CN113461951B - Preparation method of low-oxygen high-purity polycarbosilane - Google Patents
Preparation method of low-oxygen high-purity polycarbosilane Download PDFInfo
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- CN113461951B CN113461951B CN202110958994.8A CN202110958994A CN113461951B CN 113461951 B CN113461951 B CN 113461951B CN 202110958994 A CN202110958994 A CN 202110958994A CN 113461951 B CN113461951 B CN 113461951B
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- polycarbosilane
- polydimethylsilane
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/60—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule in which all the silicon atoms are connected by linkages other than oxygen atoms
Abstract
A preparation method of low-oxygen high-purity polycarbosilane comprises the following steps: melting alkali metal by using an organic solvent, and dropwise adding dimethyldichlorosilane to generate polydimethylsilane; reacting the residual reactant with anhydrous alcohol, and filtering to remove the solvent; washing alkali metal chloride and hydroxide, and filtering to obtain crude polydimethylsilane; vacuumizing to remove moisture and siloxane to obtain refined polydimethylsiloxane; cracking polydimethylsilane at normal pressure and high temperature to collect fractions; the polycarbosilane is synthesized by distillation under normal pressure and high temperature. The invention vacuumizes the polydimethylsilane to remove moisture and siloxane and reduce the oxygen content of the polydimethylsilane; the polydimethylsilane is cracked at high temperature, collected and subjected to fraction synthesis, so that the branching degree of the polycarbosilane and the content of alkali metal and free carbon are reduced, and the high purity of the polycarbosilane is ensured. The number average molecular weight of the prepared polycarbosilane is 600-1500, the oxygen content is 0.05-0.6 wt%, and the alkali metal content is lower than 25 ppm.
Description
Technical Field
The invention relates to the field of ceramic precursor materials, in particular to a preparation method of low-oxygen high-purity polycarbosilane.
Background
Silicon carbide (SiC) ceramic materials have low specific gravity, creep resistance, corrosion resistance, high strength, high hardness, high temperature resistance, and excellent high temperature oxidation resistance, and are widely used in various extreme environments. The SiC fiber is a main reinforcing material in a heat engine component due to high strength and unique high-temperature oxidation resistance, and is widely applied to the fields of aircraft engine supercharged turbines, rocket engine combustion chambers, aircraft head materials and the like. The SiC/SiC fiber reinforced composite material is a perfect high-temperature oxidation-resistant weight-reduction reinforced material. Therefore, SiC ceramic materials are highly regarded by the material world.
The silicon carbide (SiC) ceramic material is prepared by synthesis, non-melting treatment and pyrolysis ceramming conversion of precursor polycarbosilane. The excellent high-temperature oxidation resistance and mechanical property of the silicon carbide (SiC) ceramic material are mainly influenced by oxygen and impurities. Oxygen begins to slowly react with Si-C at a temperature of over 1000 ℃, so that the structure of the silicon carbide (SiC) ceramic material is damaged, and the mechanical property is reduced. Oxygen is divided into oxygen-containing precursor polycarbosilane and externally introduced. The impurities are precursor polycarbosilane impurities, mainly precursor reactant alkali metal residues and free carbon generated in the reaction process. The impurities and the ceramics have interface defects between different phases. Meanwhile, in the polycarbosilane ceramization process, impurities cause rapid nucleation and increase of local beta-SiC microcrystals at high temperature, so that the brittleness difference in the ceramics is large. These all reduce the mechanical properties of the silicon carbide (SiC) ceramic material. The impurities have a particularly significant effect on the mechanical properties of the silicon carbide fibers. Therefore, the preparation of the polycarbosilane with low oxygen content and high purity, so as to obtain the silicon carbide (SiC) ceramic material with low oxygen content and high purity, becomes the key for improving the high-temperature oxidation resistance and the mechanical property of the silicon carbide (SiC) ceramic material.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a preparation method of low-oxygen high-purity polycarbosilane, wherein the prepared polycarbosilane has the number average molecular weight of 600-1500, the oxygen content of 0.05-0.6 wt% and the alkali metal content of less than 25 ppm.
In order to achieve the purpose, the invention adopts the following technical scheme:
1) melting alkali metal by using an organic solvent, and dropwise adding dimethyldichlorosilane to generate polydimethylsilane;
wherein M represents alkali metals Na and K.
The organic solvent is preferably toluene (boiling point 110.4 ℃) or xylene (boiling point 137-140 ℃).
In this step, polydimethylsilane (CH3SiCH3) was formed as the main intermediate n And alkali metal by-product MCl. Polydimethylsilane (CH3SiCH3) n Is a powdery white particle insoluble in any solvent, and the cracking temperature is above 320 ℃.
2) Reacting the residual reactant with anhydrous alcohol, and filtering to remove the organic solvent;
due to the isolation of the polydimethyl silane particles, the reactants polydimethyl dichlorosilane and alkali metal are difficult to react sufficiently. The residual reactants react with alcohol respectively to lose activity, reduce danger and facilitate treatment.
(CH 3 ) 2 Si(Cl) 2 +2ROH→(CH 3 ) 2 Si(OR) 2 +2HCl
2M+2ROH→ROM+H 2 ↑
ROH represents an alcohol. Methanol CH is preferred 3 OH (boiling point 64.7 ℃), by-product (CH) being formed 3 ) 2 Si(O CH 3 ) 2 Boiling point of 81.4 ℃. Preferably ethanol C 2 H 5 OH (boiling point 78 ℃ C.), by-product (CH) 3 ) 2 Si(O C 2 H 5 ) 2 The boiling point of (b) is 114 ℃. The alkali metal reacts with ROH to form an alkoxide.
3) Washing by-products of alkali metal chloride, hydroxide and alcohol by pure water, and filtering to obtain crude polydimethylsilane;
(CH 3 ) 2 Si(OR) 2 +2H 2 O→(CH 3 ) 2 Si(OH) 2 +2ROH
ROM+H 2 O→MOH+ROH
(CH 3 ) 2 Si(OR) 2 hydrolysis to form (CH) 3 ) 2 Si(OH) 2 Boiling point 122.2+23 ℃; (CH) 3 ) 2 Si(OH) 2 Condensation of the majority to form siloxanes [ C ] 2 H 6 SiO] n . Siloxane [ C ] 2 H 6 SiO] n The polymer is a complex polymer system, the appearance of the polymer system is colorless transparent or yellowish liquid, and the boiling point of the main component is 155-220 ℃; the alkali metal alkoxide is hydrolyzed to form an alkali metal hydroxide and an alcohol.
The chloride and hydroxide produced as by-products of alkali metal are mainly dissolved in pure water and removed by filtration.
4) Vacuumizing the crude polydimethylsilane in a cracking kettle at RT-320 ℃, specifically, heating at a heating rate of 0.1-2 ℃/min, preserving the temperature at 220-320 ℃ for 1-36 h, and removing water and siloxane;
siloxane [ C ] as a by-product of dimethyldichlorosilane production 2 H 6 SiO] n The boiling point is 155-220 ℃. Small amount of by-product H remained in the intermediate process 2 O、ROH、(CH 3 ) 2 Si(OR) 2 、(CH 3 ) 2 Si(OH) 2 The boiling points are all below 155 ℃. These oxygen-containing by-products can be removed by distillation under reduced pressure, which is characterized by a low boiling point. The residual solvent toluene or xylene was distilled off under reduced pressure.
5) At normal pressure N 2 Or cracking at high temperature in Ar atmosphere and collecting fractions at 320-450 ℃;
because of the instability of the high molecular polymer, a small amount of poor-quality polydimethylsiloxane is cracked into cyclic silane before the temperature is lower than 320 ℃. The low molecular weight of the cyclic silane accounts for a large amount, and the cyclic silane is more easily heated and cracked into free carbon in high-temperature synthesis, so that the purity of the polycarbosilane is reduced. Most of the free carbon is dispersed in the polymeric silane in submicron particles, and the free carbon cannot be completely separated by filtration. The content of free carbon of submicron pole is usually far lower than 1%, relative to the carbon content of polycarbosilane about 40% and the detection error of carbon content of 5% of the oxygen carbon instrument, it is difficult to distinguish specifically by using the oxygen carbon instrument to measure data. In actual production, the more free carbon contained in polycarbosilane, the more the block-shaped appearance color gradually changes from colorless transparency to dark transparency. The content of free carbon in the polycarbosilane can be preliminarily judged through the block color of the polycarbosilane. In addition, the low molecular weight cyclosilane participates in the synthesis reaction, so that short branched chains of the polycarbosilane are increased, and the quality of the polycarbosilane is reduced. Therefore, the fraction below 320 ℃ for cracking polydimethylsilane is not excluded.
After the polydimethyl silane is cleaned by pure water, a small amount of alkali metal chloride and hydroxide still remain in the powder. Since both alkali chlorides and hydroxides have boiling points above 1000 c, they are not distilled at 450 c. Through the high-temperature pyrolysis of the polydimethylsiloxane, fractions at 320-450 ℃ are collected, and the content of alkali metal in the product is lower than 25 ppm.
6) Fraction at normal pressure N 2 Or synthesizing polycarbosilane at 450-520 ℃ in Ar atmosphere for 1-20 h.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. the polydimethylsiloxane is continuously vacuumized at RT-320 ℃, so that the moisture and siloxane containing oxygen components are effectively removed, and the oxygen content of the polycarbosilane is 0.05-0.6%.
2. The 320-450 ℃ fractions are collected by cracking the polydimethylsilane to synthesize the polycarbosilane, low-molecular polymers cracked at the temperature lower than 320 ℃ are excluded from participating in the synthesis reaction, the branching degree of the polycarbosilane and the generation of free carbon are reduced, and the high purity of the polycarbosilane is ensured.
3. The polycarbosilane is synthesized by cracking polydimethylsilane and collecting fractions at 320-450 ℃, so that the content of alkali metal is lower than 25ppm, and the high purity of the polycarbosilane is ensured.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention clearer and more obvious, the present invention is further described in detail below with reference to the following embodiments.
Example 1:
(1) 200 parts of dimethylbenzene and 36 parts of metallic sodium are added into a reaction kettle according to the parts by weight, stirring is started, and the mixture is stirred in N 2 Heating to 110 ℃ under protection, melting the sodium metal, then slowly dropwise adding 100 parts of dimethyldichlorosilane, and curing for 30 hours at 120 ℃.
(2) Transferring the purple black reactant to a filtering kettle, starting stirring, cooling to the temperature below 60 ℃, slowly adding 60 parts of absolute ethyl alcohol, continuously stirring for 5 hours, and filtering to remove the organic solvent.
(3) 300 parts of pure water was added to wash sodium chloride and sodium hydroxide, and filtered to obtain white crude polydimethylsilane.
(4) Transferring the crude polydimethylsiloxane to a cracking kettle, starting stirring, continuously vacuumizing, heating to 250 ℃ at the heating rate of 0.5 ℃/min, keeping vacuumizing for 6h, and removing water and siloxane. The vacuum degree is required to be below-0.1 MPa.
(5) Cracking kettle N 2 And increasing the temperature to 430 ℃ at the heating rate of 1 ℃/min to reach the micro positive pressure, and collecting the fraction at the temperature of 320-420 ℃.
(6) Transferring the distillate to a synthesis kettle at normal pressure N 2 Under protection, slowly raising the temperature from normal temperature to 475 ℃, and reacting at 475 ℃ for 8h to synthesize polycarbosilane.
Example 2:
(1) the same as in example 1.
(2) The same as in example 1.
(3) The same as in example 1.
(4) Transferring the crude polydimethylsiloxane to a cracking kettle, starting stirring, continuously vacuumizing, heating to 280 ℃ at the heating rate of 0.5 ℃/min, keeping vacuumizing for 6h, and removing water and siloxane. The vacuum degree is required to be below-0.1 MPa.
(5) The same as in example 1.
(6) The same as in example 1.
Example 3:
(1) the same as in example 1.
(2) Same as example 1
(3) The same as in example 1.
(4) Transferring the crude polydimethylsiloxane to a cracking kettle, starting stirring, continuously vacuumizing, heating to 300 ℃ at the heating rate of 0.5 ℃/min, keeping vacuumizing for 6h, and removing water and siloxane. The vacuum degree is required to be below-0.1 MPa.
(5) The same as in example 1.
(6) The same as in example 1.
Example 4:
(1) the same as in example 2.
(2) The same as in example 2.
(3) The same as in example 2.
(4) Transferring the crude polydimethylsiloxane to a cracking kettle, starting stirring, continuously vacuumizing, heating to 280 ℃ at the heating rate of 0.5 ℃/min, keeping vacuumizing for 2h, and removing water and siloxane. The vacuum degree is required to be below-0.1 MPa.
(5) The same as in example 2.
(6) The same as in example 2.
Example 5:
(1) the same as in example 2.
(2) Same as example 2
(3) The same as in example 2.
(4) Transferring the crude polydimethylsiloxane to a cracking kettle, starting stirring, continuously vacuumizing, heating to 280 ℃ at the heating rate of 0.5 ℃/min, keeping vacuumizing for 12h, and removing water and siloxane. The vacuum degree is required to be below-0.1 MPa.
(5) The same as in example 2.
(6) The same as in example 2.
Example 6:
(1) the same as in example 2.
(2) The same as in example 2.
(3) The same as in example 2.
(4) The same as in example 2.
(5) The same as in example 2.
(6) Transferring the distillate to a synthesis kettle at normal pressure N 2 Under the protection, slowly heating from normal temperature to 450 ℃, and reacting at 450 ℃ for 8h to synthesize polycarbosilane.
Example 7:
(1) the same as in example 2.
(2) The same as in example 2.
(3) The same as in example 2.
(4) The same as in example 2.
(5) The same as in example 2.
(6) Transferring the distillate to a synthesis kettle at normal pressure N 2 Under protection, slowly raising the temperature from normal temperature to 490 ℃, and reacting at 490 ℃ for 8h to synthesize polycarbosilane.
Example 8:
(1) the same as in example 2.
(2) The same as in example 2.
(3) The same as in example 2.
(4) The same as in example 2.
(5) Cracking kettle N 2 And increasing the temperature to 430 ℃ at the heating rate of 1 ℃/min under the micro-positive pressure, and collecting the fraction at the temperature of 250-420 ℃.
(6) The same as in example 2.
The molecular weight, softening point, oxygen content, appearance color and sodium content of the polycarbosilanes prepared in the examples are shown in Table 1.
TABLE 1
| Molecular weight | Softening point of | Oxygen content% | Color appearance | Sodium content ppm | |
| Example 1 | 1121 | 189.5 | 0.51 | Colorless and transparent | 11 |
| Example 2 | 1007 | 187.1 | 0.32 | Colorless and transparent | 9 |
| Example 3 | 1027 | 184.2 | 0.12 | Colorless and transparent | 12 |
| Example 4 | 1132 | 187.1 | 0.53 | Colorless and transparent | 8 |
| Example 5 | 1115 | 183.5 | 0.17 | Colorless and transparent | 15 |
| Example 6 | 856 | 155.7 | 0.34 | Colorless and transparent | 13 |
| Example 7 | 1413 | 225.7 | 0.33 | Light gray transparent | 11 |
| Example 8 | 1026 | 190.5 | 0.58 | Light gray transparent | 22 |
Analysis from the data above:
1. by adopting the embodiments 1-3, the vacuumizing temperature of the crude polydimethylsiloxane is increased, and the oxygen content of the polycarbosilane is reduced;
2. by adopting the embodiments 4, 2 and 5, the vacuumizing time of the crude polydimethylsilane is prolonged, and the oxygen content of polycarbosilane is reduced;
3. by adopting the embodiments 6, 2 and 7, the synthesis reaction temperature of the fractions is increased, the molecular weight of the polycarbosilane is increased, and the color is gradually changed into light gray and transparent, which indicates that the higher the synthesis temperature is, the more easily the free carbon is generated;
4. by adopting the embodiment 8, the fraction below 320 ℃ is collected for synthesis, the color of polycarbosilane is changed into light gray and transparent, which shows that the fraction below 320 ℃ is collected for synthesis, and free carbon is easier to generate;
5. from the examples, polycarbosilanes were synthesized using the cracked collected fractions with alkali metal contents below 25 ppm.
The method can realize the mass production of the polycarbosilane with low oxygen content and high purity. The number average molecular weight of the polycarbosilane is 600-1500, the oxygen content is 0.05% -0.6%, and the alkali metal content is lower than 25 ppm.
Claims (8)
1. A preparation method of low-oxygen high-purity polycarbosilane is characterized by comprising the following steps:
1) melting alkali metal at high temperature by using an organic solvent, and then dropwise adding dimethyldichlorosilane to generate polydimethylsilane;
2) reacting the residual reactant with anhydrous alcohol, and filtering to remove the organic solvent;
3) washing alkali metal chloride and hydroxide with pure water, and filtering to obtain crude polydimethylsilane;
4) vacuumizing the crude polydimethylsilane in a cracking kettle at RT-320 ℃ to remove moisture and siloxane to obtain refined polydimethylsilane;
5) carrying out normal-pressure high-temperature pyrolysis on the refined dimethyl silane and collecting fractions;
6) synthesizing polycarbosilane from the distillate in a synthesis kettle at normal pressure and high temperature;
in step 5), polydimethylsilane is heated at normal pressure and high temperature N 2 Or cracking in Ar atmosphereDecomposing, and collecting fractions at 320-450 ℃ for synthesis;
the alkali metal content of the polycarbosilane prepared by the method is lower than 25 ppm.
2. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: the polycarbosilane prepared by the method has the number average molecular weight of 600-1500.
3. The method for preparing high-purity polycarbosilane with low oxygen content as claimed in claim 1, wherein the method comprises the following steps: the oxygen content of the polycarbosilane prepared by the method is 0.05 wt% -0.6 wt%.
4. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: in the step 4), the crude polydimethylsilane is continuously vacuumized in a cracking kettle at RT-320 ℃, the temperature is raised at the heating rate of 0.1-2 ℃/min, and the temperature is kept at 220-320 ℃ for 1-36 h.
5. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: in step 6), the fraction is at normal pressure N 2 Or synthesizing polycarbosilane at high temperature in Ar atmosphere, wherein the highest synthesis temperature is 450-520 ℃, and the synthesis time is 1-20 h.
6. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: in step 1), the organic solvent includes toluene and xylene.
7. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: in step 1), the alkali metal includes sodium and potassium.
8. The method for preparing high-purity polycarbosilane with low oxygen content according to claim 1, wherein the method comprises the following steps: in step 2), the anhydrous alcohol includes methanol and ethanol.
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| CN112608481A (en) * | 2020-11-24 | 2021-04-06 | 福建立亚化学有限公司 | Polycarbosilane material and preparation method thereof |
| CN113248720A (en) * | 2021-04-29 | 2021-08-13 | 福建立亚化学有限公司 | Spinnable polycarbosilane and preparation method thereof |
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| US4220600A (en) * | 1977-10-26 | 1980-09-02 | The Foundation: The Research Institute For Special Inorganic Materials | Polycarbosilane, process for its production, and its use as material for producing silicon carbide fibers |
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| CN109942818A (en) * | 2019-03-06 | 2019-06-28 | 福建立亚化学有限公司 | A kind of high-purity polydimethylsiloxane pre-ceramic materials and preparation method thereof |
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