Syntheses of amphiphilic block copolymers by living cationic polymerization of vinyl ethers and their selective solvent-induced physical gelation

Amphiphilic diblock copolymers were prepared by the living cationic polymer ization of vinyl ethers in the presence of added bases, and their selective solvent-induced physical gelation behavior was investigated. The block cop olymerization of 2-phenoxyethyl vinyl ether (PhOVE) and 2-methoxyethyl viny l ether (MOVE) was carried out in the presence of ethyl acetate with Et1.5A lCl1.5 in toluene at 0 degreesC. Despite the rate difference, diblock copol ymers with a very narrow molecular weight distribution were obtained, quant itatively. By adding the selective solvent, water, to the acetone solution of the diblock copolymer, PhOVE200-b-MOVE400, physical gelation occurred su ddenly and the system ceased to flow, maintaining transparency. Viscoelasti c measurements and transmission electron microscopic observations were perf ormed to examine the characteristic gelation behavior and structure of the obtained gels. Various gelation conditions and physical gelation by other a mphiphilic block copolymers were also designed on the basis of the solubili ty of each block segment. Further, new forms of physical gelation, accompan ied by the solubilization of immiscible organic compounds, were achieved us ing similar diblock copolymers. (C) 2001 John Wiley & Sons, Inc.