Elucidation of the Alternating Copolymerization Mechanism of Epoxides or Aziridines with Cyclic Anhydrides in the Presence of Halide Salts

Abstract Organic halide salts in combination with metal or organic compound are the most common and essential catalysts ring‐opening copolymerizations (ROCOP). However, role of was neglected. Here, we have uncovered complex behavior halides ROCOP epoxides aziridine cyclic anhydride. Coordination chain‐ends to cations, electron‐withdrawing effect, leaving ability atoms, chain‐end basicity/nucleophilicity, terminal steric hindrance cause three types side reactions: single‐site transesterification, substitution, elimination. Understanding functions led us develop highly active selective aminocyclopropenium chlorides as catalysts/initiators. Adjustable H‐bonding interactions propagating anions create coordination process that generate reactive carboxylate alkoxide chain‐ends.