Upper and lower critical solution temperatures have been determined for solutions of polystyrene in cyclohexane and methylcyclohexane and lower critical solution temperatures for the polystyrene-toluene system over the molecular weight range of Mw x 10"1 234 = 3.7 to ~270. The Patterson-Delmas theory of corresponding states, based on the Prigogine theory, has been applied to the polystyrene solutions and found to afford semiquantitatively good prediction of the molecular weight dependence of their critical temperatures. Polystyrene solution in methylcyclohexane displays a smaller miscibility region than that of the polystyrene-cyclohexane system, as indicated by the relative positions of their upper and lower critical solution temperatures. The entropy parameter ipi and Flory temperature obtained from lower critical solution temperatures for the polystyrenetoluene system are -1.92 and 277°, respectively.

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Phase equilibria have been examined for solutions of narrow-distribution polystyrene (3.7 < 10-4MW < 270) in benzene, methyl ethyl ketone, and cyclopentane. Lower critical solution temperatures have been determined for polystyrene solutions in benzene and methyl ethyl ketone and upper and lower critical solution temperatures for the polystyrene-cyclopentane system. The Patterson-Delmas corresponding states theory has been applied to the experimental results through the parameter and found to afford semiquantitatively good prediction of the molecular weight dependence of their critical temperatures. The one-third of external degrees of freedom of the solvents estimated by the aid of the theory are 1.23 for benzene, 1.76 for methyl ethyl ketone, and 0.706 for cyclopentane.

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