Cryptand Addition to Polyelectrolytes: A Means of Conductivity Enhancement and a Probe of Ionic Interactions

As a means of probing ionic interactions in and enhancing the conductivity of single-ion conducting polymer electrolytes, the effect of the cryptand 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (crypt[2.2.2]) on the conductivity of the sodium salt of poly{poly{{[ω-methoxypoly(oxyethylene)]propyl}methylsiloxane}-block:-[4-(3,5-di-tert-butyl-4-hydroxyphenyl)butyl]methylsiloxane} (1) was studied. Both samples with and without cryptand display the characteristic VTF temperature dependence of their conductivities (σ = AT^–1/2exp[-B/(T – T_o)]). The addition of crypt[2.2.2] results in a 15-fold increase in conductivity, independent of temperature and concentration. The glass transitions of the materials are unchanged upon cryptand addition, even at high ion concentrations where the glass transition is dependent on ion content. Both the materials with and without crypt[2.2.2] exhibit a conductivity maximum with concentration at [Na]/[ethylene oxide] = 2% (1.4 x 10^–6 S/cm neat and 1.7 x 10^–5 S/cm with crypt[2.2.2] at room temperature). A model based on equilibrium expressions for free-carrier formation is shown to be more appropriate than one based on an activated process because the former more closely describes the temperature-independent effect of crypt[2.2.2] on the conductivity.