A new series of poly(arylene ether) copolymers containing pendant poly(ethylene oxide) (PEO) groups are presented. Copolymers were prepared via potassium carbonate mediated direct aromatic nucleophilic substitution polycondensation of dihydroxy end-functionalized PEO, bisphenol A, and 4-fluorophenyl sulfone or decafluorobiphenyl. The obtained copolymers (PAE-g-PEO and FPAE-g-PEO) showed excellent film-forming properties, high thermal stability, and glass transition temperatures up to 110 degrees C. This polymeric structure resulted in amorphous copolymers in most cases, a main requirement for high ionic conductivity of solid polymer electrolytes. The incorporation of the hydrophilic PEO units in the hydrophobic aromatic polyether backbone improved the water uptake ability, producing in some cases water-soluble polymers. Blends of sulfonated polysulfone and water-soluble poly(ether sulfone) containing PEO side chains (PES-g-PEO) were also studied in terms of fuel cell relevant parameters like thermal behavior, water uptake, morphology, and ionic conductivity. Flexible membranes prepared by casting showed high glass transition temperatures up to 215 degrees C. SEM images of blend membranes revealed the existence of hydrophilic spherical domains with average sizes of 50-100 nm. The water uptake ability of the membranes increased with increasing PES-g-PEO content and temperature, and proton conductivity values were measured in the range of 10(-3) S/cm at room temperature and relative humidity 65%. The above results demonstrate that these materials could be applied as polymer electrolytes in proton exchange membrane fuel cells (PEMFC).