Trimethylsilyl triflate as an initiator for cationic polymerization: Improved initiation through the use of promoters

Abstract

AbstractTrimethylsilyl triflate (TMSOTf) can be used as an initiator for the cationic polymerization of alkenes and heterocycles. However, TMSOTf without additives and promoters acts inefficiently. Initiation in the cationic polymerization of tetrahydrofuran is slow because of unfavorable charge distribution in the trimethylsilyltetrahydrofuranium cation—a product of the reaction of monomer with TMSOTf. Acetone, 1,3‐dioxolane, and 1,2‐propylene oxide have been used as promoters to react with TMSOTf to create more reactive initiating species and to improve efficiency of initiation. Of these promoters, 1,2‐propylene oxide has been the most successful. When TMSOTf has been used to initiate the polymerization of 2‐methyl‐2‐oxazoline, unfavorable charge distribution in the N‐trimethylsilyl‐2‐methyl‐2‐oxiranium cation has produced an unreactive imine dimeric cation which extends the time required for polymerization to several weeks. 1,2‐Propylene oxide has been utilized to prevent formation of the imine dimeric cation by producing a more reactive initiating species. In the polymerization of isobutyl vinyl ether initiated by TMSOTf, 1,2‐propylene oxide has been shown to be ineffective as a promoter, but acetone can be used successfully. © 1995 John Wiley & Sons, Inc.