Thermal decomposition behavior of main-chain thermotropic liquid crystalline polymers, Vectra A-950, B-950, and Xydar SRT-900

Abstract

ABSTRACT:We investigated the thermal decomposition behavior of three commercially available liquid crystalline polymers (LCPs), Vectra A950, Vectra B950, and Xydar SRT-900. The apparent activation energies (E a ) associated with the thermal degradation processes were determined by the Ozawa and Kissinger methods, using data from dynamic thermogravimetric analysis (TGA) experiments. The magnitudes of the E a for these LCPs follow the order: Xydar Ͼ Vectra A Ͼ Vectra B in both air and N 2 environments. The stability of the samples at the beginning of the degradation processes follows the same order. This order may result from the kink naphthoyl units in Vectra A and a relatively weak bond dissociation energy of C-N in Vectra B. However, at 560°C the weight loss values of these three LCPs in N 2 become close (around 37%). After 600°C, the stability order surprisingly changes to Vectra B950 Ͼ Vectra A950 Ͼ Xydar SRT-900. This suggests that the more stable the sample is at the beginning, the less stable the corresponding residue is. Fourier Transform Infra-red (FTIR) spectra imply that random chain scission and hydrogen abstraction are the degradation mechanisms in N 2 atmosphere and the bands of CAO stretching for all 3 LCPs decrease after 560°C, indicating the finish of the ester bond rupture process. Further increasing temperature mainly results in carbonization. For all three LCPs, CO 2 is the dominant degradation product during the entire testing periods in both N 2 and air environments and the change of CO 2 amount is consistent with the degradation rate. Residues after TGA experiments in N 2 were analyzed and found to have a relatively high percentage of oxygen element, indicating the formations of ether and ketone structures during the thermal degradation of these three LCPs. Forty-seven percent of the nitrogen element remaining in the case of Vectra B950 indicates the formation of the structures containing nitrogen.

Thermal decomposition behavior and durability evaluation of thermotropic liquid crystalline polymers

“…This result corresponds with the findings of Jin et al. 20 The average bond dissociation energy of C-N is lower than that of C-O, and the naphthoyl structure makes the HNA/HAA/TA copolyester less thermally stable than the HBA/HNA copolyester. Furthermore, because the HBA/PET copolyester is a semi-rigid, rod-like aromatic polyester, it is less thermally stable than the wholly aromatic polyester.…”

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

“…One was the Kissinger (21) method, the other was the Ozawa-Flynn method, named after both Ozawa (19) and Flynn (20) because of their independent work. The theoretical backgrounds of the two methods have been explained elsewhere (12).…”

Synthesis, characterization and thermal decomposition kinetics of poly(2-imidazolidinthione-formaldehyde)

“…The second major degradation in helium is characterized by a weight loss between 300-400 °C, which can be attributed to the evolution of most of the volatiles resulting from the depolymerization/decomposition of poly-IF and finally 400-800 °C show char-forming reaction in the solid state whereas in air the second degradation governed by various oxidation reactions [22]. A weak DTG peak in air indicates the third stage of degradation due to charring process occurring at a relatively high temperature [23,24].…”