EFFECT OF BLOCK STRUCTURE ON THE MICELLIZATION AND GELATION OF AQUEOUS-SOLUTIONS OF COPOLYMERS OF ETHYLENE-OXIDE AND BUTYLENE OXIDE

Oxyethylene/oxybutylene block copolymers E41B-8, E21B-8E21, and B4E40B 4 were prepared by sequential anionic polymerization and characterized by gel permeation chromatography and NMR spectroscopy. Their associat ion behavior in aqueous solution was investigated by surface tension a nd static and dynamic light scattering. The diblock copolymer E41B-8 a nd the triblock copolymer E21B-8E21 associated by closed processes to form micelles, those of the diblock copolymer being much larger. The t riblock copolymer B4E40B4 associated by a process having characteristi cs of open association. A low-temperature clouding-clearing effect was noted for solutions of copolymer E21B-8E21. Thermally-reversible sol --> gel --> sol transitions were observed on heating or cooling concen trated solutions of diblock copolymer E41B-8, but concentrated solutio ns of the two triblock copolymers did not gel.