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

Abstract

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 T_onset 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.