A new type of fluorine-containing polybenzimidazole, namely poly(2,2'-(2,2'-bis(trifluoromethyl)biphenyl)-5,5'-bibenzimidazole) (BTBP-PBI), was developed as a candidate for proton-conducting membranes in fuel cells. A diacid monomer, 2,2'-bis(trifluoromethyl)-4,4'-biphenyldicarboxylic acid, was synthesized by a new simplified two-step method and polymerized with 3,3',4,4'-tetraaminobiphenyl in phosphorous pentoxide/methanesulfonic acid (PPMA) to achieve high molecular weight polymers (IV=1.60 dL/g). The introduction of 2,2'-bis(trifluoromethyl)biphenyl moieties into the polymer backbone improved polymer solubility in certain polar aprotic solvents (DMAc, DMF, DMSO, etc.). PBI proton conducting membranes were prepared by solution casting and immersion into phosphoric acid with different concentrations. The maximum proton conductivity was approximately 0.019 S/cm at 160 �C with a phosphoric acid doping level of 6.95 mol phosphoric acid per PBI repeat unit.

Synthesis and characterization of a new fluorine-containing polybenzimidazole (PBI) for proton conducting membranes in fuel cells

244th National Meeting (2012)

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