A new paradigm for valorization of waste poly(glycolic acid): facile coupling with epoxides and synthesis of copolyesters with enhanced performance.

Poly(glycolic acid) (PGA) is one of the most widely used biodegradable polyesters, but its efficient valorization presents a long-standing challenge. Herein, we report the first facile PGA valorization strategy by utilizing epoxides to upcycle PGA into fused lactones under mild conditions (<100 °C), and subsequent copolymerization to produce copolyesters with wide potential tunability and enhanced performance. In the presence of epoxides and a chromium-based catalyst, PGA was efficiently transformed into fused lactones with a wide range of potential structural adjustability. Subsequently, copolymerization of the obtained lactones and ε-caprolactone (ε-CL), random copolyesters with tunable compositions and high molecular weights (MWs) were obtained. Notably, the copolyesters show a broad range of thermal and mechanical properties, which also overcomes the trade-off in tensile strength and ductility commonly observed for poly(ε-caprolactone) (PCL) or binary copolymers based on ε-CL/other lactones. For example, high MW copolyesters with optimal compositions (P(6-MDO)--PCL and P(6-MDO)--PCL) show both superior tensile strength (45.4-46.2 MPa) and ductility (1938-2186%). Apart from excellent mechanical properties and thermal stability, all copolyesters possess good chemical recyclability (>87%), establishing a closed-loop life cycle for a sustainable circular economy. This study offers the first efficient, cost-effective and versatile upcycling route for PGA.