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 ethylene oxide and 1,2-butylene oxide initiated by diethylene glycol. The difference in reactivity ratios of the two monomers ensured that the composition 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) copolymers were prepared by sequential anionic copolymerisation. Cloud point curves of aqueous solutions of the soluble copolymers were determined. These showed interesting features attributable to association, in particular sharp transitions at the points (concentration and temperature) at which the solutions attained their critical condition for micellisation. This explanation was verified by examining solutions below the cloud point by dynamic light scattering and noting the presence of micelles in appropriate cases. The range of copolymers available allowed the effects of overall composition and chain length to be explored, as well as the difference in behaviours resulting from the tapered-statistical and block copolymer architectures.