Lateral substituted liquid crystals containing epoxy groups: Synthesis, mesogens and thermal stability

Abstract

Many epoxy-based liquid crystal monomers were synthesized using protocatechuic acid as the raw material in a series of organic reactions. The effects of various spacer groups in the alkyl and side chains on the properties of liquid crystal monomers are discussed. Fourier-transform infrared and nuclear magnetic resonance were used to determine the molecular structure of the intermediates and liquid crystal monomers. Molecular polarization and configuration obtained using density functional theory calculations can provide theoretical insight. In addition, thermal stability is determined using the combination of differential scanning calorimetry and thermogravimetric analyses. We found that when the lateral epoxy substituent interval increases, the dipole moment decreases and then increases sharply as the growth of the alkyl chain will cause the dipole moment to increase continuously. Although the molecular space effect is not conducive to the formation of a liquid crystal phase, it can reduce the intramolecular energy and help improve thermal stability. As a result, the application of epoxy-containing liquid crystals with lateral substituents at high temperatures is very promising. Simultaneously, our studies provide certain guidelines for structuring liquid crystal monomers.