Since the discovery of ionic conduction properties of polyethylene oxide doped with lithium, the researchers looked for a material having conductivity suitable for separating the electrodes. The electric conductivity varies inversely with the glass transition temperature, the mobility of the polymer chain is recommended for the conduction of Li+. PDMS has a Tg of -123Â°C, a flexible and mobile chain. View of these properties, the PDMS was chosen in the synthesis of electrolyte to increase it conductivity. The present study shows the synthesis copolymer PDMS-co-PEO by a simple method, one step of catalytic ring opening polymerization using Maghnite-H+ (Mag-H+), a montmorillonite sheet silicate clay exchanged with protons, an efficient catalyst for cationic polymerisation of many heterocyclic. The reaction of copolymerization is carried out in chloroform at 60Â°C for 10h. Various techniques, including 1H-NMR, IR, DSC, XRD and TGA were used to elucidate structural characteristics and thermal properties of catalyst and products. Analyses results confirms the synthesis of the copolymer PDMS / PEO, cationic mechanism for the reaction was proposed.