Synthesis and Characterization of 4‐Vinylimidazolium/Styrene‐Cografted Anion‐Conducting Electrolyte Membranes

The β‐hydrogen‐free imidazole monomer, 2‐methyl‐N‐methyl‐4(5)‐vinylimidazole (2M4VIm), is synthesized to prepare anion exchange membranes (AEMs). The radiation‐induced graft polymerization of 2M4VIm and styrene is performed in poly(ethylene‐co‐tetrafluoroethylene), followed by N‐alkylation and ion exchange reactions to prepare 4‐vinylimidazolium‐containing AEM (2M4VIm/St‐AEM). AEMs that have a 6/4 2M4VIm/St molar ratio and 1.7 mmol g−1 ion exchange capacity (IEC) result in 75 mS cm−1 conductivity and 60% water uptake at room temperature in water, demonstrating enhanced values compared to previously reported 2‐methyl‐N‐vinylimidazolium‐containing AEMs (2MNVIm/St‐AEM) that have a similar comonomer ratio and IEC. The small‐angle neutron scattering measurements of dry and swollen 2M4VIm/St‐AEM reveal hydrophilic/hydrophobic two‐phase separation, as observed for 2MNVIm/St‐AEM with a similar Im/St composition. 2M4VIm/St‐AEMs exhibit higher alkaline stability in 1 m KOH at 80 °C at an early stage owing to the suppression of imidazolium β‐elimination but lower long‐term stability than that of 2MNVIm/St‐AEM due to the ring‐opening reaction of the imidazolium group due to its outward orientation from the graft main chain. The β‐hydrogen‐free 4‐vinylimidazolium and styrene‐cografted anion conducting membranes (AEMs) are successfully prepared by radiation‐induced graft polymerization and N‐alkylation. Compared with the corresponding N‐vinylimidazolium AEM, the 4‐vinylimidazolium AEM exhibits higher conductivity and higher alkaline stability at an early stage owing to the suppression of imidazolium β‐elimination but lower long‐term stability due to the ring‐opening reaction of the imidazolium group.