Phase behavior prediction of ternary polymer mixtures

A compressible regular solution free energy model for multicomponent polymer blends is developed and used to obtain spinodal curves for three component systems, employing only pure component properties such as coefficients of thermal expansion, densities, and solubility parameters. The ability to predict, at least qualitatively, the phase behavior of the ternary polymer mixtures tetramethylpolycarbonate (TMPC)/polycarbonate (PC) poly(styrene-r-acrylonitrile) (SAN), and polystyrene (PS)/poly(methyl methacrylate) (PMMA)/poly(styrene-r-methyl methacrylate) (PS-r-PMMA), the polymer-solvent mixture of polystyrene (PS)/poly(methyl methacrylate) (PMMA)/tetrahydrofuran (THF), and the polymer-additive mixture polystyrene (PS)/poly(phenylene oxide) (PPO)/dimethyl phthalate (DMP) is demonstrated through comparison with reported experimental phase diagrams. An expression is derived for the effective interaction energy parameter, chi(eff), relevant to chi(AB) values obtained from scattering measurements; values for chi(eff) are computed and compared with results from experiments. The model provides a first iteration toward a simple and practical predictive tool that can solve common problems in polymer compounding, for example, choosing an effective compatibilizer for an immiscible polymer blend.