FTIR STUDY OF ION-PAIRING EFFECTS IN PLASTICIZED POLYMER ELECTROLYTES

The effect of plasticizer on the ubiquitous ion-pairing observed in po lymer electrolytes has been investigated using FTIR as a probe of the local environment of the triflate ion in sodium and lithium triflate b ased electrolytes. Plasticizers having a range of properties, such as, propylene carbonate, and dimethyl formamide (DMF), have been investig ated in the pure state for comparison with the polymer (a random copol ymer of ethylene oxide at propylene oxide (mel ratio 3:1)). The differ ent plasticizers exhibited strikingly different effects on the triflat e ion bands normally observed in polyether salt systems. In particular , the cation associated triflate ion bands at 1288 and 1248 cm(-1) and the band at 1272cm(-1) which has variously been assigned to the free ion and also to the strongly aggregated anion, are different. PC produ ces a rapid disappearance of the ''free'' ion band in favour of the mo nodentate ion pair. On the other hand, DMF strongly enhances the band near 1270 cm(-1) at salt concentrations higher than 0.7 mol kg(-1). Th ese observations are discussed in terms of recent ab initio calculatio ns of the triflate vibrational bands.