Citric-Acid-Derived Cross-Linked Poly(ester–urethane) Elastomers with Intrinsic UV Blocking, Extreme Stretchability, and Rapid Controlled Degradability for Sustainable Flexible Electronics

Sustainable elastomeric substrates that simultaneously offer high stretchability, optical transparency, and intrinsic protection against ultraviolet (UV) radiation are critically needed for next-generation flexible and wearable electronics. Here, we report a family of citric-acid-derived ester–urethane elastomers synthesized via solvent- and catalyst-free melt polycondensation followed by urethane cross-linking. By controlling the prepolymer synthesis time, the network architecture and cross-link density in ester–urethane elastomers were systematically tuned, enabling stretchabilities from ∼250% to ∼825% while maintaining visible-light transparency of ∼75–80%. Notably, the elastomers exhibit strong intrinsic UV absorption without the use of additional fillers or UV-blocking additives. Degradation studies revealed that the elastomers undergo rapid or complete degradation under alkaline conditions (pH ≥ 13) within 24 h, while remaining stable in neutral and acidic environments. As a proof of device relevance, transparent and UV-blocking flexible electrodes were fabricated by spray-coating silver nanowires onto the optimized substrate, achieving a sheet resistance of ∼25 Ω sq–1 at ∼70% optical transmittance, and were further demonstrated as low-voltage transparent heaters with stable operation up to ∼90 °C. This work introduces a multifunctional, sustainable elastomer platform that integrates intrinsic UV shielding, extreme stretchability, optical transparency, and controlled end-of-life degradability, offering a viable alternative to conventional fossil-based substrates for sustainable flexible electronic systems.