Tunable Copolymerization of Oxetane and Anhydrides via a Nonsymmetric Three‐Center Four‐Electron Iodine Activation Mode

Abstract

Abstract The copolymerization of low‐strain cyclic ethers, such as oxetane and anhydrides, still presents opportunities for improving compositional control in polymer synthesis. In this study, we report a halogen‐bond catalysis platform based on a nonsymmetric three‐center four‐electron ([O···I···O] + ) iodine activation mode that enables highly selective and tunable copolymerization of oxetane and anhydride. This active catalytic structure mediates oxetane insertion through a dynamic equilibrium between nonsymmetric and symmetric iodine‐carboxylate complexes ([O_ oxetane ···I···O_ carboxylate ] + versus [O_ carboxylate ···I···O_ carboxylate ] + ), thereby regulating ester and ether linkage ratio. Mechanistic study reveals that nonsymmetric iodine activation enforces near‐perfect alternating copolymer (>99 mol% selectivity in ester linkage) between oxetane and cyclic anhydrides. Notably, the catalytic system exhibits broad monomer scope, enabling the copolymerization of oxetane with a variety of cyclic anhydrides to yield structurally diverse polyesters. Furthermore, by tuning the carboxylate/I 2 ratio, systematic control over the ester‐to‐ether content in the resulting polyesters can be achieved. This work establishes halogen‐mediated nonsymmetric activation as a versatile and programmable platform for constructing composition‐defined polyesters from low‐strain cyclic ethers.