Liquid─liquid phase separation in multicomponent polymer solutions - VIII. Stability limits and consolute states in quasi-ternary mixtures

Abstract
The relations developed previously for the spinodal and the consolute state in quasi-binary polymer solutions (single solvent and polydisperse polymer) are extended so as to cover quasi-ternary systems containing in addition a second polydisperse polymer. The equations obtained also describe polymer compatibility, solvent + non-solvent + polydisperse polymer systems and truly ternary low-molecular-weight mixtures. Some experimental examples relating to the quasi-ternary system diphenylether + linear polyethylene + polypropylene illustrate the usefulness of the equations. The interaction between polyethylene and polypropylene segments differs according as the latter belong to isotactic or atactic sequences. The mutual solvent method for determining polymer compatibility may lead to erroneous conclusions.