Synthesis and Characterization of New Aromatic Polyamides with N,N′‐Di(4‐n‐alkylphenyl)benzodiimide Unit on the Main Chain

Abstract Summary: New aromatic polyamides containing two n‐alkylphenylimide units fused to the main chain were prepared by the activated polyamidation of 3,6‐di(4‐carboxyphenyl)‐N,N′‐di(4‐n‐alkylphenyl)pyromellitimides (C_mDA, m = 0, 8, 12, 16) with oxy‐4,4′‐dianiline in a mixture of N‐methylpyrrolidone and pyridine (Py) in the presence of triphenyl phosphite and CaCl₂. The imide‐containing dicarboxylic acid monomers were synthesized by the imidization of 3,6‐di(4‐carboxyphenyl)pyromellitic dianhydride with 4‐n‐alkylanilines. The polymers showed both enhanced thermal stability and excellent solubility due to the presence of thermally stable pendent imido groups and internally plasticizing n‐alkyl chains. Their glass transition temperatures were between 225 and 285 °C and decreased with increasing side chain length. Wide‐angle X‐ray diffraction investigations revealed that all the polymers are amorphous and have typical layered structures formed by n‐alkyl side chains. magnified image