NONEQUILIBRIUM LIQUID LIQUID-PHASE SEPARATION IN CRYSTALLIZABLE POLYMER-SOLUTIONS

The relation between liquid-liquid phase separation and crystallization was investigated by applying a systematic change in the interaction in isotactic polypropylene (i-PP) solutions with a proper selection of solvents. A series of dialkyl phthalates, with a different number of carbon atoms in the alkyl chain, was used to control the solvent quality. The liquid-liquid phase separation temperature decreased remarkably when the interaction became favorable while the melting point curve remained constant. As the result of this systematic change in polymer-solvent interaction, the liquid-liquid phase separation was observed under nonequilibrium conditions below the equilibrium liquid-solid transition. Liquid-liquid phase separation of the i-PP solutions with strong interaction was probed by using atactic polypropylene (a-PP) in the same solvent systems. The results indicate that although the liquid-liquid phase separation of i-PP solutions with the strong interactions cannot be observed in situ due to the competing crystallization, liquid demixing can occur at a low temperature during rapid quenching. An additional feature oberved under the nonequilibrium conditions was liquid-liquid phase separation induced by crystallization in concentration and temperature regions outside the binodal curve. In polydisperse samples, fractionation during liquid-liquid phase separation resulted in bimodal behavior of the liquid-liquid transition and in deviation of melting points in the biphasic region.