Controlled synthesis and closed-loop chemical recycling of biodegradable copolymers with composition-dependent properties

The closed-loop recycling concept of the polymer wastes into building-block chemicals is attractive, but the closed-loop recycling of copolymers enabled by energy-efficient chemical recycling and cost-effective separations is still facing great challenges. Herein, for the first time, a one-pot sequential copolymerization of γ-butyrolactone(γ-BL) and p-dioxanone(PDO)using an economical ureas/alkoxides catalytic system is conducted to synthesize biodegradable and chemically recyclable poly-(γ-butyrolactone)-block-poly(p-dioxanone)(PγBL-b-PPDO) diblock copolymers with well-defined and controlled structures.The composition-dependent properties of PγBL-b-PPDO copolymers, including thermal properties and crystallization behavior,are investigated. The results show that the thermal stability and crystalline ability of PγBL are enhanced observably by introducing the PPDO block. Significantly, the PγBL-b-PPDO copolymers can be depolymerized efficiently into the corresponding co-monomers with a yield of over 95% by simply low-temperature pyrolysis under vacuum. Moreover, γ-BL and PDO monomers are selectively separated with an isolated purity of about 99% based on the difference in their physicochemical properties. Subsequently, their repolymerization is realized to obtain the copolymers with nearly identical structures and thermostability, demonstrating the closed-loop recycling of copolymers, i.e., polymerization-depolymerization-repolymerization. This research provides important guidance for the design of novel sustainable polymers towards more efficient chemical recycling, separation and regeneration.