Synthesis and characterization of novel hyperbranched polybenzimidazoles based on an AB₂ monomer containing four amino groups and one carboxylic group

A new kind of AB 2 monomer, 4‐[2,6‐bis(3,4‐diaminophenyl)pyridin‐4‐yl]benzoic acid, was synthesized, and several hyperbranched polybenzimidazoles (HPBIs) were prepared through self‐polymerization followed by modification reactions with end‐capping reagents such as 4‐methyl benzoic acid and 3‐[3,5‐bis(trifluoromethyl)phenoxy] benzoic acid. The HPBIs had good solubility in strongly aprotic solvents, such as N ‐methyl‐2‐pyrrolidone, N,N ′‐dimethylformamide, N,N ′‐dimethylacetamide, and dimethyl sulfoxide. They also exhibited excellent thermal properties, with glass‐transition temperatures of 318–381 °C and 10% weight loss in the range of 338–674 °C in nitrogen and 329–509 °C in air.