CA2004402A1

CA2004402A1 - Polysubstituted oligosilazanes and process for their preparation

Info

Publication number: CA2004402A1
Application number: CA 2004402
Authority: CA
Inventors: Tilo Vaahs
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1988-12-03
Filing date: 1989-12-01
Publication date: 1990-06-03
Also published as: JPH02194027A; CN1043722A; EP0372380A3; DE3840778A1; EP0372380A2

Abstract

ABSTRACT OF THE DISCLOSURE:

Polysubstituted oligosilazanes and process for their preparation The invention relates to novel polysubstituted oligo-silazanes and to a process for their preparation. The process comprises reacting excess ammonia with a starting material containing at least one of the two components (I) R1R2SiCl2 and (II) Cl2R3Si-CH2CH2-SiR3Cl2 and at least one of the two components (III) R4SiCl3 and (IV) Cl3Si-CH2CH2-SiR5Cl2, at -70 to +100°C, where the radicals independently of one another have the following meanings:
R1, R2, R4 = H, C1-C6 alkyl or C2-C6 alkenyl and R3, R5 = C1-C6 alkyl or C2-C6 alkenyl, and the molar percentage of (I) or (II) or a mixture thereof in the starting material is 30 to 99%, and where the reaction of a mixture containing only (I) and (III) with ammonia shall be excluded.

The oligosilazanes according to the invention can be converted into polymeric chlorosilazanes by means of a further reaction with chlorosilanes, and said polymeric chlorosilazanes can in turn be converted initially into polysilazanes and then into ceramic materials containing silicon nitride.

Description

2(~ 0Z
HOECHST ARTIENGESELLSCHAFT HOE 88/F 344 Dr.MA/St Description Poly~ubstituted oligosilazanes and proce~s for their preparation The invention relates to novel polysubstituted oligo~
silazanes and to a process for their preparation. The oligosilazanes accordinq to the invention can be con-verted into polymeric chlorosilazanes by means of a further reaction with chlorosilanes, and said polymeric chlorosilazanes can in turn be converted initially into polysilazanes and then into ceramic materials containing silicon nitride.

The preparation of polysilazanes from other oligomers has already been described (US patent~ 4 482 669, 4 720 532, --international patent application PCT-WO 88/01260), as has the pyrolysis of polysilazanes to form ceramic materials containing silicon nitride ( R . R . Wills et al., Ceramic Bulletin, vol. 62 (1983) 904-915).

Oligomeric or low-molecular silazanes as intermediates for polymers have 80 far generally been prepared using chlorosilanes a8 starting materials, which are reacted with ammonia or primary or secondary amines (US patent6 4 540 803, 4 543 344, 4 595 775, 4 397 828).

The present invention now provides novel starting mater- -- ~
ials for polysilazanes, i.e. oligomeric silazanes. ~ `

The present invention relates to a process for the pre-paration of oligomeric silazanes which comprises reacting 5'-~
excess ammonia with a starting material containing at ~ 5`~
least one of the two components (I) RlR2SiC12 and (II) Cl2R3Si-CH2-CH2-SiR3Cl2 and at least one of the two com-ponents ( III ) R~SiCl3 ~nd ( IV) Cl3Si-CH2-CH2-SiR5C12, at -70-C to +lOO-C, where the radicals independently of one another have the following meanings~

~ ~ "
. ,. ,:
.. ..... . . . - . . :

.
. : - :: ~ . : :
.. . . . . . . : :

Rl, R2, R4 = H, Cl-c6 alkyl or C2-C6 alkenyl and ~ -~
R3, R5 = Cl-c6 alkyl or C2-C6 alkenyl, and the molar percentage of (I) or (II) or a mixture thereof in the starting material is 30 to 99~, and where the reaction of a mixture containing only (I) and (II) -~
with ammonia shall be excluded. Preferably, the radicals independently of one another have the following meanings~
Rl, R2, R4 = H, Cl-C3 alkyl or C2-C3 alkenyl and R3, R5 =
C1-C3 alkyl or C2-C3 alkenyl. It is especially preferred if R1 = H, R2 = R3 = R5 = CH3 and R4 = CH3 or vinyl.

The chlorosilanes ( I ) RlR2SiC12 and ( III ) R4SiC13 used as starting materials are commercially available and the ethylene-bridged species (II) and (IV) can be obtained by the hydrosilylation of R3HSiC12 and ethyne or by the lS hydrosilylation of vinyltrichlorosilane and R5HSiC12 (see Experimental report). ~ ~

The reaction with ammonia i8 preferably carried out by ~ -taking the chlorosilanes in a solvent which exhibits inert behavior towards the reactants, and then mixing them with ammonia to the saturation point, which is reached when all the SiCl functional groups have been substltuted by NH group8. Example8 of solvents which are suit~ble for the reaction are saturated aliphatic or aromatic hydrocarbons such as n-pentane, cyclohexane or toluene, chlorinated hydrocarbons such as chloroform or chlorobenzene, or ethers such as diethyl ether or THF.

If appropriate, the process can also be carried out under ~ ;
reduced pressure or at pressures of 1 to 100 bar.
Ammonia can be metered in as a gas or as a liquid. The proces~ can also be carried out continuously.

The novel oligomeric silazanes prepared have a molecular structure which can be represented by formula (V) .' ~ ;:,.,,''.~''' , ,, ~'''~.';',"'.'' .: . . . . - . .
, ~. . - , .: . , . . :

Z004~

{5i - N}ES--~--Sl-N~Sl--N~ESi~,5~_N3 2 a H b ~ H~2 c H d Accordingly, the invention further relates to oligomeric silazanes of formula (V) : ~ .
R1 R3/~ ZR3 R4 NH~___ /R5 _ -Si - N- - Si_ ~_ Si-N - -~Si - NSi_ N ~Si-N- _ R2 H a H H b (IH)1/2H_ c H H d .
where the radicals independently of one another have the following meaningss 5 Rl, R2, R~ = H, Cl-C6 alkyl or C2-C6 alkenyl and R3, R5 = C,-C6 alkyl or Cz-C6 alkenyl, and the case where a > 0, b ~ 0, c = 0 and d = 0 simul-taneously shall be excluded. a, b, c and d are the mol fractions of the respective structural units.
':- ~' ,, :;.~, The suSm of a + b + c + d always gives a value of 1. Pre-ferably, Rl, R2, R~ ~ H, Cl-C3 alkyl or C2-C3 alkenyl and R3, R~ ~ Cl-C3 alkyl or C2-C3 alkenyl. It is especially preferred if Rl ' H, R2 = R3 - R5 = CH3 and R~ ' CH3 or -~
vinyl.

The oligosilazanes of formula (V) according ~o the inven- ~ ~5-~
tion can be converted in the following manner into ceramic material containing silicon nitrides First the oligosilazanes are reacted with at least one of the chlorosil~nes Cl2RBSi-CH2CH2-SiR~Cl2, Cl3Si-CH2CH2-SiR7Cl2, R8SiCl3 or R~SiHCl2 at 30-C to 300-C, where the radicals independently of one another have the following meaningss R6, R7, R3, R~ = Cl-C6 alkyl or C2-C~
alkenyl, preferably Cl-C3 alkyl or C2-C3 alkenyl. It is ~ -especially preferred if R6 ~ R7 = R~ = CH3 and R~ = CH3 or -vinyl. This reaction produces polysubstituted chlorine--containing silazane polymers, which are also called polymeric chlorosilazanes below.
.
, ~
.,: ~.

~ :,'.' ,.

In the reaction givinq the polymeric chlorosilazane, the molar ratio of the reactants, nsmely chlorosilane monomer units of the oligosilazane (n = 1), i8 preferably ;
about 0.1:1 to about 1.5:1, in particular about 0.1:1 to about 0.7:1.

The reactants are preferably reacted with one another by taking the oligosilazanes and adding at least one of said ;~
chlorosilanes thereto. As the reaction is exothermic, the temperature is preferably kept initially at 30 to ~-~
50-C when the reactants are brought together. The re-action mixture is then heated to temperatures of 100 to --- ` ~-300-C, preferably 120 to 250-C.

Some of the NH3 formed as a by-product escapes during the reaction. When the reaction i8 complete, the remainder of the more readily volatile compounds is removed from the reaction vessel, generally by the application of a ; ~ `
vacuum. ~
': ~:~ '".''''..', Most of the NH~Cl which iB also formed in the reaction sublimes out of the resction mixture in the course of the -~;~ s reaction. Any residual NH~Cl can be separated from the polymeric chlorosilazane prepared by extraction with an inert organic solvent such as n-hexane, toluene or ether. ~ ~
,.:. ' ' ':,. "', .,' The reaction time depends on the heating rate and the reaction temperature. A reaction time of 3 to 7 hours is generally sufficient- '~'`,'', ','''`",'','~"','~:7 The reaction can also be carried out in an organic 801- .~ :`: ;' vent. Suitable solvents are those which exhibit inert behavior towards the reactants and have a sufficiently - -~
high boiling point, e.g. saturated aliphatic or aromatic hydrocarbons such as n-decane, decalin, xylene or tolu-ene, chlorinated hydrocarbons such as chlorobenzene, or ~ ~-c~
ethers such as dibenzyl ether or diethylene glycol ~ -diethyl ether. When using a ~olvent in which the NH~Cl : :-,,,.. :::
,. ' ~ ,' ':

20~4402 ~:
.

formed i8 insoluble, the latter can be separated off byfiltration. The polymeric chlorosilazanes are then obtained by distillation of the solvent under reduced pressure.

If appropriate, the proces~ can also be carried out under reduced pressure or at pressures in the range from 1 to 10 atmospheres.

The polymeric chlorosilazanes can be converted into polysilszanes by reaction with ammonia (~ammonolysis"), and these in turn can be converted by pyrolysis into ceramic material containing silicon nitride.

The ammonolysis can be carried out in liguid NH3~ although it i8 advantageous to carry it out in an organic solvent.
Suitable solvents are all those which exhibit inert behavior towards the polymeric chlorosilazanes. Prefer-red solvents are those in which the ammonium chloride obtained as a by-product has a low solubility and from which it can easily be separated off, e.g. ethers, aliphatic and aromatic hydrocarbon~ and chlorinated hydrocarbons. In the ~mmonolysis, the reactants can be fed into the reaction vessel in any order, but it is normally advantageous to take the polymeric chloro silazane in solution and pass in gaseous ammonia or add liguid ammonia. If the polymeric chlorosilazanes have been prepared in a suitable organic solvent, the ammo-nolysis can be carried out in this solvent without prior separation of the NH~Cl. The ammonolysis is preferably carried out with an excess of NH3 in order to ensure that the reaction is cooplete and the end product~ are as free from chlorine as possible. Twice the stoichiometric amount is generally sufficient for this purpose.

The reaction is generally carried out at a temperature of about -50 to +IOO-C, preferably at -20 to +30-C and in particular at room temperature (in which case ice cooling is used). It is also possible, however, to carry out the '~ '"' 2(~044~1Z

reaction above room temperature, e.g. at the boilinq point of the solvent used, or below room temperature, e.g. at -33C when uæing liquid NH3.

When the } onolysis is complete, any excess NH3 is removed and the ammonium chloride obtained is filtered off. The yield can be increased by washing the pre-cipitate with one of the above-mentioned organic 601-vents. After distillation of the solvent under reduced pressure, the polysilazanes are obtained immediately as white powders. The polysilazanes are soluble in the above organic solvents, 8e they can be used either to coat surfaces or to manufacture fibers.

The polysilazanes can be pyrolyzed in an inert nitrogen or argon atmosphere, at temperatures of 800 to 1200-C, to form dense, amorphous materials which consist essentially of Si, N and C and can also contain traces of H and 0.
At pyrolysis temperatures above 1200C, for instance in the range from 1200-C to 1400-C, partially amorphous, microcrystslline ceramic materials are formed which contain ~-Si3N~ as a crystalline phase.

A particular advantage is that, before pyrolysis, the polysilazanes can be shaped by various processes to form three-dimensional shaped articles.
~....~.-~ . , . -...-:
One important method of shaping is fiber drawing, where fibers can be drawn out of high-viscosity solutions of the polysilazane in solvents such as toluene, THF or hexane. The fibers are advantageously drawn by means of spinnerets with a diameter of 80 to 150 ~m. Subsequent ~tretching makes the filament thinner, whereby a very ~ -strong fil~ment with a diameter of 2 to 20 ~m, in par-ticular 5 to 15 ~m, is formed after pyrolysis. The ;~
fibers manufactured by subsequent pyrolysis are used as ~ ~ ~
mechanical reinforcing matrices in fiber-reinforced ~ --~luminum, aluminum alloys and ceramic components.
Another important method by which the polysilazanes can :: -. . -~ ..
',~ . ~': "'... ,-: : ' 20~44t~

be processed is the manufacture of dense, strongly adhesive, amorphous or microcrystalline ceramic coatings on metals, in particular steel. ~he coatings are applied with the aid of a solution of the polysilazane in organic solvents such as toluene, THF or hexane. Pyrolytic conversion into an amorphous or microcrystalline layer takes place in the same temperature range of 800 to 1200-C or 1200 to 1400C, under an inert gas, in the manner described above for three-dimensional shaped articles.

On account of their outstanding adhesion, high hardness and surface quality, the ceramic coatings are particu~
larly suitable for improving the surface of mechanically and chemically stressed machine components.

The polysilazanes described above can also be pyrolyzed in an NH3 atmosphere rather than in an inert gas, with an equally high ceramic yield of 70 to 90%. This results in a practically carbon-free, transparent, colorless materi-al. When pyrolysis is carried out in NH3 at 1000-C or above, the carbon content is less than 0.5S by weight.
Depending on ~he pyrolysis temperature, the pyrolysis product consists of practically pure, amorphous ~ilicon nitride (pyrolysis below 1200-C) or crystalline Si3N~
(pyrolysis above 1200-C, in particular above 1300-C).
Pyrolysis in NH3 can be applied to all the shaped articles manufactured by the shaping processes described above, i.e. articles ~haped from powders, fibers and coatings.

Preferably, however, the conversion of the polymeric chlorosilazanes into ceramic material containing silicon nitride is carried out in such a way that the polysila-zanes formed as intermediates are not isolated. In this case, the polymeric chlorosilazanes are preferably reacted with gaseous ammonia and the reaction mixture formed i8 pyrolyzed in an ammonia atmo~phere.

:,.~ , ...
~' ''.`~''''`'~','''' ' -':,' ~,',,.

2(~441~Z

Experimental report 1. Preparation of 1,2-bis(methyldichlorosilyl)ethane of the formula -CH3~ ~ CH3 Cl - Si Si - Cl ;;~
Cl ~ Cl By means of hydrosilylation, two molecules of methyldi-chlorosilane, (CH3)HSiC12, were added on to one moleculeof ethyne, HCCH. This was done by taking toluene as a solvent and passing gaseous ethyne into it. 0.5 ml of a 0.05 molar solution of hexachloroplatinic acid in chloro-form was added to this solution. The mixture was heated to 100C and methyldichlorosilane (b.p. 45C) was slowly added dropwise, ethyne being passed in continuously. The course of the reaction was followed via the temperature of the reaction mixture. If this dropped below 80C, there was too much unreacted methyldichlorosilane, which ~ i~
lS was then left to react before any more was added. The ~ ~
yield of 1,2-bis(methyldichlorosilyl)ethane was almost " ~ --100% and the solution could be used to prepare the oligo-silazane without being worked up. The chlorosilane content could easily be determined with the aid of the lH
NMR spectrum. It is preferred to use the ~mallest possible proportions of solvent. The compound could be prepared in a completely solvent-free process by taking 1,2-bis(methyldichlorosilyl)ethane at the outset in order to reach the nece~sary reaction temperature.

2. Preparation of 1-methyldichlorosilyl-2-trichloro-~ilylethane of the formula H~C~ r S~ - Cl ;

Cl Cl 300 ml (381 g, 2.36 mol) of vinyltrichlorosilane were t~ken and O.S ml of ~ 0.05 molar solution of H2PtCl~ in CHC13 was added. 242 ml (271.5 g, 2.36 mol) of 2()044~
g methyldichlorosilane were 810wly added dropwise at 90C, the temperature inside the reaction vessel rising to 120C without the oil bath temperature being increased.

Yield: 650 g (99%) without working-up since the product was in the pure form Fxamples R ample 1 Preparation of the oligomeric silazane of formula (V) where Rl = H R2 = R3 = R~ = CH3, a = 0.42, b = 0.38, c ;
0.20 and d = 0 In a 2 1 four-necked round-bottomed fla~k fitted with a stirrer, a condenser and a feed tube, 50 ml (55.7 g, 0.48 mol) of CH3SiHC12, 50 ml (60 g, 0.23 mol) of Cl2CH3Si-CH2CH2-SiCH3Cl2 and 50 ml (63.6 g, 0.43 mol) of CH3SiCl3 were dissolved in 1.5 1 of absolute THF and the solution was mixed. Ammonia was then passed in to the saturation point at temperatures of between 0C and lO-C.
When the reaction was complete, the reaction mixture was allowed to thaw and the ~mmonium chloride formed was separated off on a frit and washed with twice 200 ml of ~ H~
THF. The filtrate was freed from THF and the other volatile constituents by distillation under reduced pre~
sure at 40-C to leave the solvent-free oligomer.

Yield: 74.5 g (83.2S) lH NNR datas -SiCH3 ~ = 0.0 - 0.5 ppm (br), intensity 11.0 `-NH + SiCH2CH2Si t ~ 0 . 5 - 1.1 ppm (br), ~ 6.3 `
SiH~ s 4.5 - 5.0 ppm (br), X0~4~Z ~:
1 o - . . . ~ .
~sample 2 Preparation of the oligomeric silazane of formula (V) where R1 = R2 = R3 = R4 = CH3 and a = b = c = d = 0-25 The procedure was analogous to that in Example 1, except that the chlorosilanes were as follows~
33.9 g (31.9 ml, 0.26 mol) of (CH3)2SiC12 67.4 g (56.2 ml, 0.26 mol) of Cl2CH3Si-CH2-CH2-SiCH3C12 39.3 g (30.9 ml, 0.26 mol) of CH3SiC13 72.8 g (60.6 ml, 0.26 mol) of C13Si-CH2CH2-SiCH3C12 -~

Yield: 85 g (78%) lH NMR data: :~- .:- :- -~
SiCH3 ~ = 0.0 - 0.5 ppm (br), intensity 14.1 NH + Si-CH2CH2-Si ~ = 0.5 - 1.3 ppm (br), " 10.4 ~s~ ple 3 PreparaSion of the oligomeric silazane of formula (V) ::.: :
where Rl = H, R2 ~ R9 - CH3, R~ = vinyl, a = 0.64, b =
0.16, c - 0.2 and d = 0 ;:-;;r.~.

The procedure was analogous to that in Example 1, except ; ~ ;
that the chloro~ilane~ were as followss 100.3 g (90 ml, 0.78 mol) of CH3SiHC12 -.`
48.0 g (40 ml, 0.19 mol) of Cl2CH3Si-CH2CH2-SiCH3Cl2 38.1 g (30 ml, 0.24 mol) of vinyl-SiCl3 ; ~
'~,.'.':' ,.'.., ' ,''. '.:
Yields 92 g (81S) ~H NMR datas SiCH3 6 - 0.0 - 0.5 ppm (br), intensity 11.8 .
NH + SiCH2CH2Si 6 - 0.5 - 1.2 ppm (br), ~ 7.1 -~
Si-vinyl 6 = 5.5 - 6.5 ppm (br), ~ 2.4 . ;
SiH 6 = 4.5 - 5.0 ppm (br), ~ 2.2 `~

Claims

1. A process for the preparation of oligosilazanes which comprises reacting excess ammonia with a starting materi-al containing at least one of the two components (I) R11R2SiCl2 and (II) Cl2R3Si-CH2CH2-SiR3Cl2 and at least one of the two components (III) R4SiCl3 and (IV) Cl3Si-CH2CH2-SiR5Cl2, at -70 to +100°C, where the radicals independently of one another have the following meanings:
R1, R2, R4 = H, C1-C6 alkyl or C2-C6 alkenyl and R3, R5 = C1-C6 alkyl or C2-C6 alkenyl, and the molar percentage of (I) or (II) or a mixture thereof in the starting material is 30 to 99%, and where the reaction of a mixture containing only (I) and (III) with ammonia shall be excluded.

2. A process as claimed in claim 1, wherein the radicals independently of one another have the following meanings:
R1, R2, R4 = H, C1-C3 alkyl or C2-C3 alkenyl and R3, R5 = C1-C3 alkyl or C2-C3 alkenyl.

3. A process as claimed in claim 1, wherein R1 = H, R2 =
R3 = R5 = CH3 and R4 = CH3 or vinyl.

4. An oligosilazane which can be obtained by the process as claimed in any of claims 1 to 3.

5. An oligosilazane of the formula where the radicals independently of one another have the following meanings:
R1, R2, R4 = H, C1-C6 alkyl or C2-C6 alkenyl and R3, R5 = C1-C6 alkyl or C2-C6 alkenyl, and the case where a > 0, b > 0, c = 0 and d = 0 simultaneously shall be excluded.

6. An oligosilazane as claimed in claim 5, wherein the radicals independently of one another have the following meanings:
R1, R2, R4 = H, C1-C3 alkyl or C2-C3 alkenyl and R3, R5 = C1-C3 alkyl or C2-C3 alkenyl.

7. An oligosilazane as claimed in claim 5, wherein R1 = H, R2 = R3 = R5 = CH3 and R4 = CH3 or vinyl.