JPH064701B2 - Method for producing organosilicon polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an organosilicon polymer, and more specifically, when polysilane is used as a raw material to obtain polycarbosilane by thermal decomposition polycondensation, a high yield is obtained. The present invention relates to a method for producing an organosilicon polymer having a high index and suitable as a raw material for silicon carbide fibers.

[Prior Art] Conventionally, a method for producing an organosilicon polymer such as polycarbosilane by thermally decomposing and polycondensing an organosilicon compound such as polydimethylsilane has been known.
12700, JP 54-83099, JP 58-63724
JP, JP-A-56-110733, JP-A-59-49234 and the like are proposed, since these organic silicon polymers such as polycarbosilane can be obtained by firing silicon carbide, fiber, Widely used as films, sintered binders, etc.

However, conventionally obtained organosilicon polymers such as polycarbosilane are characterized in that the yield, the molecular weight as a raw material of silicon carbide fibers, the characteristics such as the transition rate, the production apparatus becomes complicated or the scale becomes large, and the like. It was not always satisfactory.

For example, in JP-A-52-112700, the yield is low when carried out under normal pressure (Example 7 of the publication), and the pressure is high when carried out under closed condition, and the production apparatus is There is a problem that it is expensive and the reaction time is long (Example 2 of the same publication).

Further, the method described in Japanese Patent Laid-Open No. 54-83099 is not only complicated in operation in two steps, but also the manufacturing apparatus becomes expensive especially when the method is performed under high pressure. In addition, according to the example, oxygen is contained in the polycarbosilane obtained by continuously supplying several percent of air into the system in the second step, and polycarbosilane is spun, When the silicon carbide fiber is heat-treated after being infusibilized, the characteristics are deteriorated. Furthermore, the molecular weight of the polysilanes obtained in the examples cannot be continuous fibers of silicon carbide. In JP-A-58-63724, since the powder is heated, heat transfer efficiency is poor and local heating occurs, and
Since two tanks are used, the manufacturing equipment becomes large-scale.

On the other hand, the method described in JP-A-56-110733 is a method of recovering the produced low-molecular weight polysilane, mixing it with polysilane, and reacting under normal pressure in the presence of a catalyst.
Since a catalyst such as polyborosiloxane is used,
The obtained polycarbosilane is not preferable as a raw material for the silicon carbide fiber, and the synthesis of polyborosiloxane is complicated. Further, in JP-A-59-49234,
A method for obtaining a low molecular weight polymer by subjecting a cyclic or chain polysilane to thermal decomposition polycondensation and further polymerizing this to a high molecular weight polymer is described, but a low molecular weight polymer is further polymerized. At this time, even if it is carried out under normal pressure, the boiling point of the low molecular weight polymer is low, so that the temperature in the system does not rise and the polymerization becomes difficult. Further, even if such a low molecular weight polymer is not further polymerized and mixed with a cyclic or chain polysilane that is a starting material, the yield of the final high molecular weight polymer, polycarbosilane, is Does not improve.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems, and has a high yield and is inexpensive to obtain polycarbosilane suitable as a raw material for silicon carbide fibers. Another object of the present invention is to provide a method for producing a novel organic silicon polymer.

This object of the present invention is achieved by the following method for producing an organosilicon polymer.

[Means and Actions for Solving Problems] That is, according to the present invention, in a method for producing an organosilicon polymer in which polysilane is used as a raw material and is pyrolyzed and polycondensed to obtain polycarbosilane, an atmosphere containing no oxygen is used. After replacing the inside of the system with, adjust the pressure in the system to 2-10 with the pressure control valve.
Keeping kg / cm ² , the gas by-produced during the thermal decomposition polycondensation reaction is separated into gas and liquid by the partial condenser, and the separated gas is continuously removed and the separated liquid is returned to the reaction system. A method for producing an organosilicon polymer having a number average molecular weight of 1000 to 5000, which is a precursor of silicon carbide fibers.

The polysilane used as a raw material in the present invention is represented by the formula (1)
Cyclic polysilane represented by (However, integers of n ≧ 4, R ₁ and R ₂ respectively represent an alkyl group, an aryl group and an allyl group) or a chain polysilane represented by the formula (2). (However, an integer of m ≧ 2, R ₁ and R ₂ are the same as above, R ₃ and
R ₄ represents a hydrogen atom, an alkyl group, an aryl group, an allyl group, chlorine, a hydroxyl group, or a methoxy group), and is an organosilicon compound having a polysilane skeleton. The raw materials may be charged into the reaction vessel in an inert gas atmosphere at first, but it is preferable to supply them in small amounts using a feeder. Further, the feeder may be heated and the raw material may be preheated and supplied. More preferably, the raw material is supplied while being melted inside the feeder. When a bulky raw material is charged at one time without using a feeder and stirred and heated, the heat transfer efficiency is poor, local heating occurs, quality and yield are reduced, and the apparatus becomes large. On the other hand, by using a feeder,
The reaction can be easily controlled and the reaction vessel can be made small. Further, if the raw material is supplied in a state of being heated and melted, this effect is enhanced, which is more convenient.

Next, after sealing the reaction container, the polysilane is heated to perform thermal decomposition, and the generated thermal decomposition component is polycondensed.
In this case, monosilanes, low molecular weight silicon compounds, and the like, which are by-produced as the polycondensation reaction continues, are generated as a gas. Therefore, in the present invention, 2 to 10 kg / cm ² pressure in the system by a pressure regulating valve, preferably held in 3~8kg / cm ^2, the gas by-produced by the partial condenser and gas-liquid separation, The separated gas is continuously removed by the pressure control valve, and the separated liquid is returned to the system.

Thus, gas-liquid separation of the by-produced gas in the partial condenser returns the silicon compound having two or more silicon atoms, which contributes to the reaction in the by-produced gas, to the system as a liquid and does not contribute to the reaction. This is because monosilane such as silane, monoalkylsilane, dialkylsilane, trialkylsilane, and tetraalkylsilane, hydrogen, and the like are discharged as a gas out of the system. As the partial condenser used here, a packed column or a partial condenser is particularly preferable. The yield is greatly improved by using such a partial condenser.

Regarding the control of the partial condenser, there is a boiling point difference between the monosilane and the compound having two or more silicon atoms, and although it depends on the reaction pressure, the range of the boiling point difference, for example, 5 kg using polydimethylsilane as a raw material. For reaction pressures of / cm ² , it is preferred to control between 50 and 100 ° C, preferably between 60 ° C and 95 ° C.

In addition, the reason why the gas such as monosilanes and hydrogen separated by gas-liquid separation is continuously removed to control the inside of the system to the above range is that the production reaction of polycarbosilane is inhibited when the pressure rises. It is presumed that the reaction of controlling the inside of the system to a pressure within a specific range promotes the insertion reaction of the generated silylene, and the yield is improved. The holding pressure in such a system is achieved by continuously removing gas by using a pressure control valve provided on the upper part of the partial condenser attached to the reaction vessel. Here, if the reaction pressure is set higher than 10 kg / cm ² , it is presumed that the transfer reaction to polycarbosilane is relatively delayed, and the Si—Si bonds increase to deteriorate the quality of the silicon carbide fiber. If the pressure is less than 2 kg / cm ² , the yield of polycarbosilane will decrease. Since the thermal decomposition polycondensation reaction in the present invention is carried out at a low pressure in the above reaction, the device design is easy and the cost is low. The reaction temperature is preferably 300 ° C to 550 ° C.

When the reaction temperature exceeds 550 ° C, the reaction rate becomes too high, and it is difficult to control the molecular weight for silicon carbide fiber. In order to proceed the reaction while performing gas-liquid separation,
It is necessary to raise the temperature gradually.

After carrying out the thermal decomposition polycondensation reaction in this way, the thermal decomposition polycondensation product is dissolved in a solvent such as n-hexane, toluene, xylene, etc., impurities are filtered off, and the solvent is distilled off. By concentrating under reduced pressure at 3 ° C. and 3 mmHg, polycarbosilane having a preferable molecular weight as a precursor of silicon carbide fibers can be obtained in high yield.

The low molecular weight polycarbosilane distilled in this vacuum distillation is preferably mixed with the raw material polysilane at a desired ratio to be used as a raw material for producing polycarbosilane. In particular, low molecular weight polycarbosilane at 200-500 ℃
By gradually supplying the polysilane by the feeder during the preheating, the disadvantages such as the necessity of enlarging the reaction vessel due to the bulkiness of the polysilane are solved.

By reusing this low molecular weight polycarbosilane as a raw material, not only a polycarbosilane having properties suitable for silicon carbide fibers can be obtained, but also the yield is improved.
The low molecular weight organosilicon compound that is by-produced again here may be subjected to the same reaction as above.

Here, the properties of polycarbosilane as a silicon carbide fiber precursor require a number average molecular weight of 1000 to 5000. If the number average molecular weight exceeds 5,000, melt spinning is impossible, and if the number average molecular weight is less than 1000, melt spinning is possible, but fusion and infusibilization are difficult.

An example of a preferable apparatus used in the manufacturing method of the present invention is shown in FIG. In FIG. 1, 1 is a reaction vessel, 2 is a pressure control valve, 3 is a partial condenser, and 4 is a feeder.

[Examples] Hereinafter, the present invention will be described in more detail based on Examples.

Example 1 As shown in FIG. 1, 300 g of polydimethylsilane as a raw material was put into a reaction vessel made of stainless steel having a pressure control valve, a partial condenser and a feeder and having a volume of 1 without preheating, and the reaction vessel was closed and the system was closed. Was replaced with nitrogen. next,
The reaction vessel was heated from the outside to start the thermal decomposition polycondensation reaction of polydimethylsilane. The gas generated by the heating reaction is gas-liquid separated into a gas such as monosilane and a liquid of a silicon compound having 2 or more silicon atoms in a partial condenser set at 50 to 100 ° C, and the cooled liquid is returned to the system again. Will be returned. On the other hand, gases such as monosilane and hydrogen are 5
It is removed outside the system by the pressure control valve set to kg / cm ² and the pressure inside the system is always kept below 5 kg / cm ² . Gradually 470 ℃
The product is heated to n
-Dissolved in hexane, filtered off impurities and evaporated n-hexane. Further, vacuum distillation was carried out at 300 ° C. and 3 mmHg to give 30 g of a low molecular weight organosilicon compound and a melting point of 210.
180 g of polycarbosilane having a number average molecular weight of 1,300 was obtained. The yield was 60%. Further, the silicon by absorbance ratio IR1350 / 1250 and 1350 cm ^-1 in the infrared absorption spectrum of the (deformation absorption of Si-CH ₂ -Si bonds) and 1250 cm ^-1 (deformation absorption of Si-CH ₃₎ - carbon The degree of skeleton formation was calculated to be IR1350 / 1250 = 0.155. From this, the degree of transfer to polycarbosilane is estimated to be 96% or more.

Next, the polycarbosilane obtained above was heated to 340 ° C. using a melt spinning device, and 200 m / mi from the monohole die.
After melt-spinning in air at a speed of n to form a fibrous material with a diameter of 14μ, the temperature is raised from room temperature to 10 ° C / hr in air in a heating furnace and maintained at 170 ° C for 2 hours to infusibilize. Then, put the infusibilized fiber in a furnace and put it in nitrogen gas for 1200
When heated up to 10 ℃ for 10 hours and held at 1200 ℃ for 2 hours, firing was performed, and the diameter was 10μ
m silicon carbide fiber is obtained, which has a tensile strength of 280 kg.
/ Mm ² , and the tensile elastic modulus was 20.5 tons / mm ² .

Example 2 Using the same apparatus as in Example 1, first, 250 g of polydimethylsilane was charged into a reaction vessel and 250 g was charged into a feeder, the system was replaced with N ₂ gas, and then heating of the reaction vessel and the feeder was started to raise the temperature. . If the raw materials in the reaction vessel are heated to 250-350 ℃ and melted and the volume starts to decrease,
The supply of raw material preheated to about 0 ° C was started. The supply was completed in about 3 hours, the temperature of the reaction vessel was raised again, and the same operation as in Example 1 was performed.

As a result, 300 g of polycarbosilane was obtained. 60% yield
Is. The resulting polycarbosilane has a number average molecular weight of 13
00, melting point 211 ° C., IR1350 / 1250 = 0.155. From this, it can be estimated that the degree of transfer to polycarbosilane is 96%.
A silicon carbide fiber was prepared in the same manner as in Example 1. As a result, the characteristics were the same as in Example 1.

Example 3 As in Example 2, the feeder was heated to about 400 ° C. and tested, but when the raw materials were melted and fed at this time, the feeding was completed in 30 minutes. After that, the same operation as in Example 1 was performed to obtain 305 g of polycarbosilane.
The yield was 61%. The resulting polycarbosilane had a number average molecular weight of 1300, a melting point of 210 ° C., and IR1350 / 1250 = 0.155. A silicon carbide fiber was prepared in the same manner as in Example 1. As a result, the characteristics were the same as in Example 1.

Example 4 30 g of the low molecular weight organosilicon compound obtained in Example 1
After charging, the reaction vessel was heated to 300 ° C., 500 g of the melted raw material was continuously fed in 1 hour in the same manner as in Example 3, and after the end of feeding, the temperature was raised again by heating, and the reaction was carried out at 470 ° C. for 8 hours. Was done. As a result, 320 g of polycarbosilane was obtained. The yield was 64.0%. The resulting polycarbosilane had a number average molecular weight of 1250, a melting point of 208 ° C., IR1350 / 1250 = 0.16.
It was 0. From this, the degree of transition to polycarbosilane is 99.
It can be estimated as%. A silicon carbide fiber was prepared in the same manner as in Example 1. As a result, the characteristics were the same as in Example 1.

Example 5 300 g of polysilane compound obtained by dechlorinating 20% by weight of diphenyldichlorosilane and 80% by weight of dimethyldichlorosilane with sodium metal
After using the above as a raw material to carry out a reaction in the same manner as in Example 1, the same treatment as in Example 1 was performed. As a result, a polycarbosilane compound containing a phenyl group (average molecular weight 2500) 18
2 g were obtained. The yield was 61%. This product was melt-spun in the same manner as in Example 1 to obtain silicon carbide fiber, and the fiber characteristics were measured. Tensile strength of 285 kg / m
Results of m ² and tensile modulus of 20.0 ton / mm ² were obtained.

Example 6 Dodecamethylcyclohexasilane A reaction was carried out in the same manner as in Example 1 using 300 g of the raw material. As a result, 190 g of polycarbosilane was obtained. The yield was 63.3%. When this fiber was used as a silicon carbide fiber in the same manner as in Example 1 and the fiber characteristics were measured, the tensile strength was 290 kg / mm ² , and the tensile elastic modulus was 21.0 ton / mm ² .

Comparative Example 1 300 g of polydimethylsilane as a raw material was placed in an induction rotating stainless steel autoclave having a volume of 2, the autoclave was closed, and the system was replaced with nitrogen. Next, the autoclave was externally heated to start the thermal decomposition polycondensation reaction of polydimethylsilane, and the reaction was carried out at 458 ° C for 5.7 hours. The pressure at the end of the reaction was 60 kg / cm ² . Then, the reaction product was treated in the same manner as in Example 1 to obtain 145 g of polycarbosilane having a melting point of 195 ° C. and a number average molecular weight of 1350. Yield 48.3%
Met. This product had IR1350 / 1250 = 0.130.
From this, it can be estimated that the degree of transfer to polycarbosilane is 80%.

Next, the polycarbosilane obtained above was melt-spun in the same manner as in Example 1 to obtain a black and glossy silicon carbide fiber having a diameter of 10 μm, which had a tensile strength of 228 kg / mm. ² , the tensile elastic modulus was 18 tons / mm ² .

Comparative Example 2 300 g of polydimethylsilane as a raw material was placed in a glass reaction vessel having a water-cooled reflux section, heated to a predetermined temperature, and then a thermal decomposition polycondensation reaction was started under a nitrogen stream of 1 atm. The reaction was carried out at ℃ for 12 hours. Then, the reaction product was treated in the same manner as in Example 1 to give a melting point of 256 ° C. and a number average molecular weight of 1
368 polycarbosilane 99g was obtained. The yield was as low as 33%. This product had IR1350 / 1250 = 0.155.
From this, it can be estimated that the degree of transfer to polycarbosilane is 96%.

Comparative Example 3 In the same manner as in Example 1, except that the partial condenser of the apparatus in Example 1 was removed, 300 g of raw material polydimethylsilane was charged and the reaction was carried out. As a result, when the internal pressure reached 5 kg / cm ² , gas began to be released,
At the same time, a compound having a Si number of 2 or more, which seems to contribute to the reaction, was also distilled out. In the same manner as in Example 1, the reaction was carried out at 470 ° C. for 6 hours, the product was dissolved in n-hexane, filtered, and then distilled under reduced pressure. The yield was 129 g, and the yield was 43%.

[Effects of the Invention] As described above, according to the method for producing an organosilicon polymer of the present invention, polycarbosilane having a high yield and suitable as a raw material for silicon carbide fibers can be obtained at low cost. .

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus used in the method for producing an organosilicon polymer of the present invention. 1: Reaction vessel, 2: Pressure control valve 3: Partial condenser, 4: Feeder.

Claims (3)

[Claims] 1. A method for producing an organosilicon polymer, which comprises using polysilane as a raw material and subjecting it to thermal decomposition polycondensation to obtain polycarbosilane, wherein the pressure in the system is controlled by a pressure control valve in an oxygen-free atmosphere. While maintaining ² to 10 kg / cm ² , the gas by-produced during the thermal decomposition polycondensation reaction is gas-liquid separated by a partial condenser, and the separated gas is continuously removed, and the separated liquid is used as a reaction system. Number average molecular weight of 1,000 to become a precursor of silicon carbide fiber characterized by returning to the inside
A method for producing 5000 organosilicon polymers. 2. The method for producing an organosilicon polymer according to claim 1, wherein the liquid obtained by gas-liquid separation is a silane compound having 2 or more silicon atoms. 3. The method for producing an organosilicon polymer according to claim 1 or 2, wherein the partial condenser is a packed column or a partial condenser.