Polybenzimidazoles were synthesized from 3, 3', 4, 4'-tetraminobiphenyl
(diaminobenzidine, or DAB) with orthoesters, carboxylic acid derivatives (an ester and
an acid) and with m-benzenedialdehyde. The products were of low molecular weight,
as evidenced by low inherent viscosity, except in the case of the dialdehyde plus DAB.
The product of that...