Study of polystyrene-block-poly(methylmethacrylate) micelles by SEC/MALS.: Determination of molecular weights and size distribution

Polystyrene-block-poly(methyl methacrylate) micelles in 1,4-dioxane/cyclohexane were studied by size exclusion chromatography coupled with multi angle light scattering (SEC/MALS). A sufficient unimer - micelles resolution achieved by SEC made it possible to use MALS detector for the direct determination of distributions and corresponding averages of molecular weights and gyration radii of micelles. Contrary to the standard static light scattering approach, the SEC/MALS technique provided these averages in one analytic run with a minimum amount of copolymer sample. In most systems, very narrow molecular weights and size distributions of micelles were obtained. For a given copolymer, the micellar association number increased with decreasing thermodynamic quality of solvent. Under given thermodynamic conditions, it increased with increasing length of insoluble poly(methyl methacrylate) block and with decreasing length of soluble polystyrene block. The micellar radius of gyration was predominantly controlled by the molecular weight of the copolymer.