Synthesis of polybenzimidazoles from monomers containing flexible linkages

Abstract

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 system had inherent viscosities in the range of 0.7 dL/g, and formed strong, flexible films. Based on these results, a dialdehyde monomer was made from naphthalene disulfonyl dihalides and p-hydroxybenzaldehyde. In addition to the aldehyde end groups, this monomer contained internal sulfonate linkages, which were intended to increase the flexibility of the target polybenzimidazole which resulted when it was condensed with DAB. These polymerizations yielded poor poly-benzimidazoles, probably due to lack of purity of the new dialdehyde monomer. Another type of monomer was also produced by condensing DAB with p-hydroxybenzaldehyde. The resultant bibenzimidazole unit with two phenolic end groups shows promise for use in nucleophilic aromatic substitution polymerizations.