Silazane systems

When a chain or ring system is composed entirely of alternating silicon and oxygen atoms, the parent name siloxane is used with a multiplying affix to denote the number of silicon atoms present. The parent name silazane implies alternating silicon and nitrogen atoms multiplying affixes denote the number of silicon atoms present. 

In a research program to explore the possibilities of synthesizing useful polymeric materials from silazane (Si-N) containing ring compounds, reactions of the following ring systems were studied ... 

Following similar conceptual lines, a series of silazanes, siloxanes, silylhydrazines and silylhydroxylamines have also been included into the current studies, thus building connections between the Si-C-H and the related Si-N-H, Si-O-H and Si-N-O-H systems. Again the arylated intermediates served as crystalline images of the liquid and volatile basic members of the three series. 

The products of the (NH4)2S04-catalyzed reactions of (CHsSiHNH) with other silazanes and aminosilanes were subjected to the KH-catalyzed DHCD reaction (i5). This reaction converted the viscous liquids and waxes to soluble solids, as is generally the case when this procedure is applied to CH3SiHCl2-derived polysilazane systems. 

We mention here a few compounds which present points of particular interest. The planarity of N(SiH3)3 has been noted coplanar N bonds are also formed in the cyclodisilazane (a). More complex Si—N ring systems include the cyclotetra-silazane (b), which is of interest because both chair and cradle forms of the... 

Attempts have recently been made to determine the dominat electric conductivity mechanism using the results of measurements of the current flow across asymmetric systems, such as metal -polymer-metalo (Me -P-Mc2) and metal-polymer-semiconductor (M-P-Sj such studies involved plasma-polymerized styrene (2 ), silo-xane and silazane ( ). The possibility of tunnel-... 

The chemistry of cyclic oligomeric and high polymeric phosphazenes is dominated by substitution reactions, as is the chemistry of boron-nitrogen heterocycles. However, substitutive techniques play only a minor role in the chemistry of siloxane, silazane, phosphate or metaborate oligomers and polymers. It is not yet well developed in sulfur-nitrogen systems but may become more important in the future. 

The structures of several related naphtho-fused ring systems have been determined by X-ray crystallography. Thus, the cyclic silazane 112 (R = Ph) is planar at the nitrogen atom and all the rings lie almost coplanar, while the related compound 112 (R = Bu but with an anisyl group attached to one of the silicon atoms) has the silicon atoms out of the plane of the tricyclic system, and the ylide 113 has the heterocyclic ring in an envelope conformation and the ylidic carbon is pyramidal and not planar <1996CB495> (see Section 9.18.4.3.2). 

TABLE 58.11. Pyrolysis data on some silazane/polysilazane systems. 

Unlike the results seen with the PCS system there is no single optimum level associated with this binder, for densification, but good densities are obtained at 1.5 wt % excess carbon and above. There is also a veiy good correlation between the calculated minimum binder level and that observed experimentally for these silazane binders. Because of this correlation the experimental screenings of new individual silazane binder can be eliminated and the calculated content used to establish a baseline level for sintering to densities above 95 % of theoretical. 

The reactions of phenylboric acid with substituted silazanes and siloxanes have produced ring systems of the type (33) and (34) for the first time. ... 

A further extension of the concept of thermosetting polysilazanes with peroxide initiators has been the preparation of new polysilazanes with peroxide groups bound directly to the polymer 20). Potential advantages of a peroxide-substituted polysilazane over systems in which the peroxide is simply admixed with the polymer include 1) segregation of the peroxide upon storage cannot occur, 2) dissolution or dispersion of a peroxide in the polysilazane is not necessary, and 3) homogeneous distribution of e peroxide in solid, as well as liquid, polysilazanes is possible. We have prepared a new class of peroxide-substituted polysilazanes by the reaction of a hydroperoxide with a poly(methylvinyl)silazane. The liquid polymers may be thermoset, even with extremely low levels of peroxide substitution. This chemistry provides access to a class of polysilazanes previously unknown as ceramic precursors. 

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