Effect of cyclization on the association behavior of block copolymers in aqueous solution.: Comparison of oxyethylene/oxypropylene block copolymers cyclo-P34E104 and E52P34E52

Triblock copolymer E52P34E52 was prepared by sequential anionic polymerization of propylene oxide followed by ethylene oxide. Some of this copolymer was cyclized via acetal closure to yield a cyclic diblock copolymer, cyclo-P34E104, which was characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. Light scattering methods were used to study the micellization and micellar properties of the two copolymers: dynamic light scattering for hydrodynamic properties of the micelles, static light scattering for micellar molar mass and critical micellization conditions. The gelation of concentrated solutions was also studied. The critical micelle concentrations (cmc) of the two copolymers were similar for solutions at 40-50 degrees C, but the temperature dependence of the cmc was smaller for the linear copolymer. The cyclic copolymer in solution at 50-55 degrees C formed micelles with larger association numbers and hard-sphere volumes than its linear triblock counterpart.