PRECIPITATION OF SILICA-TITANIA MIXED-OXIDE FILLERS INTO POLY(DIMETHYLSILOXANE) NETWORKS

Previous studies have demonstrated techniques by which model elastomers prepared by end linking poly(dimethylsiloxane) (PDMS) chains can be reinforced by the in-situ precipitation of silica from a base-catalyzed sol-gel conversion of tetraethoxysilane (TEOS). The present investigation extends this technique to silica-titania mixed oxides through the sol-gel conversion of mixtures of TEOS and titanium n-butoxide. The elastomeric networks reinforced by this novel mixed filler were found to have very good mechanical properties, and swelling equilibrium measurements indicate that there is good adhesion between the SiO2-TiO2 filler and the elastomeric matrix. Compared with networks containing silica alone, the networks containing silica-titania mixed oxides had somewhat better combinations of high modulus and good extensibility. The particle size was typically several hundred A in diameter but was found to be inversely dependent on the crosslink density of the PDMS network. Thus, larger particle sizes can be obtained at lower crosslink densities (which give larger network mesh sizes). The distribution of particle sizes is relatively narrow, and there is very little particle aggregation. The presence of in-situ silica-titania mixed oxides can also increase the onset temperature for degradation of the PDMS host matrix.