Soluble brominated poly(arylene ether)s containing mono- or dibromotetraphenylphenylene ether and octafluorobiphenylene units were synthesized. The polymers were high molecular weight (weight-average molecular weight = 115,100-191,300; number-average molecular weight = 32,300-34,000) and had high glass-transition temperatures (> 279 degreesC) and decomposition temperatures (> 472 degreesC). The brominated. polymers were phosphonated with diethylphosphite by a palladium-catalyzed reaction. Quantitative phosphonation was possible when 50 mol % of a catalyst based on bromine was used. The diethylphosphonated polymers were dealkylated by a reaction with bromotrimethylsilane in carbon tetrachloride followed by hydrolysis with hydrochloric acid. The polymers with pendant phosphonic acid groups were soluble in polar solvents such as dimethyl sulfoxide and gave flexible and tough films via casting from solution. The polymers were hygroscopic and swelled in water. They did not decompose at temperatures of up to 260 degreesC under a nitrogen atmosphere.