Alkyl alkoxysilanes

In agreement with the NMR results, the bulky alkyl-alkoxysilanes RSi(OC2H5>3 (R = i-C4H9 and n-CgH ) are not able to form polymeric or spherical siloxanes under the conditions used for this study. The observed TOF-SIMS spectra are similar to the El spectra of the pure liquids and, therefore, underline the presence of physically adsorbed species [5,9]. 

The combination of different analytical techniques offers the possibility for a complete characterization of building materials impregnated with liquid alkyl-alkoxysilanes RSi(OC2H5)3. The results derived from IR, NMR and SIMS spectra can be summarized in the schematic layer structure shown in Figure 5. 

The methods used to increase the water resistance of a glass microsphere foam are basically those applied to glass-reinforced plastics, filled thermoplasts, and elastomers, viz. hydrophobic adhesion compounds are added to binder and microsphere dressing 147). The compounds added are alkyl alkoxysilane derivatives, amino or epoxy alkoxysilanes for epoxy and phenolic resins, vinyl or methacryloxy alkoxysilanes for polyester resins. The dressing agents used are aminoethoxysilanes (y-aminopropyl-... 

Table 4.1. Structure, siUcon/oxygen ratio, R/Si ratio of the various alkyl-alkoxysilane compounds...

The sol-to-gel conversion in hybrid systems has been studied by FTIR (Mendez-Vivar, 2000), for tetraethyl orthosilicate (TEOS)-alkyl alkoxysilane (RSi(OR3)) sols. The main assignments of methyltriethoxysilane (MTES)-TEOS systems in fresh sols are reported in Table 7-4. 

Alkyl alkoxysilanes undergo quick hydrolysis and polycondensation in acidic medium. This has been exploited in combination with self-assembly of long-chain alkyl trialkoxysilanes driven by hydrophobic interactions that opened prospects for surfectant- and template-free synthesis of ordered mesoporous silicas. This approach has been developed strongly by Shimojima and Kuroda [24]. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

ALKANE, 202 255 ALKENYL, 133 ALKOXYSILANE, 146 ALKYL HYDROXIDE, 271 ALKYL AMINE, 371 ALLYLAMINE, 372 ALPHA-OLEFIN COPOLYMER, 197... 

In contrast, the Si—SR bond is cleaved mainly with inversion. Although the Si—SR bond is longer, the unfavorable out-of-phase Nu—SR overlap prevails because of the diffuse valence orbitals around the sulfur atom. Furthermore, the o-, SR shows a smaller lobe between the Si and S atoms than does the cr 0R MO. As a consequence, the probability of a rear-side attack with inversion is enhanced. For instance, alkyl Grignard reagents cleave the Si—SR bond with inversion instead of retention, as is the case with alkoxysilanes (5). 

Abstract—A review of the literature is presented for the hydrolysis of alkoxysilane esters and for the condensation of silanols in solution or with surfaces. Studies using mono-, di-, and trifunctional silane esters and silanols with different alkyl substituents are used to discuss the steric and electronic effects of alkyl substitution on the reaction rates and kinetics. The influences of acids, bases, pH, solvent, and temperature on the reaction kinetics are examined. Using these rate data. Taft equations and Brensied plots are constructed and then used to discuss the mechanisms for acid and base-catalyzed hydrolysis of silane esters and condensation of silanols. Practical implications for using organofunctional silane esters and silanols in industrial applications are presented. 

About this time, it was postulated that the transition state was a trivalent siliconium ion followed by the rapid addition of water. In 1982, this view was supported by Schmidt et al. [15], They studied the hydrolysis of tetra-alkoxy-silanes and various alkoxyalkylsilanes. It was noted that the alkyl-containing silanes reacted significantly faster than the analogous alkoxysilanes. They attributed this result to the stabilizing effect that the electron donating character of the alkyl group (+1 effect) would have on a siliconium ion. 

The substituted ethers of orthosilicon acid, alkyl(aryl)alkoxysilanes or al-kyl(aryl)aroxysilanes, have the common formula RnSi(OR )4. where n = 1-K3, whereas R and R are any organic radicals the radicals situated at the silicon atom and in the ether group can be the same or different. 

It is necessary to prevent chemical reactions from becoming too active e.g. the hydrolysis or ammonolysis of organochlorosilanes or the Grignard reaction for the synthesis of alkyl(aiyl)alkoxysilanes. 

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