IONIC INTERACTIONS AND TRANSPORT-PROPERTIES IN METHYL TERMINATED POLY(PROPYLENE GLYCOL)(4000) COMPLEXED WITH LICF3SO3

Alternating current (ac) impedance, restricted diffusion, and vibratio nal spectroscopic (Raman and IR) measurements have been conducted on c omplexes of methyl capped poly(propylene glycol) of molecular weight 4 000 and LiCF3SO3 salt. The relative concentrations of anions in differ ent chemical environments have been calculated from an analysis of the symmetric anion SO3 stretch (Raman) over a wide concentration range. Comparisons are made to previous studies on hydroxyl capped PPG system s, and we find that polar polymer end groups play an important role in the solvation of the salt. The relative fraction of anions interactin g directly with lithium cations is considerably higher over the entire concentration range in the present study, and we infer the existence of negatively charged ionic aggregates in the solutions. We also note that the fraction of spectroscopically ''free'' anions increases with increasing salt concentration in the ether oxygen to alkali metal cati on ratio (O:M) range 502:1 to 12:1, contrary to a decrease reported fo r the analogue hydroxyl terminated electrolytes. The ionic conductivit y has a more pronounced concentration dependency in the methyl capped system; notably, the molar conductivity (Lambda) increases dramaticall y with increasing salt concentration passing through a relatively shar p maximum at O:M = 20:1 at room temperature. Restricted diffusion data are also reported which show that the salt diffusion coefficient incr eases by approximately 60% between O:M 40:1 and 20:1. The results are discussed in terms of ionic interactions and ion transport in nonideal polymer ion conductors. We comment on the characteristic concentratio n dependency of Lambda and observations of low and even negative catio nic transference numbers in similar complexes.