 Solution

Neither backbone has a partially filled, extended electronic band available for easy charge transport. In polysiloxanes the bonding and nonbonding states are filled and separated from empty states by a large band gap. phosphazene local lone-pair interactions do not create the continuously delocalized, partially occupied pi band suggested by a naive P=N drawing. Their flexibility or formal multiple-bond notation does not imply electronic conductivity. This comparison concerns the undoped materials, not conductivity supplied by added mobile ions.