Synthesis and characterization of liquid crystalline epoxy resins to study the effect of mesogenic length on the physical properties

Two liquid crystalline epoxy (LCE) resins containing different mesogenic lengths were synthesized and cured with two different aromatic diamine curing agents, diaminodiphenylsulfone (DDS) and diaminodiphenylmethane (DDM) to prepare high performance LCE networks. The spectroscopic structures of LCE resins were identified by Fourier transform infrared (FT-IR) spectroscopy, Proton nuclear magnetic resonance (¹H-NMR) spectroscopy, mass (MS) spectroscopy, and the formation of nematic and smectic liquid crystalline phase were observed by differential scanning calorimetry (DSC), and polarized optical microscopy (POM). The curing reactions and liquid crystalline textures of the LCE resins were also studied by DSC and POM on the process of curing. The thermal and mechanical properties were investigated for the cured LCE resins with different mesogenic lengths. These results show that the LCE cross-linked networks with long mesogenic group exhibited much higher storage modulus, glass transition temperature, thermal conductivity, thermal stability, and dimensional stability both in the regions of glassy and rubbery states. In addition, both LCE resins have superior thermal and mechanical properties compared to those of the commonly used epoxy resin.