Catalyst composition and application thereof, and preparation method of bimodal polypropylene

Abstract

The invention provides a catalyst composition and application thereof, and a preparation method of bimodal polypropylene, the catalyst composition comprises a combination of a titanium series main catalyst, an organic aluminum compound and an external electron donor, and the external electron donor comprises a combination of an organosiloxane compound and aliphatic dicarboxylate. A specific composite external electron donor is introduced into a Ziegler-Natta catalytic system, and the active center of the Ziegler-Natta catalyst is regulated through the combined action of the external electron donor, so that the active center with different hydrogen regulation sensitivities is formed, the molecular weight distribution of polypropylene is widened, and bimodal polypropylene is obtained. The preparation method of the bimodal polypropylene provided by the invention has the advantages of simple process, cost advantage and high production efficiency, and the product has good processing and application performance and wide large-scale application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of olefin polymerization, and particularly relates to a catalyst composition, its application, and a preparation method of bimodal polypropylene. Background Art

[0002] The typical characteristic of bimodal polypropylene is that the product includes components with relatively low molecular weight and components with relatively high molecular weight, presenting two peaks in the molecular weight distribution curve, and having a relatively wide molecular weight and distribution; among them, the high molecular weight component can provide good mechanical properties of the product, and the low molecular weight component can provide good processing properties of the product. The combination of the two makes bimodal polypropylene have characteristics such as high heat resistance, excellent mechanical properties, good creep resistance and stress relaxation properties, and is widely used in fields such as BOPP films (biaxially oriented polypropylene films), fibers, and modified materials for automobiles and household appliances.

[0003] Preparing bimodal polypropylene is an important research topic in the current industry. For example, CN114181466A discloses a method for preparing bimodal polypropylene. This method includes separately preparing polypropylenes with different weight average molecular weights and molecular weight distribution indices, then mixing them in a specific ratio, and then mixing with a main antioxidant, an auxiliary antioxidant, an acid absorbent, an optional slip agent, and an optional nucleating agent. The obtained mixture is extruded and pelletized to obtain bimodal polypropylene. CN109476780A discloses a preparation method of a bimodal polypropylene composition, which is obtained by melt blending a high molecular weight component and a low molecular weight component. Among them, the high molecular weight component is prepared under a catalytic system of a metallocene catalyst with a bridging structure, and the low molecular weight polypropylene component is prepared by any type of catalyst; this method provides a new idea from the catalyst aspect, but the process is complex and requires two-step polymerization to obtain two polypropylene products with different molecular weights respectively, and then blend them to obtain, with high technical cost and technical difficulty. CN115785312A discloses a preparation method of bimodal polypropylene, and the catalytic system used is a Ziegler-Natta catalyst containing a composite internal electron donor, where the composite internal electron donor includes internal electron donor 1 and internal electron donor 2. Internal electron donor 1 has a specific phthalene structure, which is beneficial to improving the activity and isotacticity of the catalyst; internal electron donor 2 has a specific nitroketone structure, which can poison the active center to a certain extent, enabling the catalyst system to form two different active centers, broadening the molecular weight distribution of the polymer, and obtaining bimodal polypropylene. However, the catalytic activity of the catalyst system with a composite internal electron donor involved in this method is relatively low, and it is difficult to achieve industrial application.

[0004] Generally speaking, the preparation methods of bimodal polypropylene mainly focus on the following four ideas: (1) Physical blending method, that is, physically blending low molecular weight polypropylene with high molecular weight polypropylene. This method has certain limitations. Usually, only existing brand names can be selected, which restricts its development; or preparing low molecular weight polypropylene and high molecular weight polypropylene separately and then blending them, with a long process flow. (2) Stepwise polymerization method, which has a complicated production process and low production efficiency. (3) Mixed catalyst method; (4) New catalyst method; These two methods rely on the use of catalysts, with high production costs and difficult R & D. Therefore, how to achieve the simple, efficient and low-cost preparation of bimodal polypropylene is an urgent problem to be solved in this field. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a catalyst composition, its application, and a preparation method of bimodal polypropylene. The catalyst composition introduces a specific external electron donor into the Ziegler-Natta catalytic system, and regulates the active centers of the Ziegler-Natta catalyst through the combined action of the external electron donors; the catalyst composition is used for catalyzing propylene polymerization, can broaden the molecular weight distribution of polypropylene, obtain a bimodal polypropylene product, simplifies the preparation process of bimodal polypropylene, has the characteristics of simplicity, high efficiency and low cost, and has broad application prospects.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a catalyst composition, which includes a combination of a titanium-based main catalyst, an organoaluminum compound, and an external electron donor, and the external electron donor includes a combination of an organosiloxane compound and an aliphatic dicarboxylate.

[0008] The present invention introduces a specific composite external electron donor into the Ziegler-Natta catalytic system, which includes a combination of an organosiloxane compound and an aliphatic dicarboxylate. The organosiloxane compound can complex with the titanium-based main catalyst to form a highly isotactic active center, and at the same time has low hydrogen response sensitivity and can obtain a high molecular weight component; the aliphatic dicarboxylate can complex with the titanium-based main catalyst to form an active center with high hydrogen response sensitivity and obtain a low molecular weight component. The catalyst composition is used for catalyzing propylene polymerization. While having high catalytic activity, the specific external electron donor can effectively regulate the active centers of the Ziegler-Natta catalyst to form active centers with different hydrogen response sensitivities, thereby broadening the molecular weight distribution of polypropylene and obtaining bimodal polypropylene.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0010] Preferably, the titanium-based main catalyst includes titanium halide, and more preferably includes titanium tetrachloride and / or titanium trichloride.

[0011] Preferably, the structure of the organoaluminum compound is AlR n X 3-n ;

[0012] Wherein, each R is independently selected from any one of C1-C10 straight chain or branched chain alkyl groups.

[0013] Wherein, the C1-C10 straight chain or branched alkyl group can be a straight chain or branched alkyl group of C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, illustratively including but not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-methylbutyl, n-pentyl, isopentyl, neopentyl, n-hexyl, neohexyl, 2-ethylhexyl, octyl, heptyl, nonyl, decyl and the like.

[0014] X is selected from halogen, and may be, for example, fluorine, chlorine, bromine or iodine.

[0015] n is selected from an integer of 1-3, for example 1, 2 or 3.

[0016] It should be noted that, when n≥2, multiple (eg, 2, 3) Rs are the same or different groups; and when n=1, two Xs are the same or different halogen atoms.

[0017] Preferably, the organoaluminum compound includes any one of trimethylaluminum, tripropylaluminum, triisobutylaluminum, tri-n-butylaluminum, trihexylaluminum, or a combination of at least two thereof, and triethylaluminum is further preferred.

[0018] Preferably, the molar ratio of titanium atoms in the titanium-based main catalyst to aluminum atoms in the organic aluminum compound is 1:(50-1000), for example, it can be 1:60, 1:80, 1:100, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400, 1:450, 1:500, 1:550, 1:600, 1:650, 1:700, 1:750, 1:800, 1:850, 1:900 or 1:950, etc.

[0019] Preferably, the structure of the organosiloxane compound is (R 1 ) a (R 2 ) b Si(OR3 ) 4-a-b ;

[0020] Wherein, R 1 , R 2 , R 3 are each independently selected from any one of substituted or unsubstituted C1-C20 straight-chain or branched-chain alkyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C6-C20 aryl, substituted or unsubstituted C7-C20 arylalkyl, and substituted or unsubstituted C7-C20 alkylaryl.

[0021] In the present invention, the C1-C20 straight-chain or branched-chain alkyl can all be straight-chain or branched-chain alkyl such as C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18 or C19, preferably C1-C10 straight-chain or branched-chain alkyl, and exemplary include but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-methylbutyl, n-pentyl, isopentyl, neopentyl, n-hexyl, neohexyl, 2-ethylhexyl, n-octyl, n-heptyl, n-nonyl, n-decyl, etc.

[0022] The C3-C20 cycloalkyl can all be monocyclic alkyl or polycyclic alkyl such as C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18 or C19, preferably C3-C10 cycloalkyl; exemplary include but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl, etc.

[0023] The C6-C20 aryl can all be monocyclic aryl or fused-ring aryl such as C6, C9, C10, C12, C14, C16, C18, etc., and exemplary include but are not limited to: phenyl, biphenyl, terphenyl, naphthyl, anthryl, phenanthryl, etc.

[0024] The C7-C20 arylalkyl can all be arylalkyl such as C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18 or C19, and its specific examples can be understood as monovalent groups obtained by substituting at least one H in the aforementioned straight-chain or branched-chain alkyl with an aryl.

[0025] The C7-C20 alkylaryl can all be alkylaryl such as C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18 or C19, and its specific examples can be understood as monovalent groups obtained by substituting at least one H in the aforementioned aryl with a straight-chain or branched-chain alkyl.

[0026] R1 and R 2 and R 3 The substituents in 3 are each independently selected from at least one of halogen (such as fluorine, chlorine, bromine or iodine), hydroxyl, mercapto, amino, C1-C6 (such as C1, C2, C3, C4, C5, C6) straight-chain or branched alkyl, C1-C6 (such as C1, C2, C3, C4, C5, C6) alkoxy, C1-C6 (such as C1, C2, C3, C4, C5, C6) alkylthio, and C1-C6 (such as C1, C2, C3, C4, C5, C6) alkylamino.

[0027] In the present invention, the group of "substituted or unsubstituted" may be substituted with one substituent or multiple substituents. When there are multiple substituents (at least 2), they may be the same or different substituents; when the same expression is involved hereinafter, it shall have the same meaning.

[0028] a and b are each independently selected from integers from 0 to 2, such as 0, 1 or 2, and a + b ≤ 3.

[0029] It should be noted that when a + b ≤ 2, multiple (such as 2 or 3) Rs 3 are the same or different groups.

[0030] Preferably, a is 1, b is 1, and the Rs 1 and R 2 are each independently selected from any one of substituted or unsubstituted C1-C10 straight-chain or branched alkyl and substituted or unsubstituted C3-C10 cycloalkyl.

[0031] Preferably, the Rs 3 are each independently selected from any one of substituted or unsubstituted C1-C10 straight-chain or branched alkyl, more preferably C1-C6 straight-chain or branched alkyl, and even more preferably methyl or ethyl.

[0032] Preferably, the organosiloxane compound includes any one or a combination of at least two of cyclohexylmethyldimethoxysilane, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, dimethyldimethoxysilane, and dibutyldimethoxysilane.

[0033] Preferably, the aliphatic dicarboxylic acid ester has a structure shown in Formula I:

[0034]

[0035] In Formula I, Rs 4 and R 5 are each independently selected from any one of unsubstituted or halogenated C1-C10 straight-chain or branched alkyl.

[0036] R 6 , R 7 Each is independently selected from any one of hydrogen, halogen (such as fluorine, chlorine, bromine or iodine), and unsubstituted or halogenated C1-C10 straight or branched chain alkyl.

[0037] Wherein, the C1-C10 straight chain or branched alkyl group can be a straight chain or branched alkyl group of C2, C3, C4, C5, C6, C7, C8, C9, etc., illustratively including but not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-methylbutyl, n-pentyl, isopentyl, neopentyl, n-hexyl, neohexyl, 2-ethylhexyl, n-octyl, n-heptyl, n-nonyl, n-decyl, etc.

[0038] The halogenated C1-C10 straight or branched alkyl group is a monovalent group obtained by replacing at least one H atom in the aforementioned C1-C10 straight or branched alkyl group with a halogen (eg, fluorine, chlorine, bromine or iodine).

[0039] m is an integer selected from 1-6, for example, 1, 2, 3, 4, 5 or 6, more preferably 1-4; when m≥2, multiple (for example, 2, 3, 4, etc.) R 6 are the same or different groups, and multiple (e.g., 2, 3, 4, etc.) R 7 are the same or different groups.

[0040] Preferably, the aliphatic dicarboxylic acid ester has a structure as shown in Formula II:

[0041]

[0042] In Formula II, R 11 , R 12 , R 13 , R 14 , R 15 , R 16 Each is independently selected from any one of hydrogen, halogen (such as fluorine, chlorine, bromine or iodine), unsubstituted or halogenated C1-C10 (such as C2, C3, C4, C5, C6, C7, C8, C9, etc.) straight chain or branched alkyl.

[0043] In Formula II, R 4 and R 5 has the same definition as in Formula I.

[0044] Preferably, the R 4 , R 5 Each is independently selected from any one of C1-C6 straight or branched alkyl groups, and more preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl.

[0045] Preferably, the aliphatic dicarboxylate includes any one or a combination of at least two of diethyl glutarate, dimethyl glutarate, diisopropyl glutarate, di-n-propyl glutarate, diethyl (2-ethyl) glutarate, diethyl (3-ethyl) glutarate, diethyl (2-chloro) glutarate, dimethyl (2-ethyl) glutarate, dimethyl (3-ethyl) glutarate, dimethyl (2-chloro) glutarate, diisopropyl (2-ethyl) glutarate, diisopropyl (3-ethyl) glutarate, and diisopropyl (2-chloro) glutarate.

[0046] Preferably, the molar ratio of the organosiloxane compound to the aliphatic dicarboxylate is 1:(0.01 - 100), and can be, for example, 1:0.02, 1:0.05, 1:0.08, 1:0.1, 1:0.5, 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:98 or 1:99, etc., and more preferably 1:(0.05 - 20).

[0047] As a preferred technical solution of the present invention, by regulating the ratio of the organosiloxane compound as an external electron donor to the aliphatic dicarboxylate, the active centers of the Ziegler-Natta catalyst can be adjusted to form active centers with different hydrogen response sensitivities, and bimodal polypropylene can be obtained. Further, by controlling the molar ratio of the organosiloxane compound to the aliphatic dicarboxylate to be 1:(0.05 - 1), and making the molar amount of the organosiloxane compound ≥ the aliphatic dicarboxylate, while regulating the active centers to obtain a wide molecular weight distribution, the isotacticity of polypropylene can be further improved.

[0048] Preferably, the molar ratio of the silicon atom in the organosiloxane compound to the titanium atom in the titanium-based main catalyst is (1 - 100):1, and can be, for example, 2:1, 3:1, 5:1, 6:1, 8:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1 or 99:1, etc.

[0049] Preferably, the titanium-based main catalyst further includes a carrier, and the titanium halide is supported on the carrier.

[0050] Preferably, the carrier includes magnesium halide (anhydrous magnesium halide), and more preferably magnesium chloride.

[0051] Preferably, the molar ratio of magnesium atoms in the magnesium halide to titanium atoms in the main titanium-based catalyst is (8-13):1, and can be, for example, 8.2:1, 8.5:1, 8.8:1, 9:1, 9.2:1, 9.5:1, 9.8:1, 10:1, 10.2:1, 10.5:1, 10.8:1, 11:1, 11.2:1, 11.5:1, 11.8:1, 12:1, 12.2:1, 12.5:1 or 12.8:1, etc.

[0052] Preferably, the main titanium-based catalyst further includes an internal electron donor; optionally, the internal electron donor is supported on the carrier.

[0053] Preferably, the internal electron donor includes any one or a combination of at least two of phthalate compounds and diether compounds.

[0054] Preferably, the phthalate compounds include any one or a combination of at least two of diisobutyl phthalate, dibutyl phthalate, diethyl phthalate, diisooctyl phthalate, and din-octyl phthalate.

[0055] Preferably, the diether compounds include any one or a combination of at least two of 9,9-bis(methoxymethyl)fluorene, 2,2-isopropylidene-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane, 2-(2-ethylhexyl)-1,3-dimethoxypropane, 2-isopropyl-1,3-dimethoxypropane, 2-butyl-1,3-dimethoxypropane, 2-sec-butyl-1,3-dimethoxypropane, 2-cyclohexyl-1,3-dimethoxypropane, and 2-tert-butyl-1,3-dimethoxypropane.

[0056] Preferably, the mass percentage content of the internal electron donor in the main titanium-based catalyst is 5%-30%, and can be, for example, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25% or 28%, as well as specific point values between the above point values. For the sake of brevity and limited space, the specific point values included in the scope of the present invention are not exhaustively listed herein.

[0057] Preferably, the main titanium-based catalyst is a solid sphere.

[0058] As a preferred technical solution, the main titanium-based catalyst includes a carrier (magnesium halide) and titanium halide and an internal electron donor supported on the carrier; the main titanium-based catalyst can be a commercially available product or can be self-made by a method well-known in the art.

[0059] Exemplarily, the preparation method of the titanium-based main catalyst includes: reacting a carrier, titanium halide, and an internal electron donor in the presence of a solvent to obtain the titanium-based main catalyst.

[0060] Preferably, the preparation method of the titanium-based main catalyst includes:

[0061] Providing a suspension, the suspension including a carrier and a solvent;

[0062] After mixing the suspension with titanium halide, adding an internal electron donor to react to obtain the titanium-based main catalyst.

[0063] Preferably, the solvent includes any one or a combination of at least two of aromatic solvents, alcohol solvents, and alkane solvents, and aromatic solvents are further preferred.

[0064] Preferably, the aromatic solvent includes toluene and / or xylene.

[0065] Preferably, the temperature of the mixing is ≤20°C. For example, it can be -30°C, -28°C, -25°C, -22°C, -20°C, -18°C, -15°C, -12°C, -10°C, -8°C, -5°C, -2°C, 0°C, 2°C, 5°C, 8°C, 10°C, 12°C, 15°C, or 18°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is -20°C to 15°C.

[0066] Preferably, the temperature of the reaction is 70 - 130°C. For example, it can be 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, or 125°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0067] Preferably, the reaction time is 0.5 - 4h. For example, it can be 1h, 1.5h, 2h, 2.5h, 3h, or 3.5h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0068] Preferably, after the reaction is completed, it further includes a post-treatment step. The post-treatment includes: filtering out the unreacted liquid, washing and drying the obtained solid product to obtain the titanium-based main catalyst.

[0069] In the catalyst composition provided by the present invention, the titanium-based main catalyst, the organoaluminum compound, and the external electron donor are stored independently; among the external electron donors, the organosiloxane compound and the aliphatic dicarboxylate can be stored independently, or the organosiloxane compound and the aliphatic dicarboxylate can be stored after being mixed in a predetermined ratio.

[0070] In a second aspect, the present invention provides an application of the catalyst composition as described in the first aspect in catalyzing olefin polymerization.

[0071] Preferably, the olefins include propylene, ethylene, and α-olefins of C4-C8 (such as C4, C5, C6, C7, C8).

[0072] Preferably, the olefin polymerization includes propylene homopolymerization or propylene copolymerization with a second monomer, and the second monomer includes at least one of ethylene and α-olefins of C4-C8 (such as C4, C5, C6, C7, C8).

[0073] In a third aspect, the present invention provides a method for preparing bimodal polypropylene, the preparation method comprising: reacting propylene and optionally a second monomer in the presence of a catalyst and hydrogen to obtain the bimodal polypropylene; the catalyst includes the catalyst composition as described in the first aspect.

[0074] In the method for preparing bimodal polypropylene provided by the present invention, the catalyst composition not only has high catalytic activity, but also a specific composite external electron donor can effectively regulate the active centers of the Ziegler-Natta catalyst to form active centers with different hydrogen response sensitivities. Specifically, the organosiloxane compound complexes with the titanium-based main catalyst to form highly isotactic active centers, but its hydrogen response sensitivity is relatively low, thereby obtaining a high molecular weight component; the aliphatic dicarboxylate complexes with the titanium-based main catalyst to form active centers with high hydrogen response sensitivity, obtaining a low molecular weight component. The present invention realizes the preparation of bimodal polypropylene through the design of the external electron donor and the catalyst, and can efficiently obtain bimodal polypropylene homopolymers (without a second monomer) and bimodal polypropylene random copolymers (propylene copolymerized with a second monomer). The method is simple, has low cost, high production efficiency, and has broad industrial application prospects.

[0075] Preferably, the second monomer includes any one or a combination of at least two of ethylene and α-olefins of C4-C8 (such as C4, C5, C6, C7, C8), and more preferably any one or a combination of at least two of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.

[0076] Preferably, based on the mass of the propylene being 100%, the mass of the second monomer ≤ 20000 ppm. For example, it can be 0 (to obtain bimodal homopolypropylene), 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm, 200 ppm, 500 ppm, 800 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 8000 ppm, 10000 ppm, 12000 ppm, 15000 ppm or 18000 ppm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0077] In the present invention, the term "ppm" represents parts per million, and 1 ppm represents one in a million.

[0078] Preferably, the preparation method includes a pre-contact step, including: adding a titanium-based main catalyst, an organoaluminum compound, and an external electron donor to a reaction device for pre-contact.

[0079] After the pre-contact, a catalytic system is obtained. Propylene, hydrogen, and optionally a second monomer are added to the reaction device loaded with the catalytic system for reaction to obtain the bimodal polypropylene.

[0080] Preferably, the pre-contact is carried out in an inert atmosphere.

[0081] Preferably, the reaction device used for the pre-contact can be an independent pre-contact reaction device (pre-contact reactor), or a polymerization reaction device (polymerization reactor).

[0082] Preferably, the temperature of the pre-contact is 5 - 50 °C. For example, it can be 8 °C, 10 °C, 12 °C, 15 °C, 18 °C, 20 °C, 22 °C, 25 °C, 28 °C, 30 °C, 32 °C, 35 °C, 38 °C, 40 °C, 42 °C, 45 °C or 48 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 10 - 40 °C, and more preferably 15 - 35 °C.

[0083] Preferably, the time of the pre-contact is 0.1 - 10 min. For example, it can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min or 9 min, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0084] In the preparation method of the present invention, the hydrogen is used as a polymerization regulator. Preferably, based on the mass of the propylene being 100%, the mass of the hydrogen is 500 - 5000 ppm. For example, it can be 800 ppm, 1000 ppm, 1200 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2200 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3200 ppm, 3500 ppm, 3800 ppm, 4000 ppm, 4200 ppm, 4500 ppm or 4800 ppm, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0085] Preferably, the reaction includes a prepolymerization reaction and a polymerization reaction that are carried out sequentially.

[0086] Preferably, the temperature of the prepolymerization reaction is 5 - 50 °C. For example, it can be 8 °C, 10 °C, 12 °C, 15 °C, 18 °C, 20 °C, 22 °C, 25 °C, 28 °C, 30 °C, 32 °C, 35 °C, 38 °C, 40 °C, 42 °C, 45 °C or 48 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 10 - 40 °C, and more preferably 15 - 35 °C.

[0087] Preferably, the pressure of the prepolymerization reaction is 0.5 - 2 MPa. For example, it can be 0.55 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa or 1.95 MPa, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 0.57 - 1.92 MPa, and more preferably 0.89 - 1.47 MPa.

[0088] Preferably, the time of the prepolymerization reaction is 1 - 20 min. For example, it can be 2 min, 4 min, 5 min, 8 min, 10 min, 12 min, 15 min or 18 min, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 3 - 10 min.

[0089] Preferably, the temperature of the polymerization reaction is 50 - 80°C, for example, it can be 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C or 78°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0090] Preferably, the pressure of the polymerization reaction is 1.8 - 3.5 MPa, for example, it can be 1.85 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.8 MPa, 3 MPa, 3.2 MPa or 3.4 MPa, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 1.92 - 3.2 MPa.

[0091] Preferably, the time of the polymerization reaction is 0.5 - 5 h, for example, it can be 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h, 3.8 h, 4 h, 4.2 h, 4.5 h or 4.8 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 1 - 3 h.

[0092] As a preferred technical solution of the present invention, the preparation method includes:

[0093] Adding a titanium-based main catalyst, an organoaluminum compound and an external electron donor into a reaction device, and pre-contacting them at 5 - 50°C for 0.1 - 10 min to obtain a catalytic system;

[0094] Feeding propylene, optionally a second monomer and hydrogen into the reaction device, and carrying out a reaction in the presence of the catalytic system to obtain the bimodal polypropylene;

[0095] Based on the mass of the propylene being 100%, the mass of the second monomer ≤ 20000 ppm, and the mass of the hydrogen is 500 - 5000 ppm;

[0096] The reaction includes a pre-polymerization reaction and a polymerization reaction carried out in sequence. The temperature of the pre-polymerization reaction is 5 - 50°C, the pressure is 0.5 - 2 MPa, and the time is 1 - 20 min; the temperature of the polymerization reaction is 50 - 80°C, the pressure is 1.8 - 3.5 MPa, and the time is 0.5 - 5 h.

[0097] On the other hand, the present invention provides a bimodal polypropylene, which is prepared by the preparation method as described in the third aspect.

[0098] Fourthly, the present invention provides a bimodal polypropylene, wherein the molecular weight distribution index of the bimodal polypropylene > 10; the bimodal polypropylene has a first melting peak and a second melting peak, the temperature of the first melting peak is 152 - 159 °C, and the temperature of the second melting peak is 160 - 168 °C.

[0099] As a preferred technical solution of the present invention, the bimodal polypropylene described in the fourth aspect can be prepared by the preparation method described in the third aspect.

[0100] The molecular weight and molecular weight distribution of the bimodal polypropylene of the present invention are tested by gel permeation chromatography (GPC). Its molecular weight distribution curve can present a bimodal distribution, or can present a peak shape enclosing two or more "bulges", or can present a relatively wide flat-top peak distribution, but is not limited to the above three peak shapes, and can present other peak shapes that meet the number-average molecular weight and distribution conditions.

[0101] Preferably, the molecular weight distribution index of the bimodal polypropylene > 10, for example, can be 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18 or 18.5, etc., preferably 10.1 - 18, and more preferably 10.3 - 16.9.

[0102] In the present invention, the term "molecular weight distribution index" is abbreviated as PDI, which is the ratio of the weight-average molecular weight to the number-average molecular weight. In the present invention, the data related to the molecular weight can be obtained by GPC (gel permeation chromatography) test, and the detector equipped with GPC is an infrared detector.

[0103] Exemplarily, the method for the GPC test includes: using a GPC-IR instrument of Polymer Char company, equipped with IR5MCT and a four-cell bridge viscometer detector, and the chromatographic column is Agilent PLgel Olexis 300mm × 7.5mm; using 1,2,4-trichlorobenzene (TCB) as the solvent and mobile phase, and adding 0.0125 wt% of 2,6-di-tert-butyl-4-methylphenol to the sample to be tested to avoid oxidative degradation during the test. The polymer sample is carried out at a flow rate of 1.0 mL / min at 160 °C.

[0104] The bimodal polypropylene has a first melting peak and a second melting peak, the temperature of the first melting peak is 152 - 159 °C, for example, can be 152.5 °C, 153 °C, 153.5 °C, 154 °C, 154.5 °C, 155 °C, 155.5 °C, 156 °C, 156.5 °C, 157 °C, 157.5 °C, 158 °C or 158.5 °C, etc., preferably 153 - 158 °C.

[0105] The temperature of the second melting peak is 160 - 168 °C, and for example, it can be 160.5 °C, 161 °C, 161.5 °C, 162 °C, 162.5 °C, 163 °C, 163.5 °C, 164 °C, 164.5 °C, 165 °C, 165.5 °C, 166 °C, 166.5 °C, 167 °C or 167.5 °C, etc., and preferably 162 - 167 °C.

[0106] In the present invention, the melting peak temperatures of the bimodal polypropylene can be obtained by testing with a differential scanning calorimeter (DSC). An exemplary testing method is as follows: Use DSC to test the sample to be measured, heat it to 200 °C at a heating rate of 20 °C / min, keep it at a constant temperature for 3 min, then cool it to 30 °C at a cooling rate of 10 °C / min, keep it at a constant temperature for 3 min, and then heat it to 200 °C at a heating rate of 10 °C / min. The two endothermic peaks in the second heating curve are the first melting peak and the second melting peak respectively, and the temperatures corresponding to the two endothermic peak values are the temperature of the first melting peak and the temperature of the second melting peak respectively.

[0107] Preferably, the number-average molecular weight of the bimodal polypropylene is ≥ 10000 g / mol, and for example, it can be 12000 g / mol, 15000 g / mol, 20000 g / mol, 30000 g / mol, 40000 g / mol, 50000 g / mol, 60000 g / mol or 70000 g / mol, etc., it can be 11000 - 60000 g / mol, preferably ≥ 12000 g / mol, more preferably ≥ 20000 g / mol, and further preferably ≥ 30000 g / mol.

[0108] Preferably, the isotactic index of the bimodal polypropylene is ≥ 95%, and for example, it can be 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or 98.5%, etc., and more preferably 96% - 98%.

[0109] In the present invention, the isotactic index can be obtained by testing with the method in Standard GB / T 2412 - 2008.

[0110] Compared with the prior art, the present invention has the following beneficial effects:

[0111] (1) In the catalyst composition provided by the present invention, a specific composite external electron donor is introduced into the Ziegler - Natta catalytic system, and the active centers of the Ziegler - Natta catalyst are regulated through the combined action of the external electron donors, so that active centers with different hydrogen response sensitivities are formed, thereby broadening the molecular weight distribution of polypropylene and obtaining bimodal polypropylene.

[0112] (2) In the preparation method of the bimodal polypropylene provided by the present invention, the efficient preparation of the bimodal polypropylene homopolymer and the bimodal polypropylene copolymer is realized through the design of the external electron donor and the catalyst. The process method is simple, has a cost advantage, high production efficiency, and the product has good processing performance, mechanical properties and application performance, and has broad prospects for large-scale application. Detailed Embodiments

[0113] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0114] As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device containing the listed elements is not necessarily limited to those elements, but may also include other elements not expressly listed or elements inherent to such composition, step, method, article or device.

[0115] In the following specific embodiments of the present invention, various reagents are commercially available chemicals.

[0116] In the following specific embodiments of the present invention, the test methods for the polymer product bimodal polypropylene are as follows:

[0117] (1) Molecular weight (weight-average molecular weight M w , number-average molecular weight M n ) and polydispersity index (PDI, M w / M n ): Tested by gel permeation chromatography (GPC). The instrument is GPC-IR of Polymer Char company, equipped with IR5MCT and four-way bridge viscometer detector. The chromatographic column is Agilent PLgel Olexis 300mm×7.5mm; 1,2,4-trichlorobenzene (TCB) is used as the solvent and mobile phase, and 0.0125wt% of 2,6-di-tert-butyl-4-methylphenol is added to the polymer sample to avoid oxidative degradation during the test. The polymer sample is carried out at a flow rate of 1.0 mL / min at 160 °C.

[0118] (2) Isotactic index: Determined by the n-heptane extraction method according to the records in Standard GB / T 2412-2008.

[0119] (3) Melting temperature (melting point) test: Test was carried out using a differential scanning calorimeter (DSC). Weighed 5 - 10 mg of the sample, heated from 30 °C to 200 °C at a heating rate of 20 °C / min, held at a constant temperature for 3 min, then cooled to 30 °C at a rate of 10 °C / min and held at a constant temperature for 3 min, and then heated to 200 °C at a heating rate of 10 °C / min. The temperature corresponding to the endothermic peak of the second heating curve was taken as the melting point. Taking Example 1 as an example, the second heating curve of the prepared bimodal polypropylene had a double endothermic peak (double melting peak), so 2 melting points were recorded.

[0120] In the following specific embodiments, the titanium-based main catalysts (Cat 1 and Cat 2), organoaluminum compounds, and external electron donors (organosiloxane compounds and aliphatic dicarboxylic acid esters) are all commercially available chemicals. Among them, the carriers in the titanium-based main catalysts are all anhydrous magnesium chloride, on which titanium tetrachloride and internal electron donors are supported. The specific information is as follows:

[0121]

[0122]

[0123] An exemplary preparation method of the titanium-based main catalyst Cat 3 is as follows: Added 10 g of anhydrous magnesium chloride and 80 mL of toluene to a 500 mL five-necked flask with stirring that had been fully replaced with nitrogen to prepare a suspension, then maintained at -15 °C and added 20 mL of titanium tetrachloride dropwise. After the addition was completed, the system was slowly heated to 10 °C and then 60 mL of titanium tetrachloride was added dropwise. Then it was slowly heated to 80 °C, and 3.0 g of 9,9-bis(methoxymethyl)fluorene was added, and then continued to be heated to 120 °C and held at a constant temperature for 2 h; then the liquid was filtered clean, the liquid was filtered off, and the obtained solid was washed 3 times with 120 mL of titanium tetrachloride at 125 °C; then the obtained solid was washed 2 times with 150 mL of hexane at 60 °C and 2 times at room temperature, the liquid was filtered off and dried to obtain a solid powder, which is the titanium-based main catalyst Cat 3. The mass content of titanium element is 2.8%, the molar ratio of titanium atoms to magnesium atoms is 1:10.3, and the mass content of the internal electron donor 9,9-bis(methoxymethyl)fluorene is 6.4%.

[0124] The exemplary preparation method of the titanium-based main catalyst Cat 4 is as follows: Add 10 g of anhydrous magnesium chloride and 80 mL of toluene into a 500 mL five-necked flask with stirring that has been fully replaced with nitrogen to prepare a suspension. Then, maintain the temperature at -15 °C and dropwise add 20 mL of titanium tetrachloride. After the addition is complete, slowly raise the temperature of the system to 10 °C and then dropwise add 60 mL of titanium tetrachloride. After that, slowly raise the temperature to 80 °C, add 4.0 g of diisobutyl phthalate and 2.5 g of diethyl glutarate, and then continue to raise the temperature to 120 °C and keep it at a constant temperature for 2 h. Then, filter the liquid until it is completely filtered, remove the liquid, and wash the obtained solid with 120 mL of titanium tetrachloride three times at 125 °C. Then, wash the obtained solid with 150 mL of hexane twice at 60 °C and twice at room temperature, filter off the liquid and dry it to obtain a solid powder, which is the titanium-based main catalyst Cat 4. The mass content of titanium element is 2.8%, the molar ratio of titanium atoms to magnesium atoms is 1:10.2, the mass content of diisobutyl phthalate is 8%, and the mass content of diethyl glutarate is 5.8%.

[0125] Example 1

[0126] A catalyst composition includes a combination of a titanium-based main catalyst, an organoaluminum compound, and an external electron donor. Among them, the titanium-based main catalyst is Cat 1. The organoaluminum compound is triethylaluminum, and the molar ratio of Al atoms to Ti atoms in the titanium-based main catalyst (hereinafter referred to as "Al / Ti") is 500:1. The external electron donor includes cyclohexylmethyldimethoxysilane and diethyl glutarate, and the molar ratio of the two is 95:5; the molar ratio of Si atoms to Ti atoms in the external electron donor (hereinafter referred to as "Si / Ti") is 30:1.

[0127] A method for preparing bimodal polypropylene uses the catalyst composition provided in this example as a catalytic system, and specifically includes the following steps: React in a 10 L high-pressure polymerization reactor. After the reactor is fully prepared under vacuum, in an inert atmosphere, add the titanium-based main catalyst, the organoaluminum compound, and the external electron donor into the reactor and pre-contact at 20 °C for 5 min. Then, add 2000 g of propylene into the reactor, introduce a small amount of hydrogen. Based on the mass of propylene being 100%, the mass of hydrogen is 1000 ppm. Control the temperature at 20 °C for pre-polymerization reaction for 5 min. Then, raise the temperature to 70 °C within 10 min and maintain this temperature for polymerization reaction for 120 min. After the reaction is completed, discharge the unreacted propylene to obtain the bimodal polypropylene. The test data of this polymer is shown in Table 1.

[0128] Examples 2 - 21, Comparative Examples 1 - 7

[0129] A catalyst composition and a method for preparing bimodal polypropylene using the same as a catalytic system. The components of the catalyst composition and some parameters in the preparation method are shown in Table 1, Table 2, Table 3 and Table 4. The "molar ratio" in the table represents the molar ratio of the organosiloxane compound and the aliphatic dicarboxylate in the external electron donor. Items not listed are the same as those in Example 1.

[0130] Table 1

[0131]

[0132]

[0133] Table 2

[0134]

[0135]

[0136] Table 3

[0137]

[0138]

[0139] In the preparation method provided in Example 21 of Table 3, after 1000 ppm of hydrogen was introduced, 5000 ppm of ethylene was introduced into the reaction kettle for polymerization reaction. Other parameters were the same as those in Example 1, and bimodal polypropylene was obtained.

[0140] Table 4

[0141]

[0142]

[0143] Combining the data in Table 1 - Table 3, it can be seen that the catalyst composition provided by the present invention is used to catalyze the homopolymerization of propylene or the copolymerization of propylene and a second monomer (such as ethylene). The obtained polypropylene has a bimodal characteristic, a wide molecular weight distribution, and the PDI can reach 10.3 - 16.9. At the same time, the number average molecular weight of the bimodal polypropylene ≥ 12000 g / mol, the isotactic index ≥ 95%, and it has two melting peaks. The temperature of the first melting peak is 154 - 159 °C, and the temperature of the second melting peak is 160 - 168 °C.

[0144] Furthermore, according to Embodiments 1-5, in the catalyst compositions of Embodiments 1-3, the external electron donor is mainly composed of an organosiloxane compound. While obtaining bimodal polypropylene with a broad molecular weight distribution, the isotactic index of the polymer can be ≥96%; bimodal polypropylene with a broad molecular weight distribution was also prepared in Embodiments 4-5. However, since the external electron donor is mainly an aliphatic dicarboxylate, the isotactic index of the molecular chains formed by the active centers formed is relatively low, resulting in a decrease in the overall isotactic index of the product. In the catalyst compositions of Embodiments 10-15, a titanium-based main catalyst Cat 2 or Cat 3 is used, and its internal electron donor is a diether compound. It can be seen that the obtained polymer also exhibits bimodal and broad molecular weight distribution characteristics and has a relatively high isotactic index. It can be seen that in the catalyst composition of the present invention, the external electron donor can be combined with different titanium-based main catalysts to catalyze propylene polymerization to obtain a bimodal polypropylene product. In addition, by using the catalyst composition of the present invention to catalyze propylene polymerization, bimodal polypropylene products with different molecular weights can be prepared by adjusting the catalyst components and the amount of hydrogen used.

[0145] In summary, the catalyst composition provided by the present invention uses a specific composite external electron donor, which catalyzes propylene polymerization to obtain polypropylene with a broad molecular weight distribution and bimodal characteristics. This is because: the organosiloxane compound can complex with the active center to form an active center with a high isotactic index. However, on the one hand, it will poison some of the low molecular weight active centers, and on the other hand, the hydrogen response sensitivity of this type of active center is relatively poor. Therefore, the polymer molecular chains obtained at this active center have a high isotactic index and a high molecular weight; the aliphatic dicarboxylate can complex with the active center to form an active center with a high hydrogen response sensitivity, and the polymer molecular chains that can be formed at this active center have a low molecular weight and a low isotactic index.

[0146] In the catalyst compositions of Comparative Examples 1-6, there is only a single-component external electron donor, and the prepared polypropylene has a narrow molecular weight distribution and does not have bimodal characteristics; in the catalyst composition of Comparative Example 7, there is only a single-component external electron donor, and the aliphatic dicarboxylate is used as the internal electron donor and added to the main catalyst. Using it to catalyze propylene polymerization, bimodal polypropylene cannot be obtained either.

[0147] Furthermore, the melt index and flexural modulus of the bimodal polypropylene provided by the examples and the polypropylene provided by the comparative examples were tested. Among them, the test of the melt index was carried out in accordance with the standard GB / T 3682.1-2018, the test temperature was 230 °C, and the mass of the weight was 2.16 kg; the test of the flexural modulus was carried out in accordance with the standard GB / T9341-2008; the test data are shown in Table 5:

[0148] Table 5

[0149]

[0150] It can be seen that, compared with single-peak polypropylene, the bimodal polypropylene provided by the present invention has a higher melt index and a higher flexural modulus, indicating its excellent processing performance, mechanical properties and application performance.

[0151] The applicant declares that the present invention uses the above embodiments to illustrate the catalyst composition of the present invention and its application, and the preparation method of bimodal polypropylene. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A catalyst composition, characterized in that, The catalyst composition comprises a combination of a titanium-based main catalyst, an organoaluminum compound, and an external electron donor, and the external electron donor comprises a combination of an organosiloxane compound and an aliphatic dicarboxylate.

2. The catalyst composition according to claim 1, wherein The titanium-based main catalyst includes titanium halide, preferably titanium tetrachloride and / or titanium trichloride; Preferably, the structure of the organoaluminum compound is AlR n X 3-n ; Wherein, each R independently is selected from any one of C1-C10 linear or branched alkyl groups; X is selected from halogens; n is selected from integers of 1-3; Preferably, the organoaluminum compound includes any one or a combination of at least two of triethylaluminum, trimethylaluminum, tripropylaluminum, triisobutylaluminum, tributylaluminum, and trihexylaluminum; Preferably, the molar ratio of titanium atoms in the titanium-based main catalyst to aluminum atoms in the organoaluminum compound is 1:(50-1000).

3. The catalyst composition according to claim 1, wherein The structure of the organosiloxane compound is (R 1 ) a (R 2 ) b Si(OR 3 ) 4-a-b ; Among them, R 1 , R 2 , R 3 are each independently selected from any one of substituted or unsubstituted C1-C20 linear or branched alkyl groups, substituted or unsubstituted C3-C20 cycloalkyl groups, substituted or unsubstituted C6-C20 aryl groups, substituted or unsubstituted C7-C20 arylalkyl groups, and substituted or unsubstituted C7-C20 alkylaryl groups; R 1 , R 2 , R 3 the substituents of the substitution described are each independently selected from at least one of halogen, hydroxyl group, mercapto group, amino group, C1-C6 linear or branched alkyl group, C1-C6 alkoxy group, C1-C6 alkylthio group, and C1-C6 alkylamino group; a and b are each independently selected from integers of 0-2, and a + b ≤ 3; Preferably, the organosiloxane compound includes any one or a combination of at least two of cyclohexylmethyldimethoxysilane, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, dimethyldimethoxysilane, and dibutyldimethoxysilane.

4. The catalyst composition according to claim 1, characterized in that, The aliphatic dicarboxylate has a structure shown in Formula I: wherein, R 4 and R 5 each independently selected from any one of unsubstituted or halogenated C1-C10 straight-chain or branched-chain alkyl groups; R 6 、R 7 each independently selected from any one of hydrogen, halogen, unsubstituted or halogenated C1-C10 straight-chain or branched-chain alkyl groups; m is selected from integers of 1-6; Preferably, the aliphatic dicarboxylate has a structure shown in Formula II: Wherein, R 11 , R 12 , R 13 , R 14 , R 15 , R 16 are each independently selected from any one of hydrogen, halogen, unsubstituted or halogenated C1-C10 straight-chain or branched-chain alkyl; R 4 and R 5 has the same defined scope as in formula I; Preferably, the aliphatic dicarboxylate includes any one or a combination of at least two of diethyl glutarate, dimethyl glutarate, diisopropyl glutarate, di-n-propyl glutarate, diethyl (2-ethyl) glutarate, diethyl (3-ethyl) glutarate, diethyl (2-chloro) glutarate, dimethyl (2-ethyl) glutarate, dimethyl (3-ethyl) glutarate, dimethyl (2-chloro) glutarate, diisopropyl (2-ethyl) glutarate, diisopropyl (3-ethyl) glutarate, and diisopropyl (2-chloro) glutarate.

5. The catalyst composition according to claim 1, wherein The molar ratio of the organosiloxane compound to the aliphatic dicarboxylate is 1:(0.01-100), preferably 1:(0.05-20); Preferably, the molar ratio of silicon atoms in the organosiloxane compound to titanium atoms in the titanium-based main catalyst is (1-100):

1.

6. The catalyst composition according to claim 1, characterized in that, The titanium-based main catalyst further includes a carrier; Preferably, the carrier includes magnesium halide, more preferably magnesium chloride; Preferably, the molar ratio of magnesium atoms in the magnesium halide to titanium atoms in the titanium-based main catalyst is (8-13):1; Preferably, the titanium-based main catalyst further includes an internal electron donor; Preferably, the internal electron donor includes any one or a combination of at least two of phthalate compounds and diether compounds; Preferably, the mass percentage content of the internal electron donor in the titanium-based main catalyst is 5%-30%.

7. Use of a catalyst composition according to any one of claims 1-6 in the catalytic polymerization of olefins.

8. A method for preparing bimodal polypropylene, characterized in that, The preparation method includes: propylene and optionally a second monomer are reacted in the presence of a catalyst and hydrogen to obtain the bimodal polypropylene; the catalyst includes the catalyst composition according to any one of claims 1-6.

9. The preparation method according to claim 8, characterized in that, The second monomer includes any one or a combination of at least two of ethylene and C4-C8 α-olefins; Preferably, based on the mass of the propylene being 100%, the mass of the second monomer ≤ 20,000 ppm; Preferably, based on the mass of the propylene being 100%, the mass of the hydrogen is 500 - 5000 ppm; Preferably, the reaction includes a prepolymerization reaction and a polymerization reaction that are carried out sequentially; Preferably, the temperature of the prepolymerization reaction is 5 - 50 °C, more preferably 10 - 40 °C; Preferably, the pressure of the prepolymerization reaction is 0.5 - 2 MPa, more preferably 0.57 - 1.92 MPa; Preferably, the time of the prepolymerization reaction is 1 - 20 min, more preferably 3 - 10 min; Preferably, the temperature of the polymerization reaction is 50 - 80 °C; Preferably, the pressure of the polymerization reaction is 1.8 - 3.5 MPa, more preferably 1.92 - 3.2 MPa; Preferably, the time of the polymerization reaction is 0.5 - 5 h, more preferably 1 - 3 h.

10. A bimodal polypropylene, characterized in that, The molecular weight distribution index of the bimodal polypropylene > 10; The bimodal polypropylene has a first melting peak and a second melting peak, the temperature of the first melting peak is 152 - 159 °C, and the temperature of the second melting peak is 160 - 168 °C; Preferably, the number average molecular weight of the bimodal polypropylene ≥ 10,000 g / mol; Preferably, the isotactic index of the bimodal polypropylene ≥ 95%.

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