LIQUID-CRYSTALLINE POLYIMIDES .18. THERMOTROPIC POLYIMIDES BASED ON BIPHENYL-3,3',4,4'-TETRACARBOXYLIC ANHYDRIDE

Polyimides were prepared from alpha,omega-bis(4-aminophenoxy)alkanes a nd various aromatic tetracarboxylic anhydrides. Only the polyimides de rived from biphenyl-3,3',4,4'-tetracarboxylic anhydride form a liquid crystalline (LC) melt. In contrast, polyimides of the same dianhydride and alpha,omega-diamino alkanes are crystalline but not thermotropic. The mesogenic and non-mesogenic behaviour of the various poly(ester-i mide)s is discussed on the basis of conformational differences calcula ted by a force-field program. The polyimides were characterized by ele mental analyses, viscosity measurements, infra-red and nuclear magneti c resonance spectroscopies and differential scanning calorimetry measu rements at variable temperatures. The formation of 'batonet' and 'fan- shaped' textures along with the wide-angle X-ray diffraction patterns suggest that the LC polyimides form a smectic A phase in addition to a smectic crystalline phase. Both melting and isotropization temperatur es show an odd-even effect.