Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via Na-23 static solid-state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, T(g)). The linewidth decreases with increasing concentration of ions and remains temperature independent below T(g). Below T(g) a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T1 relaxation times also depend on the T(g) of the plasticized systems. Previous Na-23 NMR literature results are reviewed and qualitative models developed to account for the variation in results. (c) 1994 John Wiley & Sons, Inc.