Phase Equilibria of Quasi-Ternary Systems Consisting of Multicomponent Polymers in a Binary Solvent Mixture I. Theoretical Basis and Suitable Choice of Solvent 1 and Solvent 2

A theory of the phase equilibrium of a quasi ternary system consisting multicomponent polymers dissolved in binary solvent mixture was proposed as an extension of that for the quasi-binary system established so far by Kamide et al. In this study, the concentration- and molecular weight-dependences of three χ parameters, χ12, χ13, and χ23 are ignored, where the suffixes 1, 2, and 3 denote solvent 1, a good solvent, solvent 2, a poor solvent, and a polymer, respectively. A computer simulation technique was established on the basis of the theory. From computer experiments on solutions of the polymer with the Schulz–Zimm type molecular weight distribution (the ratio of weight- to number-average molar volume ratio of the polymer to the solvents, Xw/Xn=2.0 and Xw=300), a suitable choice of solvent 1 and solvent 2, yielding the phase separation under given conditions, is discussed. It was found that the polymer volume fraction in a polymer-rich phase vp(2), the partition coefficient σ, the phase volume ratio R and the molecular weight distribution of the polymers in both phases are predominantly controlled by χ23, if χ23<1.0 and are influenced by χ12 and χ23, rather than χ13, if χ23>1.2.