EFFECT OF CYCLIZATION ON THE SELF-ASSOCIATION BEHAVIOR OF BLOCK-COPOLYMERS IN AQUEOUS-SOLUTION - COMPARISON OF OXYETHYLENE OXYBUTYLENE BLOCK-COPOLYMERS CYCLO-B(27)E(144) AND E(72)B(27)E(72)/

Triblock copolymer E(72)B(27)E(72) was prepared by sequential anionic polymerisation of butylene oxide followed by ethylene oxide. Some of t his copolymer was cyclised via acetal closure to yield a cyclic dibloc k copolymer, cyclo-B(27)E(144). Gel-phase chromotography (GPC) and NMR were used to characterise the copolymers. Aqueous solutions of both b lock copolymers were micellar at very low concentrations. Several meth ods were used to study the micellar solutions: dynamic light scatterin g and pulsed held-gradient spin-echo (PGSE) NMR for the hydrodynamic p roperties 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.