Synthesis and characterization of soluble aromatic polyamides derived from 2,5‐bis‐(4‐chloroformylphenyl)—3,4‐diphenylthiophene and aromatic diamines

A new polymer‐forming monomer, 2,5‐bis(4‐carboxyphenyl)—3,4‐diphenylthiophene, was synthesized either by the Friedel—Crafts reaction of tetraphenylthiophene with oxalyl chloride directly, or by the Friedel—Crafts acetylation of tetraphenylthiophene, followed by oxidation. The low temperature solution polycondensation of 2,5‐bis(4‐chloroformylphenyl)—3,4‐diphenylthiophene with various aromatic diamines in N,N‐dimethylacetamide (DMAc) afforded tetraphenylthiophene‐containing aromatic polyamides with inherent viscosities of 0.5–1.0 dL/g. Copolyamides were obtained from a mixture of the diacid chloride and isophthaloyl or terephthaloyl chloride. Except for two polyamides, all the others were readily soluble in amidetype solvents including DMAc, and were cast into transparent and flexible films. These polymers had glass transition at around 300°C. Thermal stability of the polymers was evaluated by thermogravimetry which showed no weight loss below 390°C in both air and nitrogen atmospheres.