PHASE-EQUILIBRIUM STUDY OF THE TERNARY-SYSTEM COMPOSED OF 2 MONODISPERSE POLYSTYRENES AND CYCLOHEXANE

In the reported experiments, mixtures of two ″monodisperse″ samples of polystyrene (M//1 equals 4. 53 multiplied by 10**4, M//2 equals 10. 3 multiplied by 10**4; M//w/M//n less than 1. 01) in cyclohexane were allowed to separate into two phases at different polymer concentrations and temperatures. The compositions in the two phases were measured by gel permeation chromatography, and used to determine isothermal binodals. From the binodal data the critical temperature and concentration were estimated as functions of the composition of the polymer mixture, and the separation factor sigma for each polymer component was calculated. In contrast with typical results in the literature, sigma was almost independent of molecular weight of the polymer. It is shown by deriving a general expression for sigma that theoretical prediction of sigma requires accurate knowledge about the Flory-Huggins interaction parameter as a function of the concentrations of individual polymer components.