JPH0576970B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for producing a polymer having a cyclic polymethylsilazane structure useful as a precursor for producing ceramics. [Technical Background of the Invention and its Problems] A high degree of wear resistance is required on the surfaces of various mechanical parts and electronic parts that operate by sliding or contacting each other. Furthermore, in recent years, there has been a demand for higher efficiency in various types of equipment from the perspective of energy conservation, and reducing the weight of the materials used therein has become an important issue. Various types of ceramics, such as non-oxide ceramics such as silicon nitride and silicon carbide, are generally lightweight, have high chemical stability, and have excellent heat resistance, so they are being used as materials for various parts in place of conventionally widely used metal materials. has been in the spotlight as a Ceramics such as silicon nitride are manufactured by, for example, filling raw material powder into a mold and then heating and sintering it in a nitrogen stream. However, since such raw material powders are generally difficult to sinter, the methods that are usually applied include adding a sintering aid to the raw material powder before sintering it, or sintering it at high temperature and high pressure. has been done. Therefore, with such conventional methods, it is difficult to obtain a sintered body having a particularly complex shape as desired. In order to solve these problems, methods using silazane-based polymers as raw materials have been considered. For example, in JP-A-57-117532, chlorine-containing disilane and disilazane, JP-A-58-117532,
Publication No. 63725 discloses a method of causing a catalytic reaction between chlorine-containing disilane and ammonia. Further, JP-A-57-139124 discloses a method of causing a contact reaction between organochlorosilane and disilazane. However, with these conventional methods, it is difficult to control the molecular weight of the polysilazane obtained. For this reason, it is not possible to finally obtain ceramics of constant quality.
Furthermore, since the obtained polysilazane is a glass-like solid that is insoluble in organic solvents, the usual molding method involves dissolving polymethylsilazane in an organic solvent and filling a mold with the desired shape. Molding is difficult, and it is difficult to obtain a sintered body having a desired shape, particularly a complex shape. [Object of the Invention] The present invention solves the above-mentioned problems and allows ceramics of a desired shape to be manufactured more easily under relatively mild conditions. The object of the present invention is to provide a polymer having a cyclic polymethylsilazane structure that is useful as a precursor for producing ceramics. [Structure of the Invention] That is, the method for producing a polymer having a cyclic polymethylsilazane structure of the present invention includes (A) hexamethylcyclotrisilazane; and (B) the formula (CH ₃ ) _a SiCl _4-a () (but , where a is 0, 1 or 2) is heated in the presence of a hydrogen chloride acceptor.
After polymerization, the remaining portion except for the hydrogen chloride acceptor is reacted with ammonia. Hexamethylcyclotrisilazane (hereinafter referred to as "trimer"), which is the starting material in the production method of the present invention.
), for example, John C. Baller, GRA et al., Inorganic Synthesis 5
61 (1953) [JOHN C. BALAR, Jr. et al.
Inorganic synthesis 5 61 (1953)] Brewer and Haber
Harber) can be manufactured by applying an improved method. The trimer thus obtained is reacted with the chlorosilane compound represented by the above formula (),
A polymer having a cyclic polymethylsilazane structure is produced. The chlorosilane compound represented by this formula () is specifically dimethyldichlorosilane, methyltrichlorosilane or tetrachlorosilane. This chlorosilane compound acts as a crosslinking agent by performing a dehydrochlorination reaction with the hydrogen atom bonded to the nitrogen atom of the trimer. Chlorosilane, tetrachlorosilane, especially tetrachlorosilane are preferred. In the production method of the present invention, the individual operating procedures are not particularly limited as long as the reaction between the trimer and the chlorosilane compound is carried out in the presence of a hydrogen chloride acceptor. Hereinafter, an example of the manufacturing method of the present invention will be described. First, a trimer and a hydrogen chloride acceptor (hereinafter referred to as "receptor") are charged into a reaction vessel. The receptor used here is for absorbing hydrogen chloride generated by the reaction between the trimer and the chlorosilane compound. As this receptor, commonly used tertiary amines such as pyridine, 1,8
-Diazabicyclo[5.4.0]-Undecene-7
(DBU) or N,N-dimethylacetamide (DMAC). Among these receptors, DMAC is preferred because the thermogravimetric loss rate of the product, a polymer having a cyclic polymethylsilazane structure, is small. The acceptor is added in an amount capable of completely absorbing hydrogen chloride generated by the reaction between the trimer and the chlorosilane compound, ie, a stoichiometric amount, or an excess amount. Further, the receptor may also be used as a solvent, or other organic solvents such as benzene and toluene may be used in combination. Next, a dry atmosphere is created in the reaction system. This is done by replacing the air in the system with an inert gas, such as nitrogen gas. Thereafter, a chlorosilane compound is added while heating and refluxing the system. The heating temperature in this case varies depending on the receptor used. For example, among the above-mentioned receptors, when using pyridine, it is up to the boiling point temperature, and when using other receptors, it is about
Heat to around 80℃. In order to perform a good reaction, it is preferable to add it little by little, for example, by a dropwise addition method. The amount added can be appropriately determined in relation to the amount of trimer added depending on the molecular weight of the desired polymer having a cyclic polymethylsilazane structure. For example, if 0.75 mol of tetrachlorosilane is used for 1 mol of trimer, the molecular weight is approximately
A polymer having a 900 cyclic polymethylsilazane structure or a polymer obtained by further crosslinking polymerization thereof can be produced. In this case, the amount of receptor such as pyridine is required to be 3 moles or more. After adding the chlorosilane compound, the system is further heated, stirred, and refluxed at 60 to 120°C, preferably 80 to 115°C, for 6 to 12 hours to complete the reaction. After removing the receptor, the liquid product is dissolved in an organic solvent such as benzene, toluene, xylene, or cyclohexane. This solution is then treated with ammonia. This ammonia treatment converts the Si--Cl groups bonded to the molecular ends of the product into Si-- _NH2 groups and prevents the subsequent generation of hydrogen chloride. This treatment is carried out, for example, by blowing ammonia gas into the solution. Then,
Ammonium chloride produced as a by-product in the reaction is separated by filtration. Thereafter, after removing the solvent, unreacted trimer and the like can be removed by distilling under reduced pressure under heating to obtain a polymer having a cyclic polymethylsilazane structure. [Examples of the Invention] The present invention will be described in further detail below with reference to Examples. Examples 1 to 5 Trimers were synthesized by ammonolysis of dimethyldichlorosilane by applying the above-mentioned Brewer and Haber improved method. The receptors and chlorosilane compounds shown in the table were used. In addition, in Examples 1 and 2, the theoretical amount was 1.5
Examples 3-5
Then, 400 parts by volume of each receptor was added to 100 parts by volume of the chlorosilane compound, and the chlorosilane compound was added at the molar ratio shown in the table to the trimer, and a reaction was carried out. The receptor was first charged into a three-necked flask equipped with a condenser, thermometer, and addition funnel, followed by the trimer. Then, the air in the flask was completely replaced with nitrogen gas. Thereafter, it was heated to about 80°C in Examples 1 and 2, and about 115°C in Examples 3 to 5,
While refluxing, a predetermined amount of a chlorosilane compound was added dropwise from a dropping funnel over 2 hours. Next, the mixture was further heated and refluxed at the same temperature for 8 hours to complete the reaction. After the reaction was completed, the receptor was removed, and the residual liquid containing the reaction product was dissolved in 500 ml of benzene.
Ammonia gas was then bubbled into this solution at 70/hour for 1.5 hours. Thereafter, the mixture was filtered by suction to remove ammonium chloride produced as a by-product. Then, vacuum distillation was further performed at 40 to 50° C./250 Torr to remove benzene, and a polymer having a cyclic polymethylsilazane structure was obtained. The molecular weight, properties, yield, and thermal weight loss rate of the obtained polymer having a cyclic polymethylsilazane structure are shown in the table. The thermogravimetric reduction rate was measured after heating to 800°C at a rate of 5°C/min in a nitrogen gas atmosphere.

[Table] Example 6 A polymer having a cyclic polymethylsilazane structure was prepared in the same manner as in Example 1 using pyridine as the acceptor and dimethyldichlorosilane as the chlorosilane compound in an amount of 1.5 mol per 1 mol of trimer. Obtained. This product is a colorless transparent liquid with a molecular weight of
It was 600. In addition, the yield was 42%, and the thermogravimetric reduction rate was
It was 92%. As shown in FIG. 2, the infrared absorption spectrum of this product shows an absorption of Si-N (outside the trimer ring) of 1030 cm ^-1 and a decrease in absorption of N-H. Moreover, the structural formula of this product is estimated to be as follows. However, in the formula, Me ₂ represents two methyl groups bonded to a silicon atom. The same applies below.

Example 7 A polymer having a cyclic polymethylsilazane structure was obtained in the same manner as in Example 1, using pyridine as a receptor and 0.75 mol of tetrachlorosilane per 1 mol of trimer as a chlorosilane compound. Ta. The product was a pale yellow viscous liquid with a molecular weight of 840. Moreover, the yield was 36% and the thermogravimetric reduction rate was 90%. The infrared absorption spectrum of this product is shown in FIG. Moreover, the structural formula of this product is estimated to be as follows.

Example 8 A polymer having a cyclic polymethylsilazane structure was obtained in the same manner as in Example 1 using DMAC as a receptor and tetrachlorosilane as a chlorosilane compound in an amount of 0.75 mol per 1 mol of trimer. Ta. The product was gelatinous. Yield is 73
%, and the thermogravimetric reduction rate was 41%. The infrared absorption spectrum of this product is shown in FIG. Also,
The structural formula of this product is estimated to be as follows.

Reference Example 1 Ceramics were manufactured using the polymer having a cyclic polymethylsilazane structure obtained in Example 5. After filling a desired mold with methylcyclopolysilazane, it is heated and raised to 1000°C at a rate of 5°C/minute in a nitrogen gas atmosphere. Thereafter, the mixture was further held at this temperature for 2 hours to perform firing. The surface of this ceramic was found to have a uniform smooth surface by SEM observation. Further, the Bitkers hardness was 1250Kg/mm ² . This indicates that this ceramic has a dense structure with few pores. Reference Example 2 Using the polymer having a cyclic polymethylsilazane structure obtained in Example 7, ceramics were produced in the same manner as in Reference Example 1. However, the temperature increase rate was 5°C/min, and the temperature was raised to 1400°C. Further, the holding time after the temperature increase was 2 hours. The surface of this ceramic was found to have a uniform smooth surface by SEM observation. Further, the Bitkers hardness was 1930 Kg/mm ² . This indicates that this ceramic has a dense structure with few pores. [Effects of the Invention] As explained above, according to the production method of the present invention, the molecular weight of the product polymer having a cyclic polymethylsilazane structure can be freely controlled, thereby improving the quality of ceramics after firing. can be made constant. In addition, the obtained polymer having a cyclic polymethylsilazane structure is easy to mold because it is soluble in organic solvents.
Ceramics of a desired shape, particularly a complex shape, can therefore be obtained. Furthermore, by firing this polymer having a cyclic polymethylsilazane structure under mild conditions (normal pressure, firing temperature of 800°C or higher), it is possible to obtain ceramics with high hardness and a dense structure. As a result, it becomes possible to apply it to various fields.

[Brief explanation of the drawing]

FIG. 1 shows the infrared absorption spectrum of the trimer, and FIGS. 2 to 4 show the infrared absorption spectra of the polymers having a cyclic polysilazane structure obtained in Examples 6 to 8, respectively.

Claims (1)

[Scope of Claims] 1 (A) hexamethylcyclotrisilazane; and (B) formula (CH ₃ ) _a SiCl _4-a (wherein a is 0, 1
or 2); is heated and polymerized in the presence of a hydrogen chloride acceptor, and then the remainder after removing the hydrogen chloride acceptor is reacted with ammonia. A method for producing a polymer having a structure. 2. The manufacturing method according to claim 1, wherein the hydrogen chloride acceptor is N,N-dimethylacetamide. 3. The manufacturing method according to claim 1, wherein the chlorosilane compound is tetrachlorosilane.