"Living" species-mediated propagation reactions were demonstrated to occur in the cationic vinyl-addition and ring-opening copolymerization of isopropyl vinyl ether and isobutylene oxide (IBO) with CF3SO3H(TfOH) as an initiator. The polymerization proceeded by the carbocations as propagating species formed by the dissociation of a terminal covalent carbon-OTf bond. Importantly, the covalent species were generated exclusively at the IBO-derived propagating end, which was indicated by both the incorporation of a quencher fragment into the omega-end of the product copolymer and F-19 NMR analysis of the copolymerization reaction. The generation of reversibly dissociable covalent species, or "dormant" species, from one of the two monomers was for allowing the even propagation of the propagating chains. Moreover, the reaction conditions were optimized to suppress side reactions such as chain transfer via beta-proton elimination. Copolymers with molecular weights that agree relatively well with the theoretical values were produced using C4F9SO3H as an initiator in less polar solvents at lower temperature.