GEL/SOL AND LIQUID-CRYSTALLINE TRANSITIONS IN SOLUTION OF A RIGID-ROD POLYIMIDE

Hot solutions in m-cresol of the polyimide prepared from 3,6-diphenylpyromellitic dianhydride and 2,2'-bis (trifluoromethyl)-4,4'-diaminobiphenyl exhibit during cooling for concentrations greater than 1% a mechanical sol/gel transition possibly through a nucleation-free, liquid-liquid phase separation, followed by the development of lyotropic, liquid-crystalline spherulites through a nucleation and growth mechanism. Both processes are thermally reversible. The kinetics of the liquid crystal/isotropic solution transition is studied