Tuning of the exchange dynamics of unimers between block copolymer micelles with temperature, cosolvents, and cosurfactants

The dynamics of unimer exchange between aqueous micelles, formed by two amp hiphilic block copolymers; i.e., poly(styrene-b-sodium methacrylate) and po ly(tert-butylstyrene-b-sodium methacrylate), has been investigated by stead y-state fluorescence spectroscopy. The kinetics are so slow at room tempera ture that no exchange could be detected over several hours, while at 60 deg rees C the exchange rate constants could be estimated. These results Corrob orate our previous findings that the rate is slowed down by increasing the hydrophobicity of the core. In addition to the temperature, the exchange ca n also be tuned by the addition of either a cosolvent or a cosurfactant. Th e efficiency of these additives to speed up the exchange process is related to their water solubility and their compatibility with the hydrophobic cor e of the micelles. The most pronounced effect on the exchange process is ob served when the water solubility is low and the mixing of the additive with the hydrophobic core is favorable.