Studies on the phase transition and thermal stability of Xydar and Zenite series liquid crystalline polymers

Four commercially available main-chain LCPs, Xydar and Zenite series, are characterized by FTIR spectroscopy, DSC, polarized light microscopy (PLM), TGA, TGA-FTIR, and elemental analysis. The FTIR spectrum of Zenite 8000B is found to be more similar to that of Vectra A950 than those of the other three LCPs. Xydar SRT900 and 1000 have almost the same FTIR spectra. Zenite LCPs have broader crystal-mesophase transition (T_CM) and less clear liquid crystalline textures at T_CM than those of Xydar LCPs. Xydar SRT1000 and Zenite 8000B have lower T_CM than Xydar SRT900 and Zenite 6000, respectively. For all the four LCPs, the glass transitions can not be easily observed by DSC without the aid of annealing and the isotropic phase does not appear before thermal degradation. Xydar SRT1000 and Zenite 8000B have lower thermal stabilities as well as lower T_CM(S) than Xydar SRT900 and Zenite 6000, respectively. It is interesting to find that E_a (Apparent activation energy of thermal degradation) curves of Xydar SRT900 and SRT1000 have the similar shapes as those of Zenite 6000 and 8000B, respectively. For the first time, we have found that there is a minor degradation maximum for Zenite 8000 at about 2.5% weight loss in N₂. For all the four LCPs, the E_a values in an air atmosphere begin to decrease at a temperature close to the deflection points on the first derivative curves. The first stage of the thermal degradation in an air atmosphere has similar mechanisms as that in N₂.