Cationic polymerization of isobutyl vinyl ether (IBVE) was examined using a variety of metal halides. In the presence of an appropriate added base, ester or ether, the living polymerization of IBVE proceeded for almost all Lewis acids (MCln; M: Fe, Ga, Sn, In, Zn, Al, Hf, Zr, Bi, Ti, Si, Ge, Sb) used in conjunction with an IBVE-HCl adduct in toluene at 0 degrees C. The difference in the polymerization activity of these Lewis acids was significant. As examples, polymerization with some acids, such as FeCl3, proceeded in the order of seconds, whereas it took more than a few weeks with others such as SiCl4 and GeCl4. The difference in activity is based on the strength of the interaction between the Lewis acid and the propagating end chloride anion and/or the basic carbonyl (or ether) oxygen atom of the added base, that is, the chlorophilic or oxophilic nature of each metal halide is a decisive factor. In addition, a suitable combination of a Lewis acid and an additive was indispensable for living polymerization. With metal pentachlorides, NbCl5 and TaCl5, addition of a salt (nBu(4)NCl) resulted in superior control of the reaction over that for addition of a base. Lewis acids for living cationic polymerization of vinyl ether were categorized into groups depending on the preferences for these additives.