Upper and lower solubility gaps in the system butanone‐acetone‐polystyrene

Depending on the solvent-nonsolvent ratio r of a quasibinary section through the binodial surface of the system butanone-acetone-polystyrene, two different cases for the resulting cloud-point curve (CPC) can be distinguished: (1) separated solubility gaps at relatively high values of r with intermediate temperature region of complete miscibility; (2) overlapping solubility gaps at lower values of r with no temperature of complete miscibility observable. A thermodynamic interpretation is given on the basis of the free-volume concept. The influence of preferential adsorption on the position of the critical points on the CPC is discussed.