Comparison of properties of anion conductive Parmax membranes containing imidazolium cation and quaternary ammonium

• We have prepared alkaline PARMAX membrane.
• The alkaline PARMAX 1200 membranes have all carbon–carbon bonds.
• The imidazolium functionalized PARMAX-membrane showed lower water affinity.
• The imidazolium membrane showed better performances than quaternary ammonium.

The hydroxide conductive polyphenylene membranes were synthesized by sequential chloromethylation, substitution with 1-methylimidazole, quaternization with trimethylamine and ion exchange. The alkaline Parmax 1200 membranes have all carbon–carbon bonds without ether linkages, which would be chemically strong. The polyphenylene structure of Parmax provides a stiff and chemical-resistant backbone, whereas the pendant benzoyl group provides sites for chemical modifications. The resulting ionomer membranes showed ion exchange capacities (IECs) of 2.14 mmol g−1 for imidazolium functionalized and 2.36 mmol g−1 for quaternary ammonium. The imidazolium-functionalized copolymer membrane showed lower water affinity and high durability in alkaline condition compared to that of quaternary ammonium. Both of the membranes exhibited hydroxide ion conductivity above 10−2 S cm−1 at room temperature and good chemical stability for up to seven days without significant losses of ion conductivity. The structural properties of the synthesized polymer membrane were investigated by 1H NMR spectroscopy and FT-IR. The membranes were studied by IEC, water uptake, dimensional stability, atomic force microscopy (AFM), and also conductivity assessment.

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