Stimuli-responsive diblock copolymers with a thermosensitive segment and a hydrophilic segment have been synthesized via sequential living cationic copolymerization, which involves a poly(vinyl ether) with oxyethylene pendants exhibiting LCST-type phase separation in water and a poly(hydroxyethyl vinyl ether) segment. Highly sensitive and reversible thermally induced micelle formation and/or physical gelation were observed with such diblock copolymers. For example, the flow behavior of an aqueous solution of a diblock copolymer varied from Newtonian to non-Newtonian and plastic flow within a very narrow temperature range. TEM and SANS studies showed that the observed change in viscosity was due to the formation of a macrolattice with body-centered-cubic symmetry of spherical micelles in aqueous solution. The critical temperature of micelle formation and/or physical gelation could be varied by altering the combination of two segments in the diblock copolymer. On the basis of these results, several systems incorporating various patterns of physical gelation behavior have been developed, and a strategy for constructing stimuli-responsive systems with block copolymers was established.

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 (TPS) of 42 °C. 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 TPS 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 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3300–3312, 2003

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Substituted half-titanocenes bearing coordinative ether and ester moiety in their side chains, η5:η-C5H4(CH2CH2OMe)TiCl3 (5b), η5-C5H4(CH2CH2CH2OMe)TiCl3 (5c), and η5:η1-C5H4(CH2COOMe)TiCl3 (5d), were prepared, and then their catalytic performances for the stereospecific living polymerization of 1,3-butadiene in the presence of the methylaluminoxane (MAO) were investigated. The introduction of intramolecular coordination between central titanium and the ether or ester moiety (5b,d) caused acceleration of polymer propagation rate and enhancement of cis-specificity. The catalyst 5d/MAO showed 114 times larger propagation rate constant than that of the parent nonsubstituted η5-C5H5TiCl3 (5f)/MAO catalyst. The 5b/MAO catalyzed 1,3-butadiene polymerization gave high cis-polybutadiene (99.2% cis content) with narrow molecular weight dispersity (1.14). The single-crystal X-ray crystallographic analysis of 5d and reaction pathway are also discussed.