The synthesis and characterization of liquid crystalline oligoimides and polyimides

Abstract

There are few examples of thermotropic polyimides reported in the literature. In the present article the authors report the synthesis and characterization of some novel oligoand poly-imides which exhibit mesogenic behaviour. The solution method of Yamazaki et al (Yamazaki N, Higashi F and Kawasaki J 1974 J. Polym. Sci., Polym. Chem. Ed. 12 2149) for the preparation of polyamides was successfully applied to the formation of imide compounds and oligomers. Liquid crystal phases were characterized by optical polarizing microscopy and by differential scanning calorimetry. Two anhydrides were employed which were considered to be suitable building blocks for preparing potentially mesogenic polyimides, namely biphenyl tetracarboxytic dianhydride and pyromellitic dianhydride. Low-molar-mass materials were first synthesized with monoanhydride units to endcap the chains. using nadic and maleic anhydrides. Nematic phases Awere observed in several nadic diimide compounds containing multicyclic cores and in some low-molar-mass diimides and polyimides which contained a biphenylene unit in conjunction with at least one other unsaturated ring When the nadlmldes were heated above 220 C cross-linking and decomposition occurred with loss of mesogenic properties. A fusible polyimide was synthesized containing a flexible chain which exhibited thermotropic behaviour below its decomposition temperature.