WO1995014054A1

WO1995014054A1 - Organopolysilane/alkenyl siloxane copolymers

Info

Publication number: WO1995014054A1
Application number: PCT/EP1994/003806
Authority: WO
Inventors: Stefan Loskot; Bernd Pachaly; Wilfried Kalchauer
Original assignee: Wacker-Chemie Gmbh
Priority date: 1993-11-19
Filing date: 1994-11-17
Publication date: 1995-05-26
Also published as: DE4339478A1

Abstract

The invention relates to organopolysilane/alkenyl siloxane copolymers which can be produced by allowing organopolysilanes to react in the presence of boric acid with organopolysiloxanes containing alkenyl groups, consisting of units of formulae [RaR13-aSiO1/2], [RbR12-bSiO2/2] and [R1SiO3/2] wherein R may be the same in all cases or different, signifying monovalent, possibly substituted hydrocarbon groups without aliphatic carbon-carbon multiple bonds; R1 can be identical in all cases or different, signifying monovalent, possibly substituted hydrocarbon groups with at least one aliphatic carbon-carbon multiple bond; a = 0, 1 or 2; and b = 0 or 1.

Description

Organopolysilane / alkenylsiloxane copolymers

The invention relates to organopolysilane / alkenylsiloxane copolymers, processes for their preparation from organopolysilanes and organopolysiloxanes containing alkenyl groups, and their use for the production of ceramic materials.

In the following, the term organopolysilanes Si-Si bonds should be understood to mean organosilicon compounds with at least three silicon atoms. The term organopolysiloxanes is also intended to include oligomeric siloxanes in the context of this invention.

Organopolysilanes and their use in the pyrolytic production of ceramic materials have been known for a long time. The organopolysilanes can be produced, for example, by disproportionation of mixtures of tetramethoxydimethyldisilane and trimethoxytrimethyldisilane. For this purpose, for example, US-A-4,952, 658 (Wacker-Chemie GmbH; issued August 28, 1990) or the corresponding DE-A-38 11 567 and US-A-4,667,046 (Wacker-Chemie GmbH; issued) on May 19, 1987) or the corresponding DE-A-35 32 128. In general, low molecular weight organopolysilanes are readily soluble and meltable, but these often give only low ceramic yields in processes for the pyrolytic production of ceramic materials. In the case of organopolysilanes with a higher molecular weight and high crosslinking Degree of efficiency higher ceramic yields are achieved, but the polymers are generally insoluble and infusible, which is a great disadvantage in terms of processability.

The invention relates to organopolysilane / alkenylsiloxane copolymers which can be prepared by reacting organopolysilanes with organopolysiloxanes containing alkenyl groups from units of the formula

[R _a R ¹ ₃ _ _a Si0 _{1 2} ], [R _b R ¹ ₂ _ Si0 _{2 2} ] and [R ¹ Si0 _{3 2} ], where

R can be the same or different and means monovalent, optionally substituted hydrocarbon radicals which are free of aliphatic carbon-carbon multiple bond, R ^{1 can be the} same or different and monovalent, optionally substituted hydrocarbon radicals with at least one aliphatic carbon-carbon multiple bond means a is 0, 1 or 2 and b is 0 or 1, ^'

in the presence of boric acid.

Another object of the present invention is a process for the preparation of organopolysilane / alkenylsiloxane copolymers, characterized in that organopolysilane with organopolysiloxane containing alkenyl groups from units of the formula

[R _a Rl ₃ _ _a Si0 _{1 2} ], [bR ¹ 2-b ^Ξ i ° 2/2] ^ d [Rlsiθ _3/2 ], where

R can be the same or different and means monovalent, optionally substituted hydrocarbon radicals which are free from aliphatic carbon-carbon multiple bond, - 3 -

R ^{1 can be the} same or different and means monovalent, optionally substituted hydrocarbon radicals with at least one aliphatic carbon-carbon multiple bond, a is 0, 1 or 2 and b is 0 or 1,

is reacted in the presence of boric acid.

The radical R is preferably a hydrocarbon radical with 1 to 12 carbon atoms which is free of an aliphatic carbon-carbon multiple bond, in particular the methyl radical.

Examples of radicals R are alkyl radicals, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl , neo-pentyl, tert-pentyl radical, hexyl radicals, such as the n-hexyl radical, heptyl radicals, such as the n-heptyl radical, octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as 2,2,4 Trimethylpentyl radical, nonyl radicals, such as the n-nonyl radical, decyl radicals, such as the n-decyl radical, dodecyl radicals, such as the n-dodecyl radical; Cycloalkyl radicals, such as cyclopentyl, cyclohexyl, cycloheptyl radicals and methylcyclohexyl radicals; Aryl radicals such as the phenyl and naphthyl radicals; Alkaryl radicals, such as o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals; Aralkyl radicals, such as the benzyl radical, the α- and the β-phenylethyl radical.

The radical R ¹ is preferably alkenyl radicals having 2 to 12 carbon atoms, in particular the vinyl radical.

Examples of radical R ¹ are the vinyl radical, allyl radical, n-but-1-enyl radical, n-but-2-enyl radical, n-but-3-enyl radical, n-pent-1-enyl radical, n-pent-2-enyl radical , n-pent-3-enyl group, n-pent-4-enyl group, n-hex-1-enyl group, n-hex-2-enyl group, n-hex-3-enyl group radical, n-hex-4-enyl radical, n-hex-5-enyl radical, cyclohex-1-enyl radical, cyclohex-2-enyl radical, cyclohex-3-enyl radical, cyclohex-4-enyl radical and isopropenyl radical.

The value for a is preferably 1 or 2, particularly preferably 2.

The value for b is preferably 1.

The organopolysiloxanes containing alkenyl groups used according to the invention are preferably those of the formula

{[R _a R ₃ __ _a Si0 _1/2] _v [R _b R ¹ _b _ ₂ Si0 _{_2/2]} y [R ¹ ₃ Si0 _2] _z} _c (I),

in which

R, R ¹ , a and b have the meaning given above for them and v is 0.01 to 0.5, preferably 0.05 to 0.45, particularly preferably 0.05 to 0.35, y is 0, 01 to 0.7, preferably 0.1 to 0.6, particularly preferably 0.1 to 0.5, i ^' st, z 0.01 to 0.95, preferably 0.2 to 0.9, particularly preferably is 0.4 to 0.8, with the proviso that the sum of v, y and z in formula (I) is 1 and c is a number from 3 to 50.

The organopolysiloxanes containing alkenyl groups used according to the invention are particularly preferably those of the formula (I) with a molecular weight of 300 to 5000.

Examples of the organopolysiloxanes containing alkenyl groups used according to the invention are methyl vinyl, ethyl vinyl, n-propyl vinyl, methyl allyl, ethyl allyl, phenyl vinyl and methyl isopropenyl polysiloxanes. The organopolysiloxanes containing alkenyl groups used according to the invention and processes for their preparation are already known from DE-A-41 43 203 (Wacker-Chemie GmbH; issued July 1, 1993).

Thus, the organopolysiloxanes used according to the invention can be prepared, for example, by hydrolysis of the corresponding halo, organyloxy or hydroxysilanes.

The organopolysilanes used according to the invention can be any organopolysilanes known to date.

It is preferably organopolysilanes of the formula

R ² R ² R ²

R - [(Si-) _p (Sl-) _q (Sι-) _r ] _m R ² (II),

IIIR ² OR ³ R ⁴ wherein

R ^{2 can be the} same or different and represents hydrogen, monovalent, SiC-bonded, optionally substituted hydrocarbon radicals or alkoxy radical,

R ^{3 can be the} same or different and means alkyl radical,

R ^{4 can be the} same or different and means hydrogen atom, monovalent, SiC-bonded, optionally substituted hydrocarbon radicals, alkoxy radical or silyl radical, p can be the same or different and is a number between 0.1 and 0.9, q is the same or different and can be a number between 0.01 and 0.5, r can be the same or different and a number between 0 and 0.5, with the proviso that p + q + r is 1 and m is a number is from 3 to 100. If R ^{4 has} the meaning of a silyl radical, for example in the form of a silane of the formula (II), it is a so-called branching point.

The radical R ² is preferably hydrocarbon radicals and alkoxy radicals having 1 to 6 carbon atoms, particularly preferably the methyl, ethoxy and methoxy radical.

Examples of radical R ² are the examples given for R.

The organopolysilanes according to the invention are particularly preferably those of the general formula

Y - [(SiMe ₂ ) _s (MeSiX) _t (SiMe) _u ] _n Y (III), where

Me means methyl residue,

Y is methyl, methoxy or ethoxy, X is methoxy or ethoxy, the sum s + t + u is 1, the ratio s: u is between 5: 3 and 3: 5, the ratio Me: X is between 8: 1 and 25: 1 and n is an integer from 3 to 50.

The organopolysilanes used according to the invention preferably have 3 to 50 silicon atoms and an average molecular weight of preferably 300 to 5000.

The production of such organopolysilanes is already known. In this regard, reference is made, for example, to the aforementioned US Pat. No. 4,667,046 (Wacker-Chemie GmbH; issued May 19, 1987) or the corresponding DE-A-35 32 128, in which organopolysilanes are produced by the fact that tri- methoxyorganodisilane optionally in a mixture with tetra-methoxyorganodisilane with hydrogenorganosilane in the presence of metal catalyst, such as sodium alcoholate, is implemented.

The organopolysilanes used according to the invention are preferably those which are prepared by reacting tetraalkoxydialkyldisilane and trialkoxytrialkyldisilane in a molar ratio of 1: 9 to 9: 1, preferably 4: 6 to 7: 3, with alkali metal analysis, if appropriate in a mixture with Phenylmethyl dialkoxysilanes and phenylmethyl methoxydisilanes.

The organopolysilanes used according to the invention are particularly preferably those which are prepared by reacting tetramethoxydimethyldisilane and trimethoxytrimethyldisilane in a molar ratio of 4: 6 to 7: 3 in the presence of sodium methylate, optionally in a mixture with phenylmethyldimethoxysilanes or phenylmethylmethoxydisilanes.

Boric acid is a large-scale product and is known in the professional world.

In the process according to the invention, organopolysiloxane containing alkenyl groups is used in amounts of preferably 3 to 50 percent by weight, particularly preferably 10 to 20 percent by weight, in each case based on the weight of organopolysilane.

In the process according to the invention, boric acid is used in amounts of preferably 1 to 10 percent by weight, particularly preferably 3 to 6 percent by weight, in each case based on the weight of organopolysilane.

In the process according to the invention, further substances, such as, for example, organic solvents, such as For example, toluene, xylene or alkanes of various boiling fractions can be used.

The components used in the method according to the invention are each one type or a mixture of at least two different types of such components.

The process according to the invention is carried out at a pressure of preferably 900 to 1100 hPa and a temperature of preferably 20 to 200 ° C., particularly preferably 100 to 150 ° C.

The method according to the invention is preferably carried out in an inert atmosphere, such as, for example, under nitrogen, helium or argon.

The organopolysilane / alkenylsiloxane copolymers according to the invention preferably have an average of 5 to 50 silicon atoms and an average molecular weight M _w of preferably 2,000 to 10,000.

The organopolysilane / alkenylsiloxane copolymers according to the invention are meltable and soluble in non-polar solvents such as toluene, xylene, cyclohexane and iso-octane. The viscosity of a 50 percent by weight solution of copoly er according to the invention in toluene is preferably 1 to 250 mm ² / s, particularly preferably between 2 and 10 mm ² / s.

The softening point of the copolymers according to the invention is preferably between 100 and 250 ° C., particularly preferably between 120 and 150 ° C.

The organopolysilane / alkenylsiloxane copolymers according to the invention can be used for all purposes, including those Organopolysilanes have hitherto been used. They are particularly suitable in processes for the production of high molecular weight organosilicon compounds and for the pyrolytic production of silicon carbide (SiC), preferably as a matrix element in ceramic composites, as a binder in SiC ceramics and as a high-temperature adhesive.

It is advantageous for many applications to take up the copolymers in an organic solvent, such as toluene, and to fill them with slip in order to reduce the shrinkage during pyrolysis.

Ceramic composites can be produced by all customary processes, in particular by the wet winding process, scrim infiltration or the incorporation of short fibers. All fibers that do not undergo high-temperature reactions with the matrix are suitable, in particular carbon, SiC, silicon nitride and silicon carbonitride fibers.

The organopolysilane / alkenylsiloxane copolymers according to the invention can now be crosslinked and then the crosslinking product obtained can be pyrolyzed, crosslinking and pyrolysis being able to take place in one operation.

Another object of the invention is a process for the preparation of high molecular weight organosilicon compounds, characterized in that organopolysilane / alkenylsiloxane copolymers can be prepared by reacting organopolysilanes with organopolysiloxanes containing alkenyl groups from units of the formula

[R _a Rl ₃ __ _a Si0 _1/2 ], [R _b R ¹ 2-bSi0 _{2 2} ] and [Rlsi0 _3/2 ], where

R can be the same or different and monovalent, optionally substituted hydrocarbon radicals, the are free from aliphatic carbon-carbon multiple bond means R ^{1 can be the} same or different and means monovalent, optionally substituted hydrocarbon radicals with at least one aliphatic carbon-carbon multiple bond, a denotes 0, 1 or 2 and b 0 or 1, in the presence of boric acid, if appropriate in a mixture with other substances, are allowed to crosslink at a temperature between 200 and 400 ° C.

In the process according to the invention, the copolymer is preferably used dissolved in organic solvent, such as iso-octane, cyclohexane, toluene and xylene.

The further substances optionally used in the crosslinking according to the invention are preferably fillers and additives.

Examples of fillers are inert, inherent inert fillers, such as SiC or SiOC, and reactive powders, such as silicon, titanium silicide, chromium silicide or boron, SiC preferred and SiC with an average grain size of 0.01 to 10 μm, in particular 0.4 to 2 μm, is particularly preferably used.

Preferably 30 to 70 percent by weight, particularly preferably 50 to 60 percent by weight SiC, each based on the copolymer used according to the invention.

The additives used are preferably compression aids, in particular flow agents. auxiliaries, such as, for example, highly disperse silica, triolein, talc, flame black and ammonium stearate.

Additives are preferably used in amounts of 0.1 to 5 percent by weight, particularly preferably 1.5 to 2.5 percent by weight, in each case based on the weight of the copolymer used.

The crosslinking according to the invention is preferably carried out at a temperature of 250 to 350 ° C.

The crosslinking according to the invention can be carried out at the pressure of the surrounding atmosphere or at elevated pressure. In particular, if the dimensional stability of the workpieces is to be maintained, the crosslinking according to the invention is preferably carried out at a pressure between 10,000 and 100,000 hPa, particularly preferably between 40,000 and 60,000 hPa.

The crosslinking according to the invention is preferably carried out in an inert atmosphere, such as, for example, under nitrogen, helium or argon.

The copolymers crosslinked according to the invention are infusible and insoluble.

The process according to the invention for crosslinking the copolymers according to the invention has the advantage that precursors with very good processability but poor ceramic yield can be converted to readily pyrolyzable substances with good ceramic yield.

Another object of the invention is a process for the production of SiC or SiC ceramics, characterized in that organopolysilane / alkenylsiloxane according to the invention Copolymers and / or their crosslinking products, if appropriate in a mixture with other substances, are reacted under an inert atmosphere, such as, for example, an argon, helium or nitrogen atmosphere, at temperatures of at least 800 ° C.

The process according to the invention for the production of SiC or SiC ceramics is preferably carried out at temperatures from 800 to 1500 ° C., particularly preferably 1200 to 1400 ° C.

The method according to the invention for producing SiC or SiC ceramic is preferably carried out at the pressure of the surrounding atmosphere, that is to say 900 to 1100 hPa. However, it can also be carried out at higher or lower pressures.

The use of organopolysilane / alkenylsiloxane copolymers and / or their crosslinking products in the process according to the invention for the production of SiC or SiC ceramics has the advantage that ceramic yields of over 55%, preferably 55 to 70%, are achieved.

The ceramic yield is calculated from the quotient of the weight of the ceramic obtained and the weight of the starting material.

In the process according to the invention for the production of SiC or SiC ceramic, pyrolysis products of the composition SiC-xSi0 ₂ with 0 <x <0.25 are preferably obtained.

In the examples described below, all the viscosity data relate to a temperature of 25 ° C. Unless otherwise stated, the examples below are carried out at a pressure of the surrounding atmosphere, that is at about 1000 hPa, and at room temperature, that is at about 23 ° C., or at a temperature which occurs when the reactants are combined at room temperature without additional heating or cooling. Furthermore, unless otherwise stated, all parts and percentages are by weight.

The following abbreviations are used:

Me: methyl residue Vi: vinyl residue Ph: phenyl residue

The molecular weight was determined by means of HPLC against polystyrene as a standard, M _n and M _w were determined from partial fractions, where: M _n = ∑ (ni * Mi) / ∑ni and ni = wi / Mi =>

M _w = Σ (Wi * Mi) / ∑W => M _w = Σ (i * Mi) / G

with Mi = average molecular weight of the fraction ni = particle number of this fraction Wi = weight of this fraction G = total weight

example 1

A)

1000 ml of a mixture of 60 mol% 1, 1,2-trimethyltrimethoxydisilane and 40 mol% 1,2-dimethyltetramethoxydisilane are heated to a temperature of 40 ° C. 4 ml of 30% methanolic sodium methylate solution are then added, the temperature rising to 90 to 100 ° C. without external heat supply. Then the mixture is heated to 120 ° C and held for about an hour, the majority of the resulting monosilanes being distilled off. The residue obtained is taken up with xylene as a tug and freed from residual monosilanes and undesired oligomers by distillation at a bottom temperature of 160 ° C. 230 g of organopolysilane are obtained, which is taken up in toluene to form a 50% solution and stirred with 20 g of acid-activated calcium bentonite (commercially available under the name "Tonsil" from Süd-Chemie) for 15 minutes. After adding 2 g of diatomaceous earth (commercially available under the name "Dicalite" from Dicalite Europe Nord SA), the mixture is filtered through asbestos-free filter layers (commercially available under the name "Supra 2600" from Seitz). 370 g of organopolysilane solution are obtained, which corresponds to a yield of about 19%. The organopolysilane obtained in this way has a molar ratio of methyl groups to methoxy groups of 12, a numerical average M _n of 1580, a weight average M _w of 4200 and a softening range at 120 ° C. The organopolysilane thus obtained is clearly soluble in toluene and has a viscosity of 7.5 mm ² / s in 50% solution.

500 g of a 50% solution of the organopolysilane prepared above under A) in toluene are combined with 25 g of vinyl group-containing organopolysiloxane of the formula

[ViMe ₂ SiO _1/2] ₀ ₂ 3 [ViMeSiO _{2 2]} _0, ₂ 7 [Visi0 _{_3/2]} _0/50 and a viscosity of 80 mm ² / s

and 10 g of boric acid were added, heated to 110 ° C. under a nitrogen atmosphere and kept at this temperature under reflux for 8 hours. The solution is then also passed under nitrogen over asbestos-free filter layers (commercially available under the name "Supra 2600" from Fa. Seitz) filtered and evaporated to dryness in a rotary evaporator at 100 ° C. and 1 hPa. 263 g of an organopolysilane / vinylsiloxane copolymer are obtained with a softening range at 135 ° C., the numerical average M _n of 1860 and a weight average M _w of 5980. The organopolysilane / vinylsiloxane copoly ere obtained is clearly soluble in toluene and has a viscosity of 7.5 mm ² / s in 50% solution.

10 to 20 g of the organopolysilane / alkenylsiloxane copolymer obtained in this way are placed on an aluminum sinter boat, heated to 300 ° C. within one hour under argon and left at this temperature for a further hour. The crosslinking occurs here For pyrolysis, the crosslinked product is brought up to 1200 ° C. under argon at a heating rate of 140 ° C./hour and left at this temperature for one hour, after which the sample is weighed out.

The ceramic yield is 54%.

Comparative Example 1

The organopolysilane prepared in Example 1 under A) is placed on an aluminum sinter boat, heated to 300 ° C. in the course of one hour under argon and left at this temperature for a further hour. Here, networking occurs to form insoluble and infusible products. For pyrolysis, the crosslinked product is brought to 1200 ° C. under argon at a heating rate of 140 ° C./hour and left at this temperature for one hour. After cooling, the sample is weighed back.

The ceramic yield is 21%. Comparative Example 2

B)

The procedure described in Example 1 under A) is repeated with the modification that 40 parts of 1,1,2-trimethyltrimethoxydisilane are used instead of 60 parts and 60 parts of 1,2-dimethyltetramethoxydisilane are used instead of 40 parts. The organopolysilane thus obtained has a molar ratio of methyl groups to methoxy groups of 11.3, a numerical average M _n of 2010, a weight average M _w of 6680 and a softening range at 185 ° C. The organopolysilane thus obtained is clearly soluble in toluene and has a viscosity of 12.0 mm ² / s in 50% solution.

The crosslinking and pyrolysis of the organopolysilane thus obtained is carried out as described in Comparative Example 1.

The ceramic yield is 28%.

Comparative Example 3

C)

The procedure described in Example 1 under A) is repeated with the modification that instead of 60 parts 90 parts 1, 1,2-trimethyltrimethoxydisilane and instead of 40 parts 10 parts 1,2-dimethyltetramethoxydisilane are used. The organopolysilane thus obtained, which is obtained as a pasty mass, has a molar ratio of methyl groups to methoxy groups of 10.2, a numerical average M _n of 1300 and a weight average M _w of 2890. Organopolysilane is clearly soluble in toluene and shows a viscosity of 4.0 mm ² / s in 50% solution.

The ceramic yield is 10%.

Comparative Example 4

D)

The procedure described in Example 1 under A) is repeated with the modification that instead of 60 parts 10 parts 1, 1,2-trimethyltrimethoxydisilane and instead of 40 parts 90 parts 1,2-dimethyltetramethoxydisilane are used. The organopolysilane obtained in this way is obtained as an insoluble, infusible mass.

The ceramic yield is 49%.

Comparative Example 5

250 g of a 50% solution of the organopolysilane prepared in Example 1 under A) in toluene are heated to 110 ° C. with 5 g of malononitrile under a nitrogen atmosphere and kept at this temperature under reflux for 3 hours. After cooling to room temperature, this mixture is now available with 10 g of acid-activated calcium bentonite (commercially available added under the name "Tonsil" at Süd-Chemie), filtered through asbestos-free filter layers (commercially available under the name "Supra 2600" from Seitz) and evaporated to dryness in a rotary evaporator at 100 ° C. and 1 hPa.

The ceramic yield is 26%.

Comparative Example 6

250 g of a 50% solution of the organopolysilane in toluene prepared in Example 1 under A) are heated to 110 ° C. with 2.5 g of benzoyl peroxide under a nitrogen atmosphere and the procedure described in Comparative Example 5 is followed.

The ceramic yield is 45%.

Comparative Example 7

250 g of a 50% solution of the organopolysilane in toluene prepared in Example 1 under A) are heated to 110 ° C. with 5 g of boric acid under a nitrogen atmosphere and the procedure described in Comparative Example 5 is followed.

The ceramic yield is 44%. Example 2

E)

The procedure described in Example 1 under A) is repeated with the modification that 30 parts of 1,1,2-trimethyltrimethoxydisilane are used instead of 60 parts and 70 parts of 1,2-dimethyltetramethoxydisilane instead of 40 parts. The organopolysilane thus obtained has a molar ratio of methyl groups to methoxy groups of 12.2, a numerical average M _n of 2100, a weight average M _w of 7300 and a softening range at 280 ° C. The organopolysilane obtained in this way is soluble in toluene with a slight turbidity and shows a viscosity of 15 mm ² / s in 50% solution.

The procedure described in Example 1 is repeated with the modification that instead of the organopolysilane produced in Example 1 under A), the same amount of the organopolysilane prepared under E) is used. 250 g of an organopolysilane / vinylsiloxane copolymer with a softening point above 200 ° C., the numerical mean M _n of 2360 and a weight mean M _w of 15520 are obtained. The organopolysilane / vinylsiloxane copolymer obtained is clearly soluble in toluene and shows a viscosity of 180 mm ² / s in 50% solution.

The ceramic yield after curing and pyrolysis is 68%. Example 3

F)

The phenyl-methyl-polysilane, the production of which, for example, in Z. anorg. general chemistry 618 (1992) 148-52, has a molar ratio of methyl groups to methoxy groups to phenyl groups of 100: 0.5: 3.5, a numerical mean M _n of 900, a weight average M _w of 1350 and a softening range at 140 ° C.

250 g of the phenyl-methyl-polysilane thus obtained and 250 g of the organopolysilane prepared in Example 2 under E) are dissolved in 500 g of toluene and with 50 g of vinyl-containing organopolysiloxane of the formula

[ViMe ₂ SiO _1/2] _0, 23 [ViMeSiθ _2/2] _{0 f 27} [ViSiθ _3/2] ₀ ^{.50, and} a viscosity of 80 mm / s

and 10 g of boric acid, heated under nitrogen to 110 ° C and ^'8 hours under reflux at this temperature Tempe¬ maintained. The solution is then also filtered under nitrogen over asbestos-free filter layers (commercially available under the name "Supra 2600" from Seitz) and evaporated to dryness in a rotary evaporator at 100 ° C. and 1 hPa. 530 g of an organopo Lysilane / vinylsiloxane copolymers obtained with a softening range at 125 ° C., the numerical mean M _n of 1500 and a weight mean M _w of 6610. The organopolysilane / vinylsiloxane copolymer obtained is clearly soluble in toluene and, in 50% strength solution, has a viscosity of 14.1 mm ² / s (speed of rotation 185 cpm). According to ¹ H and ²⁹ Si NMR measurements and chemical analysis, the organopolysilane / vinylsiloxane copolymer consists of the structural elements R-Si≡: R -Si =: R ₃ -Si- in a ratio of 55.1: 41.0 : 3.9 [mol%], where R can mean Me, OMe, Ph or Vi, which are in a molar ratio of 92.0: 5.8: 1.5: 0.7. The structural elements are mostly connected directly via Si-Si bonds, only about a quarter of the Si-O-Si bonds are present, some of which come from the vinylsiloxane used, but mainly from O insertion into the organopolysilane chain ¬ men.

10 to 20 g of the organopolysilane / alkenylsiloxane copolymer obtained in this way are placed on an aluminum sinter boat, heated to 300 ° C. under argon within one hour and left at this temperature for a further hour. The crosslinking to insoluble and non-meltable products occurs here. For pyrolysis, the crosslinked product is brought to 1200 ° C. under argon at a heating rate of 140 ° C./hour and left at this temperature for one hour. After cooling, the sample is weighed back.

The ceramic yield is 53%.

Example 4

100 g of a 50% solution of the organopolysilane / vinylsiloxane copolymer, the preparation of which is described in Example 3, in toluene are mixed with 50 g of silicon carbide (Acheson-SiC, available under the name "NF O-860" from Elek - troεchmelzwerk Kempten GmbH, Munich), which is ground to an average particle size of approx. 1 μm, and mixed with 0.5 g triolein and 1 g ammonium stearate by grinding in a ball mill for 4 hours. The slip is drawn off at 100 ° C. and 1 hPa and dried in vacuo at 120 ° C. 50 g of the dry mass are then introduced into a 100-100 mm press mold and heated under vacuum to 300 ° C. in the course of 30 minutes a holding time of 90 minutes A pressure of 10 ⁵ hPa is built up within 30 minutes and maintained for a period of 30 minutes. After the pressure has been released, the sample is cooled to room temperature within 90 minutes.

The compact is brought to pyrolysis under nitrogen at a heating rate of 140 ° C./h to 1200 ° C. and, after a holding time of one hour, is cooled to room temperature within 9 hours. The weight of the sample thus obtained is 39.8 g, which corresponds to a ceramic yield of 59.2%, based on the copolymer. The density (helium method) is 3.02 g / cm ³ , the BET specific surface area is 167 m ² / g. Pyrolysis caused a linear shrinkage of 15%. The porosity is 36%.

The chemical analysis gives the following values in%:

Si 63.8 - C 29.9 - H 0.17 - O 6.35 - N 0.06, which has an atomic ratio of Si: C: H: O: N of 1.00:

1.10: 0.17: 0.17: 0.

Example 5

100 g of a 50% solution of the organopolysilane / vinylsiloxane copolymer, the preparation of which is described in Example 3, in toluene are mixed with 50 g of silicon carbide (Acheson-SiC, available under the name "NF O-860" from Elek - troschmelzwerk Kempten GmbH, Munich), which is ground to an average grain size of approx. 1 μm, and mixed with 0.5 g triolein and 1 g ammonium stearate by grinding in a ball mill for 4 hours. With the slip obtained in this way, silicon carbide fibers (obtainable under the name "Nicalon fibers NL 200" from Nippon Carbon) are coated into so-called prepregs (110-110 mm) by the wet winding process which is well known in the art. On inert gas Protection can be dispensed with here, since filling with silicon carbide largely prevents the photooxidation of the copolymer. After drying at 50 ° C and 1 hPa, six prepregs are placed on top of each other bidirectionally (90 °) and cut to a size of 100-100 mm. Subsequently, for crosslinking, the mixture is heated under vacuum to a temperature of 250 ° C. within 15 minutes. After a holding time of 30 minutes, a pressing pressure of 10 ⁵ hPa is built up within 15 minutes. The sample is left under these conditions for two hours. The sample is then cooled to room temperature over a period of 3 hours under a pressure of 10 ⁵ hPa The weight of the sample is 97.1 g, of which the fiber content is 18.4 g and the SiC content is 25.1 g.

The sample is brought to pyrolysis under nitrogen at a heating rate of 140 ° C./h to 1200 ° C. and, after a holding time of one hour, is cooled to room temperature within 9 hours. The weight of the sample thus obtained is 74.1 g, which corresponds to a ceramic yield of 57%, based on the copolymer. The composite body thus obtained shows a density (helium method) of 2.69 g / cm ³ and a porosity of 20.8%. The flexural strength of the composite bodies obtained using the four-point method is 43.72 N / mm ² .

Claims

Organopolysilane / alkenylsiloxane copolymers, producible by reacting organopolysilanes with organopolysiloxanes containing alkenyl groups from units of the formula

[R _a R ¹ ₃ _ _a Si0 _{1 2} ], [RbR ¹ 2-b ^si0 2/2] ^and [R ^ iO ^], where

R can be the same or different and means monovalent, optionally substituted hydrocarbon radicals which are free from aliphatic carbon-carbon multiple bond, R ^{1 can be the} same or different and monovalent, optionally substituted hydrocarbon radicals with at least one aliphatic carbon-carbon -Multiple bond means a is 0, 1 or 2 and b is 0 or 1,

in the presence of boric acid.

Process for the preparation of organopolysilane / alkenylsiloxane copolymers, characterized in that organopolysilane with organopolysiloxane containing alkenyl groups consists of units of the formula [R _a Rl ₃ _ _a Si0 _{1 2} ], [RbR ¹ 2-bSi0 _{2 2} ] and [R ¹ Si0 _{3 2} ], where

R can be identical or different and means monovalent, optionally substituted hydrocarbon radicals which are free from aliphatic carbon-carbon multiple bond, R ^{1 can be} identical or different and monovalent, optionally substituted hydrocarbon radicals with at least one aliphatic carbon Carbon multiple bond means a is 0, 1 or 2 and b is 0 or 1,

is reacted in the presence of boric acid.

3. The method according to claim 2, characterized in that as organopolysiloxanes containing alkenyl groups those of the formula

{[R _a Rl ₃ _ _a Si0 _1/2 ] _v [R _b Rl ₂ _ _b Si0 _2/2 ] _y tR ¹ Siθ _3/2 ] _z } _c (I),

are used, whereby

R, R ¹ , a and b have the meaning given in claim 1 and v is 0.01 to 0.5, y is 0.01 to 0.7 and z is 0.01 to 0.95, with the proviso that that the sum of v, y and z in formula (I) is 1, and c is a number from 3 to 50.

4. The method according to claim 2 or 3, characterized gekennzeich¬ net that those of the formula as organopolysilanes

R ² R ² R ²

Ttt [(Si) _p (Si) _q (Si) _r] _m R ² (II) - R ²

R ² OR ³ R ⁴

are used in which

R ^{2 may be the} same or different and means hydrogen atom, monovalent, SiC-bonded, optionally substituted hydrocarbon radicals or alkoxy radical, R ^{3 can be the} same or different and means alkyl radical, R ^{4 can be the} same or different and hydrogen atom, monovalent, SiC-bonded, optionally substituted hydrocarbon radicals, alkoxy radical or

Silyl radical means, p can be the same or different and a number between 0.1 and 0.9, q can be the same or different and a number between 0.01 and 0.5, r can be the same or different and a number is between 0 and 0.5, with the proviso that p + q + r is 1 and m is a number from 3 to 100.

5. A process for the preparation of high molecular weight organosilicon compounds, characterized in that organopolysilane / alkenylsiloxane copolyers according to claim 1 are crosslinked, if appropriate in a mixture with other substances, at a temperature between 200 and 400 ° C.

6. The method according to claim 5, characterized in that silicon carbide is used as a further substance.

7. A process for the production of SiC or SiC ceramics, characterized in that organopolysilane / alkenylsiloxane copolymers according to claim 1 and / or their crosslinking products according to claim 5 optionally in a mixture with other substances under an inert atmosphere at temperatures of at least 800 ° C.