Pyridine-Based Polybenzimidazoles PPBI

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. 

Different diacid monomers give different substitution patterns on the pyridine ring. The incorporation of the extra nitrogen in the polymer backbone significantly improves the solubility of the po- 

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Fig. 7.14 Temperature dependence of proton conductivity of a 2,5-PPBI membrane with 20.4 mol H3PO4 doping. Reprinted with permission from Ref. [54] L. Xiao, et al.. Synthesis and characterization of pyridine-based polybenzimidazole for high temperature polymer electrolyte membrane fuel cell application. Fuel Cell, 5, 287-295 (2005). Copyright Wiley-VCH...

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