Sol-gel hybrid materials based on hydroxylated poly[bis(methoxy-ethoxy-ethoxy)phosphazene] and silica: A ceramic ionic conductor

The sol-ge[ synthesis of hybrid materials based on poly[bis(methoxy-ethyoxy-ethoxy) phosphazene] (MEEP) and silica and their characterization are described. MEEP is a polymer with a low glass transition temperature of -71 degrees C, that bears ethyleneoxide oligomers as phosphorus side groups, able to impart to the macromolecule metal co-ordination ability. This property makes MEEP an ionic conductor, but unfortunately its flow behaviour at room temperature limits its industrial development. The linkage of MEEP to a rigid inorganic network, which would overcome this problem, was pursued using the set-gel method. The functionalization of MEEP by the introduction of free hydroxyl groups allows the formation of chemical bonds with hydrolysed tetraethoxysilane. Phosphazene-based hybrid materials with no phase separation could be obtained by this procedure. The ionic conductivity of these materials doped with lithium triflate has been investigated using a.c. impedance techniques. A conductivity value of about 3 x 10(-5) Omega(-1) cm(-1) was measured which is comparable to typical values of poly(ethylene oxide) solid electrolytes. A thermal treatment of the Li-doped samples decreases the conductivity but it still remains above 5 x 10(-6) Omega(-1) cm(-1).