CA1340025C - Polysilazanes and related compositions, processes and use - Google Patents

Abstract

Silazanes and related compounds are prepared by (a) providing a precursor containing at least one Si-N
bond, cleaving an Si-N bond in the precursor in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial silazane product having at least one newly formed Si-N bond or (b) providing one or more reactants which contain an Si-H bond and an N-H
bond, and causing reaction to occur between the two bonds in the presence of a transition metal catalyst to form an initial silazane product having newly formed Si-N bonds. Further products may result from additional reaction of either type. Novel compounds, including siloxazanes and high molecular weight polysilazanes, are provided. The compounds may be pyrolyzed to yield ceramic materials such as silicon nitride, silicon carbide and silicon oxynitride. In a preferred embodiment, substantially pure silicon nitride and articles prepared therefrom are provided. Fibers, coatings, binders, and the like may be prepared from the novel materials.

Description

¦ POLYSILAZANES AND RELATED
COMPOSITIONS, PROCESSES AND USES

Description Technical Field The invention relates to the synthesis of compounds (by which it is intended to include monomers, oligomers and polymers) containing the structure Si-N in the molecule.
The invention concerns primarily silazanes and their derivatives"
which may be pyrolized to yield a variety of ceramic products, and also relates to siloxazanes tby which it is meant monomers, oligomers and polymers containing the O-Si-N unit) and other compounds containing one or more Si-N bonds. The invention additionally relates to the synthesis of novel, high molecular weight polysilazanes and their precursors, and the use of these unique compounds for the fabrication of ceramic coatings, fibers, binders, and injection-molded articles. The invention also -2- 13'10025 relates to the use of polysiloxazanes and eolyhydridosiloxanes as ceramic precursors.

Backqround Polysilazanes and their derivatives are useful among other things, for the preparation of silicon nitride (Si3N4), silicon carbide (SiC), Si3N4/SiC alloys, Si3N4/carbon alloys, Si3N4/boron nitride alloys. and mixtures thereof.
These ceramic materials can be used as structural materials, erotecti~e coatings, and electronic materials because of their hardness, strength, structural stability under extreme environmental conditions and their wide variety of electronic properties. In particular, these materials can be formed into ceramic fibers of value for reinfoecement of comeosite materials. See, for example, (a) Department of Defense Proceedings, Fourth Metal Matrix Composites Technical Conference, May 19-21, 1981, prepared for DOD Metal Matrix Composites Information Analysis Center; and (b) J.J. Brennan, "Program to Study SiC Fiber-Reinforced Matrix Composites", Annual Report to Dept. of Navy (Nov.
1980), Contract No. NO0014-78-C-0503 Historically, polysilazanes were first synthesized by Stock et al almost 60 years ago (see, e.g., Stock, ~. and K. Somieski, Ber. Dtsch. Chem. Ges.
54:740 (1921)) via a simele ammonolysis technique (Scheme I). However, this Me SiCl + NH -------> ~ Me SiNH ~ +

-~Me2siNH ~ ~ NH4Cl Scheme I

-3- i~i~iO2~

approach usually produces mixtures of cyclomers where x is 3 to 5 that are obtained as the major products and small amounts of linear oligomers where y is less than or equal to about 10. Because of their low molecular weight, however, these linear oligosilazanes are too volatile to be used as preceramic materials.
In order to obtain higher molecular weight, nonvolatile materials, it was necessary to promote cross-linking ceactions. In this manner, moderate molecular weight polysilazanes have been synthesized using a variety of techniques. See, e.~., Kruger, C.R.
and E.G. Rochow, J. Polymer Sci. 2A:3179-3189 (1964).
Rochow et al. discovered that ammonium chloride catalyzes cross-linking in simple oligodimethylsilazanes to form polysilazanes (Scheme II) which ( 2)0.5 NH Cltl40~C
~ Me2SiNH3~ ----------> ~ Me2SiNH~x~Me<;iN]y Mn = 10,000 D

Scheme II

were proposed to contain cyclic monomer units cross-linked through nitrogen as suggested by the structure of Formula 1.

~ S iR2 ~ ~ 5; ~2,,~
N N
SiR2 ~;

X

Formula 1 1~1032~

The Penn et al work follows up on U.S. Patent Nos. 3,853,567 to Verbeek and 3,892,583 to Winter et al, wherein a high temperature elimination/condensation reaction was shown to lead to soluble, highly cross-linked polymers as shown in Scheme III. Pyrolysis at high temperatures provides ceramic 520~C
MeNH
MeSi(NHMe)3 ----------~ [MeSiNMe]x~MeSi(NMe)l 5]y + MeNH2 M -= 4200 D
Scheme III

yields of 60% with a mixture of ';i3N4 and SiC ceramic materials.
A related cross-linking approach described, inter alia, in U.S. Patent Nos. 4,312,970; 4,340,619; 4,535,007 and 4,543,344 begins with the preparation of tractable polysilazanes having Me3Si groups linked to the polymer backbone (Scheme IV) with the highest molecular weights reported in the available literature, i.e. about Mw 15,000 D
and Mz 39,000 D:
HSiC13 + (Me3Si)2NH --~ [HSi(NH)l 5]x[HSiNH(NHSiMe3)]y Mw =- 15,000 D
Mz =- 39,000 D
Scheme IV
Ceramic yields obtained from pyrolysis of fibres formed from this polymer are on the order of 45-55% with compositions of 96% Si3N4, 2% carbon and 2~ oxygen after curing.

0 ~ ~

U.S. Patent No. 4,482,669 to Seyferth et al.
discloses that it is eossible to cross-link low molecular weight cyclic oligomers containing Si-H bonds adjacent to N-H bonds via the following reaction:
~ N-SiMe~-4 MeSiHNH~4 9 ------> -(MeSi-N)x + H2 Mn = 1800-2200 D

Scheme V

The NH bond is catalytically activated by the strong base in this reaction. This type of cross-linking generates two-dimensional polymers, the solubility of which is limited by their sheet-like character. Ceramic yields of these materials are often quite high, up to about 86~, and typically provides Si3N4, SiC and carbon in a mole ratio of 0.88:1.27:0 75. If the pyrolysis is carried out in an NH3 atmosphere, then the only product is Si3N4 with the other products remaining as slight impurities.
Zoeckler and Laine in J. Org. Chem. (1983) 48:2539-2541 describe the catalytic activation of the Si-N bond and in particular the ring opening of octamethylcyclotetrasilazane and eolymerization of the ring-opened intermediate. Chain termination is effected by introducing [(CH3)3Si~2NH as a coreactant giving rise to polymers (cH3)3si-tNHsi(cH3)2]n-NHsi(cH3)3 where n may be 1 to 12 or more depending upon the ratio of the chain terminator to the cyclic silazane. The catalyst used was Ru3(CO)12. Other publications are as -6- 1~'10025 follows: W. Fink, Helv. Chem. Acta., 49:1408 (1966);
Belgian Patent 665774 (1965): Netherlands Patent 6,507,996 (1965); D.Y. Zhinkis et al., Rus. Chem. Rev., 49:2814 (1980): K.A. Andrianov et al., Dok Akad. Nauk.
SSSR, 227:352 (1976); Dok Akad. Nauk. SSSR 223:347 (1975): L.H. Sommer et al., JACS 91:7061 (1969); L.H.
Sommer, J. Org. Chem. 32:2470 (1969): L.H. Sommer, J.
Org. Chem. 32:2470 (1967): L.H. Sommer et al., JACS
89:5797 (1967).
In general, control of the polysilazane molecular weight, structural composition and viscoelastic properties play a considerable role in determining the tractability (solubility, meltability or malleability) of the polymer, the ceramic yield, and the selectivity for specific ceramic products. In particular, the tractability plays a major role in how useful the polymer is as a binder, or for forming shapes, coatings, spinning fibers and the like. The more cross-linked a polymer is, the less control one has of its viscoelastic eroeerties. Thus, highly cross-linked and low molecular weight polymers are not particularly useful for spinning fibers because the spun preceramic fiber often lacks tensile strength and is therefore unable to support its own weight. By contrast, high molecular weight, substantially linear polymers as provided herein are extremely important.
Such polymers represent a significant advance in the art, as they provide chain entanglement interactions in the fiber-spinning process and thus enhance the overall tensile strength of the spun fibers.
An example of how molecular weight correlates with the properties of a particular polysilazane can be illustrated by the properties of -~H2SiNMe ~ . The original synthesis of this material was reported by -7- 1~025 Seyferth et al. in Ultrastructure Processinq of Ceramics, Glasfies and Compo6ites, Ed. Hench et al.
(Wiley & Sons, 1984) via an aminolysis reaction:

SEt20/0~C
H SiCl + MeNH ~ H SiNMe~-+ ~ H2SiNMe ~ + MeNH3Cl 10Scheme VI

This method of preparation gives a mixture of a volatile cyclotetramer (35%) and nonvolatile oligomers. This mixture has an Mn of about 330 D and gives only a 28%
ceramic yield u~on pyrolysis. Distillation of the volatile cyclomer yields 65% of low molecular weight nonvolatile oligomer (Mn=560) which is pyrolyzed to give a 39% ceramic yield. An improved method of preparing these oligomers is illustrated by Scheme VII:
THF/-78~C
H SiCl + 3MeNH2 --~~~--~ ~> ~ 2 n 4 25Scheme VII

By the method of this invention, working at temperatures of lower than about 0~C provides mostly nonvolatile linear oligomers (between about 85% and 95%) that require no distillation/purification step. For this eroduct, the Mn is about 800-1,100 D (n~14-19).
Pyrolysis of this imeroved oligomer gives significantly higher ceramic yields of 50% with some improvement in ~ i3~002~i product quality, with Si3N4 eurities of above about 80~, the remainder being carbon.
By the method of this invention, the silazane product of Scheme VII can be further polymerized to give novel polymers with Mn greater than about 10,000 D, in some cases greater than about 20,000 D, Mw greater than about 16,000 D and in some cases greater than about 32,000 D, Mz greater than about 40,000 D and in some cases greater than 80,000 D, or with observable species having a molecular weight of higher than about 50,000 and in some cases higher than about 500,000 D.
Molecular weights as high as 2,500,000 D (see Example 23) have been detected for the polysilazanes as provided herein. Py~rolysis of these true polymer species will give significantly higher ceramic yields than previously obtained, the ceramic yield to a large extent depending on the molecular weight distribution and the polymer processing. Si3N4 purities of 80%
or higher may be obtained, depending on the reaction conditions.
These novel high molecular weight polymers are soluble, exhibit a high degree of linearity and give higher ceramic yields and Si3N4 purities than the oligomeric starting mateeial. In addition, the viscoelastic properties of the novel compounds can be carefully controlled using the method of this invention. In particular, at higher molecular weights, these polymers exhibit non-Newtonian viscoelastic properties, allowing for chain entanglement which will increase the tensile strength required to draw the thin precursor fibers required to form ceramic fibers.
The high ceramic yields are.of considerable value in binder applications, injection molded parts and in matrix applications. During pyrolysis the 2 ~

I densityJvolume change from preceramic polymer (1-1.3 g/cc)to ceramic (3.2 g/cc for Si3N4) can be significant. Thus, ceramic yields far below theoretical will only magnify the resulting density/volume change. For example, a 50%
ceramic yield for a Si3N4 precursor of density 1.0 will result in a final decrease in volume of approximately 80%.
It should be noted that certain aspects of the present invention are discussed in PCT Application No. PCT/
US86/00458 (published 6 November 1986 as W086/06377), U.S.
Patent No. 4,788,309, and U.S. Patent No. 4,612,383, all of which are of common assignment herewith.

Disclosure of the Invention It is thus a primary object of the present invention to overcome the aforementioned disadvantages of the prior art.
It is another object of the invention to provide improved methods of preparing silazanes, and, in particular, high molecular weight polysilazanes.
It is still another object to provide methods of preparing siloxazanes and high molecular weight polysi-loxazanes.
Still another object of the invention is to provide a method of making silazanes and related compounds using transition metal catalysts which provide an extremely rapid initial rejection rate.
A further object of the invention is to provide novel compounds including siloxazanes and high molecular weight polysilazanes and polysiloxazanes.

-10- 134~2~

Still a further object of the invention is to provide a method of ma~ing ceramic materials having a high silicon nitride content, and to prepare and pyrolyze precursors to silicon oxynitride and silicon carbide f ine powders.
Another object of the invention is to provide a method of pyrolyzing preceramic materials ~o as to control the ceramic yield obtained, e.g. by controlling temperature, temperature ramping, pressure, the particular gaseous atmosphere selected, etc.
Still another object of the invention is to provide a method of coating sub6trates with ceramic materials.
Other objects of the invention include methods of making fibers, fine or monodispersed powders, coatings, porous articles such as ceramic foams, filters and membranes, and compression-molded and injection-molded articles using, inter alia, the preceramic polymers and the ceramic materials as provided herein.
Still other objects of the invention include methods of using the polymers of the invention as binders, as adhesives, in infiltration applications, and in matrix and composite materials.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art on examination of the following, or may be learned by practice of the invention.
In one aspect of the invention, a monomeric, oligomeric or polymeric precursor containing at least one Si-N bond is provided. An Si-N bond in the precursor is cleaved in the presence of hydrogen or a 13~0d2~

hydrogen donor, and the cleavage product is reacted with another cleavage product or with a compound containing an Si-H bond, an N-H bond, or both.
In the presence of a transition metal catalyst. The initial silazane product so formed has at least one newly formed Si-N bond.
In another aspect of the invention, one or more reactants are provided having an Si-H and an N-H bond, and reaction is caused to occur so as to form hydrogen and a silazane product having at least one newly formed Si-N
bond and at least two Si-N bonds in its structure Reaction of one type may be caused to follow reaction of the other type; alternatively, both types may be caused to proceed simultaneously, for example, if one or more starting materials are provided having in combination Si-N, Si-H and N-H bonds. Thus, a variety of reaction products can be prepared with these processes.
According to another aspect of the invention, there is provided a method of producing tractable, high molecular weight polysilazanes useful as preceramic polymers and containing at least one newly formed Si-N bond which comprises:
(a) providing a precursor containing at least one Si-N bond, catalytically cleaving an Si-N bond in the precursor in the presence of a transition metal catalyst effective to activate Si-N bonds, wherein the catalyst is selected from the group consisting of: H4Ru4~CO)1 2~ Fe(CO)s, Rh6(CO)1 6 Co2(CO)g, (Ph3P)2Rh(CO)H, H2PtCI6, nickel cyclooctadiene, Os3(CO) 12 Ir4(CO) 12~ (Ph3P)21r(CO)H, NiCI2, Ni(OAC)2, CP2TiCI2~ (Ph3P)3RhCI~
H20s3(CO)10, Pd(Ph3P)4, Fe3(CO)12, Ru3(CO)12, RuC13, NaHRu3(CO)11, PdC12, Pd(OAc)2, (~CN)2PdCI2, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt!C, Pt/BaS04, Cr, Pd/C, Co/C. Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/AI203, Pt/SiO2, Ru/TiO2, Rh/La203, Pd/Ag alloy, LaNis, PtO2, and mixtures thereof, such , ,, -lla-cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second such cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial polysilazane product; or ~b) providing one or more reactants which contain an Si-H bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst effective to activate Si-H and N-H
bonds, to produce an initial polysilazane product having at least two Si-N
bonds;
wherein the polysilazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof .
Preferably, a compound having an M-H bond reacts with either the cleavage product in said type (a) reaction or with a reactant in said type ~b) reaction or both, wherein M is B, Al, Ga, In, Ge, Pb, Sn or S.
The transition metal catalyst may be a palladium catalyst. The reaction temperature may be between about -78~ and about 250~C.
Preferably, the reaction is of type (b), and one or more of the reactants includes a siloxane, and said silazane products include siloxazanes.
According to another aspect of the invention, there is provided a method of preparing tractable, high molecular weight silazanes and siloxazanes suitable as preceramic polymers, comprising the steps of:
(a) providing a linear, branched or cyclic starting material having the structure R'2Si-A- in its molecule, in which A is hydrogen, NR, or Si and wherein the starting material is oligomeric, polymeric or copolymeric;

'J

-llb- 13~ 002~

(b) providing a transition metal catalyst effective to activate Si-N, Si-Si and/or Si-H bonds, wherein the catalyst is selected from the group consisting of: H4Ru4(C0)1 2~ Fe(CO)s, Rh6(C~)16~ C~2(C~)8~ (Ph3p)2Rh(co) H2PtC16~ nickel cyclooctadiene, ~S3(C~)12~ Ir4(co)12~ (Ph3p)2lr~co)H
NiC12, Ni(OAC)2, CP2TiC12, (Ph3P)3RhCI, H20s3(C0) 10~ Pd(Ph3P)4, Fe3(C~)12~ RU3(CO)12~ RuC13, NaHRu3(C0)1 1, PdC12, Pd(OAc)2, (~
CN)2PdC12, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt/C, Pt/BaS04, Cr, Pd/C, Co/C. Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/A1203, Pt/SiO2, Ru/TiO2, Rh/La203, Pd/Ag alloy, LaNis, PtO2, and mixtures thereof; and (c) reacting the starting material in the presence of such catalyst with (1) hydrogen or a hydrogen donor where A is NR and the starting material is part of a silazane or (2) H-X-R where A is hydrogen or Si, wherein:
the R groups are independently selected from the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl or polysilyl; said hydrocarbyl or silyl optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical;
The R' moieties are independently selected from the group consisting of hydrogen; amino; hydrocarbyl; lower alkoxy; silyl or polysilyl; said hydrocarbyl, alkoxy or silyl optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, or a fused aromatic radical of 8 to 20 carbon atoms, and wherein R and R' may be part of an oligomeric or polymeric structure; and X is selected from the group consisting of NR, NR-NR, and NR-R-NR;
wherein the polysilazanes and polysiloxazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater ~i -I lc-1~'1002~

than about 16,000 D, an Mz greater than about 50,000 D, or combinations thereof .
The hydrocarbyl may be selected from the group consisting of lower alkyl, alkenyl, alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic. The starting material may be one of the following structures:
R' z Ha HXsi(NR2)y -Si-NR-P'b where x is an integer from 0 to 4 inclusive, y is an integer from 0 to 4 inclusive, z is an integer from 0 to 2 inclusive, the sum of x, y and z is 4, a and b are integers from 0 to 2 inclusive, the sum of a and b is 2, and m is an integer defining the number of monomer units in the oligomer, polymer or copolymer .
Preferably, the starting material is of the formula R'aSiHb, wherein a is an integer from 0 to 2 inclusive, b is an integer from 2 to 4 inclusive, and thesum of a and b is 4.
According to another aspect of the invention, there is provided a method of making a ceramic composition, comprising pyrolyzing a polymer selected from the group consisting of (a) siloxazanes, (b) polysiloxazanes, (c) polysilazanes having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz of at least about 40,000 D, or a polysilazane species having a molecular weight of at least about 50,000 D, or a combination thereof, (d) mixtures thereof, in a preceramic polymer composition under a selected atmosphere to a temperature higher than about 500~C.
Preferably, the pyrolysis is conducted in the presence of a catalyst. The preceramic polymer composition may be provided as a coating on a substrate -lld- 13~0~25 prior to said pyrolyzing step. In addition, the substrates coated with the preceramic polymer composition comprise another aspect of the invention.
According to another aspect of the invention, there is provided a tractable preceramic polysilazane composition having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz greater than about 40,000 D, or containing a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.
Preferably, the polysilazane composition has either an Mn greater than about 20,000 D, an Mw greater than about 32,000 D, an Mz greater than about 80,000 D, containing a polysilazane species having a molecular weight of at least about 500,000 D, or a combination thereof.
Yet another aspect of the invention comprises silazanes prepared by the process comprising providing at least one reactant which contains an Si-H
bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst to produce an initial silazane product having at least two Si-N bonds, and wherein said at least one reactant additionally includes an Si-N bond and said initial silazane product includes two distinguishable Si-N bond species, wherein the silazanes are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.
Yet another aspect of the invention comprises silazanes and ceramic compositions prepared by the above-described processes. .
According to another aspect of the the invention, there are provided silazanes containing structural units of the formula:

-I le-Ha -Si-NR--_R'b m wherein:
a is Oor 1;
b is 1 or 2 the sum of a and b is 2;
m is an integer defining the number of monomer units in the structure;
the R moieties are independently selected from the group consisting of hydrogen; boryl; hydrocarbyl; silyl; and polysilyl; said hydrocarbyl, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical; and the R' moieties are independently selected from the group consisting of: hydrogen; amino; hydrocarbyl; lower alkoxy; silyl; and polysilyl; said hydrocarbyl, lower alkoxy, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety; lower alkoxy, or a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical, and further wherein the R and R' may be parl: of a cyclic or polymeric structure, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or containing a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.
Preferably, the hydrocarbyl is selected from the group consisting of:
lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.

-llf- 134002~

According to another aspect of the invention, there are provided oligomeric or polymeric siloxazanes containing rec,urring units having the structural formula:
R' R' -O-Si-N-Si-R'R R' wherein:
the R moieties are independently selected from the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl; and polysilyl, said hydrocarbyl, silyl, or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical; and the R' moieties are independently selected from the group consisting of: hydrogen; amino; hydrocarbyl; said hydrocarbyl, lower alkoxy, silyl, or polysilyl, optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical, and further wherein the R and R' may be part of a cyclic or polymeric structure, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.
Preferably, the hydrocarbyl is selected from a group consisting of:
lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.
According to another aspect of the invention, there is provided a method of making ceramic articles, comprising the steps of:

-"g- ~3~0n25 providing a solution of a polymer or a liquid polymer, such polymer selected from the group consisting of (a) polysilazanes having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz of at least about 40,000 D, or including a species having a molecular weight of at least 5 about 50,000 D, or combinations thereof, (b) siloxazanes and (c) mixtures thereof;
admixing said polymer solution with ceramic powders, ceramic whiskers, ceramic fibers, or with a porous or non-porous ceramic article; and thermally treating said admixture so as to form a ceramic article.
According to another aspect of the invention, there are provided fibers spun from the above-described silazanes and siloxazanes.
According to another aspect of the invention, there are provided silazanes prepared by the process comprising providing a precursor containing at least one Si-N bond in the precursor, catalytically cleaving an Si-N bond in the precursor in the presence of a transition metal catalyst, such cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product to produce an initial silazane product wherein the silazanes are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof.
According to another aspect of the invention, there are provided silazanes prepared by the process comprising causing both of the following reaction types (a) and (b) to occur simultaneously:
(a) providing a precursor containing at least one Si-N bond, catalytically cleaving an Si-N bond in the precursor in the presence of a transition metal catalyst effective to activate Si-N bonds, wherein the catalyst is selected from the group consisting of H4Ru4(C0)12, Fe(CO)s, Rh6(C0)16, Co2(CO)g, .~

-I Ih-(Ph3P)2Rh(CO)H, H2PtC16, nickel cyclooctadiene, Os3(C0)12, Ir4(C0)12, (Ph3P)21r(CO)H, NiC12, Ni(OAc)2, CP2TiC12, (Ph3P)3RhCI, H20s3(C0) 10 Pd(Ph3P)4~ Fe3(C~)12~ RU3(cO)l 2~ RuC13, NaHRu3(C0)1 1, PdC12, Pd(OAc)2, ~CN)2PdC12, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt/C, Pt/BaS04, Cr, Pd/C, Co/C, Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/A1203, Pt/SiO2, Ru/TiO2, Rh/La203, Pd/Ag alloy, LaNis, PtO2, and mixtures thereof, such cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second such cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial polysilazane product; and (b) providing at least one reactant which contains an Si-H bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst effective to activate Si-H and N-H
bonds, to produce an initial polysilazane product having at least two Si-N
bonds;
wherein the polysilazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof.
According to another aspect of the invention, there are provided silazanes containing structural units of the formula:

-Si(H)a(NR2)b-NR-wherein:
aisOor 1;
bis 1 or2;
the sum of a and b is 2;

.

002~

the R moieties are independently selected from the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl; and polysilyl, said hydrocarbyl, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 S carbon atoms, or an organometallic radical, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.
Preferably, the hydrocarbyl is selected from a group consisting of:
lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.
The silazane products may be provided as preceramic polymers having moderate or very high molecular weight, which polymers in turn provide a 15 correspondingly high ceramic yield upon pyrolysis. As will be discussed below, these high molecular weight polymers may be produced in such a way so as to provide substantially pure silicon nitride upon pyrolysis..
In a preferred embodiment of the invention, the catalysts which are used in the above-described reactions provide rapid reaction rates, on the 20 prder of about fifteen to fifty times faster than reactions employing standard catalysts .
The invention also encompasses novel silazane and siloxazane compounds and a variety of applications.

Brief Description of the Drawinqs Figure 1 illustrates the GPC results of a silazane (tH2SiNMe]x polymerization catalyzed by Ru3(CO)12:
Figure 2 graphically cepresents TGA pyrolysis of a polysilazane at different tempe~ature ramping rates:
Figuce 3 is an SEM photograph o~ a formed Si3N4/polysilazane body after heating to 800~C in 2; ;
Figure 4 is an SEM photograph of a formed Si3N4/polysilazane body after heating to 1725~C in N2 ~

Modes of Carryinq out the Invention "Silazanes" as used herein are compounds which contain one or more silicon-nitrogen bonds. The term ~polysilazane" is intended to include oligomeric and polymeric silazanes, i.e. compounds which include two or more monomeric silazane units.
"Siloxazanes" as used herein are compounds which contain the unit [o-si-N]~ The term llpolysiloxazane" is intended to include oligomeric and polymeric siloxazanes, i.e. compounds which include two or more monomeric siloxazane units.
"High moleculac weight" polymers as provided herein are polymers that have an Mn qreater than about 10,000 D, in some cases greater than about 20,000 D, Mw greater than about 16,000 D and in some cases greater than about 32,000 D, Mz greater than about 40,000 D and in some cases greater than 80,000 D, or with observable species having a molecular weiqht higher than about 50,000 D and in some cases greater than 500,000 D.

-13- 13~25 "Mn", "Mw~ and "Mz" are defined as follows.
The number average molecular weight Mn of a polymer distcibution is given by Mn = ~.Wi ~Ni, the weight average molecular weight Mw of a polymer distribution is given by Mw = ~wiMi ~Ni, and the Mz value is given by ~,WiMi2 Mz = ~WiMi wherein Wi is the weight of each individual polymeric or oligomeric species, Ni is the number of individual species in the distcibution, and Mi is the mass fraction of each individual species. Where not otherwise specified, molecular weights for a particular polymec distribution obtained directly will be given as calculated prior to any separation or distillation step.
"Substantially linear" oligomers or polymers are noncyclic structures having two or more monomeric units and which are not extensively cross-linked or branched.
A ~substantially eure" ceramic material is intended to mean a ceramic material comprising at least about 75 wt.% of a particular compound.
The "ceramic yield" of a compound upon pyrolysis indicates the catio of the weight of the ceramic product after pyrolysis to the weight of the compound before eyrolysis.
The "purity" of a earticular comeound in a mixture of ceramic matel:ials is defined as the weight percent of that compound in the mixture.
"Cyclic silazanes" are cyclic compounds having one or more Si-N bonds in the molecule.
"Silyl," unless otherwise specified, includes siloxyl, siloxazyl and <,ilazyl.
~0 Silazane and siloxazane "copolymers"
incorporate more than one tyee of monomer unit defined as a ececursor or reactant in reactions of type (a) or type (b) herein which follow.
A l'tractable" polymer is one which is meltable, soluble or malleable or which can be processed like an organic polymer to form a desired shaee.
The compounds provided by the processes of the present invention are monomeric, oligomeric or polymeric structures having one oc more newly formed Si-N bonds.
The reactions which form these structures may be broadly grouped into two types.
In the reaction which will sometimes hereinafter be referred to as the type (a) reaction, a precursor is initially provided which contains at least Z5 one Si-N bond. Cleavage of an Si-N bond in the precursor is catalytically effected in the presence of hydrogen or a hydrogen donor, and the cleavage product is then caused to react with a second cleavage product or with a compound containing an Si-~ bond, an N-H bond, or both, to produce an initial silazane product having at least one newly formed Si-N bond.
In what will sometimes hereinafter be referred to as the type (b) reaction, one or more reactants are provided which in combination contain an Si-H bond and -15- 13iO~32~

an N-H bond, and reaction is caused to occur between the two bonds in the presence of a transition metal catalyst, whereby an initial silazane peoduct is provided having at least two Si-N bonds, at least one of which is newly formed.
The "initial" silazane products so provided may be caused to react: further, according to either the type (a) or type (b) ceactions, oc both, simultaneously or sequentially. These further reactions may include reaction with othec M-H bonds where M is, for example, B, Al, Ga, In, Ge, Pb, S, or Sn.

A. Preparation of Precucsor Materials The precursor material may be monomeric, oligomeric or polymeric, and, in addition to at least one Si-N andtor Si-H bond, may contain one or more Si-Si, Si-C, Si-0, or N-H bonds. Ultimately, an Si-N
bond or Si-H bond and, in some cases, one or more of the "Si-A" bonds of these precursors, wherein A is Si, C or O will be caused to break and one or more new Si-N bonds are caused to focm. In general, precursors having Si-N, Si-H bonds or both are illustrated by Formulae 2 and 3:

R' Ha i Z

H Si(NR2) -~-Si-NR
R~b Formula 2 Formula 3 In the above formulae, x is an integer from 0 to 4 inclusive, y is an integer from 0 to 4 inclusive, z is an integer from 0 to 2 inclusive,- the sum of x, y and z is 4, a is an integer from 0 to 2 inclusive, b is an in~eger from 0 to 2 inclusive, the sum of a and b is 2, -16- 134~2~

and m i6 an integer defining the number of monomer units in the oligomer, polymer or copolyme~. The R moieties, i.e. the substituents on the nitrogen atom(s), which may be the same or diffecent and may form part of a cyclic or polymeric structure, are independently selected from the group consisting of: hydrogen; boryl: hydrocarbyl including lower alkyl (1-6C), lower alkenyl (1-6C), lower alkynyl (1-6C), aryl including phenyl, benzyl and the like, lower alkyl substituted aryl, cycloaliphatic;
silyl or polysilyl, including silazane, siloxane, and siloxazane groups (hereinafter sometimes "silazyl", "siloxyl", and "siloxazyl"): said hydrocarbyl and said silyl functionalities being optionally substituted with amino. hydroxyl, an ether moiety or an ester moiety, lower alkoxy (1-6C), a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical which may include elements such as B, ~1, Ga, In, Ge, Pb, 5, or Sn. The nit~ogen may also be present in various forms such as -NH-, -NH-NH-. -NH-NR-. -NR-NR-, -NR-R-NR-, polyamines, and the like.
The R~ groups, i.e. the substituents on the silicon atom, which may be the same or different and may form part of a cyclic or polymeric structure, are independently selected ~rom the group consisting of:
hydrogen: amino; hydrocarbyl including lower alkyl (1-6C), lower alkenyl (1-6C), lower alkynyl (1-6C), aryl including phenyl, benzyl and the like, lower alkyl substituted aryl, cycloaliphati~ lower alkoxy (1-6C); silyl or polysilyl including silazyl, siloxyl, and siloxazyl: said hydrocarbyl or silyl being optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, oc an organometallic radical which may include elements such as B, Al, Ga, In, Ge, Pb, S, -17- L~1~3 a 2~

or Sn. The silicon moiety, as above, may be present in various forms, i.e. as --SiR'3, -SiR~2-, -SiR'2-SiR'2-, polysilane, etc. Although R' may in some instances be a hydrocarbyl moiety, it is ereferable for many applications that the precursor be substantially free of Si-C bonds, e.g., for the ultimate preparation of ceramic products which are substantially carbon-free These precursors or reactants are preferably prepared by methods as will be described and claimed herein.
Scheme VIII illustrates a preferred synthetic route used in making a monomeric precursor useful in the peesent method.~5 low temperature H SiX + 4HNR ~ H2Si(NR2)2 +

Scheme VIII

In the above reaction sequence, X is a halogen substituent, preferably chloride, and the R moiety are as set forth above.
Procedurally, the halogen-substituted silane H2SiX2 is provided in a solvent, preferably a polar solvent such as tetrahydrofuran, diethyl ether, and the like, and approximately four equivalents of the di-substituted amine are gradually added. The temperature during this addition and admixture step is low, preferably maintained between about 5~C and -30~C.
The reaction mixture is slowly allowed to warm, and the aminosilane "precursor" product is isolated by any known method, e.g. by filtration and subsequent extraction.

)0~

Scheme IX illustrates the preferred method of making oligomeric or polymeric precursors containing Si-N bonds R
H2SiX2 + 3NHzR ----> HN -~-SiH2NR1mH + 2RNH3X
<oo L0 Scheme IX

The reaction of Scheme IX involves preearation of oligomers or polymers from halogen-substituted silanes and mono-substituted amines, X and R beinq defined as abo~e for the compounds of Scheme VIII. ~See Examples 1-3.) Use of the mono--substituted rather than the di-substituted amine provides an oligomeric or polymeric product rather than a monomeric species. Procedurally, the reaction is carried out as described for the monomer preparation reaction of Scheme III. Approximately three equivalents of mono-substituted amine are needed to complete the reaction (a ratio of between about 2.7:1 2 2 2 P btain higher molecular weights). In a modified process, an excess of amine base containing no N-H bonds, e.g. tri-ethylamine, may be added to neutralize the HCl formed during the reaction, in which case, less of the mono-substituted amine is required (e.g., between about 0.9:1 and 1.1:1 RNH2:1 Si-X bond~. ~s in the reaction of Scheme VIII, a eolar solvent is preferred here as well.
The compound reeresented by Formula 3 is a novel composition of matter where R'= H, NR2 or NR-with R as defined above, and m representing the number of monomer units in the polymeric or coeolymeric :13 -1~025 structure; for R = CH3, m being such that Mn is greater than about 600 D before any distillation or separation of the product.
Modification of the oligomeric or polymeric precursor represented by Formula 3 may be carried out as follows, in order to erovide a copolymer which in 60me instances may be preferred for further synthesis or for pyrolysis. An example of such a copolymer is represented by Formula 4:
~IR C~IR7O~
-~-H2SiNR ~ [ HSiNR-~- [ HSiNR ]

Formula 4 One or more compounds of formula R SiX3 or SiX4, where X is halogen and R is preferably H but may be lower alkyl (1-6C) or aryl, e.g., phenyl or benzyl, are added to the reaction mixture to control carbon content in the form of Si-C bonds. By control of the H2SiX2:R SiX3:SiX4 mixture ratio, the Mn, Mw and Mz values can be increased while maintaining tractability of the product as well as substantial linearity. In addition, a higher fraction of amine reactant RNH2 is incorporated into the copolymeric product. These additional amine moieties may serve as latent reactive groups during pyrolysis. It should be noted that substantially the same result may be achieved by replacing a portion of the amine reactant RNH2 with ammonia in addition to or instead of the RSiX3 or SiX4. Such a procedure, in conjunction with applicants' basic method of synthesizing precursor -20- 1 3 10l~2S

species, as outlined above, represents an improvement over known methods insofar as the molecular weight of the product is concerned.
All oligomeric or eolymeric precursors represented by Formula 3 may be pyrolyzed by themselves or may be further reacted catalytically according to the reactions of either type (a) or type (b).
Suitable precursor materials for further reaction of type (a) or type (b) or both thus include o alkylamines such as monomethylamine, dimethylamine, monoethylamine, hydrazine and hydrazine derivatives, polyamines, and the like, as well as a variety of silanes silazanes, polysilazanes, siloxanes, siloxazanes, and the like. These precursors may be modified by inclusion of additional latent reactive groups such as hydrogen, amine, alkoxy, sulfide, alkenyl, alkynyl, etc., or cross-linked with suitable cross-linking reagents.

B. Formation of Silazanes The aforementioned precursor or reactant materials may be used in either the type (a) reactions, wherein an Si-N bond is cleaved and a new Si-N bond is formed, or in type (b) reactions, wherein an Si-H moiety is caused to react with an N-H moiety so as to form a compound having a newly formed Si-N bond. Either reaction is carried out catalytically, under suitable conditions as will be outlined below.
Catalysts suitable for carrying out subsequent reaction of these precursors or reactants according to reactions of either type (a) or type (b) as described above are any type of transition metal catalysts such as those indicated in Table I, below, which are homogeneous catalysts that either dissolve in the reactants or in a solvent used to dissolve the reactants. Heterogeneous -21- L~4~0~5 catalysts such as those of Table II may also be used or mixtures of homogeneous catalysts and/oc heterogeneous catalysts. (It should be pointed out here that the "homogeneous" and "heterogeneous" classifications are made herein on the basis of solubility in organic solvents. However, it is not uncommon that during the reactions, homogeneous catalysts may be converted into a heterogeneous form and vice versa.) These catalysts may include any number of ligands, including amino, silyl and organic ligands, as discussed below and as illustrated in Tables 1 and 2.
Preferred catalysts are transition metals, and in particular the transition metals of Group VIII.
Especially preferred catalysts are ealladium catalysts, e.g. of the formula Pd, PdX2, L2PdX2 or L4Pd, where X is an anionic species such as a halide, and L is a covalent ligand, which may be organic, phosphine, arsine, amine, nitrile, and may additionally include silicon substituents. Examples are PdC12, Pd(OAc)2, (~CN)2PdC12 and Pd/C. As demonstrated in Example 30, these catalysts provide initial reaction rates on the order of fifteen to fifty times faster than that achieved with standard catalysts such as Ru3(CO)12 and Rh6(CO)16 under the same conditions.
The catalyst(s) may be supported on a polymer, inorganic salt, carbon, or ceramic material or the like. The heterogeneous catalyst may be provided in a designed shape, such as particles, porous plates, etc.
The catalyst can be act;vated by heating alone or by concurrent treatment of the reaction medium with particulate or nonearticulate radiation. The catalyst may al60 be activated by promoters such as acids, bases, oxidants or hydrogen, or may be stabilized by reagents -22_ 1 3~ 0 such as amines, phosphines, arsines cind cacbonyl. The concentration of catalyst will usual:Ly be less than or equal to about 5 mole % based on the total number of moles of reactants, usually between about 0.1 and 5 mole ~. In some instances, however, catalyst concentration will be much lower, on the order of ppm.

Table 1, Homoqeneous Catalysts H4Ru4(C0)12J Fe(CO)s, Rh6(C~)16/ C~2(C~)8 (~h3P)2Rh(CO)H, HzPtC16, nickel cyclooctadiene~
~53(C~)12~ Ir4(C~)12, (Ph3P)2IC(CO)H, NiC12, Ni(OAC)2. CP2TiC12, (ph3p)3Rhcl~ H20s3(Co) Pd(Ph3P)4, Fe3(C0)12~ Ru3(C0)12~
tlansition metal hydrides, transition metal salts (e.g.~ ZnC12, RuC13~ NaHRu3(C0)11) and derivatives, PdC12~ Pd(OAc)2~ (~CN)2PdC12~ and mixtures thereof.
Table 2, Heterogeneous Catalysts Pt/C, Pt/BaS04~ Cr~ Pd/C~ Co/C, Pt black~ Co black~
Ru black~ Ra-Ni, Pd black, Ir/A1203, Pt/Sio2, Rh/TiO2, Rh/La203~ Pd/Ag alloy~ LaNi5~ PtO2 and mixtures thereof.
The reaction is carried out in solution with the solvent comerising either the reactants themselves or an added nonreactive organic solvent such as a hydrocarbon, an ether (e.g., ethyl ether, tetrahydro~uran), a halogenated hydrocarbon (CHC13, CH2C12, ClCHF2, ClCH2CH2Cl), an aromatic such as benzene. toluene, or methylphenyl ether, or a polar solvent such as acetonitrile, pyridine, or a tertiary amine. Some reactions may, if desired, be carried out in the gas phase by flowing the reactant(s) over a metal catalyst.
MLld temperatures that will activate the catalyst are typically used. Such temperatures will normally be in the range of -78~C tc 250~C. Higher temperatures are necessary especially where steric hindrance is a problem. In general, higher temperatures provide for a faster reaction, but will result in a greater degree of cross-linking. Type (b) reactions require a lower temperature than type (a) reactions, generally, as cleavage of the Si-N bond in the type (a) reactions requires a higher activation energy.
Where the reaction is of type (a) (cleavage of an Si-N bond and formation of a new Si-N bond, i.e.
rearrangement or metathesis reactions), the reaction is carried out in the presence of hydrogen or a hydrogen donor. Suitable hydrogen donors include silicon hydrides, metal hydrides optionally activated with a proton source, alcohols, amines. mono-, di- and tri-alkylamines, tetralin, tetrahydroquinoline, and the like.
In type (a) reactions, the cleavage product reacts with a comeound containing an Si-H bond, an N-H
bond, or both, to form an initial silazane product having at least one newly formed Si-N bond. In type (b) reactions, one or more reactants which in combination contain an Si-H and an N-H bond are caused to react. In both of these ~eactions, the compound containing the N-H
bond may be ammonia, RNH2, R2NH, with R as defined above, for precursor compounds. One or more compounds containing an M-H bond may also be present, wherein M
is, for example, B, Al, Ge, In, Ga, Pb, S, or Sn, which reacts with either the cleavage product of type (a) reactions or with a reactant in type (b) reactions.
In reactions of type (b), the Si-H and N-H
bonds which are caused to react may be in the same compound, causing cyclization or polymerization, oc they may be in two or more different compounds.

-24- i 3 1 Q 0 2 5 Example6 of type (a) reaction~ thu~ include the following:
. ~ .

R Si--NR' + R" Si--NR" ' ---> R Si--NR " ' + R" Si--NR ' s Scheme X

R Si - NR ' + R "SiH ----> R3"Si - NR ' + R SiH

Scheme XI

-- Si-N 2 ~> + R NH2Si-N - Si-N -Scheme XII

- NR2 R " _ ~JQ" ~
Si - N + R' 2NH ---> + R2NH~Si_N_ _ R

Scheme XIII

Example~ of type (b) reaction~ include:
r ~
SiH4 + RNH2 ~~~~~~~ N~Si - + H2 3 0 S c heme XIV

H NR2 ' 2 2 HNR2 ~~~~~ R2Si - NR + H

Scheme XV

l3.~no2~

R3"SiH ~ R3Si-NR'H ---> R3SiNR'SiR3" + H2 Scheme XVI

H R _ NR2'~ -~i-N - ~ R'zNH ---> Si -N - + H2 _ R - _ R

Scheme XVII

After an initial reaction according to type (a) or type (b) (or both), further reaction of the initial silazane pcoduct(s) may result, by lapse of time, type of catalyst, amount of catalyst, choice of solvent, increase in temperature, or addition of further reactive species. During the reaction process, or after completion thereof, the low and high molecular weight fractions may be separated by size exclusion chromatography, ultrafiltration, membrane separation, distillation, or partial precipitation techniques.
Either fraction so obtained may be recycled through the type (a) oc type (b) reaction sequence again. For example, the low molecular weight fraction can be further reacted so as to yield another crop of high molecular weight polymecs.
A variation of the type (b) reaction is where ammonia is reacted with a compound of formula R3'SiH, with R' as given above:
R 'SiH + NH -_--_> R 'Si -NH + H

Scheme XVIII

-26- 13~2~

Polysilazane6 prepared by the method of the present invention may be provided as preceramic polymers having a molecular weight far higher than that achieved by the prior art. Previously, tractable polysilazanes having molecular weights only as high as about Mn 10,000 D (Mw~16,000 D, Mz~40,000 D) were known, and these polymers displayed a number of problems with regard to volatility, purity, cross-linking, molecular structure, carbon content, etc. By contrast, tractable polymeric silazanes having much higher molecular weights have been achieved with the present method (see Example 23). Thus, the invention herein encompasses compositions of matter having the recurring structure R' -~-Si-NR-]-Formula 5 wherein R and R' are as defined above for the nitrogen and silicon substituents, respectively, wherein the polymer is tractable and wherein Mn is higher than about 10,000 D, preferably higher than 20,000 D, the Mw is higher than about 16,000 D, preferably higher than about 32,000 D, Mz is higher than about 40,000 D, preferably higher than about 80,000 D or combinations thereof, and the overall polymer distribution provided contains compounds with molecular weight6 greater than about 50,000 D, preferably greater than about 500,000 D as observed by, e.g., size exclusion chromatography. These Mn, Mw and Mz values are given for the polymer distribution obtained directly without any separation or distillation step. Polysilazanes containing the -27- t3-1002~

repeating unit ~H2SiNCH3] in the polymer or the copolyme~ having ~n greater than about 600 D be~ore vacuum distillation of volatile compounds and greatec than about 800 D after distillation or with Mw greater than 2000 D or Mz greater than about 4000 D or combinations thereof are also new compositions of matter. "N" and "Si" may represent polyamino or eolysilyl structures as outlined above.
The invention also encompasses novel silazane 0 structures preeared by the reactions of type (a) and type (b) wherein a precurso~ or ceactant has at least one Si-N bond and an Si-H bond or an N-H bond or both, and the reaction p~oduct has at leas~ two different types of Si-N bond species, wherein an ~'Si-N bond species" (i.e., two nonidentical structures) is defined as an R'3Si-NR2 moiety with R and R' as given earlier. Novel compounds are also prepa~ed by the reaction o~ silane or a mono-substituted silane (R'SiH3) with an ~HR2 compound.
The invention fu~ther includes no~el siloxazane oligomers and polymers which include the structure R" ~ O-Si-N]. These can be prepared ~rom siloxane precursors, i.e. precursors having one or more Si-O and two or more Si-H bonds, according to the method outlined as type (b). The following scheme illustrates the various ways in which polysiloxazanes may be prepared according to the method of the present invention.
H

~ z--c, H SiR'z(OR")y + aHNR2 ~~~ (R2N)aSiRz"(OR")y + aH2 (a=O-x) Scheme XIX

-28- ,~4 o ~

R' R' ~ R' R' ~
HSi--O--SiH + H2NR ----> Si-O-Si-N + H2 R' R' R' R' x Scheme XX

~ ~ O R -H -Si-H + H NR ----~ ~ Si -N - + H2 O O - x 10 ~ ~1 ' Scheme XXI

OR" ,~ OR" R 7 H--Si-H + H NR ----> _ Si--N ~ + H2 OR" _ OR"

Scheme XXII

_ R' R~ ~ r ~R~ R~ ~
Si-O -si-o - + HNR -----> Si O~Si~O + H2 - H H -x _ NR2 ~L

Scheme XXIII

Novel siloxazanes as provided herein are of the general structure R"-~-O-Si-N~

wherein R" i6 silyl or hydrocarbyl. More specifically, novel siloxazane monomers are of the structure ~L-f~ 2 ~

R'z (R2N)XSi(OR'')y Fo~mula 6 s wherein x is an integer from 2 to 3 inclusive, y is an integer from 1 to 2 inclusive, z is an integer from O to 1 inclusive, R and R' are as given above and R" is in this case defined as R but excludes amino and alkoxy substituents. Novel polysiloxazanes al80 include oligomeric and polymeric species, which are given by (NR2) ~si--o ]
L5 R~b m Formula 7 wherein a is an intege~ from O to 2 inclusive, b is an integer from O to 1 inclusive, the sum of a and b is 2, m is an integer defining the number of monomer units in the compound, and R and R' are as given above. If desired, high molecular weight polysiloxazanes, having Mn > 10,000 D, preferably > 20,000 D, Mw > 16,000 D, ereferably > 32,000 D, or Mz > 40,000 D, preferably >
80,000 D or combinations thereof, may be obtained by the methods outlined above. Synthesis of these compounds is carried out according to the type (b) reaction sequence.

C. PyrolYsis to Ceramic Materials Another important advantage of the compo6itions and methods of the present invention is the specificity and degree of ceramic yield upon eyroly6is. For example, the high molecular weight polysilazane6 diselay _30~ 25 a correspondingly high ceramic yield, the ceramic materials so provided having a high silicon nitride content, if desired. Silicon nitride may be provided with purity higher than about 80% ueon pyrolysis of the polysilazanes provided herein when pyrolysis is conducted under nitrogen, argon or other inert atmosphere, or higher than about 95% upon pyrolysis of the polysilazanes in an ammonia or other amine atmosphere. Carbon-free polysilazanes which may be erepared according to the method herein may provide silicon nitride of even higher purity, i.e. 95-99% or higher.
Similarly, high ceramic yields of silicon oxynitride (Si2oN2) mixtures may be obtained upon eyrolysis using the methods described herein. The novel methods represent a significant advance in the art, as known synthetic procedures for making silicon oxynitride, a desirable ceramic material having refractory properties of both oxides and nitrides, are problematic. Two novel pathways for production of silicon oxynitride are provided herein.
In the first of these, siloxane oligomers or polymers such as ~CH3SiHo]x can be reacted with ammonia oe amine to introduce nitrogen moieties into these species (see, e.g., Schemes XIX-XXIII). These reactions can lead to the formation of a nitrogen cross-linked polymer having a homogeneous distribution of si-o and Si-N bonds in the polymer. The siloxazane ~ so provided may be pyrolyzed under an inert gas such as nitrogen or argon, or under ammonia or a gaseous amine compound, to yield ceramic mixtures containing silicon oxynitride.
Alternatively, nitrogen-free siloxane starting materials which may be oligomeric or polymeric are _31- 1 3'10n2 ~

pyrolyzed under ammonia or a gaseous amine atmosphere to give silicon oxynitride directly. In this case, the nitrogen is introduced into the siloxane during rather than prior to eyrolysis. The siloxane may be a sesquisiloxane (IR'SiOl 51n), a polyhydridosiloxane (Formula 8) or a cross-linked polysiloxane (Formula 9) or a polysiloxane with latent reactive groups (Formula 8) such as hydrogen, amine, alkoxy, sulfide, alkenyl, alkynyl, etc., which can be cross-linked during heating or replaced durinq curing.

{ si_o R~b Fo~mula 8 -s~-o-(siR2l~~)n~

-~ i -O- ( S iR2 ' -~ ) '-R' Fo~mula 9 In the above formulae, a, b, and R' are defined as for Formula 3~
If desired, silicon carbide, also, may be prepared in high yield upon pyrolysis, using polyhydridosiloxane-ba6ed preceramic polymers and selected eyrolysi6 conditions. The common method for production of SiC fine powder is a high temperature reaction between silica and carbon powders, although more recently, SiC powders have been prepared by -32~ 1002~

pyrolysis of sesquisiloxanes (see, e.g., Fox et al., "Better Ceramics through Chemistry" Symposium, J.
Brinker, Ed.: Mat. Res. Soc. (1986), in presfi). The present method provides an ino~ganic polymer-controlled route to silicon carbide fine eowders and coatings which are more homogeneous than previously obtained and a process by which the comeosition of the product and the amount of cross-linking therein can be carefully controlled. This method decreases the oxygen content of the the p-revious method in the polymeric precursor, leading to higher purity SiC powders.
The general procedure described above in type (b) reactions can be used to prepare preceramic polyhydridosiloxanes, e.g. by cross-linking siloxane precursors with amines such as monoalkylamines, ammonia, hydrazine, and the like, using Si-H catalytic activation In alternative embodiments, other cross-linking agents such as water, diols, ethers, sulfides, alkenyl, alkynyl, and dienoic compounds may be used, as can organic substituents (e.g. lower alkyls) modified with latent reactive groups such as amines, hydroxides, alkoxides, sulfides, ethers, etc., also using an Si-H catalytic activation method.
Procedurally, pyrolysis, according to the preferred method of the pcesent invention, is carried out as follows. A polysilazane, polysiloxazane or polysiloxane is heated in an inert atmosphere such as in nitrogen or argon, or in an ammonia or amine atmosphece, at a predetermined heating rate. As will be demonstcated in Examples 31 and 32, the heating rate during pyroly6is is strongly cocrelated to the yield of ceramic material obtained. Pceferred heating rates for bulk pyrolysis are between about 0.1~C and 10.0~C per minute, preferably between about 0.5~C and 2.0 C per _33_ 1 3~ 002 minute, with a particularly effective heating rate, optimizing ceramic yield, of about 0.5~C per minute. In some applicationfi, however, flash pyrolysis may be preferred. The temperature of the polymer is tyeically raised to between about 500~C and about 900~C, optionally higher, to about 1600~C-1800~C, to provide sintering or grain growth of the ceramic material. The heating process may include one or more isothermal holding steps, in order to control the eyrolysis, to provide more cro6s-linking at moderate temperature (less than about 400~C) and to further increase the yield of the final product. If desired, pyrolysis may be carried out in the presence of a catalyst: examples of suitable catalysts are set forth in Tables I and II.
Optionally, pyrolysis may be carried out only partially, i.e. in aeplications where it is not necessary to obtain a fully pyrolyzed material. Such applications include coatings, siloxazane or silazane rubbers, glasses, etc., or where the substrate can be damaged by high temperatures. Such "partial pyrolysis" or partial curing may be cacried out at temperatures lower than 500~C.
Depending on the preceramic polymer pyrolyzed, then, the ceramic products may include silicon nitride, silicon carbide, silicon oxynitride, silicon nitride~silicon carbide alloys, silicon nitride/boron nitride alloys, silicon carbide/boron nitride alloys, and mixtures thereof.

D. Ceramic Coatinq Procedures ~ he ceramic materials provided herein are useful in a number of applications, including as coatings for many different kinds of substrates.

-34- 13 1~2S

Silicon nitride and silicon oxynitride coatings may be provided on a substrate, for example, by a variation of the pyrolysis method just described. A
substrate selected such that it will withstand the high temperatures of pyrolysis (e.g., metal, glass, ceramic, fibers, graphite) is coated with a preceramic polymer material by dipping in a selected silazane or siloxazane polymer solution, or by painting, seraying, or the like, with such polymer solution, the solution having a predetermined concentration, preferably between about 0.1 and 100 wt.%, more preferably between about 5 and 10 wt.% for most applications. The polymer is then pyrolyzed on the substrate by heating according to the pyrolysis procedure outlined above. In such a method, pyrolysis can be conducted relatively slowly, i.e. at a heating rate between about 0.1~C and 2.0~C per minute, in order to allow evolved gas to escape without forming bubbles in the coating, and can include one or more ~"
isothermal holding steps. In some instances, for example with relatively temperature-sensitive materials, or where a rapid-coating process is desired, a flash pyrolysis step may be preferred. Repeated, multiple coatings may be applied where a thicker layer of material is desired, with partial curing or gradual or flash pyrolysis following each individual coating step.
The pyrolysis temperature will vary with the type of coating desired. Typically, temperatures will range from about 350~C to about 1100~C. Lower temperatures, below about 500~C, can result in only partially pyrolyzed polymer, as discussed in Section C.
Optionally, the liquid or dissolved polymer may be admixed with ceramic powders such as silicon nitride or silicon carbide optionally admixed with sintering aids such as aluminum oxide, silica, yttrium oxide, and -35- i3'iO02~

the like, prior to coating. Ceoss-linking agents as set forth in Section C may be included in the coating mixture as well.
The above coating procedure is a substantial improvement over the conventional, chemical vapor deposition (CVD) method of producing silicon nitride coatings in which the appropriate compounds (e.g., SiH4 and NH3 or volatile silazane) react in the vapor phase to form the ceramic which deposits on the target substrate. CVD is typically an inefficient, time-consuming pcocess which requires costly and specialized equipment. The procedure described above for producing coatings containing silicon nitride can be done with a conventional furnace. Further, the method leads to heat-stable, wear-, erosion--, abrasion, and corcosion-resistant silicon nitride ceramic coatings.
Because silicon nitride is an extremely hard, durable material, many applications of the coating process are possible. One specific application is in gas turbine engines, on parts which are particularly susceptible to weac. ~lso, because silicon nitride is an insulator, the coating process could be used as the dielectric material of capacitors, or for providing insulating coatings in the electronics industry. Other applications are clearly possible.
In an alternative embodiment of the invention, a substcate is spray-coated with ceramic or preceramic materials. Such a procedure provides for a higher density coating, as well as for a greater degree of homogeneity. Preceramic coatings may be provided on a substrate, or at higher temperatures, one or moce ceramic coatings may be provided. Gaseous species, such as silane and ammonia, which are capable of reacting to form preceramic polymers, are introduced into a nozzle.

-36~ 02 The gasefi are admixed within the nozzle and passed over a transition metal cataly6t bed contained within the nozzle, suitable transition metal catalysts herein are selected from those set forth in Tables I and II. The catalyst bed initiates the formation of preceramic materials from the gaseous seecies. At the nozzle, the gaseous prececamic mateeials are mixed with inert or reactive gases introduced into the apparatus through one or more inlets, and the substrate surface is coated with ~0 a mixture of these materials. Such a procedure, which provides a suspension of liquid preceramic materials in air, may be used for the preparation of fine powders, as well.
The desired polymerization reaction designated herein as type (a~ or type (b) thus takes place as the gases are passed over the catalyst bed. The inert gas delivers the preceramic materials to the substrate surface, or, if the gas phase is heated, it can delivec actual ceramic powders or mixtures of powders and preceramic polymer having controlled-size particles.
The process can be used to form ultrafine aerosols of precursors and homogeneous catalyst solutions for ultrafine particle applications.

E. Fabrication of Molded Ceramic Bodie~
The preceramic polymers as provided herein, admixed with ceramic powders, may be used to form three-dimensional articles by injection- or compression-molding. In a preferred embodiment of the invention, a preceramic polymer/ceramic powder system is used to form three-dimensional bodies by compression molding. The inventors herein have surprisingly discovered that there is chemical or physical interaction between the novel polysilazanes or 13~Q~25 polysiloxazanes and a ceramic powder which includes Si3N4 at temperatures as low as 800~C. Such chemical or physical reactions are not expected because even ultrafine-grained Si3N4 powder containing sintering aids does not sinter at such low temperatures. After heating at ~00~C in N2, cylindrical pellets containing both silicon nitride and polysilazane show volume shrinkage of up to 5% and considerable mechanical strength, while pellets of dry powder with no polymer added, heated under the same conditions, show neither shrinkage nor enhanced mechanical strength relative to a powder compact pressed at room temperature. This aspect of the invention exploits the discovery of this chemical interaction to L5 produce ceramic bodies which can have, if desired, a very low pore volume. By using carefully selected conditions, three-dimensional ceramic forms can be prepared which have a green density of about 85% (or a pore volume of 0.06 cm /g or less). (If desired, however, lower density materials can be made by the same process; see Examples 35-43.) A polymer solution containing a polysilazane, e.g., [H2SiNCH3]X, polysiloxane, or polysiloxazane is prepared and mixed with a ceramic powder composition comprising, for example, silicon nitride, sintering aids such as yttrium oxide: aluminum oxide; and silica and, optionally, fibers and whiskers of, for example, silicon nitride, silicon carbide, or carbon. The composition of the polymer/powder mixture is such that it contains between about 5 and about 50 wt.% polymer, and, correspondingly, between about 50 and about 95 wt.%
ceramic powder. The mixture is loaded into a suitable form and compression molded at between about 25,000 and about 50,000 psi. The formed body is then heated under 1340Ç~2~

an inert gas (or under ammonia or a gaseou~ amine comeound) at a temeerature between about 500~C and about 900~C to convert the polymer to ceramic material. The body is then sintered at a temeerature of at least about S 1600~C at a eressure of at least about 3 atm N2 or other gas in order to provide a very dense, substantially nonporous material. The results as demonstrated in the examples indicate that the erocedure may also be successful in the absence of sintering agents.

F. Preparation of Fibers The polymers provided in the eresent invention, and the substantially linear high molecular polysilazanes in earticular, can be used for preceramic fiber spinning.
Three general spinning techniques are commonly used: (a) melt spinning, in which the polymer is spun from its melt and solidified by cooling; (b) dry seinning, in which the polymer is at least partially dissolved in solution and eulled out through the spinneret into a heat chamber, then solidified by solvent evaporation; and (c) wet seinning, in which a concentrated polymer solution is spun into a coagulation or regeneration bath containing another fiolvent in which the polymer is not soluble. These methods are suitable for tractable high molecular polysilazanes having Mn >
lO,OOOD or Mw > 16,000D or Mz > 40,000D or combinations thereof, or containing a eolymeric species in the resultant polymer distribution having a molecular weight over 50,000D. While these polymers may be either meltable, malleable, or soluble in some types of solvents, they may be insoluble in others (e.g., for wet spinnlng ) .

-39- 13'i~2~

Additional, relatively small quantities (0.1-5.0 wt.%) of a very high molecular weight substantially linear organic polymer (100,000-5,000,000D) may be mixed with the inorganic polymer to supeort and improve the fiber strenqth after spinning, as taught in, e.g., U.S. patents Nos.
3,853,567 to Verbeek and 3,892,583 to Winter et al.
The supporting technique is especially useful when low molecular weight and/or nonlinear polymers having a very low degree of chain entanglement are used.
One problem encountered in ceramic fiber fabrication derives from the fusability of inorganic polymers during pyrolysis. This fusability results in structural problems in the spun fiber. Polymers produced by the present invention, however, overcome the fusability problem, providing that the catalytic process as described herein is actually incorporated into the fiber-spinning process. For example, a high molecular weight polysilazane may be mixed with homogeneous catalyst and heated in the spineret or in the curing chamber to cause reactions of type (a) or (b) or both to occur and increase the degree of cross-linking in the fiber. Alternatively, the spineret can itself be a catalytic bed. Cross-linking agents such as those set forth in Section C may also be included in the fiber-spinning process to provide additional cross-linking; similarly, latent reactive groups (e.g., free amino moieties) may be present, as well, for the same reason, even in the absence of catalyst.
G. Other ApPlications Many other applications of the novel eolymers of the invention are clearly possible.

1~002A5 The results summarized in part G, for example, suggest combination of polysilazanes, polysiloxazanes, and related compounds with other ceramic powders (e.g., SiC, BN, B4C) to produce composite articles. Such a composite of, e.g., a siloxazane polymer/SiC powder mixture may give an article having improved oxidation resistance. Another application would be to use the novel polymers in dissolved or liquid form as binders combined with ceramic powders so as to provide a fluid polymer/powder mixture.
Infiltration and impregnation processes are additional possibilities, as discussed, for example, in U.S.
patent No. 4,177,230 to Mazdiyasni et al. and in W.S. Coblenz et al. in Emergent Process Methods of High-Technology Ceramics, ed. Davis et al. (Plenum Publishing, 1984). Two general methods are typically used. One is a high vacuum technique in which a porous ceramic body contacted under vacuum with a liquid or dissolved preceramic polymer. After a high vacuum infiltration, the article is pyrolyzed to achieve a higher density. The second method is high-pressure infiltration. Either of these methods can be adapted for the polymers of the invention. In addition, low molecular weight oligosilazane solutions having higher mobility in the porous ceramic body can be incubated with the ceramic body and a transition metal catalyst, followed by curing of the oligomeric reactants to obtain reactions of type (a) or (b) or both. In situ chain extension or cross-linking will reduce the mobility and volatility of the oligomeric starting materials.
Other applications of the novel polymers include use as a cement to "bond" ceramic materials such as powders, ceramic fibers, and three-dimensional forms. Bonding of fibers followed by pyrolysis can _41- 134002~

yield matrices or matrix composite6. In some application, ceramic articles may be joined by the polymers, undec preasure, followed by pyrolysi6. The chemical interactions discussed in part F between the polymer and ceramic powders may occur in bonding to enhance the strength of the cement.
It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, that the foregoing description a6 well as the examples which follow are intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

Examples Experimental: Unless otherwise indicated, the reagents used were obtained fcom the following sources: silanes, from Petrarch Systems, Inc., ~ristol, Pennsylvania;
organic reagents including amines, from Aldrich Chemical Col, Milwaukee, Wisconsin: gases, from Matheson, Seacaucus, New Jersey; and catalysts, from Strem, Newburyport, Massachusetts.

Example 1 Precursor Formation Into a flame-dried three-neck flask equipped with an overhead mechanical stirrer and an N2 inlet wa6 placed 500 ml anhydrous ether. This was cooled to <
-70~C in a dry ice/acetone bath. Dichlorosilane (150 g;
1.5 moles) was then condensed into the flask. An exces6 -42- 13'1002~

of ~ 198 g (4.5 moles) monoethylamine wa6 then added over a two-hour ~eriod. The reaction mixture was stirred for an additional four hours, and the fla6k was then allowed to warm slowly overnight to room tem~erature. The contents were diluted with 500 ml ether and filtered to remove monoethylamine hydrochloride salt.
The solids were then elaced in a 21 Erlenmeyer flask and stirred for 10 minutes in 500 ml boiling THF.
The mixture was filtered hot. The extraction was repeated and the solids were rinsed with an additional 500 ml hot THF. 89.0 g of ~roducts were obtained after solvent removal (8~% yield) with Mn = 490 D; Mw = 1,720 D; Mz = 11,370 D. Fractionation by high vacuum distillation (150~/300 ~) gives 60~ o~ volatile eroducts having Mn o~ 307 D and 40% residue with Mn =
420 D, Mw = 2670 D, and Mz = 17,560 D

Example 2 Precursor Formation Into a flame-dried three-neck ~lask equi~ed with an overhead mechanical stirrer and an N2 inlet was placed 500 ml anhydrous ether. This was cooled to <
- 70~C in a dry ice/acetone bath. Dichlorosilane (150 g: 1.5 moles) was then condensed into the ~lask. An excess o~ ~ 300 ml monomethylamine was then added over a two-hour period. The reaction mixture was stirred for an additional two hours. The flask was then allowed to warm 610wly overnight to room tem~erature. The contents were diluted with 500 ml ether and filtered to remove monomethylamine hydrochloride salt. The 601vent fractions were evaporated under reduced pressure to yield 10-20 g (11-23%) of oil.

_43_ i~10~2-~

The low yield was attributed to poor extraction of the solids, as the weight of the solids was much higher than expected.
An improved method foc the solid cake extraction was developed. The reaction mixture was filtered and the solids rinsed with ether and THF. The solids were then elaced in a 21 Erlenmeyer flask and stirred for 10 minutes in 500 ml boiling THF. The mixture was filtered hot. The extraction was repeated and the solids were rinsed with an additional 500 ml hot THF. With this extcaction method followed by solvent evaporation the yield improved to 60-75%. The viscous oligomers obtained aftec evapocation of the solvent had nocmal average moleculac weight (Mn) of Mn = 800-1250 D. More than 85-95% ol ociginal product matecial cemained aftec high vacuum distillation (150~C/300 ~) having Mn = 1400 D and highec. Soxhlet extraction can be used for the above cake extcaction.

20Example 3 Pcecucsoc Formation (Modified) Into a flame-dried three-neck flask equipped with an overhead mechanical sticrer and an N2 inlet was placed 1 L anhydrous ether. This was cooled to <
-70~C in a dry ice/acetone bath. Dichlorosilane (154 g;
1.5 moles) was then condensed into the flask.
Trichlorosilane, SiHC13, 15.4 g (0.11 mole), was added into the reactoc. An excess of ~ 400 ml monomethylamine was then bubbled into the solution over a three hour period. The reaction mixture was stirred for an additional two hours. The flask was allowed to warm slowly overnight to room tempecatuce. The contents ~44~ 1~40~2~

were then diluted with 500 ml ether and filtered to ~emove monomethylamine hydrochloride salt.
The solids were then placed in a 21 Erlenmeyer flask and stirred for ~0 minutes in 500 ml boiling THF.
The mixture was filtered hot. The extraction was repeated and the solids were rinsed with an additional 500 ml hot THF. An excess of 20 ml monomethylamine was bubbled through the extracted solution at room temperature to complete removal of chloride impurities.
The cloudy solution was then filtered, followed by evaporation of solvent. The 89 g of oligomers obtained after evaporation of the solvent had Mn = 1,780 D, Mw =
7,460 D, and Mz = 28,020 D. No distillation or purification was necessary.
Example 4 Reaction of Diethylsilane with Ammonia To 20.0 mmole of diethylsilane (1.76 g) were added 25 ~mol of Ru3(C0)12 (16 mg). The solution was heated at 60~C under approximately 80 psi of NH3.
~fter 1 hour, 85% of the silane was converted to a mixture of oligomers and the pressure increased by 200 psi due to H2 evolution. Although Et2SiH2 disappeared totally after 2 hours, chain oligome~ization and cyclization continued for 12 hou~s. Oligomers of types A (n = 3-5: major), B (n = 1-4: major), C (n + n' = 2 or 3), and D (n + n' + n" + n'" = 2) were found in the product mixture. Small quantities of other serie6 -H[Et2SiNH]nH (n = 2-4) and H2N[Et2SiNH]nH (n =
2) also appeared in the solution.

-45- 1 3~a2 ~

4Et2SiNH~n H[Et2SiNH] SiEt2H

1{Et2siNHln-siEt2N-tsiEt2NH]n~-siEt2H ~SiEt2NH]n-siEt2H

C --N-[Et2SiNH] ,_SiEt2 Si- tNHSiEt2 ] n" -N
~-I
HEt2Si-tHNSiEt2~.

Thus, while some cyclomers were eroduced, most of the products were substantially linear oligomers.

Example 5 Reaction of TMDS with Ammonia To 30 mmole of tetramethyldisilazane (TMDS) were added 25 ~mol of Ru3(CO)12. The solution was heated at 135~C under 80 esi of NH3. TMDS disaeeeared totally after 20 h and eolymerization continued for 28 h. The polymeric residue (heavy oil) was 2.44 gm (yield 61 wt~) after distillation at 180~/0.3 mm Hg, with an Mn of 764 D. The major eolymeric series was the linear HSiMe2[NHSiMe2~xNHsiMe2H, Smaller, branched chain polymers appeared as well. Molecular weight~
greater than 26000 D can be obtained by varying of reaction conditions.

-46- ~34~02.~

Example 6 Reaction of TMDS with Ammonia and Hydrazine To 20 mmole of TMDS were added 25 ~mol of Ru3(C0)12. The solution was heated at 135~C under 100 psi of NH3. The conversion of TMDS was 94% after 1 h. 0.1 g of hydrazine were added and the solution was heated again for 3 hours. The GC results showed that most of volatile eroducts disappeared. The high polymeric residue was 68 wt% after distillation at 180~C/0.3 mm Hg. Similar results are achieved by using 200 mg of 5% Pt/C (activated under H2) using identical conditions. The number average molecular weight (Mn) is 1200 D.
Example 7 Reaction of TMDS with Ammonia To 75 mmole of TMDS were added 25 ~mol of Ru3(C0)12 and the solution was heated at 135~C undec 60 psi of ammonia. The hydrogen pressure produced in the reaction was released every 1 hour and the reactor was charged again with 60 psi of NH3. TMDS
disappeared after 5 h. The initial turnover frequency (TF) for TMDS disappearance was 260. The net total turnover number for Si-N bond production was close to ~,480 after 8 hours.

Example 8 Reaction of TMDS with Hydrazine To 20 mmole of tetramethyldisilazane (TMDS) and 20 mmole anhydrous hydrazine (NH2NH2) were added 25 ~mol of Ru3(CO)12 and the solution was heated at -47- 1 34 ~2-~

135~C under nitrogen. All the TMDS disappears after 3 hours and H2 pressure was obtained (TF - 528). The yield of the polymeric residue after distillation of the volatile products was 75 wt. %. The number average molecular weight (Mn) was 968 D.

Example 9 Reaction of n-Hexyl Silane with Ammonia Ten (10.0) grams of n-hexyl silane and 16 mg of Ru3(CO)12 as catalyst wece heated at 60~C under L50 psi of ammonia in a stainless steel reactor. ~ pressure of 300 psi was produced during the first hour. The reactor was cooled to room temperature, the pressure was released and the reactor was charged again with 150 psi of ammonia. This procedure was repeated several times. ~fter 1 hour, 68% of the substrate disappeared (according to calculations based on NMR analysis) and the reaction slowed down. ~fter 17 hours, only 12% of the starting material remained in the oily solution. Only a slight additional conversion was detected when the temperature was raised to 90~C. The addition of another 16 mg of Ru3(CO)12 promoted further conversion to a viscous material which appeared concurrently with the disappearance of hexylsilane. The NMR and the VPO (vapor pressure osmometry) analyses are shown in Table 3.

-48- 1~41~2-~

TimeFo~m ofConYe~iona Unït'6 Ratiob (hou~)Product~ (%~ si-H N-H Mn 5 1 light oil 68 1.2~ 0.72 --17 ~lightly vi~cou~ 88 1.18 2.18 921 24 viscou6 oil91 1.06 2.Z0 962 28d,e ve~y viscous oil 100 0.70 1.~4 2772 36d,e wax 100 0.43 l.B3 qO53 a Overall conversion was determined by NMR spectra in CDC13 (epm). For n-hexylsilane: Si-H 3.52 (t, 3):
C-H 1.36 (m, 8) and 0.9Z (m, 5). For polysilazanes:
Si-H 4.78 (m), 4.57 (m) and 4.36 (m); C-H 1.32 (m) and 0.91 (m); N-H 0.62 (m, br).
b Si-H and N-H unit ratios were determined by NMR
using the hexyl group integration as an internal standard.
c At 60~C-d At gooc~

e After addition of 16 mg Ru3(CO)12.
The reaction mixtu{e was analyzed by NMR and GC-MS techniques to determine types of polymer. In Table 5, possible polymer types A, B, C, D, and E are set forth with the elemental (C, H and N) analysis for each in the upper part of the table. Actual analyses of the reaction mixture after 24 and 36 h are set forth in the lower part of the table.
Certain conclusions may be drawn from Table 4, as follows:
a. The initial conversion was very fast; the initial turnover frequency for silane conversion was 2350 per hour.

1 ~g' 4 Q ~

b. The polymer at 24 hours contained large quantities of Si-H bonds even when the molecular weights are high. Crosslinking was therefore ~revented, possibly as a result of steric hindrance.
c. At 36 hours the high integration ratio of N-H to C-H strongly suggests that there are significant quantities of the -HN-Si- and (NIH)1~2 ; NH2 -Si-NH-functional grou~s. Si-NH2 was also detected by I.R. (absorbance in 1550 cm 1 in CC14. t (NH)1/2 signifies that the NH groue was shared with another fragment of the polymer. ]
d. The polymer product is believed to be a new composition of matter The GC-MS of the reaction solution showed a seeies of linear and cyclic oligomers with substituents on both the silicon, e.g., [(-N)3 Si-)] and nitrogen, e.g., [( _ Si)3N~. The terminal Si-NH2 unit was not observed in the GC-MS fragmentation patterns.
Referring to Table 4, the types of reeeating units of A through E are set forth below.

i3~g~25 n-hexyl ,1- hel~y~
- I -~Si-NH~ 5(~

H ( ~ 5 A (3 ~- h~y ,~ - h~ S; ~, 1 5 - 5 ~ S; - ~, t I
n - h~y I

C

n-hexyl i {Si-N~
H (H-S i-n-hexyl ) 0 5 -51- 1~ 1002 Elemental ~nalysis Type/hours %C %H %N
A 55.81 11.63 10.85 B 52.94 10.66 15.44 C 50.00 11.11 19.44 D 59.25 11.93 5.76 E 58.37 11.35 7.57 28 h 54.51 10.95 10.84 36 h 52.54 10.73 12.93 The following conclusions are drawn from Table 4. The actual analyses at 28 h conform closely to the linear type A polymer.
This example illustrates additional reaction of tyee (a) or type (b) following an initial such reaction, (where, here, cross-linked polymers are prepared from initially synthesized linear oligomers. The polymer obtained by this method is believed to be a new composition of matter.

Example 10 Reaction of Phenylsilane with Ammonia Phenylsilane (10.0 g) and Ru3(C0)12 (16 mg) were heated at 60~C under 150 esi of ammonia in a stainless steel reactor. The reactor was cooled 6everal times during the reaction to sample and to recharge with -52- '~ 100~5 ammonia. After 3 hours, 84% of the ehenylsilane was converted to oligomeric products (calculated from NMR
data). After 14 hours, the reaction temperature was increased to 90~C, and after 18 hours 8 mg Ru3(CO)12 5 were added to the mixture. Table 5 summarizes the observations and the results from the NMR and VPO
analyses.

Time Form o~ ConversionaUnit's Ratiob (hours) Pcoducts(~) si-HN-H Mn 3 sliqhtly viscous 84 1.21 0.98 549 9 sli~htly ~iscous 95 1.13 1.32 --14 very viscous 98L.07 l.Zl 695 18 hard wax100 0.98 1.03 L058 1528d,e solid lO0 0.47 1.47 __ 32d,e solid 100 0.34 1.70 L432 a Overall conversion was determined by NMR spectra in CDC13.

b Si-H and N-H unit ratios were determined by NMR
using the phenyl groue integration as an internal standard.
c At 60~C-d At go~C.

e Addition of 8 mg Ru3(CO)12 and 2 ml of toluene (removed before molecular weight measurements).
The data for the L8 hour sam~le indicate the formation of linear Type E polymers (see Table 6). A~
additional catalyst was added and the temperature 0 ~ 2 5 raised, more ammonia was incorporated into the polymer.
After 32 h, the elemental and the NMR analyses indicate that the polymer contained units of types F, G, and H in the following aeproximate catios: -(NH) lH2 I = [PhSiHNH]o 36~PhSiNH~o 59[PhSiNH~o 05 F G H
;

The polymer containing units F, G and H is indicated as I above.

This solid polymer I after 32 hours was solublein CC14, CH2C12, CHC13 and toluene. It had a glass transition point at 70-72~C and softened considerably at 90~C. Pyrolysis at 900~C gave a 70%
ceramic yield and finally a 35% yield when heated to 1550~. Only alpha and beta Si3N4 were observed by X-ray powder diffractometry although the final ceramic product contained 29% carbon (as determined by elemental analysis). The product is believed to be a new composition of matter.

~3~0q2-~

Elemental Analysis Type/hours %C %H %N
F 59.50 5.78 11.57 56.25 5.47 16.40 H 52.94 5.88 20.58 L8 h 5~.37 5.67 11.81 32 h 57.42 5.58 14.21 I 57.25 5.60 14.97 GC-MS analysis o~ the mixlure after 3 hours of heating revealed that majority of the oligomers (n = 1-3) were type F; minor products included cyclic compounds, cyclomers with branchinq on a silane unit and straight and cyclic compounds branched on the nitrogen.
Amine capped polymers were not observed.

Example 11 Reaction of a Hydridosilazane HMeN ~H2SiNMe~xH and (2.0 g; Mn = 560) and Ru3(C0)12 (16 mg) were heated under several reaction conditions. The results are shown in Table 7. The starting reactant HMeN~H2SiNMe~ H was prepared from H2SiC12 and MeNH2 in ether solution as reported by Seyfecth and Wiseman (Polymer Chem. Div. Preprints;
Paper presented at the spring meeting of ACS, April l9B4). The products were [H2SiNMe]4 and a linear oligomer HNMerSiH2NMe] - H (x was approximately 10).

_55_ 13~a2~

~ u _ C
5d~l o a~
~~' n C~ c N 3~ t~ r ~' ~ z~ ~

o .~ " _ ~
~ 0 U L~ o . vc ~
u , . 0 ~ o C ucr o u ~ O

~ ~ ~ ~ c 5~ ~~ ~ ~ .~ .n u u L ~ ~ N ~ ,,, .
E ~ C ~ O
~ C ~.,~ ~ t) 2 0 z 0 N
U ~~
O O ~ O ~ o E 4 ~ ~ ~ 1.1 t7' U
~ C ~
as ~ -- -- o u 2 5 C ~ ~ ~ ~ ~ ~ O O
0-- ~ ~ ~ ~ ~Z-- ~ ~' Cl ~ C'~ ~ U ~C

Example 12 Polymerization of Ethylsilane with Ammonia Ethylsilane, (EtSiH3, 8 g) was condensed into a stainless steel reactor, containing Ru3(CO)L2 (16 mg) in 1 ml of toluene, and cooled in a dey ice~acetone container. The reactor was then pressurized with 100 psi of ammonia (at -78~C). A total preSsure of 250 psi was obtained when the reactor was heated to room temperature. The solution was heated at 60~C. The reactor was cooled after 1 hour to room temperature, depressuri~ed (releasing H2), loaded with an additional 150 psi of ammonia and reheated at 60~C for an hour, then cycled again for 2 hours. The resulting solution (after 4 h) was very viscous. The solvent was evacuated (R.T., 0.1 mm) and the waxy polymer was heated again at 90~C for another Z hours to form a soft rubber. Pyrolysis of the rubber at between 200 and 900~C gave 58% of ceramic material. The NMR and IR
spectra of the polymer produced after 4 hours show the following peaks: NMR (8, CDC13):Si--H (4.90-4.40, m);
CH3 (0.95, t); N-H (1.0-0.8 br); CH2 (0.58, q).
(The ratio of the Si-H to the Et-Si and N-H absorbance was l:Z4 which suggests that the polymer consists of approximately 30% [EtSiHNH~ units and the rest were [Et(NH2)SiNH and [Et(NH)o 5SiNH]). The product is believed to be a new composition of matter.
I.R. (cm , CH2C12), Si-NH--Si (3385, 1170, 950); Si-NH2 (1545); Si-H (2108); Si-Et [lZ35, 1012)--57~ 4~02~

Example 13 Preparation of Polysiloxazane 1,1,3,3-Tetramethyldisiloxane (5.36 g, 40 mmole (HMe2Si)zO) and Ru~(CO)12 (32 mg, 50 ~mol) were heated at 60~C under NH3 (150 psi). The pressure produced in the reactor was released and the reactor was recharged with NH3 several times. 80% of the disiloxane was converted after 1.5 hours. The reaction was heated continuously for 20 hours.

GC-MS analysis indicates the following pattern:

A = 4 MezSiOMezSiNH ~ (~ = 2-5) B = H-{Me2SiOMe2SiNH] SiMe20SiMe2H ~n = 1-6) A 70% yield was obtained after high vacuum distillation (180~C~0.5 mm). A(n 2) was isolated as solid white crystals, mp. 37~C, with a single NMR absorption at 0.12 ppm. The residue was a viscous oil with Mn = 5690 D. (Mn values were measured by VPO techniques. Later results indicate that VPO may be insufficient .for polymers having Mn over 2000. GPC results usually show higher values; see Example 14.) Elemental analysis:
%C %H %N Si O
Polymer B 32.65 8.84 9.52 38.10 10.88 Found 3Z.67 9.10 8.56 41.89 7.02 This is an example of preparing a polysiloxazane having the general structure:

134002~

R' R'-O ~ Si- N - Si-I
_ R' H R'-These eolysiloxazanes are believed to be novel co~positions of matter. R' is as defined in the text.
The nitrogen may be substituted, e.g. by an organic group R, also defined earlier. The subscript n may have various values.

Example 14 Reaction of Octamethylcyclotetrasilazane Octamethylcyclotetrasilazane was reacted under various conditions with (+) and without (-) [(CH3)3Si]2NH and with various catalysts. Results are set forth in Table 8.

~CC~3)~si~ ~

Octamethycyclotetrasilazane 134002~;

~ r ~ r o r 3 r u7 ~ o o r u~
.~ c o o ~ cJ
o ~ c c u v o _~ ~ o ~ ~ ~ ~ ~n 3 c ~J ~ ~ ~ ~ ~ r~ ~ ~ ~J C
-- ~ c o ~ ~ ~a ~~ c ._~
._ a. cJ ~,~
aJ ~ ,1 ~ ::
3 u o u ,~
U ~ o ~~ ~
U .,~ U
1 0 -- E~
tU O ~ 3 C CD N C~
~-' ~ ~ ~ ~ ~ ~ ~ 3 -- O
._ ~ .-- O ~
Ul ~' ~ Z
; ~ C U~
O ~~ C --' O ~
c 3 1 5 -- -- o C ~
-- C ~ o C

~ ~ C ,C

~,, O U~
-- ~J -- C~ ~.) O o . ,~
r~ O D ~
~~ ~ w C ~ ~" ~ C
V' ~r1 O C o~ 3 ~ ~

zl C 3 C ~1 U
+ I + ~ + ~a C) E Cu~ C
~ n ~ ~ v C ~ ~ C C
~ o C ~ ~ .
U ~~
_ " a) J~

C O o C .~ ~~ C U
o U o C
n v ~ r~ ~ C 3 r~
O
C
O O u ~ O
U CJ
~ O O ~ ~ ~ U C
r~ ~ ~ ~ ~ v ~J ~ C
n o L~ u .~1 c.~ u 3 5 CCJ E~
U U o c ~ I ~ ~ r C ~ 'D C C
~, .~ V O

-60- 13~002~

GC-MS Analysis Identification of polymer tyees produced in the reactions described in Table 8, were performed by GC-MS. This method was limited to polymers with molecular weights less than 1000. We have observed types A and B in run (1). B was the major product in run 4 (n = 1-8) and A

o ~e~S; ~ Me3SiNH[Me2SiNH]nSiMe3 appears in small quantities (n = 3-7). Another set of polymecs observed in even smaller quantities wece C
(n + n~ = Z-7) and D (n ~ n~ + n'' + n~'' = 2 - 6). C
and D wece ccosslinked through nitrogen groups.
~Si~" S;-_ 5;~ S; ~1 H} S; ~J ~S ;~ h,S;--)~ S ~ S~ n C - S~ S; 3~

In the above, Si signifies -SiMe2- and Si_ signifies -SiMe .
In run 3, because of the high moleculac weiqht, no significant products could be detected by the GC-MS.
Most likely there were more crosslinks from this run which also explains the high molecular weight. Run 6 shows the same types as the parallel reaction with Ru3(C0)12 but the quantities of C and D were larger. The Pt/C catalysis without the capping agent gives series A and other quantitative series E, F that indicate bi- and tri-cyclo crosslinked compounds.

r Si-[NHSi]
N-Si-tNHSi] , -N
L Si-[NHSi]n,, ~

F contains another ring. In E, n 1 (i.e.
~ + n~) = 5-8; in F~ ntotal The polymers produced by HzS04 catalysis contains types A (n = 5,6), B ~n = Z-8; major products), and C(n = Z-5) in run Z and A (n = 5-9) in run 4. In both cases the GC-MS analyses show an amount of oxygenated products in which oxygen replaced amine groups.

Z0 Example 15 Reaction of Polydimethylsilylhydrazine To 1.8 g polydimethylsilylhydrazine H2NNH-[Me2SiNHNH]x]-H prepared as follows:

3 ~ 2 2 2 ~ [(CH3)2 SiNHNH] + NH NH Cl (Mn ~ 1130) dissolved in 5 ml of toluene were added Z5 ~mol of Ru3(C0)12 and the solution was heated at 135~C under hydrogen. The clear solution turned cloudy and viscous (at room temperature) 1.3 g of a soft solid product was obtained after distillation of the volatile products and solvent at 180~C/0.3 mm Hg. The solid had an Mn of 1220 D and started to soften at -62- ~3~0025 60~C. The same treatment for the staeting material in the absence of catalyst gave a slightly cloudy solution at eoom tempeeatuee (cleac during heating). The Mn decreased to 612 D. The product was a solid after distillation and did not soften up to 250~C.
This example illustrates the use of precursors having an N-N moiety within the molecular steucture.

; Example 16 Catalytic Studies Octamethylcyclotetrasilazane was reacted with [(CH3)3Si]2NH in the presence of various catalysts. The reaction conditions, catalysts and results are set forth in Table 9.

13'1002~

., ., .
C~
F ra S ~r~
.~ ~
a O

1 0 ~-- ~ O ~ r~) ~D O O O I a~ ,~ ~ ~ a: I O ~o .n ~ r5~ U:l N r~) r ,~ I r r- r ~n r I r r r ~ r ..
r o ~) 1 5 ~O ~ ~ ~ ~D ~ r.-l r,~ I O ~O r~ O r~ I ~ ~ 7 Ln r~
E

._ V' -.a ~ -- ~ O ~7 ~ ~ ~ ~ u ~ O ~n .n ~ ~ ~ O ~ ~ O u~
2 0 ~I G r~
E-~n ~
~ O
O
O -- ~
1 t'J ~ N
r o ~r N ~ N ~J (~I -- ~ 'O
3 ~ .0 _ _ ~ _ _ ~ _ _ _ -- -- u ~ ooooooooooo--ooooo _uuuuuuuuuu~uuuuu ~__________~u~----------u~u ~ ~ O 'D ~O ~ ~ ~ ~ O ~
~ r~ r u u u v v ~
~ ~ o o o ~

c~ o r a~ ~ o .~ ~

13 1002~

Comments on Table 9 are as follows: The molar ratio of octamethylcyclotetrasilazane, silazane [(CH3)3Si]2NH and catalyst was 250:84:1. The reaction was carried out under hydrogen where indicated, 5 as in Run No. 3, or with water in Run No. 4, otherwise under nitrogen. The hydrogen was at 1 atm. The time figures indicate the shortest time in which there was no further conversion of the starting silazane reactant.
But;yl ether was used as an intecnal standard for gas 10 chromatographic analysis. In the decomposition of catalyst column, "s" means slow, "m'' means moderate and "f" means fast. In Run No. 4 the ratio of Ru3(C0)12 to H20 was 1:22. In Run No. 18, 200 mg of 5% Pt/C
were used and in Run No. 20, 150 mg of 5% Pd/C were used 15 with 4.15 grams of octamethylcyclotetrasilazane.

Example 17 J Reaction of Hexamethylcyclotrisilazane with Ammonia and Hydroqen A reactor loaded with hexamethylcyclotrisilazane, (4.4 g~ and Ru3(C0)1z (16 mg) was pressurized with NH3 (150 psi) and Hz (150 psi), then heated at 135~C for 18 hours. .The 25 cyclotrimer was converted in 84% yield to form two major series of products: cyclomers (A; n = 4-13) and branched cyclomers (B; n = 1-6) analyzed by GC-MS.

13~002~

4(c~3~s ~

Hexamethylcyclotrisilazane ~e~

4~caS, N~ e~S;~

A

B

Example 18 Copolymerization of Phenylsilane 20and 1,1,3,3-Tetramethyldisilazane To a mixture of phenylsilane (4.32 g, 40 mmole) and l,1,3,3-tetramethyldisilazane (5.32 g, 40 mmole) was added Ru3(CO)12 (16 mg, 25 ~mol). The solutio~
was heated at 60~C under lS0 psi of ammonia. After 5 h, the GC shows high boiling products and the loss of 95%
of the starting materials. After 8 hours, the reaction temperature was increased to 90~C and after another 2 hours to 135~C. The reaction was run for 30 hours. The final result was a viscous oil consisting of a mixtuce of products. Very little material came off the GC at this point which was indicative of high molecular weight products. Evaporation of the remaining volatile products (Z30~C~2 mm~ leaves a waxy residue. IR, NMR

-66- 13 40l~25 and GC~MS of this product were taken to examine the copolymerization between the two starting substrates.
An Si-H bond appears clearly in the IR spectrum (although it is not observed in the NMR spectrum which was analytically less sensitive). The elemental analysis and the NMR integration suggest that the copolymer contains the following average structure.

~e~s;ol~la ¦ ~er~yl~ S; ~

This copolymer is believed to be a new composition of matter-Elemental analysis:

C H N Si Calculated foc sug-20gested structure: 46.69 7.61 15.23 30.44 Found : 46.45 7.05 15.91 30.88 Example 19 Reaction Between 25Hexamethylcyclotcisilazane and Diethylsilane 15 mg (25 ~mol) of Ru3(CO)12 were added to 2.19 g (10 mmole) of hexamethylcyclotrisilane (-{Me2SiNH ~ ) and 0.88 g (10 mmole) of diethylsilane (Et2SiH2). The solution was heated at 135~C for 20 h.
N-diethylsilane-hexamethylcyclotrisilazane -67- 13~002~

HN N-SiHEtz 1 l 2 SiMe2 , HN
was the major product (3.7 mmole/ identified by GC-MS
and NMR. Other minor products were (HEt2Si)2NH and bis- (N-diethylsilyl)-hexamethylcyclotrisilazane. A
residue of 28% yield remained after evaporation at 180~C
(0,5 mm). The (N-diethylsilyl)-cyclotrisilazane, believed to be a new composition of matter, was isolated by distillation and identified by GC-MS and NMR.

Example 20 Reaction of 1,2,3,4,5,6-Hexamethyl-cyclotrisilazane with Ammonia To 4.39 g of [MeSiH-NMe]3 were added 16 mg of Ru3(CO)lz The solution was heated under 150 psi of ammonia at, 60~C. The reactant disappeared after 5 hours. The reactor was again charged with ammonia and heated at 90~C for 33 hours. The product was a viscous oil having Mn = 691 which gave a 57% yield of cecamic material. GC-MS analysis of the oligomeric fraction indicated the substitution of Si-H groups by Si-NH
groups together with the substitution of N-Me groups by N-H in the cyclomeric structure. The product is believed to be a new composition of matter.

-68- 13~d2S

Example 21 Polymerization of Tetramethyldisilazane in the Presence of Ammonia (a) To 100.0 mmole of TMDS (13.3 g) were added 50.0 ~mol of Ru~(C0)1z (32.0 mg) and the solution was heated under ammonia under various reaction conditions as noted in Table 10. The volatile oligomers were separated from the solution by vacuum distillation (up to 180~C/300 ~). The residue was the nonvolatile fraction.
Our initial evaluation of this reaction, using either the homogeneous ruthenium catalyst or activated Pt/C gave cyclomecs (n=3-7), linear oligomers (n=2-11), and very small amounts of branched oligomers, (n=1-7: <5%) as evidenced by the GC-MS analyses.

. ,. ~
., ~

-69- 13~10~J2~

~- r ~: c c~ O
o o _ ~ ~ r~ _ Z

O _~
~ ~ C
~ ~ ~' O
.,1 Ql _ r 1 F ~J E
r~ O
~ ~ U
O ~ >
~ ~ C
C O :~ O O
Z ,~ r~7 Z Ll C
O
l V C aJ -- ~-- ~
CJ rO E ~~
U O V -- ~J Ln r~ C O .
ro C ~J
O O -~
E-' 'J ~ u u G C ~ ~1) U .~ -- r~
tlJ (~ O C r~ J -- --ro aJ ~ ~J U '~ E
--' 3 ~ rO ~ ---1 5 c J O ~ C ro o a~ c r~ ~ ~ C ~
E a~ o E r l :~ E- ----- ~ '.;~
,<;: C
O ~ U: ro - r.
U~O --O C .J
~ r~5r~ o CJ ~~5 C
~ c 3 ~ ~ ~
~ c) ~ aJ ~0 ~ ~ ,c ~ c m ~ c ~ ,c o o o co ~ O ,_ o ~ o r~ ~ o . V E~ c v7 .,4 ~ o u J a) ~ . ~ ~ ~ r~
a) u rll ~Jc ._ ~--~ C ~ .0 ~ ~a r~ o c ~
E ~ ~ u ~ . ~ tJ ~ _ u a1 ~ ~ c C~ u E~ ~ ,c ~ ~J ~-- c c~
J ~1 0 ~ ,CI O
~~1 C CJ .J~-- ~:
O ~ C U ~ C U~ ~ U
U O ' ~
~ 3~a _ ~ ~ ~ O,~ ~
,~ ~ ~ u o o o o o _~ u -- C
U~ C ~1 ~ ~' C,C U
O C~
~ u .J a~
GJ ~ ~ ~rO1:~
c ~ E OC) G
o ~
U Ul ~ o ,_~
~L ~ U c ~E
3 0 1 ~o o ~ ~o ~ ~
J ~~ c ~ ~l ~
~ ~~C., u a~ rn ~ ~ O o o o ~ 5~n E U ~o ~ ~o o~ tD~v ~ ~ ~ c~_ _ E~ -- cu O u~
~--Z I ~ D ~ O
a~ ~
._1 D' Cl C ~
o c c~ _ 0 2 ~

Example 22 Catalytic Formation of Extended Polymers An N-methylpolysilazane, CH3NH-(H2SiNCH3~ -H
(Mn=llO0) was reacted with Ru3(CO)12 under different conditions (e.g., reaction time and temperature, ammonia and monomethylamine environment). Samples were taken out of the reactions solutions; solvents were evaporated and Mn measurements were performed on VP0 equipment.
The results are shown in Table 11.

-71~ ') Q 2 $

~, ~o o o oo o o -- C N ~ ~In C~ O a) ~
O ~ N ~'1 ~ C~ C ~1 a) ~ ,_ -,I c o o o o o o o o E~ / N N

1 ~
~a o ~ _ '~- ~ O O O O O O O O
. ~

N
1 5 a~ ~a z C ~1 ~ N N N N 3~ I
~5 C1 ~ Z Z Z Z Z Z Z O
E~
-' O O O
,( O O I ~ ~ ~ O O
:I: e ~ ~ I N N N

2 0 ~a ,_ o o o o o o o o ~) -- d' ~ N ~r ~r N 'D 'O
C al ,~ N N ~1 e ~ t~' o O ~ ~ ~ ~ ~ ~
" _ . . . . .. . .
O r-l N'O'D~D~e~
P~

C ~l N ~ ~U~'D1' a~
O;

-72- 13~002~

The polymers obtained in runs 7 and 8 were soluble in the reaction solution and cross-linked upon solvent evaporation. Therefore, they are excellent candidates for binder and coatinq applications. Runs 7 and 8 prove the reactivity of the SiH polymers toward N-H bond additives and the formation of increased amount of latent reactive groups providing thermosetting properties to the polymers.

Example 23 Catalytic Focmation of Extended Polymers To 50g N-methylsilazane, CH3NII-(H2SiNCH3)x-H
(Mn = 1050) wece added 100 mg Ru3(CO)L2 and the mixture was heated at 90~C. Samples were taken out of the solution and measured by GPC (Gel Permeation Chromatography), VP0 and Rheometry instruments. The results are shown in Table 12 and plotted in Figure 1.
All samples, including starting material, show a very broad distcibution. The higher molecular weight limit (for observable species) was increased from 50,Z00 D in the starting materials to 1,000,000 to 2,000,000 a~ter 100 hours. Two new maximum peaks are built up around 28,000 and 55,000 D. Although increases in Mn,were not observable afte~ 40 hours, the higher molecular weight fraction continues to grow as indicated by the high Mw and Mz values, determined by GPC. These results are evidence of the extremely high polymers which are obtained by the direct ammonolosis and by the catalytic activation, chain extension and cross-linking. Such tractable high molecular weight products were never reported in the current literature. Separation of the high molecular weight fraction(s) may be effected by eithec size exclusion chromatography, membrane or _73_ ~4002~

ultrafiltcation, ultracentrifugation, or solvent/solvent fractionation from solutions or high vacuum distillation. The polymer viscosity increased dramatically during the reaction, starting at ~ 1.0 S poise and ending at ~ 400-4500 poise. All samples except the 100 hour one behave in a newtonian fashion.
The 100 hour sample shows a non-Newtonian viscosity between 4780 poise at a shear rate of 1.0 sec to 400 poise at a shear rate of 10.0 sec O ul O ~n o Table 12: GPCa and Related VPO and Viscosity Resulta Time 1st Max.b 2nd Max.b ~d Max.~ Hig~e~t Mnc MwcMzC MndDe Viscosity ~hou~s~ b (G~PC~(GPC) (CPC~(VPO~ ~Poise~f~ I
0 2.1K -- -- SOK 1,100 3,970 13,0801050 3.6 5 2.6K 23~ -- 120K 2,04010,450 38,2201290 5.1 --2.6K Z3~ 50K 160K 2,13012.660 47,0101390 S.9 --2.6~ 2~K 50K 320K 2.14017,990 86,8401430 ~.418 2.6K 32K SSK 230K 2,2~019,510 7~,4301530 a.s55 S0 2.6K 35K SSK 320~ 2,57020,990 ~6,7101710 ~.258 2.6K 3ZK 60K 520K 2,320h23,620 127,620 176010.6 98 1009 2.6~ 33K 320K 2,4~0K 2,06046,290 553,020 -- 23.0 4,800 a. GPC equipped with 4 size exclusion columns suitable fo~ sepa~ation bet~een 100 and 1.000.000 D. THF
~as used a6 a solvent and polystytene standardi2at~0n cu~ve.
b. Maxima of the GPC disttibution curve and highe~t molecular weight species observed by GPC.
c. Molecular weight determined by GPC.
d. Mea~ured by VPO technique~.
e. D . dispersion o~ polymer: D , Mw~Mn.
f. Measu~ed by ~heometet at 30~C.
q. Difficultles ~ere ~ound in flltration; ttue value6 may be highet.
h. Lowe~ Mn may suggest branching or croas-llnkIng of the polymet. ~_~
The polymer behaves In a non-Nc~tonian ~ashlon. For a aheer rate o~ 1.0 ~ec~l, the viacosity value waa 4,80oi pol~e. For a fiheer rate or 10 ~ec~l, the vlsco~ity value ifi 400 polae.

G
~n 13~1)02~
Example 24 Reactions of Methylsiloxanes with Dimethylamine ~ ro 6 0 g (100 mmOle) 4CH S1HO ~
3Z g (0.05 mmole) of Ru3(CO)L2. ~e so~ution was charged with approximately 100 esi of dimethylamine.
The reaction was carried out at 60~C and detected by the observed pressure formed in the reactor. The pressure was released every 0.5-1 hour and t,he reactor was recharged with fresh dimethylamine. After 6 hours, a total pressure of 1100 psi dimethylamine was charged into the ceactor yielding a total pressure of 770 psi.
No more gas evolution was observed. 8.1 g of viscous oily products were obtained, indicating 49% yield of amino substitution. This yield is correlated with the H-NMR analysis of the solution showing 53% of amine substitution and 29% of Si-H groups. GC-MS analysis shows that bis and tris substituted cyclotetramers were the major products when mono and tetrakis appear only in small quantities. The Mn of the product was 604 D.
Elemental analysis: Si(25.33); N(~2.59); C(30.71);
H(8.15): 0(19.8'7). Pyrolysis under N2 gave a ceramic yield of 14% and under NH3 a ceramic yield of 61%.

b. 4CH3SiHo ~
The reaction was run with the same quantities of starting materials and under the same conditions as the tetramer reaction of (a). Only 50 psi of dimethylamine was charged into the reactor each time. A
total peessure of 500 psi dimethylamine was charged and 375 psi of hydrogen were evolved after 6 hours. 7.4 g of a very viscous polymer was obtained (33% yield of amino substitution) which was correlated to the H-NMR

-76- 13~02~

analysis showing similar results (36% of amine substitution and 45% of Si-H referred to the Si-CH3 group). The Mn of the product was L976.0 D.
Elemental Analysis: Si(28.89); N(7.77); C(Z8.68);
H(7.51); 0(20.85). Pyrolysis under N2 and NH3 gave ceeamic yields of 25% and 70%, respectively.

Example 25 Reaction of Silane with Ammonia To a stainless steel reactor containing a solution of 32 mg Ru3(C0)12 in 10 ml THF were charged 40 psi of SiH4 and 60 psi of NH3. The reactor was heated for 6 hours at 60~C. IR analysis indicates the formation of silazanes. A insoluble solid material (300 mg) obtained after solvent removal was characterized as intractable silazane resin. Elemental analysis of this product shows THF or THF products trapped in the solid material. This analysis fits the molecular structure of [(NH)o 5SiHNH]X after calculated corrections for the presence of THF products and catalyst. Pyrolysis of the solid gave an 86%
ceramic yield.

IR AnalYsiS:
Solvent IR (THF), ref THF, cm : NH2 3380-3320; NH 3280; Si-H 2157, 2142, 880; Si-NH2 11555; Si-NH-Si 1150, 972.
Solid IR (KBr, cm ): NH2, NH 3700-3000:
Si-H 2166, 885; Si-NH-Si 1150, 1045, 960, (all very broad) 13~0~2~

Elemental Analysis of Polymer Product (~):
Si N H C O Ru 36.25 14.10 4.68 12.11 23.06 9.08 Such a reaction may also be used in the preparation of ceramic products.

Example 26 Reaction of Silane with Methylamine To a stainless steel reactor containing a solution of 16 mg Ru3(CO)12 in 10 ml THF were charged 60 psi SiH4 and 60 psi MeNH2. The reactor was heated at 60~C for 4 hours. A pressure of 120 psi was built up during the reaction period. The solution was homogeneous and 380 mg of oily products remained after solvent removal. This oil became more viscous as a result of cross-linking at room temperature under inert atmos~here. Several ~H-NMR singlets of Si-H as well as 2 N-CH3 singlets suggest different types of silazane bonds. Indeed, GC-MS analysis pLovides evidence to the formation of cyclosilazanes containing aminic and silylaminic side groups. H-NMR: Si-H
4.62, 4.49, 4.38 (7H); N-CH3 2.52, 2.48 (30H).
Example 27 Synthesis of Et3SiNH2 To 20 mmole (3.2 ml) Et3SiH were added 0.05 mmole (11 mg) Pd(OAc)2 and the solution was heated at 100~C under N2 for 5 minutes to reduce PdII to Pd . The solution was cooled to 21~C and then dry ammonia was bubbled through the solution to complete the silane transformation to silylamine in 4 hours.

13~002s Completion of the reaction was observed by gas chromatography as well as by tapering off of the vigocous hydrogen evolution which occurred ducing the reaction. The reaction mixture was filtered under N2 and distilled under N2 (138~C) to provide analytically pure silylamine with yields higher than about 90%.

Example 28 Reaction of Et3SiNH2 with Et3SiH
To a solution of 9 mmole (2 ml) Et3SiNH2 in 5 ml THF were added 16 mg of Ru3(CO)lz and 9 mmole of Et3SiH. The reaction was completed after ZO min at 70~C, and product formation (over 95% yield) was followed by GC.

Example 29 Reactions of Oliqo- and Polymethylsiloxane With Ammonia ZO a. 0.05 mmole (32 mg) Ru3(CO)lz was added to 100 mmole (6.0 g) 4CH3SiHo ~ and the solution was heated at 60~C under 200 psi of ammonia. Gas evolution formed a pressure of 400 psi in 19 hours and hard rubber was formed. The product's elemental analysis showed the presence of 5.55 Wt% which indicated a nitrogen-silicon ratio of 0.28 (Table 13). Oxygen content was in a ratio of 1.29 per silicon. Some of the oxygen excess was a result of oxygen contamination found in the commercial starting material and detected by NMR intensity ratio of Si-H/Si-CH3 absorbance (0.~:1.0).
The product was pyrolyzed at 850~C both under nitrogen and ammonia atmosphere. Elemental analysis of the pyrolyzed material suggested a mixture of the following ceramic components (mol ratio): SiO2(0.62);

_79_ 1~40~2S

Si3N4(o.23); SiC(0.14): C(0.58). Pyrolysis under a slow stream of ammonia reduced, almost totally, the carbon content as well a some of the oxygen excess and increased significantly the nitrogen content.
Very similar results were observed when the cyclotetramer was ceplaced by polymethylsiloxane having a number average molecular weight (Mn) of 1880 (degree of polymecization was 29) as shown in Tables 13 and 14.
The compacison between cyclo and polysiloxane reactions revealed that less nitrogen interacted with the polymer than with the cyclomer and the SiC fraction in the eroduct pyrolyzed under nitrogen was higher for the polymer reaction. However, no real difference was shown when both were eyrolyzed under ammonia. The pyrolysis was not completed as there was an excess of oxygen (assuming that Si2oN2 was the major product and that the silicon excess forms SiO2). The ceramic yields were very high for all types of reactions and pyrolysis p~ocedureci .
t). A solution of 100 mmole (6.0 g) of 4CH3SiHo ~ and 25.0 ~mol (8 mg) Ru3(C0)12 was heated at 60~C under L00 psi of ammonia After 2 hours 220 psi of pressure were formed and the product was obtained as a viscous liquid having Mn = 1230 D. The pcessure was released and recharged with an additional 100 psi of ammonia. 200 psi of gas were evolved in a 2-hour peciod and the viscous liquid was converted to a soft rubber H NMR integration revealed that 41~ of Si-H
bonds were replaced by ammonia to form Si-NH2 and Si-NH- bonds. Elemental analysis showed that the incorporation ratio of 0.24 nitrogen per carbon, which indicated the formation of cyclosilazane chain polymer -80- 13400~5 bridged by ammonia. A dimer of two cyclotetramers bridged by a single -NH was the major product found by GC-MS analysis.
IR of CC14 solutions shows new sharp stretches at 3420 (w), 3380 (m) cm together with new shoulders at 1240 and 1160 cm H NMR (CDC13 ~, Ref CHC13~: Si-H
(4.69, 0.59H), NH {1.10, 0.16H) CH3 (0.22, 3H).

10 Elemental AnalySiS:
C H N Si Found (%) 19.94 6.14 5.39 42.23 mol ratio l.Oo 3.70 o.Z4 0.91 Table 13: The ~lemental Analysis of Polymers and Ceramics Ob-tained in a Catalyzed Reaction Between Methylsiloxane~
and Ammonia Product Analysis % (mol ratio) _Si_ O_ N C H
Cyclotetramer Reaction Polymer 40.70 29.85 5.55 18.02 5.88 (1.00) (1.29)(0.28)(1.03) (q.06) Ceramic material 45.73 32.53 6.94 14.10 0.79 under N2 (1.00) (1.25)(0.31)(0.72) (0.48) Ceramic material 47.76 28.26 21.81 1.35 0.57 under NH3 (1.00) (1.04)(0.91)(0.06) (0.33) Po lymer Reaction Polymer 42.47 27.80 4.06 19.67 6.00 (1.00) (1.14)(0.19)(1.07) (3.95) Ceramic material 48.12 32.81 5.02 13.65 0.76 under N2 (1.00) (1.19)(0.21)(0.66) (0.44) Ceramic material 48.29 28.35 21.01 1.75 0.54 under NH3 (1.00) (1.03) (0.87)(0.09) (0.31) -81- 13 40 ~ 2.

Table 14: Ceramic Yield of the Pycolyzed Polymers Ob-tained in a Catalytic Reaction Between Methyl-siloxanes and Ammonia 5 ReactantPyrolysis Conditions Ceramic Yield (%) Cyclotetramer N2 77 Cyclotetramer NH3 84 Polymec 2 75 Polymer NH3 88 Example 30 Kinetic Studies In a typical kinetic reaction, a small quantity of the solid catalyst was carefully weighed and placed in a glass reactor. The reactor was then capped with a septum sealed head and the system was purged with argon for at least 15 minutes. Freshly dried THF, followed by 3.14 mmole of triethylsilane, 0.513 mmole of n-decane and 2.38 mmole of n-butyl amine were introduced into the reactor via syringe. The solution mixture was then placed in an oil bath at 70~C for reaction. Aliquots were drawn out at timed intervals for GC analyses. In cases where reaction did not occur at 70~C, the temperature was raised to 100~C.

-82- ~ 0 2 g Table 15: Initial Reaction Rate of Catalytic Reaction Between Et3SiH and n-BuNH2 Initial Reaction Rate Catalyst Relative to Ru3(C0)12 Ir4(C0)12 0.25 Os3(C0)1z 0.30 H20S3(CO)1O 0 45 Rh6(C0)16 0.17a RU3(CO)12 L,OOa H4Ru4(C0)1z a PdC12 13.3 Pd~C 5.62 Pd(oAc)2 lZ.8 (~ )2 2 16.9a Pt/C 0.18a a Bath temperature 70~C.
b Bath temperature 100~C.

Example 31 Gradual Pyrolysis of Silazanes For polysilazane polymers based on n-methyl polysilazane, (H2SiNMe) with average x > 10, that were reacted with Ru3(C0)12 catalyst and other components, e.g., MeNH2, Me2NH, and NH3, we have determined that the yield for conversion to ceramic material when heated in N2 atmospheres were strongly dependent on heating rate. Polymers heated in N2 at 0.5~C~min gave yields between 67-70 wt% (ceramic -83- i34no2~

material) while polymers heated at 5~C/min gave yields of under 60%. The maximum temperature for these pyrolyses reactions was ~800~C. It has also been found that isothermal holds during pyrolysis at ~1~0~C
for 3 hours additionally increased the ceramic yields by up to 6 wt%. Yield differentials with respect to heating cate variations can be correlated with differences in weight loss versus temperature between 300-500~C While not wishing to be bound by any particular theory, it is postulated that yield differentials with cespect to the presence or absence of isothermal curing steps during pycolysis may be due to latent reactivity of Si-H bonds and the presence of small amounts of catalyst in the polymec.
Example 3Z
TGA Pyrolysis To 1~ of ~3NH-(H2SiNCH3) -H prepared ~ in ex~le 2 were added 2C~
Z0 of Ru (C0) 2 and the solution was heated at 90~C for 8 h. The viscous polymec obtained in the ceaction was then pyrolyzed in TGA equipment at temperature ramping rates of 5.ooc/min and 0.5~C per minute. Figure 2 shows the dependence of the ceramic yield on the heating rate. The weiqht lost between 200~C and 400~C was retarded by about 10% in the slow pyrolysis due to the increase in thermal cross-linking reactions and the decrease in volatilization of compounds. At this temperature range, the products evaporated out of the resin material were mostly low molecular weight silazane oligomers. Below 200~C, the weight lost was primarily due to hydrogen and methylamine release, suggesting that control of the temperature within this cange increases the amount of cross-linking in the pyrolyzed material.

-84- 134002~

Example 32 Pyrolysis Under N2 or NH3 Various polymers containing [H2SiNCH3]
monomeric units were pyrolyzed under N2 and ammonia at different temperature ramping rates (see Table 16).
Table 16 indicates the following: 1) slow pyrolysis rates increase the ceramic yields; 2) low temperature holds during the pyrolysis schedule slightly increase the ceramic yields; 3) higher molecular weights give in general higher ceramic yields; 4) extended polymers produced by catalytic activity give higher ceramic yields; and 5) polymers treated with catalyst in the presence of ammonia give higher ceramic yields than in the absence of ammonia.
Table 17 shows the elemental analysis of pyrolyzed polymers from different runs set forth in Table 16. As may be seen in Table 17, the carbon content of ceramics derived from polymer reacted with catalyst in an ammonia or gaseous amine atmosphere was significantly lower than polymer reacted under nitrogen. Pyrolysis under ammonia or other amine thus substantially reduces the carbon content of the ceramic product.

W W N N ~ 1 Table 16: Pyrolysis of [H2S:NCH31x-based Polymers Run Poly~ec Type Reaction Conditions Product Phase Pyrolysis Conditions Ceramic Yield Mn; synthesis: polymec: Temp Time Gas Phase Heatlng Gas Holds (900~C) catalyst wt ratio: (~C) (hours)(psi) ~C/min phase (~C;hrs) 1 affn=323: dicect ami- - - - nonvisc liq 5.0 N2 ~ 28 nolosis at 0~C.
2 aMn=566: nonvolatile - - _ nonvisc liq 5,0 N2 - 38 ~raction of 1.
3 Mn=800: direct aminol- - - - visc liq 0.5 N2 ~ 45 osis at -78~C; with-out volatiles distil-lation.
4 Mn=llO0: as in 3. - - - visc liq 0.5 N2 ~ 49 Mn=1770; as in 3 with - - - visc liq 0.5 N2 ~ 45 10~ ~S:C13 6 Mn=1490; with 1~u3(C0)~2:90 U Nz visc liq 5.0 N2 - 54 500; startin~ Mn-1150 7 ~s in 6 90 8 Nz vi5c 1 iq o 5 N2 ~ 64 8 ~s in 6 90 U N2 visc liq O.S N2 130;Z4 66 9 ~s in 6 90 U N2 visc liq 0.S N2 Z00;24 68 ~n o ~ o ~n o ~n Table 16: Pyrolysis of ~HzS:NCH3lx-based Polymers(cont.) Run Polymer Type Reaction Conditions Product Phase Pyrolysis Conditions Ceramic Yield Mn; synthesis; polymeL. Temp Time Cas Phasc lleatinq Gas Holds (900~C) catalyst wt ratio: (~C) (hours)(psi) ~C/min phase (~C;hrs) 10 Mn=1600; as in 9 9020 N~ v~ ,c liq 0.', ~2 ~ h7 Il h.~,r,i~nO~ aG in 10 ~HIIlN2 visc ~i~ (wax) o.s Nz . 69 IZ ~s in Il 9~2h ~ NH2 visc liq (wax) S.(l Nz - 5 13 c9el; wi~h RU9(CO)12; 60 10 NH3 soLt cubber 0 5 N2 - 7 in THF; 250 14 As in 13 60 20 NH3 sott rubber o 5 N2 - e3 As in 4 - - - visc liq 0.5 NH3 - 49 16 As in 6 90 ~3 N2 visc liq 0.5 NH3 - 65 a Reported by Sey~erth et al.
b Partially insoluble in toluene ~or VP0 measucements.
c Saluble in THF solution, cross-linked during solvent cemovai.

-86- ~34002~

Table 17: Elemental Analy6is Run ~lemental Analysis (F[o~ Table 16) (mole ratio) si N C H O
5 4 45.8 32.5 18.8 ~.0 2.0 6 40.8 32.8 17.5 0.8 0.1 lZ 45.0 34.0 18.9 0.8 1.4 13 49.3 31.5 ~6.2 l.L0 2.2 52.0 34.0 0.7 1.2 1.55 16 56.0 32.6 4.3 0.7 0.1 Example 34 Silicon Oxynitride Ceramic X-ray eowder diffraction analyses of the ceramic products obtained by the procedure described in Example 29 show a clear spectral pattern of orthorhombic Si2oN2 when the polymeric products were pyrolyzed under NH3 (pyrolysis under Nz gave relatively poor crystallization under the same conditions). These pattecns are found~ only when the total amorphous ceramic products eroduced at 900~C are reheated to 1600~C under N2. No other types of ceramic crystallites were observed in the X--ray powder diffraction spectra. Less than 0.45 wt.% carbon was found, and the silicon content of the pcoduct was 51-56 wt.% (theoretical: 56 wt.%), suggesting substantially pure silicon oxynitride in the ceramic mixture.

Example 35 Fabrication of Ceramic Articles Usinq Silicon Nitride as a Binder This example illustrates a process for the fabrication of ce~:amic bodies from a mixture of -87- 134002~i preceramic polysilazane and cecamic powders. The silicon and niteogen containing polymers as prepared in the previous Examples display controllable chemical, mechanical, rheolo~ical, and pyrolytic properties that make them suitable as binders or forming aids. When mixed with ceramic powders such as Si3N4, the polymer/powder system can be compression molded into a variety of shapes. Pyrolytic release of the organic components bound to the polysilazane above 800~C
provided an amorphous Si3N4 material that partially fills the pore system that exists in powder compacts.
This eartial filling decreases the porosity of the body and increases its green density, which is advantageous for subsequent sintering steps at temperatures in excess of 1700~C.
The pceceramic polymer used in this process was a polysilazane having the approximate structure (H2SiNCH3)X. This polysilazane was synthesized by the proceduce described in U.S. Patent No. 4,612,383, cited supra. This method allows for control of the degree of polymerization and the viscosity of the polysilazane, an important characteristic for any binder material. In a typical expeciment, (H2SiNCH3)X
(M = lZ65 D; viscosity ~ 1 poise) was heated at 90~C for 55 h with RU3 (C0)12 as catalyst. It was then dissolved in THF and filtered. The solvent was removed by vacuum evaporation (PHg ~ 1 mm). The resulting polymer (M = 1420 D; viscosity ~ 50 poise; density = 1.03g/cm ) was redissolved in THF to form a standard solution of 0.059 g/ml. A powder such as Si3N4 was added to the standard solution in different mixing ratios and dispersed ultrasonically.
THF was again removed by vacuum evacuation, leaving a homogeneous polymer/powder mixture. The mixture was -88- 13~0025 loaded into a stee] die and under an inert atmosphere of N2 and compression molded at pressures of 5000 to 45,000 psi. The die was coated with tetramethyldisilazane or hexamethyldisilazane as a mold release. The formed body, already a rigid article hard enough to be displaced without any significant precautionary measures (other than reduction of exposure to moisture), was t:hen heated to ~800~C in Nz at 0.5-5~C/min to convert the polymer to ceramic material.
The pyrolyzed bodies have densities up to 2.9 g/cc, indicating porosities of less than 15% for unsintered pieces. Sintering of the body to final density occurs at 1725~C in an overpressure of N2.
By contrast, polymer/powder mixtures were also processed by mechanical mixing of liquid polysilazanes with ceramic powder. This variation of the above procedure resulted in inferior formed bodies caused by insufficient homogeneity of the polymer/powder mixture due to inadequate mixing. The consequence of this was an unsatisfactory distribution of polymer with respect to the ceramic powder. The sintered bodies fabricated by this method had final densities of Z.7 g/cc or less.
This demonstrates the efficacy of solution mixing of polymer and powder to achieve homogeneity. Using a stock solution of polymer also simplifies handling of these oxygen- and water-sensitive polymers.
A range of polymer/powder ratios have been examined from 10-30 wt% polymer. Polymer/powder ratio can have a crucial effect on the green density of the pyrolyzed body and the degree of damage during pyrolysis. The optimum ratio of 15-20 wt% polymer ensures the maximum green density with enough porosity in the pressed body to ensure that volatile components -89- 134 002~

of the polymer can be cemoved during pyrolysis without damage to the body.

Example 36 Pceparcltion of Ceramic Bodies from Preceramic Polysilazane and Ceramic Powders A polysilazane C'H3NH-(H2SiNCH3)x-H as prepared in Example 2 (M =110() D; viscosity~l poise) was heated at 90~C for 55 h with Ru3(CO)12 as catalyst. It was then dissolved in T~F and filtered. The solvent was removed by vacuum evaporation (PH ~L mm). The resulting polymer l~Mn=L420 D; viscosity~50 poise;
density=1.03 g/cm ~ was redissolved in THF to form a standard solution of 0.059 g/ml. A ceramic powder consisting of 79.8:L wt.% Si3N4, 11.37 wt.% Y203, 5.69 wt.% Alz03, and 3.L3 wt.% SiO2 was mixed in a ball mill for 24 h with Si3N4 balls and methanol.
After evaporation of the methanol, 8.002 g of powder were added to 33.90 ml of polymer solution and dispersed ultrasonically. The THF was removed by vacuum evacuation, leaving a homogeneous powder/polymer that was 80 wt.% ceramic powder and 20 wt.% polymer. The mixture was loaded in a steel die under N2 and compression molded at 27,000 psi. The die was coated with tetramethyldi:,ilazane as a mold release. The formed body was heated under L atm Nz at 0.5~C/min to 800~C to convert tlhe polymer to ceramic material. The volume of pores in this pre-sintered piece was 0.114 cm /g, which corresponds to a green density of 75% .
The piece was then sintered at 1725~C at 8 atm of N2 for 6 h. After si,ntering, the piece was over 95% of theoretical density with no open porosity.

go~ )02~

Example 37 Preparation of Ceramic Bodies A polysilazane solution and a ceramic powder composition were prepared as in the previous Example.
The ceramic powders were mixed with Si3N4 and methanol as in the previous Example, and the methanol was evaporated. 10.20 g of powder were added to 30.40 ml of polymer solut:ion and dispersed ultrasonically.
The THF was removecl by vacuum evacuation, leaving a homogeneous powderi'polymer that was 85 wt.% ceramic powder and 15 wt.% polymer The mixture was loaded in a steel die under N2 and compression molded at 27,000 psi. The die was coated with hexamethyldisilazane as a mold release. The formed body was heated under 1 atm N2 at 0.5~Ctmin to 800~C to convert the polymer to ceramic material. The volume of pores in this pre-sintered piece was 0.15 cm /g, which corresponds to a green density of 68% The piece was then sintered at 1725~C at 8 atm of N2 for 6 h. As in the previous Example, after sint;ering, the piece was over 95% of theoretical density with no open porosity.

Example 38 Preparation of Ceramic Bodies A polysilazane solution and a ceramic powder composition were prepared as in Example 35. The ceramic powders were mixed with Si3N4 and methanol as in Example 35, and the methanol was evaporated. 7.51 g of powder were added 1:o 42.40 ml of polymer solution and dispersed ultrasonically. The THF was removed by vacuum evacuation, leaving a homogeneous powder/polymer that was 75 wt.% ceramic powder and 25 wt.% polymer. The 91- -~ 3400 2~

mixture was loaded in a steel die under N2 and compression molded at 45,000 psi. The die was coated with hexamethyldisilazane as a mold release. The formed body was heated uncler ~ atm N2 at 0.5~C/min to 800~C
to convert the polymer to ceramic material. The volume of pores in this pre-sintered piece was 0.09 cm /g, which corresponds t:o a green density of 79%. The bodies showed damage after molding and pyrolysis due to excess polymer in the mixt;ure which prevented an optimal powder/polymer rati-o from being achieved. The volume fraction of the powder fell below 50%, indicating that the powder particles were not in contact in the molded body.

Example 39 Pceparation of Ceramic Bodies A polysilazane solution and a ceramic powder composition were prepared as in Example 35. The ceramic powders were mixed with Si3N4 and methanol as in Example 35, and the methanol was evaporated. 7.51 g of powder were added to 42.40 ml of polymer solution and dispersed ultrasonically. The THF was removed by vacuum evacuation, leavin~ a homogeneous powder/polymer that was 75 wt.% ceramic powder and Z5 wt.% polymer. The mixture was loaded in a steel die under N2 and compression molded at 27,000 psi. The die was coated with tetramethyldisilazane as a mold release. The formed body was heated under 1 atm N2 at 0.5~C/min to 800~C to convert the polymer to ceramic material. The volume of pores in this pre-sintered piece was 0.06 cm /g, which correseonds to a green density of 85%.
The bodies showed damage after molding and pyrolysis due to excess polymer in the mixture which erevented an optimal powder/polymer ratio from being achieved. The volume fraction of the powder fell below 50%, indicating that the powder particles were not in contact in the molded body.

Example 40 Prep~aration of Ceramic Bodies A polysilazane solution and a ceramic powder composition were prepared as in Example 35. The ceramic powders were mixed with Si3N4 and methanol as in Example 35, and th* methanol was evaporated. 9.00 g of powder were added to 17.00 ml of polymec solution and dispersed ultrasonically. The THF was removed by vacuum evacuation, leaving a homogeneous powderJpolymer that was 90 wt.% ceramic powder and 10 wt.% polymer. The mixture was loaded in a steel die under N2 and compression molded at 27,000 psi. The die was coated with tetramethyldisilazane as a mold release. The Z0 focmed body was heated under 1 atm Nz at 0.5~C/min to 800~C to convert the polymer to ceramic material. The volume of pores in this pre-sintered piece was O.Z5 cm Jg, which corresponds to a green density of 56% .
The piece is then sintered at 17Z5~C at 8 atm of Nz Z5 for 6 h. As in the foregoing Examples, after sintering, the piece is over ~5% of theoretical density with no open porosity.

Example 41 30Prel~aration of Ceramic Bodies A polysilazane solution was prepared as in Example 35. To 30.4 ml of this solution were added lO.Z0 g of pure silicon nitride powder, and the -93- 13~0025 suspension was disE)eesed ultrasonically. The THF was removed by vacuum evacuation, leaving a homogeneous powder/polymer that was 85 wt.% ceramic powder and 15 wt.% polymer. The mixture was loaded in a steel die under N2 and compression molded at Z7,000 psi. The die was coated with hexamethyldisilazane as a mold release. The formed body was heated under 1 atm N2 at 0.5~C/min to 800~C to convert the polymer to ceramic material. The volume of pores in this pre-sintered piece was 0.106 cm /g, which corresponds to a green density of 77% In<,pection of the microstructure of the piece with SEM anaLyses showed chemical or physical reaction between tlle polymer-derived material and the silicon nitride powder (see Figure 3). This indicated the capability of using this system for solid state sintering of Si3N4 powder. Upon treatment to 1725~C
at 8 atm N2. considerable grain growth occurred, although pore closure was not achieved (see Figure 4).
This is further evidence of solid state reactions occurring in a silicon nitride powder/polymer-derived glass system.

Example 42 Pre~)aration of Ceramic Bodies A polymer solution was prepared as in Example 35, and mechanically mixed with a ceramic powder consisting of 79.81 wt.% Si3N4, 11.37 wt.% Y2O3, 5~69 wt.% A12O3, and 3.13 wt.~ SiO2. The mixture contained 2.04 g of cecamic powder and 0.83 g of polymer for a mixture that was 71 wt.% powder and 29 wt.%
polymer. The mixture was compression molded in a steel die at 15,000 psi using a hexamethyldisilazane mold release, and heated in vacuum at 150~C while in the 13~0025 mold. The molded body was inferior in quality to that of the previous Examples because of insufficient homogeneity of the powder/polymer mixture, in turn due to inadequate mixing. The body was heated to 500~C in N2 at 2~C/min, held at 500~C for 3 h, and then heated to 900~C at 1~C/min. Cracks were seen in the body before and after pyrolysis. Upon sintering at 1725~C
for 6 h in 8 atm N2, the body achieved only 80% of theoretical density.
Example 43 Preparation ~f Ceramic Bodies A polysilazane CH3NH-(H2SiNCH3) -H
Mn~llO0 D~ was prepared substantially as in the previous Examples; in this Example, howevee, the polysilazane was not previously treated with catalyst 8.502 g of cecamic powders (as set forth in Example 35) were mixed with 1.5 g polymer in a THF solution. The mixtuce was compression-molded in a steel die at 15,000 psi and pyrolyzed under N2 as in the preceding Example.
Upon heating according to the heating schedule described in the previous examples, a green density of about 72%
was found.
Z5 Example 44 Polysilazane Coatinqs Coatings of polysilazane precursors were prepared by dipping flat, polished, stainless steel plates (1 1/4 x 1 1/4 x 1/16 inch) into polysilazane solutions (type CH3NH--(H2SiNCH3)X-H, Mn~l~) in THF having concentrations of 5 wt.%, 10 wt.% and 20 wt.%. The samples were cured under the slow pyrolysis regime (heating rate of 100~C/hr) to a final temperature of 13~10d25 700~C. The cured coatings were shiny, transparent and smooth. Coatings on the stainless steel plates were brightly colored from the interference of reflected light. The thickn~ess of the cured coating was estimated from the interference colors to be between 0.1 and 0.5 microns for the two dilute solutions and between 0.5 and 1.5 microns for the 20% solution. Light micrographs of the thin and the thick coatings showed that while thin coatings appeared ~quite uniform, thicker coatings displayed cracks and irregularities due to shrinkage during pyrolysis.

Example 45 Polysilazane Coatinqs l'o obtain thicker ceramic coatings, tciple layered coatings of polysilazane precursors were prepared by dipping flat stainless steel plates (as in Example 44) in polysilazane/THF solutions having weight concentrations of 5% and 10%. The polysilazane used was the same as that in Example 44. Pyrolysis was conducted between each coating step according to a gradual pyrolysis regime (100~C/min temperature ramping) to a final temperature of 700~C. The coatings so prepared had a thickness of about 0.1-2.0 ~ and appeared substantially smooth and uni~orm.

Example 46 Fiber Preparation A polymer of type CH3NH-(H2SiNCH3)x-H was extended by catalytic treatment with Ru3(C0)12 substantially as discussed in Example 23. The extended polymer had an Mn of 2100 D and viscosity of 90 poise.

-96- 134~02.~

The polymer (4.0 g) was mixed with 1.0 wt.% of monodispersed polyslyrene (0.4 g) having an Mn=1 800 000 D in 20 ml THF. The solvent was removed by evapoeation after both polymers were comeletely dissolved in the solution. The very viscous liquid was transferred into a narrow-mouth glass container and placed under argon in a sealed glass cylinder equipped with a stainless steel wire inlet and outLet for gases and a heating element and thermocouple. The argon atmosphere was replaced by ammonia and fibers of 4 to 8 were pulled out of the viscous polymer mi~ture by the wire. These fibers maintained their shape after a curing period of O.S h under ammonia without any flaws or breakage.

~O

.'5 :~0

Claims (29)

1. A method of producing tractable, high molecular weight polysilazanes useful as preceramic polymers and containing at least one newly formed Si-N
bond which comprises:
(a) providing a precursor containing at least one Si-N bond, catalytically cleaving an Si-N bond in the precursor in the presence of a transition metal catalyst effective to activate Si-N bonds, wherein the catalyst is selected from the group consisting of: H4Ru4(CO)12, Fe(CO)5, Rh6(CO)16, CO2(CO)8, (Ph3P)2Rh(CO)H, H2PtCl6, nickel cyclooctadiene, Os3(CO)12, Ir4(CO)12, (Ph3P)2Ir(CO)H, NiCl2, Ni(OAc)2, CP2TiCl2, (Ph3P)3RhCl, H2Os3(CO)10, Pd(Ph3P)4, Fe3(CO)12, RU3(CO)12, RuCl3, NaHRu3(CO)11, PdCl2, Pd(OAc)2, (~CN)2PdCl2, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt/C, Pt/BaSO4, Cr, Pd/C, Co/C. Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/Al2O3, Pt/SiO2, Ru/TiO2, Rh/La2O3, Pd/Ag alloy, LaNi5, PtO2, and mixtures thereof, such cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second such cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial polysilazane product; or (b) providing one or more reactants which contain an Si-H bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst effective to activate Si-H and N-H
bonds, to produce an initial polysilazane product having at least two Si-N
bonds;
wherein the polysilazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof.

2. The method of Claim 1, wherein a compound having an M-H bond reacts with either the cleavage product in said type (a) reaction or with a reactant in said type (b) reaction or both, wherein M is B, Al, Ga, In, Ge, Pb, Sn or S.

3. The method of Claim 1, wherein said transition metal catalyst is a palladium catalyst.

4. The method of Claim 1, wherein the reaction temperature is between about -78° and about 250°C.

5. A method of preparing tractable, high molecular weight silazanes and siloxazanes suitable as preceramic polymers, comprising the steps of:
(a) providing a linear, branched or cyclic starting material having the structure R'2Si-A- in its molecule, in which A is hydrogen, NR, or Si and wherein the starting material is oligomeric, polymeric or copolymeric;
(b) providing a transition metal catalyst effective to activate Si-N, Si-Si and/or Si-H bonds, wherein the catalyst is selected from the group consisting of: H4Ru4(CO)12, Fe(CO)5, Rh6(CO)16, Co2(CO)8, (Ph3P)2Rh(CO)H, H2PtC1 6, nickel cyclooctadiene, OS3(CO)12, Ir4(CO)12, (Ph3P)2Ir(CO)H, NiCl2, Ni(OAc)2, CP2TiCl2, (Ph3P)3RhCl, H2Os3(CO)10, Pd(Ph3P)4, Fe3(CO)12, RU3(CO)12, RuCl3, NaHRu3(CO)11, PdCl2, Pd(OAc)2, (~CN)2PdCl2, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt/C, Pt/BaSO4, Cr, Pd/C, Co/C. Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/Al2O3, Pt/SiO2, Ru/TiO2, Rh/La2O3, Pd/Ag alloy, LaNi5, PtO2, and mixtures thereof; and (c) reacting the starting material in the presence of such catalyst with (1) hydrogen or a hydrogen donor where A is NR and the starting material is part of a silazane or (2) H-X-R where A is hydrogen or Si, wherein:

the R groups are independently selected from the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl or polysilyl; said hydrocarbyl or silyl optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical;
The R' moieties are independently selected from the group consisting of hydrogen; amino; hydrocarbyl; lower alkoxy; silyl or polysilyl; said hydrocarbyl, alkoxy or silyl optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, or a fused aromatic radical of 8 to 20 carbon atoms, and wherein R and R' may be part of an oligomeric or polymeric structure; and X is selected from the group consisting of NR, NR-NR, and NR-R-NR;
wherein the polysilazanes and polysiloxazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 50,000 D, or combinations thereof.

6. The method of Claim 5 wherein said hydrocarbyl is selected from the group consisting of lower alkyl, alkenyl, alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.

7. The method of Claim 5, wherein the starting material is one of the following structures:

where x is an integer from 0 to 4 inclusive, y is an integer from 0 to 4 inclusive, z is an integer from 0 to 2 inclusive, the sum of x, y and z is 4, a and b are integers from 0 to 2 inclusive, the sum of a and b is 2, and m is an integer defining the number of monomer units in the oligomer, polymer or copolymer.

8. The method of Claim 5, wherein the starting material is of the formula R'aSiHb, wherein a is an integer from 0 to 2 inclusive, b is an integer from 2 to 4 inclusive, and the sum of a and b is 4.

9. The method of Claim 1, wherein said reaction is of type (b), and one or more of the reactants includes a siloxane, and said silazane products include siloxazanes.

10. A method of making a ceramic composition, comprising pyrolyzing a polymer selected from the group consisting of (a) siloxazanes, (b) polysiloxazanes, (c) polysilazanes having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz of at least about 40,000 D, or a polysilazane species having a molecular weight of at least about 50,000 D, or a combination thereof, (d) mixtures thereof, in a preceramic polymer composition under a selected atmosphere to a temperature higher than about 500°C.

11. The method of Claim 10, wherein said pyrolysis is conducted in the presence of a catalyst.

12. The method of Claim 10, wherein said preceramic polymer composition is provided as a coating on a substrate prior to said pyrolyzing step.

13. Coated substrates provided according to the method of Claim 12.

14. A tractable preceramic polysilazane composition having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz greater than about 40,000 D, or containing a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.

15. The polysilazane composition of Claim 14 having either an Mn greater than about 20,000 D, an Mw greater than about 32,000 D, an Mz greater than about 80,000 D, containing a polysilazane species having a molecular weight of at least about 500,000 D, or a combination thereof.

16. Silazanes prepared by the process comprising providing at least one reactant which contains an Si-H bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst to produce an initial silazane product having at least two Si-N
bonds, and wherein said at least one reactant additionally includes an Si-N
bond and said initial silazane product includes two distinguishable Si-N bond species, wherein the silazanes are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.

17. Silazanes prepared by the process of Claims 1 or 5.

18. Ceramic compositions prepared by the process of Claim 10.

19. Silazanes containing structural units of the formula:

wherein:
a is 0 or 1;
b is 1 or 2 the sum of a and b is 2;
m is an integer defining the number of monomer units in the structure;
the R moieties are independently selected from the group consisting of hydrogen; boryl; hydrocarbyl; silyl; and polysilyl; said hydrocarbyl, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical; and the R' moieties are independently selected from the group consisting of: hydrogen; amino; hydrocarbyl; lower alkoxy; silyl; and polysilyl; said hydrocarbyl, lower alkoxy, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety; lower alkoxy, or a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical, and further wherein the R and R' may be part of a cyclic or polymeric structure, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or containing a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.

20. The silazanes of Claim 19 wherein the hydrocarbyl is selected from the group consisting of: lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.

21. Oligomeric or polymeric siloxazanes containing recurring units having the structural formula:

wherein:
the R moieties are independently selected fronn the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl; and polysilyl, said hydrocarbyl, silyl, or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety or an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical; and the R' moieties are independently selected from the group consisting of: hydrogen; amino; hydrocarbyl; said hydrocarbyl, lower alkoxy, silyl, or polysilyl, optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical, and further wherein the R and R' may be part of a cyclic or polymeric structure, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.

22. Siloxazanes of Claim 21 wherein said hydrocarbyl is selected from a group consisting of: lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.

23. A method of making ceramic articles, comprising the steps of:
providing a solution of a polymer or a liquid polymer, such polymer selected from the group consisting of (a) polysilazanes having either an Mn of at least about 10,000 D, an Mw of at least about 16,000 D, an Mz of at least about 40,000 D, or including a species having a molecular weight of at least about 50,000 D, or combinations thereof, (b) siloxazanes and (c) mixtures thereof;
admixing said polymer solution with ceramic powders, ceramic whiskers, ceramic fibers, or with a porous or non-porous ceramic article; and thermally treating said admixture so as to form a ceramic article.

24. Fibers spun from the silazanes of Claims 14, 15, 16, 17 or 19.

25. Fibers spun from the siloxazanes of Claim 21.

26. Silazanes prepared by the process comprising providing a precursor containing at least one Si-N bond in the precursor, catalytically cleaving an Si-N
bond in the precursor in the presence of a transition metal catalyst, such cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product to produce an initial silazane product wherein the silazanes are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof.

27. Silazanes prepared by the process comprising causing both of the following reaction types (a) and (b) to occur simultaneously:
(a) providing a precursor containing at least one Si-N bond, catalytically cleaving an Si-N bond in the precursor in the presence of a transition metal catalyst effective to activate Si-N bonds, wherein the catalyst is selected from the group consisting of H4Ru4(CO)12, Fe(CO)5, Rh6(CO)16, Co2(CO)8, (Ph3P)2Rh(CO)H, H2PtCl6, nickel cyclooctadiene, Os3(CO)12, Ir4(CO)12, (Ph3P)2Ir(CO)H, NiCl2, Ni(OAc)2, CP2TiCl2, (Ph3P)3RhCl, H2Os3(CO)10, Pd(Ph3P)4, Fe3(CO)12, Ru3(CO)12, RuCl3, NaHRu3(CO)11, PdCl2, Pd(OAc)2, (~CN)2PdCl2, and mixtures thereof, or a heterogeneous catalyst selected from the group consisting of Pt/C, Pt/BaSO4, Cr, Pd/C, Co/C, Pt black, Co black, Ru black, Ra-Ni, Pd black, Ir/Al2O3, Pt/SiO2, Ru/TiO2, Rh/La2O3, Pd/Ag alloy, LaNi5, PtO2, and mixtures thereof, such cleavage being carried out in the presence of hydrogen or a hydrogen donor, and reacting the cleavage product with a second such cleavage product or with a compound containing an Si-H bond, an N-H bond, or both, to produce an initial polysilazane product; and (b) providing at least one reactant which contains an Si-H bond and an N-H bond, and causing reaction to occur between such Si-H and N-H bonds in the presence of a transition metal catalyst effective to activate Si-H and N-H
bonds, to produce an initial polysilazane product having at least two Si-N
bonds;

wherein the polysilazanes produced are in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an Mz greater than about 40,000 D, a polysilazane species having a molecular weight higher than about 50,000 D, or combinations thereof.

28. Silazanes containing structural units of the formula:

-Si(H)a(NR2)b-NR-wherein:
a is 0 or 1;
b is 1 or 2;
the sum of a and b is 2;
the R moieties are independently selected from the group consisting of:
hydrogen; boryl; hydrocarbyl; silyl; and polysilyl, said hydrocarbyl, silyl or polysilyl functionalities optionally substituted with amino, hydroxyl, an ether moiety, an ester moiety, lower alkoxy, a fused aromatic radical of 8 to 20 carbon atoms, or an organometallic radical, said silazanes being present in a polymer composition having either an Mn greater than about 10,000 D, an Mw greater than about 16,000 D, an M
greater than about 40,000 D, or a polysilazane species having a molecular weight higher than about 50,000 D, or a combination thereof.

29. Silazanes of Claim 28 wherein said hydrocarbyl is selected from a group consisting of: lower alkyl, lower alkenyl, lower alkynyl, aryl, lower alkyl substituted aryl, and cycloaliphatic.