SIMPLIFIED HOLE THEORY EQUATION OF STATE FOR LIQUID POLYMERS AND SOLVENTS AND THEIR SOLUTIONS

In the simplified hole theory equation of state proposed by our group (Zhong, C.; Wang, W.; Lu, H. Fluid Phase Equilib. 1993, 86, 137), the occupied site fraction for the Simha-Somcynsky equation of state (Simh a, R.; Somcynsky, T. Macromolecules 1969, 2, 342) was derived as a sim ple exponential function of temperature alone, in terms of the theory for all imperfect crystal with thermal defects. In this work, the simp lified hole theory equation of state has been applied to an accurate d escription of the pressure-volume-temperature relationship for 67 liqu id polymers and 61 solvents and compared with four commonly used equat ions of state. An approximate expression for the activity coefficient of a solvent in polymer-solvent solutions has been derived, which enab les one to calculate the activity coefficient for the solvent analytic ally. The grand absolute average deviation between the calculated and experimental solvent activity coefficients for 95 data sets is 2.4%, w hich indicates that this equation of state is also capable of accurate ly describing polymer-solvent solutions.