Mesogenic azomethine based diepoxides - monomers for the synthesis of ''liquid crystal'' thermoset networks

A series of azomethine linked di-and triaromatic (diad and triad) mesogenic diepoxides was synthesized. The easy accessibility of the corresponding bisphenols from suitable aminophenols, hydroxybenzaldehydes, terephthalaldehyde, and p-phenylenediamine allows to investigate the influence of substituents and of the arrangement of aromatic rings in the mesogenic core on the thermal and phase behaviour. The unsubstituted triad terephthaldialdehyde based diepoxide forms a smectic mesophase while all the others exert nematic mesophases. Melting points of the unsubstituted triad diepoxides are around 200 degrees C being lowered by the introduction of methyl substituents. The greatest decrease (m.p. about 130 degrees C) is caused by a methyl or a chloro substituent in the central ring, while the clearing point decreases from 260 degrees C for the unsubstituted compounds to app. 230 degrees C.