Synthesis and Crosslinking of a Series of Dimeric Liquid Crystalline Epoxy Resins Containing Imine Mesogens

Abstract

Eight aromatic imine liquid crystalline (LC) diepoxides with dimeric architecture from readily available commercial reagents were synthesized and characterized by spectroscopic techniques. We characterized their liquid crystalline mesophases by differential scanning calorimetry (DSC), hot-stage polarized-light optical microscopy (POM) and wide-angle X-ray diffraction (WAXS). The mesomorphism of the products was related to their structure, which varies in the length of the central spacer. Odd-membered spacer mesogens lead to the formation of smectic C mesophases, whereas even-membered samples of this series lead to the formation of smectic A and/or nematic mesophases. By relating the calculated molecular parameters to the layer spacings obtained by WAXS, we deduced the organization of the mesogens in the smectic phases, since the dimeric compounds present a variety of possible arrangements. Liquid crystal thermosets (LCTs) were obtained from these monomers by isothermal curing with equimolar amounts of 2,4-diaminotoluene (DAT). The curing process was studied by calorimetry and their thermal stability was evaluated by thermogravimetry (TGA). Most monomers produced nematic-like networks, but in one case a smectic C mesophase was also locked.