Enhanced ion dissociation of LiCF(sub 3)SO(sub 3) by new carbonate plasticizers: Raman and IR studies.

摘要

The extent of ion dissociation of LiCF(sub 3)SO(sub 3) in propylene carbonate (PC) and new, modified carbonates (MC-3, MC-5) prepared in our laboratory has been determined by Raman spectroscopy. In the modified carbonates the polyether groups -CH(sub 2)(OCH(sub 2)CH(sub 2))(sub n)OCH(sub 3) (n=3 for MC-3 and n=5 for MC-5) replace the 4-CH(sub 3) substituent of PC. The spectra clearly show that both MC-3 and MC-5 promote ion dissociation of the Li triflate salt relative to PC. Furthermore, MC-5 solutions contain more free ions than MC-3 solutions, and are less affected by concentration changes. Infrared spectra demonstrate that Li(sup +) cations associate less with the carbonyl of the modified carbonates than with the carbonyl of PC. These results suggest that the enhanced ion dissociation of Li triflate in MC-3 and MC-5 arises from complexation of the Li(sup +) to the oxygens of the polyether sidechains, and that MC-5 with its six ether oxygens forms the more stable complex.