Effect of molecular weight dependence of the १-parameter on phase equilibrium of multicomponent polymer-single solvent system: Comparison of theory with experiment

Abstract

A generalized theory has been established for describing the phase equilibrium of multicomponent polymer-single solvent system, by introducing the concept of molecular weight-and concentration-dependence of the polymer-solvent thermodynamical interaction parameter १ to the previous theory. In this theory १ is expressed by१=१00(1+k/X)(1+pƃvp)where, १00 is a constant independent of both polymer molecular weight and concentration, X, the molar volume ratio of X-mer to the solvent, vp, the polymer volume fraction, k and p, the molecular weight- and concentration-dependence coefficients, respectively. The mathematical phase separation and fractionation were carried out and the effect of k and p-parameters on the phase separation and fractionation characteristics were studied in detail. The positive molecular weight dependence of १ paramerer (k>0) indices a large polydispersity of the polymers in the polymer-rich and lean-phases, particularly where k>3. In the small ॡp (ॡp= the relative weight fraction of the polymer in a polymer-rich phase to the total polymer dissolved) region, the ratio of the weight- to number-average X, Xw/Xn of the polymer remaining in a polymer-rich.phase is remarkably influenced by both p and k. In a large ॡp region, the polydispersity of the polymer in a polymer-lean phase is predominantly controlled by k. For polystyrene-cyclohexane and polystyrene-methylcyclohexane systems, k, estimated by three methods, was found to lie between 0 and 10. The k values for these systems decrease with increasing temperature. © 1981 The Society of Polymer Science, Japan.