Terpolymer-Based Anion Exchange Membranes: Effect of Pendent Hexyl Groups on Membranes Properties

In the pursuit of better functioning anion exchange membranes, pendent hexyl side chains were introduced onto terpolymers composed of perfluorohexylene (PHB), hexafluoroisopylidene (BAF), and quaternized fluorene groups. The resulting QBPHBA membranes exhibited similar water absorbability and gas (hydrogen and oxygen) permeability to those of the previous terpolymer-based AEMs without aliphatic side chains. In contrast, hexyl groups contributed to improving the OH-conductivity. The highest OH-conductivity (163 mS cm-1at 80 °C) was achieved with the QBPHBA membrane with 2.49 meq. g-1of ion exchange capacity (IEC). Furthermore, mechanical properties were also improved; the strain at break increased from 12% (BAF-containing copolymer membrane) to 284%. The terpolymer composition for the best-balanced properties turned out to be 17 mol% of the side-chain substituted PHB groups, in particular, with high IEC (2.49 meq. g-1).We designed and synthesized a series of partially-fluorinated terpolymers containing hexafluoroisopropylidene (BAF), perfluoroalkyl with hexyl side chain (PHB), and ammonium-functionalized fluorene (AF) groups for multi-functional ionic membranes. Hydrophobic composition and hexyl side chains influenced membrane properties, especially mechanical properties. High-performance anion-conductive membrane was realized by optimizing the hydrophobic composition and enhanced ion exchange capacity.