Controlled cationic polymerization of isobutyl vinyl ether was demonstrated to proceed in an ionic liquid (IL), 1-butyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, using a 1-(isobutoxy) ethyl acetate/TiCl4 initiating system, ethyl acetate as an added base, and 2,6-di-tert-butylpyridine as a proton trap reagent. Judicious choices of metal halide catalysts, counteranions of ILs, and additives were essential for controlling the polymerization. The polymerization proceeded much faster in the IL than in CH2Cl2, indicating an increased population of ionic active species in the IL due to the high polarity. Polymers with a relatively narrow molecular weight distribution were obtained in the IL with a bis (trifluoromethanesulfonyl)imide (NTf2-) anion even in the absence of an added base, which suggested possible interactions of the counteranion of the IL with the growing carbocations. Moreover, the direct cationic polymerization of a vinyl ether with pendant imidazolium salts, 1-(2-vinyloxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl) imide, proceeded in a homogeneous state in 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl) imide. The solubilities of the obtained polymers were readily tuned by counteranion exchange. (C) 2016 Wiley Periodicals, Inc.