Abstract
A series of sulfonated polybenzimidazoles (sPBI-SF) were prepared from 2,2-bis(4-carboxyphenyl)hexafluoro- propane (BIS-B-AF), 3,3'-disulfonyl-4,4'-dicarboxyldiphenylsulfone (DSDCDPS) and 3,3'-diaminobenzidine (DAB) at various stoichiometric ratio by solution copolycondensation in poly(phosphoric acid). The chemical structure of the resulting sPBI-SF was confirmed by FTIR and 1 H-NMR. The sPBI-SFs with high molecular-weights (Mn = 39400−65500) were soluble in DMF, DMSO or DMAc. Therefore, they could form some transparent and flexible membranes easily by solution casting. The glass-transition temperatures of the acidic form sPBI-SF were in the range from 222°C to 269°C. The extrapolated onset decomposition temperatures were up to 440°C. The sulfonic groups grafted in the PBI chain had higher initial thermal degradation activation energy and exhibited excellent thermal stability. In addition, these membranes with good mechanical properties presented the swelling degree below 12% and the water uptake about 16%. The proton conductivities of sPBI-SF membranes measured by alternating-current impedance spectroscopy attained to 1.64 × 10 −3 S/cm at 70°C.
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