Sulfonated aromatic copoly(ether–amide) membranes II: Influence of chain length and sulfonic groups concentration on membrane ionic conductivity and mechanical properties

Several aromatic sulfonated copoly(ether-amide)s, based on the aromatic diamines 4,4-(hexafluoroisopropylidene)bis(p-phenyleneoxy)-dianiline (HFD) and 2,4-diaminobenzensulfonic acid (DABS) and 4,4-oxybis(benzoic acid) (OBA), were synthesized through a polycondensation reaction. The sulfonation degree was controlled by introducing different concentrations of 2,4-DABS from 40 mol% up to 80 mol%. Proton nuclear magnetic resonance validated the expected concentrations of sulfonic acid groups in the sulfonated aromatic copoly(ether-amide)s. Thermal decomposition of sulfonic groups was found to initiate at 280 degrees C, while main chain decomposition initiates at 410 degrees C. Proton conductivity between 30 degrees C and 75 degrees C was 19.0 and 45.0 mS/cm, respectively, for the copolymer with the highest concentration of sulfonic groups (-SO3H). Comparison with structurally similar sulfonated copolyamides and copoly(ether-amide)s indicates that these new sulfonated copoly(ether-amide)s based on 4,4-OBA show improved mechanical properties, but a decrease in ion exchange capacity and proton conductivity.