Synthesis and Ionic Conductivity of Cyclosiloxanes with Ethyleneoxy-Containing Substituents

Pentamethylcyclopentasiloxanes (D 5 H ) with oligo(ethylene glycol) substituents, D 5 N3 and D 5 S3, and a short-chain siloxane derivative MD 6 N3M were synthesized by B(C 6 F 5 ) 3 -catalyzed dehydrogenative coupling and by platinum-catalyzed hydrosilylation reactions. Conductivities were studied when doped with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The oxygen-linked cyclic siloxane D 5 N3 exhibits higher conductivity than trimethylene-linked siloxane D 5 S3. The substituted linear oligmeric siloxane MD 6 N3M has a lower T g than the D 5 siloxanes, and showed much higher conductivity at the same Li + concentration. The curvature of the plot of conductivity vs temperature dependence indicates a free volume mechanism of ion transport.