Abstract
An equation of state for polymer melts has been devised from observation on pressureβvolumeβtemperature data for several thermoplastics. The final equation has the form (P + Ξ β mT ln (cV^*^)) ln (cV^*^) = gT, where P is pressure; T, absolute temperature, V^*^, the volume normalized by van der Waal's volume, and Ξ , m, g, and c, parameters. Pertinent ancillary relationships include a βuniversalβ bulk modulus vs. a normalized volume function and an observation that the thermal expansion coefficient is solely dependent on pressure. We find that the parameter βΞ β is precisely the first derivative of internal energy with respect to volume and is evaluated from the thermal expansion coefficient and bulk modulus. It appears that βΞ β is constant over a wide range of conditions. The parameters βmβ and βgβ are related through the bulk modulus relation. Finally, βcβ has been found to be nearly a constant whose action is to change the volume reference state to the melt volume when extrapolated to absolute zero. The βuniversalβ nature of the temperatureβreduced bulk modulus and the constancy of Ξ suggest that the melt state is controlled by entropy rather than by potential energy. Β© 1994 John Wiley & Sons, Inc.