Europa,schesP_ MM M II M MM M M MM Ml M I II J European Patent Office _ _ _ _ _ ^ © Publication number: 0 389 084 B1 Office_„. europeen des brevets © EUROPEAN PATENT SPECIFICATION © Date of publication of patent specification: 20.09.95 © Int. CI.6: C08G 77/56, C08G 77/60, //C04B35/58 © Application number: 90300690.6 @ Date of filing: 23.01.90 The file contains technical information submitted after the application was filed and not included in this specification © Process for producing a polyborosilazane. © Priority: 23.03.89 JP 69169/89 © Proprietor: Tonen Corporation 1-1 Hitotsubashi, 1-Chome @ Date of publication of application: Chiyoda-Ku 26.09.90 Bulletin 90/39 Tokyo 100 (JP) © Publication of the grant of the patent: @ Inventor: Funayama, Osamu 20.09.95 Bulletin 95/38 4-6, Nishitsurugaoka 1-chome, Oi-machi Iruma-gun, Saitama-ken (JP) © Designated Contracting States: Inventor: Arai, Mikiro DE FR GB NL 4-6, Nishitsurugaoka 1-chome, Oi-machi Iruma-gun, Saitama-ken (JP) © References cited: Inventor: Tashiro, Yuuji EP-A- 0 175 382 4-3, Nishitsurugaoka 1-chome, Oi-machi EP-A- 0 278 734 Iruma-gun, Saitama-ken (JP) US-A- 4 482 689 Inventor: Isoda, Takeshi US-A- 4 535 007 11-5, Tohoku 1-chome Niiza-shi, Saitama-ken (JP) Inventor: Sato, Kiyoshi 5-18, Nishihara 1-chome Kamifukuoaka-shi, Saitama-ken (JP) 00 © Representative: Allam, Peter Clerk et al LLOYD WISE, TREGEAR & CO. Norman House 00 105-109 Strand London WC2R 0AE (GB) 0) 00 oo 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 European patent granted. Notice of opposition CL shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee LU has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) EP 0 389 084 B1 Description This invention relates to a process for producing polyborosilazanes. Si-N-B series ceramics produced from a precursor polyborosilazane are useful as reinforcing materials for composite materials to be used at elevated temperatures because of the high heat resistance and high hardness thereof. They are expected to find wide applications in the space-aircraft and automobile industries. Borosiloxanes, organoborosilanes and boron-containing carbosilanes obtained by the reaction between a boron compound such as boric acid (including derivative thereof), a metal borate or a boron halogenide 10 and an organosilicon compound are well known. The reported organosilicon compounds have a low molecular weight, i.e. at most are oligomers (JP-A-57-26608). EP-A-0278734 discloses, inter alia, preceramic borazine polymers, which can be converted to boron nitride ceramics, of the formula: 75 SiR, 20 25 30 wherein R is C1-C4 alkyl and x is a relatively small integer, e.g. about 5. EP-A-01 75382 teaches that the ceramic yield of a ceramic material obtained by firing a R3SiNH- containing silazane polymer (R is hydrogen, vinyl, C1-C3 alkyl or phenyl) may be increased by adding a suitable boron compound to the silazane polymer prior to firing. Organoboron compounds of the formula BR"3 wherein R" represents e.g. C1-C5 alkyl, phenyl etc may be used for this purpose. It is postulated that 35 the boron compound additive interacts with the R3SiNH-containing silazane during the early stages of the pyrolysis reaction, possibly to form or promote crosslinkages. US-A-4535007 discloses a process for preparing a silicon nitride-containing ceramic material by heating an RsSiNH-containing silazane polymer (R is as defined in relation to EP-A-01 75382) which has been rendered infusible by treatment with certain reactive metal halides, including boron tribromide, BBr3, 40 possibly through crosslinking reactions. US-A-4482689 teaches R3SiNH-containing metallosilazane polymers (R is as previously defined in relation to EP-A-01 75382) useful as precursors for ceramic materials and obtained by reacting chlorine- containing disilanes and, e.g. boron halides, with a disilazane of the formula (R3Si)2NH. The present invention is aimed at the provision of an improved process for making polyborosilazanes 45 from which may be obtained by pyrolysis ceramics having a marked heat resistance. In accordance with the present invention there is provided a process for producing a polyborosilazane having a boron/silicon atomic ratio of 0.01 to 3 and a number-average molecular weight of up to 500,000, which comprises reacting, in the presence of a basic compound selected from trialkylamines, tertiary amines, pyrrole, 3-pyrroline, pyrazole, 2-pyrazolyl, dimethylsulfide and mixtures thereof, a polysilazane 50 having a number-average molecular weight of up to 50,000 and containing a skeletal structure of at least three consecutive units represented by the general formula (I): 55 si - N - (I) RJ 2 EP 0 389 084 B1 wherein R1, R2 and R3, independently from each other, represent hydrogen, a hydrocarbyl group, a substituted hydrocarbyl group, an alkylsilyl group, an alkylamino group or an alkoxy group, with the proviso that at least one of R1, R2 and R3 is hydrogen, with a boron compound represented by the following general formula (II), (III), (IV) or (V): B(R*)3 (II) (R*BO)3 (III) w (IV) 15 B(R*)3 : L (V) wherein R+ may be the same or different and represents hydrogen, halogen, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkoxy group, an alkylamino group, a hydroxy group or an 25 amino group, and L represents a compound capable of forming a complex with B(R+)3. The present invention will now be described in detail with reference to the accompanying drawings, in which Figs. 1 to 3 are X-ray diffraction patterns of ceramics obtained by pyrolysis of polyborosilazanes made by the process of this invention, and Figs. 4 and 5 are X-ray diffraction patterns of ceramics obtained by pyrolysis of polyzirconosilazane and polytitanosilazane, respectively. 30 The reaction between the polysilazane and the boron compound, and the structure of the polymer obtained by the reaction, vary with the kind of the boron compound which is used. In the case of using, for example, a boron alkoxide as the boron compound, the polyborosilazane obtained has a structure wherein side chains, cyclization and/or crosslinkages are formed by the reaction between hydrogen atoms bound to at least some of the silicon atoms and/or nitrogen atoms of the 35 polysilazane main skeleton and the boron alkoxide to effect condensation between the silicon atom and/or nitrogen atom and the boron alkoxide. For instance, in the reaction between a Si-H bond of a polysilazane and a boron alkoxide [B(OR)3], the organic group (R+) of the boron alkoxide pulls the hydrogen atom off the Si-H bond to form R+H and a Si-O- B bond as follows. 40 I i \ ^ N-Si-H + B(OR4) > N-Si-0-B(OR4)? + R4H 45 Again, in the reaction between a N-H bond of a polysilazane and a boron alkoxide, the boron alkoxide pulls the hydrogen atom off the N-H bond to thereby form N-O-B bond or N-B bond (hereinafter these are represented as "N-Y-B" bond) as follows. 50 -Si-N-H + B(OR4), > -Si-N-0-B(OR4)? or -Si-N-B (OR4) P I I II 55 Since the boron alkoxide can be trifunctional at the most, the resulting polyborosilazane can be obtained by reacting one, two or three of the reactive groups of the boron compound depending upon the 3 EP 0 389 084 B1 kind of starting boron alkoxide or the reaction conditions employed. A polymer obtained by reaction with a single reactive group has the following structure wherein pendant groups are bound to Si and/or N of the main chain of the polysilazane: 5 R1 H R1 I I I vAJWV^Si - N wa^v^ V^w^ si - N v/^/w-v (VI) I I i w O H Y B(OR4)2 B(OR4)2 15 In a polymer formed by reaction with two or all three reactive groups of the boron alkoxide, a cyclic and/or crosslinked structure is formed in or between the polysilazane skeletons through B atoms as shown below. The cyclic structures include a structure wherein two reactive groups within one molecule of the boron alkoxide are condensed with a silicon atom and a nitrogen atom located adjacent to each other on the polysilazane. A crosslinked structure is formed when two or more reactive groups of the boron alkoxide are 20 condensed with two or more molecules of the polysilazane. R H R1 I I 25 Si - N ■ Si N I I O H Y B(OR4) B(OR4) 30 0 R1 Y I Si - N Si - N I 35 R' H H (VII) R1 H R1 I v/w/w'x s i N Si N 40 o Y \ / B(OR4) B(OR4)4 45 Y H I I N - Si 50 The polymers formed by reaction with all three reactive groups of the boron compound may possess both the cyclic structure and the crosslinked structure described above at the same time. The reaction between the polysilazane and a boron alkoxide usually yields a polymer represented by (VI) or (VII). 55 Thus, the structural changes involved when the polysilazane is converted to the polyborosilazane includes the formation of pendant groups, cyclic structures and/or crosslinked structure on the polysilazane fundamental skeletons.