Partners in Epoxide Copolymerization Catalysis: Approach to High Activity and Selectivity

The ring-opening alternating copolymerization processes of epoxides with small-molecule monomers, such as carbon dioxide (CO2), carbonyl sulfide (COS) and cyclic anhydrides, are powerful strategies for preparing polymeric materials with degradable carbonate/ester/thiocarbonate main-chain backbone units. The catalysts selected for copolymerization processes play crucial roles in determining their reaction rates and productivities, as well as the selectivity, regio- and stereochemistry, compositions, and the molecular weights of their resultant copolymers. These processes often generate undesirable byproducts such as polyether or ether linkages dispersed randomly within the copolymer’s chain, and/or more thermodynamically stable cyclic products. In this account, we outline our efforts of over a dozen years on developing highly active well-defined metal catalysts based on inter- and intra-molecular synergistic strategies to selectively produce completely alternating copolymers from epoxides and various small-molecule monomers. Much attention was paid to the enantioselective resolution copolymerization processes of racemic epoxides via regioselective ring-openings, and the asymmetric copolymerization processes of meso-epoxides with CO2, COS, or cyclic anhydrides via dissymmetrical ring-openings using multichiral catalytic systems, and affording isotactic copolymers with main-chain chirality. In addition, this account provides a thorough mechanistic understanding of the high reactivities, excellent selectivity, and unprecedented stereochemical controls of these copolymerization systems, mediated by inter-and intramolecular synergistic catalysis.