Trifunctional silane, structure

There is reason to believe that the molecular structure of crosslinked trifunctional silanes/siloxanes may also influence the durability of the resulting silicone resin network [14, 40 - 42]. Allowance must be made here for the fact that such considerations are models in nature and also that we still do not have adequate knowledge of the molecular principles of fully condensed silicone resin networks [15]. 

Monofunctional silane reagents yield efficient stationary phases with flexible furlike or brushlike structure of the chains bonded on the silica surface. When bifunctional or trifunctional silanes are used for modification, Cl or alkoxy groups are introduced into the stationary phase, which are subject to hydrolysis and react with excess molecules of reagents to form a polymerized spongelike bonded phase structure. Stationary phases prepared in that way usually show stronger retention but lower separation efficiency (plate number) than mono-merically bonded stationary phases. 

Figure 6.1 The reaction between organosilanes and surface hydroxyl groups (silanization). In these structures X is a reactive group such as Cl or 0(CH3). Depending on the number of reactive groups on each silane one or two links can be made to the surface. Trifunctional silanes can go on to give polymeric multilayers in the presence of traces of water.

The term silsesquioxanes refers to all the structures with the empirical formula (RSiOi.sln, where R is a hydrogen or any alkyl, aryl, alkylene, arylene, or organofunctional derivative. Such compounds are synthesized by hydrolytic condensation of trifunctional silanes. The trifunctional nature of the silsesquioxane moieties allows the formation of a variety of structures, ranging from oligomeric cages to ordered ladder-like structure to three-dimensional network structure to functionalized silicates (called spherosilicates). 

The adhesive used was a model semi-structural PU, similar to one described in an earlier work [7]. The two component formnlation consisted of methylene bis-4-cyclohexyl isocyanate prepolymer and trifunctional polyols with molecnlar masses in the range 500-900. A small amount of tin catalyst (UL-28, Witco Chemicals) was also present. The PU was used as control without additives and was modified by the following silanes ... 

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