Smart Access to Sequentially and Architecturally Controlled Block Polymers via a Simple Catalytic Polymerization System

Self-switchable polymerization is an attractive strategy for precisely controlling the microstructures and monomer sequences of polymers. To date, catalysts for the polymerization are generally limited to metal complex catalysts and some organocatalysts. In this article, we report that simple, inexpensive, and environmentally benign alkali metal carboxylate catalysts smartly switch between the ring-opening alternating copolymerization of epoxides with cyclic anhydrides and the ring-opening polymerization of cyclic esters to create a single synthetic step and thus achieve sequence-controlled multiblock polyesters. This polymerization system shows extremely high effectiveness and versatility for different combinations of epoxides, cyclic anhydrides, cyclic esters, and initiators. As a result, various types of complex block copolymers, such as AB diblocks, BAB triblocks, star copolymers, hyperbranched copolymers, and CAB triblocks, can be simply prepared and postpolymerization modification can be performed. As a proof of concept, polyester-based elastomers and adhesives were successfully synthesized via one-step procedures by reasonably designing the monomer structures of triblock copolymers, showing great potential for industrial applications of polyesters.