Correlation of solvent activities in polymer solutions

The activity coefficient models that have been proposed for correlation of Vapor-Liquid Equilibrium (VLE) of polymer solutions are usually based on an ad-hoc coupling of the combinatorial (free-volume) and residual terms available in the literature. The combinatorial terms studied here are the Entropic free volume, p-free volume and Freed FH and the residual terms the NRF, UNIQUAC and Wu-NRTL along with a segment based UNIQUAC term, sUNIQUAC. All the models investigated have two adjustable parameters and a two-parameter Flory-Huggins model was used as benchmark for comparative purposes. It is shown that models based on the p-free volume combinatorial term with a segment based residual pan derived from either the NRTL or UNIQUAC models can provide an excellent correlation of VLE data for polymer systems.