A continuous polydisperse thermodynamic algorithm for a modified Flory-Huggins model: The (polystyrene plus nitroethane) example

A modified Flory-Huggins model is presented, considering a concentration- a nd temperature-dependent interaction parameter, and using the methodology o f Continuous Thermodynamics to take into account both polydispersity and it s effect on phase equilibrium of polymeric systems. This model describes al l commonly found, as well as other unusual polymer + solvent and polymer polymer, liquid-liquid phase diagrams and is easily extended to take all po ssible pressure effects into consideration. Modeling and least-squares fit of polystyrene + nitroethane liquid-liquid cloud-point data have produced r esults in good accord with the experimental ones by using meaningfully phys ical parameters. These results have been used to discuss polystyrene molecu lar weight, pressure, and isotopic substitution effects on polystyrene + ni troethane systems. A first-order interpretation of phase equilibrium isotop ic substitution effect has also been applied. It combines the simplest form of the Flory-Huggins model with the statistical theory of condensed phase isotope effects. (C) 2000 John Wiley & Sons, Inc.