DE4320784A1 - Co-polymeric boro-silazane(s) prodn. useful for prodn. of ceramics - by reacting mixts. of tris-di:chloro silyl-ethyl-borane(s) and di- or tri-chloro silane(s) with ammonia, for coating steel - Google Patents

Abstract

The prodn. of copolymeric boro-silazanes (II) comprises reacting a mixt. of tris-silyl-borane(s) of formula B-(CH2H4-SiCl2X)3 (I) and chlorosilane(s) of formula R1SiCl3 or R2R3SiCl2 with ammonia; -C2H4- = -CH2-CH3- or -CHMe-; X = Cl or 1-4C aliphatic residue; and R1-R3 = H or 1-4C aliphatic residue. Also new are boro-silazane copolymers of formula (II), obtd. by the above prodn. R = 1-4C aliphatic residue; and a + b + c + d = 1. The amt. of ammonia used is pref. sufficient to saturate all the Si-Cl gps. and bind the obtd. HCl as NH4Cl, and cpd. (I) and the chlorosilane are reacted as a soln. in organic solvent. The reactants are mixed at -10 to +10 deg. C and the mixt. is heated to 10-100 deg. C. (I) are prepd., e.g. by reaction of corresp. vinyl silanes of formula CH2=CH-SiCl2X with BH3-THF as described in J. Organomet. Chem. 34 (1972) C0 and 135 (1977) 249, and in Zhur. Obshchei. Khim. 30 (1960) 3615. Pref. solvents are, e.g. cyclohexane, toluene, THF etc. USE/ADVANTAGE - (II) are new B-contg. polyislazanes, useful for the prodn. of B- and Si-contg. ceramics with improved adhesion, hardness and surface quality, which are useful for coating steel etc., esp. for the surface coating of machine components which are mechanically and chemically stressed. (II) may also be shaped before pyrolysis, e.g. to form ceramic fibres which are useful for reinforcement of Al (alloys) and ceramic components. The prodn. of ceramic materials comprises pyrolysis of (II) at 500-2000 deg. C under nitrogen or argon (for materials contg. Si, B, C and N) or in an ammonia-contg. atmos. (for materials contg. Si, B and N). Also new are ceramic materials as above, produced by the prodn.

Description

The invention relates to novel copolymers borosilazanes, their preparation, their Further processing to boron and silicon-containing ceramic materials, as well as these materials themselves. The cited ceramic materials are obtained by pyrolysis of the copolymer borosilazanes.

The preparation of certain borosilicon organic polymers and their pyrolysis to boron and silicon-containing ceramic materials is already known. RR Wills et al. (Cer. Bulletin 62 (1983) 905) describe the preparation of boron-containing polysiloxanes by mixing alkoxysilanes with boron alkoxides B (OR) ₃ and subsequent sol-gel process. Sol-gel processes, however, are known to be very tedious; In addition, inhomogeneities can occur because by mechanical mixing an ideally homogeneous solution with ideal distribution of siloxanes and boron alkoxide can not be produced.

According to EP-A-0 325 483, boroxines, cyclic boron-oxygen molecules, implemented with silazanes. The boroxines and silazanes must be separated be synthesized and then reacted together. These Multistep synthesis is complicated and yet there are inhomogeneities possible.

According to EP-A-0 337 843, BCl ₃ is reacted with bis (trimethylsilyl) alkali amide. However, alkali metal amides are highly flammable compounds that cause difficulties in handling.

According to US Pat. No. 4,906,763, silicon-containing borazines are in SiBN ceramic  transferred. It starts from chloroborazine and leaves it with Hexamethyldisilazane react.

According to US-PS 4,780,337 SiH-containing polymers, u. a. Siloxanes, with Boralkenoxiden in a hydrosilylation reaction (with platinum compounds as Catalysts) implemented. This leads u. a. also to boron-containing polysilazanes. Difficulties arise in the recovery of the catalyst and in the Production of Boralkenoxide.

It has now been found that new organosilicon polymers, namely copolymers borosilazanes, in a simple manner from a mixture of tris silylboranes of the formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical having 1-4 C-atoms, and the chlorosilanes R ₁ SiCl ₃ and / or R ₂ R ₃ SiCl ₂ , wherein independently of one another R ₁ , R ₂ and R _{3 are} H atoms or aliphatic radicals having 1-4 C atoms, can be prepared by reaction with ammonia. From the copolymer borosilazanes obtained can then be prepared by pyrolysis in a simple manner boron and silicon-containing ceramic materials.

An object of the invention is therefore a process for the preparation of copolymer borosilazanes, characterized in that at least one Tris-silylborane of the formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical having 1-4 C-atoms, in admixture with at least one of Chlorosilanes R ₁ SiCl ₃ or R ₂ R ₃ SiCl ₂ , wherein independently of one another R ₁ , R ₂ and R _{3 are} H atoms or aliphatic radicals having 1-4 C atoms, with ammonia.

The tris-silylboranes of the formula B [-C ₂ H ₄ -SiCl ₂ X] ₃ used as starting materials can be prepared according to PR Jones et al. (J Organomet Chem 34 (1972) C9), TFO Lim et al. (J. Organomet. Chem. 135 (1977) 249) and BM Mikailev et al. (Zhur. Obshchei, Khim., 30 (1960) 3615; CA (55) 20920) can be prepared by reacting corresponding vinylsilanes of the formula CH ₂ = CH-SiCl ₂ X with BH ₃ .THF (tetrahydrofuran). This generally produces a mixture of 1- and 2-substitution products (with -CH (CH ₃ ) - or -CH ₂ -CH ₂ groups). These can be separated and then reacted individually according to the invention, but it is also readily possible to use the mixture as it arises in the reaction as such. However, it is also possible to first prepare various tris-silylborane mixtures from several different vinylsilanes by reaction with BH ₃ .THF, then to separate these mixtures into their two 1- and 2-substitution products and to prepare new mixtures thereof, eg. B. only from 1-substitution products or only from 2-substitution products and then implement according to the invention. This mixing of previously isolated pure components can lead to mixtures which can not be obtained directly by the vinylsilane reaction with BH ₃ .THF.

The chlorosilanes R ₁ SiCl ₃ and R ₂ R ₃ Cl ₂ further used in the process according to the invention are commercially available.

For the preparation of the copolymer borosilazanes are preferably the Tris-silylboranes and the chlorosilanes together in an organic solvent which is inert towards the reactants - tris-silylborane, Chlorosilane and ammonia - behaves. Suitable z. Saturated aliphatic or aromatic hydrocarbons such as n-pentane, cyclohexane, toluene or chlorinated hydrocarbons such as chloroform or chlorobenzene, or ethers such as Diethyl ether or THF, and then mixed with ammonia to saturation. The Saturation occurs when all Si-Cl functions are due to NH groups are substituted. Ammonia can be added as a gas or as a liquid become.  

Since the reaction is exothermic, mixing of the reactants becomes Preferably, first the temperature is kept at -10 ° C to + 10 ° C and subsequently heated to temperatures of 10 ° C to 100 ° C, preferably on 20 ° C to 50 ° C.

The reaction produces NH ₄ Cl, which can be separated from the copolymer borosilazane by extraction with an inert organic solvent. For this purpose, the same solvents are suitable as for dissolving the tris-silylborane and the chlorosilanes.

If desired, the process can also be carried out under reduced pressure be performed. Even at pressures in the range of 1 to 10 bar can to be worked.

The process can also be designed continuously.

The novel copolymeric borosilazanes prepared in this way have one molecular structure represented by the formula (II)

in which the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) -, R is an aliphatic radical having 1-4 C atoms and independently of one another R ₁ , R ₂ and R _{3 are} H atoms or aliphatic radicals having 1-4 C atoms, and a, b, c, d denote the mole fractions of the four structural units. Where a + b + c + d = 1.

If B [-C ₂ H ₄ -SiCl ₃ ] ₃ and R ₂ R ₃ SiCl ₂ (in each case 50 mol%) are used, then

a = 0.5, c = 0.5 and b = d = 0.

When B [-C ₂ H ₄ -SiCl ₂ CH ₃ ] ₃ (30 mol%) and CH ₃ SiCl ₃ (70 mol%) are used, b = 0.3, d = 0.7 and a = c = 0, and R = R ₁ = CH ₃ .

If a mixture of 25 mol .-% B [-C ₂ H ₄ -SiCl ₃ ] ₃ , 25 mol .-% B [-C ₂ H ₄ -SiCl ₂ CH ₃ ] ₃ , 25 mol% (CH ₃ ) ₂ SiCl ₂ and 25 mol .-% CH ₃ SiCl _{3 is} used, then a = b = c = d = 0.25 and R = R ₁ = R ₂ = R ₃ = CH ₃ .

In order to distinguish the 1- and 2-borane units in the polymer, the mole fraction a of the alkyl-free borane unit is divided into a ₁ for the proportion of 1-borane unit (-CH (CH ₃ ) -) and a ₂ for the proportion of 2-borane unit (-CH ₂ -CH ₂ -) and analogously the molar fraction b of the borane moiety containing the alkyl radical R in b ₁ (1-borane unit) and b ₂ (2-borane unit).

Similarly, the proportion of different alkyl radicals R of different lengths can be given by the molar fractions b ₁ (1-borane unit) and b ₂ (2-borane unit) in b ₁ ¹ , b ₁ ² , b ₁ ³ , b ₁ ⁴ and b ₂ ¹ , b ₂ ² , b ₂ ³ , b ₂ ^{4 are} divided, wherein the upper index represents the number of C atoms in the radical R, ie z. B. b ₁ ² and b ₂ ² as Mole fractions for the 1- or 2-borane unit with R = C ₂ H. ₅ Analogously for R ₁ , R ₂ , R ₃ .

Another object of the present invention are accordingly copolymers Borosilazanes of the general formula (II)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ or -CH (CH ₃ ) -, R is an aliphatic radical having 1-4 C atoms and independently R ₁ , R ₂ and R ₃ H Are atoms or aliphatic radicals with 1-4 C atoms and a, b, c and d denote the mole fractions of the respective structural units, where a + b + c + d = 1.

Another object of the present invention are copolymers borosilazanes obtainable by reacting at least one tris-silylborane of the formula (I)

B [-C₂H₄-SiCl₂X] ₃ (I)

wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical having 1-4 C-atoms, in admixture with at least one of Chlorosilanes R ₁ SiCl ₃ or R ₂ R ₃ SiCl ₂ , wherein independently of one another R ₁ , R ₂ and R _{3 are} H atoms or aliphatic radicals having 1-4 C atoms, with ammonia.

The preferred embodiments of this reaction are already above been specified. About the composition of the mixture Tris-silylborane and chlorosilane can be the composition of the copolymers Borsilazane control.

The copolymer borosilazanes according to the invention are very homogeneous in relation on the elemental distribution of B, Si, C, N. They can be prepared by pyrolysis in inert Nitrogen or argon atmosphere at temperatures of 500 to 2000 ° C, preferably 800 to 1400 ° C, pyrolyzed to amorphous, dense materials consisting essentially of Si, C, N and B and in traces also H and O may contain.

A particular advantage is that the copolymeric borosilazanes prior to pyrolysis can be formed into three-dimensional shaped bodies by various methods.

An important method of shaping is the drawing of fibers. Let it go fibers from highly viscous solutions of the copolymer borosilazane in  Solvents such as toluene, THF or hexane pull. The fiber drawing happens advantageously by means of spinnerets of 80 to 350 microns in diameter. By subsequent stretching, the thread is tapered, so that after pyrolysis very strong thread of 2 to 20 microns, in particular 5 to 15 microns in diameter arises. Find the fibers produced by subsequent pyrolysis Use as mechanical reinforcements in fiber reinforced Aluminum, aluminum alloys and ceramic components.

Another important processing option for the copolymeric borosilazanes is the production of dense, well adhering, amorphous ceramic coatings on metals, in particular steels. The coating is done with the help of a Solution of the copolymer borosilazane in organic solvents such as toluene, THF or hexane. The pyrolytic transformation into an amorphous layer takes place in the same temperature range from 500 to 2000 ° C, preferably 800 to 1400 ° C, under inert gas as above for the three-dimensional moldings described.

The ceramic coatings are suitable because of their excellent Adhesion, high hardness and surface quality especially for surface finishing of mechanically and chemically stressed machine components.

Next you can pyrolyze the copolymer borosilazanes described above with the same high ceramic yield of 70 to 90% instead of in inert gas in NH ₃ atmosphere. This results in a virtually carbon-free, crystal clear, colorless material. In the pyrolysis in NH ₃ at 1000 ° C or higher, the C content is below 0.5 wt .-%. The pyrolysis product consists of practically pure amorphous SiBN. The pyrolysis in NH ₃ can be applied to all moldings produced by the shaping processes described above, that is to say from powders shaped bodies, fibers, coatings.

Further objects of the invention are therefore the production of Si, B, C and N-containing ceramic material, characterized in that the  mentioned above, by their formula or their method of production characterized copolymeric borosilazanes in inert nitrogen or Argon atmosphere at 500 to 2000 ° C, preferably 800 to 1400 ° C, pyrolyzed, as well as the thereby obtainable ceramic material itself.

Further objects of the invention are the production of Si, B and N. containing ceramic material, characterized in that the mentioned above, by their formula or their method of production characterized copolymeric borosilazanes in ammonia-containing Atmosphere at 500 to 2000 ° C, preferably 800 to 1400 ° C, pyrolyzed, as well as the thereby obtainable ceramic material itself.

The following examples illustrate the invention.

Experiment report 1 Preparation of tris [(dichloromethylsilyl) ethyl] borane

To a cooled to 0 ° C solution of 200 ml (216 g, 1.53 mol) of dichloromethylvinylsilane in 255 ml of toluene was added dropwise with vigorous stirring 255 ml of a 2 molar solution of Dimethylsulfidboran (0.51 mol BH ₃ ) in toluene , The temperature was kept below 10 ° C. After the dropwise addition, the reaction mixture was stirred for 5 hours at 0 ° C and then for a further 36 hours at room temperature. After removal of the solvent in vacuo, 223 g of tris [(dichloromethylsilyl) ethyl] borane could be isolated.

Test report 2 Preparation of tris [(trichlorosilyl) ethyl] borane

To a cooled to 0 ° C solution of 200 ml (254 g, 1, 57 mol) of trichlorovinylsilane in 255 ml of toluene, with vigorous stirring 262 ml of a 2 molar solution of dimethylsulfide borane (0.52 mol of BH ₃ ) in toluene slowly dropwise. The temperature was kept below 10 ° C. After the dropwise addition, the reaction mixture was stirred for 5 hours at 0 ° C and then for a further 36 hours at room temperature. After removal of the solvent in vacuo 190 g of tris [(trichlorosilyl) ethyl] borane could be isolated.

Both prepared tris-silylboranes are colorless, oily liquids that adhere to ignite the air of their own accord if they have a large surface available (eg on pulp).

example 1 Reaction of a mixture of tris [(dichloromethylsilyl) ethyl] borane and Dimethyldichlorosilane with ammonia

10 g (0.022 mol) of tris [(dichloromethylsilyl) ethyl] borane and 2.8 g (0.022 mol) Dimethyldichlorosilane were placed in 150 ml of THF, and over a Gas inlet tube was introduced ammonia. At the same time the Reaction mixture cooled to about 5 ° C.

After saturation of all SiCl groups with ammonia, recognizable by the onset of reflux of NH ₃ on a dry ice condenser, was heated to 25 ° C and the precipitated NH ₄ Cl was separated via a filter device under N ₂ as a protective gas.

The solvent and all volatile components of the reaction mixture were removed by distillation under reduced pressure. It remained that way copolymers borosilazane back as a colorless powder.  

This is to be assigned the following structure:

This structure was confirmed by elemental analysis and corresponds to the general formula (II) with a = d = 0 and b = c = 0.5 and R = R ₂ = R ₃ = CH ₃ .

Examples 2-6

The procedure was similar to Example 1, but other mixtures were reacted with NH ₃ . The following abbreviations are used:
Tris [(dichloromethylsilyl) ethyl] borane: TDS
Tris [(trichlorosilyl) ethyl] borane: TTS

Example 7 Reaction of a mixture of tris [(dichloromethylsilyl) ethyl] borane and Trichlorovinylsilane with ammonia

In a 1000 ml three-necked flask with internal thermometer, dry ice condenser (with Cooling mixture of acetone and dry ice), gas inlet tube and Magnetic stirrer 62.5 g (0.144 mol) of tris [(dichloromethylsilyl) ethyl] borane and 63.5 g (0.393 mol) of trichlorovinylsilane in 500 ml of THF submitted, and over a Gas inlet tube was introduced ammonia with stirring. simultaneously The reaction mixture was cooled to about -10 ° C.

After saturation of all SiCl groups with ammonia, recognizable by the onset of reflux of NH ₃ on dry ice, was stirred for one more hour under ammonia reflux, then heated to 25 ° C and separated the precipitated NH ₄ Cl via a filter device under N ₂ as a protective gas.

This gave a milky turbid solution, which only by centrifuging at 15000 rpm as a clear solution.

GPC measurements of this solution showed two peaks with the following values:

The solution was freed from the solvent using the polymeric material finally came as a pale yellow powder.

Elemental analysis showed (in wt%):

C 25.47 H 7.48 N 6.28 Cl 0.3 Si not determined B not determined total 39.53

Example 8 Pyrolysis of the polymer obtained in Example 7 in argon

After drying the polymer obtained in Example 7 in an argon stream at 50 to 60 ° C, the pyrolysis was carried out in a Schlenk vessel made of quartz glass Argon atmosphere. With a heating rate of 1 degree per minute was up to a final temperature of 1100 ° C heated, with 1 hour hold time at this Temperature.

The ceramic yield was 54% by weight.

The elemental analysis showed:

C 23.3% by weight O 1.7% by weight N 21.3% by weight Si 48.0% by weight

Example 9 Pyrolysis of the polymer obtained in Example 7 in NH ₃

After drying the polymer from Example 7 in the ammonia stream at 50 to 60 ° C, the pyrolysis was carried out in a Schlenk vessel made of quartz glass Ammonia atmosphere. With a heating rate of 2 degrees per minute was up heated to a final temperature of 1100 ° C, with 1 hour hold at this temperature.

The ceramic yield was 60% by weight.

The elemental analysis showed a C content of 0.1 wt .-%.

Claims (10)

1. A process for the preparation of copolymer borosilazanes, characterized in that at least one tris-silylborane of the formula (I) B [-C₂H₄-SiCl₂X] ₃ (I) wherein the group -C ₂ H ₄ - the structure -CH ₂ - CH ₂ - or -CH (CH ₃ ) - and X is a chlorine atom or an aliphatic radical having 1-4 C atoms, in admixture with at least one of the chlorosilanes R ₁ SiCl ₃ or R ₂ R ₃ SiCl ₂ , wherein independently R ₁ , R ₂ and R _{3 are} H atoms or aliphatic radicals having 1-4 C atoms, reacted with ammonia. 2. The method according to claim 1, characterized in that one uses ammonia in an amount which saturates all SiCl groups and resulting HCl as NH ₄ Cl binds. 3. The method according to claim 1 or 2, characterized in that the Tris-silylborane and the chlorosilane dissolved in an organic solvent and then be implemented. 4. The method according to any one of claims 1 to 3, characterized that when combining the reactants, a temperature of -10 ° C to + 10 ° C and then heated to 10 to 100 ° C. 5. Copolymers Borsilazanes of the general formula (II) wherein the group -C ₂ H ₄ - has the structure -CH ₂ -CH ₂ or -CH (CH ₃ ) -, R is an aliphatic radical having 1-4 C atoms and independently R ₁ , R ₂ and R ₃ H Are atoms or aliphatic radicals having 1-4 C atoms, and a, b, c, d denote the mole fractions of the structural units, where a + b + c + d = 1. 6. Copolymers Borosilazanes, obtainable by the process according to one of Claims 1 to 4. 7. A process for the preparation of Si, B, C and N containing ceramic Material, characterized in that copolymeric borosilazanes according to Claim 5 or 6 in inert nitrogen or argon atmosphere at 500 ° C to Pyrolyzed at 2000 ° C. 8. Si, B, C and N containing ceramic material obtainable according to the Method according to claim 7. 9. A process for the preparation of Si, B and N containing ceramic Material, characterized in that copolymeric borosilazanes according to Claim 5 or 6 in ammonia-containing atmosphere at 500 ° C to Pyrolyzed at 2000 ° C. 10. Si, B and N containing ceramic material obtainable according to the Method according to claim 9.