Polypropylene composition for extrusion molding and preparation method thereof

Abstract

The invention discloses a polypropylene composition for extrusion molding and a preparation method thereof, the melt index of the polypropylene composition is 0.1-3g / 10min, the preparation method comprises the following steps: adding a propylene monomer and a catalyst system into a first reaction kettle to carry out body liquid-phase pre-polymerization, then transferring the material of the first reaction kettle into a second reaction kettle, and carrying out heat preservation at the temperature of 50-60 DEG C to obtain the polypropylene composition for extrusion molding. Adding propylene and hydrogen into a second reaction kettle, carrying out propylene homopolymerization, transferring materials in the second reaction kettle into a third reaction kettle, adding propylene and ethylene into the third reaction kettle, and carrying out ethylene-propylene copolymerization, so as to obtain heterophase polypropylene with high ethylene content; the preparation method comprises the following steps: adding peroxide, an antioxidant and a nucleating agent into heterophase polypropylene, and carrying out extrusion granulation to obtain the polypropylene composition for extrusion molding. The polypropylene composition for extrusion molding has good processing fluidity and low-temperature impact resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefin materials, and in particular relates to a low-temperature high-impact polypropylene composition for extrusion molding and a preparation method thereof. Background Art

[0002] Polypropylene is facing problems such as a rapid increase in industry products and fierce competition in product homogeneity. It is an extremely urgent task to develop new products and improve the added value of polypropylene products and industry competitiveness.

[0003] Although olefin polymerization catalysts with new structures and new properties are constantly being discovered and applied in the research of high-performance polyolefins, some high-performance polyolefin resins with broad application prospects still lack effective catalytic polymerization preparation methods. For example, polypropylene in-reactor alloys represented by impact copolymer polypropylene (hiPP) have great application potential in the fields of automobiles, instruments and equipment, and durable consumer goods. However, the rubber content of hiPP is currently low during the synthesis process, and the rubber content can only be increased by post-polymerization modification to further improve its toughness. The main reason is that during the polymerization process, polypropylene particles act as particle reactors, and rubber is easily migrated to the particle surface when it is generated, resulting in pore blockage in the "particle reactor" (polymer particles). This will lead to two results: (1) The activity decays too quickly in the later stage of polymerization, and it is difficult to increase the rubber content even if the reaction time is extended; (2) Due to the migration of rubber to the surface of polymer particles, the polymer particles stick together, and even the polymer particles adhere to the reactor, resulting in polymer agglomeration and transportation difficulties, which ultimately leads to serious production accidents such as suspension and parking.

[0004] Chinese patent CN113105575B discloses a method for preparing a special material for ultra-high ethylene content and high toughness polypropylene. A new type of organic phosphite compound is used as an electron donor to improve the copolymerization performance of the catalyst and prepare high-impact polypropylene. The ethylene content of the product can reach 28.5%, and the impact strength (-20°C) of the product can reach 25.9KJ / m 2 However, the low-temperature impact performance of the polypropylene product obtained by this method is not sufficiently improved.

[0005] Chinese patent CN201811220018.7 discloses a low-temperature, high-toughness, impact-resistant polypropylene composition and its preparation method, which uses a β-composite nucleating agent, mainly containing nano-powder rubber and a β-nucleating agent, and the product impact strength (-20°C) can reach 69.1KJ / m 2 However, the polypropylene product obtained by this method is relatively unstable in the β-crystal form during the product processing, and the product processing window is narrow.

[0006] Chinese patent CN102079841A discloses a high-flow impact-resistant polypropylene composition, the components of which include: 85-95 parts of block copolymer polypropylene, 5-15 parts of high-density polyethylene, 0.1-0.25 parts of processing aids, 0.15-0.2 parts of nucleating agents and 5-8 parts of peroxide masterbatch. However, the melt index of the polypropylene composition is greater than 30g / min, and the product is a high melt index polypropylene, which can only be used in the field of injection molding, but not in the field of extrusion molding; and the low-temperature impact strength of the obtained polypropylene composition at -20°C is not higher than 7KJ / m 2 , low temperature impact resistance is poor. Summary of the invention

[0007] The technical problem to be solved by the present invention is that the existing polypropylene material has poor low temperature impact resistance. The present invention adds a combination of multiphase polypropylene and peroxide, antioxidant and nucleating agent to obtain a polypropylene composition with good processing fluidity and low temperature impact resistance.

[0008] In order to solve the above technical problems, the present invention discloses a method for preparing a polypropylene composition for extrusion molding, wherein the melt index of the polypropylene composition is 0.1-3g / 10min, and the preparation method comprises the following steps:

[0009] (1) adding propylene monomer and a catalyst system into a first reactor to carry out bulk liquid phase prepolymerization, then transferring the material in the first reactor to a second reactor, adding propylene and hydrogen into the second reactor to carry out propylene homopolymerization, transferring the material in the second reactor to a third reactor, adding propylene and ethylene into the third reactor to carry out ethylene-propylene copolymerization, and obtaining a heterophasic polypropylene with a high ethylene content;

[0010] (2) adding peroxide, antioxidant and nucleating agent to the heterophasic polypropylene obtained in step (1) and performing extrusion granulation to obtain a polypropylene composition for extrusion molding;

[0011] The multiphase polypropylene is composed of homopolymer polypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolymer polypropylene is 92-97%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 30-40%, the ratio of the unit content of ethylene structure to that of propylene structure is 0.8-3:1, and it contains long sequence polyethylene segments. The ethylene-propylene random copolymer has a branched or cross-linked structure and has two melting peaks located at 160-170°C and 110-130°C respectively; the melt index of the multiphase copolymer polypropylene is 0.3-3g / 10min.

[0012] In the method for preparing the polypropylene composition for extrusion molding of the present invention, the polymerization temperature of the first reaction kettle is 10-30° C., and the residence time is 5-30 min.

[0013] In the method for preparing the polypropylene composition for extrusion molding of the present invention, the mass ratio of the propylene monomer to the main catalyst in the first reactor is 1.5×10 6 ~1×10 5 .

[0014] The invention discloses a method for preparing a polypropylene composition for extrusion molding. The catalyst system comprises a main catalyst, a co-catalyst, an external electron donor and a branched cross-linking auxiliary agent.

[0015] The method for preparing the polypropylene composition for extrusion molding of the present invention, wherein the main catalyst is a ZN catalyst;

[0016] The co-catalyst is selected from at least one of alkyl aluminum compounds, preferably triethyl aluminum; the mass ratio of the main catalyst to the co-catalyst is calculated on the basis of titanium / aluminum mass, and the ratio of the main catalyst to the co-catalyst is 1:15 to 1:300, preferably 1:30 to 1:80;

[0017] The general formula of the external electron donor is R1R2Si(OR3)2, R1 and R2 are the same or different, and are independently selected from C1-C6 straight chain or branched aliphatic groups, and there is at most one cyclic aliphatic group in R1 and R2; R3 is a C1-C2 straight chain alkane group; the mass ratio of the added amount of the cocatalyst to the external electron donor is 1 to 10, preferably 3 to 7;

[0018] The branched crosslinking auxiliary agent is at least one of non-conjugated α, ω-dienes and di(7-octenyl)dichlorosilane; when the non-conjugated α, ω-dienes and di(7-octenyl)dichlorosilane are added simultaneously, the mass ratio of the non-conjugated α, ω-dienes to di(7-octenyl)dichlorosilane is 0.1 to 1:1; and the mass ratio of the added amount of the branched crosslinking auxiliary agent to the main catalyst is 2:1 to 6:1.

[0019] The method for preparing the polypropylene composition for extrusion molding of the present invention, wherein the external electron donor is selected from at least one of methylcyclohexyldimethoxysilane, di-2-methylpropyl-dimethoxysilane, cyclohexyl-methyl-dimethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, and di-2-methylphenyl-dimethoxysilane;

[0020] The non-conjugated α,ω-diene is selected from at least one of 1,9-decadiene, 1,7-octadiene and 1,5-hexadiene.

[0021] In the method for preparing the polypropylene composition for extrusion molding of the present invention, in the second reactor, the concentration of hydrogen is 500-5000 ppm, the reaction temperature is 60-70° C., and the reaction pressure is 4000-5000 Kpa.

[0022] In the method for preparing the polypropylene composition for extrusion molding of the present invention, in the third reactor, the reaction temperature is 70-80° C., the reaction pressure is 1000-1500 Kpa, and the molar ratio of the added amounts of propylene and ethylene is 1:1 to 1:3.

[0023] The present invention also discloses a polypropylene composition for extrusion molding, wherein the polypropylene composition has a melt index of 0.1-3 g / 10 min and is mainly composed of the following raw materials in parts by weight: 100 parts of heterophasic polypropylene, 0.01-0.30 parts of peroxide, 0.1-0.5 parts of antioxidant and 0.1-0.5 parts of nucleating agent;

[0024] The multiphase polypropylene is composed of homopolymer polypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolymer polypropylene is 92-97%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 30-40%, the ratio of the unit content of ethylene structure to that of propylene structure is 0.8-3:1, and it contains long sequence polyethylene segments. The ethylene-propylene random copolymer has a branched or cross-linked structure and has two melting peaks located at 160-170°C and 110-130°C respectively; the melt index of the multiphase copolymer polypropylene is 0.3-3g / 10min.

[0025] The polypropylene composition for extrusion molding of the present invention, the peroxide is preferably added in an amount of 0.02 to 0.10 parts, has a decomposition temperature of ≤260°C, and is selected from at least one of 2,5-dimethyl-2,5 (di-tert-butyl peroxy) hexane, diisopropylbenzene peroxide, di-tert-butyl peroxide and benzoyl peroxide; preferably, the peroxide is 2,5-dimethyl-2,5 (di-tert-butyl peroxy) hexane and / or di-tert-butyl peroxide.

[0026] In the polypropylene composition for extrusion molding of the present invention, the added amount of the antioxidant is preferably 0.15-0.30 parts; and the antioxidant is at least one selected from the group consisting of antioxidant 1010, antioxidant 1680, antioxidant 264, and antioxidant 215.

[0027] The polypropylene composition for extrusion molding of the present invention, the addition amount of the nucleating agent is preferably 0.1 to 0.3 parts; the nucleating agent is substituted aromatic heterocyclic phosphates, sorbitol acetals, nucleating agents, etc., selected from at least one of methylene bis (4,6-di-tert-butylphenyl) sodium phosphate, bis (2,4-di-tert-butylphenyl) sodium phosphate, and sorbitol acetals.

[0028] The preparation method of the polypropylene composition for extrusion molding of the present invention comprises the following steps: the melt index of the multiphase copolymerized polypropylene is 0.1-3g / 10min; the ethylene-propylene random copolymer is 30-40%, the ratio of the content of the ethylene structure to the content of the propylene structure unit in the ethylene-propylene random copolymer is 0.8-3:1, and the 0°C simple supported beam notched impact strength of the multiphase polypropylene is greater than 40KJ / m 2 .

[0029] The polypropylene composition for extrusion molding and the preparation method thereof of the present invention add a branched crosslinking auxiliary agent during the polymerization process, which can effectively inhibit the bonding of polymer particles due to excessively high molecular chain content of linear molecular chain copolymer components during the polymerization process. The addition of the multiphase polypropylene of the present invention can provide a higher rubber phase composition and improve the impact resistance of the product. At the same time, the mechanical properties of the product can be further improved by adding peroxide and nucleating agent during the granulation process. The present invention can increase the content of ethylene-propylene rubber and change the molecular chain structure from the two aspects of catalyst system composition and reactive extrusion, and finally synthesize a polypropylene composition with good processing fluidity and low-temperature impact resistance, which can be used as a toughening modifier in the fields of automobiles, home appliances, etc., and can also be used as an elastomer in the fields of coils and foaming. DETAILED DESCRIPTION

[0030] Evaluation and analysis methods:

[0031] In the following examples, the properties involved are tested in the following ways: The tensile strength of the product is tested according to the method specified in the national standard "GB / T 1040.1-2018 Determination of tensile properties of plastics". The impact strength of the product is tested according to the method specified in the national standard "GB / T 1843-2008 Determination of cantilever beam impact strength of plastics". The melt flow index of the product is tested according to the method specified in "GB T 3682.1-2018 Plastics Thermoplastics Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) Determination Part 1: Standard Method". Ethylene content is determined by infrared spectroscopy. The determination of xylene soluble content is carried out according to "GB / T 24282-2021 Determination of xylene soluble content in plastic polypropylene".

[0032] Example 1

[0033] The ZN catalyst component was prepared by the method described in Example 1 of Chinese patent CN101735346A.

[0034] The reactants were added to the first reactor, wherein the propylene monomer flow rate was 30 kg / h, the main catalyst ZN catalyst flow rate was 0.02 g / h, the cocatalyst triethylaluminum flow rate was 0.6 g / h, and the external electron donors methylcyclohexyldimethoxysilane, 1,9-decadiene and di(7-octenyl)dichlorosilane were prepolymerized at a temperature of 10°C and a residence time of 30 min. Among them, the mass ratio of 1,9-decadiene and di(7-octenyl)dichlorosilane was 0.2:1, the mass ratio of the total amount of 1,9-decadiene and di(7-octenyl)dichlorosilane to the main catalyst was 2:1, and the mass ratio of the cocatalyst to the external electron donor was 3:1.

[0035] The material in the first reactor was transferred to the second reactor, and propylene and hydrogen were added to the second reactor to carry out propylene homopolymerization, with a hydrogen concentration of 500 ppm, a reaction temperature of 60°C, a reaction pressure of 4000 KPa, and a residence time of 40 min.

[0036] The material in the second reactor was transferred to the third reactor, and propylene and ethylene were added to the third reactor to carry out ethylene-propylene copolymerization. The molar ratio of propylene to ethylene was 1:1, the reaction temperature was 70°C, the reaction pressure was 1000Kpa, and the residence time was 60min to obtain a heterophasic polypropylene with a high ethylene content.

[0037] After testing, the multiphase polypropylene is composed of homopolymer polypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolymer polypropylene is 92%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 40%, the ratio of the unit content of ethylene structure to that of propylene structure is 3:1, it contains long sequence polyethylene segments, the ethylene-propylene random copolymer has a branched or cross-linked structure, and has two melting peaks located at 160°C and 110°C respectively; the melt index of the multiphase copolymer polypropylene is 0.3g / 10min.

[0038] 100 parts of the above-mentioned heterophasic polypropylene, 0.01 parts of 2,5-dimethyl-2,5 (di-tert-butylperoxy) hexane, 0.05 parts of antioxidant 1010, 0.1 parts of antioxidant 1680, and 0.1 parts of nucleating agent methylene bis (4,6-di-tert-butylphenyl) sodium phosphate were melt-extruded and granulated at a granulation temperature of 210°C.

[0039] The test results of the heterogeneous copolymer polypropylene and the pellets after granulation are shown in Table 1.

[0040] Example 2

[0041] The reactants were added to the first reactor, wherein the propylene flow rate was 25 kg / h, the main catalyst ZN catalyst flow rate was 0.25 g / h, the cocatalyst triethylaluminum flow rate was 20 g / h, and the external electron donor di-2-methylpropyl-dimethoxysilane, 1,5-hexadiene and di(7-octenyl)dichlorosilane were prepolymerized, the reaction temperature was 30°C, and the residence time was 5 min. Among them, the mass ratio of 1,5-hexadiene and di(7-octenyl)dichlorosilane was 1:1, the mass ratio of the total amount of 1,5-hexadiene and di(7-octenyl)dichlorosilane to the main catalyst was 6:1, and the mass ratio of the cocatalyst to the external electron donor was 7:1.

[0042] The material in the first reactor was transferred to the second reactor, and propylene and hydrogen were added to the second reactor to carry out propylene homopolymerization, with a hydrogen concentration of 5000 ppm, a reaction temperature of 70°C, a reaction pressure of 5000 KPa, and a residence time of 30 min.

[0043] The material in the second reactor was transferred to the third reactor, and propylene and ethylene were added to the third reactor to carry out ethylene-propylene copolymerization. The molar ratio of propylene to ethylene was 1:3, the reaction temperature was 80°C, the reaction pressure was 1500Kpa, the hydrogen concentration was 500ppmu, and the residence time was 80min to obtain a heterophasic polypropylene with a high ethylene content.

[0044] After testing, the multiphase polypropylene is composed of homopolypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolypropylene is 97%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 30%, the ratio of the unit content of ethylene structure to that of propylene structure is 0.8:1, it contains long sequence polyethylene segments, the ethylene-propylene random copolymer has a branched or cross-linked structure, and has two melting peaks located at 170° C. and 130° C. respectively; the melt index of the multiphase copolymer polypropylene is 3 g / 10 min.

[0045] The nucleating agent used is sodium bis(2,4-di-tert-butylphenyl)phosphate.

[0046] Other conditions are the same as in Example 1.

[0047] The test results of the heterogeneous copolymer polypropylene and the pellets after granulation are shown in Table 1.

[0048] Example 3

[0049] The process of Example 3 is similar to that of Example 1, except that the external electron donor is cyclohexyl-methyl-dimethoxysilane, and 100 parts of the above-mentioned multiphase copolymer polypropylene, 0.3 parts of diisopropylbenzene peroxide, 0.5 parts of antioxidant 1010, 0.1 parts of antioxidant 1680, and 0.5 parts of nucleating agent sodium bis(2,4-di-tert-butylphenyl) phosphate are melt-extruded and granulated at a granulation temperature of 210°C.

[0050] Example 4

[0051] The process of Example 4 is similar to that of Example 1, except that the external electron donor is diphenyldimethoxysilane, the flow rate of the main catalyst ZN catalyst is 0.1 g / h, the flow rate of the co-catalyst triethylaluminum is 10 g / h, the mass ratio of the co-catalyst to the external electron donor is 1:1, the reaction temperature is 20°C, and the residence time is 20 min; the residence time of the second reactor is 20 min, and the residence time of the third reactor is 100 min; the non-conjugated α, ω-dienes in the branched crosslinking aid are only di(7-octenyl)dichlorosilane, and the mass ratio of the added amount of the branched crosslinking aid to the main catalyst is 4:1; the hydrogen concentration of the second reactor is 2000 ppm, and the reaction pressure is 4500 Kpa; the temperature of the third reactor is 75°C, the reaction pressure is 1200 Kpa, and the molar ratio of the added amount of propylene to ethylene is 1:2; the antioxidant is 0.3 parts of antioxidant 264.

[0052] Example 5

[0053] The process of Example 5 is similar to that of Example 1, except that the external electron donor is diphenyldiethoxysilane, the flow rate of the main catalyst ZN catalyst is 0.1 g / h, the flow rate of the co-catalyst triethylaluminum is 10 g / h, the mass ratio of the co-catalyst to the external electron donor is 10:1, the reaction temperature is 20°C, and the residence time is 20 min; the branched cross-linking auxiliary agent is only a non-conjugated α, ω-diene, which is 1,7-octadiene, and the mass ratio of the branched cross-linking auxiliary agent to the main catalyst is 4:1; the hydrogen concentration of the second reactor is 2000 ppm, and the reaction pressure is 4500 Kpa; the temperature of the third reactor is 75°C, the reaction pressure is 1200 Kpa, and the molar ratio of the added amount of propylene to ethylene is 1:2. 100 parts of the above-mentioned multiphase copolymer polypropylene, 0.1 parts of diisopropylbenzene peroxide, 0.05 parts of antioxidant 1010, 0.1 parts of antioxidant 1680, and 0.2 parts of nucleating agent methylene bis(4,6-di-tert-butylphenyl) sodium phosphate were melt-extruded and granulated at a granulation temperature of 220°C.

[0054] Example 6

[0055] The process of Example 6 is similar to that of Example 1, except that the temperature of the second reaction kettle is 65°C.

[0056] Example 7

[0057] The process of Example 7 is similar to that of Example 1, except that the temperature of the third reactor is 80° C., the reaction pressure is 1500 Kpa, and the molar ratio of the added amounts of propylene and ethylene is 1:2.

[0058] Comparative Example 1

[0059] During the granulation process, 100 parts of the heterophasic polypropylene, 0.05 parts of antioxidant 1010 and 0.1 parts of antioxidant 1680 were melt extruded and granulated at a granulation temperature of 210° C. Other conditions were the same as in Example 1.

[0060] The properties of the heterophasic polypropylene and the pellets after pelletization are shown in Table 1.

[0061] Comparative Example 2

[0062] No 1,9-decadiene and di(7-octenyl)dichlorosilane were added to the first reaction vessel.

[0063] Other conditions are the same as in Example 1.

[0064] The properties of the heterophasic polypropylene and the pellets after pelletization are shown in Table 1.

[0065] Table 1

[0066]

[0067] The present invention may also have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention. The experimental methods without specific conditions in the embodiments are usually based on conventional conditions.

Claims

1. A method for preparing a polypropylene composition for extrusion molding, characterized in that: The melt index of the polypropylene composition is 0.1-3 g / 10 min, and the preparation method comprises the following steps: (1) adding propylene monomer and a catalyst system into a first reactor to carry out bulk liquid phase prepolymerization, then transferring the material in the first reactor to a second reactor, adding propylene and hydrogen into the second reactor to carry out propylene homopolymerization, transferring the material in the second reactor to a third reactor, adding propylene and ethylene into the third reactor to carry out ethylene-propylene copolymerization, and obtaining a heterophasic polypropylene with a high ethylene content; (2) adding peroxide, antioxidant and nucleating agent to the heterophasic polypropylene obtained in step (1) and performing extrusion granulation to obtain a polypropylene composition for extrusion molding; The multiphase polypropylene is composed of homopolymer polypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolymer polypropylene is 92-97%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 30-40%, the ratio of the unit content of ethylene structure to that of propylene structure is 0.8-3:1, and it contains long sequence polyethylene segments. The ethylene-propylene random copolymer has a branched or cross-linked structure and has two melting peaks located at 160-170°C and 110-130°C respectively; the melt index of the multiphase copolymer polypropylene is 0.3-3g / 10min.

2. The preparation method according to claim 1, characterized in that: The polymerization temperature of the first reactor is 10-30° C., and the residence time is 5-30 min.

3. The preparation method according to claim 1, characterized in that: The catalyst system includes a main catalyst, a co-catalyst, an external electron donor and a branched cross-linking auxiliary agent; The main catalyst is a ZN catalyst; The co-catalyst is selected from at least one of alkyl aluminum compounds; the mass ratio of the main catalyst to the co-catalyst is calculated on the basis of titanium / aluminum mass, and the ratio of the main catalyst to the co-catalyst is 1:15 to 1:300; The general formula of the external electron donor is R1R2Si(OR3)2, R1 and R2 are the same or different, and are independently selected from C1-C6 straight chain or branched aliphatic groups, and there is at most one cyclic aliphatic group in R1 and R2; R3 is a C1-C2 straight chain alkane group; the mass ratio of the added amount of the co-catalyst to the external electron donor is 1 to 10; The branched crosslinking auxiliary agent is at least one of non-conjugated α, ω-dienes and di(7-octenyl)dichlorosilane; when the non-conjugated α, ω-dienes and di(7-octenyl)dichlorosilane are added simultaneously, the mass ratio of the non-conjugated α, ω-dienes to di(7-octenyl)dichlorosilane is 0 to 1:1; and the mass ratio of the added amount of the branched crosslinking auxiliary agent to the main catalyst is 2:1 to 6:

1.

4. The preparation method according to claim 3, characterized in that: The mass ratio of propylene monomer to main catalyst in the first reactor is 1.5×10 6 ~1×10 5 .

5. The preparation method according to claim 1, characterized in that: The external electron donor is selected from at least one of methylcyclohexyldimethoxysilane, di-2-methylpropyl-dimethoxysilane, cyclohexyl-methyl-dimethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, and di-2-methylphenyl-dimethoxysilane; The non-conjugated α,ω-diene is selected from at least one of 1,9-decadiene, 1,7-octadiene and 1,5-hexadiene.

6. The preparation method according to claim 1, characterized in that: In the second reactor, the concentration of hydrogen is 500-5000 ppm, the reaction temperature is 60-70° C., and the reaction pressure is 4000-5000 Kpa.

7. The preparation method according to claim 1, characterized in that: In the third reactor, the reaction temperature is 70-80° C., the reaction pressure is 1000-1500 Kpa, and the molar ratio of the added amounts of propylene and ethylene is 1:1 to 1:

3.

8. A polypropylene composition for extrusion molding, characterized in that The polypropylene composition has a melt index of 0.1-3 g / 10 min, and is mainly composed of the following raw materials in parts by weight: 100 parts of heterophasic polypropylene, 0.01-0.30 parts of peroxide, 0.1-0.5 parts of antioxidant, and 0.1-0.5 parts of nucleating agent; The multiphase polypropylene is composed of homopolymer polypropylene and ethylene-propylene random copolymer polypropylene, wherein the isotacticity of the homopolymer polypropylene is 92-97%; the content of xylene solubles in the ethylene-propylene random copolymer polypropylene is 30-40%, the ratio of the unit content of ethylene structure to that of propylene structure is 0.8-3:1, and it contains long sequence polyethylene segments. The ethylene-propylene random copolymer has a branched or cross-linked structure and has two melting peaks located at 160-170°C and 110-130°C respectively; the melt index of the multiphase copolymer polypropylene is 0.3-3g / 10min.

9. The polypropylene composition for extrusion molding according to claim 1 or 8, characterized in that The peroxide is added in an amount of 0.02 to 0.10 parts, has a decomposition temperature of ≤260°C, and is selected from at least one of 2,5-dimethyl-2,5 (di-tert-butylperoxy)hexane, diisopropylbenzene peroxide, di-tert-butyl peroxide and benzoyl peroxide.

10. The polypropylene composition for extrusion molding according to claim 1 or 8, characterized in that The antioxidant is added in an amount of 0.15-0.30 parts; and is selected from at least one of antioxidant 1010, antioxidant 1680, antioxidant 264, and antioxidant 215.

11. The polypropylene composition for extrusion molding according to claim 1 or 8, characterized in that: The added amount of the nucleating agent is 0.1 to 0.3 parts; the nucleating agent is selected from at least one of methylene bis(4,6-di-tert-butylphenyl) sodium phosphate, bis(2,4-di-tert-butylphenyl) sodium phosphate, and sorbitol acetal.

12. The polypropylene composition for extrusion molding according to claim 1 or 8, characterized in that: The melt index of the multiphase copolymer polypropylene is 0.1-3g / 10min; in the ethylene-propylene random copolymer, the ratio of the ethylene structure to the propylene structure unit is 0.8-3:1, and the 0°C simple supported beam notched impact strength of the multiphase polypropylene is greater than 40KJ / m 2 .

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