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) (P γ BL- b -PPDO) diblock copolymers with well-defined and controlled structures. The composition-dependent properties of P γ BL- b -PPDO copolymers, including thermal properties and crystallization behavior, are investigated. The results show that the thermal stability and crystalline ability of P γ BL are enhanced observably by introducing the PPDO block. Significantly, the P γ BL- 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.