Preparation of polyamides containing tetraphenyl-imidazolyl units from 1,2-bis(4-iodophenyl)-4,5-diphenyl-1H-imidazole via C–N coupling reaction and their characterization

A new aromatic diiodide compound, 1,2-bis(4-iodophenyl)-4,5-diphenyl-1H-imidazole was synthesized by a one-pot sequential diazotization-iodination reaction using 1,2-bis(4-aminophenyl)-4,5-diphenyl-1H-imidazole as the starting material in a KI/NaNO2/p-TsOH/CH3CN system at room temperature. A series of aromatic polyamides (PAs) containing tetraphenyl-imidazolyl units were prepared in good yields via a Pd(PPh3)2Cl2 catalyzed carbonylation polymerization of this diiodide, diamines and carbon monoxide in DMAc in the presence of PPh3 and 1,8-diazabicyclo[5,4,0]-7-undecene. These new PAs with inherent viscosities of 0.63–0.72 dL/g were amorphous and easily soluble in amide type aprotic solvents such as N-methyl-2-pyrrolidone (NMP), N,N’-dimethylacetamide (DMAc), N,N′-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and pyridine at room temperature. Thermal analyses data of the resulting PAs up to 800 °C in nitrogen showed their high thermal behavior with 5% weight loss temperature of 425–517 °C and char yield of 43–58%. The present PAs could be classified as “self-extinguishing polymers” based on the limiting oxygen index in the 34.7–40.7 range. Such attractive properties make these PAs promising as a new type of processable heat-resistant polymer materials.