The infrared and Raman spectra of P(EO)(n)-LiTFSI complexes (n = 30, 20, 15, 8, 6) have been investigated at 25, 60 and 80 degrees C. The conformational changes of the polymer are discussed with reference to the phase diagram and to cation solvation. A tentative assignment of some characteristic vibrations of the TFSI anion is performed using for comparison the spectra of aqueous solutions in order to analyze conformational isomerism and ion-pairing effects. The latter seem to be negligible for n greater than or equal to 8 in the melt at 80 degrees C.