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Lars Schwarzer, Emilia Fulajtar, Seema Agarwal

Advanced Functional Materials, 2025, https://doi.org/10.1002/adfm.202527257

Recycling of thermosets remains a challenge, as their permanent networks prevent reprocessing and lead to persistent waste and microplastic pollution. As a potential solution, covalent adaptable networks (CANs) offer reprocessability through dynamic bond-exchange reactions but typically rely on toxic additives (organometallic catalysts) raising concerns about leaching and environmental persistence. To advance beyond recyclability alone, CANs can be designed with biodegradable polymer backbones, creating materials that not only allow reprocessing but also undergo degradation, thereby reducing environmental risks and microplastic pollution from accidental release. Here, a catalyst-free, biodegradable CAN based on star-shaped poly(lactide-co-glycolide) (PLG) cross-linked with pyromellitic dianhydride is reported, which introduces internal carboxylic acid groups to drive transesterification. The resulting networks exhibit high gel content (≈95%), mechanical performance comparable to poly(L-lactide) (Young's modulus ≈1.6 GPa), and complete retention of stiffness after thermal recycling. Stress-relaxation analysis confirms Arrhenius-like dynamics with an activation energy of 119 kJ mol^-1, consistent with reversible anhydride exchange. The PLG CAN also demonstrates rapid biodegradation (>60% within 25 days in compost) and functional properties including robust shape-memory and applicability as reusable adhesive (60 mg film supporting 6.3 kg load). This work establishes biodegradable, catalyst-free CANs as a sustainable materials platform, uniting mechanical robustness, reprocessability, and environmentally benign degradation.