APPLICATION OF THE VAN-DER-WAALS-EQUATION OF STATE TO POLYMERS .1. CORRELATION

A reliable methodology for evaluating the energy and co-volume parameters of cubic equations of state for polymers is proposed. Only two low-pressure volumetric data points are used. The procedure is applied to the van der Waals equation of state and bubble-point pressure calculations are performed for a number of polymer solutions. The usual combining and mixing rules are used. It is shown that the van der Waals equation can correlate the equilibrium pressures of polymer solutions using one binary interaction parameter. The accuracy of the correlation is very good; it is comparable to or better than that achieved using the Flory-Huggins model. It is also shown that the necessary binary interaction parameters for the van der Waals equation of state can be estimated using a simple scheme based on the Berthelot combining rule. It is, thus, demonstrated that the van der Waals equation of state can be a simple and successful tool for the description of the vapor-liquid equilibria in polymer solutions.