LIGHT-SCATTERING STUDY OF THE ASSOCIATION BEHAVIOR OF STYRENE ETHYLENE-OXIDE BLOCK COPOLYMERS IN AQUEOUS-SOLUTION

Static and dynamic light-scatterning studies on the micellization behavior in aqueous solution of poly(styrene-oxyethlene) diblock and poly(oxyethylene-styrene-oxyethylene) triblock copolymer are presented. Two narrowly distributed populations of particles are found in the solution. The sizes of the large particles and the small particles remain unchanged in a concentration range from 2 x 10-5 to 2 x 10-3 g/mL. The weight fraction of the large particles, however, decreases with increasing concentration, unlike in most common aggregation processes. Detailed analysis reveals that the small particles (R(h) approximately 20 nm) are regular micelles with association number of a few hundreds, and the large particles (R(h) approximately 65 nm) are loose micellar clusters consisting of tens of micelles. The micelle structure is core-shell type with a dense and glassy polystyrene core and a highly swollen poly(oxyethylene) shell.