DIBLOCK COPOLYMERS OF ETHYLENE-OXIDE AND 1,2-BUTYLENE OXIDE IN AQUEOUS-SOLUTION - EFFECT OF E-BLOCK-LENGTH DISTRIBUTION ON SELF-ASSOCIATIONPROPERTIES

Block copolymers were prepared by copolymerization of ethylene oxide a nd butylene oxide to have identical overall composition and chain leng th but to differ in their distributions of oxyethylene (E) block lengt h by virtue of the sequence of polymerization of the two monomers: eth ylene oxide first to obtain copolymer E41B8, and butylene oxide first to obtain B8E11. Gel permeation chromatography was used to show that t he chain length distributions were in accord with the prediction of th e kinetic scheme of Weibull and Nycander. The effect of E-block-length distribution on the self-association (micellization) of the two copol ymers in water was determined by means of surface tension and light sc attering (dynamic and static) measurements. Compared with copolymer E4 1B8 under similar conditions, it was found that copolymer B8E11 micell ized more readily and formed larger micelles. The effect of the differ ence in micellar properties on the gelation of moderately concentrated solutions of the two copolymers is described and discussed.