DYNAMIC PROPERTIES OF CONCENTRATED-SOLUTIONS ABOVE THE GLASS-TRANSITION TEMPERATURE

Concentrated solutions of polybutylacrylate (PBA) in dioxane and polybutadiene (PBD) in cyclohexane and carbon tetrachloride have been studied at 50-degrees-C in the concentration range 0.1-0.9 g/ml using Rayleigh-Brillouin scattering (RBS) and static and dynamic light scattering. The purpose was to extend measurements to concentrated solutions of "soft" polymers in a temperature range well above the glass transition temperature. The high frequency modulus from RBS is much larger than the low frequency osmotic modulus, but they have identical power law behavior. Contrary to the pronounced maximum in D(c) observed as a function of PHI(p) in concentrated polystyrene/toluene solutions [Brown et al., J. Chem. Phys. 95, 8568 (1991); Macromolecules 24, 5484 (1991)], the concentration dependence of D(c) increases strongly above PHI(p) almost-equal-to 0.56 in the PBA/dioxane system. This change is attributed to a reduction in the effective solvent viscosity caused by the presence of the polymer and analogous to the effect noted by Lodge and co-workers in polybutadiene solutions using oscillatory electric birefringence and pulsed-field-gradient nuclear magnetic resonance (NMR) measurements.