MICELLIZATION OF A POLYSTYRENE-B-POLY(ETHYLENE PROPYLENE) BLOCK COPOLYMER IN N-DODECANE 1,4-DIOXANE MIXTURES .2. STRUCTURE AND DIMENSIONS OF MICELLES

The concentration and temperature dependencies of micelle formation by a polystyrene-block-poly(ethylene/propylene) copolymer in n-dodecane, 1,4-dioxane, and mixtures of both solvents are examined by light scattering and viscometry. At concentrations just above the critical micelle concentration an unusually large scattering intensity is found. The experimental dependencies of light scattering and viscosity data on concentration were always linear within the concentration range 1 x 10(-3)-5 x 10(-3) g.cm-3 for the extremes and middle of the composition range of the solvent mixture. The molar mass and dimensions of the micelles formed in n-dodecane and 1,4-dioxane are different due to the nature of the blocks that form the core and the shell of both types of micelles. Aggregation number seems to be related to the standard entropy of micellization. a comparison is made between the effect of the addition of the selective solvent for one block and the temperature increase. As the percentage of the minority solvent increases, or at constant composition as the temperature increases, dissociation of the copolymer chains occurs. We have found that temperature and selective solvent addition markedly influence the free chain-micelle equilibrium. However, this influence is relatively small on the molar mass and size of the micelles. Heller equations have been employed to determine the limiting viscosity number of the micelles, since the Huggins and Kraemer equations do not lead to the same value.