Closed-loop polymer upcycling by installing property-enhancing comonomer sequences and recyclability

The concept of upcycling postconsumer plastics into higher-value products is attractive, but the challenges remain to develop a cost-effective upcycling scheme, discover property-enhancing structures, and, most importantly, install recyclability into upcycled plastics to enable a circular lifecycle. Reported herein is a convenient and effective strategy to upcycle polyester, exemplified by poly(glycolic acid) (PGA), via transesterification (TEster) in bioderived, commercially available γ-butyrolactone (BL) that serves as both the solvent and comonomer, which generates sequence-defined copolymer poly(GA-co-BL). Owing to the isolated glycolic sequence present in the copolymer created uniquely by TEster, it exhibits much-enhanced thermal stability (≥44 °C) over both homopolymers or copolymers without such sequences. This upconverted copolymer is chemically recyclable, enabling a complete recovery of pure glycolic acid and BL feedstocks.