SOLVENT-FREE CATION-CONDUCTING POLYSILOXANE ELECTROLYTES WITH PENDANT OLIGO(OXYETHYLENE) AND SULFONATE GROUPS

Solvent-free polymeric alkali-metal ion conductors consisting of a comblike polysiloxane with oligo(oxyethylene) side chains and pendant sulfonate groups were synthesized by the hydrosilylation of an allylmethoxypoly(ethylene glycol) and allyl glycidyl ether, followed by sulfonation of the oxirane ring. Due to the tightness of the alkali-metal sulfonate ion pair, conductivities (sigma) reach values of only 10(-6) S cm-1 at 25-degrees-C and 10(-5) S cm-1 at 70-degrees-C. They increase in the order Li < Na < K < Cs and exhibit a maximum at a ratio of ethylene oxide (EO) units to cation almost-equal-to 13. The temperature dependence of sigma obeys the Vogel-Tammann-Fulcher relationship sigmaT0.5 = A exp[-B/(T - T0)], implying a free-volume cation transport mechanism Additives such as linear and macrocyclic polyethers strongly enhance sigma by stretching the interionic SO3-M+ ion pair bond and by lowering the glass transition temperature. Particularly effective is tetra(ethylene glycol) (TEG) which at TEG/Na = 1 raises sigma to 2 X 10(-5) S cm-1 at 25-degrees-C and to 10(4) S cm-1 at 70-degrees-C.