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Preparation of Polysilazane Polymers and the Polymers Therefrom

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Preparation of Polysilazane Polymers and the Polymers Therefrom Europâisches Patentamt European Patent Office (ÏÏ) Publication number: 0 075 826 Office européen des brevets B1 ® EUROPEAN PATENT SPECIFICATION (§) Date of publication of patent spécification : 30.04.86 © mtci.4: C 08 G 77/62, C 04 B 35/56 (D Application number: 82108675.8 (g) Date offiling: 20.09.82 @ Préparation of polysilazane polymers and the polymers therefrom. (§) Priority: 21.09.81 US 304446 (73) Proprietor: DOW CORNING CORPORATION 3901 S. Saginaw Road Midland Michigan 48640 (US) (§) Date of publication of application: 06.04.83 Bulletin 83/14 ' (72) Inventor: Gaul, John Henry, Jr. 3212 Lawndale Drive (§) Publication of the grant of the patent: Midland Michigan (US) 30.04.86 Bulletin 86/18 (74) Représentative: Hann, Michael, Dr. (H) Designated Contracting States: Patentanwâlte Dr. Michael Hann Dr. H.-G. BEDEGB IML Sternagel Marburger Strasse 38 D-6300 Giessen (DE) (58) Références cited: DE-A-2 243 527 US-A-2 564 674 US-A-3 311571 CM 00 If) o o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the Notice of shail a. European patent granted. opposition be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been ui paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. disilanes in the preparation of silazane polymers has been limited to the formation of relatively low This invention relates to the preparation of molecular weight materials. In one example, polysilazane polymers. These polymers are useful Wannagat et aI., Ang. Chem. 75(7) 345(1963), as chemical intermediates to synthesize organo- reported the reaction of tetramethyldichlorodi- silicon compounds. They are also useful, when silane with gaseous ammonia to give a six- fired at high temperatures, to form silicon carbide membered cyclic silazane, and silicon carbide containing ceramic materials. What is disclosed herein is a novel process to obtain novel polysilazane polymers which consists of contacting and reacting chlorine- rather than the expected linear silazane polymer containing disilanes with ammonia in an inert, and Hengge et. al., Montach, Chem. essentially anhydrous atmosphere. 101192)325(1970), prepared dimethylamino sub- As is well known in the art, halosilane stituted mixtures of disilanes from dimethylamine monomers will react with ammonia and most and the chlorine-containing disilane mixture organic compounds containing a primary or obtained from the Direct Process for the prepara- secondary amino group to give a variety of tion of chlorosilanes. silazanes. For example, the reaction of trimethyl- What has been discovered now is the co- chlorosilane and ammonia produces hexamethyl- reaction between chlorine-containing disilanes disilazane, a silazane monomer, while dimethyldi- and ammonia to give high molecular weight chlorosilane and ammonia produce dimethyl- silazane polymers. cyclic silazanes. These two reactions probably The instant invention concerns a new class of constitute the majority of commercial uses of the silazane polymers prepared from chlorodisilanes. silazane chemistry. In essence, a single chlorine-containing disilane Silazanes in general have been academic or a specified mixture of chlorine-containing curiosities for many years and a variety of such disilanes is treated with ammonia, as the nitrogen siiazanes, including monomers, oligomers, source, in sufficient amounts to react with all of cyclics and even low molecular weight resins and the chlorine on the chlorine-containing disilanes. linear polymers have been prepared by a variety This is usually an excess amount of ammonia of methods. For example, L. W. Breed et al., in the based on the chlorine content of the disilane. Journal of Organic Chemistry, 27, 1114(1962) When the mixture is heated in an essentially report the formation of silazanes from the poly- anhydrous atmosphere at elevated temperature, merization of sterically hindered silazane oligo- the reactions take place. mers, while in the Journal of Polymer Science, A2 The advantage of this process is the ability to 45(1964), cyclic trimer and tetramer silazanes are stop the reaction at any point by cooling the reported to be thermally cracked using catalysts reaction mass resulting in polymers with any to give linear polymers. desirable viscosity, hence any desirable In contrast fluids, rubbery polymers and resins molecular weight. The silazane polymers range in prepared from CH3SiCI3, (CH3)2SiCI2 and excess physical appearance from liquids, to high ammonia have been reported by Kruger et al. in viscosity liquids, to hard glassy materials. The the Journal of Polymer Science, A 2 3179(1964) materials are therefore very easy to handle. They and Redl, Silazane Polymer, ARPA-19, Advanced are essentially hydrolytically stable. Research Projects Agency, October, 1965. Thus, this invention consists of a process for The patent literature also contains disclosures preparing polysilazane polymers characterized in of the preparation of silazanes. Cheronis, in U.S. that it consists of contacting and reacting in an Patent 2,564,674 discloses the preparation of low inert, essentially anhydrous, atmosphere at a molecular weight linear silazane polymers by the temperature in the range of 25°C to 370°C. reaction of halosilanes with excess ammonia in a (A) ammonia and solvent solution. Bausma, et al., in U.S. Patent (B) chlorine-containing disilanes selected from 3,809,713 discloses a similar reaction scheme the group consisting of with the added modification of removing the by-produced solid ammonium halide using (i) a chlorine-containing disilane having the ethylene diamine. More recently, Verbeek, et al., general formula in U.S. Patent 3,853,567 and U.S. Patent 3,892,583 disclosed that mixtures of CH3SiCI3 and and (CH3)3SiCI3 can be treated with ammonia or (ii) a mixture of chlorine-containing disilanes organoamines to form materials that can be having the general formula pyrolyzed to yield SiC/Si3N4 ceramics. As should be recognized by those skilled in the art, the present invention differs in at least one respect from all of the above art in that the wherein present invention is based on chlorine-containing a has a value of 1.5-2.0; disilanes as opposed to the use of chlorine- b has a value of 1.0-1.5; containing monosilanes. the ratio of c to d is in the range of 1:1 to In another segment of the prior art, the use of 2:1; the sum of a+b is equal to three; stable, easy to handle polysilazane polymers can the sum of c+d is equal to three; and be prepared. Further, the polysilazane polymers R in each case is selected from a group lead to an improvement in the art of formation of consisting of the vinyl group, an alkyl silicon carbide and they can be used as binders in radical of 1-3 carbon atoms and the phenyl ceramic materials. group. The invention results from reacting ammonia with chlorine-containing disilanes, mixtures of This disclosure also deals with a new and novel disilanes or mixture of disilanes with mono- composition of matter which is a polysilazane silanes in an inert, essentially anhydrous atmo- polymer prepared by the method of this sphere and then firing the resulting polysilazane invention. polymer to get silicon carbide or silicon carbide Furthermore, this disclosure also deals with a containing ceramic materials. method of silicon carbide containing preparing a The chlorine-containing disilanes of this ceramic material which consists of heating a invention those disilanes having the general obtained the of are polysilazane polymer by process formulae this invention, in an inert atmosphere or in a vacuum to at least a temperature of 750°C until is converted silicon the polysilazane polymer to and carbide ceramic material. Still another object of this invention is a method of silicon carbide ceramic preparing a containing In these formulae, R is vinyl, an alkyl radical article which consists of (A) article of forming an containing 1-3 carbon atoms or the phenyl the desired from shape a polysilazane polymer Thus, those which are contem- of this (B) group. groups obtained by the process invention; useful in this invention are the article formed in (A) in inert plated as being heating an methyl, ethyl, propyl, vinyl and phenyl. For atmosphere or in a vacuum to an elevated of this invention, the R groups can all be of at least 750°C until the poly- purposes temperature the same or they can be different. The chlorine- silazane is converted to silicon carbide polymer containing disilanes can be those found in the containing ceramic. residue from the Direct Process for producing Still another object of this invention is a method halosilanes (Eaborn, C., "Organosilicon Com- for filled ceramic article which preparing a pounds", Butterworth Scientific Publications, consists of (A) mixing a polysilazane polymer London, 1960, pg. 1). obtained by the process of this invention with at least one conventional ceramic filler, (B) forming It is contemplated in this invention that single an article of the desired shape from the mixture of chlorine-containing disilanes can be used in this polysilazane polymer and filler and (C) heating invention. Such silanes having the formula (i) the article formed in (B) in an inert atmosphere or above require that the values of a and b are from in a vacuum to an elevated temperature of at least 1.5-2.0 and 1.0-1.5 respectively and the sum of 750°C until the polysilazane polymer
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