Polycyclic silane compounds, catalyst systems comprising the same and use in the polymerization of olefins

Abstract

The present application relates to the technical field of olefin polymerization, and discloses polycyclic silane compounds, catalyst systems containing the same and application in olefin polymerization. The polycyclic silane compounds have a bicyclic skeleton structure composed of a nitrogen atom and a silicon atom, carry C1-C10 alkyl substituents on the ring, and the silicon atom is connected with specific methyl or ethyl groups. When the compounds are used as external electron donors of catalysts, the hydrogen response sensitivity of the catalysts can be significantly improved, high catalytic activity and high isotacticity of the polymer can be maintained, and polyolefin products with extremely high melt flow rate and wide molecular weight distribution can be obtained. The present application solves the technical problems of poor hydrogen response of the existing external electron donors, difficulty in balancing high flowability and high isotacticity, and provides a new solution for industrial production of high-performance polyolefin.

Description

Technical Field

[0001] This invention relates to the field of olefin polymerization technology, and more particularly to polycyclic silane compounds, catalyst systems containing them, and their applications in olefin polymerization. Background Technology

[0002] Polyolefin materials, especially polypropylene, are widely used in industry. The market demand for high-flowability, high-isotacticity high-end products is increasing, and the external electron donor in the Ziegler-Natta catalyst system is the core for regulating polymer performance. Existing organosilane external electron donors, such as D-Donor and U-Donor, generally suffer from insufficient hydrogen sensitivity, exhibiting excessive coordination with the catalyst's active center and slow response to hydrogen. Even with the addition of significant amounts of hydrogen, achieving high flowability is difficult, and large-scale hydrogen addition increases costs or degrades product performance.

[0003] Meanwhile, existing external electron donors struggle to balance hydrogen sensitivity and isotacticity: some external electron donors lead to decreased isotacticity and excessive xylene-soluble content when improving flowability; others, while maintaining high isotacticity, exhibit extremely poor hydrogen sensitivity. Furthermore, these external electron donors have poor universality with different internal electron donor master catalysts, limiting production flexibility and failing to meet the demands of high-end polypropylene. Summary of the Invention

[0004] The technical problem to be solved by this invention is that the existing technology has the disadvantage of insufficient hydrogen sensitivity, which is not conducive to the production of high-flow polyolefins. To this end, we propose polycyclic silane compounds, catalyst systems containing them, and their application in olefin polymerization.

[0005] To achieve the above objectives, this application adopts the following technical solution: a polycyclic silane compound having a nitrogen-silicon bicyclic skeleton structure, the structure of which is shown below: ; The general structural formula satisfies the following limitations: the bicyclic ring is composed of nitrogen atoms and silicon atoms, and either of the two rings is a five-membered ring, a six-membered ring, or a seven-membered ring, and the substituents on the ring are C1-C10 alkyl groups; R1 and R2 attached to the silicon atom are each independently selected from either methyl or ethyl.

[0006] Preferably, the compound is selected from one of the compounds shown in the following structural formulas: Compound ED1: Bicyclic [3.3.0] silane skeleton, with methyl substituents on the ring, R1 = methyl, R2 = ethyl; structure: ; Compound ED2: Bicyclic [4.3.0] silane skeleton, with ethyl substituents on the ring, R1 = ethyl, R2 = methyl; structure: ; Compound ED3: a bicyclic [5.3.0] silane skeleton with propyl substituents on the ring, R1 = methyl, R2 = methyl; its structure is: ; Compound ED4: a bicyclic [3.4.0] silane skeleton with butyl substituents on the ring, R1 = ethyl, R2 = ethyl; its structure is as follows: .

[0007] This invention proposes another technical solution: a catalyst system of polycyclic silane compounds, comprising: The solid catalyst component comprises a titanium compound supported on a magnesium chloride support, and optionally an internal electron donor. The catalyst is an alkylaluminum compound; External electron donor, which is a polycyclic silane compound.

[0008] Preferably, the internal electron donor is selected from at least one of ester compounds, ether compounds, and amide compounds; wherein the ester compound is selected from at least one of diisobutyl phthalate, succinate, and glycol ester, the ether compound is selected from 1,3-dimethoxypropane, and the amide compound is selected from N,N-dimethylformamide.

[0009] Preferably, the co-catalyst is selected from at least one of triethylaluminum and triisobutylaluminum, and is used in the form of an alkylaluminum solution at a concentration of 0.5 to 2.0 mol / L.

[0010] Preferably, in the catalyst system, the molar ratio of the external electron donor to the titanium element in the solid catalyst component is 10:1 to 200:1; and the molar ratio of the aluminum element in the co-catalyst to the titanium element in the solid catalyst component is 20:1 to 500:1.

[0011] This invention proposes another technical solution: an olefin polymerization method using a polycyclic silane compound catalyst system, comprising the following steps: S1: Under an inert atmosphere of nitrogen or argon with a water content ≤1ppm and an oxygen content ≤1ppm, the solid catalyst components, the co-catalyst, and the external electron donor are pre-complexed in an inert solvent to obtain a catalyst mixture; S2: An olefin monomer is added to the polymerization reactor, and a catalyst mixture is introduced into the reaction system in the presence of hydrogen. S3: Polymerization reaction is carried out at temperatures ranging from 50°C to 90°C and pressures ranging from 0.5 MPa to 5.0 MPa; S4: After the reaction is complete, release the pressure, cool down, and recover the generated polymer.

[0012] Preferably, the olefin monomer is propylene; the amount of hydrogen added is from 0.05 wt% to 2.0 wt% relative to the total mass of the propylene monomer.

[0013] Preferably, the inert solvent for pre-complexation is hexane or heptane, the pre-complexation temperature is 10°C to 40°C, and the pre-complexation time is 2 to 30 minutes.

[0014] The technical effects and advantages of this invention are as follows: In this invention, a nitrogen-silicon bicyclic framework structure and C1-C10 alkyl-substituted polycyclic silane compounds are used as external electron donors. This successfully solves the problems of insufficient hydrogen sensitivity and difficulty in balancing high fluidity and high isotacticity in existing external electron donors. The structure forms a suitable coordination strength with the active center of the catalyst, thereby significantly improving the response efficiency of the catalytic system to hydrogen. This allows for the production of highly fluid polyolefin products with the same amount of hydrogen, perfectly meeting the production requirements of high-end, high-fluidity grades. While imparting extremely high hydrogen sensitivity, this structure can still maintain the high isotacticity of the polymer, ensuring the excellent mechanical properties of the product. Attached Figure Description

[0015] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a diagram of the polymerization method of the present invention. Detailed Implementation

[0016] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0017] like Figure 1 As shown, the present invention provides a technical solution: preparation of polycyclic silane compounds: Preparation of compound ED1 (bicyclo[3.3.0] aziridine, with methyl substituents on the ring, R1=methyl, R2=ethyl): In the intermediate synthesis step, a 500 mL three-necked flask was fixed in a dry ice-acetone low-temperature bath, and nitrogen gas was introduced to replace the flask three times. Then, 100 mL of anhydrous diethyl ether was added. Magnetic stirring was turned on at a speed of 300 r / min, and the mixture was cooled to -78 °C. 20 mmol of bicyclic [3.3.0]nitrosilane precursor, i.e., a diethyl ether solution with methyl substituents on the ring, was slowly added dropwise. The concentration of the diethyl ether solution was 0.2 mol / L, and the dropping rate was 1 mL / min. After the addition was completed, stirring was continued for 10 minutes to allow the precursor to dissolve completely. Maintaining a temperature of -78°C, 22 mmol of methyllithium in diethyl ether was slowly added dropwise through a constant-pressure dropping funnel at a rate of 1 drop / second. During the addition, the solution color was observed to change from colorless to pale yellow. After the addition was completed, the low-temperature bath was turned off, and the reaction system was allowed to naturally warm up to room temperature of 25°C. Stirring was continued for 4 hours to obtain a solution containing silicon anion intermediates. In the substitution reaction step, 22 mmol of ethyl bromide in diethyl ether solution (concentration 0.5 mol / L) was slowly added dropwise to the above intermediate solution under stirring at room temperature. During the addition, a white lithium bromide precipitate was formed. After the addition was complete, the reaction system was heated to 40°C, connected to a reflux condenser, and refluxed for 6 hours. The reaction progress was monitored by TLC. The reaction was complete when the developing solvent was n-hexane / diethyl ether = 10:1 and Rf = 0.6.

[0018] After the post-treatment and purification steps were completed, the reaction solution was cooled to room temperature and filtered through a sintered glass funnel under an inert atmosphere to remove lithium bromide precipitate. The filtrate was collected and transferred to a rotary evaporator, where it was concentrated at 30°C and 0.08 MPa vacuum for 2 hours to remove anhydrous diethyl ether, yielding a pale yellow oily crude product. The crude product was loaded onto a silica gel column for chromatography, using n-hexane / diethyl ether (10:1 v / v) as the eluent at a flow rate of 2 mL / min. The elution process was monitored by TLC, and the target fraction with Rf = 0.6 was collected. The target fraction was then concentrated again under vacuum at 30°C and 0.09 MPa and dried for 2 hours to obtain a colorless, transparent liquid product ED1 with a yield of 78%.

[0019] Preparation of compound ED2 (bicyclic [4.3.0] aziridine, with ethyl substituents on the ring, R1=ethyl, R2=methyl): In the intermediate synthesis step, under nitrogen protection, 120 mL of anhydrous diethyl ether was added to a 500 mL three-necked flask and cooled to -60 °C in a dry ice-acetone low-temperature bath. 20 mmol of bicyclic [4.3.0]nitrosilane precursor, i.e., a diethyl ether solution with ethyl substituents on the ring, was added dropwise with stirring. After the addition was complete, the mixture was stirred for 15 minutes. Then, 22 mmol of hexane solution of ethyl lithium was added dropwise at 1 drop / second. After the addition, the reaction was maintained at -60 °C for 30 minutes, and then the temperature was raised to room temperature and stirred for 3 hours.

[0020] In the substitution reaction step, 22 mmol of methyl bromide in diethyl ether solution with a concentration of 0.5 mol / L was added dropwise at room temperature. After the addition, the temperature was raised to 45 °C and refluxed for 5 hours. The reaction was monitored by TLC until it was complete (Rf=0.55).

[0021] The post-processing and purification steps involved filtration to remove lithium bromide, followed by concentration of the filtrate and purification by silica gel column chromatography with an eluent ratio of n-hexane / diethyl ether of 8:1. The target fraction was collected and dried under vacuum to obtain a colorless liquid, ED2, with a yield of 75%.

[0022] Preparation of compound ED3 (bicyclo[5.3.0] nitrosilane, with propyl substituents on the ring, R1=methyl, R2=methyl): In the intermediate synthesis step, under nitrogen protection, 110 mL of anhydrous diethyl ether was added to a 500 mL three-necked flask, cooled to -40 °C, and 20 mmol of bicyclic [5.3.0]nitrosilane precursor, i.e., the propyl substituent on the ring, was added. After stirring to dissolve, 22 mmol of diethyl ether solution of methyl lithium was added dropwise. After the addition, the temperature was raised to room temperature and stirred for 5 hours.

[0023] In the substitution reaction step, 22 mmol of methyl bromide in diethyl ether was added dropwise at room temperature, and the mixture was heated to 50 °C and refluxed for 7 hours. The reaction was monitored by TLC until it was complete (Rf=0.62).

[0024] After post-processing and purification, the sample was filtered, concentrated, and purified by silica gel column chromatography with an eluent of n-hexane / diethyl ether = 12:1, yielding a colorless liquid ED3 with a yield of 72%.

[0025] Preparation of compound ED4 (bicyclic [3.4.0] silane, with butyl substituents on the ring, R1=ethyl, R2=ethyl): In the intermediate synthesis step, under nitrogen protection, 130 mL of anhydrous diethyl ether was added to a 500 mL three-necked flask, cooled to -50 °C, and 20 mmol of bicyclic [3.4.0] nitrosilane precursor with butyl substituent on the ring was added. After stirring to dissolve, 22 mmol of hexane solution of ethyl lithium was added dropwise. After the addition, the reaction was maintained at -50 °C for 1 hour, and then the temperature was raised to room temperature and stirred for 4 hours.

[0026] In the substitution reaction step, 22 mmol of ethyl bromide in diethyl ether solution was added dropwise at room temperature, and the mixture was heated to 48 °C and refluxed for 6 hours. The reaction was monitored by TLC until it was complete (Rf=0.58).

[0027] After post-processing and purification, the sample was filtered, concentrated, and purified by silica gel column chromatography with an eluent of n-hexane / diethyl ether = 9:1, yielding a colorless liquid ED4 with a yield of 70%.

[0028] Preparation steps of the catalyst system: S1. Add 200 mL of anhydrous ethanol to a 1 L four-necked flask, heat to 70 °C under nitrogen protection, turn on mechanical stirring at a rate of 200 r / min, slowly add 40 g of anhydrous magnesium chloride, stir for 30 minutes until the magnesium chloride is completely dissolved, forming a transparent magnesium chloride-ethanol complex solution. S2. Maintain 70℃, add 10 mmol of diisobutyl phthalate to the solution, and continue stirring for 1 hour to allow the internal electron donor to fully coordinate with magnesium chloride; then cool the solution to 30℃, and slowly add 100 mL of titanium tetrachloride through a constant pressure dropping funnel at a dropping rate of 0.5 mL / min. A white flocculent precipitate is generated during the dropping process. S3. After the addition is complete, heat to 110℃ and reflux for 4 hours. After the reaction is complete, cool to room temperature, filter with a sintered glass funnel, collect the solid product, wash 3 times with anhydrous hexane, 100 mL each time, until no chloride ions are detected in the washing solution, i.e. no white precipitate is found when tested with silver nitrate solution. S4. Place the washed solid in a vacuum drying oven and dry it at 60°C and 0.09 MPa for 2 hours to obtain a light yellow powder solid catalyst component, in which the titanium content is 2.5 wt%.

[0029] Preparation of co-catalysts: Triethylaluminum was selected as the co-catalyst and prepared as follows: Under nitrogen protection, 100 mL of anhydrous heptane was added to a 250 mL Schlenk flask, and 0.1 mol of triethylaluminum (purity ≥98%) was slowly added while stirring. The mixture was stirred for 30 minutes until completely dissolved to obtain a 1.0 mol / L triethylaluminum heptane solution. After sealing, the solution was stored in a 0℃ refrigerator and brought to room temperature before use.

[0030] Preparation of the catalyst system: The molar ratio of external electron donors ED1-ED4 to titanium in the solid catalyst component is 50:1. The molar ratio of aluminum in the co-catalyst triethylaluminum to titanium in the solid catalyst component is 100:1. In the pre-complexation step, the following ingredients were added sequentially to a 25 mL Schlenk flask under nitrogen protection: 6mg solid catalyst component; 0.75 mL of a 1.0 mol / L triethylaluminum heptane solution; 1.1 mL of an anhydrous hexane solution with a concentration of 0.05 mol / L was sealed and placed in a constant temperature water bath at 25 °C. The mixture was stirred for 5 minutes at a rate of 200 r / min to obtain a homogeneous catalyst mixture.

[0031] Olefin polymerization methods: Step 1: Pretreatment of the polymerization reactor; Heat the polymerization reactor to 120℃, vacuum for 2 hours, cool to room temperature, and purge with high-purity nitrogen 3 times, 5 minutes each time, at a pressure of 0.5MPa, to ensure that the water and oxygen content in the reactor is ≤1ppm; Step 2: Raw material addition; At room temperature, add 0.55L of liquid propylene into the polymerization reactor through the feeding valve; Add the set amount of hydrogen through the mass flow meter, and then close the feeding valve; Step 3: Catalyst injection; Inject the pre-complexed catalyst mixture into the polymerization reactor through the catalyst feed pipe, quickly close the feed valve, and start mechanical stirring at a rate of 300 r / min; Step 4: Polymerization reaction; start the electric heating mantle, heat to the set polymerization temperature at a rate of 2℃ / min, maintain the set polymerization pressure, and react for the set time; Step 5: Product recovery; After the reaction is complete, stop heating, slowly vent the pressure in the reactor to atmospheric pressure, with a venting rate ≤0.1MPa / min, and cool to room temperature; open the polymerization reactor, take out the polymer product, and place it in a 30℃ vacuum drying oven to dry for 2 hours to remove residual monomers and solvents, and obtain a dried polypropylene product.

[0032] Example 1 This embodiment details the specific polymerization parameters, operational details, and product performance results of the external electron donor ED1: Aggregation parameters: Hydrogen consumption: 1.2g, relative to 0.22wt% of the total mass of propylene monomer; Polymerization temperature: 70℃; Polymerization pressure: 2.0 MPa; Reaction time: 60 minutes; Pre-complexation conditions: solvent: hexane, temperature: 25°C, time: 5 minutes.

[0033] Operating details: Liquid propylene is added to the polymerization reactor through the pressure reducing valve of the cylinder, with an initial pressure of 0.3 MPa. Hydrogen is then precisely metered through a mass flow meter and introduced into the reactor, raising the pressure inside the reactor to 0.5 MPa. The catalyst mixture is injected into the reactor through a syringe. When the temperature reaches 70°C, the pressure inside the reactor rises to 2.0 MPa, and this pressure is maintained until the reaction is complete.

[0034] Product performance results: Catalyst activity: 33.4 kg / g Cat h -1 ; Xylene-soluble matter (XS): 6.91%; Melt flow rate (MFR): 980.6 g / 10 min; Isotacticity: 93.09%; Molecular weight distribution: 5.5.

[0035] Example 2 This embodiment details the specific polymerization parameters, operational details, and product performance results of the external electron donor ED2: Polymerization parameters: Except for replacing the electron donor with ED1, the other parameters are completely consistent with those in Example 1.

[0036] Product performance results: Catalyst activity: 35.3 kg / g Cat h -1 ; Xylene-soluble matter (XS): 6.1%; Melt flow rate (MFR): 1005.3 g / 10 min; Isotacticity: 93.9%; Molecular weight distribution: 6.2.

[0037] Example 3 This embodiment details the specific polymerization parameters, operational details, and product performance results of the external electron donor ED3: Polymerization parameters: Except for replacing the electron donor with ED3, the other parameters are completely consistent with those in Example 1.

[0038] Product performance results: Catalyst activity: 29.7 kg / g Cat h -1 ; Xylene-soluble matter (XS): 5.9%; Melt flow rate (MFR): 870.2 g / 10 min; Isotacticity: 94.1%; Molecular weight distribution: 5.8.

[0039] Example 4 This embodiment details the specific polymerization parameters, operational details, and product performance results of the external electron donor ED4: Polymerization parameters: Except for replacing the electron donor with ED4, the other parameters are completely consistent with those in Example 1.

[0040] Product performance results: Catalyst activity: 31.9 kg / g Cat h -1 ; Xylene-soluble matter (XS): 7.1%; Melt flow rate (MFR): 1231.1 g / 10 min; Isotacticity: 92.9%; Molecular weight distribution: 6.0.

[0041] Comparative Example 1 This comparative example replaces the external electron donor with the prior art organosilane external electron donor D-Donor. Specific polymerization parameters, operating details, and product performance results are as follows: Polymerization parameters: Except for replacing the electron donor with the existing organosilane D-Donor, the other parameters are completely consistent with those in Example 1.

[0042] Product performance results: Catalyst activity: 32.3 kg / g Cat h -1 ; Xylene-soluble matter (XS): 4.99%; Melt flow rate (MFR): 66.9 g / 10 min; Isotacticity: 95.01%; Molecular weight distribution: 6.4.

[0043] Comparative Example 2 This comparative example replaces the external electron donor with the prior art organosilane external electron donor U-Donor. Specific polymerization parameters, operating details, and product performance results are as follows: Polymerization parameters: Except for replacing the electron donor with the existing organosilane electron donor U-Donor, the other parameters are completely consistent with those in Example 1.

[0044] Product performance results: Catalyst activity: 28.7 kg / g Cat h -1 ; Xylene-soluble matter (XS): 6.93%; Melt flow rate (MFR): 1181.5 g / 10 min; Isotacticity: 93.07%; Molecular weight distribution: 4.5.

[0045] The following is a summary table of performance data:

[0046] Technical effectiveness verification: In Examples 1-4, when ED1-ED4 acted as external electron donors, the MFR of the polyolefins was ≥870.2 g / 10 min, which was much higher than the MFR of 66.9 g / 10 min in Comparative Example 1 of the prior art. This proves that the compound structure of nitrogen-silicon bicyclic skeleton, C1-C10 alkyl substitution, and R1 / R2 being methyl / ethyl can significantly improve the hydrogen regulation sensitivity of the catalyst and solve the problem of poor hydrogen regulation effect of external electron donors in the prior art.

[0047] In Examples 1-4, the catalyst activity remained stable at 29.7–35.3 kg / g Cat. h -1 A catalyst system using magnesium chloride-supported titanium compounds, alkyl aluminum co-catalysts, and polycyclic silane external electron donors was demonstrated to have a scientifically sound composition and parameter constraints, enabling highly efficient catalysis.

[0048] Examples 1-4 successfully prepared high-flow polypropylene under the polymerization conditions defined in the claims, and the process steps were clear and repeatable, proving that the polymerization method has practical operability and industrial application potential.

[0049] The MFR of Examples 1-4 is 870.2-1231.1 g / 10min, all of which meet the requirement of "not less than 800 g / 10min", making them suitable for applications with high fluidity requirements such as thin-wall injection molding and fiber spinning. The isotacticity of Example 3 is 94.1%, which meets the requirement of "not less than 94%", thus ensuring the mechanical strength of the polymer. The molecular weight distribution of Examples 1-4 is 5.5-6.2, which broadens the processing adaptability of the polymer.

[0050] Hydrogen-modulated sensitivity: The hydrogen-modulated sensitivity of the compounds of this invention is more than 13 times that of the prior art D-Donor; Molecular weight distribution regulation: The molecular weight distribution of the existing U-Donor is only 4.5, while the compound of this invention can regulate the molecular weight distribution within a reasonable range of 5.0 to 7.0, taking into account both processability and mechanical properties.

[0051] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A polycyclic silane compound, characterized in that, The compound has a nitrogen-silicon bicyclic framework structure, and its structure is shown below: ； The general structural formula satisfies the following limitations: the bicyclic ring is composed of nitrogen atoms and silicon atoms, and either of the two rings is a five-membered ring, a six-membered ring, or a seven-membered ring, and the substituents on the ring are C1-C10 alkyl groups; R1 and R2 attached to the silicon atom are each independently selected from either methyl or ethyl.

2. The polycyclic silane compound according to claim 1, characterized in that, The compound is selected from one of the compounds shown in the following structural formulas: Compound ED1: Bicyclic [3.3.0] silane skeleton, with methyl substituents on the ring, R1 = methyl, R2 = ethyl; structure: ； Compound ED2: Bicyclic [4.3.0] silane skeleton, with ethyl substituents on the ring, R1 = ethyl, R2 = methyl; structure: ； Compound ED3: a bicyclic [5.3.0] silane skeleton with propyl substituents on the ring, R1 = methyl, R2 = methyl; its structure is: ； Compound ED4: a bicyclic [3.4.0] silane skeleton with butyl substituents on the ring, R1 = ethyl, R2 = ethyl; its structure is as follows: 。 3. A catalyst system of a polycyclic silane compound as described in any one of claims 1-2, characterized in that, Include: A solid catalyst component comprising a titanium compound supported on a magnesium chloride support, and optionally an internal electron donor; The co-catalyst is an alkylaluminum compound; An external electron donor, wherein the external electron donor is a polycyclic silane compound.

4. The catalyst system of the polycyclic silane compound according to claim 3, characterized in that, The internal electron donor is selected from at least one of ester compounds, ether compounds, and amide compounds; wherein the ester compound is selected from at least one of diisobutyl phthalate, succinate, and glycol ester, the ether compound is selected from 1,3-dimethoxypropane, and the amide compound is selected from N,N-dimethylformamide.

5. The catalyst system of the polycyclic silane compound according to claim 3, characterized in that: The co-catalyst is selected from at least one of triethylaluminum and triisobutylaluminum, and is used in the form of an alkylaluminum solution at a concentration of 0.5 to 2.0 mol / L.

6. The catalyst system of the polycyclic silane compound according to claim 1, characterized in that, In the catalyst system, the molar ratio of the external electron donor to titanium in the solid catalyst component is 10:1 to 200:1; the molar ratio of aluminum in the co-catalyst to titanium in the solid catalyst component is 20:1 to 500:

1.

7. A method for olefin polymerization using a catalyst system of polycyclic silane compounds as described in claims 3-6, characterized in that, Includes the following steps: S1: Under an inert atmosphere of nitrogen or argon with a water content ≤1ppm and an oxygen content ≤1ppm, the solid catalyst component, the co-catalyst, and the external electron donor are pre-complexed in an inert solvent to obtain a catalyst mixture; S2: An olefin monomer is added to a polymerization reactor, and the catalyst mixture is introduced into the reaction system in the presence of hydrogen. S3: Polymerization reaction is carried out at temperatures ranging from 50°C to 90°C and pressures ranging from 0.5 MPa to 5.0 MPa; S4: After the reaction is complete, release the pressure, cool down, and recover the generated polymer.

8. The olefin polymerization method using a polycyclic silane compound catalyst system according to claim 7, characterized in that, The olefin monomer is propylene; the amount of hydrogen added is from 0.05 wt% to 2.0 wt% relative to the total mass of the propylene monomer.

9. The olefin polymerization method using a polycyclic silane compound catalyst system according to claim 8, characterized in that, The inert solvent for pre-complexation is hexane or heptane, the pre-complexation temperature is 10°C to 40°C, and the pre-complexation time is 2 to 30 minutes.

10. The olefin polymerization method using a polycyclic silane compound catalyst system according to claim 9, characterized in that, The polyolefins prepared by using the aforementioned polycyclic silane compound as an external electron donor have at least one of the following characteristics: a) The melt flow rate is not less than 800 g / 10 min; b) Isochronism is not less than 94%; c) The molecular weight is between 5.0 and 7.0.

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