LIQUID-LIQUID EQUILIBRIA FOR SOLUTIONS OF POLYDISPERSE POLYMERS - CONTINUOUS THERMODYNAMICS FOR THE CLOSE-PACKED LATTICE MODEL

A continuous thermodynamic framework is presented for phase-equilibrium calculations for solutions of polydisperse polymers. An expression for the Helmholtz function of mixing is based on a mathematically simplified Freed model developed previously. A binary mixture requires a size parameter c(r) and an energy parameter epsilon; the former can be temperature dependent, while the latter can depend on temperature and chain length. The functional approach is adopted to define thermodynamic functions and to derive expressions for chemical potentials, spinodals, and critical points. Computation programs are established for cloud-point-curve, shadow-curve, spinodal, and critical-point calculations for polymer solutions where the molecular-mass distribution of the polymer is specified. Examples for phase-equilibrium calculations are shown for cyclohexane-polydisperse polystyrene systems. Satisfactory results indicate the utility of the proposed framework and the computation procedures.