Clouding of aqueous solutions of difunctional tapered-statistical copolymers of ethylene oxide and 1,2-butylene oxide

Eight statistical copolymers were prepared by anionic copolymerisation of e thylene oxide and 1,2-butylene oxide initiated by diethylene glycol, The di fference in reactivity ratios of the two monomers ensured that the composit ion of the copolymers tapered from high E content (E denotes an oxyethylene unit) at the centre of a chain to high B content (B denotes an oxybutylene unit) at the chain ends, giving the copolymers the character of a triblock copolymer, type BEB. For comparison two true triblock (type BEB) copolymer s were prepared by sequential anionic copolymerisation, Cloud point curves of aqueous solutions of the soluble copolymers were determined. These showe d interesting features attributable to association, in particular sharp tra nsitions at the points (concentration and temperature) at which the solutio ns attained their critical condition for micellisation. This explanation wa s verified by examining solutions below the cloud point by dynamic light sc attering and noting the presence of micelles in appropriate cases. The rang e of copolymers available allowed the effects of overall composition and ch ain length to be explored, as well as the difference in behaviours resultin g from the tapered-statistical and block copolymer architectures. (C) 2000 Elsevier Science Ltd. All rights reserved.