Isotope and Pressure Dependence of Liquid−Liquid Equilibria in Polymer Solutions. 7. Solute and Solvent H/D Isotope Effects in Polystyrene−Propionitrile Solutions

Cloud and spinodal loci have been obtained as functions of pressure ( P ), temperature ( T ), polymer segment number ( r ), segment fraction (ψ), and H/D substitution on solute ( z D ) or solvent ( y D ) for polystyrene- h /propionitrile- h (PSh/PNh) solutions, polystyrene- h /propionitrile-2,2- d 2 solutions (PSh/PNd), and polystyrene- d /propionitrile- h solutions (PSd/PNh). A light scattering technique was employed. An increase in pressure or an increase in the H/D ratio in the solvent (or decrease in the polymer H/D ratio) increases the region of miscibility. The solutions show upper and lower branches which may join at hypercritical points depending on the pressure, molecular weight, or solvent H/D ratio. A least-squares technique to fit experimental data to the continuous mean-field thermodynamic description of polymer−solvent demixing developed by Luszczyk, Rebelo, and Van Hook ( Macromolecules 1995, 28, 745) is described and then illustrated by application to the PS/PN data.