ASSOCIATION AND PHASE-BEHAVIOR OF STATISTICAL AND BLOCK-COPOLYMERS OFETHYLENE-OXIDE AND BUTYLENE OXIDE IN WATER

Three copolymers of ethylene oxide (EO) and 1,2-butylene oxide (BO) we re prepared by anionic polymerization to have similar molar masses (M( n) approximate to 7000 g mol(-1)), molar mass distributions (M(w)/M(n) < 1.1) and compositions (80 mol% oxyethylene) but different chain str uctures. A triblock copolymer was prepared by sequential copolymerizat ion of EO followed by BO, and two statistical copolymers were prepared from mixed monomers, either to low (15%) or to high (93%) conversion. The disparity in reactivity ratios in the EO/BO copolymerization resu lted in pronounced composition drift along the chains of the high conv ersion statistical copolymer, giving it the character of a block copol ymer. This composition profile was checked by C-13 n.m.r. spectroscopy . The association behaviour of the statistical copolymers in aqueous s olution at 25 degrees C was studied by dynamic and static light scatte ring. The low conversion statistical copolymer remained in its molecul ar state across the concentration range studied (up to 100 g dm(-3)), but the high conversion statistical copolymer associated into molecula r clusters and micelles. Cloud point curves were determined for soluti ons of the three copolymers. The effect of association on phase behavi our is discussed. (C) 1997 Elsevier Science Ltd.