The polymer electrolyte system La(CF3SO3)(3)PEOn has been examined with differential scanning calorimetry (DSC) and NMR spectroscopy in order to analyze some of its structural and dynamic properties. Above the glass transition temperature, the fully amorphous samples with n less than or equal to 16 give rise to H-1 NMR spectra that consist of two components of different width, corresponding to different dynamic properties of cation-coordinated and noncoordinated polymer chain segments. For n = 9, almost all chain segments interact with the cation, resulting in an ether oxygen coordination number close to 9. This conclusion is supported by DSC measurements. For the more dilute samples with n = 12 and n = 16, the NMR data result in a strongly temperature dependent effective coordination number. The changes in coordination number with temperature are explained in terms of polymer chain conformation, on the basis of an earlier IR spectroscopy study. As a consequence of the La3+ ion’s strong ability to coordinate the polymer chain, the chain mobility is severely restricted and the ionic conductivity low, even in totally amorphous samples.