Liquid crystalline epoxy resin based on biphenyl mesogen: Thermal characterization

An epoxy monomer of 4,4′-diglycidyloxybiphenyl (BP) was synthesized and cured with a tetra-functional amine, sulfanilamide (SAA), to produce novel liquid crystalline epoxy resins (LCERs). The thermal properties, liquid crystalline morphologies, and cure behavior of the monomer were studied using differential scanning calorimetry, wide angle X-ray diffraction, and polarized optical microscopy. The effects of curing condition on the glass transition temperature, coefficient of thermal expansion, and dynamic mechanical properties of the resins were determined through thermomechanical analysis and dynamic mechanical analysis, respectively. The effects of cure condition on the formation of the liquid crystalline phase were also examined. The results show that BP is not a liquid crystalline epoxy monomer and an irreversible crystal transition exists in the temperature range of 120 °C–140 °C. The use of SAA results in the formation of a smectic liquid crystalline phase. Compared to the resins cured into an amorphous network, the LCERs exhibited a polydomain structure with individual liquid crystalline domain distributed in the resin matrix, which results in better thermomechanical properties.