THERMODYNAMICS OF POLYMER-SOLUTIONS AND MIXTURES

A review is provided for the present situation concerning theoretical predictions of phase equilibria in polymer solutions. Special attention is paid to ternary systems consisting of two polymers and one solvent or of one polymer and two solvents. A survey of the experimental data on various ternary systems has revealed that phase separation behavior is significantly and subtly affected by three interaction parameters for each pair of components, and that a quantitative description of the phase relations requires a very accurate expression of the interaction parameters as a function of temperature, composition of the system, molecular weight of the polymer, and so forth. One promising approach has recently been developed and is based on classical thermodynamic relations of general validity. This is described in some detail. It will be shown that this approach is useful for the characterization of thermodynamic properties of a given ternary system as a function of all relevant variables, and that it allows for the prediction of phase equilibrium behavior with sufficient accuracy.