Abstract:

Introduction of meta-aramid units into poly（p-phenylene terephthalamide） （PPTA） allows regulation of its crystallization and processing properties， therefore， quantitation of the meta units in PPTA is of practical importance. In this paper， blends of PPTA with poly（m-phenylene isophthalamide） （PMIA） were prepared and analyzed by infrared and Raman spectroscopies. In the infrared spectra， it was found that the absorption band at 659 cm^-1 attributed to C—H in-plane wagging vibration of the m-disubstituted benzene ring can be utilized for quantitative analysis of PMIA， the intensity of which exhibited good linear relationship with PMIA content， allowing detection of meta units of 2.0%（mass percent） and above. In the Raman spectra of the blends， the breathing vibration of the meta-disubstituted benzene ring at 1002 cm^-1 characteristic of PMIA was found to exhibit an intensity proportional to its content with excellent linear correlation， which enabled detection of meta units of a low content of 0.25%（mass percent）. In conclusion， the Raman method is more accurate with a lower detection limit， and therefore is superior to the IR method for quantitation of meta units in para-aramids.

Key words: Aramids, Quantitation, Raman spectroscopy, Infrared spectroscopy