Effect of structure on properties of aromatic polyamides

Polyamides were prepared by reacting 3,5‐diamino benzoic acid (DAB) and/or 1,3‐bis (3‐amino benzamido) benzene (ABB) with terephthaloyl chloride in N, N‐dimethylacetamide. Five polymer samples having different contents of pendant carboxyl groups were prepared by changing the molar ratios of DAB: ABB in the initial monomer feed as 1: 0 (C), 3:1 (C3 A), 1:1 (CA), 1:3 (CA3), and 0:1 (A). The inherent viscosities of the polymers ranged from 0.198 to 0.478 dL/g. DSC and TG studies indicated loss in weight in the temperature range of 80–200°C due to absorbed moisture. The major loss in weight was observed above 400°C. The anaerobic char yield at 800°C depended on the backbone structure and was found to range from 25 to 40%. The resistivities of polyamide film was determined at 110 and 130°C and was found to decrease with an increase in carboxyl content. The dielectric constant of C and C3A polymer films was determined at frequencies ranging from 100 Hz to 1 MHz and at 110 and 130°C and was found to decrease with an increase in frequency or decrease in COOH content in the backbone.