Interaction Parameter Predicted by Pressure-Volume-Temperature Properties of Miscible Polymer Blends

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. OReilly, 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)].