Synthesis of polymers containing benzimidazole ring and investgation of their properties

ABSTRACT In this study, a series of polybenzimidazole derivatives were synthesized. Two different methods have been used in the synthesis, that the first one is solution polycondensation, based on the heating of different aromatic dicarboxylic acid derivatives and 3,3ʹ-diaminobenzidine (DAB) with polyphosphoric acid (PPA) under nitrogene (N2) environment (I. method). By this method a series of polybenzimidazole derivatives were obtained by using eight different aromatic dicarboxylic acids as; isophthalic acid, terephthalic acid, 4,4ʹ-sulfonyldibenzoic acid, 5-hiydroxisophthalic acid, 4,4ʹ-oxybis(benzoic acid), fumaric acid, 2,6-pyridinedicarboxylic acid and 5-tert-butylisophthalic acid. The other method is based on the interaction of dialdehyde-bisulfite adducts and 3,3ʹ-diaminobenzidine (DAB) under N,N-dimethylformamide (DMF) and N2 environment (II. method). All the synthesis were repeated at different temperature and reaction time conditions. The second method is very favored due to preventing the formation of by-products like phosphate esters and requiring extremely simple purification procedure. The structures of synthesized polybenzimidazole derivates were idendified by using IR and 1H-NMR spectroscopic techniques. Thermal properties of polymers were investigated by TGA, DTA and DSC. Synthesized polybenzimidazoles have exceptional thermal stabilities. When heated up to 1000 °C in nitrogen atmosphere they lose only 19-58 % of their mass. Unsubstituted structures like ABPBI and PBI-T have higher thermal stabilities than others. DSC curves of polymers optained at 0-500 ºC region shows that they are mostly amorphous in nature not in crystalline form.