Solid-State Chemical Recycling of Anhydride-Based Polymers: From Linear Copolyesters to Cross-Linked Epoxy Networks

Abstract

Chemical recycling of polymers to the parent monomers (CRM) represents a cornerstone strategy for establishing a sustainable circular plastic economy. Polyesters prepared by ring-opening copolymerization of epoxides with cyclic anhydrides feature highly tunable properties and represent promising alternatives to petroleum-derived polymers. Nevertheless, direct and selective chemical recycling of such copolyesters into pristine monomers continues to pose a substantial challenge. Herein, we report a versatile and highly efficient strategy for the solid-state depolymerization of both linear copolyesters and cross-linked epoxy networks derived from diphenylmaleic anhydride (DPMA) and epoxides. The depolymerization process is catalyzed by ZnCl2 via a random chain-scission mechanism, delivering exceptional DPMA selectivity (>99%) and high recovery yield (≥85%). Combined mechanistic investigations and density functional theory (DFT) calculations elucidate a stepwise depolymerization route involving spirolactone intermediates as critical species. Notably, DPMA-based epoxy resins exhibit attractive thermomechanical performance, with glass transition temperatures spanning 101–136 °C and a tensile strength at break of ∼74.7 MPa, while retaining efficient closed-loop chemical recyclability. This work thus establishes a reliable platform for the rational design of high-performance polymer materials that integrate robust mechanical properties with fully reversible chemical recycling.