Polymerization method of polypropylene with high melt strength and catalyst system used in polymerization method

Abstract

The invention relates to the technical field of high polymer material synthesis, and discloses a high-melt-strength polypropylene polymerization method and a used catalyst system. In order to solve the problems that an existing high-melt-strength polypropylene preparation process is complex, high in cost and poor in stability, and conventional polypropylene is low in melt strength and poor in foaming performance, the catalyst system adopts Ziegler-Natta with the specific titanium content as a main catalyst and adopts triethyl aluminum as a cocatalyst; a novel silane compound with a polycyclic structure is used as an external electron donor, so that the polymer has the characteristics of low xylene soluble substance content and wide molecular weight distribution; the polymerization process is performed in a stirred tank reactor, and the high-melt-strength polypropylene is synthesized in situ by regulating and controlling the reaction temperature, the pressure, the ratio of hydrogen to propylene and the polymerization time; the melt strength of the product is obviously higher than that of conventional polypropylene, the product has typical strain hardening characteristics, and the method is short in process, low in cost and high and stable in catalyst activity.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to a method for polymerizing polypropylene with high melt strength and the catalyst system used therein. Background Technology

[0002] Polypropylene is widely used in automobiles, packaging, building materials and consumer goods due to its low price, excellent comprehensive performance and easy processing. However, in foaming applications, conventional polypropylene has low melt strength and cannot withstand sufficient tensile stress during bubble growth, which easily leads to cell rupture, merging and collapse. This makes it difficult to reduce the density of foamed products and results in uneven cell structure, which has become a key problem limiting the further application of foamed polypropylene.

[0003] Existing technologies for improving the melt strength of polypropylene can be mainly divided into three categories: Irradiation method: For example, the Beijing Chemical Research Institute disclosed a method for introducing long-chain branching into polypropylene by electron beam irradiation in the journal Synthetic Resins and Plastics. Although it can obtain polypropylene with high melt strength, the process is complicated, the equipment investment is large, and the irradiation process is prone to causing material oxidation and degradation, resulting in poor product color and decreased stability.

[0004] Chemical crosslinking or grafting methods: For example, patent CN101092500A proposes using peroxides to initiate a free radical reaction in polypropylene, introducing long-chain branched or grafted polar groups to improve melt strength. While such methods are effective, they usually require additional post-processing steps, consume more energy, and leave residual additives, affecting material purity and food contact safety.

[0005] Catalyst system improvement method: Some patents attempt to improve the process from the polymerization source. For example, patent CN103665583A discloses a new type of catalyst system for the production of long-branched polypropylene. However, these catalyst systems are expensive, have strict requirements for the addition process control, and the properties of the long-branched polypropylene with high melt strength still have room for further optimization.

[0006] Regarding the aforementioned and existing related technologies, the inventors believe that the following defects often exist: Existing technologies share common problems: First, the processes are complex and costly, with most solutions relying on post-processing or irradiation steps, increasing production steps and costs; second, they have poor stability, with free radical-induced chemical modification easily leading to batch-to-batch performance fluctuations; third, they lack purity, with residual small molecule additives, peroxides, etc., potentially affecting product safety; and fourth, they are difficult to scale up industrially. Fluidized bed gas-phase polymerization is the mainstream process for polyolefin production, with advantages such as short process flow, low investment, and flexible product grade switching. However, currently, this process is mainly used to produce ordinary polypropylene or polyethylene with linear molecular structures. The core difficulty in directly using it to produce high melt strength polypropylene lies in the lack of a catalyst system that can efficiently catalyze the generation of ultra-high molecular weight components or long-chain branched structures in a gas phase environment. The lack of existing mature solutions limits industrial application.

[0007] Therefore, there is an urgent need to develop a novel catalyst system and method for directly preparing high melt strength polypropylene in fluidized bed gas-phase polymerization process, in order to simplify the production process, reduce costs, and obtain high melt strength polypropylene with stable performance to meet the application needs of novel foaming fields. Summary of the Invention

[0008] The technical problem to be solved by this invention is that there are shortcomings in the synthesis of polymer materials in the prior art. To address this, we propose a high melt strength polypropylene polymerization method and the catalyst system used therein.

[0009] To achieve the above objectives, this application adopts the following technical solution: a catalyst system for high melt strength polypropylene, comprising: Main catalyst: Under oxygen- and anhydrous conditions, dibutyl phthalate (an internal electron donor) is mixed with titanium tetrachloride and magnesium chloride support, and a complexation reaction is carried out at 60-120°C. After the reaction, the mixture is washed multiple times with an inert solvent and dried to obtain a solid catalyst component. The titanium content in the main catalyst is 3.0 wt%. Co-catalyst: Triethylaluminum; External electron donor: a silane compound having a polycyclic skeleton, wherein the general molecular formula of the polycyclic silane compound is as follows:

[0010] Among them: A, B and C are each independently selected from N or O; R1, R2 and R3 are each independently selected from either methyl or ethyl; The molecular structure of the silane compound contains three heteroatom sites A, B, and C, each of which is independently selected from N or O atoms; the silicon atom of the silane compound is attached to three alkoxy substituents R1, R2, and R3, each of which is independently selected from methyl or ethyl.

[0011] Preferably, the external electron donor is 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane, in which A, B, and C are all nitrogen atoms, and R1, R2, and R3 are all methyl groups. The molecular formula of 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane is as follows: Where: A / B / C=N, R1 / R2 / R3=methyl.

[0012] Preferably, the aluminum / titanium molar ratio of the co-catalyst to the main catalyst in the system is 40-60, and the silicon / aluminum molar ratio of the external electron donor to the co-catalyst is 0.05-0.12, wherein the molar ratio is calculated based on the mass of titanium in the main catalyst.

[0013] Preferably, the mass ratio of the internal electron donor dibutyl phthalate to the magnesium chloride carrier is 0.08~0.15:1.

[0014] Preferably, another technical solution proposed by the present invention is a polymerization method for high melt strength polypropylene, comprising the following steps: S1: Prepare a stirred tank reactor or a fluidized bed gas-phase reactor, and replace the reactor with an inert gas to ensure an oxygen-free and water-free environment; S2: Add liquid propylene monomer to the reactor as a raw material for the polymerization reaction; S3: Introduce hydrogen into the reactor and adjust the molar ratio of hydrogen to propylene to 0.01~0.25 to control the melt index of the polymer; S4: Raise the temperature inside the reactor to 60~85℃ and adjust the pressure of the reactor to 1.5~3.5MPa to maintain the stability of the reaction system; S5: Mix the main catalyst, co-catalyst triethylaluminum and external electron donor in proportion and inject them into the reactor, or inject them into the reactor sequentially to start the polymerization reaction. The reaction lasts for 1.5 to 5 hours. S6: After the reaction is complete, the unreacted propylene monomer is discharged from the reactor and solid polypropylene product is collected.

[0015] Preferably, in step S4, the optimal reaction temperature of the reactor is 65~75℃ and the reaction pressure is 2.0~2.8MPa.

[0016] Preferably, in step S5, the main catalyst, co-catalyst, and external electron donor are added in the following manner: first, the co-catalyst is injected, then the external electron donor is injected, and finally the main catalyst is injected, with an injection interval of 5 to 15 minutes.

[0017] Preferably, in step S5, the aluminum / titanium molar ratio is 50, the silicon / aluminum molar ratio is 0.08, and the polymerization reaction lasts for 1 hour.

[0018] Preferably, the prepared polypropylene, when subjected to a test temperature of 230°C and a load of 2.16 kg, has a melt index value of 2 g / 10 min.

[0019] Preferably, the prepared polypropylene has a melt strength greater than 30 cN at 190°C, a molecular weight distribution greater than 5.5, and a xylene-soluble content not exceeding 2.5 wt%.

[0020] The technical effects and advantages of this invention are as follows: In this invention, integrated production is achieved: high melt strength polypropylene is directly synthesized in a single reactor, eliminating the need for post-modification processes, resulting in a shorter process flow, lower costs, and higher production efficiency.

[0021] Significantly improved melt strength: Through a novel external electron donor catalyst system and precise control of process parameters, high molecular weight and wide distribution components are introduced in situ into the polypropylene molecular chain, resulting in high melt strength, a wide foaming processing window, and easy production of high-end foamed products with fine and uniform cells, low density, and good mechanical properties.

[0022] High efficiency and stability of the catalyst, controllable molecular structure: The novel external electron donor catalyst system of this invention exhibits high activity, excellent molecular weight enhancement ability, and good stability in the polymerization environment, making it suitable for continuous industrial production.

[0023] With broad application prospects, the high melt strength polypropylene produced provides a high-performance, low-cost solution to meet the urgent need for core basic materials in the field of new foaming.

[0024] In summary, this invention, through innovations in the design of novel external electron donor catalyst systems and the control of polymerization conditions, enables the direct synthesis of high melt strength polypropylene during polymerization. This overcomes the shortcomings of existing technologies, such as complex processes, unstable product performance, and high costs, and provides a solution with high efficiency, low cost, and excellent application performance. Attached Figure Description

[0025] 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 flowchart of the high melt strength polypropylene polymerization method of the present invention. Detailed Implementation

[0026] 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.

[0027] This invention provides a technical solution: a catalyst system for high melt strength polypropylene, comprising: a main catalyst: a solid catalyst component obtained by mixing dibutyl phthalate (an internal electron donor) with titanium tetrachloride and magnesium chloride support under oxygen-free and anhydrous conditions, carrying out a complexation reaction at 60-120°C, and washing and drying it multiple times with an inert solvent after the reaction, wherein the titanium content in the main catalyst is 3.0 wt%; and a co-catalyst: triethylaluminum. External electron donor: a silane compound having a polycyclic skeleton, wherein the general molecular formula of the polycyclic silane compound is as follows:

[0028] Among them: A, B and C are each independently selected from N or O; R1, R2 and R3 are each independently selected from either methyl or ethyl; The molecular structure of the silane compound contains three heteroatom sites A, B, and C, each of which is independently selected from N or O atoms; the silicon atom of the silane compound is attached to three alkoxy substituents R1, R2, and R3, each of which is independently selected from methyl or ethyl. The external electron donor is 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane, in which A, B, and C are all nitrogen atoms, and R1, R2, and R3 are all methyl groups. The molecular formula of 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane is as follows: Where: A / B / C=N, R1 / R2 / R3=methyl; The aluminum / titanium molar ratio of the co-catalyst to the main catalyst in the system is 40~60, the silicon / aluminum molar ratio of the external electron donor to the co-catalyst is 0.05~0.12, and the molar ratio is calculated based on the mass of titanium in the main catalyst. The mass ratio of the internal electron donor dibutyl phthalate to the magnesium chloride support is 0.08~0.15:1.

[0029] Reference Figure 1As shown, another technical solution proposed by this invention is a polymerization method for high melt strength polypropylene, comprising the following steps: Step 1: Prepare a stirred tank reactor or a fluidized bed gas-phase reactor, and replace the reactor with an inert gas to ensure an oxygen-free and water-free environment; Step 2: Add liquid propylene monomer to the reactor as a raw material for the polymerization reaction; Step 3: Introduce hydrogen into the reactor and adjust the molar ratio of hydrogen to propylene to 0.01~0.25 to control the melt index of the polymer; Step 4: Raise the temperature inside the reactor to 60~85℃ and adjust the pressure of the reactor to 1.5~3.5MPa to maintain the stability of the reaction system, wherein the reaction temperature is 65~70℃. The reaction temperature is 5℃, and the reaction pressure is 2.0~2.8MPa; Step 5: The main catalyst, co-catalyst triethylaluminum, and external electron donor are mixed in proportion and injected into the reactor, or injected into the reactor separately in sequence to start the polymerization reaction. The reaction lasts for 1.5~5 hours. The main catalyst, co-catalyst, and external electron donor are added in the following manner: first inject the co-catalyst, then inject the external electron donor, and finally inject the main catalyst. The injection interval is 5~15 minutes. The aluminum / titanium molar ratio is 50, the silicon / aluminum molar ratio is 0.08, and the polymerization reaction lasts for 1 hour; Step 6: After the reaction is completed, the unreacted propylene monomer in the reactor is discharged, and solid polypropylene product is collected.

[0030] The prepared polypropylene, when subjected to a test temperature of 230℃ and a load of 2.16 kg, had a melt index of 2 g / 10 min. The prepared polypropylene had a melt strength greater than 30 cN, a molecular weight distribution greater than 5.5, and a xylene-soluble content not exceeding 2.5 wt% at 190℃.

[0031] The present invention relates to the application of high melt strength polypropylene in the preparation of foamed materials, wherein the foamed material is a microporous foam foamed by supercritical CO2, expanded PP beads for automotive interiors, or foamed sheets for food packaging, wherein the average cell size of the microporous foam is less than 100 μm, and the cell density is high and uniformly distributed.

[0032] In this implementation plan: I. Experimental Reagents All reagents used in this embodiment are commercially available or conventionally prepared, as detailed below: Magnesium chloride carrier: industrial grade, purity not less than 99.5%, no special pretreatment is required before use, it can be used directly; Titanium tetrachloride: Analytical grade, purity not less than 99.8%, must be dehydrated before use to remove moisture and impurities; Dibutyl phthalate: analytical grade, purity not less than 99.0%, used as an internal electron donor in catalyst systems to help regulate the reaction activity of catalysts; Triethylaluminum: Industrial grade, purity not less than 98.0%. As a co-catalyst for the reaction, its core function is to activate the main catalyst. It must be stored in a sealed container in an inert gas atmosphere to avoid contact with air and moisture, which would cause it to become ineffective. External electron donor: chemical name 1,4,5,8-dimethylbridge-1H-carbazolylcycloaminotrimethoxysilane, which was prepared in this example and has a purity of not less than 99.0%; its molecular structure has three key features: first, a stable skeleton composed of multiple rings; second, three nitrogen atoms as heteroatom binding sites; and third, three alkoxy substituent groups containing methyl groups. Liquid propylene: Polymer grade high purity, with a purity of not less than 99.95%, and the content of impurities such as water and oxygen does not exceed five parts per million. It is the core raw material for synthesizing polypropylene. Hydrogen: High purity, with a purity of not less than 99.99%, mainly used to control the molecular weight of polypropylene; Inert solvent: n-hexane, analytical grade, dehydrated and deoxygenated before use, with a water content not exceeding 10 ppm and an oxygen content not exceeding 10 ppm after treatment, used for dilution, washing and other steps in the reaction; Comparative reagents: Commercially available conventional Zn catalysts, whose internal electron donor is phthalate and external electron donor is dicyclopentyldimethoxysilane, with an overall purity of not less than 98.0%, are used to compare the performance with the catalyst system of this embodiment.

[0033] II. Preparation of the catalyst system Example 1: Preparation of the main catalyst The main catalyst was prepared under oxygen- and anhydrous conditions according to the following steps: Add 100g of magnesium chloride carrier to a dry 500mL three-necked flask, then inject 200mL of dehydrated titanium tetrachloride, turn on the mechanical stirrer at 200r / min, and mix thoroughly. Place the three-necked flask in a constant temperature heating mantle, heat it to 80°C, stir continuously for 10 minutes, and then slowly add 10g of dibutyl phthalate. The mass ratio of dibutyl phthalate to magnesium chloride carrier is 0.1:1. The complexation reaction was carried out at 80°C for 4 hours, with the stirring rate kept stable during the reaction. After the reaction is complete, stop heating and allow the system to cool naturally to room temperature. Wash the solid product multiple times with n-hexane that has been dehydrated and deoxygenated. Add 150 mL of n-hexane each time, stir for 30 min, and then filter. Repeat the washing until no chloride ions are detected in the washing solution. The washed solid product was placed in a vacuum drying oven and dried at 60°C for 6 hours to obtain a white powdery solid main catalyst component. The titanium content in the main catalyst was determined by inductively coupled plasma mass spectrometry, and the result was 3.0 wt%.

[0034] Example 2: Blending of a complete catalyst system; The main catalyst prepared in Example 1 (based on titanium), the co-catalyst triethylaluminum, and the external electron donor 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane were compounded in the following proportions: Aluminum / titanium molar ratio = 50; Silicon / aluminum molar ratio = 0.08; After being mixed evenly, the mixture is sealed and stored in an inert gas atmosphere to obtain the catalyst system of the present invention.

[0035] III. Polymerization Methods for High Melt Strength Polypropylene Example 3: Propylene polymerization was carried out in a stirred tank reactor using the catalyst system formulated in Example 2, following steps S1 to S6 as defined in claim 5: S1: Reactor pretreatment: Dry the inner wall of the 20L high-pressure stirred tank reactor, and replace it with nitrogen three times. During each replacement, the nitrogen pressure is increased to 0.5MPa and maintained for 10 minutes before being depressurized to atmospheric pressure to ensure that there is no oxygen or water in the reactor, with moisture ≤10ppm and oxygen ≤10ppm. S2: Raw material addition: Add 10L of liquid propylene monomer to the reactor and close the feed valve; S3: Hydrogen regulation: High-purity hydrogen is introduced into the reactor and monitored in real time by an online gas monitor. The molar ratio of hydrogen to propylene is adjusted to 0.012 to regulate the polymer melt index. S4: Reaction condition control: Start the reactor heating system to raise the temperature inside the reactor to 70°C, and introduce liquid propylene into the reactor through the pressurization device to raise the pressure inside the reactor to 3.4 MPa. Maintain the temperature and pressure stable for 30 minutes. S5: Catalyst injection and polymerization: First inject the co-catalyst, then inject the external electron donor at 10 min intervals, and then inject the main catalyst at 10 min intervals. Inject the compounded catalyst system into the reactor, start stirring at 300 r / min, start the polymerization reaction, and the reaction lasts for 1 hour. S6: Post-processing: After the polymerization reaction is completed, slowly release the pressure to atmospheric pressure at a rate ≤0.1MPa / min, discharge the unreacted propylene monomer, open the reactor, collect the white solid polypropylene product in the reactor, weigh the product to obtain the product mass, and calculate the catalyst activity as 46kgPP / gCat.

[0036] Example 4: Fluidized bed gas-phase reactor polymerization using the catalyst system formulated in Example 2. Propylene polymerization was carried out in a fluidized bed gas-phase reactor, and the steps are as follows: S1: Reactor pretreatment: Nitrogen purging is performed on the elh bed gas phase reactor to ensure an oxygen-free and water-free internal environment; S2: Feeding: Liquid propylene monomer is continuously fed into the reactor to maintain a stable propylene gas phase concentration in the reactor; S3: Hydrogen regulation: Synchronously introduce hydrogen gas and adjust the molar ratio of hydrogen to propylene to 0.02; S4: Reaction condition control: Raise the temperature inside the reactor to 72℃ and adjust the pressure to 2.5MPa to maintain system stability; S5: Catalyst injection and polymerization: The catalyst system is injected in the order of co-catalyst to external electron donor to main catalyst, with the aluminum / titanium molar ratio controlled at 55 and the silicon / aluminum molar ratio controlled at 0.10. The injection interval is 8 minutes. The polymerization reaction is started and lasts for 3 hours. S6: Post-processing: Stop feeding, discharge unreacted monomers, collect solid polypropylene products through a separation device, and obtain high melt strength polypropylene granules.

[0037] Comparative Example 1: Polymerization Comparison of Conventional Catalyst Systems Using a commercially available conventional Zn catalyst and an external electron donor, dicyclopentyldimethoxysilane, the polymerization process was carried out according to the same steps as in Example 3. The polymerization reaction control conditions in the stirred tank reactor were set as follows: the reaction temperature was stabilized at 70°C; the reaction pressure was maintained at 3.4 MPa, which ensured that the propylene monomer remained in a suitable polymerization state, providing a stable environment for molecular chain growth; the molar ratio of hydrogen to propylene was adjusted to 0.012, that is, 0.012 molars of hydrogen were used for every 100 moles of propylene monomer, and the key role of hydrogen was to regulate the molecular weight of polypropylene; the entire polymerization reaction lasted for 1 hour to ensure that the propylene monomer was fully converted and that the polypropylene molecular chains reached the required length and structure, ensuring stable product performance. The stirred tank reactor was used for homopolymerization of propylene, and only the catalyst system was replaced to obtain a conventional polypropylene product.

[0038] III. Product Performance Testing and Verification The polypropylene products obtained in Examples 3, 4, and Comparative Example 1 were subjected to performance testing. The test methods and results are shown in the table below:

[0039] Test results show that the performance indicators of the polypropylene products obtained in Examples 3 and 4 are significantly better than those of the conventional polypropylene product in Comparative Example 1, proving that the catalyst system and polymerization method of the present invention can effectively achieve the preparation of polypropylene with high melt strength.

[0040] IV. Application Validation The high melt strength polypropylene product obtained in Example 3 and the conventional polypropylene product obtained in Comparative Example 1 were both subjected to supercritical CO2 foaming verification. The foaming process conditions were uniformly set as follows: foaming temperature 120℃, foaming pressure 20MPa, holding time 30min, and depressurization rate 5MPa / s. The cell structure was observed using SEM after foaming, and the results are as follows: Example 3 Product: The average cell size of the foamed material is 85 μm, and the cell density is 1.2 × 10⁻⁶. 6 The foam has a density of 10 cells / cm³, with uniform cell distribution and no cell merging, cracking, or collapse, which meets the requirements of claim 10 for foamed materials. Comparative Example 1 Product: The foamed material exhibits severe cell merging and collapse, uneven cell size, with the largest cell size exceeding 500μm, rendering it unusable in practical applications.

[0041] The product obtained in Example 3 was further used to prepare expanded PP beads for automotive interiors and foamed sheets for food packaging: EPP products: apparent density 35kg / m³, compression rebound rate ≥85%, meeting the requirements for lightweighting and mechanical performance of automotive interiors; Foamed sheets for food packaging: The foam cells are fine and uniform, and the odor test results are qualified. They can be directly used in the food packaging field.

[0042] 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 catalyst system for high melt strength polypropylene, characterized in that, include: Main catalyst: Under oxygen- and anhydrous conditions, dibutyl phthalate (an internal electron donor) is mixed with titanium tetrachloride and magnesium chloride support, and a complexation reaction is carried out at 60-120°C. After the reaction, the mixture is washed multiple times with an inert solvent and dried to obtain a solid catalyst component. The titanium content in the main catalyst is 3.0 wt%. Co-catalyst: Triethylaluminum; External electron donor: a silane compound having a polycyclic skeleton, wherein the general molecular formula of the polycyclic silane compound is as follows: Among them: A, B and C are each independently selected from N or O; R1, R2 and R3 are each independently selected from either methyl or ethyl; The molecular structure of the silane compound contains three heteroatom sites A, B, and C, each of which is independently selected from N or O atoms; the silicon atom of the silane compound is attached to three alkoxy substituents R1, R2, and R3, each of which is independently selected from methyl or ethyl.

2. The catalyst system for high melt strength polypropylene according to claim 1, characterized in that: The external electron donor is 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane, in which A, B, and C are all nitrogen atoms, and R1, R2, and R3 are all methyl groups. The molecular formula of 1,4,5,8-dimethylbridged-1H-carbazole cycloaminotrimethoxysilane is as follows: Where: A / B / C=N, R1 / R2 / R3=methyl.

3. The catalyst system for high melt strength polypropylene according to claim 1, characterized in that: In the system, the aluminum / titanium molar ratio of the co-catalyst to the main catalyst is 40-60, and the silicon / aluminum molar ratio of the external electron donor to the co-catalyst is 0.05-0.

12. The molar ratios are calculated based on the mass of titanium in the main catalyst.

4. The catalyst system for high melt strength polypropylene according to claim 1, characterized in that: The mass ratio of the internal electron donor dibutyl phthalate to the magnesium chloride carrier is 0.08~0.15:

1.

5. A polymerization method for high melt strength polypropylene, implemented based on the catalyst system for high melt strength polypropylene as described in claims 1-4, characterized in that: Includes the following steps: S1: Prepare a stirred tank reactor or a fluidized bed gas-phase reactor, and replace the reactor with an inert gas to ensure an oxygen-free and water-free environment; S2: Add liquid propylene monomer to the reactor as a raw material for the polymerization reaction; S3: Introduce hydrogen into the reactor and adjust the molar ratio of hydrogen to propylene to 0.01~0.25 to control the melt index of the polymer; S4: Raise the temperature inside the reactor to 60~85℃ and adjust the pressure of the reactor to 1.5~3.5MPa to maintain the stability of the reaction system; S5: Mix the main catalyst, co-catalyst triethylaluminum and external electron donor in proportion and inject them into the reactor, or inject them into the reactor sequentially to start the polymerization reaction. The reaction lasts for 1.5 to 5 hours. S6: After the reaction is complete, the unreacted propylene monomer is discharged from the reactor and solid polypropylene product is collected.

6. The high melt strength polypropylene polymerization method according to claim 5, characterized in that: In step S4, the optimal reaction temperature of the reactor is 65~75℃ and the reaction pressure is 2.0~2.8MPa.

7. The high melt strength polypropylene polymerization method according to claim 5, characterized in that: In step S5, the main catalyst, co-catalyst, and external electron donor are added in the following manner: first inject the co-catalyst, then inject the external electron donor, and finally inject the main catalyst, with an injection interval of 5 to 15 minutes.

8. The high melt strength polypropylene polymerization method according to claim 5, characterized in that: In step S5, the aluminum / titanium molar ratio is 50, the silicon / aluminum molar ratio is 0.08, and the polymerization reaction lasts for 1 hour.

9. The high melt strength polypropylene polymerization method according to claim 5, characterized in that: The prepared polypropylene was tested at 230℃ with a load of 2.16 kg, and the melt index was measured to be 2 g / 10 min.

10. The high melt strength polypropylene polymerization method according to claim 5, characterized in that: The prepared polypropylene has a melt strength greater than 30 cN at 190℃, a molecular weight distribution greater than 5.5, and a xylene-soluble content not exceeding 2.5 wt%.

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