Phosphonium-Functionalized Polyethylene: A New Class of Base-Stable Alkaline Anion Exchange Membranes

A tetrakis­(dialkylamino)­phosphonium cation was evaluated as a functional group for alkaline anion exchange membranes (AAEMs). The base stability of [P­(N­(Me)­Cy)4]+ was directly compared to that of [BnNMe3]+ in 1 M NaOD/CD3OD. The high base stability of [P­(N­(Me)­Cy)4]+ relative to [BnNMe3]+ inspired the preparation of AAEM materials composed of phosphonium units attached to polyethylene. The AAEMs (hydroxide conductivity of 22 ± 1 mS cm–1 at 22 °C) were prepared using ring-opening metathesis polymerization, and their stabilities were evaluated in 15 M KOH at 22 °C and in 1 M KOH at 80 °C.