Liquid crystalline twin epoxy monomers based on azomethine mesogen: synthesis and curing with aromatic diamines

Abstract

Liquid crystalline (LC) epoxy monomers with twin mesogenic azomethines connected by different alkylene spacers (x = 6, 7, 8, and 9) were synthesized to prepare LC thermosets. The epoxy monomers were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC) and polarized microscopy. All four epoxy monomers were found to form nematic phase in the melt, and their melting (T-m) and isotropization temperatures (T-i) as well as corresponding thermodynamic values (Delta H-m, Delta H-i, Delta S-m and Delta S-i) decreased with increase of x in a zig-zag fashion, revealing the even-odd effect. Cure behavior of a stoichiometric mixture of an epoxy monomer with x = 9 and diaminodiphenlysulfone (DDS) was investigated by DSC for specimens cured under various cure conditions. Nematic LC texture for the cured specimen was identified by polarized microscopy and X-ray diffractometry. From the DSC results and microscopic observations, phase diagram of cure time vs. transition temperature was constructed for the epoxy Oc = 9)/DDS system. This diagram shows the changes of T-m, T-i and glass transition temperatures (T-g) as cure proceeds. Regions for nematic LC phase are indicated in the diagram. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.