APPLICATION OF THE VAN-DER-WAALS-EQUATION OF STATE TO POLYMERS .3. CORRELATION AND PREDICTION OF UPPER CRITICAL SOLUTION TEMPERATURES FOR POLYMER-SOLUTIONS

The van der Waals equation of state is used for correlation (using a s ingle binary interaction parameter) and prediction of liquid-liquid eq uilibrium in many mixtures including a solvent and a polymer. The equa tion of state parameters for the polymer are estimated from experiment al volumetric data at low pressures. For the solvent, the equation of state parameters are estimated via the classical method, i.e. using th e critical properties of the solvent and generalized expressions of th e acentric factor. When extended to mixtures, the van der Waals one-fl uid mixing rules along with the Berthelot combining rule for the molec ular cross energy parameter are used. The arithmetic mean combining ru le is used for the cross co-volume parameter. A correction to the Bert helot combining rule which is obtained from vapor-liquid equilibrium d ata of polymer solutions is used for predicting the upper critical sol ution temperatures for many different binary polymer solutions, includ ing polar and non-polar systems. The results are remarkably successful . Typically, the difference between the predicted and the experimental upper critical solution temperatures is less than twenty degrees. Fur ther, in all cases, correlation is achieved in an easy and straightfor ward way without difficulty and excellent results are obtained. Unlike other theories and models, the van der Waals equation of state is cap able of predicting the flatness of the coexistence curves, which often occurs in polymer solutions.