Broad‐line NMR of aromatic polyamides

Broad‐line NMR spectra have been obtained at 90 MHz in the temperature region 140–530°K for four aromatic polyamides: poly(1,3‐phenylene isophthalamide), poly(1,4‐phenylene terephthalamide), poly(4,4,‐diphenylene terephthalamide), and poly(4,4,‐diphenylene isophthalamide). For the latter three materials, a broad‐line narrowing process occurs in the 210–370°K region. At temperatures above 340°K a complex line shape is observed for all samples. Possible causes of these processes are discussed, and comparison made with dynamic mechanical results.