The infrared vibrational spectra of high molecular weight poly(ethylene oxide) and complexes of poly(ethylene oxide) with lithium trifluoromethanesulfonate at two different salt concentrations have been measured from 25 to 150 degrees C. Bands observed in the polymer-salt complexes can be assigned to either the pure crystalline poly(ethylene oxide) phase or a 3:1 polymer-salt compound. The temperature-dependent spectrum is interpreted in terms of the published phase diagram. Cation-anion association is observed at all temperatures. The degree of ionic association in the amorphous region appears to be higher than that observed in the crystalline compound.