FTIR spectroscopic investigations coupled with ionic conductivity and viscosity measurements on lithium imide (LiN(CF3SO2) 2)-propylene carbonate (PC)-poly(methyl methacrylate) (PMMA) based liquid and gel electrolytes over a wide range of salt (0.025-3 M) and polymer (5-25 wt.%) concentration range furnish a novel insight into the ion-ion and ion-solvent-polymer interactions. Vibrational spectral data for LiN(CF 3SO2)2-PC electrolytes reveal that the solvation of lithium ions manifests from Li+-O=C and Li +-O (ring oxygens) interactions as the νs(CO), the ring breathing and the δ(CH) modes of the pentagonal solvent ring are strongly perturbed for all salt concentrations. The split of the ν(SO 2) mode (that appears at 1355cm-1 for the "free imide ion") into two components at 1337 and 1359cm-1 confirms the existence of contact ion-pairs possessing two different stable optimized geometries wherein the Li+ ion coordinates in a bidentate fashion in liquid and gel electrolytes of 3 M LiN(CF3SO2) 2-PC strength. Perturbations observed for the νa(SNS) and νs(SNS) modes of the imide ion and the symmetric ring deformation mode of PC confirms the presence of ion-pairs in both 2 and 3 M electrolytes. Incorporation of even upto 25 wt.% of PMMA in a solution of LiN(CF3SO2)2-PC of 3M strength results in an insignificant conductivity decline (as σ25 > 10 -3S cm-1) which is simultaneously accompanied by a massive increase in its macroscopic viscosity (as η25 > 108 cSt). Gels containing 25 wt.% of PMMA exhibit a complex pattern of Li+-PMMA interactions through the carbonyl oxygen of its ester group which is evidenced from the perturbations observed for the ν s(CO) mode of PMMA. Ionic conductivity decline that occurs at salt concentrations ≥ 1.25 M LiN(CF3SO2)2-PC in both liquid and gel electrolytes, is therefore attributable to (i) ion-pairing phenomenon and (ii) an enhancement in the solution viscosity due to a high salt proportion. © 2003 Elsevier Ltd. All rights reserved.