Investigation of block copolymer micellization by high-performance size-exclusion chromatography

The formation and decomposition of micelles of the three-block copolymer polystyrene-block-poly(ethene-stat-butene)-block-polystyrene (Kraton G 1652, Shell) were investigated by high-performance size-exclusion chromatography in a mixed solvent dioxan–heptane. The association equilibrium may be shifted from the pure unimer to pure micelles by changing the composition of the mobile phase, and also (at constant composition) by a change in temperature. The shape of the chromatograms observed under conditions of comparable equilibrium concentrations of both species may be explained by the disturbance and reestablishment of the association equilibrium during separation in the chromatographic column. Experiments with changing flow rate show the dominating effect of degrading separation efficiency with increasing linear velocity of the mobile phase.