Silazane

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. 

Table 2. Properties of Hydride Functional Organosilanes, Siloxanes, and Silazanes ...

The most effective additive for dry grinding is fumed sihca that has been treated with methyl silazane [Tulis,y. Hazard. Mater, 4, 3 (1980)]. 

Reactions (l)-(5) illustrate known methods for forming silicon-nitrogen bonds of potential use in the formation of oligo- and polysilazanes. The most common method of forming silazanes is via ammo-nolysis or aminolysis as shown in reaction (1) (4,5) ... 

Thus, Andrianov et al. (26) attempted to catalyze polymerization of a number of alkyl and alkyl/aryl cyclosilazanes using catalytic amounts of KOH or other strong bases at temperatures of up to 300°C. In general, the reactions proceed with evolution of NHj, hydrocarbons and the formation of intractable, crosslinked, brittle products even at low temperatures. Contrary to what is observed with cyclotri-siloxanes, no evidence was found for the formation of linear poly-silazanes. Copolymerization of mixtures of cyclosilazanes and cyclosiloxanes gave somewhat more tractable polymers with less evolution of hydrocarbons or ammonia, however very little was done to characterize the resulting materials. 

The coammonolysis of CH3SiHCl2 and CH3(Un)SiCl2 in the indicated ratios was carried out by the procedure as described for the ammonolysis of CH3SiHCl2 [8]. A mixture of cyclic oligomeric silazanes is to be expected in these reactions, [(CH3(H)SiNH)x(CH3(Un)SiNH)y]n, with more than one ring size present. In each preparation, the soluble, liquid products were isolated and used in the base-catalyzed polymerizations. When a ratio CH3SiHCl2/CH3(Un)SiCl2 of x l (x>l) was used in the ammonolysis reaction, the CH3(H)Si/CH3(Un)Si ratio in the soluble ammonolysis product usually was somewhat less than x l. 

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 ... 

Silazoxane and Silazane Linear and Cyclo-linear Polymers... 

Introductory Remarks. In contrast with the popularity and usefulness of the polysiloxane chains, which constitute the structural backbone of silicones, the knowledge of polymers based on the silazane unit is still limited. In the sixties there was still some hope of the possibility of producing long chain polysilazane molecules and a number of laboratories were active in seeking convenient methods for their synthesis (e.g. see review by Aylett (12)). 

In the present research program, which is directed to synthesizing useful polymers from silazane containing ring compounds, three general pathways were followed ... 

From these results it is evident that there is a definite limiting number of silazane units that can be introduced into a siloxane chain by copolymerization of silazoxane and siloxane rings. The six-membered and eight-membered... 

Polycondensation of difunctional oligomeric cyclodisilazanes with a,co-dihydroxypolysiloxanes proved to be another successful attempt to synthesize silazane modified polysiloxanes of improved thermostability. The cyclodisilazane oligomers IHa (see scheme below) are readily available from common and cheap materials, dichlorodimethylsilane and ammonia (fi). The chlorine atoms in these compounds can be easily exchanged to other functional groups, such as amino, hydroxyl, etc. 

The susceptibility of cyclodisilazanes to nucleophilic attack by aromatic amines has also been used to prepare silazane containing polymers. Polysilazane cyclo-linear chains with aromatic spacing groups, synthesized by polycondensations of difunctional cyclodisilazanes with bis-phenols and N.N -diorganosilane diamines, have been reported (13). 

Thus, the tendency of silazanes to form ring structures, including macrorings, is extraordinary. 

Cyclosilazanes are found to be reluctant to polymerize by the ring-opening process, probably for thermodynamic reasons. On the other hand, six- and eight-membered silazoxane rings are able to undergo anionic polymerization under similar conditions to those which have been widely used for cyclosiloxane polymerization provided there is no more than two silazane units in the cyclic monomer. They can also copolymerize with cyclosiloxanes however, the chain length of the linear polymer formed is substantially decreased with increasing proportion of silazane units. 

The thermostability of siloxane-silazane copolymers of both random and block structure is found to be much higher (i.e. 100-200°C) with respect to polysiloxanes. This effect is brought about by introducing only a few silazane entities into the polymer chain. The reasons for the effect are not clear and the mechanism of thermal degradation of polysilazoxanes will require further experimental studies. 

The new silazane 5 may be reacted with activated metals, organometallic compounds or simple metal amides, or may first be transformed to its lithium salt and then reacted with metal(II) chlorides [11]. In all these cases, metal derivatives of 5 are obtained with the general formula j [Mc (/BuO)Si 9N(9M, which have no further base coordinated to the metal. So far we have synthesized amides with M = Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ba, all elements in oxidation state +2. X-ray structure determinations have been performed on the calcium, manganese, iron, zinc, and barium derivatives. 

Pioneering work by Verbeek and Winter [12,13] showed that the reaction of alkyl- or aryl-chlorosilanes with ammonia, amines, or amides yields aminosilanes or silazanes which can be converted into polysilazanes (Eqs. 5,6). 

Andrianov et al. 47) studied the addition of a series of disilazanes, (HSiMe2)2NR (R = H, Et, i-Bu, Ph, PhCH2,p-N02C6H4), to allyldiethyl-amine in anisole at concentrations of silazane, 1 mole/liter amine, 2 moles/liter and H2PtCl -6H20, 1 x 10-4 moles/liter. They measured the rate of disappearance of SiH at 45° and at 57°C. 

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