SIZE-EXCLUSION CHROMATOGRAPHY OF SOLUTIONS OF BLOCK-COPOLYMERS IN SELECTIVE SOLVENTS

Solutions of polystyrene-block-poly(ethylene/propylene) and ne-block-p oly(ethylene/butylene)-block-polystyrene copolymers in 5-methyl-2-hexa none and 4-methyl-2-pentanone were studied by size exclusion chromatog raphy. The association equilibrium was studied shifting from micelles to free copolymer chains by increasing the temperature. A remarkable t ailing was observed in diblock copolymer micelle peaks that may be exp lained by the disturbance and reestablishment of the association equil ibrium during separation in the chromatographic column. This phenomeno n was very small for triblock copolymers. In this case, micelle hydrod ynamic volumes obtained from SEC curves were compared to those calcula ted from light scattering and viscosity measurements. The data agreeme nt was very good. Comicellization was analysed by mixing two different micelle solutions and injecting the solution mixture at different ela psed times. The SEC curves showed an intermediate peak corresponding t o mixed micelles. The results show that three micelle species coexist in solution during the first period after mixing, which suggests that comicellization proceeds via dissociation of pure micelles and associa tion of both copolymer free chains to form uniform mixed micelles.