Conductivities greater than or equal to 10(-8) S cm(-1) at T-g are reported in polymer electrolytes based on lithium triflate salt and a series of polymers whose T-g is greater than 90 degrees C. The highest conductivities were observed for poly(acrylonitrile) based systems with salt concentrations greater than 60 wt.%. The conductivity in all cases investigated increases with increasing salt concentration. H-1-NMR T-2 relaxation measurements suggest that T-g decreases with increasing salt content and confirms that these materials are glassy at room temperature and hence that the conductivity is significantly decoupled from the structural relaxations. It appears that the nature of the polymer is important in determining the level of ionic conductivity, possibly due to differences in polymer coordinating ability or differences in T-g. Polymer-in-salt mixtures based on a tetra-alkyl ammonium imide molten salt and several high T-g polymers are also reported. The conductivities of these mixtures appear to be independent of the polymer type. (C) 2000 Elsevier Science Ltd. All rights reserved.