THE SCHOUTEN ET-AL MODEL APPLIED TO POLYMER MIXTURE SOLUTIONS

The lattice-gas model of Schouten, ten Seldam and Trappeniers is exten ded to mixtures of polymers. This model allows for three options on ea ch lattice site: a molecule of type one, a molecule of type two or a h ole. It describes a binary gas-liquid system in the molecular-field ap proximation. Following Flory, the chain length r is introduced as addi tional parameter in order to express the fact that the molecules occup y several lattice sites. In this paper we introduce two Flory chain le ngth parameters (leading to the model of Tompa) in order to describe p olymer mixtures in the presence of their vapor phase. The model can al so be applied to a ternary mixture consisting of two polymers in a com mon solvent. The conditions under which the critical line becomes self -crossing are given and explicit expressions are evaluated for the coo rdinates of this point. The critical line is displayed for a number of such cases in the pressure-temperature projection.