Method for preparing polycarbosilane by catalytic rearranging

Abstract

This invention provides a method for preparing a polycarbosilane by decomposition and rearrangement a cyclic silane compound or chain polysilane under the catalysis of a boron-containing catalyst in a trace amount (less than 1 wt %). In the method, poly(dimethylsilane) (denoted as PDMS) or a thermal decomposition product thereof, i.e., a liquid silane-carbosilane compound (denoted as LPS), is used as the raw material, less than 1 wt % of the boron-containing catalyst (with respect to the amount of the raw material) is added, and then the temperature is gradually increased to the reaction temperature under atmospheric pressure or high pressure to perform the thermal decomposition/rearrangement reaction so as to obtain solid polycarbosilane (PCS) with a higher ceramic yield. This method has advantages, such as short reaction time, high synthetic yield, good product quality, simple equipment and safe operation; and the polycarbosilane prepared is a polymeric precursor for SiC, and can be used for the preparation of SiC fibers and SiC-based composite materials.

Claims

1. A method for preparing a polycarbosilane, comprising: mixing a raw material with a boron-containing catalyst to obtain a reaction mixture; heating the reaction mixture under atmospheric pressure or an elevated pressure to obtain polycarbosilane (PCS), wherein the raw material is poly(dimethylsilane) (PDMS) or a liquid silane-carbosilane compound (LPS), and wherein the boron-containing catalyst is a compound of formula (1) or a complex the compound of formula (1) with ether or water,
B(C.sub.6R.sub.5).sub.3(1) wherein, each R group is independently H, halogen, or a C1-C4 alkyl group.

2. The preparation method of claim 1, wherein said reaction temperature is 365-400 C.

3. The preparation method of claim 2, wherein a reaction time is 1-10 hours.

4. The preparation method of claim 1, wherein an amount of the boron-containing catalyst is less than 1 wt % based on a total mass of the raw material.

5. The preparation method of claim 4, further comprising: distilling the reaction mixture under atmospheric pressure to remove low molecular weight compounds.

6. The preparation method of claim 4, wherein the amount of the boron-containing catalyst is less than 0.5 wt %.

7. The preparation method of claim 4, wherein the amount of the boron-containing catalyst is 0.05-0.3 wt %.

8. The preparation method of claim 1, wherein each R is independently selected from the group consisting of H, F, Cl, Br, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl.

9. The preparation method of claim 1, wherein the boron-containing catalyst is tri(pentafluorophenyl)borane (B(C.sub.6F.sub.5).sub.3) or a complex thereof with ether or water, said complex is B(C.sub.6F.sub.5).sub.3.H.sub.2O, B(C.sub.6F.sub.5).sub.3.Et.sub.2O, B(C.sub.6F.sub.5).sub.3.CH.sub.3OCH.sub.2CH.sub.2OCH.sub.3.

10. The preparation method of claim 9, wherein the boron-containing catalyst is tri(pentafluorophenyl)borane (B(C.sub.6F.sub.5).sub.3).

11. The preparation method of claim 1, further comprising heating PDMS to obtain LPS.

12. The preparation method of claim 1, wherein said reaction temperature is 375-395 C.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a .sup.1H-NMR spectrum of the raw material LPS.

(2) FIG. 2 is a .sup.29Si-NMR spectrum of the raw material LPS.

(3) FIG. 3 is a GC-MS spectrum of the raw material LPS.

(4) FIG. 4 is the thermo-gravimetric curves of PCS-D1 (COMPARATIVE EXAMPLE 1) and PCS-D2 (COMPARATIVE EXAMPLE 2).

(5) FIG. 5 is a .sup.1H-NMR spectrum of PCS-D1 (COMPARATIVE EXAMPLE 1).

(6) FIG. 6 is a .sup.1H-NMR spectrum of PCS-D2 (COMPARATIVE EXAMPLE 2).

(7) FIG. 7 is the .sup.29Si-NMR spectra of PCS-D1 (COMPARATIVE EXAMPLE 1) and PCS-D2 (COMPARATIVE EXAMPLE 2).

(8) FIG. 8 is a .sup.1H-NMR spectrum of PCS-S1 (EXAMPLE 1).

(9) FIG. 9 is a .sup.29Si-NMR spectrum of PCS-S1 (EXAMPLE 1).

(10) FIG. 10 is the FTIR spectra of PCS-S1 (EXAMPLE 1) and the raw material LPS.

(11) FIG. 11 is a thermo-gravimetric curve of PCS-S1 (EXAMPLE 1).

DETAILED DESCRIPTION OF VARIOUS EXAMPLES

(12) Hereinafter, the present invention will be illustrated with reference to the specific examples. However, these examples are not a limitation to the protection scope of the present invention. Those skilled in the art should recognize that many changes and modifications based on the above-described examples belong to the protection scope of the present invention.

Preparation Example 1 (Preparation of the Raw Material LPS)

(13) The solid PDMS powder (1200 g) was added to a 3 L three-necked reactor, evacuated and purged with argon or nitrogen to remove air three times, and then under argon gas stream protection, heated with heating units up to 390-420 C., thermal decomposed and distilled to give a colorless, transparent liquid silane (LPS) (about 1080 g). The .sup.1H-NMR, .sup.29Si-NMR, GC-MS and FTIR spectra are shown in FIG. 1-3 and FIG. 10(a), respectively. The result of the characterization indicates that LPS is a complex mixture composed of more than 20 kinds of silanecarbosilane ring molecules and small amounts of linear small molecules. The molecular structure can be represented by [(SiMe.sub.2).sub.0.7 (CH.sub.2SiMeH).sub.0.3].

Comparative Example 1

(14) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 200 g of the liquid LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor; (3) The temperature in the reactor was heated up to 430 C. by means of programmed temperature, and kept for 8 hours at the temperature, the total reaction time was about 51 hours; (4) Cooled to room temperature, changed to the distillation apparatus. The low-boiling products were removed at 360 C. by distillation. After cooled, 105 g of a pale yellow PCS product (denoted as PCS-D1) was obtained, which the synthetic yield of 52.5% and the ceramic yield of 35.5%, as shown in FIG. 4. The melting point of PCS-D1 is 135-150 C., and the NMR spectra are shown in FIG. 5 and FIG. 7.

Comparative Example 2

(15) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 200 g of the liquid LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor; (3) The temperature in the reactor was heated up to 450 C. by means of programmed temperature, and kept for 4 hours at the temperature. The total time was about 64 hours; (4) Cooled to room temperature, xylene was added to dissolve the mixture, filter, and remove the insoluble substances; (5) The filtrate was distilled at 360 C., then the solvent and the low-boiling products were removed. After cooled, 96 g of a pale yellow PCS product (denoted as PCS-D2) was obtained, which the synthetic yield of 48% and the ceramic yield of 56.7%, as shown in FIG. 4. The melting point of PCS-D2 is 200-210 C., and the NMR spectra are shown in FIG. 6 and FIG. 7.

(16) Compared to the spectra of the raw material LPS, the content of SiH/CH in .sup.1H-NMR spectra is increased from 0.05 to 0.096, i.e., the content of SiH has doubled, and the SiSi bond disappears.

Example 1

(17) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.38 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.20 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 395 C. by 35 hours, and reacting for 5 hours at the temperature, the total reaction time was 40 hours; (6) Cooled to room temperature, 131.89 g of a crude product was obtained, and then the crude product was heated to 370 C. and the low molecular weight components were removed by distillation; (7) after cooled to room temperature, 122.31 g of a product was obtained.

(18) The synthesis yield of the PCS crude product of this example is 69.4%, the yield of the final product (PCS-S1) is 64.4%. As shown in the thermal gravimetric (TGA) curve in FIG. 11, the ceramic yield of PCS-S1 is 70.5%. The melting point of PCS-S1 is 235-250 C. The ratio of the peak area of CH and SiH shown in FIG. 8 and FIG. 9 is 9.25, and the ratio of the peak area of SiC.sub.3H and SiC.sub.4 shown in FIG. 10 is 0.85. Compared to PCS-D2 that is without catalytic rearrangement under atmospheric pressure, the content of the SiH is similar or slightly higher, indicating that the content of the SiH existing in the PCS product catalytically synthesized by the present invention is higher.

(19) As seen in the example above, by catalyzing with a small amount of above-mentioned boron-containing compound, the present invention provides a method for safely and stably converting liquid polysilane into the polycarbosilane, which is a precursor for silicon carbide ceramics. The invention has advantages, such as significantly shorten reaction time, increased synthetic yield, less catalyst, no harmful elements or impurities introduced in the product, good product quality, and so on. The synthesized polycarbosilane product can be used for the preparation of SiC fibres and SiC-based composite materials.

Example 2

(20) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.38 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.20 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 395 C. by 23.5 hours, and reacting for 4 hours at the temperature, the total reaction time was 27.5 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 113.05 g of a product (PCS-S2) was obtained, which the yield of 59.5% and the ceramic yield of 70.5%.

Example 3

(21) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.28 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.15 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 400 C. by 24 hours, and reacting for 2 hours at the temperature, the total reaction time was 26 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 113.05 g of a product (PCS-S3) was obtained, which the yield of 59.5% and the ceramic yield of 73%.

Example 4

(22) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.19 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.10 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 400 C. by 28 hours, and reacting for 3 hours at the temperature, the total reaction time was 31 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 117.8 g of a product (PCS-S4) was obtained, which the yield of 62% and the ceramic yield of 75%.

Example 5

(23) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.19 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.10 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 390 C. by 26 hours, and reacting for 6 hours at the temperature, the total reaction time was 32 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 121.6 g of a product (PCS-S5) was obtained, which the yield of 64% and the ceramic yield of 67%.

Example 6

(24) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 190 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.19 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.10 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 385 C. by 27 hours, and reacting for 9 hours at the temperature, the total reaction time was 36 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 131.2 g of a product (PCS-S6) was obtained, which the yield of 69% and the ceramic yield of 62%.

Example 7

(25) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 200 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.1 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.05 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 395 C. by 30 hours, and reacting for 8 hours at the temperature, the total reaction time was 38 hours; (6) The low molecular weight components were removed by distillation at 370 C.; (7) After cooled to room temperature, 118 g of a product (PCS-S7) was obtained, which the yield of 70% and the ceramic yield of 62%.

Example 8

(26) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 200 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.4 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.20 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 365 C. by 28 hours, and reacting for 8 hours at the temperature, the total reaction time was 36 hours; (6) The low molecular weight components were removed by distillation at 360 C.; (7) After cooled to room temperature, 125.2 g of a product (PCS-S8) was obtained, which the yield of 62.6% and the ceramic yield of 60%.

Example 9

(27) Experimental procedures: (1) The synthesis apparatus for decomposition and rearrangement under atmospheric pressure was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 200 g of the LPS prepared in PREPARATION EXAMPLE 1 was added in the reactor, and then introducing 0.4 g of the B(C.sub.6F.sub.5).sub.3 catalyst (0.20 wt % with respect to the amount of LPS) with stirring; (3) Programmed temperature, which heating up to 385 C. by 28 hours, and reacting for 5 hours at the temperature, the total reaction time was 33 hours; (4) The low molecular weight components were removed by distillation at 360 C.; (5) After cooled to room temperature, 131.2 g of a product (PCS-S9) was obtained, which the yield of 65.6% and the ceramic yield of 63%.

Example 10

(28) Experimental procedures: (1) The 2 L high temperature and high pressure reactor was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 900 g of the LPS prepared in PREPARATION EXAMPLE 1 was added, and then introducing 13.5 g of 10 wt % of B(C.sub.6F.sub.5).sub.3 in xylene solution (i.e., containing 0.15 wt % of the catalyst) with stirring; (3) Programmed temperature, which heating up to 375 C. by 4 hours, and reacting for 4 hours at the temperature, the total reaction time was 8 hours, and the maximum pressure during the reaction was 7.5 MPa; (4) Cooled to room temperature, xylene was added to dissolve the mixture, and filtered; (5) The filtrate was transferred into a 3 L three-necked glass flask. At first, the solvent was evaporated at 150-180 C. under the protection of nitrogen, and then heated up to 360 C. under atmospheric pressure or 250 C. under reduced pressure to remove the low molecular weight products by distillation; (7) After cooled to room temperature, 648 g of a product (PCS-S10) was obtained, which the yield of 72% and the ceramic yield of 66%.

Example 11

(29) Experimental procedures: (1) The 2 L high temperature and high pressure reactor with the reflux condenser was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 900 g of the LPS prepared in PREPARATION EXAMPLE 1 was added, and then introducing 9 g of 10 wt % of B(C.sub.6F.sub.5).sub.3 in xylene solution (i.e., containing 0.10 wt % of the catalyst) with stirring; (3) Programmed temperature, which heating up to 395 C. by 4 hours, and reacting for 2 hours at the temperature, the total reaction time was 6 hours, and the maximum pressure during the reaction was 5 MPa; (4) Cooled to room temperature, xylene was added to dissolve the mixture, and filtered; (5) The filtrate was transferred into a 3 L three-necked glass flask, at first, the solvent was evaporated at 150-180 C. under the protection of nitrogen, and then heated up to 360 C. under atmospheric pressure or 250 C. under reduced pressure to remove the low molecular weight products by distillation; (7) After cooled to room temperature, 612 g of a product (PCS-S11) was obtained, which the yield of 68% and the ceramic yield of 68%.

Example 12

(30) Experimental procedures: (1) The 2 L high temperature and high pressure reactor with the reflux condenser was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 900 g of the PDMS powder was added, 1.08 g of B(C.sub.6F.sub.5).sub.3 (0.12 wt %) was added, and then stirred homogenously for 30 minutes; (3) Heating the temperature up to 360 C. by 2 hours, and reacting for 3 hours at the temperature, and then heating the temperature gradually up to 380 C. by 2 hours, and keeping for 3 hours, the total reaction time was 10 hours, and the maximum pressure during the reaction was 5 MPa; (4) Cooled to room temperature, xylene was added to dissolve the mixture, and filtered; (5) The filtrate was transferred into a 3 L three-necked glass flask, at first, the solvent was evaporated at 150-180 C. under the protection of nitrogen, and then heated up to 360 C. under atmospheric pressure or 250 C. under reduced pressure to remove the low molecular weight products by distillation; (7) After cooled to room temperature, 558 g of a product (PCS-S12) was obtained, which the yield of 62% and the ceramic yield of 67%.

Example 13

(31) Experimental procedures: (1) The 2 L high temperature and high pressure reactor with the reflux condenser was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of high purity nitrogen, 900 g of the LPS prepared in PREPARATION EXAMPLE 1 was added, and then introducing 9 g of 10 wt % of B(C.sub.6F.sub.5).sub.3 in xylene solution (i.e., containing 0.10 wt % of the catalyst) with stirring; (3) Programmed temperature, which heating up to 365 C. by 4 hours, and reacting for 5 hours at the temperature, the total reaction time was 9 hours, and the maximum pressure during the reaction was 5 MPa; (4) Cooled to room temperature, xylene was added to dissolve the mixture, and filtered; (5) The filtrate was transferred into a 3 L three-necked glass flask, at first, the solvent was evaporated at 150-180 C. under the protection of nitrogen, and then heated up to 360 C. under atmospheric pressure or 250 C. under reduced pressure to remove the low molecular weight products by distillation; (7) After cooled to room temperature, 643.5 g of a product (PCS-S13) was obtained, which the yield of 71.5% and the ceramic yield of 62%.

Example 14

(32) Experimental procedures: (1) The 2 L high temperature and high pressure reactor with the reflux condenser was evacuated and refilled with high purity nitrogen three times; (2) Under the protection of the high purity nitrogen, 900 g of the LPS prepared in PREPARATION EXAMPLE 1 was added, and introducing 4.5 g of 10 wt % of B(C.sub.6F.sub.5).sub.3 in xylene solution (i.e., containing 0.05 wt % of the catalyst) and 0.9 g of ITQ-2 zeolite powder, and then stirred for 10 minutes; (3) Programmed temperature, which heating up to 380 C. by 3.5 hours, and reacting for 4.5 hours at the temperature, and the total reaction time was 8 hours; (4) Cooled to room temperature, xylene was added to dissolve the mixture, and filtered; (5) The filtrate was transferred into a 3 L three-necked glass flask, at first, the solvent was evaporated at 150-180 C. under the protection of nitrogen, and then heated up to 380 C. under atmospheric pressure to remove the low molecular weight products by distillation; (7) After cooled to room temperature, 675 g of a product (PCS-S14) was obtained, which the yield of 75% and the ceramic yield of 72%.