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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 (zD) or solvent (yD) for polystyrene-h/propionitrile-h (PSh/PNh) solutions, polystyrene-h/propionitrile-2,2-d2 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 polymersolvent demixing developed by Luszczyk, Rebelo, and Van Hook (Macromolecules 1995, 28, 745) is described and then illustrated by application to the PS/PN data.

The crystallization and melting transitions for tetracontane in propane, measured in this work at pressures up to about 1200 bar, are found to exhibit a temperature minimum, which implies crystallization upon decompression (retrograde crystallization). The supercooling effect, which is the difference between the crystallization and melting temperature, is found to decrease with increasing tetracontane concentration. The transitions induced by varying temperature at constant pressure are found to fall near the same curve as those induced by varying pressure at constant temperature. The difference between the crystallization and melting pressure represents the super-compression effect.

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