Synthesis and Ionic Conductivity of Cyclosiloxanes with Ethyleneoxy-Containing Substituents

Pentamethylcyclopentasiloxanes (D5 H) with oligo(ethylene glycol) substituents, D5N3 and D5S3, and a short-chain siloxane derivative MD6N3M were synthesized by B(C6F5)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 D5N3 exhibits higher conductivity than trimethylene-linked siloxane D5S3. The substituted linear oligmeric siloxane MD6N3M has a lower T g than the D5 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.