Title of Invention

"A PROCESS FOR THE PREPARATION OF POLYCARBOSILANES FOR USE AS PRECURSOR OF CERAMIC MATERIALS"

Abstract This invention relates to a process for the preparation of polycarbosilanes for use as precursor of ceramic materials comprising of preparing polysilane by taking 0.08-1.0 mol of dichloro silane in equal volume of binary solvent system, taking 0.05 to 0.2 wt% of phase transfer catalyst and the binary solvent 6 to 8 times v/v of dichloro diorgano silane, adding 35 to 40 wt% of sodium, refluxing at 100-120°C, adding dropwise dichloro diorgano silane over a period of 3 to 5 hours, refluxing further for 6-10 hrs removing the solvent by distillation, cooling the reaction mixture to a 25-30°C, quenching with alcohols in an amount of 10-20% to that of sodium (w/w) taken in the reaction, stirring, precipitating polysilane by adding water 20-30% v/v of solvent, washing the precipitate with water 8-10 times till the aqueous layer becomes neutral, shaking the precipitate with methanol taken as 1.5 to 2 times v/v of dicholoro diorgano silane to remove trapped water in polysilane, drying at 200-250°C for 12-30 hrs. preferably 20-24 hrs under a flow of inert gas preferably nitrogen and polysilane to disperse the said catalyst throughout the polysilane preferably under inert atmosphere, preparing polycarbosilane by heating the said reaction mixture of polysilane and catalyst at 250-425 °c preferably 300-415 °c for 40-72 hrs, preferably 45-50 hrs. under inert gas atmosphere, isolating liquid polycarbosilane from solid polycarbosilane by heating the viscous material containing polycarbosilane to 370-500 °c and increasing the flow rate of the inert gas to 25-35 ml/mm to vaporize the liquid polycarbosilane, collecting the vapours of polycarbosilane, cooled in a freezing mixture bath, further cooling to collect liquid polycarbosilanes, adding hexane or petroleum, ether to dissolve the polycarbosilane, filtering under inert atmosphere, collecting the organic layer in a flask and removing the solvent leaving behind solid polycarbosilane.
Full Text F1ELD OF INVENTION
The invention relates to a process for the preparation of polycarbosilanes as precursor of ceramic materials for making p-silicon carbide fibers and resin matrix of silicon carbides.
PRIOR ART
Thermal backbone rearrangement of polysilanes is a versatile process for the synthesis of the polycarbosilanes for use as precursor of ceramic materials.
One of the known process as reported in US Patent Nos. 4,052,430: 5,171,722 and 5,278.110 is to earn,' out thermal back bone rearrangement of polysilanes, bearing methyl, methyl phenyl or a combination of other organic pendant groups by carrying out the reaction under high temperature and pressure in a pressure reactor (80-130 psi, 400- 480 °C).
The main disadvantage of the above knovm thermal back bone rearrangement of polysilanes is that it requires a high pressure and temperature reactor and for commercial production of the material it is very difficult to make very big high pressure and temperature reactors
Another disadvantage of the above known process is that to earn,- out such reactions very skilled work man ship is required along with strict security precautions lo handle pressure reactor.
Yet another disadvantage of the above known process is thai the polvcarbosHanes obtained are polymodal in nature comprising of a large amount of low molecular weight liquid and viscous products which are not useful for making fibers or shaped article of ceramics thus reducing the yield of useful material.
Another method known in the art for the thermal backbone rearrangement as reported in patent nos. US:5.830:972; US:4.377,677: US:4,310.482; US 4.472.591. JP
7179478A2; JP7247359A2. EP 375994 Bl; US: 4.220.600; US. 4.889.904 is by heating the polysilanes under inert atmosphere at ambient pressure for quite a long time at a very high temperature continuously.
The main disadvantage of the above known processes is that the temperature and time range is too wide which makes the'handling of the reaction difficult.
Another disadvantage of the above known processes is that the reaction requires an added step and facility to re-circulate the low boiling products into reaction vessel to increase the yield of the product.
Yet another disadvantage of the above known processes is that they yield a poly-dispersed product which has to be further fractionated or polymerized after isolation, in presence of a catalyst.
In another known prior art patent nos. US: 5.665,998; JP7196807 A2; US: 5,204,434 the polycarbosilanes were synthesized by the ring opening polymerization of disilacyclobutene derivatives in presence of chloroplatinic acid as catalyst.
The main disadvantage of the above known processes is that the raw materials are not readily available in the market and are very costly so the process is not of commercial utility.
Another disadvantage of the above known processes is that the product obtained is strictly linear and thus requires fictionali/ation of the pendant groups for creating certain degree of cross linking so that the elastomers shape could be given.
Another method of making poiycarbosilane as reported in the patent nos. US 5.357,019: US: 5.171. 992. JP 6032907 A2. JP7233259 A2 is by the reaction of dichlorodiorganosilanes having at least one vmylic organic group and sodium metal in organic solvents.
The mam disadvantage of the above known processes is that the raw materials are not available commerciallv.
Another disadvantage of the above known processes is that the vinylsilanes used are highly toxic
Yet another disadvantage of the above known processes is that the yields are very low.
In view of above there is a need to develop a process, which could be facilitated by readily available materials in the market with simple reaction assemblies and preferably one pot reactions. Moreover, the process should give satisfactory high yields of the product
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a process for the preparation of polycarbosilanes for use as precursor of ceramic materials.
Another object of the present invention is to provide a process for the preparation of polycarbosilanes which yields the polycarbosilanes by thermal backbone rearrangement of polysilanes bearing at least one methyl group along with same or other organic groups on silicon back bone of the polymer at atmosphenc pressure conditions
Yet another object of the present invention is to provide a process for making polycarbosilane which is in the form of liquid, semisolid or solid polycarbosilane.
Still another object of the present invention is to provide a process for making polycarbosilane which provides solid, uncross linked polycarbosilanes at comparatively lower temperature range and in less time.
Further object of the present invention is to provide a process for the preparation of polycarbosilane which requires only one pot and one step synthesis to get desired molecular weight polycarbosilanes.Yet further object of the present invention is to provide a process for the preparation of polycarbosilane in which lower molecular weight liquid polycarbosilanes are simultaneously separated with the help of inert gas flow.
Still further object of the present invention is to provide a process for the preparation of polycarbosilane which do not require any sophisticated reaction assembly.
DESCRIPTION OF THE INVENTION
According to this invention there is provided a process for the preparation of polycarbosilanes for use as precursor of ceramic materials comprising of the steps of:
a) preparing polysilane by taking 0.08-1.0 mol of dichloro silane (R=Me, Ph or R = Me or Ph) in equal volume of binary solvent system, followed by taking 0.05 to 0.2 wt% of phase transfer catalyst as herein described and the binary solvent as herein described 6 to 8 times v/v of dichloro diorgano silane, adding 35 to 40 wt% of sodium into the flask followed by refluxing the binary solvent at a temperature of 100-120°C and then adding dropwise dichloro diorgano silane over a period of 3 to 5 hours to be refluxing solution, refluxing further for 6-10 hrs removing the solvent by distillation, cooling the reaction mixture to a temperature 25-30°C, quenching the reaction mixture with alcohols in an amount of 10-20% to that of sodium (w/w) taken in the reaction, stirring the reaction mixture, precipitating polysilane by adding water in a quantity 20-30% v/v of solvent, washing the precipitate of polysilane thoroughly with water 8-10 times till the aqueous layer becomes neutral, shaking the precipitate with alcohols preferably methanol taken as 1.5 to 2 times v/v of dicholoro diorgano silane to remove trapped water in polysilane, filtering the precipitated polysilane to remove alcohols and water if any and then drying the precipitate at 200-250°C for 12-30 hrs. preferably 20-24 hrs under a flow of inert gas preferably nitrogen,

b) preparing polyborodipheynlsiloxane catalyst by taking boric acid and diphenyldichlorosilane in a ratio of 1 to 1.2:5 to 5.5 and dissolving in 2 to 3 times of its volume in a solvent preferably n-butyl ether, heating the reactants at 100-120°C for 5-8 hrs to yield a resinous white mass, heating the resinous white mass further at 400-410°c under vacuum then cooling the residue to yield solid polyborodipheylsiloxane catalyst,
c) mixing 1-3% w/w polyborodiphenylsiloxane catalyst prepared in step b) and polysilane prepared in step a) thoroughly to disperse the said catalyst through out the polysilane preferably under inert atmosphere,
d) preparing polycarbosilane by heating the said reaction mixture of polysilane and catalyst as prepared in step c) to a temperature of 250-425 °c preferably 300-415 °c for a period of 40-72 hrs. Preferably 45-50 hrs. under inert gas atmosphere preferably N2 or Ar;
e) isolating liquid polycarbosilane from solid polycarbosilane by heating the viscous material containing polycarbosilane from step d) to a temperature of 370-500 °c and increasing the flow rate of the inert gas to 25-35 ml/mm to vaporize the liquid polycarbosilane, collecting the vapours of polycarbosilane along with the inert gas in a receiver cooled in a freezing mixture bath, further cooling the vapour mixture in a receiver to collect liquid polycarbosilanes, then maintaining the temperature of the reaction bath at 410-430 °c for about 30 minutes, cooling slowly to 23-25 °c, adding hexane or petroleum ether to dissolve the polycarbosilane, filtering the organic solution containing polycarbosilane under inert atmosphere, collecting the organic layer in a flask and removing the solvent viz. petroleum ether/hexane by vacuum distillation leaving behind solid polycarbosilane in the flask.
In accordance with the present invention, the process of the preparation of polycarbosilane comprises of following steps :
a) Preparing Polysilane
A three necked flask fitted with an efficient mechanical stirrer, dropping funnel condensor and inert gas inlet tube to purge inert gas is taken. In the dropping funnel 0.08-1.0 mol of dichloro diorgano silane (R=Me, Ph or R=Me or Ph) is taken in equal volume to that of a binary solvent system, comprising of high boiling aromatic hydrocarbon solvent (b.p.>100°C) preferably toluene and a polar solvent like tetrahydrofuran, dimethyldigloxime or 1,4-dioxane preferably 1,4-dioxane in a ratio of 80:20 to 95:5 preferably in a ratio of 90:10. In the flask binary solvent is taken as 6 to 8 times v/v of dichloro diorgano silane, in which 0.05 to 0.2 wt% of a phase transfer catalyst like polyethylene glycols, crown ethers or cryptates preferably 15-crown-5 is added. Next 35 to 40wt% preferably 36 wt% of sodium is added into the flask. The flask is heated to the refluxing temperature of the binary solvent from 100-120°C. To the refluxing solution dichloro diorgano silane is added dropwise from the dropping funnel over a period of 3 to 5 hours. It is further refluxed for 6-10 hrs
preferably 8 hrs. The solvent is then removed by distillation. Afterwards the reaction mixture is cooled to a temperature of 25 - 30 CC and then the reaction mixture is quenched with alcohols like methanol, ethanol, n-propanol isopropanol or n-butanol preferably iso propanol in an amount 10-20% to that of sodium (vv/\\') taken in the reaction and the reaction mixture is stirred for about one hour. Afterwards, water (20 - 30% v/v of solvent) is added to precipitate the polysilane. The precipitate of polysilane is thoroughly washed with water 8-10 times till the aqueous layer becomes neutral. The precipitate is now shaken for 10 - 15 minutes with alcohol preferably methanol taken as 1.5 to 2 times v/v of dichloro diorgano silane to remove trapped water in polysilane. The precipitated polysilane is then filtered through a Buckner funnel to remove alcohol and water if any. The precipitate is finally dried at 200 - 250°C for 12-30 hrs. preferably 20-24 hrs. under a flow of inert gas preferably nitrogen which yielded polysilane ~ 85% yield.
b) Preparing polyborodiphenvlsiloxane catalyst
A mixture of boric acid and diphenyldichlorosilane is taken in a ratio of 1 to 1.2 : 5 to 5.5 preferably 1:5.3 and dissolved in 2 to 3 times preferably 2 times of its volume in a solvent preferably n-butyl ether. The reactants are heated at 100-120°C for 5-8 hrs to yield a resinous white mass. This resinous white mass is further heated at 400 - 410 °C under vacuum (0.1 - 0.2 mm/Hg) for about Ih. The residue on cooling yielded a solid polyborodiphenvlsiloxane catalyst (yield -92% vv/w).
c) Mixing of polyborodiphenvlsiloxane catalyst and Polysilane
1-3% vv/w of the polyborodiphenylsiloxane catalyst prepared in step b) is mixed with polysilane prepared in step a), mechanically in such a way so that it is dispersed thoroughly through out the polysilane. The mixing is done preferably under inert atmosphere.
d) Preparing polycarbosilane -
The reaction mixture of polysilane and polyborodiphenylsiloxane catalyst as prepared in step c) is heated in a three-necked quart/, flask fitted with a vigreux column and receiver, an inert gas inlet tube, a pyroprobe with a digital temperature indicator The assembly is fitted in an electrically heating mantel. The reaction mixture is healed to 250-425"C preferably 300-415°C for a period of 40-72 hrs.
preferably 45-50 hrs. under inert gas atmosphere preferably NN or Ar to yield viscous material containing polycarbosilane.
e) Isolating liquid polvcarbosilane from solid polvcarbosilane
The viscous material containing polycarbosilane from step d) is heated to a temperature of 370-500 °C and the flow rate of the inert gas is increased to 25 - 35 ml/min so that the liquid polycarbosilane vapors come out along with the inert gas and collected in a receiver cooled in a freezing mixture bath. The vapour mixture is cooled in a receiver to collect liquid polycarbosilanes (yield 20 - 25% w/w of polysilane) No average Mol Wt.300-500.
Once the liquid polycarbosilane is removed from the reaction bath, the temperature of the melted residue is raised to 410 - 43()°C. This temperature is maintained for about 30 minutes and then cooled slowly to 23 - 25°C. Now to the reaction flask about 10 times w/v of hexane or petroleum ether is added to dissolve the polycarbosilane. The organic solution is filtered in a closed sintered funnel (preferably G-4) under inert atmosphere. The organic layer is collected in a flask and fitted with a vacuum distillation assembly to remove the solvent viz. petroleum ether/hexane. The solid polycarbosilane remains in flask, yield 40 - 45% (vv/w of polysilane)
This invention will now be illustrated with a working example, which is intended to be typical example to explain the technique of the present invention and is not intended lo be taken restnctively to imply any limitation to the scope of the present invention.
WORKING EXAMPLE
To a three necked flask (10 liter) fitted with a efficient mechanical stirrer. dropping funnel (2.0 liter) and condenser and inert gas inlet tube to purge inert gas was taken sodium (920 gm; -40 M) in toluene (5.0 liter) and dioxane (0.50 liter) in presence of 15-cro\vn-5 (0.5 gm) as phase transfer catalyst. The flask was kept on a electrical healing mantel • and the solvent was heated to reflux. On refluxing the solvent the sodium melts which dispersed into small globules due to stirring. To this

refluxing solution dichlorodimelhylsilane (2.42 liter, 20 M) in toluene (579.0 ml) was added slowly within four hours After complete addition of dichlorodimethylsilane the solution was further refluxed for 5 hours.
After completion of the reaction, the solvent was removed by distillation (3.5 liter) and the reaction mixture was- cooled to room temperature To the reaction mixture n-butanol (92 ml, -10% w/vv of sodium) was added slowly and the reaction mixture was stirred for one more hour. Afterwards water (25% v/v of solvent) was added in the flask to precipitate the PDMS. The precipitate was wasted 10 times with water i.e. till the aqueous layer become neutral. The PDMS was then washed with methanol (1.5 liter) and filtered through a Buckner funnel. The solid white PDMS was then dried at 250°C for 24 hours to remove trapped solvent and water if any, yield ~950g, 95%.
The catalyst i.e. polyborodiphenylsiloxane was synthesized by heating 253 gm diphenyldichlorosilane and 41.5 g of boric acid in n-dibutyl ether (400 ml) at a temperature of 100 - 120°C for 5 hrs which yielded a white resinous material. The resinous material was heated at a temperature of 400 - 410°C in vacuum 0.1 mm/Hg for 1 hr to yield 175 gm of polyborosiloxane.
The polydimethylsilane (100 g.) was grinded mechanically with catalyst (30 g) in the form of powder. The powdered mixture is then mixed with the rest of the polydimethyl silane (-900 g) and further grinded to obtain a fine powder. This mixture of polydimethylsilane (lO(K)g) and catalyst (30 g) was taken in a three necked flask fitted with a vigreux column, inert gas inlet tube and a pyroprobe to read the temperature At the top of vigreux column a distilling head equipped with a receiver and flask was fitted. The three-necked flask was placed in a heating mantel and the temperature was raised at the rate of 1"C per minute and kept for 52 hrs. at 300-415"C. During such lime the PDMS melts completely and converts into polycarbosilanes. The melt contains both liquid and solid polycarbosilanes. The liquid polycarbosilane was distilled out under a current of argon gas at 450"C (bath temperature) yield 200 g. After removal of liquid polycarbosilane a solid residue
remained in the flask. The residue was dissolved in n-hexane and filtered. The organic solvent on distillation yielded solid polycarbosilane (-400 g) Mn 1800, m.p. ~"80°C.
It is to be understood that the process of the present invention is susceptible to modifications, changes, adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention which is further set forth under the following claims.








WE CLAIM;
1. A process for the preparation of polycarbosilanes for use as precursor of ceramic materials comprising of the steps of:
a) preparing polysilane by taking 0.08-1.0 mol of dichloro silane (R=Me, Ph or R = Me or Ph) in equal volume of binary solvent system, followed by taking 0.05 to 0.2 wt% of phase transfer catalyst as herein described and the binary solvent as herein described 6 to 8 times v/v of dichloro diorgano silane, adding 35 to 40 wt% of sodium into the flask followed by refluxing the binary solvent at a temperature of 100-120°C and then adding dropwise dichloro diorgano silane over a period of 3 to 5 hours to be refluxing solution, refluxing further for 6-10 hrs removing the solvent by distillation, cooling the reaction mixture to a temperature 25-30°C, quenching the reaction mixture with alcohols in an amount of 10-20% to that of sodium (w/w) taken in the reaction, stirring the reaction mixture, precipitating polysilane by adding water in a quantity 20-30% v/v of solvent, washing the precipitate of polysilane thoroughly with water 8-10 times till the aqueous layer becomes neutral, shaking the precipitate with alcohols preferably methanol taken as 1.5 to 2 times v/v of dicholoro diorgano silane to remove trapped water in polysilane, filtering the precipitated polysilane to remove alcohols and water if any and then drying the precipitate at 200-250°C for 12-30 hrs. preferably 20-24 hrs under a flow of inert gas preferably nitrogen,

b) preparing polyborodipheynlsiloxane catalyst by known method taking boric acid and diphenyldichlorosilane in a ratio of 1 to 1.2:5 to 5.5 and dissolving in 2 to 3 times of its volume in a solvent preferably n-butyl ether, heating the reactants at 100-120°C for 5-8 hrs to yield a resinous white mass, heating the resinous white mass further at 400-410°c under vacuum then cooling the residue to yield solid polyborodipheylsiloxane catalyst,
c) mixing 1-3% w/w polyborodiphenylsiloxane catalyst prepared in step b) and polysilane prepared in step a) thoroughly to disperse the said catalyst through out the polysilane preferably under inert atmosphere,
d) preparing polycarbosilane by heating the said reaction mixture of polysilane and catalyst as prepared in step c) to a temperature of 250-425 °c preferably 300-415 °c for a period of 40-72 hrs. Preferably 45-50 hrs. under inert gas atmosphere preferably N2 or Ar;
e) isolating liquid polycarbosilane from solid polycarbosilane by heating the viscous material containing polycarbosilane from step d) to a temperature of 370-500 °c and increasing the flow rate of the inert gas to 25-35 ml/mm to vaporize the liquid polycarbosilane, collecting the vapours of polycarbosilane along with the inert gas in a receiver cooled in a freezing mixture bath, further cooling the vapour mixture in a receiver to collect liquid polycarbosilanes, then

Documents:

2254-DEL-2004-Abstract (11-1-2010).pdf

2254-DEL-2004-Abstract-(27-06-2011).pdf

2254-del-2004-abstract.pdf

2254-DEL-2004-Claims (11-1-2010).pdf

2254-DEL-2004-Claims-(27-06-2011).pdf

2254-del-2004-claims.pdf

2254-DEL-2004-Correspodence Others-(27-06-2011).pdf

2254-DEL-2004-Correspondence-Others (11-1-2010).pdf

2254-del-2004-correspondence-others.pdf

2254-del-2004-correspondence-po.pdf

2254-DEL-2004-Description (Complete) (11-1-2010).pdf

2254-del-2004-description (complete).pdf

2254-DEL-2004-Form-1-(27-06-2011).pdf

2254-del-2004-form-1.pdf

2254-del-2004-form-18.pdf

2254-DEL-2004-Form-2-(27-06-2011).pdf

2254-del-2004-form-2.pdf

2254-DEL-2004-GPA (11-1-2010).pdf

2254-DEL-2004-GPA-(27-06-2011).pdf


Patent Number 249015
Indian Patent Application Number 2254/DEL/2004
PG Journal Number 39/2011
Publication Date 30-Sep-2011
Grant Date 21-Sep-2011
Date of Filing 11-Nov-2004
Name of Patentee DIRECTOR GENERAL
Applicant Address DEFENCE RESEARCH AND DEVELOPMENT ORGANISATOIN MINISTRY OF DEFENCE, GOVT OF INDIA WEST BLOCK-VIII, WING-1 SECTOR-1 RK PURAM, NEW DELHI-110066
Inventors:
# Inventor's Name Inventor's Address
1 ARVIND KUMAR SAXENA DEFENCE MATIRIALS AND STORES RESEARCH AND DEVELOPMENT ESTABLISHMENT, G.T. ROAD, KANPUR-208013
2 ASHOK RANJAN DEFENCE MATIRIALS AND STORES RESEARCH AND DEVELOPMENT ESTABLISHMENT, G.T. ROAD, KANPUR-208013
3 RAJESH KUMAR TIWARI DEFENCE MATIRIALS AND STORES RESEARCH AND DEVELOPMENT ESTABLISHMENT, G.T. ROAD, KANPUR-208013
4 GYANESH NARAIN MATHUR DEFENCE MATIRIALS AND STORES RESEARCH AND DEVELOPMENT ESTABLISHMENT, G.T. ROAD, KANPUR-208013
PCT International Classification Number C04B 35/14
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA