Cationic polymerization of isobutyl vinyl ether in an imidazole-based ionic liquid: characteristics and mechanism

Abstract

Cationic polymerization of isobutyl vinyl ether (IBVE) in an ionic liquid 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF₄]) was thoroughly examined at 0 °C. A variety of coinitiators were used in conjunction with the IBVE-HCl adduct acting as a cationogen. Compared with polymerization in organic solvents, the cationic polymerization of IBVE in [omim][BF₄] proceeded in a milder exothermic manner, yielding polymers with higher molecular weight, and giving a higher monomer conversion. Although the polymerization reaction in [omim][BF₄] could not be controlled due to the presence of β-proton elimination, the monomer addition experiments confirmed the existence of long-lived species. Introducing a small amount of 2,6-di-tert-butylpyridine (DTBP) into the system may lead to a controlled polymerization. The corresponding elementary reactions and stabilization mechanism of propagating the carbocation in [omim][BF₄] were also proposed.