Sustainable and Eco-Compatible Copolyesters with Applicable Properties: Controlled One-Pot Synthesis and Chemically Closed-Loop Recycling

The vast usage of conventionally nondegradable petrochemical-based plastics and their improper disposal have posed depletion of energy, shortage of resources, and some environmental concerns, which impels to develop new eco-compatible and sustainable alternatives with considerable performances and economic benefits. Herein, we report a class of novel degradable and chemically recyclable copolyesters with desired and controlled properties. These copolyesters with a near-random sequence structure are rationally designed and controllably synthesized by one-pot bulk ring-opening polymerization (ROP) of p-dioxanone and δ-hexanolactone (HL) using a commercial organic catalyst. The effect of the random sequence on the properties of copolyesters is investigated systematically. It is found that the introduction of a small amount of HL monomer to make a slight degree of random in copolyesters can effectively balance their comprehensive performance. Significantly, a good trade-off of tensile strength and elongation-at-break of the copolyesters, being comparable to general plastics and those of most widely used degradable plastics, is realized. In addition, the copolyesters posess excellent thermal stability (a decomposing temperature of approximately 300 °C) and delayed hydrolytic degradability that meets the demands of melt-processing and practical applications. Moreover, not only is direct thermal depolymerization of the copolyesters to comonomers achieved with a yield of exceed 95% and purity of up to 99.7% but also the repolymerization of recycled comonomers to prepare the regenerative copolyesters with nearly identical structures and properties to the initial copolyesters is successfully implemented, solidly demonstrating the chemically closed-loop recycling of this copolyester for the first time.