Synthesis and properties of low dielectric thermotropic liquid crystal polyarylates

In this study, a series of low dielectric liquid crystal polyarylates were designed and synthesized through the acetylation of hydroxyl-containing monomers followed by melt polycondensation with 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), bisphenol A (BPA), bisphenol AF (BPAF), terephthalic acid (TA) acid and 2,3,5,6-tetrafluoroterephthalic acid (TFTA). The molar ratio of HBA to HNA was controlled at 7:3. The structures of the acetylated monomers and polyarylates were characterized using FTIR and NMR spectroscopy, while the elemental composition of the polyarylates was analysed via XPS. WAXD and POM analyses revealed that the prepared polyarylates exhibit a single crystalline form and are capable of forming liquid crystals. DSC and TGA analyses indicated that the incorporation of bisphenol-type monomers (BPA or BPAF) disrupted the regularity of the main chain, leading to a decrease in both the melting point and thermal stability. Finally, the incorporation of bulky monomers (BPA or BPAF) and fluorinated monomers (BPAF and TFTA) into polyarylates increases free volume and decreases polarization, leading to a significant reduction in the dielectric constant.