Liquid-liquid phase equilibrium in polymer-solvent systems: Correlation and prediction of the polymer molecular weight and the pressure effect

A G(E) model is used for the correlation and prediction of partial miscibil ity in polymer solutions that exhibit both upper critical solution temperat ure and lower critical solution temperature as well as hourglass-type phase separation in some cases. The model employs a combinatorial/free-volume te rm and the residual term of UNIQUAC, for which interaction parameters betwe en the solvent molecule and the repeating unit (segment) of the polymer are determined. The obtained parameters are then used to predict the effect of the polymer molecular weight on the solvent/polymer partial miscibility. T he model is also successfully applied in the prediction of the pressure eff ect on mutual solubility by incorporating it through the free volumes of th e components. Finally the prediction of excess properties using the propose d model is investigated.