Abstract
Expressions for Flory interaction parameter, χsc, were derived from the second derivative of the free energy of mixing by the following three equation of state theories: lattice fluid model of Sanchez and Lacombe [J. Phys. Chem., 80, 2352, 2568 (1976)], model of Flory, Orwoll, and Vrij [J. Am. Chem. Soc., 86, 3507 (1964)], and modified cell model by Dee and Walsh [Macromolecules, 21, 815 (1988)]. In each case, composition dependence of the characteristic pressure parameter, P*, was used to account for excess intermolecular interaction energy. The liquid state pressure-volume-temperature (PVT) properties of both pure components and mixtures of polystyrene and tetramethylbisphenol-A polycarbonate were measured at the weight fraction of polystyrene of 1/3 and 2/3, which were accordingly analyzed. The absolute values of χsc were always significantly larger than those obtained by small angle neutron scattering [H. Yang and J.M. O’Reilly, Mater. Res. Soc. Symp. Proc., 79, 129 (1987)] and diffusion [E. Kim et al., J. Polym. Sci., Polym. Phys. Ed., 33, 467 (1995)] measurements by a factor of 102. The PVT properties of blends misleadingly overstimate the enthalpic contribution, as also noted for the polystyrene (PS)/poly(vinyl methyl ether) mixture system by Ougizawa, Dee, and Walsh [Macromolecules, 24, 3834 (1991)].
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