Synthesis and characterization of block sulfonated amphiphilic aromatic copolyamides for cation conductive membranes

Preparation of novel amphiphilic block copolyamide membranes synthesized by a polycondensation reaction was investigated as potential materials for polymer electrolyte fuel cells. The block copolyamides were prepared by reacting 5-tert-butylisophthalic acid, 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy)-dianiline (HFD), hydrophobic block, and 4,4′-Diaminobiphenyl-2,2′-disulfonic acid (DFS), hydrophilic block, varying the mole ratio of the hydrophilic/hydrophobic block by controlling the degree of sulfonation. The chemical structure of the amphiphilic block copolymers was confirmed by 1H NMR. Membranes obtained exhibited excellent thermal stability with degradation temperature above 400 °C, and their water uptake was 9.6 to 23 wt% at 30 °C and 10.2–27 wt% at 75 °C. Block copolymer membranes ion exchange capacities (IEC) range from 0.6 to 1.38 (meq g−1), and their proton conductivity strongly depends on the block chain lengths and increase with DFS increase. CP-4 and CP-5 copolyamide membranes presented a remarkable improvement on IEC and water uptake as compared to Nafion 115. Thus, the proper balance between hydrophilic/hydrophobic blocks and DS in the rigid block copolyamides allows fine-tuning the IEC and water absorption in order to modulate an adequate cation conductivity for their application in processes such as proton exchange fuel cell membranes, use as catalytic membranes, sorbents to remove dyes and water treatment.