylmethacrylate (MMA) catalyzed by Ic resulted in high molecular weight polymethylmethacrylate (PMMA) with moderate yields. The reaction of 1a or 2b with MMA did not give PMMA. Insoluble polynorbornene was obtained in low yields by reaction of norbornene/methylaluminoxane (MAO) with 1a, 1c, or 2b. The ring opening polymerization of epsilon-caprolacton or delta-valerolacton catalyzed by 2b resulted in corresponding polylactones in quantitative yields.
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71) Reactivity of Sm(II) compounds as ring-opening polymerization initiators for lactones
Author(s): Agarwal, S (Agarwal, S); Brandukova-Szmikowski, NE (Brandukova-Szmikowski, NE); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 20  Issue: 5  Pages: 274-278  DOI: 10.1002/(SICI)1521-3927(19990501)20:5<274::AID-MARC274>3.0.CO;2-J  Published: MAY 1999  
Abstract: Successful room temperature ring-opening polymerization (ROP) of epsilon-caprolactone and delta-valerolactone has been carried out using SmX2 (X = I, Br, and cyclopentodienyl (Cp)) catalysts. SmI2 in the presence of metallic Sm was found to have enhanced reactivity as room temperature ROP initiator for lactones as compared to pure SmI2. SmBr2 and SmCp2 showed increased reactivity compared with the Sm/SmI2 system due to their higher reductive power. The catalyst concentration and time of polymerization showed a marked effect on number-average molecular weight ((M) over bar(n)). There was a decrease in (M) over bar(n) on increasing reaction time and decreasing catalyst concentration. The initiation mechanism is discussed based on end group analysis of low molecular weight polymers.
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70) Synthesis of OH-functionalized poly(p-xylylene)s by reductive coupling polymerization of aromatic dialdehydes with catalytic amounts of divalent samarium compounds
Author(s): Brandukova-Szmikowski, NE (Brandukova-Szmikowski, NE); Greiner, A (Greiner, A)
Source: ACTA POLYMERICA  Volume: 50  Issue: 4  Pages: 141-144  Published: APR 1999  
Abstract: The focus of this study is on reductive couplings of aromatic monoaldehydes and dialdehydes utilizing catalytic amounts of Sm(II) compounds and different co-reductants such as Mg turnings and Mg/Hg alloy in the presence of trimethylsilylchloride (TMSiCl). High educt and no side products have been observed using 10 mol% of SmI2 and excess of Mg turnings activated by C2H4Br2 in the presence of TMSiCl. Low yields of hydrobenzoin were observed when SmCp2 replaced SmI2.
The reductive coupling polymerization of aromatic dialdehydes can be conducted under catalytic conditions with 12 moI% of SmI2 and excess of Mg or Mg/Hg in the presence of TMSiCl in THF. OH-functionalized PPXs were obtained with moder ate yields polymer and M-n of up to 16 000 g/mol.
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69) Control of crystalline modifications of poly(p-xylylene) by copolymerization
Author(s): Smarsly, B (Smarsly, B); Brink-Spalink, F (Brink-Spalink, F); Schafer, O (Schafer, O); Schmidt, C (Schmidt, C); Greiner, A (Greiner, A); Ruland, W (Ruland, W); Wendorff, JH (Wendorff, JH)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 200  Issue: 4  Pages: 714-718  Published: APR 1999  
Abstract: Poly(p-xylylene) (PPX), phenylethyl-substituted PPX (PEPPX) and copolymers of both were synthesized by base-induced dehydrohalogenation of corresponding 4-chloromethyltoluenes. Analysis of the crystal structure of PEPPX by X-ray diffractometry reveals close resemblance of its unit cell with the unit cell of PPX in its alpha-modification. The crystalline morphology of as-polymerized PPX can be described as a mixed modification consisting of alpha- and beta-crystals. However, copolymers of PPX and PEPPX show predominantly the alpha-crystals, even at very low ratio of PEPPX moieties in the copolymer. Conversion of the alpha-modification to the beta-modification cannot be accomplished by annealing of copolymers above 200 degrees C, which is in contrast to PPX homopolymers.
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68) Synthesis of poly(p-xylylene)s by base-induced 1,6-dehydrohalogenation - Control of the degree of polymerization
Author(s): Schafer, O (Schafer, O); Brink-Spalink, F (Brink-Spalink, F); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 20  Issue: 4  Pages: 190-193  DOI: 10.1002/(SICI)1521-3927(19990401)20:4<190::AID-MARC190>3.0.CO;2-Z  Published: APR 1999  
Abstract: Phenylethyl-substituted poly(p-xylylene) (PEPPX) was prepared by base-induced 1,6-dehydrohalogenation of the corresponding 4-chloromethyltoluene. Very high degrees of polymerization of about 3150 were obtained already at low conversions. Several standard retarders for radical polymerizations failed to limit the degree of polymerization significantly. However, best control was accomplished by the addition of dibenzoyl peroxide. The degree of polymerization of PEPPX was depressed to about 110 by addition of 10-15 mol-% of dibenzoyl peroxide.
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67) Vinyl-type polymerization of norbornene by a nickel-based catalyst with phosphoraneiminato ligands
Author(s): Mast, C (Mast, C); Krieger, M (Krieger, M); Dehnicke, K (Dehnicke, K); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 20  Issue: 4  Pages: 232-235  DOI: 10.1002/(SICI)1521-3927(19990401)20:4<232::AID-MARC232>3.0.CO;2-A  Published: APR 1999  
Abstract: High molecular weight vinyl-type polynorbornene was obtained in high yields with a highly active nickel-based phosphoraneiminato complex in the presence of methylaluminoxane. This polynorbornene is soluble at room temperature in chlorobenzene and shows no indication of crystallinity in the solid state. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by variation of reaction parameters.
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66) Synthesis of OH-functionalized poly(p-xylylene)s by reductive coupling polymerization of aromatic dialdehydes with stoichiometric amounts of divalent samarium compounds
Author(s): Brandukova-Szmikowski, NE (Brandukova-Szmikowski, NE); Agarwal, S (Agarwal, S); Greiner, A (Greiner, A)
Source: ACTA POLYMERICA  Volume: 50  Issue: 1  Pages: 35-39  Published: JAN 1999  
Abstract: Reductive coupling of aromatic carbonyl compounds in the presence of stoichiometric amounts of Sm(II) compounds such as SmI2, SmI2/TMSiCl, SmBr2, Sm/TMSiBr, SmCp2 resulted in hydrobenzoin derivatives. OH-functionalized poly(p-xylylene)s (OH-PPX) were obtained by reductive coupling of aromatic dialdehydes. The usage of solubilizing groups as well as the use of trimethylsilylchloride (TMSiCl) and trimethylsilylbromide (TMSiBr) enhanced the polymerizability of monomers under study. In spite of moderate yields high molecular weight polymers were obtained.
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65) Film-forming poly(p-phenylenevinylene)s for light-emitting applications via poly(p-xylylene)s by a solvent-free process
Author(s): Schafer, O (Schafer, O); Ishaque, M (Ishaque, M); Greiner, A (Greiner, A); Spiegel, S (Spiegel, S); Moller, C (Moller, C); Spiess, HW (Spiess, HW)
Source: DESIGNED MONOMERS AND POLYMERS  Volume: 2  Issue: 3  Pages: 231-238  DOI: 10.1163/156855599X00052  Published: 1999  
Abstract: Film-forming functionalized poly(p-xylylene)s (PPXs) were synthesized by vapor-phase pyrolysis of 4-dichloromethyl-toluenes and chemical vapor deposition (CVD) of the pyrolysis products followed by their spontaneous polymerization. These PPXs served as precursor polymers which were converted to poly(p-phenylenevinylene)s (PPVs) by thermally induced HCl elimination. Following this route, film-forming PPVs with cyano- and chloro-substituents in the alpha-position were obtained by polymer-analogous conversion of the corresponding PPX precursor polymers.
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1998

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64) Poly(p-xylylene) and its derivatives by chemical vapor deposition: Synthesis, mechanism, and structure
Author(s): Simon, P (Simon, P); Mang, S (Mang, S); Hasenhindl, A (Hasenhindl, A); Gronski, W (Gronski, W); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 31  Issue: 25  Pages: 8775-8780  DOI: 10.1021/ma9808070  Published: DEC 15 1998  
Abstract: Poly(p-xylylene) (PPX) and its derivatives were prepared by vapor-phase pyrolysis and subsequent chemical vapor deposition (CVD) of the pyrolysis products. Readily available esters of alpha,alpha'-dihydroxy-p-xylylenes were utilized as starting materials. Mechanistical studies prove that 1,4-quinodimethane is formed by pyrolysis of diesters. The PPXs obtained compare well to PPXs obtained by the classical route using [2.2]paracyclophanes. C-13 CP-MAS NMR spectroscopy indicates that the arrangement of substituents along the polymer main chain is controlled by the size of substituents.
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63) Synthesis of polybenzyls by Suzuki Pd-catalyzed crosscoupling of boronic acids and benzyl bromides: Model reactions and polyreactions
Author(s): Klarner, C (Klarner, C); Greiner, A (Greiner, A)
Source: MACROMOLECULAR RAPID COMMUNICATIONS  Volume: 19  Issue: 12  Pages: 605-608  Published: DEC 1998  
Abstract: The palladium-catalyzed crosscoupling reaction of boronic acids and benzyl bromides can be used successfully for the preparation of benzyls in high yield. This C-C coupling reaction was optimized for the synthesis of polybenzyls by model reactions. Different reaction channels were observed here with meta- and para-bis(bromomethyl)benzenes. The main product with 1,3-bis(chloromethyl)benzene was the corresponding 1,3-dibenzylbenzene, but the main product with 1,4-bis(chloromethyl)benzene was the corresponding biaryl resulting from homocoupling of aromatic boronic acid. 1.3-linked polybenzyls were synthesized based on the results of the model reactions. (M) over bar(n)'s of 2380 corresponding to a DP of 26 were found based on GPC. No structural defects were detected within the limits of detection.
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62) Polymer-based LEDs
Author(s): Greiner, A (Greiner, A)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 9  Issue: 7  Pages: 369-369  DOI: 10.1002/(SICI)1099-1581(199807)9:7<369::AID-PAT819>3.0.CO;2-F  Published: JUL 1998  
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61) Design and synthesis of polymers for light-emitting diodes
Author(s): Greiner, A (Greiner, A)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 9  Issue: 7  Pages: 371-389  DOI: 10.1002/(SICI)1099-1581(199807)9:7<371::AID-PAT817>3.0.CO;2-7  Published: JUL 1998  
Abstract: Polymers with aromatic phi-conjugated moieties were utilized as electroluminescent materials. In order to meet the requirements for light-emitting diodes (LED), the design and synthesis of electroluminescent polymers had to be developed and viewed in this review. Focus is on polymers with arylene vinylene, arylene ethinylene, phenylene, thiophene and arylene amine moieties as light-emitting, hole-transporting and electron-transporting materials in LED devices. An attempt has been made to arrange a structural classification of electroluminescent polymers in nonsegmented and segmented polymers. (C) 1998 John Wiley & Sons, Ltd.
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60) Structural analysis of PPX prepared by vapor phase pyrolysis of [2.2]paracyclophane
Author(s): Schmidt, C (Schmidt, C); Stumpflen, V (Stumpflen, V); Wendorff, JH (Wendorff, JH); Hasenhindl, A (Hasenhindl, A); Gronski, W (Gronski, W); Ishaque, M (Ishaque, M); Greiner, A (Greiner, A)
Source: ACTA POLYMERICA  Volume: 49  Issue: 5  Pages: 232-235  DOI: 10.1002/(SICI)1521-4044(199805)49:5<232::AID-APOL232>3.0.CO;2-L  Published: MAY 1998  
Abstract: Poly(p-xylylene) (PPX) was prepared by vapor phase pyrolysis of [2.2]paracyclophane following the procedure of Gorham. PPX was obtained in different crystalline modifications by dry annealing, dissolution and reprecipitation under different conditions. These samples were analyzed by WAXS and C-13 CP-MAS NMR spectroscopy. Clear evidence was found that the presence of different crystalline modifications is responsible for the unexpected C-13 CP-MAS NMR spectrum as observed for as-polymerized PPX. An attempt was made to explain the differences observed in the C-13 CP-MAS NMR spectra of different crystalline modifications by different chemical environments utilizing simulations of the crystal unit cells.
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59) Simple poly(p-xylylene)s as precursor polymers for poly(p-phenylenevinylene)s and segmented poly(p-phenylenevinylene)s: synthesis, polymer analogous reactions, and thermal and optical properties
Author(s): Schafer, O (Schafer, O); Mang, S (Mang, S); Arici, E (Arici, E); Lussem, G (Lussem, G); Unterlechner, C (Unterlechner, C); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 199  Issue: 5  Pages: 807-813  DOI: 10.1002/(SICI)1521-3935(19980501)199:5<807::AID-MACP807>3.0.CO;2-W  Published: MAY 1998  
Abstract: The preparation of a high molecular weight soluble derivative of poly(p-xylylene) by vapor phase pyrolysis followed by chemical vapor deposition (CVD) and its dehydrogenation with 1,2-dichloro-3,4-dicyanoquinone (DDQ) to yield the corresponding derivative of poly(phenylenevinylene) is reported. Derivatives of poly(phenylenevinylene)s with nonconjugated segments were prepared by partial dehydrogenation with substoichiometric amounts of DDQ. The thermal and optical properties of segmented and nonsegmented poly(p-phenylenevinylene)s are compared as well as their electroluminescence properties with particular focus on the quantum yields.
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58) Laser emission from a solid conjugated polymer: Gain, tunability, and coherence
Author(s): Wegmann, G (Wegmann, G); Giessen, H (Giessen, H); Greiner, A (Greiner, A); Mahrt, RF (Mahrt, RF)
Source: PHYSICAL REVIEW B  Volume: 57  Issue: 8  Pages: R4218-R4221  DOI: 10.1103/PhysRevB.57.R4218  Published: FEB 15 1998  
Abstract: Over the last few years, there has been a considerable effort to achieve lasing from solid-state conjugated polymers. Here, we present measurements on tunable laser emission from an optically pumped solid-slate pi-conjugated polymer blend system placed into an external cavity. We measured the threshold characteristics, the tunability range, and the coherence properties of the laser. By means of femtosecond pump-probe spectroscopy we recorded the gain spectra of the material and investigated their intensity dependence and temporal evolution. Our measurements allow us to shed light on the fundamental question of the gain mechanism in this class of materials. [S0163-1829(98)50308-6].
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57) Aromatic main chain liquid crystalline polymers.
Author(s): GREINER, A; SCHMIDT, H.W.
Source: Handbook of Liquid Crystals; Eds. D. Demus, J. Goodby, G.W. Gray, H. W. Spiess; Wiley-VCH, Weinheim  Volume: 3  Pages: 1-25  Published: 1998  
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56) Thermoreversible gelation of rigid and semirigid polymers.
Author(s): GREINER, A; ROCHEFORT, E.
Source: Polymer Liquid Crystals – Mechanical and Thermophysical Properties; Editor W. Brostow;  Chapman & Hall, London  Pages: 431-447  Published: 1998  
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55) Photonic and optoelectronic polymers (book critics)
Author(s): GREINER, A.
Source: Adv. Mater.  Volume: 10  Pages: 1055  Published: 1998  
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1997

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54) Preparation of palladium colloids in block copolymer micelles and their use for the catalysis of the Heck reaction
Author(s): Klingelhofer, S (Klingelhofer, S); Heitz, W (Heitz, W); Greiner, A (Greiner, A); Oestreich, S (Oestreich, S); Forster, S (Forster, S); Antonietti, M (Antonietti, M)
Source: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  Volume: 119  Issue: 42  Pages: 10116-10120  DOI: 10.1021/ja9714604  Published: OCT 22 1997  
Abstract: Colloidal dispersions of nanometer sized palladium colloids with very high stability were prepared in block copolymer micelles of polystyrene-b-poly-4-vinylpyridine and analyzed by electron microscopy and X-ray analysis. The resulting polymer/metal hybrids can easily be dissolved and handled in standard organic solvents such as toluene, tetrahydrofuran, and cyclohexane. They were successfully used for the Pd-catalyzed carbon(-) carbon coupling of aryl halides with alkenes (Heck reaction). Such block copolymer stabilized palladium colloids exhibit about the same reactivity as low molecular weight Pd complexes classically used for the Heck reaction, but show a much higher stability: in most reactions, the hybrids remain catalytically active even after 50000 turn-over cycles, Reaction rates were significantly controlled by the reactivity of the educts, but also respond to micelle architecture and dispersity of the palladium. Other advantages of the block copolymer stabilizer are that they are more simple and readily accessible than the phosphor-containing chelates, and that they dissolve even in ''simple'' solvents such as toluene (instead of amidic solvents).
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53) Polythienylenevinylene as promoter of hole injection from ITO into bilayer light emitting diodes
Author(s): Tak, YH (Tak, YH); Mang, S (Mang, S); Greiner, A (Greiner, A); Bassler, H (Bassler, H); Pfeiffer, S (Pfeiffer, S); Horhold, HH (Horhold, HH)
Source: ACTA POLYMERICA  Volume: 48  Issue: 10  Pages: 450-454  DOI: 10.1002/actp.1997.010481006  Published: OCT 1997  
Abstract: Due to the low oxidation potential of poly-(2,5-thienylenevinylene) (PTV) an ohmic contact for hole injection is established at an indium tin oxide (ITO)/PTV interface. It gives rise to space-charge-limited conduction in an ITO/PTV/Al diode. The ohmic nature of the ITO/PTV contact can be exploited to increase hole injection into multilayer organic light emitting diodes in which internal charge accumulation would otherwise lower majority carrier injection by virtue of electric field screening at the anode.
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52) Synthesis of hydrolytically degradable aromatic polyesters with lactide moieties
Author(s): Haderlein, G (Haderlein, G); Schmidt, C (Schmidt, C); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 8  Issue: 9  Pages: 568-573  Published: SEP 1997  
Abstract: A synthetic route to higher molecular weight processable polyesters with bisphenol A terephthalate/isophthalate moieties and lactide moieties which are of potential interest for tissue engineering is described. The combination of aliphatic and aromatic moieties is a promising concept for processable polyesters with potential sites for physiological degradation and improved mechanical properties. The molecular structure of the copolyesters prepared by melt condensation via an acid chloride route and incorporation of the lactide moieties by transesterification of an oligo DL-lactide was confirmed by infrared, H-1 and C-13 nuclear magnetic resonance spectroscopy as well as gel permeation chromatography. The thermal and mechanical properties of copoIyesters with different amounts of lactide moieties are reported and correlated with their composition. The reaction mechanism by transesterification was proved by a model reaction with a physical blend of the components and the hydrolytical behavior of the copolyesters under physiological conditions has been investigated. (C) 1997 by John Wiley & Sons, Ltd.
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51) Regioselectivity of the Pd-catalyzed synthesis of arylenevinylenes and its impact on polymer properties: Model reaction and polyreactions
Author(s): Klingelhofer, S (Klingelhofer, S); Schellenberg, C (Schellenberg, C); Pommerehne, J (Pommerehne, J); Bassler, H (Bassler, H); Greiner, A (Greiner, A); Heitz, W (Heitz, W)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 198  Issue: 5  Pages: 1511-1530  DOI: 10.1002/macp.1997.021980516  Published: MAY 1997  
Abstract: The regioselectivity of Pd-catalyzed coupling reactions of functionalized benzenes and olefins with respect to the ratio of 1.2-product/1.1-product was monitored by model reactions. The coupling of halobenzenes, benzene triflate, and aryldiazonium salts was studied under various reaction conditions. In order to simulate corresponding polyreactions, special focus was on the coupling of ortho-substituted functionalized benzenes with ethylene or styrene in order to evaluate the input of mono- and disubstituted aryl monomers and the choice of the olefin on the regioselectivity of polyreactions. The results of the model reactions were transferred to the polyreactions. The polymers were characterized by NMR, absorption and photoluminescence spectroscopy as well as electroluminescence.
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50) Multicoloured chromophore for white-light-emitting diodes
Author(s): Christ, T (Christ, T); Greiner, A (Greiner, A); Sander, R (Sander, R); Stumpflen, V (Stumpflen, V); Wendorff, JH (Wendorff, JH)
Source: ADVANCED MATERIALS  Volume: 9  Issue: 3  Pages: 219-&  DOI: 10.1002/adma.19970090305  Published: FEB 1997  
Abstract: Light-emitting diodes that emit white light require active materials that are able to emit throughout the entire visible spectrum. A simple approach is reported here, based on host-guest systems in which the guest is a single chromophore and the host a polymer blend. It is demonstrated that the emission of the chromophore may depend strongly on the choice of the matrix polymer. The absorption, photoluminescence, and electroluminescence spectra of the chromophore PSA in matrices of polynorbornene, Durel (a polyarylate), polyvinylpyridine, and blends are presented.
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49) Poly(p-xylylene)s: Synthesis, polymer analogous reactions, and perspectives on structure-property relationships
Author(s): Greiner, A (Greiner, A); Mang, S (Mang, S); Schafer, O (Schafer, O); Simon, P (Simon, P)
Source: ACTA POLYMERICA  Volume: 48  Issue: 1-2  Pages: 1-15  DOI: 10.1002/actp.1997.010480101  Published: JAN-FEB 1997  
Abstract: A critical overview of different synthetic approaches to poly(p-xylylene)s (PPXs) is coupled with perspectives on particular structure-property relationships and challenging applications. An attempt is made to emphasize the potential of different synthetic approaches to PPXs focused on different applications. Additionally, the synthesis and polymer analogous reactions of PPXs without leaving groups and functionalized PPXs (with leaving groups in the a-position) serving as processable precursors for non-processable polymers are evaluated.
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48) Columnar discotics for light emitting diodes
Author(s): Christ, T (Christ, T); Glusen, B (Glusen, B); Greiner, A (Greiner, A); Kettner, A (Kettner, A); Sander, R (Sander, R); Stumpflen, V (Stumpflen, V); Tsukruk, V (Tsukruk, V); Wendorff, JH (Wendorff, JH)
Source: ADVANCED MATERIALS  Volume: 9  Issue: 1  Pages: 48-&  Published: JAN 1997  
Abstract: The suitability of columnar discotics for applications in light emitting diodes (LEDs) has been investigated following the demonstration of their unusually large charge carrier mobilities. Results of X-ray diffraction, computer simulations, and electroluminescence measurements are presented and discussed for discotic systems such as that shown in the Figure. Their use in LEDs is expected to be advantageous.
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47) Polystyrenes modified by short arylenevinylene segments for light-emitting applications: Synthesis and structure-property relationships
Author(s): Hesemann, P (Hesemann, P); Greiner, A (Greiner, A)
Source: POLYMERS FOR ADVANCED TECHNOLOGIES  Volume: 8  Issue: 1  Pages: 23-29  Published: JAN 1997  
Abstract: The synthesis of 4-vinylstilbenes was accomplished by the Heck and Wittig reactions. Bromination of polystyrene was achieved by an iron-catalyzed electrophilic substitution reaction. Polymer-analogous coupling reactions of styrenes with respect to stilbenes with poly(bromostyrene)s was accomplished by Heck- reactions under optimized reaction conditions and is reported with respect to the molecular weight of the poly(bromostyrene)s. Thermal and optical properties are discussed with respect to light-emitting diode applications.
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46) Poly(1,4-xylylene)s: Polymer films by chemical vapour deposition
Author(s): Greiner, A (Greiner, A)
Source: TRENDS IN POLYMER SCIENCE  Volume: 5  Issue: 1  Pages: 12-16  Published: JAN 1997  
Abstract: Coating of sensitive or irregular substrates with solvent-free and pinhole-free thin films of poly(1,4-xylylene)s (PPXs) can be performed efficiently by chemical vapour deposition (CVD). The performance of the films of PPXs can be controlled by the reaction parameters. Many PPXs prepared by CVD exhibit excellent solvent resistance and have high melting points. Current applications are mostly in the field of anticorrosive or insulating coatings in microelectronics and for conservational coatings. PPXs with halogeno substituents in the alpha-position can be prepared by CVD and converted by annealing to visible-light-emitting poly(1,4-phenylene vinylene) which can be used for the fabrication of light-emitting diodes.
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1996

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45) Polarized electroluminescence of light emitting liquid crystalline polymers
Author(s): Lussem, G (Lussem, G); Geffarth, F (Geffarth, F); Greiner, A (Greiner, A); Heitz, W (Heitz, W); Hopmeier, M (Hopmeier, M); Oberski, M (Oberski, M); Unterlechner, C (Unterlechner, C); Wendorff, JH (Wendorff, JH)
Source: LIQUID CRYSTALS  Volume: 21  Issue: 6  Pages: 903-907  DOI: 10.1080/02678299608032908  Published: DEC 1996  
Abstract: Smectic liquid crystalline arylenevinylene main chain polymers were used in light emitting diodes (LEDs) to produce linearly polarized electroluminescence. The degree of orientational order induced by a rubbed polyimide layer amounted to S=0 . 64, as extracted from the electroluminescence spectra. The great advantages of these LC polymers are their good thermal stability, processability and broad mesophase range, and the possibility of applying established orientation techniques in order to achieve a macroscopic orientation.
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44) Synthesis, properties, and guest-host systems of triphenylamine-based oligo(arylenevinylene)s: Advanced materials for LED applications
Author(s): Sander, R (Sander, R); Stumpflen, V (Stumpflen, V); Wendorff, JH (Wendorff, JH); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 29  Issue: 24  Pages: 7705-7708  DOI: 10.1021/ma960743y  Published: NOV 18 1996  
Abstract: The synthesis of triphenylamine-based oligo(arylenevinylene)s was accomplished by Pd-catalyzed one-pot coupling of styrenes and tris(4-bromophenylamine). These oligo(arylenevinylene)s are characterized by temperature-induced crystallization in bulk but are amorphous in guest-host systems with polysulfone from which high-quality films for optical applications were obtained. The photoluminescence spectra of the oligo(arylenevinylene)s differed significantly in different solvents as well as in different polymer hosts which is of interest for multicolored LEDs.
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43) Synthesis and properties of a soluble, rigid poly(p-xylylene) with high molecular weight
Author(s): Schafer, O (Schafer, O); Greiner, A (Greiner, A); Antonietti, M (Antonietti, M); Zisenis, M (Zisenis, M)
Source: ACTA POLYMERICA  Volume: 47  Issue: 9  Pages: 386-390  Published: SEP 1996  
Abstract: The synthesis of a linear, soluble poly(p-xylylene) with high molecular weight, the phenethyl-substituted PPX (PEPPX), via a base-induced polyreaction is presented. The resulting polymers are characterized by GPC and static and dynamic light scattering. The light scattering data clearly demonstrate that PEPPX in THF is a very stiff, shape-persistent polymer with a persistence length of the order of at least 18 nm. This is rather unexpected since PPX contains two main chain cc-bonds in each monomer unit, which allow free rotation.
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42) Poly(p-phenylenevinylene) by chemical vapor deposition: Synthesis, structural evaluation, glass transition, electroluminescence, and photoluminescence
Author(s): Schafer, O (Schafer, O); Greiner, A (Greiner, A); Pommerehne, J (Pommerehne, J); Guss, W (Guss, W); Vestweber, H (Vestweber, H); Tak, HY (Tak, HY); Bassler, H (Bassler, H); Schmidt, C (Schmidt, C); Lussem, G (Lussem, G); Schartel, B (Schartel, B); Stumpflen, V (Stumpflen, V); Wendorff, JH (Wendorff, JH); Spiegel, S (Spiegel, S); Moller, C (Moller, C); Spiess, HW (Spiess, HW)
Source: SYNTHETIC METALS  Volume: 82  Issue: 1  Pages: 1-9  DOI: 10.1016/S0379-6779(97)80001-X  Published: AUG 30 1996  
Abstract: Poly (p-phenylenevinylene) (PPV) was prepared via chemical vapor deposition (CVD) by vapor phase pyrolysis of alpha,alpha'-dihalogenated p-xylenes or alpha,alpha-dihalogenated p-xylenes. Differences in the product composition obtained are discussed. The advantages for the film formation as well as the limitations are reported with respect to the fabrication of light-emitting diode (LED) cells. PPV films were characterized by various techniques. They show a glass transition temperature at 220 degrees C, a hypsochromic shift of the S-1 --> S-0 transition and higher degree of disorder as compared to ordinary PPV. The current-voltage characteristics of LED cells with PPV prepared via CVD show an unusually high rectification ratio. In contrast to PPV annealed at lower temperatures the formation of an unidentified defect structure was detected by C-13 CP-MAS/TOSS spectroscopy with PPV films annealed at higher temperatures.
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41) Soluble and amorphous, phenyl-substituted poly(1,4-xylylene) by chemical vapor deposition
Author(s): Schafer, O (Schafer, O); Greiner, A (Greiner, A)
Source: MACROMOLECULES  Volume: 29  Issue: 18  Pages: 6074-6075  DOI: 10.1021/ma960681b  Published: AUG 26 1996  
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40) Preparation and structure-property relationships of polymeric materials containing arylenevinylene segments - Perspectives for new light-emitting materials
Author(s): Greiner, A (Greiner, A); Bolle, B (Bolle, B); Hesemann, P (Hesemann, P); Oberski, JM (Oberski, JM); Sander, R (Sander, R)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 197  Issue: 1  Pages: 113-134  DOI: 10.1002/macp.1996.021970109  Published: JAN 1996  
Abstract: Well defined oligo(arylenevinylene)s were prepared by Pd-catalyzed coupling of dibromoarenes and styrenes. The mixing behavior of these oligo(arylenevinylene)s with polymers is significantly influenced by the structure of the oligo(arylenevinylene)s. Potential consequences for optical properties are discussed. Segmented polymers with arylenevinylene segments in the main chain are presented and discussed in detail. Light-emitting thermotropic polymers were obtained with modified distyrylbenzene segments in the main chain, These thermotropic light-emitting polymers show polarized photoluminescence on orientation on rubbed polyimide substrates. Light-emitting amorphous polymers with high fluorophore concentrations and high glass transition temperatures were obtained by polymers with arylenevinylene segments in the side chain.
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39) Photochemische und thermische Stabilität eines Phenylen-Vinylen-Polymeren.
Author(s): DAMERAU, T; SABELUS, S; WACHTENDORF, V.; HENNECKE, M.; GREINER, A
Source: GIT, Fachzeitschrift Labor und Technik  Volume: 40  Pages: 710-712  Published: 1996  
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38) Optical characterization of tris-(stilbene) amine and application in microcavities
Author(s): Hopmeier, M (Hopmeier, M); Siegner, U (Siegner, U); Lemmer, U (Lemmer, U); Hennig, R (Hennig, R); Guss, W (Guss, W); Pommerehne, J (Pommerehne, J); Sander, R (Sander, R); Greiner, A (Greiner, A); Mahrt, RF (Mahrt, RF); Bassler, H (Bassler, H); Feldmann, J (Feldmann, J); Gobel, EO (Gobel, EO)
Source: SYNTHETIC METALS  Volume: 76  Issue: 1-3  Pages: 117-119  DOI: 10.1016/0379-6779(95)03432-J  Published: JAN 1996  
Abstract: We report on the optical properties of tris-(stilbene)amine (TSA) and its application as a light-emitting layer in a microcavity. Time-resolved photoluminescence spectroscopy on a blend of TSA in polycarbonate (PC) demonstrates that the dynamics of the optical excitations significantly depend on the detection energy and temperature. This behaviour is characteristic for hopping relaxation within an inhomogeneously broadened density of states. We have realized a microcavity based on TSA where the emission shows spectral narrowing, intensity enhancement and a change of the radiative lifetime at the wavelength resonant to the cavity mode.
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37) Poly(p-xylylene)s (structure, properties, and applications).
Author(s): GREINER, A.
Source: The Polymeric Materials Encyclopedia; Ed. J. C. Salamone; CRC Press, Bocca Raton  Volume: 9  Pages: 7171-7180  Published: 1996  
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36) Pd-catalyzed synthesis (monomers and polymers).
Author(s): GREINER, A.; HEITZ, W.
Source: The Polymeric Materials Encyclopedia; Ed. J. C. Salamone; CRC Press, Bocca Raton  Volume: 7  Pages: 4865-4871  Published: 1996  
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1995

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35) SYNTHESIS AND STRUCTURE-PROPERTY RELATIONSHIPS OF PROCESSABLE LIQUID-CRYSTALLINE POLYMERS WITH ARYLENEVINYLENE SEGMENTS IN THE MAIN-CHAIN FOR LIGHT-EMITTING APPLICATIONS
Author(s): OBERSKI, J (OBERSKI, J); FESTAG, R (FESTAG, R); SCHMIDT, C (SCHMIDT, C); LUSSEM, G (LUSSEM, G); WENDORFF, JH (WENDORFF, JH); GREINER, A (GREINER, A); HOPMEIER, M (HOPMEIER, M); MOTAMEDI, F (MOTAMEDI, F)
Source: MACROMOLECULES  Volume: 28  Issue: 25  Pages: 8676-8682  DOI: 10.1021/ma00129a029  Published: DEC 4 1995  
Abstract: Polymers were synthesized with modified trans-bis(styryl)benzene segments in the main polycondensation of OH-functionalized oligo(arylenevinylenes) and aliphatic diacid chlorides. Most of the visible light emitting polymers were soluble at room temperature and fusible below the range of decomposition. The formation of a smectic A phase was observed in the melt state. Isotropization temperatures of polymers with phenyl-substituted arylenvinylene segments were detected below 200 degrees C. A remarkable thermal stability in the melt state with respect to cross-linking was observed for polymers containing CF3-substituted arylenevinylene segments. The polymers were investigated by spectroscopic methods, thermogravimetrical analysis, differential scanning calorimetry, polarizing microscopy, wide angle X-ray scattering, small angle X-ray scattering, dielectric relaxation spectroscopy, and by stress-strain experiments.
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34) POLARIZED PHOTOLUMINESCENCE OF LIQUID-CRYSTALLINE POLYMERS WITH ISOLATED ARYLENEVINYLENE SEGMENTS IN THE MAIN-CHAIN
Author(s): LUSSEM, G (LUSSEM, G); FESTAG, R (FESTAG, R); GREINER, A (GREINER, A); SCHMIDT, C (SCHMIDT, C); UNTERLECHNER, C (UNTERLECHNER, C); HEITZ, W (HEITZ, W); WENDORFF, JH (WENDORFF, JH); HOPMEIER, M (HOPMEIER, M); FELDMANN, J (FELDMANN, J)
Source: ADVANCED MATERIALS  Volume: 7  Issue: 11  Pages: 923-&  Published: NOV 1995  
Abstract: Anisotropic charge transport, or polarized photo- and electroluminescence are possible applications for materials combining the optical properties of arylenevinylene polymers with the characteristic orientational order of the liquid-crystalline state. Thermally stable, soluble materials with a broad mesophase, which can be oriented macroscopically using conventional processing techniques and which exhibit highly anisotropic luminescence behavior of use in polarized LEDs are presented.
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33) NEW SYNTHETIC APPROACH TO OH-FUNCTIONALIZED POLY(P-XYLYLENE)S BY COUPLING OF AROMATIC DIALDEHYDES AND DIKETONES IN THE PRESENCE OF SMI2
Author(s): WEGE, VU (WEGE, VU); GREINER, A (GREINER, A)
Source: ACTA POLYMERICA  Volume: 46  Issue: 5  Pages: 391-395  DOI: 10.1002/actp.1995.010460507  Published: OCT 1995  
Abstract: 1,2-dihydroxysubstituted poly(p-xylylene)s were synthesized in the presence of samarium(II)-iodide. The structure and endgroups of the polymers were verified by spectroscopy and chromatography. The structure-property relationships of the poly-1,2-diol structures obtained were investigated. Polymer analogous transformations were carried out for poly-(1,4-phenylene-1,2-ethanediol). The reaction parameters were investigated with respect to degrees of polymerization. Although some of the polymers were soluble, precipitation was found to be the reason for limited molecular weights.
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32) SAMARIUM(II) IODIDE - A DIASTEREOSELECTIVE REAGENT FOR THE SYNTHESIS OF AROMATIC 1,2-DIOL STRUCTURES - MODEL REACTIONS
Author(s): WEGE, VU (WEGE, VU); GREINER, A (GREINER, A)
Source: ACTA POLYMERICA  Volume: 46  Issue: 5  Pages: 396-403  DOI: 10.1002/actp.1995.010460508  Published: OCT 1995  
Abstract: Variation of the reaction conditions for the C-C coupling reaction of aromatic carbonyl compounds to their 1,2-diol structures in the presence of samaraium(II)-iodide led to different diastereoselectivities. The molar ratio of the starting materials, substituents, and solvent variation had a significant influence on 1,2-diol formation. An interpretation of the observed results is suggested. Sterical demands of the active complex and an intramolecular samarium-oxygen interaction could lead to the diastereomer ratio obtained.
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31) A BLUE-LIGHT-EMITTING POLYMER WITH PHENYLENEVINYLENE SEGMENTS IN THE SIDE-CHAINS
Author(s): HESEMANN, P (HESEMANN, P); VESTWEBER, H (VESTWEBER, H); POMMEREHNE, J (POMMEREHNE, J); MAHRT, RF (MAHRT, RF); GREINER, A (GREINER, A)
Source: ADVANCED MATERIALS  Volume: 7  Issue: 4  Pages: 388-390  DOI: 10.1002/adma.19950070409  Published: APR 1995  
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30) MICROCAVITY EFFECTS IN A SPIN-COATED POLYMER 2-LAYER SYSTEM
Author(s): LEMMER, U (LEMMER, U); HENNIG, R (HENNIG, R); GUSS, W (GUSS, W); OCHSE, A (OCHSE, A); POMMEREHNE, J (POMMEREHNE, J); SANDER, R (SANDER, R); GREINER, A (GREINER, A); MAHRT, RF (MAHRT, RF); BASSLER, H (BASSLER, H); FELDMANN, J (FELDMANN, J); GOBEL, EO (GOBEL, EO)
Source: APPLIED PHYSICS LETTERS  Volume: 66  Issue: 11  Pages: 1301-1303  DOI: 10.1063/1.113222  Published: MAR 13 1995  
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29) MAJORITY CARRIER INJECTION FROM ITO ANODES INTO ORGANIC LIGHT-EMITTING-DIODES BASED UPON POLYMER BLENDS
Author(s): VESTWEBER, H (VESTWEBER, H); POMMEREHNE, J (POMMEREHNE, J); SANDER, R (SANDER, R); MAHRT, RF (MAHRT, RF); GREINER, A (GREINER, A); HEITZ, W (HEITZ, W); BASSLER, H (BASSLER, H)
Source: SYNTHETIC METALS  Volume: 68  Issue: 3  Pages: 263-268  DOI: 10.1016/0379-6779(94)02301-E  Published: FEB 1995  
Abstract: The current-field characteristics of organic light-emitting diodes (LEDs), formed by sandwiching blends of hole-transporting molecules and various polymer binders between indium-tin oxide (ITO) and Al contacts, have been measured. It is concluded that the rate-limiting step is hole injection at the ITO anodes. At high fields, temperature-independent tunneling injection prevails, the efficiency of which scales with the mobility of the charge carriers in the transport layer. Increasing the polarity of the matrix enhances injection because of barrier lowering. The low field behaviour (E<10(6) V cm(-1)) is controlled by a superposition of thermionic injection and fluctuation induced tunneling, the latter being more pronounced with polar systems.
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1994

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28) ELECTROLUMINESCENCE FROM POLYMER BLENDS AND MOLECULARLY DOPED POLYMERS
Author(s): VESTWEBER, H (VESTWEBER, H); SANDER, R (SANDER, R); GREINER, A (GREINER, A); HEITZ, W (HEITZ, W); MAHRT, RF (MAHRT, RF); BASSLER, H (BASSLER, H)
Source: SYNTHETIC METALS  Volume: 64  Issue: 2-3  Pages: 141-145  DOI: 10.1016/0379-6779(94)90105-8  Published: JUN 1994  
Abstract: Electroluminescence fro light-emitting diodes (LEDs) based upon poly(phenylphenylenevinylene) (PPPV), PPPV blended with polystyrene (PS), and a molecular solution of tris(4-methoxystilbene)amine (MSA) in polycarbonate (PC) as active material sandwiched between indium-tin-oxide (ITO) and Al contacts is reported. In all cases the cell current is limited by field emission of holes from the ITO anode. With a single-layer LED based upon the PPPV-PS blend a quantum yield of 0.001 photons per transported electron is achieved. The temporal behavior of the electroluminescence from an ITO/MSA(PC)/Al cell after application of a rectangular driving voltage is analyzed and found to be governed by the transport of both holes and electrons.
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27) TIME-RESOLVED LUMINESCENCE SPECTROSCOPY OF CONJUGATED POLYMERS
Author(s): MAHRT, RF (MAHRT, RF); LEMMER, U (LEMMER, U); GREINER, A (GREINER, A); WADA, Y (WADA, Y); BASSLER, H (BASSLER, H); GOBEL, EO (GOBEL, EO); KERSTING, R (KERSTING, R); LEO, K (LEO, K); KURZ, H (KURZ, H)
Source: JOURNAL OF LUMINESCENCE  Volume: 60-1  Pages: 479-481  DOI: 10.1016/0022-2313(94)90196-1  Published: APR 1994  
Abstract: The dynamics of photoexcitations in conjugated polymers and polymer blends is studied by means of time resolved luminescence spectroscopy. After excitation into the vibronic progression, the luminescence rises quasi-instantaneously. The luminescence decay depends strongly on the detection energy and the polymer concentration. The results are explained within a hopping model.
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26) PHOTOREACTIVITY OF POLY(P-PHENYLPHENYLENEVINYLENE)
Author(s): DAMERAU, T (DAMERAU, T); HENNECKE, M (HENNECKE, M); GREINER, A (GREINER, A)
Source: POLYMER BULLETIN  Volume: 32  Issue: 2  Pages: 201-205  DOI: 10.1007/BF00306389  Published: FEB 1994  
Abstract: In films of Poly(para-phenylphenylenevinylene) a photoreaction has been observed. The significant feature is a decrease of the fluorescence emission intensity during irradiation. It is assumed that a cycloaddition between C=C- double-bonds leads to crosslinks in the material.
Under similar conditions of excitation a photoreaction has not been observed in poly(p-phenylenevinylene) prepared via the precursor-route.
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25) CONTROL OF THE EMISSION PROPERTIES OF CONJUGATED POLYMERS - TRAPPING AND MICROCAVITY EFFECTS
Author(s): OCHSE, A (OCHSE, A); LEMMER, U (LEMMER, U); DEUSSEN, M (DEUSSEN, M); FELDMANN, J (FELDMANN, J); GREINER, A (GREINER, A); MAHRT, RF (MAHRT, RF); BASSLER, H (BASSLER, H); GOBEL, EO (GOBEL, EO)
Source: MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS  Volume: 256  Pages: 335-342  DOI: 10.1080/10587259408039264  Published: 1994  
Abstract: We report on two different approaches to modify the emission spectra of poly(phenyl-phenylenevinylene). By doping with different amounts of a laser dye, the fluorescence spectra shift to lower energies due to picosecond transfer of the excitations from conjugated segments of the polymer to the acceptor molecules. As an alternative approach we show that Fabry-Perot microcavities can be used to control and enhance the spontaneous emission of a conjugated polymer layer.
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24) Synthesis and blending behavior of an oligoarylenevinylene. Design towards processable materials for LED appplications
Author(s): OBERSKI, J; BOLLE, B.; SCHAPER, A; GREINER, A
Source: Polym. Adv. Technol.  Volume: 5  Pages: 105-109  Published: 1994  
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23) Chemistry and industry of macromonomers (book critics)
Author(s): GREINER, A.
Source: Acta Polym.  Volume: 45  Pages: 397  Published: 1994  
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1993

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22) PICOSECOND HOPPING RELAXATION IN CONJUGATED POLYMERS
Author(s): LEMMER, U (LEMMER, U); MAHRT, RF (MAHRT, RF); WADA, Y (WADA, Y); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H); GOBEL, EO (GOBEL, EO)
Source: CHEMICAL PHYSICS LETTERS  Volume: 209  Issue: 3  Pages: 243-246  DOI: 10.1016/0009-2614(93)80101-T  Published: JUL 2 1993  
Abstract: The energy relaxation of optical excitations in poly(p-phenyl-phenylenevinylene) (PPPV) and PPPV blended in polycarbonate (PC) is investigated by means of picosecond time-resolved luminescence spectroscopy. In PPPV a pronounced dependence on the photon energy of the excitation laser is found. For excitation into the tail states of the inhomogeneously broadened density of states distribution, the spectral shape of the luminescence remains almost constant with time. However, a transient red-shift is observed for excitation at higher energies. Experiments on the diluted system PPPV/PC allow us to distinguish between intra-and inter-chain processes. The experimental results can be explained with a hopping model.
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21) POLYMERIC MATERIALS WITH ARYLENEVINYLENE SEGMENTS - SYNTHESIS AND ARCHITECTURE
Author(s): GREINER, A (GREINER, A)
Source: ADVANCED MATERIALS  Volume: 5  Issue: 6  Pages: 477-479  DOI: 10.1002/adma.19930050616  Published: JUN 1993  
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20) TIME-RESOLVED LUMINESCENCE STUDY OF RECOMBINATION PROCESSES IN ELECTROLUMINESCENT POLYMERS
Author(s): LEMMER, U (LEMMER, U); MAHRT, RF (MAHRT, RF); WADA, Y (WADA, Y); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H); GOBEL, EO (GOBEL, EO)
Source: APPLIED PHYSICS LETTERS  Volume: 62  Issue: 22  Pages: 2827-2829  DOI: 10.1063/1.109223  Published: MAY 31 1993  
Abstract: Picosecond luminescence studies on poly(p-phenylene vinylene) (PPV) and related compounds in the temperature range of 10-300 K are reported. We identify a fast nonradiative and considerably slower radiative recombination channel. The fastest decay is observed in PPV. In the phenyl substituted derivative poly(phenyl-p-phenylenevinylene) a significant contribution from a slow component (approximately 1.3 ns) is found. Dilution of the polymer in a blend leads to an increase of the contribution of the slow component. We attribute the fast decay to luminescence quenching due to energy dependent trapping of mobile excitations whereas the slow component reflects the radiative recombination.
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19) NOVEL STRUCTURAL DERIVATIVES OF POLY-P-PHENYLENEVINYLENE
Author(s): GREINER, A (GREINER, A); HESEMANN, P (HESEMANN, P); OBERSKI, J (OBERSKI, J)
Source: ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  Volume: 205  Pages: 362-POLY  Part: 2  Published: MAR 28 1993  
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18) TIME-RESOLVED STUDIES OF 2-PHOTON ABSORPTION PROCESSES IN POLY(P-PHENYLENEVINYLENE)S
Author(s): LEMMER, U (LEMMER, U); FISCHER, R (FISCHER, R); FELDMANN, J (FELDMANN, J); MAHRT, RF (MAHRT, RF); YANG, J (YANG, J); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H); GOBEL, EO (GOBEL, EO); HEESEL, H (HEESEL, H); KURZ, H (KURZ, H)
Source: CHEMICAL PHYSICS LETTERS  Volume: 203  Issue: 1  Pages: 28-32  DOI: 10.1016/0009-2614(93)89304-Z  Published: FEB 12 1993  
Abstract: Transient absorption spectroscopy and two-photon fluorescence techniques were used to study the nonresonant optical nonlinearities in poly(p-phenylenevinylene) (PPV) and its phenyl substituted derivative (PPPV). Strong two-photon absorption with a coefficient beta in the range of 5 cm/GW was found. The temporal behavior of the two-photon absorption process in PPV and PPPV, however, is significantly different, which is attributed to the different morphology of the polymer samples. The two-photon resonance lies energetically well above the first excited state in
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17) CONFORMATIONAL EFFECTS IN POLY(P-PHENYLENE VINYLENE)S REVEALED BY LOW-TEMPERATURE SITE-SELECTIVE FLUORESCENCE
Author(s): HEUN, S (HEUN, S); MAHRT, RF (MAHRT, RF); GREINER, A (GREINER, A); LEMMER, U (LEMMER, U); BASSLER, H (BASSLER, H); HALLIDAY, DA (HALLIDAY, DA); BRADLEY, DDC (BRADLEY, DDC); BURN, PL (BURN, PL); HOLMES, AB (HOLMES, AB)
Source: JOURNAL OF PHYSICS-CONDENSED MATTER  Volume: 5  Issue: 2  Pages: 247-260  DOI: 10.1088/0953-8984/5/2/012  Published: JAN 11 1993  
Abstract: Low-temperature site-selective fluorescence (SSF) Spectroscopy is employed to study morphological effects on the conformation of poly(p-phenylene vinylene) (PPV) and its phenyl-substituted, soluble derivative poly(phenylphenylenevinylene) (PPPV). Samples of PPV prepared as spin-coated thin films and stretch-aligned free-standing films, and samples of PPPV prepared as cast films and as blends with poly(methylmethacrylate) and polycarbonate have been studied. The results that we present are consistent with the notion that each polymer sample consists of an army of ordered chain segments whose average length reflects the perfection of the local structure. The statistical distribution of the segment lengths is responsible for inhomogeneous broadening of the optical spectra (absorption and emission). The dominant electronic excitation created by photoexcitation across the pi-pi* energy gap is a singlet exciton that can execute a random walk among the chain segments. SSF spectroscopy allows us to distinguish the contributions to the apparent fluorescence Stokes shift that arise from energy relaxation through excitation migration (spectral diffusion) and from structural relaxation of the polymer chain (self-localization). The structural contribution to the Stokes shift approaches zero in well aligned PPV and reaches values of up to 500 cm-1 in highly disordered PPPV films. The SSP method also provides a means of assessing the extent of phase separation that occurs in PPPV blends.
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16) Electroluminescence from phenylenevinylene-based polymer blends.
Author(s): VESTWEBER, H.; OBERSKI, J.; GREINER, A.; HEITZ, W.; MAHRT, R.F.; BAESSLER, H.
Source: ADV. MAT. OPT. ELECTR.  Volume: 2  Pages: 197-204  Published: 1993  
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15) Preparation and characterization of fibres from a thermotropic liquid crystal polyester with non-coplanar biphenylene units.
Author(s): MOTAMEDI, F.; JONAS, U.; GREINER, A.; SCHMIDT, H.W.
Source: Liquid Cryst.  Volume: 14  Pages: 959-970  Published: 1993  
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1992

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14) PROGRESS TOWARDS PROCESSIBLE MATERIALS FOR LIGHT-EMITTING DEVICES USING POLY(P-PHENYLPHENYLENEVINYLENE)
Author(s): VESTWEBER, H (VESTWEBER, H); GREINER, A (GREINER, A); LEMMER, U (LEMMER, U); MAHRT, RF (MAHRT, RF); RICHERT, R (RICHERT, R); HEITZ, W (HEITZ, W); BASSLER, H (BASSLER, H)
Source: ADVANCED MATERIALS  Volume: 4  Issue: 10  Pages: 661-662  DOI: 10.1002/adma.19920041008  Published: OCT 1992  
Abstract: Molecularly doped polymers are replacing inorganic photoreceptors in modern electrophotography. A future aim is to replace inorganic materials in light-emitting diodes, but this requires polymers that luminesce and are also processible in their polymeric form. A promising candidate is poly(p-phenylphenylenevinylene), shown in the figure.
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13) NEW SYNTHETIC APPROACH TO FILM FORMING POLY(P-XYLYLENE) BY GAS-PHASE PYROLYSIS OF ESTERS DERIVATED FROM ALPHA,ALPHA'-DIHYDROXY-P-XYLYLENE
Author(s): SIMON, P (SIMON, P); GREINER, A (GREINER, A)
Source: POLYMER JOURNAL  Volume: 24  Issue: 11  Pages: 1317-1320  DOI: 10.1295/polymj.24.1317  Published: 1992  
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12) Formation of thermoreversible gels from liquid-crystalline polyesters.
Author(s): GREINER, A.; ROCHEFORT, E.; GREINER, K.; SCHMIDT, H.W.; PEARSON, D. S.
Source: Makromol. Chem., Rapid Commun.  Volume: 13  Pages: 25-30  Published: 1992  
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1991

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11) NOVEL PALLADIUM-CATALYZED BIARYL SYNTHESIS WITH HALOARENES
Author(s): BRENDA, M (BRENDA, M); KNEBELKAMP, A (KNEBELKAMP, A); GREINER, A (GREINER, A); HEITZ, W (HEITZ, W)
Source: SYNLETT  Issue: 11  Pages: 809-810  Published: NOV 1991  
Abstract: Novel palladium-catalyzed couplings of bromo- and iodoarenes to give biaryls were accomplished in the presence of equimolar amounts of trialkylamine. Bromoarenes require triphenylarsine as cocatalyst. The trialkylamine was found to cause dehalogenation of haloarenes as a side reaction.
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10) ABSORPTION-SPECTRA OF THE ANIONS OF PHENYLENEVINYLENE OLIGOMERS AND POLYMER
Author(s): OBERSKI, JM (OBERSKI, JM); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H)
Source: CHEMICAL PHYSICS LETTERS  Volume: 184  Issue: 5-6  Pages: 391-397  DOI: 10.1016/0009-2614(91)80007-K  Published: OCT 4 1991  
Abstract: The absorption spectra of chemically prepared mono- and di-valent anions of phenylenevinylene oligomers and polymer are reported. The spectra consist of three features, each subject to vibronic splitting. Retaining their general character, the spectra shift towards lower energies with increasing chain length akin to the shift of the neutral molecule absorption bands. The spectrum of the monovalent polymer anion resembles the photoinduced absorption spectrum of polyphenylenevinylene suggesting that the latter is due to a monovalent rather than a divalent species. It is argued that no transitions among localized (polaron) and delocalized (band) states need to be invoked to interpret oligomer as well as polymer anion spectra.
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9) PALLADIUM CATALYZED SYNTHESIS OF POLY(1,4-PHENYLENEVINYLENE)
Author(s): GREINER, A (GREINER, A); MARTELOCK, H (MARTELOCK, H); HEITZ, W (HEITZ, W)
Source: SYNTHETIC METALS  Volume: 41  Issue: 3  Pages: 881-884  DOI: 10.1016/0379-6779(91)91517-E  Published: MAY 6 1991  
Abstract: A wide variety of derivatives of poly(1,4-phenylenevinylene) can be synthesized by the Pd catalyzed arylation of ethylene with dihalogenoarenes. Model reactions of bromobenzene and ethylene to trans-stilbene indicated complete conversion of bromobenzene, few side products, and almost exclusively trans-stilbene.
Many of the synthesized derivatives of PPV are soluble and fusible. The fusible derivatives are thermotropic. Although, thermogravimetry indicates good thermal stability of most of the fusible derivatives of poly(1,4-phenylenevinylene) irreversible changes were observed in the molten state combined with a loss of anisotropy, solidification, and insolubility.
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8) DC AND TRANSIENT PHOTOCONDUCTIVITY OF POLY(2-PHENYL-1,4-PHENYLENE-VINYLENE) (PPPV)
Author(s): GAILBERGER, M (GAILBERGER, M); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H)
Source: SYNTHETIC METALS  Volume: 41  Issue: 3  Pages: 1269-1272  DOI: 10.1016/0379-6779(91)91603-8  Published: MAY 6 1991  
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7) STRUCTURAL MODIFICATIONS OF POLY(1,4-PHENYLENEVINYLENE) TO SOLUBLE, FUSIBLE, LIQUID-CRYSTALLINE PRODUCTS
Author(s): MARTELOCK, H (MARTELOCK, H); GREINER, A (GREINER, A); HEITZ, W (HEITZ, W)
Source: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 192  Issue: 4  Pages: 967-979  Published: APR 1991  
Abstract: The synthesis, solubility, and thermal behavior of soluble, fusible, liquid-crystalline derivatives of poly(1,4-phenylenevinylene) (1) is described. The improved solubility and fusibility were accomplished by reducing interchain interactions without change of the rigid rod-like character. The interchain interactions were lowered by decreasing the structural regularity of the repeating units. The synthesis of derivatives of 1 was accomplished by the palladium-catalyzed coupling of dihalogenoarenes and ethylene to avoid cis-vinylene units. Irreversible crosslinking was observed from fusible products on annealing above the softening point.
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1990

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6) SYNTHESIS OF ARYLSUBSTITUTED MONOMERS FOR HIGH-PERFORMANCE POLYMERS
Author(s): LAND, HT (LAND, HT); HATKE, W (HATKE, W); GREINER, A (GREINER, A); SCHMIDT, HW (SCHMIDT, HW); HEITZ, W (HEITZ, W)
Source: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 191  Issue: 9  Pages: 2005-2016  Published: SEP 1990  
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5) SITE-SELECTIVE FLUORESCENCE SPECTROSCOPY OF POLY(P-PHENYLENEVINYLENE)S AND OLIGOMERIC MODEL COMPOUNDS
Author(s): MAHRT, R (MAHRT, R); YANG, JP (YANG, JP); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H); BRADLEY, DDC (BRADLEY, DDC)
Source: MAKROMOLEKULARE CHEMIE-RAPID COMMUNICATIONS  Volume: 11  Issue: 9  Pages: 415-421  Published: SEP 1990  
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4) MODEL REACTIONS FOR THE SYNTHESIS OF POLY(1,4-PHENYLENEVINYLENE) - THE PALLADIUM-CATALYZED ARYLATION OF ETHYLENE WITH HALOGENATED ARENES OR BENZOYL CHLORIDES
Author(s): BRENDA, M (BRENDA, M); GREINER, A (GREINER, A); HEITZ, W (HEITZ, W)
Source: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 191  Issue: 5  Pages: 1083-1100  Published: MAY 1990  
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1989

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3) Site-selective Spectroscopy of Matrix-isolated Conjugated Polymers
Author(s): RAUSCHER, U (RAUSCHER, U); SCHUTZ, L (SCHUTZ, L); GREINER, A (GREINER, A); BASSLER, H (BASSLER, H)
Source: JOURNAL OF PHYSICS-CONDENSED MATTER  Volume: 1  Issue: 48  Pages: 9751-9763  DOI: 10.1088/0953-8984/1/48/022  Published: DEC 4 1989  
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1988

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2) New Synthetic Approach to Poly(1,4-Phenylenevinylene) and its Derivatives by Palladium Catalyzed Arylation of Ethylene
Author(s): GREINER, A (GREINER, A); HEITZ, W (HEITZ, W)
Source: MAKROMOLEKULARE CHEMIE-RAPID COMMUNICATIONS  Volume: 9  Issue: 8  Pages: 581-588  Published: AUG 1988  
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1) Synthesis of Monomers and Polymers by the Heck Reaction
Author(s): HEITZ, W (HEITZ, W); BRUGGING, W (BRUGGING, W); FREUND, L (FREUND, L); GAILBERGER, M (GAILBERGER, M); GREINER, A (GREINER, A); JUNG, H (JUNG, H); KAMPSCHULTE, U (KAMPSCHULTE, U); NIESSNER, N (NIESSNER, N); OSAN, F (OSAN, F); SCHMIDT, HW (SCHMIDT, HW); WICKER, M (WICKER, M)
Source: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR CHEMISTRY AND PHYSICS  Volume: 189  Issue: 1  Pages: 119-127  Published: JAN 1988  
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Universität Bayreuth -