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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). © 1993 John Wiley & Sons, Inc.

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Submicrometer-sized N-isopropylacrylamide(NIPA) gel particles with various composition of cross-linker are prepared by precipitation polymerization and their swelling behaviors are examined by using photon correlation spectroscopy(PCS) technique. Theoretically, Hu et al.'s double-lattice model has been modified by introducing a new universal constant and simplifying the expression of the Helmholtz energy of mixing. The modified double-lattice model(MDL) describes very well the lower critical solution temperature (LCST) behavior of linear PNIPA/water system. For cross-linked NIPA gel particles in water, we have combined MDL theory with Flory and Erman's theory of elasticity, which takes into account the nonaffine displacements of network junctions under high degree of swelling. Energy parameters obtained from the linear PNIPA/water system were directly used to predict swelling equilibria for the NIPA gel/ water system. Our results represented that an affine network model explained the swelling behavior at high swelling ratio more accurately than that of the phantom network model. To correct the deviation of the continuous volume transition temperature, we have considered the interaction energy parameter between cross-linker segment and solvent molecule. The corrected model was applied to the swelling equilibria of gel particles with various cross-linking density and agreed well with their experimental data with no adjustable model parameters.