CN113429574A

CN113429574A - Polycarbosilane and preparation method thereof

Info

Publication number: CN113429574A
Application number: CN202110815846.0A
Authority: CN
Inventors: 王军
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-07-19
Filing date: 2021-07-19
Publication date: 2021-09-24
Anticipated expiration: 2041-07-19
Also published as: CN113429574B

Abstract

The invention discloses polycarbosilane and a preparation method thereof, wherein the preparation method comprises the steps of taking polydimethylsilane as a raw material, firstly carrying out high-temperature pyrolysis on the polydimethylsilane to completely crack the polydimethylsilane into micromolecule polysilane, then carrying out electron beam irradiation on the polysilane, then carrying out pyrolysis rearrangement polymerization on the polysilane subjected to electron beam irradiation to obtain polycarbosilane coarse material, and finally purifying the polycarbosilane coarse material to obtain polycarbosilane. Compared with the prior art, the preparation method provided by the invention obviously shortens the preparation period, improves the yield of polycarbosilane, and reduces the content of byproducts, thereby reducing the preparation cost of polycarbosilane.

Description

Polycarbosilane and preparation method thereof

Technical Field

The invention relates to the technical field of ceramic precursor preparation, in particular to polycarbosilane and a preparation method thereof.

Background

Polycarbosilane (PCS) is an important raw material for preparing silicon carbide (SiC) fibers and ceramic matrix composites by a precursor method, and is mainly synthesized by a high-temperature pyrolysis rearrangement method of Polydimethylsilane (PDMS). In the synthesis process, besides the obtained product PCS, a large amount of liquid byproducts with low molecular weight are generated, so that the yield of PCS is low, the price is high, the use of PCS is restricted, and the liquid byproducts are difficult to directly utilize, easy to combust and can pollute the environment.

Disclosure of Invention

The invention provides polycarbosilane and a preparation method thereof, which are used for overcoming the defects of low yield, more byproducts and the like of polycarbosilane in the prior art.

In order to achieve the purpose, the invention provides a preparation method of polycarbosilane, which comprises the following steps:

s1: performing pyrolysis on polydimethylsilane serving as a raw material in an inert atmosphere to obtain polysilane;

s2: performing electron beam irradiation on the polysilane in an inert atmosphere;

s3: carrying out pyrolysis rearrangement polymerization on the polysilane subjected to S2 in an inert atmosphere, and naturally cooling to obtain polycarbosilane coarse material;

s4: and purifying the polycarbosilane coarse material to obtain polycarbosilane.

In order to achieve the purpose, the invention also provides polycarbosilane prepared by the preparation method.

Compared with the prior art, the invention has the beneficial effects that:

the preparation method of the polycarbosilane provided by the invention takes the polydimethylsilane as a raw material, firstly carries out high-temperature pyrolysis on the polydimethylsilane to ensure that the polydimethylsilane is completely cracked into micromolecular polysilane, then carries out electron beam irradiation on the polysilane to ensure that the micromolecular polysilane is activated to generate a large number of free radicals, then carries out pyrolysis rearrangement polymerization on the polysilane irradiated by the electron beam to obtain polycarbosilane coarse material, and finally carries out purification on the polycarbosilane coarse material to obtain the polycarbosilane. Compared with the prior art, the preparation method provided by the invention increases the free radicals of the micromolecular polysilane, improves the reaction activity, obviously shortens the preparation period, improves the yield of the polycarbosilane, and reduces the content of byproducts, thereby reducing the preparation cost of the polycarbosilane.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.

The drugs/reagents used are all commercially available without specific mention.

The invention provides a preparation method of polycarbosilane, which comprises the following steps:

s1: taking Polydimethylsilane (PDMS) as a raw material, and pyrolyzing the polydimethylsilane in an inert atmosphere to obtain polysilane (LPS);

Preferably, in step S1, the pyrolysis temperature is 300-350 ℃ to ensure complete pyrolysis of the polydimethylsiloxane.

Preferably, in step S2, the beam density of the electron beam is 0.1-1.5 kGy/S for 5-60 min.

Preferably, step S3 is specifically:

and (3) putting the polysilane subjected to the S2 into a reaction kettle with a pyrolysis rearrangement polymerization device, and carrying out pyrolysis rearrangement polymerization on the polysilane under an inert atmosphere.

Preferably, in the process of the pyrolysis rearrangement polymerization of polysilane, the temperature in the reaction kettle is 350-400 ℃, and the temperature in the pyrolysis rearrangement polymerization device is 380-420 ℃; the time for pyrolysis rearrangement polymerization is 2-8 h.

Polymerizing the micromolecular polysilane in a reaction kettle, and breaking and rearranging silicon-silicon bonds into silicon-carbon bonds in a pyrolysis rearrangement device.

Preferably, the inert atmosphere in the steps S1 to S3 is nitrogen or argon with a purity of 99.999%.

Preferably, in step S4, the purification process is specifically:

dissolving the polycarbosilane crude material in dimethylbenzene, filtering, and distilling at normal pressure.

Preferably, the normal pressure distillation is distillation for 1-3 hours at 300-350 ℃ in an inert atmosphere to ensure that the xylene is completely removed.

The invention also provides polycarbosilane prepared by the preparation method.

Preferably, the number average molecular weight of the polycarbosilane is 1500-2500, and the softening point is higher than 150 ℃.

Example 1

The embodiment provides a preparation method of polycarbosilane, which comprises the following steps:

s1: taking polydimethylsilane as a raw material, putting 5000g of PDMS into a cracking reaction kettle with an inlet, outlet and condensation receiving device, vacuumizing to replace high-purity nitrogen, repeating for 3 times, then heating to 300 ℃, and completely cracking the PDMS into LPS.

S2: and putting the obtained LPS into an electron beam irradiation device, vacuumizing to replace high-purity nitrogen, and repeating for 3 times. Starting the electron accelerator, controlling the beam current density to be 0.1kGy/s, irradiating for 60min, and stopping irradiation.

S3: transferring the irradiated LPS into a reaction kettle with a pyrolysis rearrangement polymerization device, heating under the protection of high-purity nitrogen, controlling the temperature in the reaction kettle to be 400 ℃, the pyrolysis rearrangement polymerization temperature to be 420 ℃, preserving the temperature for 2h, and naturally cooling to obtain the PCS coarse material.

S4: the crude PCS material was dissolved in xylene, filtered, distilled at 300 ℃ for 1h under the protection of high purity nitrogen and cooled to room temperature to give 3120g of PCS in 62.4 wt% yield. The PCS number average molecular weight of the product is 2180, the softening point is 218-236 ℃, and the PCS number average molecular weight of the product contains 47.87 wt% of Si, 41.93 wt% of C and 10.15 wt% of H.

Example 2

s1: taking polydimethylsilane as a raw material, putting 3000g of PDMS into a cracking reaction kettle with an inlet, outlet and condensation receiving device, vacuumizing to replace high-purity argon, repeating for 3 times, then heating to 350 ℃, and completely cracking the PDMS into LPS.

S2: and putting the obtained LPS into an electron beam irradiation device, vacuumizing to replace high-purity argon, and repeating for 3 times. Starting the electron accelerator, controlling the beam current density to be 1.5kGy/s, irradiating for 5min, and stopping irradiation.

S3: and transferring the irradiated LPS into a reaction kettle with a pyrolysis rearrangement polymerization device, heating under the protection of high-purity argon, controlling the temperature in the reaction kettle to be 350 ℃, the pyrolysis rearrangement polymerization temperature to be 400 ℃, preserving the temperature for 4h, and naturally cooling to obtain the PCS coarse material.

S4: the crude PCS was dissolved in xylene, filtered, distilled at 250 ℃ for 3h under a high purity argon blanket, and cooled to room temperature to give 1978g of PCS in 65.9 wt% yield. The PCS product has the number average molecular weight of 1820 and the softening point of 189-201 ℃, wherein the Si content is 47.25 wt%, the C content is 42.01 wt%, and the H content is 10.48 wt%.

Example 3

s1: taking polydimethylsilane as a raw material, putting 8000g of PDMS into a cracking reaction kettle with an inlet, outlet and condensation receiving device, vacuumizing to replace high-purity nitrogen, repeating for 3 times, heating to 320 ℃, and completely cracking the PDMS into LPS.

S2: and putting the obtained LPS into an electron beam irradiation device, vacuumizing to replace high-purity nitrogen, and repeating for 3 times. Starting the electron accelerator, controlling the beam current density to be 0.5kGy/s, irradiating for 45min, and stopping irradiation.

S3: transferring the irradiated LPS into a reaction kettle with a pyrolysis rearrangement polymerization device, heating under the protection of high-purity nitrogen, controlling the temperature in the reaction kettle to be 380 ℃, keeping the temperature for 6h at the pyrolysis rearrangement polymerization temperature of 380 ℃, and naturally cooling to obtain the PCS crude material.

S4: the crude PCS was dissolved in xylene, filtered, distilled at 280 ℃ for 2h under the protection of high-purity nitrogen, and cooled to room temperature to give 6257g of PCS in 68.2 wt% yield. The PCS product has the number average molecular weight of 1695 and the softening point of 165-180 ℃, wherein the Si content is 47.29 wt%, the C content is 42.16 wt%, and the H content is 10.26 wt%.

Example 4

s1: taking polydimethylsilane as a raw material, putting 5000g of PDMS into a cracking reaction kettle with an inlet, outlet and condensation receiving device, vacuumizing to replace high-purity argon, repeating for 3 times, heating to 350 ℃, and completely cracking the PDMS into LPS.

S2: and putting the obtained LPS into an electron beam irradiation device, vacuumizing to replace high-purity argon, and repeating for 3 times. Starting the electron accelerator, irradiating for 30min with the beam density of 1.0kGy/s, and stopping irradiation.

S3: and transferring the irradiated LPS into a reaction kettle with a pyrolysis rearrangement polymerization device, heating under the protection of high-purity argon, controlling the temperature in the reaction kettle to be 360 ℃, the pyrolysis rearrangement polymerization temperature to be 410 ℃, preserving the temperature for 8 hours, and naturally cooling to obtain the PCS coarse material.

S4: the crude PCS material was dissolved in xylene, filtered, distilled at 260 ℃ for 2h under the protection of high purity argon, and cooled to room temperature to give 3477g of PCS, 69.5 wt% yield. The PCS product has the number average molecular weight of 2050 and the softening point of 196-210 ℃, wherein the Si content is 47.65 wt%, the C content is 42.4 wt%, and the H content is 9.91 wt%.

Comparative example 1

The comparative example provides a method of preparing polycarbosilane, comprising the steps of:

(1) same as example 1, step (1);

(2) and transferring the LPS into a reaction kettle with a high-temperature rearrangement polymerization device, heating under the protection of high-purity nitrogen, controlling the temperature in the reaction kettle to be 400 ℃, the pyrolysis rearrangement polymerization temperature to be 420 ℃, preserving the temperature for 8 hours, and naturally cooling to obtain the PCS coarse material.

(3) The crude PCS was dissolved in xylene, filtered, distilled at 300 ℃ for 1h under the protection of high purity nitrogen and cooled to room temperature to give 1085g of PCS with a yield of 21.7 wt%. The PCS number average molecular weight of the product is 980, the softening point is 120-130 ℃, and the PCS number average molecular weight comprises 46.95 wt% of Si, 42.3 wt% of C and 10.62 wt% of H.

Comparative example 2

Compared with the comparative example 1, the preparation method of polycarbosilane has the advantages that the temperature in the reaction kettle is controlled to be 450 ℃, the pyrolysis rearrangement polymerization temperature is controlled to be 520 ℃ in the step (2), and the temperature is kept for 24 hours. The other procedures were the same as in comparative example 1. This comparative example finally gave 2250g of PCS in a yield of 45 wt%. The PCS number average molecular weight of the product is 2120, the softening point is 205-218 ℃, and the PCS number average molecular weight of the product contains 47.40 wt% of Si, 42.1 wt% of C and 10.25 wt% of H.

As can be seen from the examples 1-4 and the comparative examples 1-2, by adopting the electron beam irradiation and the pyrolysis rearrangement polymerization, the PCS synthesis time is greatly shortened, and the synthesis yield is greatly improved.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the present specification and directly/indirectly applied to other related technical fields within the spirit of the present invention are included in the scope of the present invention.

Claims

1. The preparation method of polycarbosilane is characterized by comprising the following steps:

2. The method according to claim 1, wherein the pyrolysis temperature is 300 to 350 ℃ in step S1.

3. The method according to claim 1, wherein in step S2, the beam current density of the electron beam is 0.1-1.5 kGy/S for 5-60 min.

4. The method according to claim 1, wherein step S3 specifically comprises:

5. The method according to claim 4, wherein the temperature in the reaction vessel is 350 to 400 ℃ and the temperature in the apparatus for thermal rearrangement polymerization is 380 to 420 ℃ during the thermal rearrangement polymerization of polysilane; the time for pyrolysis rearrangement polymerization is 2-8 h.

6. The method according to any one of claims 1 to 5, wherein the inert gas atmosphere in the steps S1 to S3 is nitrogen or argon having a purity of 99.999%.

7. The method according to claim 1, wherein in step S4, the purification treatment is specifically:

8. The method according to claim 7, wherein the atmospheric distillation is carried out at 300 to 350 ℃ for 1 to 3 hours under an inert atmosphere.

9. Polycarbosilane prepared by the preparation method of any one of claims 1 to 8.

10. The polycarbosilane of claim 9 having a number average molecular weight of between 1500 and 2500 and a softening point greater than 150 ℃.