Equation of state for polymer liquids

An empirical pressure–volume–temperature (PVT) equation of state is presented for polymers in the liquid state, i.e., above the melting point of a crystalline polymer or the glass transition of an amorphous polymer. In terms of reduced variables, the equation is given by {article}{empty}{document}PV⁵ ̄ = T^3 / 3 2 . - 2 - ln V{document} . Values of the three reducing parameters are given for 23 polymers. Comparison of the predictions of this equation with experimental data are made for all of the polymers. The data are generally available up to a pressure of 2 kbar and a temperature 100°C above the melting or glass transition temperature. Measured and calculated volumes agree within about 0.001 cm 3 /g, which is the accuracy of the measurements. Detailed comparisons with the empirical Tait equation are made. Equations are also presented for isothermal bulk modulus, thermal expansion coefficient, and Gruneisen parameter.