PRESSURE-DEPENDENCE OF THE PHASE-BEHAVIOR OF POLYSTYRENE IN METHYLCYCLOHEXANE

The influence of pressure on the upper critical solution temperature ( UCST) as well as on the lower critical solution temperature (LCST) beh aviour of the system methylcyclohexane (MCH)/polystyrene PS 405 was st udied. Cloud-point pressures up to 120 bars were measured with a Caill etet apparatus. Cloud-point and spinodal pressures were obtained with a pressure pulse-induced critical scattering apparatus (PPICS) up to 8 00 bars. Also, some three-phase equilibria liquid-liquid-vapour were d etermined. The lower demixing temperature is found to decrease with in creasing pressure. The upper demixing temperature increases with incre asing pressure. The experimental data were described qualitatively wit h a simple G(E)-model. This G(E)-model is able to describe the depende nce of the demixing temperature on the pressure. Also, the model is ab le to predict the merging of the regions of immiscibility that can occ ur in systems of methylcyclohexane/polystyrene. (C) 1997 Elsevier Scie nce B.V.