MICELLIZATION OF POLY(2-(DIMETHYLAMINO)ETHYL METHACRYLATE-BLOCK-METHYL METHACRYLATE) COPOLYMERS IN AQUEOUS-SOLUTION

A range of water-soluble hydrophilic-hydrophobic diblock copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate were show n to form micelles if first dissolved in a nonselective solvent (THF o r methanol) and subsequently diluted with water. Critical micelle conc entrations were found to increase with the length of the hydrophobic b lock if the the hydrophilic block length is fixed. Increasing the over all molar mass of the copolymer also increased the cmc for a given com position. The hydrodynamic diameters and approximate association numbe rs of these micelles were obtained by dynamic light scattering and ana lytical ultracentrifugation. Micellar diameters and association number s were in the range 10-18 nm and 10-33 chains per micelle, respectivel y, depending on copolymer composition. Increasing the overall molar ma ss of the copolymer for a given composition produces larger micelles w ith 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 si ze and the association number of the micelles can be varied in predict able ways by changing the temperature, the pH, or the ionic strength o f the solution.