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Block copolymer micelles formed by diblock and triblock copolymers of styrene and methacrylic acid were characterized in solution in a mixed solvent with 80 vol % of dioxane and 20 vol % of water. Methods of static light scattering, quasielastic light scattering, differential refractometry, viscometry, sedimentation velocity, and densitometry were used. No unattached unimer molecules were observed. Three independent methods were employed for obtaining micellar weights. They agreed well with each other. No anomalous behavior was observed by any method. The micellar solutions were shown to contain almost exclusively single micelles; only a few samples (those producing the largest micelles) contained micellar clusters. The micelles behaved hydrodynamically and thermodynamically as impermeable spheres. The structure of the micellar shell was characterized in some detail. Relations between the aggregation number and the hydrodynamic radius of the micelles on the one hand and the sizes of the styrene and methacrylic acid blocks on the other were presented as scaling type phenomenological equations.Physicochemical properties of self-assembling molecules are of ever increasing experimental and theoretical interest. This is not only due to the intriguing phenomenon of selfassembling but also due to important applications of such materials in coatings, adhesives, thin films, microfabrication of electronic devices, pharmaceutical and photographic technologies, oil recovery, etc. Among the most important self-assembling systems are polymeric micelles.

A range of water-soluble hydrophilic−hydrophobic diblock copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate were shown to form micelles if first dissolved in a nonselective solvent (THF or methanol) and subsequently diluted with water. Critical micelle concentrations were found to increase with the length of the hydrophobic block if the the hydrophilic block length is fixed. Increasing the overall molar mass of the copolymer also increased the cmc for a given composition. The hydrodynamic diameters and approximate association numbers of these micelles were obtained by dynamic light scattering and analytical ultracentrifugation. Micellar diameters and association numbers were in the range 10−18 nm and 10−33 chains per micelle, respectively, depending on copolymer composition. Increasing the overall molar mass of the copolymer for a given composition produces larger micelles with lower association number. Both micelle size and association number decrease with the length of the hydrophobic block if the hydrophilic block length is fixed. The results suggest that the solubility of the hydrophilic block is at least as important as that of the hydrophobic block, although nonequilibrium effects cannot be excluded. Both the size and the association number of the micelles can be varied in predictable ways by changing the temperature, the pH, or the ionic strength of the solution.