A sustainable approach for the synthesis of recyclable cyclic CO-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO and epoxides have attracted much attention since they can enable CO-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO-based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe), 1) to rapidly copolymerize -CHO and CO into poly(cyclohexene carbonate) (PCHC) with an unprecedentedly cyclic structure. Moreover, in the presence of trace amounts of water, a heterogeneous multi-nuclear zinc catalyst ((BDI-(ZnMe·HO)) , 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to -CHO and CO. This strategy not only achieves the first case of cyclic CO-based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO-based polycarbonates.