THEORY OF PHASE-BEHAVIOR OF (OXYETHYLENE)-POLY(OXYPROPYLENE)-POLY(OXYETHYLENE) TRIBLOCK COPOLYMERS IN AQUEOUS-SOLUTIONS

The phase behavior of ABA triblock copolymers in aqueous solutions is studied theoretically, using both continuum and lattice mean-field the ories. A variety of lyotropic liquid crystalline phases is found for t he Pluronic family, and the effects of temperature, copolymer concentr ation, Overall molecular weight, and block sizes are investigated. The theoretical scheme incorporates ''internal'' monomeric states as well as the effects of the spatial arrangement of the molecules and may be viewed as a generalization of the traditional theory of ordered phase s in block copolymers. The interaction parameters determined for poly( oxyethylene) and poly(oxypropylene) homopolymers in aqueous solutions are found to give good agreement for the theoretically predicted order ed structures when compared with measurements on different Pluronic po lymers using H-2 NMR of deuterated water and small-angle X-ray scatter ing.