Novel polyimides containing benzimidazole for temperature proton exchange membrane fuel

A novel asymmetric diamine, 2-benzimidazolyl-4,4'-oxydianiline (6), containing a bulky benzimidazole substituent and flexible ether linkage was synthesized successfully. Novel polyimides PI 8a-c were prepared by two-step polycondensation of diamine (6) and three commercially available aromatic dianhydrides. PI 8a-c showed excellent thermal stability with glass transition temperatures of 277 to 342 degrees C and 5% weight loss temperatures 01 528-573 degrees C in nitrogen. PI 8a-c with high molecular weights also exhibited good mechanical properties in both their dry and phosphoric acid doped states. They demonstrated better oxidative stability in Fenton Lest than m-PBI. Their proton conductivity ranged from 0.017 to 0.043 S cm(-1) at 160 degrees C under anhydrous conditions with phosphoric acid (PA) uptakes from 89 to 116%. PI 8b containing hydrophobic trifluoromethyl groups had the highest proton conductivity of 0.043 S cm with the lowest PA uptake (89%). In the fuel cell test performed with H-2/O-2 under anhydrous conditions at 160 degrees C, the peak power density of PI 8b with a PA uptake of 89% was 567 mW cm(-2), which was higher than that of m-PBI (423 mW cm(-2)) with a PA uptake of 221%. The higher proton conductivity and peak power density of PI 8b were attributed to the hydrophobic trifluoromethyl groups that might facilitate the formation of the ionic channels at lower PA uptakes. (C) 2015 Elsevier By. All rights reserved,