Sulfonated aromatic copoly(ether–amide) membranes: preparation and characterization for possible application in polymer electrolyte membrane fuel cells

Abstract

Sulfonated membranes from highly aromatic copoly(ether–amide)s with sulfonation degrees (SDs) between 20 mol% and 55 mol% were prepared from the combination of diamines, 4,4′-(hexafluoroisopropylidene)-bis-( p-phenyleneoxy)dianiline (HFD), and different molar concentrations of 2,4-diaminobenzenesulfonic acid (DABS) that were reacted with equimolar amounts of isophthalic acid (ISO). The ionic membranes show–SO3H groups in the expected concentrations as assessed by Fourier transform infrared and proton nuclear magnetic resonance. Sulfonated copoly(ether–amide) membranes show the first thermal decomposition at 281°C for the sulfonic moieties and a second thermal loss at 439°C for the rigid nonsulfonated backbone which imparts them their high thermal stability. The ion-exchange capacity and water absorption in the sulfonated copoly(ether–amide)s increase steadily with SD. The copoly(ether–amide) with the larger SD, 55 mol% of DABS, HFD- co-ISO/DABS-55, shows the highest proton conductivity (91 mS cm−1) at 75°C. These results situate HFD- co-ISO/DABS-55 as a possible electrolyte membrane for use in polymer electrolyte membrane fuel cell with high thermal and mechanical stability.