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

Liquid crystalline (LC) epoxy monomers with twin mesogenic azomethines conn ected by different alkylene spacers (x = 6, 7, 8, and 9) were synthesized t o prepare LC thermosets. The epoxy monomers were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, differential scanni ng calorimetry (DSC) and polarized microscopy. All four epoxy monomers were found to form nematic phase in the melt, and their melting (T-m) and isotr opization 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 s toichiometric mixture of an epoxy monomer with x = 9 and diaminodiphenlysul fone (DDS) was investigated by DSC for specimens cured under various cure c onditions. Nematic LC texture for the cured specimen was identified by pola rized microscopy and X-ray diffractometry. From the DSC results and microsc opic observations, phase diagram of cure time vs. transition temperature wa s constructed for the epoxy Oc = 9)/DDS system. This diagram shows the chan ges of T-m, T-i and glass transition temperatures (T-g) as cure proceeds. R egions for nematic LC phase are indicated in the diagram. (C) 2000 Publishe d by Elsevier Science Ltd. All rights reserved.