Thermodynamics of ternary mixtures of random copolymers

A most general formalism based on the Lattice-Fluid theory of polymer solutions is presented for multicomponent mixtures of random copolymers which may consist of any number of different types of monomers. Particular emphasis is given to the phase stability in these mixtures. Equations for the spinodals and the critical points are presented. The formalism is subsequently applied to a number of interesting cases of ternary (co)polymer mixtures such as: mixtures of three random copolymers with the same monomers A and B but in different proportions (A B + A B + A B) mixtures of homopolymers A_m and B_n with the random copolymer A_i B_j, and mixtures of the random copolymers (A B + A B + A C). The effect of temperature on the phase behavior of these systems is discussed. The agreement of theoretical predictions with available experimental information is satisfactory. Because of its simplicity, the model may be used as a tool for studying multicomponent mixtures exhibiting lower or upper critical solution temperature behavior.