DIBLOCK COPOLYMER MICELLES IN SOLVENT BINARY-MIXTURES .2. SELECTIVE SOLVENT GOOD SOLVENT/

Solutions of polystyrene-b-poly(ethylene/propylene) block copolymer in mixtures of 4-methyl-2-pentanone (a selective solvent of the polystyr ene block) and 2-chlorobutane (a good solvent of both copolymer blocks ) were studied by static and dynamic light scattering and viscometry, Micelle structural parameters and micellization thermodynamics have be en analyzed as a function of the solvent composition. The micelle mola r mass decreased as the 2-chlorobutane percentage in the binary mixtur e increased. However the apparent radius of gyration, the second viria l coefficient, and the hydrodynamic radius hardly showed variations. S tatic light scattering was used to establish the dependencies of the c ritical micelle temperature on concentration. The standard Gibbs energ ies, enthalpies, and entropies of micellization have been calculated f or the different solvent mixtures from these relationships, The three thermodynamic magnitudes became less negative as the good solvent perc entage increased.