Synthesis and characterization of sulfonated polyimide polymer electrolyte membranes

Several copolyimides have been synthesized with different combinations of comonomers in order to study the relationship between conductivity and water insolubility. m-Phenylenediamine (m-PDA), an angled comonomer, was introduced into the polymer backbone to increase water absorption, and resulted in higher proton conductivity. 2,2-bis(trifluoromethyl)benzidine (TFMB) was used as the comonomer to promote water insolubility. There is a good correlation between the water uptake and conductivity of the polyimides. The copolyimides that had high water uptake also generated high proton conductivity. Those polyimides had good mechanical properties. The copolyimides that have 27 mol% of TFMB and 9 mol% of m-PDA have reasonable conductivities and are insoluble in water at 90degreesC, even though they have lower conductivities than those of the homopolymer.