Synthesis of biodegradable PGA-PBC-PGA triblock copolymers and closed-loop recycling via a thermal depolymerization strategy

The emergence of biodegradable polymers has brought hope for solving the problem of plastic pollution. Chemical recovery of biodegradable polymers not only avoids CO2 emissions from polyester degradation, but also enables sustainable utilization of feedstocks. In this study, biodegradable PGA-PBC-PGA triblock copolymers with chemical recovery characteristics were synthesized using ring-opening polymerization (ROP) of glycolide (GL). The Tonset of the triblock copolymers was higher than 315 °C. Mechanical tests showed that the tensile strengths of the copolymers were in the range of 27.5–98.2 MPa, and the elongations at break were in the range of 9.2–409%. The gas permeation test showed that the triblock copolymers had excellent O2 and CO2 barrier performance, which was better than PBS, PBAT and PLA. Besides, the triblock copolymers have excellent degradation properties under both enzymatic and non-enzymatic conditions. What's more, the triblock copolymers were allowed to recover GL by thermal depolymerization. Among them, PGA-PBC-PGA60 could recover GL in 82% yield at 240 °C in 3 hours. The recovered GL could be reused for the next polymerization after recrystallization and purification. The performances of the copolymers after re-polymerization were comparable to that of the original copolymer, successfully completing the closed-loop process from a monomer to a polymer and then to a monomer.