Thermosensitive homopolymers and copolymers with hydroxy groups were synthesized via the living cationic polymerization of Si-containing vinyl ethers. The cationic homopolymerization and copolymerization of five vinyl ethers with silyloxy groups, each with a different spacer length, were examined with a cationogen/Et1.5AlCl1.5 initiating system in the presence of an added base. When an appropriate base was added, the living cationic polymerization of Si-containing monomers became feasible, giving polymers with narrow molecular weight distributions and various block copolymers. Subsequent desilylation gave well-defined polyalcohols, in both water-soluble and water-insoluble forms. One of these polyalcohols, poly(4-hydroxybutyl vinyl ether), underwent lower-critical-solution-temperature-type thermally induced phase separation in water at a critical temperature (T-PS) of 42 degreesC. This phase separation was quite sensitive and reversible on heating and cooling. The phase separation also occurred sensitively with random copolymers of thermosensitive and hydrophilic or hydrophobic units, the T-PS values of which in water could be controlled by the monomer feed ratio. The thermal responsiveness of this polyalcohol unit made it possible to prepare novel thermosensitive block and random copolymers consisting solely of alcohol units. One example prepared in this study was a 20 wt % aqueous solution of a diblock copolymer consisting of thermosensitive poly(4-hydroxybutyl vinyl ether) and water-soluble poly(2-hydroxyethyl vinyl ether) segments, which transformed into a physical gel above 42 degreesC. (C) 2003 Wiley Periodicals, Inc.