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-et hyoxy-ethoxy) phosphazene] (MEEP) and silica and their characterizatio n are described.MEEP is a polymer with a low glass transition temperat ure 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 unfortunatel y its flow behaviour at room temperature limits its industrial develop ment. The linkage of MEEP to a rigid inorganic network, which would ov ercome this problem, was pursued using the set-gel method. The functio nalization of MEEP by the introduction of free hydroxyl groups allows the formation of chemical bonds with hydrolysed tetraethoxysilane. Pho sphazene-based hybrid materials with no phase separation could be obta ined by this procedure. The ionic conductivity of these materials dope d with lithium triflate has been investigated using a.c. impedance tec hniques. 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 decr eases the conductivity but it still remains above 5 x 10(-6) Omega(-1) cm(-1).