| Thermotropic liquid crystal polymers (TLCPs) have been synthesized from4-hydroxybenzoic acid(HBA) and6-hydroxyl-2-naphthoic acid(HNA), which were used as polycyclic stiff rod-like mesogenic groups, and the obtained liquid crystal polymers were characterized by Fourier transform infrared(FT-IR), elemental analyzer (EA), X-ray diffraction(XRD), thermo-gravimetric analysis(TGA), differential scanning calorimetry (DSC) and polarized light microscopy(POM) etc.The influence of reaction time, types and concentrations of catalyst on the acetylation process of HBA and HNA have been investigated. The results showed that organocatalyst had better catalyst activity. Under the condition of reaction time1.5h and catalyst with the concentration of400ppm, the melting points of the obtained p-acetoxybenzoic acid and6-acetoxy-2-naphthoic were198℃and232℃, respectively. The influence of reaction temperature, types and concentrations of catalyst on the melt polycondensation process were further investigated, the results showed that zinc catalyst had better catalyst activity. Under the condition of reaction temperature320℃and catalyst with the concentration of275ppm, the TLCPs with melt temperature280～29℃could be prepared. TGA results showed that obtained TLCPs had excellent thermal stability, with pyrolysis temperature higher than500℃. XRD and POM results verified that the obtained TLCP was characterized by typical nematic structure.Isothermal crystallization behavior of the TLCP was studied by DSC, double melting peaks were observed. The higher melting peak corresponded with the melting of the crystals formed in the fast crystallization process and it would not change with isothermal crystallization conditions. The lower melting peak was related to the melting of the crystals formed in the slow crystallization process and it strongly depended on the crystallizing condition and thermal history, which would gradually shift towards higher temperature with increasing annealing time and would shift faster with increasing crystallizing temperature due to the perfection of crystal defects. |
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