Gas chromatographic and capillary gas chromatographic-mass spectrometric analysis of thermal decomposition products of liquid crystal polymers

Abstract

The thermal decomposition products of a series of liquid crystalline poly(azomethine ester)s and their model compounds of low molecular mass were investigated. The volatile gaseous products evolved in Curie-point pyrolysis at 500° C were analysed using a Porapak S column and a thermal conductivity detector of high sensitivity. The less volatile aliphatic and aromatic products evolved in flash pyrolysis at 500° C were analysed by gas chromatography-mass spectrometry. The decomposition of the ester group resulted in carbon monoxide and carbon dioxide. The polymers containing methoxy substituent groups gave higher amounts of carbon monoxide and methane, indicating cleavage of the methoxy group. The phenyl undecanoate moiety of the polymers resulted in phenol and p-cresol. In contrast, the phenyl hexanoate sequence of the model compounds appeared in the pyrolysate as p-hexenylphenol and p-hexenylphenyl hexanoate, which were attributed to intra/intermolecular reactions of the pentyl radicals formed through decarbonylation of the hexanoate ester. In general, the formation of nitrogen-containing compounds was found to be negligible. The infrared spectroscopic analysis of the residue left after pyrolysis at 400 and 500° C indicated that the azomethine moiety had altered but the nitrogen remained mostly in the char.