Micellization protocols for amphiphilic polyelectrolytes in water. How do polymers undergo intrapolymer associations?

Copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and N-dodecylmethacrylamide (C(12)MAm) undergo intrapolymer hydrophobic association in water, but depending on micellization procedures, the polymers may or may not form completely unimolecular micelles. Various protocols for the preparation of aqueous solutions of the polymers were examined to clarify how the polymers form preferentially unimolecular micelles. In solid polymer samples purified by reprecipitation followed by lyophilization, kinetically-frozen multimolecular micelles, formed by hydrophobic associations in entangled polymer chains during purification, may already exist. When a solid polymer sample is added to water, kinetically-frozen micelles are simply re-dissolved in water as such. Virtually unimolecular micelles were obtained when the solid sample was first dissolved in pure water at an elevated temperature (greater than or equal to 90 degreesC), followed by addition of salt at the same temperature. Micelles formed from the copolymers with C(12)MAm content greater than or equal to 40 mol% were not equilibrium micelles but kinetically-frozen. The micelles were not completely unimolecnlar. The number of polymer chains comprising a micelle increased with C(12)MAm content.