Effect of cyclisation on the self-association behaviour of block copolymers in aqueous solution. Comparison of oxyethylene/oxybutylene block copolymers cyclo-B27E144 and E72B27E72

Abstract

Triblock copolymer E₇₂B₂₇E₇₂ was prepared by sequential anionic polymerisation of butylene oxide followed by ethylene oxide. Some of this copolymer was cyclised via acetal closure to yield a cyclic diblock copolymer, cyclo-B₂₇E₁₄₄. Gel-phase chromotography (GPC) and NMR were used to characterise the copolymers. Aqueous solutions of both block copolymers were micellar at very low concentrations. Several methods were used to study the micellar solutions: dynamic light scattering and pulsed field-gradient spin–echo (PGSE) NMR for the hydrodynamic properties of the micelles, static light scattering for micellar molar mass and association number, and surface tension and light scattering for critical micellisation concentration (c.m.c.). The cyclic diblock copolymer formed larger micelles than its linear triblock counterpart, and had a lower c.m.c.