Jr. Quintana et al., DIBLOCK COPOLYMER MICELLES IN SOLVENT BINARY-MIXTURES .1. SELECTIVE SOLVENT PRECIPITANT/, Macromolecules, 28(12), 1995, pp. 4139-4143
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.