Chemical Recycling of Poly(cyclohexene carbonate)s via Synergistic Catalysis.

Chemical recycling of polymers to the corresponding monomers offers a valuable solution to address the current plastics crisis for creating an ideal and circular polymer economy. Here, we present a bimetallic synergistic depolymerization of the widely studied CO-based polycarbonates, poly(cyclohexene carbonate)s, to epoxide monomers efficiently. The bimetallic Cr-complex-mediated highly selective depolymerization and repolymerization was achieved via the regulation of reaction temperature, thus closing the circular loop of poly(cyclohexene carbonate)s . Mechanistic investigation has revealed that the formation of epoxides undergoes a direct chain-end unzipping process. A bimetallic catalysis involving a nucleophilic attack of the metal-alkoxide species toward the methine carbon atom bound with an adjacent carbonyl that is activated by the other metal center features a lower energy barrier in DFT calculations, which promotes the epoxide extrusion.