tert‐Butyl Esters as Potential Reversible Chain Transfer Agents for Concurrent Cationic Vinyl‐Addition and Ring‐Opening Copolymerization of Vinyl Ethers and Oxiranes

Abstract tert ‐Butyl esters are demonstrated to function as chain transfer agents (CTAs) in the cationic copolymerization of vinyl ether (VE) and oxirane via concurrent vinyl‐addition and ring‐opening mechanisms. In the copolymerization of isopropyl VE and isobutylene oxide (IBO), the IBO‐derived propagating species reacts with tert ‐butyl acetate to generate a copolymer chain with an acetoxy group at the ω‐end. This reaction liberates a tert ‐butyl cation; hence, a polymer chain with a tert ‐butyl group at the α‐end is subsequently generated. Other tert ‐butyl esters also function as CTAs, and the substituent attached to the carbonyl group affects the chain transfer efficiency. In addition, ethyl acetate does not function as a CTA, which suggests the importance of the liberation of a tert ‐butyl cation for the chain transfer process. Chain transfer reactions by tert ‐butyl esters potentially occur reversibly through the reaction of the propagating cation with the ester group at the ω‐end of another chain.