Nonequilibrium liquid-liquid phase separation in crystallizable polymer solutions (original) (raw)

The relation between liquid-liquid phase separation and crystallization was investigated by applying a systematic change in the interaction in isotactic polypropylene (i-PPI 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. symbol alkylgroup M, preaeure(mmHg)4 supplier bp ("C)/ C, butyl 278 3401760 Aldrich C6 hexyl 334 21015 Exxon C7 heptyl 362 22015 Euon CS OCtYl 391 23015 Euon cab 2-ethylhexyl 391 3901760 Aldrich CS nonyl 419 25115 Euon Cio d w l 447 25615 Euon 4 From the information provided by the suppliers.