Syntheses of various stimuli-responsive diblock copolymers by living cationic polymerization-thermally-induced micellization and physical gelation

The authors have synthesized various stimuli-responsive diblock copolymers by living cationic polymerization and have investigated their characteristi c thermosensitive micellization and physical gelation behavior in water. Th e sequential living polymerization of vinyl ethers with oxyethylene units i n the pendant was carried out in the presence of added base with E1.5AlCl1. 5 at 0 degreesC in toluene. to give diblock copolymers with a very narrow M WD. When the aqueous solution of diblock copolymers was warmed, characteris tic multi-stage phase separation (polymer concentration=0.1 similar to 1 wt %) or physical gelation (polymer concentration greater than or equal to 13 wt%) occurred sensitively and reversibly. The temperature of phase separati on and physical gelation could be changed by the combination of diblock seg ments. During the physical gelation. micelle formation was confirmed by the measurement of dynamic light-scattering and by determining the cmc and cmt by the solubilization of nonionic dye. To observe directly the state of ge ls and elucidate the mechanism, the authors also measured electron microgra phs from a freeze-fracture method of physical gel.