ORDERING OF LIQUID-CRYSTALLINE SOLUTIONS OF RIGID-ROD ARAMIDS USING MECHANICAL SHEARING AND ELECTRIC-FIELD POLING

2',5'-Diamino-4-(dimethylamino)-4'-nitrostilbene was polymerized with terephthaloyl dichloride and 2,6-difluoroterephthaloyl dichloride in a low-temperature solution polycondensation to give two novel, fully ar omatic rigid-rod polyamides. Nematic solutions of these polymers were processed into fibers and films that were characterized by wide-angle X-ray diffraction measurements. A post-spin annealing process was empl oyed to enhance the chain orientation in the fibers. The dominating cr ystal structure was found to be similar to ''modification II'' of the fibers from poly(p-phenyleneterephthalamide), but the fibers do not su ffer a comparable structural transformation upon heat treatment. A cor ona-discharge poling process gave rise to a remarkable gain in average chain orientation in the films. Again the crystal structure was found to be similar to ''modification II''. The aramids investigated in thi s work represent a new approach to the design of liquid-crystalline ri gid-rod polymers, where different mechanisms of orientation can be com bined. In the nematic phase, the rigid-rod molecules form highly orien ted domains that can be oriented using mechanical processes such as sh earing. In addition the stilbene units that are fixed in the polymer b ackbone with their dipole moments oriented transverse to the main chai n can be oriented in an electric field. The combination of both orient ation mechanisms seems to cause a synergistic effect, probably since e ach affects different levels of the polymer microstructure in the soli d.