A sustainable approach for the synthesis of recyclable cyclic CO 2 -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 2 and epoxides have attracted much attention since they can enable CO 2 -fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO 2 -based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe) 2 , 1) to rapidly copolymerize meso -CHO and CO 2 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 2 · x H 2 O)) n , 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to meso -CHO and CO 2 . This strategy not only achieves the first case of cyclic CO 2 -based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO 2 -based polycarbonates.