Poly (ethylene oxide) (PEO) and poly [oxymethylene-oligo (oxyethylene)] (PEM) disks are cross-linked by exposure to 254 nm radiation. The rate of formation of cross-links is greatly enhanced by the presence of benzophenone, and an average cross-link density of up to 6 mol % of ethoxy units can be obtained after several hours of irradiation. The highly cross-linked polymers are insoluble in water or organic solvents and show improved physical properties for handling and the formation of free-standing films. Scanning calorimetry and polymer swelling are employed to characterize the polymers, and impedance measurements are reported for sodium salt complexes prepared from the cross-linked polymers. Dynamic modulus measurements show that, upon irradiation, PEO and PEM become cross-linked, elastomeric solids.