Oligomeric silanes

The absolute shift value decreases from tri- over bi to monodentate silane molecules. Hydrolysis of the silane molecules is not visible for the bidentate type, but gives a downfield shift for the monodentate molecules. Because the formation of three siloxane bonds with the surface is excluded for sterical reasons, the tridentate form corresponds to oligomerized silane molecules. A general trend of decreasing number of tridentate linked molecules and increasing number of monodentate molecules with increasing pretreatment temperature can be seen. This trend will be discussed below. 

Catalytic (Lewis base-induced) disproportionation of tetrachlorodimethyldisilane or dichlorotetramethylsilane is another efficient process to generate oligomeric silanes without formation of solid by-products. - ° The inexpensive starting compounds are obtained as a by-product during the synthesis of chlorosilanes in the Muller-Rochow process. Depending on the molecular structure, that is, the number of chlorine atoms per silicon atom, mixtures of linear or branched polymers form. 

Industrially produced organo-silicon compounds include monomeric low molecular compounds, almost exclusively belonging to the class of silanes, and oligomers and polymeric compounds including oligomeric silanes, polysilanes, oligomeric silazanes, polysilazanes and particularly oligomeric siloxanes and polysiloxanes (silicones). 

Figure 6. Schematic representation of the adsorption of silane coupling agent molecules onto glass fiber surface. A) The silane solution is a low concentration below the onset of association, and B) the silane solution is a high concentration above the onset of association. Open cirde indicates isolated silanes whereas the closed circle denotes hydrogen bonded or oligomeric silanes. Note the disturbance in packing is created at a high concentration.

Fig. 2. Schematic diagrams of (a) a polysiloxane deposit on glass fibre M is the methacry-loxypropyl group in y-methacryloxypropyl trimethoxy silane and (b) the composite interface. Here R-M is the interpenetrating copolsmer with the resin matrix (R), ( ) is the dissolved binder and/or size PS = polysiloxane, HBS = hydrogen bonded oligomeric silanes. IPN = intapenetrating network, INT = interface...

Silane hydrolysis and condensation take place on the surface of the mineral filler, thus, forming oligomeric silane structures. Oligomeric silanes (Figure 4.3) are commercially available under the Dynasylan trade name. They are low-viscosity... 

Figure 4.3 Chemical structure of a vinyl oligomeric silane.

Tensile properties of different EVA/ATH formulations are summarized in Table 4.3. The basic formulation contained 160phr of ATH, 1 phr stabilizer, and variable amounts of monomeric and oligomeric silanes and peroxide. A corotating twin-screw extruder was used to produce sheets for the tests. SUane content is based on filler, the silane was preblended with the EVA, dicumyl peroxide (DCP) and Irganox 1010 (phenolic stabilizer, Qba) were used as peroxide and stabilizer, respectively. A control without silane is not included since it leads to scorch. 

We recently reported the reaction of PhSiH or CySiH (Cy = cyclohexyl) with Pt(PEt3)2Cl2 and sodium which produces Pt-Si 4MR of novel structure and oligomeric silanes. We have extended our work on this reaction and find that TolSiH (Tol = para-tolyl) also undergoes a similar transformation. A byproduct of all these reactions appears to be finely divided platinum (Eq.l). The oligomeric silanes are largely dimeric or trimeric. 

X-ray crystallography. The observation that our platinum-silicon 4MR can be formed from reagents with Si-Si single bonds is also consistent with the P2 h bonding description. West has prepared monoplatinum complexes of disilenes from disilenes or disilanes by three routes. One route, which is similar to the reaction depicted in Eg.4, is shown in Eg.5. The platinum disilene complexes are described by the two resonance forms drawn in Eg.5. (It is interesting to note that oligomeric silanes are obtained as by-products of Eg.5.)... 

We have obtained oligomeric silanes from Eg.l but we have decided not to focus our initial studies on this route because of the inherent complexities. There are several possible platinum catalyst precursors present in Eg.l the platinum-silicon 4HR, the starting material (Et3P)2PtCl2, and finely divided platinum (colloids). Preliminary studies of these latter two catalyst precursors with PhSiH3 indicate that both are considerably slower than any platinum-silicon 4MR (see below) and both give primarily redistribution products. ... 

Table 4 Shift ranges (ppm) of some classes oligomeric silanes.

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