Liquid crystalline polyimides: 18. Thermotropic polyimides based on biphenyl-3,3′,4,4′-tetracarboxylic anhydride

Abstract

Polyimides were prepared from α,ω-bis(4-aminophenoxy)alkanes and various aromatic tetracarboxylic anhydrides. Only the polyimides derived from biphenyl-3,3′,4,4′-tetracarboxylic anhydride form a liquid crystalline (LC) melt. In contrast, polyimides of the same dianhydride and α,ω-diamino alkanes are crystalline but not thermotropic. The mesogenic and non-mesogenic behaviour of the various poly(ester—imide)s is discussed on the basis of conformational differences calculated by a force-field program. The polyimides were characterized by elemental analyses, viscosity measurements, infra-red and nuclear magnetic resonance spectroscopies and differential scanning calorimetry measurements 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 temperatures show an odd—even effect.