Polybenzimidazole synthesis molecular weights

In order to modify the state-of-the-art PBI stmcture and consequently its properties, significant effort has been focused on the synthesis of pyridine-based polybenzimidazoles. A systematic synthesis with different stractures was initiated to study the effect of the polymer molecular stmcture on the final film properties. The substitution of pyridine dicarboxylic acids (PDA) for the iso-/terephthalic acids is particularly interesting, because it increases the number of basic groups in the polymer backbones. The general stmcture of the series of pyridine-based polybenzimidazole (PPBI) homopolymers from 3,3 -4,4 -tetraaminobiphenyl (TAB) and 2,4-, 2,6-, 2,5- or 3,5-pyridine dicarboxylic acids using the PPA synthetic process is shown in Fig. 6. Monomer purity and accurate stoichiometry are cmcial to obtain high molecular weight polymers. 

G. Qian, B.C. Benicewicz, Synthesis and characterization of high molecular weight hexafluoroisopropylidene containing polybenzimidazole for high-temperature polymer electrolyte membrane fuel cells, J. Polym. Sci. Part A Polym. Chem. 47 (16) (2009) 4064-4073. 

Polymers with heteroaromatic repeat units have been known for many years to exhibit good thermal and oxidative stability. Polybenzimidazoles (1),polybenzothiazoles (2), and polybenzoxa-zoles (3,4) were first reported in the late 50 s and early 60 s and have since been under widespread investigation. Both AA-BB and AB monomer systems have been employed in the synthesis of high molecular weight polymers. (5) The thermal stability in nitrogen atmosphere of the completely aromatic AB polymers prepared from the various 3,4-disubstituted benzoic acids de- creased in the order benzimidazoles>benzothiazole>benzoxazole. 

---