Fumarate-based copolyesters with long-term stability and temperature-gated enzymatic degradation.

Designing polyesters that combine long-term storage stability with controlled enzymatic deconstruction remains a formidable challenge in sustainable polymer development. Herein, we report a fumarate-based copolyester platform, poly(butylene terephthalate-co-fumarate) (PBTFu), that achieves this balance through stereoelectronic and conformational control. PBTFu exhibits exceptional mechanical robustness (>33.5 MPa strength and 760% elongation) and superior gas and water-vapor barrier properties, while retaining macroscopic integrity and substantial mechanical performance after 20 months of ambient storage. Crucially, PBTFu displays a sharp "on/off" degradability switch: it remains inert to hydrolysis and Candida antarctica lipase B at 37 °C but undergoes rapid depolymerization by Humicola insolens cutinase (HiC) at 55 °C. Combined experimental and computational investigations elucidate the molecular basis: the conjugated fumarate moiety lowers carbonyl electrophilicity to confer intrinsic hydrolytic resistance, while HiC's open catalytic cleft and a temperature-driven conformational match enable efficient nucleophilic attack. This work establishes PBTFu as a promising platform that leverages stereoelectronic stabilization and conformational dynamics to achieve durable yet HiC-depolymerizable packaging materials, offering a viable strategy for balancing storage stability with controlled enzymatic deconstruction.