Characterization of abnormal structures in thermally treated liquid crystalline aromatic polyesters by pyrolysis-gas chromatography in the presence of organic alkali

The abnormal structures formed in a liquid crystalline aromatic polyester (LCP), 4-hydroxybenzoic acid (HBA)/2-hydroxy-6-naphthoic acid (HNA) copolymer, thermally treated up to 500 degreesC were characterized in detail by pyrolysis-gas chromatography in the presence of an organic alkali, tetramethylammonium hydroxide (TMAH). On the pyrograms of the thermally treated LCP samples observed at the reactive pyrolysis temperature of 300 degreesC, the peaks reflecting the abnormal structures such as the branching and condensed structures were observed together with those of the dimethyl derivatives of HBA and HNA reflecting the main chain and those originated from the end groups. Generally, the yields of all the characteristic products reflecting the abnormal structures increased with the rise of the thermal treatment temperature. Furthermore, it was confirmed that the condensation reactions might occur in preference to the branching formations in the LCP sample at higher treatment temperature around 500 degreesC. Finally, it was suggested from the average molar composition between HBA and HNA units observed in the specific products that the preferential elimination of the HBA unit in the polymer chain might take place during the thermal treatment of the LCP sample, while the abnormal structures such as the branching and the condensed structures were also confirmed to occur preferentially at the HNA units rather than the HBA ones. (C) 2002 Elsevier Science Ltd. All rights reserved.