Liquid-liquid equilibria in polystyrene solutions: the general pressure dependence

In spite of numerous studies on liquid-liquid (LL) solubility in weakly interacting polymer solutions (such as polystyrene/methylcyclohexane), as yet there has been no general description of the pressure dependence of LL loci. Most likely this is a consequence of the diversity of shapes experimentally observed for LL loci under pressure. In this paper we present phase equilibrium measurements of LL precipitation from binary weakly interacting polystyrene/solvent systems which confirm the existence of a LL 'master-curve' which may be used to describe LL equilibria for Type III, IV and V systems in the Scott-Konynenburg formalism. More particularly, in Type III the entire demixing curve is located in the stable liquid region, in Type IV some part is located at negative pressure, and in Type V some part is located in the supercooled region. Secondly, we present a transformation which describes the LL diagrams (asymmetric in (T,P) space) using a symmetric scaling equation in reduced space.