Control of Ionic Interactions in Silver Salt−Polymer Complexes with Ionic Liquids: Implications for Facilitated Olefin Transport

The ionic liquids 1-butyl-3-methyl imidazolium BMIM + NO 3 - and BMIM + BF 4 - have been successfully utilized to increase the activity in reversible π-complexation with olefins of silver cations in silver polymer electrolytes consisting of AgNO 3 dissolved in poly(2-ethyl-2-oxazoline) (POZ). In the absence of the ionic liquids, AgNO 3 is not readily dissolved in POZ and is instead because of its high lattice energy present mostly as chemically less active ion pairs or higher order aggregates. The activation of Ag + in silver polymer electrolytes in the presence of these ionic liquids is principally due to the reduction of the interactions between Ag + and NO 3 - produced by the interaction between BMIM + and NO 3 -, and this effect does not occur in the presence of common salts such as NaNO 3 . We investigated these systems with FT-IR, FT-Raman, and XPS and calculated the theoretical electronic structures of the relevant species. The increased activity in these membranes of Ag + in reversible π-complexation with olefins was further confirmed by evaluating the sorption and desorption behavior of propylene and the performances of the membranes in the separation of olefin/paraffin mixtures.