DIBLOCK COPOLYMER MICELLES IN SOLVENT BINARY-MIXTURES .1. SELECTIVE SOLVENT PRECIPITANT/

The association of a block copolymer polystyrene-b-poly(ethylene/propy lene) in mixtures of 5-methyl-2-hexanone (a selective solvent of polys tyrene block) and 2-pentanol (a precipitant of both copolymer blocks) has been studied by static and dynamic light scattering and viscometry . Micelle structural parameters have been analyzed as a function of th e solvent composition. As the precipitant percentage increases in the solvent mixture, the molar mass increases, the apparent radius of gyra tion and the second virial coefficient decrease, and the hydrodynamic radius remains constant. Static light scattering was used to establish the dependence of the critical micelle temperature on concentration. Dynamic light scattering measurements have shown that the micelles hav e narrow size distributions and micellization can be thermodynamically treated as a closed association. The light scattering results were us ed to calculate the standard Gibbs energies, enthalpies, and entropies of micellization. As the 2-pentanol percentage increases, the standar d Gibbs energy becomes more negative, whereas the standard enthalpy an d entropy remain almost constant.