PRESSURE VOLUME TEMPERATURE PROPERTIES AND EQUATIONS OF STATE IN POLYMER BLENDS - CHARACTERISTIC PARAMETERS IN POLYSTYRENE POLY(VINYL METHYL-ETHER) MIXTURES

The pressure-volume-temperature(P-V-T) properties of miscible polymer blends of polystyrene (PS)/poly(vinyl methyl ether) (PVME) have been studied experimentally in the liquid state. The data for the liquid state in the one-phase region were fitted to the equations of state of Flory, Orwoll, and Vrij and to the cell model. The characteristic parameters in these equations of state at various compositions were obtained from the fitting procedure. From the composition dependence of the characteristic parameters, the interaction parameter X12 was obtained. In the PS/PVME blend, it was found that the value of X12 obtained from the characteristic pressure P* is large and negative, but that obtained from the characteristic temperature T* is large and positive. This discrepancy could be explained if the assumption of additive external degrees of freedom on mixing is incorrect. However, in spite of the negative X12, the external degrees of freedom appear to be larger in the blends. Since this is not consistent with the observed limits of miscibility, one must look for other explanations. It was found that a moderately large temperature-dependent interaction can produce the sort of behavior observed in the P-V-T properties of the mixtures.