JPH0517248B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a polycarbosilastyrene copolymer, which is a novel polymeric organosilicon compound useful as a silicon carbide precursor. [Prior Art] Practical methods for manufacturing silicon carbide (SiC) molded products such as fibers, films, sheets, and sintered products include a method using polycarbosilane as a silicon carbide precursor (in particular, Publication No. 57-53893, Special Publication No. 58-38534, Special Publication No. 58
−38535, Special Publication No. 59-33691, Special Publication No. 1987-
28927, Japanese Patent Publication No. 60-50884) and a method using polysilastyrene as a precursor (Japanese Patent Publication No. 58-58)
-215426) etc. are known. However, the former method using polycarbosilane requires a long and complicated process and increases manufacturing costs, while the latter method using polysilastyrene has the problem of significant shrinkage and welding of the molded product during the infusibility treatment. Not practical. Therefore, the present inventors previously proposed a new polycarbosilastyrene copolymer as a silicon carbide precursor free from such problems (patent application
61-236299). This copolymer has excellent moldability and does not cause the problems seen in conventionally known high-molecular organosilicon compounds during the infusibility and sintering processes, and can be used to form silicon carbide molded products (fibers, films, etc.) with good physical properties. However, when the silicon carbide products obtained in this way are heated to high temperatures, they crystallize and become brittle, and the corrosion resistance against metals such as aluminum is still insufficient. The problem remains. [Object of the Invention] The object of the present invention is to provide an improved polycarbosilastyrene copolymer that can be formed into silicon carbide molded articles or sintered molded articles with excellent heat resistance and corrosion resistance by molding and firing. The purpose of this invention is to provide a method for industrially manufacturing. [Structure of the Invention] The object of the present invention as described above is to heat-treat polysilastyrene in an inert gas atmosphere to produce a polycarbosilastyrene copolymer, and to produce a copolymer of polysilastyrene represented by the following general formula []. The present invention produces a partially crosslinked polycarbosilastyrene copolymer through silicon or titanium by adding and mixing a specific amount of at least one organic compound of silicon or titanium, and heat-treating the mixture under specific conditions. This is achieved by the following method. M(OR) ₄ (However, R is silicon or titanium, and titanium may be Ti-O-Ti. At least two of R are lower alkyl groups or aromatic groups, and the rest are hydrogen or halogen. ) Polysilastyrene, which is a raw material in the method of the present invention, has the following general formula []: (However, R is _-CH3 or _-C6H5 , n is 10 _~
(an integer of 3000, x is a numerical value of 0.2 to 0.9, preferably 0.3 to 0.7); It can be easily synthesized by using a sodium metal catalyst in an active solvent and reacting at a temperature above its melting point. Regarding the manufacturing method of such polysilastyrene,
For example, U.S. Patent No. 2,563,005 and U.S. Pat.
It is described in No. 4324901 etc. In the method of the present invention, the above-mentioned polysilastyrene is used as the main raw material, and the following general formula []: M(OR) ₄ ... [] (where M is silicon or titanium and Ti-O
-Ti may be used. At least two of R's are lower alkyl groups or aromatic groups, and the rest may be hydrogen or halogen. ) are added and mixed, and the mixture is heat treated. In the above general formula [], R is methyl, ethyl, propyl, i-propyl, butyl,
Aliphatic groups such as t-butyl or

【formula】

Aromatic groups such as [Formula] are preferred. Particularly preferred compounds in the process of the invention include tetraethyl silicate, tetrabutyl silicate, tetra-i-propyl silicate, dichlorodiethoxysilane, titanium, i-propoxide, titanium-i-butoxide, and (Ti-
Examples include compounds represented by O-Ti)(OR) ₆ . The mixing ratio of polysilastyrene and the above metal compound is suitably 0.1 to 30% by weight, particularly preferably 1 to 10% by weight, based on the weight of polysilastyrene. If the amount of the metal compound mixed is less than the above range, the effect of mixing the metal compound will be ineffective, and if it exceeds the above range, crosslinking will be significant in the resulting polycarbosilastyrene copolymer, resulting in poor moldability. becomes worse. To mix polysilastyrene and the above metal compound, both components may be mixed in powder form, but water or an organic solvent (for example, an aromatic hydrocarbon such as toluene or xylene, or a cyclic ether such as tetrahydrofuran or dioxane) may be used. , a polar amide solvent such as N-methyl-2-pyrrolidone, etc.), the above metal compound is added to a solution of polysilastyrene, stirred, and then a non-solvent is added to produce polysilastyrene containing the above metal compound. It is also possible to adopt a method of precipitation. In any case, it is preferable to mix both components as uniformly as possible. The mixture of both of the above components is then subjected to heat treatment, and the heat treatment is carried out at a temperature of 180 to 480°C, preferably 200 to 450°C, in an inert gas atmosphere or under reduced pressure. This heat treatment is preferably carried out under as gentle conditions as possible; for example, it is preferable to gradually raise the temperature while stirring the system, then maintain it at a predetermined temperature, and discharge low-boiling substances generated during the treatment to the outside of the system. . The heat treatment time is appropriately selected within the range of 5 minutes to 20 hours, preferably within the range of 10 minutes to 10 hours, depending on the heat treatment temperature. For example, heat treatment at 180°C takes about 20 hours, but at 480°C, it only takes about 10 minutes. If heat treatment is performed for a longer time, the softening point of the resulting copolymer will increase, and the molding temperature will exceed 400°C. This is not preferable because infusible substances are generated in the molded product. Therefore, the suitable heat treatment temperature and time are:
At 350-400°C it is 10-100 minutes, and at 200°C it is 10-20 hours. In the method of the present invention, among the low-boiling fractions produced during the above heat treatment and discharged outside the system, the fraction with a boiling point of 200°C or higher is collected and mixed with the raw material polysilastyrene to produce polycarbosilastyrene. The yield of the copolymer can be improved. Through such heat treatment, benzene is produced as a low-boiling substance, and at the same time, carbosilane is produced by rearrangement of methyl groups in the polymer.

[Formula] A bond is formed, and some of the above metals (Ti or Si)
Crosslinking occurs and the molecular weight is increased, the softening point rises, and the molding temperature also rises. After heat treatment, the polycarbosilastyrene copolymer becomes silastyrene.

[Formula] bond, carboxy run

[Formula] bond, and some of the bonds are cross-linked through the above metals, and this structure is confirmed by infrared absorption spectroscopy. The polycarbosilastyrene copolymer after heat treatment preferably has a molecular weight of about 1000 to 50000,
Further, the molar ratio of silastyrene bonds to carbosilane bonds in the copolymer is preferably within the range of 7/3 to 3/7. The polycarbosilastyrene copolymer obtained by the method of the present invention as described above has good moldability, and can be made into fibers by a melting method or a solution method (dry method).
The molded product is formed into a tape, film, sheet, or other arbitrary shape, and if necessary, the molded product is heated in air to make it crosslinked and infusible.
A high quality silicon carbide molded product can be obtained by firing at ℃. In addition, high-quality silicon carbide sintered molded products can be made by mixing this polycarbosilastyrene copolymer with silicon carbide powder, molding it, and firing it at 800 to 1400°C in an inert gas. can. Furthermore, a silicon carbide composite material can be obtained by manufacturing a composite molded product together with other materials such as carbon powder fibers and firing the composite molded product. In either case, when the polycarbosilastyrene copolymer produced by the method of the present invention is used, it is less likely to crystallize at high temperatures and has excellent oxidation resistance than those made of ordinary silicon carbide, and is resistant to metals such as aluminum. Corrosion resistance is also good. For crosslinking and infusibility of polycarbosilastyrene copolymer molded articles, heat treatment at 50 to 300°C or ultraviolet irradiation treatment under reduced pressure or in an inert gas atmosphere is employed. In addition, firing is performed in an inert gas atmosphere for 800~
This is done by heating to 1400℃, but in advance
After heating from 200°C to 800°C at a temperature increase rate of 1 to 10°C/min, it is preferable to heat at 800 to 1400°C for about 0.5 to 5 hours. The conditions for such infusibility and firing are also disclosed in the patent application filed in 1983.
-Details are given in No. 236299. In the case of molded products such as fibers and tapes, infusibility can be omitted by doping the polycarbosilastyrene copolymer molded product with halogen, particularly iodine. [Effects of the Invention] According to the method of the present invention, a partially crosslinked polycarbosilastyrene copolymer can be efficiently produced, and the copolymer is made of silicon carbide having good heat resistance and corrosion resistance. It is extremely useful as a precursor for molded articles (fibers, films, sheets, etc.) or sintered articles. After firing, the silicon carbide product is
It can be widely used in various fields where heat resistance and corrosion resistance are required. [Examples] Next, Examples of the present invention will be described in detail, but the present invention is not limited to these Examples in any way. In addition, in the examples, "parts" simply represent parts by weight. Example 1 Using equimolar moles of dichlorodimethylsilane and dichloromethylphenylsilane, a polymerization reaction was carried out at 100 to 100°C using a sodium dispersion catalyst of 22 equimolar to the raw material silane in a toluene solution, resulting in a black-purple color. A reaction mixture was obtained. After cooling the reaction mixture to room temperature, methanol was added to decompose the unreacted sodium catalyst, and the mixture was washed with water several times to remove methanol and NaCl to obtain a cloudy white mixture. The cloudy white mixture was filtered to gradually remove the precipitate to obtain a transparent toluene reaction mixture solution, and then toluene was distilled off from this solution to obtain a polysilastyrene solid content with a yield of about 90%. Titanium-I was added to 200 parts of this polysilastyrene.
-Add 5 parts of butoxy to 250% in nitrogen atmosphere under normal pressure.
The reaction was carried out at ~300°C for 60 minutes, and further treated at 250°C for 10 minutes under reduced pressure (3 torr) to obtain polycarbosilastyrene with a pour point (minimum temperature that can be melt-spun at a spinning take-off speed of 400 m/min) of 210°C. A polymer was obtained. The spinnability of this polycarbosilastyrene copolymer is good, and the maximum spinning speed at 230°C is 900 m/min.
It was hot in minutes. The polycarbosilastyrene copolymer fibers spun here are exposed to ultraviolet light (lamp output) at 50°C in the air.
110 W/cm) for 2 hours to make it infusible. Next, this infusible fiber is placed in a nitrogen gas atmosphere.
After pre-firing for 3 hours at 200-400℃, further 1100℃
C. for 60 minutes to obtain silicon carbide fibers with a strength of 310 Kg/mm ² . When this fiber was analyzed, the TiO ₂ contained in the fiber was approximately 2%.
Moreover, the heat resistance of this fiber at 1200°C was extremely good. Examples 2 to 5 A mixture of dichlorodimethylsilane and dichloro phenylmethylsilane in a 0.45:0.55 molar equivalent was used in a toluene solvent at 100 to 110°C using a sodium dispersed catalyst in a 2.1 molar equivalent to the raw material silane.
A polymerization reaction was carried out. After the reaction was completed, the reaction mixture was cooled to room temperature, methanol was added to decompose unreacted sodium catalyst, and the mixture was washed with water several times to dissolve and remove methanol and NaCl to obtain a cloudy white mixture. The mixture was filtered to remove precipitates, and then passed through an ultracentrifuge to obtain a clear toluene solution. Toluene is distilled off from this toluene solution, and 95
% theoretical yield of polysilastyrene was obtained. Tetraethylsilicate was added to this polysilastyrene and reacted in an autoclave under a nitrogen atmosphere under the conditions shown in Table 1 below.
A polycarbosilastyrene copolymer was obtained by processing under reduced pressure (5 torr) at a temperature of ~300°C. The results are shown in Table 1 below. Furthermore, each of the obtained copolymers was melt-spun, and the spinnability was "good" in all cases.

[Table] Examples 6 to 9 Experiments were carried out in exactly the same manner as in Examples 2 to 5, except that the metal compound added to polysilastyrene was titanium i-propoxide, and the amount was changed as shown in Table 2. repeated. The results are shown in Table 2. Further, when each of the obtained copolymers was melt-spun, the spinnability of Examples 6 to 8 was "good", and the spinability of Example 9 was "slightly good".

[Table] (Note) The definition of pour point in the table is the same as in Table 1.
As is clear from the above examples, whereas the conventional method required a long reaction time (5 to 20 hours) in the presence of a catalyst, the method of the present invention requires no catalyst and a short reaction time. The reaction yields a polycarbosilastyrene copolymer with good spinnability.

Claims (1)

[Claims] 1. Polysilastyrene represented by the following general formula [], (However, R is _-CH3 or _-C6H5 , n is 10 _~
An integer of 3000, x is a value between 0.2 and 0.9. ) in an inert gas atmosphere at 180 to 480°C for 10 minutes to 10 hours, the silastyrene bond and carbosilane bond are reduced to 7/3 to 7/3 in the molecular chain.
When producing a polycarbosilastyrene copolymer with a molar ratio of 3/7, at least one compound represented by the following general formula [] is added to polysilastyrene based on the weight of the polysilastyrene. A method for producing a polycarbosilastyrene copolymer, which comprises adding and mixing 1 to 10% by weight and heat-treating the mixture. M (OR) ₄ ... [] (However, M is silicon or titanium, and titanium may be Ti-O-Ti. At least two of R are lower alkyl groups or aromatic groups, and the rest are (Can be hydrogen or halogen.)