A monomer; (3-cyanopropyl)methylsiloxane cyclics, is prepared by a hydrosiliylation reaction of 2,4,6,8-tetramethylcyclotetrasiloxane with allyl cyanide in toluene using a platinum(0)-1,3-divinyl-1,1,3,3-tetramethyl disiloxane complex as the catalyst. The cross-linkable polysiloxane is synthesised by ring-opening polymerisation with (3-cyanopropyl) methylsiloxane cyclics using fuming sulfuric acid. The polymers, abbreviated as D4D2-n indicates the number of cyanide groups in the side chain), are characterised by FT-IR and 1 H NMR. The solid polymer electrolyte is prepared by UV irradiation in an Indium–tin oxide cell. The cyanide pendants on the network backbones make the lithium salt easy to dissolve, accelerate the migration of free lithium ions, and can lower the glass transition temperature (T g) of the electrolyte. The maximum conductivity of the polymer with n=55 is 3.38×10−5 Scm−1 at room temperature. The temperature dependence of ionic conductivity (σ) obeys the Vogel–Tammann–Fulcher relationship which implies ionic conductivity (σ) obeys the Vogel–Tammann–Fulcher relationship which implies a free-volume cation transport mechanism.