Monofunctional organosilanes

TABLE 13. Stereochemical behaviour of monofunctional organosilanes in the substitution l-NpPh(R)Si-X + NuM- l-NpPh(R)Si-Nu + MX... 

Hogg, S. E. T., McPhail, D. S., Rogers, P. S., Oakley, P. L. (1998). Monofunctional organosilanes as candidates for treatments of crizzling in glasses. In A. B. Paterakis (Ed.), Glass, ceramics and related materials. EVTEK - Institute of Arts and Design. 

Monofunctional organosilanes terminating the surfaces of porous xerogels or coatings can be used as catalyst supports, membranes, or sensors [241]. For example, Fig. 16a shows that incorporation of aminosilanes in a porous silicate coating results in significant COj adsorption, despite rather low surface areas. In order to reduce the influence of water vapor, hydro-phobic components can be incorporated. Figure 16b shows the effect of a propylsilane addition on the water uptake of an aminosilane-silicate film. 

Si(OC2H5). In the two-step process of hydrolysis of the silane to the silanol species and the condensation (silanols to siloxane), the reaction-determining step is the rate of hydrolysis [54]. However, for polyfunctional silanes, hydrolysis and condensation overlap. Under defined reaction conditions, the reaction between the surface hydroxyl groups of the sihca and the silane compound follows a distinct stochiometry, which can be expressed by the number of surface hydroxyl groups that react with the organosilane. For monofunctional silanes this ratio is unity. 

Figure 2.25. Reaction of a (a) monofunctional or (b) trifunctional organosilane with silanol groups on the silica surface.

The organosilane stationary phase has been called a brush phase. It consists of reacting a silica surface with dimethyloctylsilyl-chlorosilane at elevated temperatures, which causes the bonding of the dimethyloctylsilyl group to the surface (Fig. 2.1). As a result, the product is a surface covered with dimethyloctylsilyl chains, like bristles of a brush. Thus, the term brush phase sometimes is used. This derivatization is monofunctional in that only one Si-O-Si link exists between the silica particle and the alkyl-bonded phase. 

An alternative way to ereate elosed porosity in mieeUe-templated silicas and organosilicas is to remove the template and then elose the passages between the pores through the surface grafting of monofunctional organosUanes (organosilanes having... 

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