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

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.