Aromatic polyamides. V. Substituent effect on thermal properties

Abstract

Some wholly aromatic polyamides derived from unsubstituted and chloro- and nitro-substituted diamines have been studied from the viewpoint of their thermal stability, thermo-oxidative stability, and thermal transitions. General relationships between thermal stability of a polymer and its chemical structure are described. Decrease in thermal stability of poly(1,3-phenyleneisophthalamide) and poly(1,4-phenyleneterephthalamide) due to substituents has been explained and supported in part by infrared spectral data. The effect of electron-withdrawing substituents such as chloro and nitro in increasing the thermo-oxidative resistance of the polyamides is pointed out. The thermal transitions (Tg and Tm) of these polymers are also reported. All the polyamides exhibit a broad exothermic peak in the 630–700°C temperature range, which probably corresponds to reactions (crosslinking and cyclization) responsible for the high char yield of these systems.