Representation of vapor–liquid and liquid–liquid equilibria for binary systems containing polymers: Applicability of an extended flory–huggins equation

For some binary systems, an extended Flory–Huggins equation is applicable to both vaporliquid equilibria (VLE) and liquid–liquid equilibria (LLE) using the same adjustable parameters. New LLE and VLE data are reported for polystyrene (PS) (MW = 100,000)/cyclohexane and for poly(ethylene glycol) (PEG) (MW = 8,000)/water. Experimental results for the PS/cyclohexane system agree well with the semiempirical model, whereas those for PEG/water do not, probably because, for PEG/water, the temperature range of the VLE data is about 55°C lower than that of the LLE data. Excellent fits were obtained for our previously published experimental results for PS/cyclohexane (upper critical solution temperature, UCST), PS/ethyl acetate (lower critical solution temperature, LCST), PS/ tert ‐butyl acetate and PS/methyl acetate (both UCST and LCST), and PEG/water (closed‐loop). The semiempirical model also fits well with new data obtained for the polymer blend PS/poly(vinyl methyl ether).