关键词: continuous thermodynamics;polymer solution;polydispersity;lattice-fluid model;cloud-point curve;shadow curve;spinodal;upper-critical-solution temperatures;lower-critical-solution temperature., upper-critical-solution temperatures, lower-critical-solution temperature.

Abstract: Using lattice-fluid model,a continuous thermodynamic framework is presented forphase-equilibrium calculations for binary solutions with a polydisperse polymer solute.A two-stepprocess is deslgned to form a real polymer solution containing a solvent and a polydisperse polymersolute occupying a volume at fixed temperature and pressure.In the first step,close-packed purecomponents including solvent and polymers with different molar masses or different chain lengths aremixed to form a closed-packed polymer solution.In the second step,the close-packed mixture,con-sidered to be a pseudo-pure substance is mixed with holes to form a real polymer solution with a vol-ume dependent on temperature and pressure.Revised Freed’s model developed previously is adoptedfor both steps.Besides pure-component parameters,a binary size parameter c_r and a binary energyparameter ε_(12) are used.They are all temperature dependent.The discrete-multicomponent approach isadopted to derive expressions for chemical potentials,spinodals and critical points.The continuousdistribution function is then used in calculations of moments occurring in those expressions.Computation procedures are established for cloud-point-curve,shadow-curve,spinodal and criti-cal-point calculations using standard distribution or arhitrary distribution on molar mass or on chainlength.Illustrative examples are also presented.

Key words: continuous thermodynamics, polymer solution, polydispersity, lattice-fluid model, cloud-point curve, shadow curve