APPLICATION OF THE VAN-DER-WAALS-EQUATION OF STATE TO POLYMERS .2. PREDICTION

For polymers, the energy and co-volume parameters of cubic equations o f state can be reliably estimated using only two low-pressure volumetr ic data points. This procedure is applied to the van der Waals equatio n of state, and bubble-point pressure calculations are performed for a number of polymer solutions. The van der Waals one-fluid mixing rules are used. The Berthelot combining rule is used for estimating the cro ss energy parameter, while the usual arithmetic mean combining rule is used for evaluating the cross co-volume parameter. Deviations from Be rthelot's combining rule are taken into account via a simple method re quiring only the molecular weight of the solvent. It is shown that whe n the proposed method is applied, the van der Waals equation of state can predict the equilibrium pressures of polymer solutions. The accura cy of the predictions is very good, comparable to those of other more complex equations of state, but it is in general inferior to those of the free-volume activity coefficient models. The simplicity, accuracy and general applicability of the proposed method makes it an attractiv e alternative to previously proposed complex models for prediction of equilibrium pressures of nearly athermal and non-polar polymer solutio ns.