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 degrees C) were prepared using ring-opening metathesis polymerization, and their stabilities were evaluated in 15 M KOH at 22 degrees C and in 1 M KOH at 80 degrees C.