Hybrid materials TEOS network

Poly(vinyl-acetate), the polymer chosen for this study, is functionally incapable of covalently bonding with the polymerizing silicon alkoxide, TEOS. Therefore, the Si02/PVAc composites may be considered class I hybrid materials. Reasons for interest in mixing PVAc with silica include its excellent optical transparency, a refractive index close to that of silica, and its solubility in ethanol-water mixtures. The solubility of PVAc in ethanol-water mixtures allows the polymer to be added directly to a typical alkoxide sol-gel formulation of alkoxide, alcohol, water, and catalyst, followed by tiie polymerization of the inorganic network around the organic polymer domains. 

Table IV lists the mechanical stress-strain data for a series of hybrid TEOS-PTMO materials containing different levels of Ti-isop in the starting reaction mixture. These materials, with the exception of the first one, were all made using a modified reaction scheme (see experimental section) in order to incorporate the titanium into the network. The starting reaction mixtures in all cases contained 50% by weight of the glass precursors (TEOS and Ti-isop) and 50% by weight of PTMO(2000) (endcapped with triethoxysilane). One set of samples without titanium was made in order to compare the effects of the reaction scheme on the observed mechanical properties.

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