Phase equilibria studies of polystyrene and cyclohexane solutions at various pressures

Abstract

The precipitation temperature for each volume fraction of polystyrene in cyclohexane tested increased with increasing pressure. The Flory theta temperature increases almost 1° K for a pressure increase of 200 atmospheres. The entropy parameter psi is only slightly dependent upon the pressure, if at all; however, this is contingent upon the hypothesis that the product of theta and psi is a constant independent of pressure. The inclusion of a X (subscript 2Ø3) for a solvent helps to broaden the theoretical curve of the interaction parameter x� versus the volume fraction of polymer Ø, for certain values of X ₂, so that there is better agreement between the theoretical curves and the experimental curves. A value of x₂ = 1/9 brings about a better agreement between the theoretical and the experimental curves for a weight-average molecular weight of 82,000 for polystyrene in cyclohexane. A slightly larger value than 1/9 for x₂ may bring an even better agreement. A value of x₂ = 1/18 seems to be the value for x₂ for the weight-average molecular weight of 267,000. These values contradict those suggested by Orofino and Flory. Another problem is that as x₂ increases in size, the critical value for x� decreases below that found by experiment.