Silylalkylboranes, oligo or polyborocarbosilazanes and silicon c

Details Silylalkylboranes, oligo or polyborocarbosilazanes and silicon c Silylalkylboranes, oligo or polyborocarbosilazanes and silicon c

1999-09-27

2000-07-25

Shaver, Paul F.

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

528 5, 423276, 501 96, 501 97, 501 961, 501 963, 501 965, C07F 502, C07F 708

Patent

active

060938404

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to molecular silylalkylboranes, a process for their preparation, oligo- or polyborocarbosilazanes, a process for their preparation and their use and silicon carbonitride ceramics and a process for their preparation.
The process for producing multinary, non-oxidic ceramics via molecular single-component precursors has achieved outstanding importance. It has opened up the path to nitridic, carbidic and carbonitridic systems which are not accessible via conventional solid-state reactions. The products are distinguished by high purity, homogeneous distribution of elements and uniform particle size.
Materials which consist of Si, B and N and, if appropriate, also C, demonstrate particular properties with respect to thermal stability and resistance to oxidation. They can be used as bulk material or else for coatings and as fibrous material. The boron-containing materials exhibit an increased inhibition of crystallization, whereas the carbon-containing ceramics have, in addition, higher decomposition temperatures than carbon-free ceramics.
According to U.S. Pat. No. 5,233,066, synthesis of the amorphous ceramics Si.sub.3 B.sub.3 N.sub.7 and SiBN.sub.3 C from the precursor trichlorosilylaminodichloroborane (TADB) is achieved by crosslinking with ammonia or amines and subsequent pyrolysis in a gas stream.
In this method, the composition of the products is set firstly by the single-component precursor and secondly by the type of crosslinking. Whereas the Si:B ratio is set by the precursor to 1:1, the N:C ratio is a function of the choice of methylamine as crosslinking reagent.
The carbon is incorporated into the ceramics here via the organic amine side chain. However, this takes place in an uncontrolled manner via a reaction which has not been described in detail. The disadvantage of this procedure is the low possibility of varying the C content. Extending the side chain does not lead inevitably to a higher C content in the ceramics, but to graphite deposits in the material. This has an adverse effect on the properties. In addition, a large part of the carbon is lost during the pyrolysis, since the side chains are eliminated in the form of volatile alkanes, alkenes etc.
According to Appl. Organomet. Chem. 10 (1996) 241-256, polymeric boron-containing carbosilanes are obtained by reacting vinyl-containing polysilanes or polysilazanes with boron adducts of the formula BH.sub.3 .multidot.SR.sub.2 where R.dbd.C.sub.1 -C.sub.18 -alkyl.
According to DE-A 43 20 785, trissilylalkylboranes of the formula B[--C.sub.2 H.sub.4 --SiCl.sub.2 X].sub.3 are obtained by reacting vinylsilanes of the formula CH.sub.2 .dbd.CH--SiCl.sub.2 X with BH.sub.3 .multidot.THF.
In these methods, either polymers are obtained directly or the ratio of Si to B does not correspond to the ideal ratio of 1:1.
The object of the present invention was therefore the provision of novel precursors which are simple to prepare and provide an opportunity for the controlled introduction of carbon, without having the disadvantages of the prior art.


DESCRIPTION OF THE INVENTION

Surprisingly, the object was achieved with compounds of the type ##STR1## where each Si atom is coordinated to 3 radicals R and each B atom is coordinated to 2 radicals R and silicon and boron are linked by a C(CR.sup.5 R.sup.6 H)(R.sup.4) bridge, where R.sup.1 to R.sup.3 independently of one another are C.sub.1 -C.sub.6 -alkyl, vinyl, phenyl, hydrogen or halogen, R.sup.4 to R.sup.6 =C.sub.1 -C.sub.6 -alkyl, vinyl or phenyl groups and/or hydrogen and R.sup.7 and R.sup.8 are chloride and/or bromide.
By means of these compounds which have already incorporated carbon in the backbone, the incorporation into the ceramics is promoted and elimination of volatile carbon compounds is reduced.
The invention therefore relates to molecular silylalkylboranes of the general structural formula ##STR2## where each Si atom is coordinated to 3 radicals R and each B atom is coordinated to 2 radicals R and silicon and boron are linked by a C(CR.sup.5

REFERENCES:
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Applied Organometallic Chemistry, vol. 10, (month unavailable) 1996, pp. 241-256.
Ralf Riedel, Joachim Bill and Andreas Kienzle, Boron-modified Inorganic Polymers-Precursors for the Synthesis of Multicomponent Ceramics.

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