Estimation of vapor-liquid equilibria for polymer solutions by a group-contribution method

A new group-contribution method is presented for prediction of vapor-liquid equilibria of polymer solutions. It is based on a close-packed lattice model developed previously; this model contains a revised Flory-Huggins entropy and a series expression for excess internal energy, as well as a double-lattice model to account for specific, oriented interactions. The group-contribution method includes three contributions: the combinatorial and free-volume contribution which is primarily responsible for entropy, the van der Waals energy contribution responsible for dispersion and polar forces, and the specific energy contribution from hydrogen bonding. Most of the model parameters can be estimated using pure-component properties, either from experimental data or from group-contribution methods in the literature. The group-contribution method described in this work gives parameters for the cross specific interaction energy from hydrogen bonding between segments of polymers and segments of solvents. Parameters for pairs of groups are obtained by correlating experimental data for vapor pressures and infinite-dilution activity coefficients of solvents in polymer solutions. The method shown here gives improved results for prediction when compared with those of other group-contribution models.