Method for continuous block polymerization of propylene and alpha-olefin

Abstract

The invention provides a propylene and alpha-olefin continuous block polymerization method, which comprises: uniformly mixing a solvent, propylene, alpha-olefin, a main catalyst and a co-catalyst, and feeding the obtained mixture into a first-stage reaction kettle to carry out a reaction so as to obtain a first-stage reaction product; the flow ratio of the propylene to the alpha-olefin is (0.8-1.0): (0.1-0.3); the first-stage reaction product and alpha-olefin enter a second-stage reaction kettle for second-stage reaction, and a second-stage reaction product is obtained; the flow ratio of the alpha-olefin in the second-stage reaction kettle to the propylene in the first-stage reaction kettle is (0.04-0.07): (0.8-1.0); and mixing the second-stage reaction product with an antioxidant and an inactivator, carrying out first-stage devolatilization and second-stage devolatilization, and granulating to obtain the propylene-alpha-olefin block copolymer. According to the method, double-kettle continuous production is adopted, and the propylene content in the product is adjusted by controlling the ratio of propylene to alpha-olefin in each stage of reaction kettle, so that the product has excellent high and low temperature resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of elastomer preparation, and in particular relates to a method for continuous block polymerization of propylene and alpha-olefin. Background Art

[0002] Propylene-based elastomer (PBE) is also a type of polyolefin elastomer. It is a unique propylene-ethylene and propylene-butene semi-crystalline copolymer composed mainly of repeating units of isotactic polypropylene and randomly distributed ethylene, butene, etc. The principle of propylene-based elastomers is to use the polypropylene crystal segment as the hard segment, and ethylene propylene, butene propylene, etc. are randomly arranged as retractable soft segments. Through the soft and hard arrangement, the effect of elastic recovery and increased toughness is achieved, thereby showing elasticity. The mass fraction of propylene is >70%, and the density is 0.85~0.92g / cm 3 .

[0003] At present, the synthesis method of propylene-based elastomers in the market all adopts solution polymerization. Generally, the treated monomers and catalysts are added to the reactor in a certain proportion and kept constant during the polymerization process. Then, the stirred solvent is blown in to reach a saturated state, and the initiator is added to start the reaction. The monomers and initiators are continuously added to the inlet of the reactor to make the reaction system in a saturated state. During the reaction, the condenser on the reactor, the jacket of the reactor, or the condenser tubes inside and outside the reactor are used to continuously remove the polymerization heat. After a period of reaction, the mixed material enters the mixer, and after flash evaporation, the evaporated monomer is recycled and reused. The remaining mixture is washed, condensed, screened, etc. The solvent is recycled and the solvent residue is separated, granulated, formed, and packaged.

[0004] However, the PBE products prepared by the above process can only have low temperature resistance or high temperature resistance; a variety of catalysts and chain transfer agents are also required, which increases the production cost. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for continuous block polymerization of propylene and α-olefin, wherein the product prepared by the method has excellent high and low temperature resistance.

[0006] The present invention provides a method for continuous block polymerization of propylene and α-olefin, comprising the following steps:

[0007] The solvent, propylene, α-olefin, main catalyst and co-catalyst are uniformly mixed and then introduced into a primary reaction kettle for reaction to obtain a primary reaction product; the flow ratio of propylene and α-olefin is (0.8-1.0):(0.1-0.3);

[0008] The primary reaction product and α-olefin are introduced into a secondary reaction kettle for secondary reaction to obtain a secondary reaction product; the flow ratio of α-olefin in the secondary reaction kettle to propylene in the primary reaction kettle is (0.04-0.07):(0.8-1.0);

[0009] The secondary reaction product is mixed with an antioxidant and a deactivator, and then subjected to primary devolatilization and secondary devolatilization, and granulated to obtain a propylene-alpha-olefin block copolymer.

[0010] Preferably, the α-olefin is selected from one or more of ethylene, 1-butene, 1-hexene and 1-octene;

[0011] The solvent is selected from one or more of isomeric saturated alkanes, n-pentane, n-hexane, methylcyclopentane, n-heptane, methylcyclohexane, an isomeric saturated alkane mixture and toluene.

[0012] Preferably, the catalyst comprises a main catalyst and a co-catalyst;

[0013] The main catalyst is selected from a mixture of dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-dimethyltitanium and a boron agent in a molar ratio of 1:1.2 to 5.0, or dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-titanium dichloride;

[0014] The boron agent is selected from one or more of perfluorophenyl boron, triphenylcarbon-tetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate and N,N-di(hexadecyl)aniliniumtetrakis(pentafluorophenyl)borate;

[0015] The co-catalyst is selected from one or more of triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane, perfluorophenylboron, triphenylcarbon-tetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate and N,N-dicetylaniliniumtetrakis(pentafluorophenyl)borate.

[0016] Preferably, the reaction temperature in the primary reactor is 30 to 100°C;

[0017] The pressure of α-olefin is 0.4 to 4 MPa.

[0018] Preferably, the inactivating agent is selected from deionized water, water vapor or carbon monoxide;

[0019] The antioxidant is selected from one or more of antioxidant 1010, antioxidant 288, antioxidant 4030, antioxidant A and antioxidant D.

[0020] Preferably, the temperature of the first stage devolatilization is 205-215°C, and the pressure of the first stage devolatilization is 1.4-1.6 MPa;

[0021] The temperature of the secondary devolatilization is 205-215°C, and the pressure of the secondary devolatilization is 0.015-0.025 MPa.

[0022] Preferably, the residence time in the primary reactor is 5 to 30 min;

[0023] The residence time in the secondary reactor is 5 to 30 minutes.

[0024] Preferably, the stirring rate in the mixing kettle is 30 to 60 rpm;

[0025] The stirring speeds in the primary reactor and the secondary reactor are both 100-600 rpm.

[0026] Preferably, the propylene-α-olefin block copolymer is a propylene-based elastomer;

[0027] The melting point of the propylene-based elastomer is 55 to 100°C, and the glass transition temperature is -35 to -10°C.

[0028] The present invention provides a method for continuous block polymerization of propylene and α-olefin, comprising the following steps: uniformly mixing a solvent, propylene, α-olefin, a main catalyst and a co-catalyst, and then entering a primary reactor to react to obtain a primary reaction product; the flow ratio of the propylene and α-olefin is (0.8-1.0): (0.1-0.3); the primary reaction product and the α-olefin are entering a secondary reactor to carry out a secondary reaction to obtain a secondary reaction product; the flow ratio of the α-olefin in the secondary reactor to the propylene in the primary reactor is (0.04-0.07): (0.8-1.0); the secondary reaction product is mixed with an antioxidant and a deactivator, and then primary and secondary devolatilization and granulation are carried out to obtain a propylene-α-olefin block copolymer. The method provided by the present invention adopts double-kettle continuous production, and by controlling the ratio of propylene and α-olefin in each stage of the reactor, the propylene content in the product is adjusted, so that the product has both a "soft segment" with a low propylene content and a "hard segment" with a high propylene content, so that the product has excellent high and low temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a schematic diagram of the process of continuous block polymerization of propylene and α-olefin used in the embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a method for continuous block polymerization of propylene and α-olefin, comprising the following steps:

[0031] The solvent, propylene, α-olefin, main catalyst and co-catalyst are uniformly mixed and then introduced into a primary reaction kettle for reaction to obtain a primary reaction product; the flow ratio of propylene and α-olefin is (0.8-1.0):(0.1-0.3);

[0032] The primary reaction product and α-olefin are introduced into a secondary reaction kettle for secondary reaction to obtain a secondary reaction product; the flow ratio of α-olefin in the secondary reaction kettle to propylene in the primary reaction kettle is (0.04-0.07):(0.8-1.0);

[0033] The secondary reaction product is mixed with an antioxidant and a deactivator, and then subjected to primary devolatilization and secondary devolatilization, and granulated to obtain a propylene-alpha-olefin block copolymer.

[0034] The method provided by the present invention adopts double-kettle continuous production, and adjusts the propylene content in the product by controlling the ratio of propylene and α-olefin in each stage of the reactor, so that the product has both a "soft segment" with a low propylene content and a "hard segment" with a high propylene content, thereby making the product have excellent high and low temperature resistance.

[0035] In the present invention, the solvent, propylene, alpha-olefin, main catalyst and co-catalyst are uniformly mixed and then introduced into a primary reaction kettle for reaction to obtain a primary reaction product.

[0036] Before the experiment, under nitrogen protection, the main catalyst and the co-catalyst in the catalyst are respectively mixed with the solvent to form a solution, and stored in respective feed tanks; the solvent, propylene, and α-olefin are refined and impurity-free to meet the polymerization requirements. The present invention cleans the reactor and the pipeline with a solution of triisobutylaluminum and the solvent to remove water and oxygen.

[0037] The present invention preferably mixes the solvent, propylene and α-olefin uniformly in a mixing kettle before entering the primary reactor; the stirring rate in the mixing kettle is 30-60 rpm. After uniform mixing, the mixture is entered into the primary reactor with the catalyst and the co-catalyst for reaction; the reaction in the primary reactor is carried out under stirring conditions, and the stirring rate in the primary stirred reactor is 100-600 rpm; the residence time in the primary reactor is 5-30 min. The reaction temperature in the primary reactor is 30-100° C.; the pressure of the α-olefin is 0.4-4 MPa.

[0038] The α-olefin in the present invention is selected from one or more of ethylene, 1-butene, 1-hexene and 1-octene;

[0039] The solvent is selected from one or more of isomeric saturated alkanes, n-pentane, n-hexane, methylcyclopentane, n-heptane, methylcyclohexane, an isomeric saturated alkane mixture and toluene; the isomeric saturated alkane mixture includes at least two of isobutane, isopentane and isooctane.

[0040] The catalyst comprises a main catalyst and a co-catalyst; the main catalyst is selected from a mixture of dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-dimethyltitanium and a boron agent in a molar ratio of 1:1.2-5.0, or dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-titanium dichloride; the boron agent is selected from perfluorophenyl boron, triphenylcarbon-tetra(pentafluorophenyl)borate, N,N-dimethylanilinium tetra(pentafluorophenyl)borate or N,N-di(hexadecyl)anilinium tetra(pentafluorophenyl)borate; the present invention only needs to use one main catalyst to complete the reaction, thereby reducing the production cost.

[0041] The co-catalyst is selected from one or more of triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane (MMAO), perfluorophenylboron, triphenylcarbon-tetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate and N,N-dicetylaniliniumtetrakis(pentafluorophenyl)borate.

[0042] The flow ratio of propylene and α-olefin in the primary reactor of the present invention is (0.8-1.0):(0.1-0.3).

[0043] After obtaining the primary reaction product, the present invention introduces the primary reaction product and α-olefin into a secondary reaction kettle for secondary reaction to obtain a secondary reaction product. The flow ratio of α-olefin in the secondary reaction kettle to propylene in the primary reaction kettle is (0.04-0.07):(0.8-1.0).

[0044] The residence time in the secondary reactor is 5 to 30 minutes. The reaction temperature in the secondary reactor is 30 to 100° C. The stirring rate in the secondary reactor is 100 to 600 rpm.

[0045] The present invention adjusts the propylene content in the product by controlling the ratio of propylene and α-olefin in the primary reactor and the secondary reactor, so that the product has both a "soft segment" with a low propylene content and a "hard segment" with a high propylene content, thereby making the product have excellent high and low temperature resistance.

[0046] After obtaining the secondary reaction product, the present invention mixes the secondary reaction product with an antioxidant and a deactivator, performs primary devolatilization and secondary devolatilization, and granulates to obtain a propylene-α-olefin block copolymer.

[0047] The inactivator in the present invention is selected from deionized water, water vapor or carbon monoxide; the antioxidant is selected from one or more of antioxidant 1010, antioxidant 288, antioxidant 4030, antioxidant A and antioxidant D.

[0048] In the present invention, the temperature of the primary devolatilization is 205-215° C., and the pressure of the primary devolatilization is 1.4-1.6 MPa; the temperature of the secondary devolatilization is 205-215° C., and the pressure of the secondary devolatilization is 0.015-0.025 MPa.

[0049] The propylene-α-olefin block copolymer prepared in the present invention is preferably a propylene-based elastomer; the melting point of the propylene-based elastomer is 55 to 110° C., and the glass transition temperature is -35 to -10° C.

[0050] The olefin temperature and high pressure double reactor continuous solution polymerization reaction engineering experimental platform of the present invention is carried out. The platform is highly automated, and the main body is equipped with an automatic temperature control system, an automatic pressure control system, and an automatic feed control system. All temperature, pressure, and flow data in the system can be monitored and stored online in real time, and all liquid and gas materials are automatically and continuously fed and discharged. The platform auxiliary system also includes a gas purification system, a solvent purification system, and an inert gas protection system.

[0051] The reactor is heated by the heat transfer oil in the jacket, and the heat transfer oil is circulated and heated by the circulating oil bath. The circulating oil bath is equipped with a cooling water pipe with a solenoid valve. The pressure in the reactor is controlled by a pneumatic proportional valve installed on the discharge pipe. The control method is as follows: the pressure in the reactor is converted into an analog signal by the pressure sensor, which is received by the AI ​​module in the PLC controller and converted into a digital signal, and then transmitted to the CPU module for calculation. After that, the CPU module outputs a new digital signal and converts the output analog signal through the AO module. The analog signal is transmitted to the electrical conversion connector on the pneumatic proportional valve and converted into an air pressure of 0.2-0.4MPa, driving the actuator of the proportional valve to move up and down: when the pressure in the reactor is greater than the pressure setting value, the proportional valve opens to release the pressure, and when the pressure in the reactor is less than the pressure setting value, the proportional valve closes to hold the pressure, thereby achieving a dynamic balance of the pressure in the reactor, so that the pressure in the reactor is stabilized at ±1.5bar of the set value.

[0052] The block product prepared by the present invention has the characteristics of "hard segment" and "soft segment", that is, the melting point is relatively high and the glass transition temperature is relatively low.

[0053] Figure 1 The present invention is a schematic flow diagram of the continuous block polymerization of propylene and α-olefins used in an embodiment of the present invention; n-hexane, propylene and ethylene enter a mixing kettle after passing through respective refining columns and flow meters; the materials in the mixing kettle are evenly mixed and then cooled in a cooler before entering a reaction kettle #1, and a catalyst and a co-catalyst also enter a reaction kettle #1 to perform a primary reaction; the product of the primary reaction kettle enters a reaction kettle #2, and ethylene and a catalyst are added to the kettle #2 at the same time, the product of the secondary reaction is mixed with an antioxidant and a deactivator and then subjected to a primary devolatilization, and then subjected to a secondary devolatilization after heat exchange, granulated to obtain a product, and packaged; the n-hexane, ethylene and propylene are recovered.

[0054] In order to further illustrate the present invention, a method for continuous block polymerization of propylene and α-olefin provided by the present invention is described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0055] Preparatory Example

[0056] 1. Before the experiment, clean the reactor and pipelines with a solution of triisobutylaluminum and solvent to remove water and oxygen;

[0057] 2. Before the experiment, under nitrogen protection, the main catalyst and co-catalyst were mixed with the solvent to form solutions and stored in their respective feeding tanks; the solvent, propylene and α-olefin were refined and impurities were removed to meet the polymerization requirements;

[0058] 3. Open the solvent flow, start the mixing kettle, the first reactor (reaction kettle 1#), and the second reactor (reaction kettle 2#) for stirring, set the stirring speed of the mixing kettle to 50r / min, and the speed of the reactor to 500r / min, open the feed valve of the solvent metering pump, and gradually increase the set flow rate of the metering pump. After the material fills the mixing kettle and the two reactors, it overflows from the discharge valve on the top of the kettle, and the pressure in the kettle is controlled by a proportional valve;

[0059] 4. After the pressure and flow rate are stable, open the valves for propylene, α-olefin, and co-catalyst to enter the mixing kettle and the valves for α-olefin to enter the reaction kettle No. 2, use a metering pump to adjust the flow rate of propylene, α-olefin, and co-catalyst, add propylene and α-olefin co-catalyst to the mixing kettle, and add α-olefin to the reaction kettle No. 2; the residence time of the materials in the reactor can be adjusted by changing the flow rate of each material.

[0060] 5. After the solvent, propylene, α-olefin and co-catalyst are fed for 1 hour and are considered to be evenly mixed, start feeding the catalyst so that the flow rate of the catalyst into the two reactors remains consistent; adjust the temperature of the oil bath and cooler according to the temperature of the reactor to keep the temperature in the reactor under control.

[0061] 6. The reaction product is subjected to primary devolatilization (flash kettle) at 210°C / 1.5MPa and secondary devolatilization (twin-screw extruder) at 210°C / 0.02MPa, and then enters the granulator for granulation. The volatile matter removed is recycled after condensation and distillation.

[0062] Comparative Example 1

[0063] The following processes are carried out based on the preparation example:

[0064] The main catalyst used is dimethylsilyl bridge-tetramethylcyclopentadienyl-tert-butylamino-titanium dichloride; the co-catalyst is MMAO; the solvent is n-hexane; the α-olefin is ethylene;

[0065] The polymerization kettle volume is 1L, the temperature is set to 80°C; pressure: 2.0MPa; the stirring speed is set to 500r / min, the n-hexane feed rate is 1.57kg / h, the propylene feed rate is 0.9kg / h, the ethylene feed rate of reaction kettle 1# is 0.2kg / h, the ethylene feed rate of reaction kettle 2# is 0kg / h, the concentration of the co-catalyst is 300mmol / L, the feed rate is 60mL / h, the main catalyst feed concentration is 1.0mmol / L, the feed rate is 60mL / h; after the reaction is stable for 3h, samples are taken for detection.

[0066] The results are as follows: the product weight average molecular weight is 248,000, the molecular weight distribution is 2.52, the melting point is 55.22°C, the glass transition temperature is -20.99°C, the melt index is 6.2g / 10min, the tensile strength is 5.22MPa, and the elongation at break is 1205.76%.

[0067] Example 1

[0068] Different from Comparative Example 1, the ethylene feed flow rate of reaction kettle #1 is 0.15 kg / h, and the ethylene feed flow rate of reaction kettle #2 is 0.05 kg / h.

[0069] The results are as follows: the product weight average molecular weight is 267,000, the molecular weight distribution is 2.42, the melting point is 59.5°C, the glass transition temperature is -28.15°C, the melt index is 4.7g / 10min, the tensile strength is 10.09MPa, and the elongation at break is 925.8%.

[0070] Example 2

[0071] Different from Comparative Example 1, the ethylene feed flow rate of reaction kettle #1 is 0.15 kg / h, and the ethylene feed flow rate of reaction kettle #2 is 0.1 kg / h.

[0072] The results are as follows: the product weight average molecular weight is 298,000, the molecular weight distribution is 2.48, the melting point is 78.5°C, the glass transition temperature is -29.52°C, the melt index is 3.8g / 10min, the tensile strength is 15.29MPa, and the elongation at break is 1025.4%.

[0073] Example 3

[0074] Different from Comparative Example 1, the ethylene feed flow rate of reaction kettle #1 is 0.15 kg / h, and the ethylene feed flow rate of reaction kettle #2 is 0.15 kg / h.

[0075] The results are as follows: the product weight average molecular weight is 307,000, the molecular weight distribution is 2.54, the melting point is 101.3°C, the glass transition temperature is -31.52°C, the melt index is 2.5g / 10min, the tensile strength is 20.15MPa, and the elongation at break is 1225.4%.

[0076] As can be seen from the above embodiments, the present invention provides a method for continuous block polymerization of propylene and α-olefin, comprising the following steps: uniformly mixing a solvent, propylene, α-olefin, a main catalyst and a co-catalyst and then entering a primary reactor for reaction to obtain a primary reaction product; the flow ratio of the propylene and α-olefin is (0.8-1.0): (0.1-0.3); the primary reaction product and the α-olefin enter a secondary reactor for secondary reaction to obtain a secondary reaction product; the flow ratio of the α-olefin in the secondary reactor to the propylene in the primary reactor is (0.04-0.07): (0.8-1.0); the secondary reaction product is mixed with an antioxidant and a deactivator and then subjected to primary devolatilization and secondary devolatilization, granulation, and a propylene-α-olefin block copolymer is obtained. The method provided by the present invention adopts double-kettle continuous production, and by controlling the ratio of propylene and α-olefin in each reactor, the propylene content in the product is adjusted, so that the product has both a "soft segment" with a low propylene content and a "hard segment" with a high propylene content, so that the product has excellent high and low temperature resistance.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuous block polymerization of propylene and α-olefin, comprising the following steps: Putting solvent, propylene, α-olefin, main catalyst and co-catalyst into a primary reaction kettle for reaction to obtain a primary reaction product; the flow ratio of propylene and α-olefin is (0.8-1.0):(0.1-0.3); The primary reaction product and α-olefin are introduced into a secondary reaction kettle for secondary reaction to obtain a secondary reaction product; the flow ratio of α-olefin in the secondary reaction kettle to propylene in the primary reaction kettle is (0.04-0.07):(0.8-1.0); The secondary reaction product is mixed with an antioxidant and a deactivator, and then subjected to primary devolatilization and secondary devolatilization, and granulated to obtain a propylene-alpha-olefin block copolymer.

2. The method according to claim 1, characterized in that The α-olefin is selected from one or more of ethylene, 1-butene, 1-hexene and 1-octene; The solvent is selected from one or more of isomeric saturated alkanes, n-pentane, n-hexane, methylcyclopentane, n-heptane, methylcyclohexane, an isomeric saturated alkane mixture and toluene.

3. The method according to claim 1, characterized in that The catalyst comprises a main catalyst and a co-catalyst; The main catalyst is selected from a mixture of dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-dimethyltitanium and a boron agent in a molar ratio of 1:1.2 to 5.0, or dimethylsilyl bridge group-tetramethylcyclopentadienyl-tert-butylamino-titanium dichloride; The co-catalyst is selected from one or more of triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum dichloride, methylaluminoxane, modified methylaluminoxane, perfluorophenylboron, triphenylcarbon-tetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate and N,N-dicetylaniliniumtetrakis(pentafluorophenyl)borate.

4. The method according to claim 1, characterized in that: The reaction temperature in the primary reactor is 30-100°C; The pressure of α-olefin is 0.4 to 4 MPa.

5. The method according to claim 1, characterized in that The inactivator is selected from deionized water, water vapor or carbon monoxide; The antioxidant is selected from one or more of antioxidant 1010, antioxidant 288, antioxidant 4030, antioxidant A and antioxidant D.

6. The method according to claim 1, characterized in that The temperature of the first stage devolatilization is 205-215°C, and the pressure of the first stage devolatilization is 1.4-1.6MPa; The temperature of the secondary devolatilization is 205-215°C, and the pressure of the secondary devolatilization is 0.015-0.025 MPa.

7. The method according to claim 1, characterized in that The residence time in the primary reactor is 5 to 30 minutes; The residence time in the secondary reactor is 5 to 30 minutes.

8. The method according to claim 1, characterized in that The stirring rate in the mixing kettle is 30-60 rpm; The stirring speeds in the primary reactor and the secondary reactor are both 100-600 rpm.

9. The method according to claim 1, characterized in that: The propylene-α-olefin block copolymer is a propylene-based elastomer; The propylene-based elastomer has a melting point of 55 to 110°C and a glass transition temperature of -35 to -10°C.

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