Liquid-liquid equilibria of polydisperse polymer systems showing both UCSTand LCST phase behaviors

To describe liquid-liquid equilibria of polydisperse polymer/solvent system s in the framework of continuous thermodynamics, a continuous distribution function for describing the composition of polydisperse polymers must be co nsidered. In this study, we introduce the log-normal distribution function and then calculate the molar mass distributions of both principal phases an d conjugate phases. We apply these different molar mass distributions to th e extended Flory-Huggins model. Experimentally, we investigate both the upp er critical solution temperature (UCST) and the lower critical solution tem perature (LCST) phase behavior of various polydisperse polystyrene/cyclohex ane systems and compare the proposed model with experimental data. Although the proposed model does not theoretically consider the free volume and the specific interaction effects related to LCST, it is suitable for the repre sentation of liquid-liquid equilbria of polydisperse polymer solutions, usi ng a few semiempirical adjustable parameters.