The method of producing polycarbosilane

 

(57) Abstract:

Usage: upon receipt of inorganic fibers and other products consisting of silicon carbide. The inventive polycarbosilane get by thermal decomposition of polydimethylsilane at a gauge pressure of 1.5 - 6 ATM with shutter speed at 350 - 380oC for 2 to 10 h, the reset lehajtasa components and subsequent exposure at 390 - 450oWith over 30 - 80 hours 2 Il. , 1 table.

The invention relates to methods of producing organosilicon polymer of polymer of the formula:

< / BR>
(patent N 4220600, class C 07 F 7/08, 1980).

Polycarbosilane (in pixels) of the formula (1) is used to obtain the inorganic fibers and other products, consisting mainly of silicon carbide.

Structure and rheological characteristics of the polymer determines its ability to fiberizing and operational properties of SiC materials.

A known method of producing polycarbosilane (1), partly containing siloxane links:

< / BR>
(patent N 4159259, class C 07 F 7/60, 1979).

The polymer is produced by heating a mixture of powdered polydimethylsilane (PDMS) and polypropyleneoxide in an inert atmosphere.

Nedostatki and reduces oxidative and thermal stability of SiC fibers.

The closest in technical essence of the present invention and adopted for the prototype is the way to get polycarbosilane formula (1) by thermal decomposition of polydimethylsilane at high temperature (470-500oC), a pressure of 95 - 100 ATM [1] for 15 - 20 hours

The disadvantage of this method is the formation of large amounts of coke forming insoluble product, relatively low uniformity of polymer molecular mass composition, which leads to high breakage jet melt and stuck on filiere when the molding on the molding machine, as well as the complexity of the hardware design process.

The task of the invention is to improve the quality of the product and the simplification of the apparatus registration process.

The technical result is achieved due to the fact that polycarbosilane formula (1) obtained by step thermal decomposition of polydimethylsilane in an inert atmosphere. The process is carried out in three stages. In the first stage produce exposure at 350 - 380oC and a pressure 1.5 - 6 bar. In the second stage discharge boiling liquid components. The third stage is heated to a temperature of 390 the low temperature with the speed of its rise and a relatively small overpressure allows you to make this process more automated and to improve the quality of the PCB, that manifests itself in a more narrow molecular weight distribution polymer, a high content of Si - H groups, the regularity of the structure of the PCB, which is assessed according to the relative content of HSiC3groups, as well as the ability of the polymer to the formation, oxidation and strength characteristics of the SiC fibers.

The difference of the proposed method is to conduct the process at a pressure of 1.5 to 6 ATM and heat treatment using manual mode (350 - 380oC for 2 to 10 h, and then 390 - 450oC for 30-80 h) and removal of boiling liquid fractions in the intermediate stages of polymerization.

The invention is illustrated in Fig. 1, 2.

The essence of the method consists in the following: polydimethylsilane load in an inert atmosphere in the reactor with a stirrer and heated with stirring to a temperature of 350 - 380oC. At this temperature the decomposition of polydimethylsilane with the formation of gaseous and liquid products, supporting the pressure in the reactor of 1.5 - 6 bar. After treatment for 2 to 10 hours to produce the reset boiling liquid components in the receiver and maintain the reaction mass under continuous stirring at 390 - 450oC for 30 - 80 hours temperature Below 350oaction consobrina components. The reaction products are dissolved in toluene, hexane or other non-polar solvents, insoluble part is separated by centrifugation and filtration. The filtrate is concentrated under atmospheric pressure and a temperature of 70 - 180oC, then a residual pressure of 1 mm RT.article and the temperature in the mass of up to 360oC. Yield of fibre-forming polycarbosilane from download PDMS is 40 - 50%, softening temperature under inert atmosphere - 180-200oC, the temperature of the fiberizing 210 - 2600oC, the content of hydrogen atoms linked to silicon atom, a certain method, synthesized, is 0.65 - 0.75 wt. % share links HSiC3determined by the method of IR-spectroscopy, of 0.68 to 0.75 (Fig. 1).

The polymers have a narrow distribution of molecular weight (polydispersity of 1.6 to 2.5). The stable formation test data on the device Roscop" 220 - 260oC.

Polycarbosilane obtained by the proposed method consistently are formed on a molding machine of the melt. After heat and heat treatment, the strength of the SiC fibers with a diameter of 8 to 12 microns 270 - 350 kg/mm2.

The example for comparison. In a rocking autoclave V = 10 l, equipped with a thermocouple , manometrically, fill it with argon to Pwt.= 100 ATM and heated with stirring to 500oC. as a result of thermal degradation of polydimethylsilane pressure spontaneously increases to 100 ATM. At a temperature of 500oC and a pressure of 100 atmospheres, the reaction mass was kept for 20 hours After cooling, get polycarbosilane (0.8 kg), dissolved in toluene, the solution is lighten by centrifugation and filtration. The number cocoabased sludge amounted to 0.03 kg (3%).

After removal of the solvent and low-boiling fractions allocate 0.38 kg (38%) of polycarbosilane with temperatures softening and fiberizing, respectively 190 and 230oC, the content of H atoms with Si atoms to 0.73 wt.% (according to the synthesized) and the relative content of HSiC3groups of 0.50 (according to IR-spectroscopy). The average molecular weight of 780, the number of links n = 6, the polydispersity of 4.0, but the curve of the molecular mass distribution of polycarbosilane obtained by the method of gel permeation chromatography (GPC) (Fig. 1, curve (a)) are high molecular weight components (Mz = 20000). The strength of SiC fibers with a diameter of 15 to 20 μm is 150 to 300 kg/mm2.

Example 1. In a standard reactor, equipped with tarmac argon, and nitrogen), load 2 kg of polydimethylsilane and heated under stirring up to 370oC, kept at this temperature for 6 hours, then discharged into the receiver boiling liquid products. Then the temperature was raised to 425oC and kept under stirring for 60 hours the Mass is then cooled, dissolved in toluene, the solution to lighten. The amount of insoluble coke 0.02 kg (1%).

After removal of the solvent and low-boiling components at atmospheric pressure and under vacuum at a residual pressure of 1 mm RT.article and the temperature in pairs to 280oC produce 1 kg (50% yield) of polycarbosilane with temperatures softening 190oC and fiberizing 230oC, the content of H atoms with Si of 0.68%, and the share of HSiC30,70. The polydispersity of the polymer is 1.7, Mn = 940, n = 7, Mz = 3100 (Fig. 2, curve b). The area of the molding according to the rheology 220 - 260oC.

The formation occurs without breaks and gas. After oxidation and pyrolysis get SiC fibers with a diameter of 8 to 12 microns and an average strength of 270 - 350 kg/mm2.

Other examples are given in the table.

Thus polycarbosilane synthesized by the proposed method are soluble, fusible polymers that are easily n the C fibers.

The method is simple, requires no special equipment and expensive initiating additives.

Proceeding from the known views about the process of turning PDMS in the PCB, it was considered impossible to perform a complete thermal rearrangement otherwise than with the use of initiators or high pressure.

Obtain this effect it is proposed should be considered by surprise, and the proposed solution meets the criterion of "inventive step".

The method of receiving polycarbosilane by thermal decomposition of polydimethylsilane in an inert atmosphere, wherein thermal decomposition is carried out at a gauge pressure of 1.5 - 6 ATM in three stages: exposure at 350 - 380oC for 2 to 10 h, the reset boiling components and subsequent exposure at 390 - 450oWith over 30 - 80 hours

 

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