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

Solvent-free polymeric alkali-metal ion conductors consisting of a com blike polysiloxane with oligo(oxyethylene) side chains and pendant sul fonate groups were synthesized by the hydrosilylation of an allylmetho xypoly(ethylene glycol) and allyl glycidyl ether, followed by sulfonat ion of the oxirane ring. Due to the tightness of the alkali-metal sulf onate ion pair, conductivities (sigma) reach values of only 10(-6) S c m-1 at 25-degrees-C and 10(-5) S cm-1 at 70-degrees-C. They increase i n the order Li < Na < K < Cs and exhibit a maximum at a ratio of ethyl ene oxide (EO) units to cation almost-equal-to 13. The temperature dep endence of sigma obeys the Vogel-Tammann-Fulcher relationship sigmaT0. 5 = A exp[-B/(T - T0)], implying a free-volume cation transport mechan ism Additives such as linear and macrocyclic polyethers strongly enhan ce sigma by stretching the interionic SO3-M+ ion pair bond and by lowe ring 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.