EFFECTS OF COMPRESSED CARBON-DIOXIDE ON THE PHASE-EQUILIBRIUM AND MOLECULAR ORDER OF A LYOTROPIC POLYAMIDE SOLUTION

The effects of compressed carbon dioxide at slightly subcritical tempe ratures on solutions of a chloro-substituted, para-linked aromatic pol yamide (PPTA-Cl) in dimethylacetamide were investigated by depolarized light spectroscopy. Pressurization of isotropic solutions resulted in polymer precipitation at a sharply defined pressure. Pressurization o f nematic solutions resulted in an increase in the intensity of scatte red light with no evidence of precipitation. A plausible interpretatio n of this observation is the occurrence of liquid-liquid phase separat ion into polymer-rich (anisotropic) and polymer-lean (isotropic) phase s induced by the compressed carbon dioxide. The results suggest that c ompressed, near-critical antisolvents can be used to control the degre e of anisotropy in liquid-crystalline polymeric systems.