A partially fluorinated polyether ionomer from polycondensation of decafluorobiphenyl with 2,2-bis(4-hydroxyphenyl)-hexafluoropropane, followed by sulphonation with H2SO4 (60% SO3), has been prepared and optimised in terms of molecular weight and sulphonation degree. The partially fluorinated ionomer has been blended with poly(2,2'-mphenylene-5,5'-bibenzimidazole) (PBI), yielding base-acid blends with PBI in excess. The base-acid blend membranes have been characterised in terms of solubility in DMAc, water uptake and oxidative stability by immersion in aqueous 5 wt.-% H2O2 solutions and Fenton's Reagent, respectively. Ionomers with molecular masses of up to 140,000 Da (non-sulphonated) and 178,000 Da (sulphonated) with excellent thermal stabilities and high sulphonation degrees of up to 2.06 SO3H groups per repeat unit have been produced. Their base-excess blend membranes, where the ionomer blend component served as acidic ionomeric cross-linker, showed excellent oxidative stabilities which were better than that of pure PBI and comparable to the oxidative stability of Nafion (R) in Fenton's Reagent.