SYNTHESES OF THERMALLY-RESPONSIVE BLOCK COPOLYMERS WITH SIDE OXYETHYLENE GROUPS BY LIVING CATIONIC POLYMERIZATION AND THEIR PHASE-SEPARATION BEHAVIOR

Thermally-induced phase separating block (AB, ABA, and BAB types) or random copolymers of 2-ethoxyethyl vinyl ether and 2-methoxyethyl vinyl ether were prepared by the living cationic polymerization. The sequential block copolymerizations were carried out with CH3CH(OiBu)OCOCH3(2)/Et1.5AlCl1.5 in the presence of ethyl acetate in toluene at 0-degrees-C to give block copolymers with narrow molecular weight distributions (M(w)BAR/M(n)BAR is similar to 1.2). Effects of the monomer sequence distribution on the thermally-induced phase separation were investigated on aqueous polymer solutions by turbidimetry at 500 nm. Phase separation of the random copolymers was quite sensitive to temperature changes and reversible, similar to that of the homopolymers. On the other hand, the aqueous solution of the diblock and triblock copolymers exhibited a multistage phase separation at about the phase separating temperatures of the corresponding homopolymers. On the basis of these results, various types of aggregation of the macromolecules were discussed.