Polyether/Polythioether Synthesis via Ring-Opening Polymerization of Epoxides and Episulfides Catalyzed by Alkali Metal Carboxylates

Abstract

Alkali metal carboxylates were evaluated as simple and green catalysts for the ring-opening polymerization (ROP) of various epoxides (e.g., alkyl-substituted epoxides and glycidyl ethers) and episulfides (alkyl-substituted episulfides and thioglycidyl ethers). The thus-produced functional polyethers (end-functionalized polyethers, block copolyethers, polyether–polyester block copolymers, topologically unique polyethers, and isotactic-enriched polyethers) and polythioethers featured well-defined structures and controlled molecular weights (Mn,SEC = 1.0–32 kg mol–1). The most effective catalyst was identified as cesium pivalate, and the variation of carboxylate moieties and alkali metal cations enabled the tuning of acid/base characteristics and thus allowed one to control polymerization behavior and expand the scope of functional monomers and initiators. Kinetic analysis confirmed the controlled/living nature of the polymerization process, while mechanistic studies revealed that carboxylate moieties did not directly initiate the ring-opening of epoxide monomers via nucleophilic attack but rather activated the alcohol initiators/chain ends via H-bonding and thus rendered the corresponding OH groups sufficiently nucleophilic to attack the alkali metal cation-activated epoxides.