A high-molecular-weight fluorinated poly(aryl ether) with a 4-bromophenyl pendant group has been synthesized based on a bromo-bisphenol. A phosphonic acid derivative is readily prepared from this in high conversion yield. The phosphonated polymer possesses excellent thermal, oxidative, and dimensional stability, low methanol permeability, and reasonable proton conductivity, and may be a candidate polymeric electrolyte membrane for fuel cell applications.