A branched polyethylene and a method for its preparation

Abstract

The application discloses branched polyethylene and a preparation method thereof. The preparation method of the branched polyethylene comprises the following steps: taking an alpha-diimine nickel catalyst shown in formula (1) as a main catalyst; taking at least one selected from aluminoxane, modified aluminoxane, alkyl aluminum, alkyl aluminum hydrolyzate, halogenated alkyl aluminum, aryl boron, alkyl boron and borate as a cocatalyst; under the condition that a polymerization temperature is 60-85 DEG C and a polymerization pressure is 1.2-3.0 MPa, ethylene is polymerized by using a polymerization solvent containing a halogen-based organic solvent to obtain branched polyethylene. Compared with traditional EPDM, the branched polyethylene prepared by the method has excellent low-temperature impact performance on polypropylene base material.

Description

Technical Field

[0001] This invention relates to a branched polyethylene, a method for preparing the branched polyethylene, a polyolefin composition comprising the branched polyethylene, and the use of the branched polyethylene for improving the low-temperature impact properties of polyolefins. Background Technology

[0002] Branched polyethylene, due to the branches on its carbon chain, has low viscosity in both solution and molten states, and exhibits good mechanical properties, melt stretchability, transparency, and good processing performance, making it a major variety of polyolefin products.

[0003] Branched polyethylene has superior processing properties, better film-forming properties, and better film transmittance compared to linear polyethylene. Moreover, as the degree of branching increases, the glass transition temperature (Tg) decreases. As a result, branched polyethylene exhibits a rubber-like elastomer at room temperature, thus possessing significant industrial application value.

[0004] Currently, the conventional method for preparing branched polyethylene is to use post-transition metal catalysts. In 1995, Professor Brookhart of North Carolina State University first reported that (α-diimine) nickel catalyst I, as shown below, with chain-walking ability, could prepare high molecular weight, branched polyethylene. Subsequent researchers synthesized catalysts with other structures (Catal. Sci. Technol. 2013, 3, 1172; Macromolecules 42, 2009, 7789; Angew. Chem. Int. Ed. 2004, 43, 1821; J. Am. Chem. Soc. 2013, 135, 16316; Organometallics 23, 2004, 3276-3283), such as (α-diimine) nickel catalysts II to VII shown below. The thermal stability of these catalysts has been improved to some extent.

[0005]

[0006] On the other hand, polyethylene materials, especially polypropylene, are prone to low-temperature embrittlement in cold environments. Therefore, during transportation, construction, and use in cold northern regions, embrittlement damage easily occurs, limiting the application of polyolefins, particularly polypropylene. Thus, improving the low-temperature impact resistance of polyolefins, especially polypropylene, has always been a goal of researchers.

[0007] The structural characteristics of branched polyethylene determine that it can be used as a toughening modifier to improve the impact resistance of polypropylene. However, in actual production, there are no reports of industrial-scale branched polyethylene production processes. Furthermore, there are even fewer reports on the toughening modification of polypropylene by branched polyethylene. Moreover, the specific structure of the polymer can lead to significant differences in its toughening modification effect. Summary of the Invention

[0008] In view of the technical problems of the prior art, the inventors of this invention, through in-depth research, discovered that by using the branched polyethylene of this invention as an additive, the low-temperature impact properties of polyolefins, especially polypropylene, can be significantly improved. This expands the application range of polyolefins, particularly polypropylene, and enhances their mechanical properties.

[0009] Specifically, based on prior art, the inventors conducted in-depth research and discovered that the branched polyethylene of this invention can be prepared by controlling specific polymerization conditions, using specific polymerization catalysts, and specific polymerization solvents. The branched polyethylene of this invention can significantly improve the low-temperature impact properties of polyolefins, especially polypropylene. Thus, this invention was completed.

[0010] More specifically, the present invention relates to the following aspects.

[0011] A method for preparing branched polyethylene, characterized by comprising the following steps:

[0012] Using the α-diimine nickel catalyst shown in formula (1) as the main catalyst, and at least one selected from aluminoxanes, modified aluminoxanes, alkylaluminum, alkylaluminum hydrolysates, haloalkylaluminum, arylboron, alkylboron, and borates as a co-catalyst, ethylene is polymerized using a polymerization solvent containing a halogenated organic solvent at a polymerization temperature of 60-85°C (preferably 65-70°C) and a polymerization pressure of 1.2-3.0 MPa (preferably 1.4-2.3 MPa) to obtain branched polyethylene.

[0013]

[0014] In equation (1), R1 and R2 are each independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon groups, or R1 and R2 together with their bonded carbon atoms to form a 5-6 membered ring; R3, R5, R7, R8, R 10 R 12 Each is independently selected from C 3-10 Straight-chain or branched hydrocarbon groups, R4, R6, R9, R 11 Each is independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon group, where X is a halogen.

[0015] A polyolefin composition comprising a polyolefin and the branched polyethylene of the present invention.

[0016] The use of branched polyethylene of the present invention in improving the low-temperature impact properties of polyolefins.

[0017] Technical effect

[0018] The branched polyethylene prepared by the method of the present invention, when added as an additive to polyolefins, especially polypropylene, to form polyolefin compositions, can significantly improve the low-temperature impact strength of polyolefins (polypropylene), while simultaneously maintaining or even improving the tensile strength to a certain extent. Moreover, compared with EPDM, the polyolefin compositions of the present invention have a more significant effect on improving the low-temperature impact strength of polyolefins, and the improvement in tensile strength is also better than that of EPDM. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0020] In the context of this specification, except where expressly stated, any matters or issues not mentioned herein shall apply directly to those known in the art without any modification. Furthermore, any implementation described herein may be freely combined with one or more other implementations described herein, and any resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider such combination to be clearly unreasonable.

[0021] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not be in accordance with the common understanding of those skilled in the art.

[0022] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the appended claims.

[0023] In the context of this invention, unless otherwise specified, the physical properties of substances (such as boiling point) are measured at room temperature (25°C) and normal pressure (101325 Pa).

[0024] [Preparation method of branched polyethylene]

[0025] This invention provides a method for preparing branched polyethylene, characterized by comprising the following steps:

[0026] Using the α-diimine nickel catalyst shown in formula (1) as the main catalyst, and at least one selected from aluminoxanes, modified aluminoxanes, alkylaluminum, alkylaluminum hydrolysates, haloalkylaluminum, arylboron, alkylboron, and borates as a co-catalyst, ethylene is polymerized using a polymerization solvent containing a halogenated organic solvent at a polymerization temperature of 60-85°C (preferably 65-70°C) and a polymerization pressure of 1.2-3.0 MPa (preferably 1.4-2.3 MPa) to obtain branched polyethylene.

[0027]

[0028]

[0029] In equation (1), R1 and R2 are each independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon groups, or R1 and R2 together with their bonded carbon atoms to form a 5-6 membered ring; R3, R5, R7, R8, R 10 R 12 Each is independently selected from C 3-10 Straight-chain or branched hydrocarbon groups, R4, R6, R9, R 11 Each is independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon group, where X is a halogen.

[0030] The main catalyst of the present invention uses the α-diimine nickel catalyst shown in the following formula (1).

[0031]

[0032] In equation (1), R1 and R2 are each independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon groups, or R1 and R2 together with their bonded carbon atoms to form a 5-6 membered ring; R3, R5, R7, R8, R 10 R 12 Each is independently selected from C 3-10 Straight-chain or branched hydrocarbon groups, R4, R6, R9, R 11 Each is independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon group, where X is a halogen.

[0033] In one embodiment of the present invention, R1 and R2 are each independently selected from hydrogen and C. 1-4 Straight-chain or branched alkyl groups.

[0034] In one embodiment of the present invention, R1 and R2 are each independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0035] In one embodiment of the present invention, R1 and R2 are each independently selected from hydrogen, methyl, and ethyl.

[0036] In one embodiment of the invention, R1 and R2 together with their bonded carbon atoms form a 5-6 membered ring, thereby the compound of formula (1) can form the structure shown in formula (2) or formula (3):

[0037]

[0038] In one embodiment of the present invention, R4, R6, R9, R 11 Each is independently selected from hydrogen and C. 1-4 Straight-chain or branched alkyl groups.

[0039] In one embodiment of the present invention, R4, R6, R9, R 11 Each is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl.

[0040] In one embodiment of the present invention, R4, R6, R9, R 11 Each is independently selected from hydrogen, methyl, and ethyl.

[0041] In one embodiment of the present invention, R3, R5, R7, R8, R 10 R 12 Each is independently selected from C 3-10 Straight-chain or branched alkyl groups, more preferably selected from C 3-6 Straight-chain or branched alkyl groups.

[0042] In one embodiment of the present invention, R3, R5, R7, R8, R 10 R 12 Each is independently selected from propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl and its isomers, hexyl and its isomers, heptyl and its isomers, octyl and its isomers, nonyl and its isomers, decyl and its isomers.

[0043] It should be noted that, unless otherwise specified, the molar amount of the main catalyst in this invention is expressed in terms of the molar amount of Ni element.

[0044] In this invention, the cocatalyst can be selected from aluminoxanes, modified aluminoxanes, alkylaluminum, alkylaluminum hydrolysates, haloalkylaluminum, borofluoroalkanes, alkylboron, alkylboron ammonium salts, or mixtures thereof.

[0045] Among them, the aluminum oxane used as a co-catalyst can be, for example, a linear aluminum oxane represented by the following general formula (I): (R)(R)Al-(Al(R)-O) n-O-Al(R)(R), and cyclic aluminum oxanes represented by the following general formula (II): -(Al(R)-O-) n+2 -

[0046]

[0047] In the aforementioned general formulas (I) and (II), the groups R are the same or different from each other (preferably the same), and are each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, most preferably methyl and isobutyl; n is any integer in the range of 1-50, preferably any integer in the range of 10-30.

[0048] As the aluminum oxane, methyl aluminum oxane, ethyl aluminum oxane, isobutyl aluminum oxane and n-butyl aluminum oxane are preferred, and methyl aluminum oxane and isobutyl aluminum oxane are even more preferred.

[0049] These aluminum oxanes can be used alone or in combination in any proportion.

[0050] Examples of alkylaluminum compounds include those represented by general formula (III):

[0051] Al(R)3 (III)

[0052] In general formula (III), the groups R are the same or different from each other (preferably the same) and are each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, with methyl and isobutyl being the most preferred.

[0053] Specifically, examples of alkylaluminum include trimethylaluminum (Al(CH3)3), triethylaluminum (Al(CH3CH2)3), tri-n-propylaluminum (Al(C3H7)3), triisopropylaluminum (Al(i-C3H7)3), triisobutylaluminum (Al(i-C4H9)3), tri-n-butylaluminum (Al(C4H9)3), and triisopentylaluminum (Al(i-C5H)3). 11 )3) Tri-n-pentyl aluminum (Al(C5H) 11 )3) Tri-n-hexyl aluminum (Al(C6H) 13 )3) Triisohexylaluminum (Al(i-C6H) 13 3) Diethylmethylaluminum (Al(CH3)(CH3CH2)2) and dimethylethylaluminum (Al(CH3CH2)(CH3)2), etc., wherein trimethylaluminum, triethylaluminum, tripropylaluminum and triisobutylaluminum are preferred, and triethylaluminum and triisobutylaluminum are most preferred.

[0054] These alkylaluminums can be used alone or in combination in any proportion.

[0055] Examples of such haloalkylaluminum compounds include those represented by the general formula (IV):

[0056] Al(R) n X 3-n (IV)

[0057] In general formula (IV), the groups R are the same or different from each other (preferably the same) and are each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl and isobutyl, most preferably methyl and isobutyl; X represents fluorine, chlorine, bromine or iodine; n represents 1 or 2.

[0058] Specifically, examples of the aforementioned alkyl halogenated aluminum include, for instance, dichlorodimethylaluminum (Al(CH3)2Cl), dichloromethylaluminum (Al(CH3)Cl2), dichlorodiethylaluminum (Al(CH3CH2)2Cl), dichloroethylaluminum (Al(CH3CH2)Cl2), dichlorodipropylaluminum (Al(C3H7)2Cl), dichloropropylaluminum (Al(C3H7)Cl2), dichlorodi-n-butylaluminum (Al(C4H9)2Cl), dichlorodi-n-butylaluminum (Al(C4H9)Cl2), dichlorodiisobutylaluminum (Al(i-C4H9)2Cl), dichloroisobutylaluminum (Al(i-C4H9)Cl2), and dichlorodi-n-pentylaluminum (Al(C5H9)Cl2). 11 )2Cl), dichloro-n-pentyl aluminum (Al(C5H) 11 Cl2), diisopentylaluminum chloride (Al(i-C5H) 11 )2Cl), dichloroisopentylaluminum (Al(i-C5H) 11 Cl2), di-n-hexyl aluminum chloride (Al(C6H) 13 )2Cl), dichloro-n-hexyl aluminum (Al(C6H) 13 Cl2), aluminum monochlorodiisohexyl (Al(i-C6H) 13 )2Cl), dichloroisohexylaluminum (Al(i-C6H) 13The preferred materials are diethylaluminum chloride, diethylaluminum chloride, dibutylaluminum chloride, dibutylaluminum chloride, diisobutylaluminum chloride, diisobutylaluminum chloride, dihexylaluminum chloride, and dihexylaluminum chloride. Further preferred materials include diethylaluminum chloride, diethylaluminum chloride, and dihexylaluminum chloride. Diethylaluminum chloride is the most preferred material.

[0059] These alkyl halogenated aluminum halide can be used alone or in combination in any proportion.

[0060] In this invention, the alkylboron and arylboron can be compounds having the following general formula (V):

[0061] B(R')3(V)

[0062] In general formula (V), each of the three R' groups may be the same as or different from the others, and each R' is independently selected from C. 1-6 Straight-chain or branched alkyl groups and C 6-10 aryl groups, each optionally bonded by one or more halogen atoms or halogenated carbons. 1-6 The R' is substituted with straight-chain or branched alkyl or phenoxy groups. Preferably, the R' is selected from methyl, ethyl, propyl, butyl, isobutyl, phenyl, tolyl, trifluoromethylphenyl, and pentafluorophenyl.

[0063] Specific examples of alkylboron include trimethylboron, triethylboron, triisobutylboron, tripropylboron, or tributylboron. Specific examples of arylboron include triphenylboron, tris(pentafluorophenyl)boron, and tris[3,5-bis(trifluoromethyl)phenyl]boron.

[0064] These alkylboron and arylboron compounds can be used alone or in combination in any proportion.

[0065] In this invention, the borate can be a compound having the following general formula (VI):

[0066] [L] + [BE4] m - (VI)

[0067] In general formula (VI), L is a cationic group, and each E can be the same or different, and each is independently selected from halogen atoms, C 6-10 aryl group, wherein the aryl group is optionally surrounded by one or more halogen atoms, C 1-6 Straight-chain or branched alkyl, halogenated C 1-6 Straight-chain or branched alkyl groups, C 1-6 The group is substituted with a straight-chain or branched alkoxy or phenoxy group. m represents the numerical value of the valence of the group in the L portion. Preferably, the E group is selected from fluorine, phenyl, trifluoromethylphenyl, and pentafluorophenyl.

[0068] In general formula (VI), [L] + Some of these can be cations common in borates, for example, Li can be listed. + Na + K + Ca 2+ Mg 2+ [Fe(C5H5)2] + (Ferrocene group), etc. Additionally, the L moiety can also be an organic amine, in which case the L moiety can be represented as N(R')3, where each R' is independently selected from H, C, etc. 1-6 Straight-chain or branched alkyl groups and C 6-10 aryl, but not both H; or two R' and N can bond together to form an optional C 1-6 A straight-chain or branched alkyl-substituted 5-7 membered nitrogen-containing heterocycle, preferably in which each R' is independently selected from H, C 1-4 Straight-chain or branched alkyl and phenyl groups, but not both H; or two R' and N can be bonded together to form an optional C-shaped group. 1-4 A 5-7 membered nitrogen-containing heterocyclic or heterocyclic hydrocarbon with straight or branched alkyl substituted groups. Examples of the L-group include methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, N,N-dimethylaniline, N,N-diethylaniline, imidazole, 1-butyl-3-methylimidazolium, pyridine, piperidine, etc. [L] + Some can also be groups carrying carbocations, such as triphenylmethyl carbocations.

[0069] Specific examples of borates include trimethylammonium tetraphenylborate, triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tributylammonium tetraphenylborate, trimethylammonium tetra(p-tolyl)borate, tripropylammonium tetra(p-tolyl)borate, trimethylammonium tetra(o-,p-dimethylphenyl)borate, triethylammonium tetra(o-,p-dimethylphenyl)borate, trimethylammonium tetra(p-trifluoromethylphenyl)borate, tributylammonium tetra(p-trifluoromethylphenyl)borate, tributylammonium tetra(pentafluorophenyl)borate, N,N-diethylphenylammonium tetraphenylborate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, N,N-diethylphenylammonium tetrapentafluorophenylborate, triethylammonium tetra(pentafluorophenyl)borate, triphenylcarbon tetra(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium tetrafluoroborate, and ferrocene tetrafluoroborate.

[0070] These borates can be used alone or in combination in any proportion.

[0071] Furthermore, according to the present invention, the co-catalyst can be used alone, or multiple co-catalysts can be combined in any proportion as needed. Moreover, there is no particular limitation on the proportion of each component in the mixture, and they can be selected arbitrarily as needed.

[0072] According to the present invention, the cocatalyst is generally used in solution form. When preparing the solution of the cocatalyst, there are no particular limitations on the solvent used, as long as it can dissolve the cocatalyst. Generally, alkane solvents are selected, such as n-pentane, isopentane, cyclopentane, neopentane, etc., or aromatic solvents, such as toluene, ethylbenzene, xylene, etc. According to the present invention, for ease of subsequent separation, the solvent is preferably the same as the polymerization solvent; or the same as at least one solvent in the mixed solvents used for polymerization.

[0073] It should be noted that, unless otherwise specified, in this invention, when the cocatalyst is an aluminoxane, a modified aluminoxane, an alkylaluminum, an alkylaluminum hydrolysate, or a haloalkylaluminum, the molar amount of the cocatalyst is calculated as the molar amount of Al element; when the cocatalyst is an alkylboron, an arylboron, or a borate, the molar amount of the cocatalyst is calculated as the molar amount of B element.

[0074] In one embodiment of the present invention, the main catalyst is preferably selected from aluminoxane, alkylaluminum, haloalkylaluminum or a mixture thereof, more preferably selected from alkylaluminum, haloalkylaluminum or a mixture thereof.

[0075] In one embodiment of the present invention, the molar ratio of the co-catalyst, calculated as aluminum and / or boron, to the main catalyst, calculated as metallic Ni, is 50-500:1, preferably 80-300:1.

[0076] In the preparation of branched polyethylene of the present invention, a chain transfer agent may or may not be used. Other metal alkyl compounds besides the co-catalyst of the present invention can be listed as chain transfer agents, such as one or more of n-butyllithium, diethylzinc, dipropylzinc, dibutylzinc, diisobutylzinc, diethylmagnesium, dibutylmagnesium, or n-butylethylmagnesium. In one embodiment of the present invention, when a chain transfer agent is used, the molar ratio of the amount of chain transfer agent (based on its metal content) to the main catalyst (based on metallic Ni) is 5-300:1, preferably 10-200:1.

[0077] In the method for preparing branched polyethylene of the present invention, the polymerization solvent is a polymerization solvent containing a halogenated organic solvent. More specifically, the polymerization solvent of the present invention is a polymerization solvent containing a halogenated organic solvent, which is a conventional polymerization solvent commonly used in the preparation of polyethylene.

[0078] As a conventional polymerization solvent, it can be a commonly used polymerization solvent in polyethylene polymerization reactions, such as, but not limited to, C 4-10 Alkanes (such as butane, hexane, heptane, octane, nonane, or decane, etc.), C 6-10 Aromatic hydrocarbon solvents (such as toluene and xylene), etc. Among them, hexane, heptane, toluene, etc. are preferred as the conventional polymerization solvents.

[0079] As a halogenated organic solvent, it refers to an organic solvent containing halogen elements. Specifically, examples include halogenated C... 1-10 Alkanes, Halogenated C 6-10 Aromatic hydrocarbons, preferably halogenated C 1-4 Alkanes and halobenzenes. The halogen element is selected from fluorine, chlorine, bromine, and iodine, with chlorine being more preferred.

[0080] As chlorinated C 1-10 Alkanes include, for example, chloromethane, dichloromethane, trichloromethane, chloroethane, dichloroethane and their isomers (e.g., 1,1-dichloroethane, 1,2-dichloroethane), and trichloroethane and its isomers (e.g., 1,1,1-trichloroethane, 1,1,2-trichloroethane, etc.). As chlorinated C... 6-10 Aromatic hydrocarbons include chlorobenzene, dichlorobenzene and its isomers, and chlorotoluene. As fluorinated C... 1-10 Alkanes, fluorinated C 6-10 Aromatic hydrocarbons, brominated C 1-10 Alkanes, Brominated C 6-10 Aromatic hydrocarbons, iodinated C 1-10 Alkanes, iodinated C 6-10 Aromatic hydrocarbons, such as the chlorinated C hydrocarbons mentioned above, can be listed as examples. 1-10 Alkanes, Chlorinated C 6-10 Compounds obtained by replacing chlorine in aromatic hydrocarbons with fluorine, bromine, or iodine, respectively.

[0081] The inventors of this invention have surprisingly discovered that by including a halogenated organic solvent in the polymerization solvent, the branched polyethylene prepared exhibits excellent toughening properties for polyolefins (especially polypropylene).

[0082] In this invention, the amount of halogenated organic solvent used relative to the conventional polymerization solvent (i.e., the polymerization solvent before the addition of the halogenated organic solvent), by volume ratio, is 0.001-0.2 parts by volume, preferably 0.003-0.1 parts by volume, and more preferably 0.005-0.05 parts by volume. In this invention, if the content of the halogenated organic solvent is too low, the specific branched polyethylene of this invention cannot be obtained; on the other hand, if the content of the halogenated organic solvent is too high, it will adversely affect the polymerization reaction and the post-processing of the product, thus affecting the performance of the branched polyethylene.

[0083] In this invention, the halogenated organic solvent can be a halogenated organic solvent added alone to a conventional polymerization solvent, or it can be a solvent used as a main catalyst and / or co-catalyst, or a halogenated organic solvent added together with the main catalyst and / or co-catalyst to a conventional polymerization solvent, as long as the polymerization solvent contains a halogenated organic solvent during the ethylene polymerization reaction.

[0084] In this invention, preferably, the α-diimine nickel catalyst shown in formula (1) is dissolved in the halogenated organic solvent described above, along with at least one selected from aluminoxane, modified aluminoxane, alkylaluminum, alkylaluminum hydrolysate, haloalkylaluminum, arylboron, alkylboron and borates, and then added to the polymerization solvent to carry out the ethylene polymerization reaction.

[0085] In this invention, the polymerization temperature is 60-85℃, preferably 65-70℃. If the polymerization temperature is too low, the resulting branched polyethylene cannot provide sufficient toughening effect; on the other hand, if the polymerization temperature is too high, the stability of the catalyst is greatly affected, and the resulting branched polyethylene cannot provide sufficient toughening effect.

[0086] In this invention, the polymerization pressure is 1.2-3.0 MPa, preferably 1.4-2.3 MPa. If the polymerization pressure is too low, the resulting branched polyethylene will not provide sufficient toughening effect; if the polymerization pressure is too high, the branched polyethylene of this invention cannot be obtained.

[0087] In this invention, the polymerization time of ethylene is not particularly limited and varies depending on the amount of catalyst system used, the amount of ethylene, and the polymerization temperature. Those skilled in the art can adjust it arbitrarily as needed. For example, it can be 10 minutes to 2 hours, 20 minutes to 90 minutes, 30 minutes to 1 hour, etc.

[0088] The branched polyethylene of the present invention is preferably prepared by solution polymerization.

[0089] In this invention, preferably, only ethylene is used as the olefin raw material in the preparation method of this invention. That is, in the preparation method of this invention, ethylene is homopolymerized.

[0090] In this invention, by using the main catalyst shown in formula (1) of this invention, combined with the specific polymerization conditions and specific polymerization solvent of this invention, the branched polyethylene prepared can effectively improve the low-temperature impact performance of polyolefins, especially polypropylene.

[0091] The method for preparing branched polyethylene of the present invention can be carried out by continuous polymerization or by batch polymerization.

[0092] In this invention, after the polymerization reaction is completed, the reaction can be terminated in a manner known in the art. For example, the polymerization reaction can be terminated using hydrochloric acid-ethanol, which is prepared by mixing concentrated hydrochloric acid and ethanol. The volume percentage of the concentrated hydrochloric acid relative to ethanol can be 1 v / v%-25 v / v%, or 3 v / v%-20 v / v%, for example, 5 v / v%.

[0093] In this invention, after the polymerization reaction is completed, branched polyethylene can be obtained by separation using the conventional methods of this invention.

[0094] Furthermore, the branched polyethylene of the present invention has a low density, typically 0.85 g / cm³. 3 -0.87g / cm 3 .

[0095] The kinematic viscosity of the branched polyethylene of the present invention at 260°C is typically 400,000 to 4,000,000 CP.

[0096] [Polyolefin Composition]

[0097] The present invention also provides a polyolefin composition, particularly a polypropylene composition.

[0098] The polyolefin composition of the present invention comprises the branched polyethylene described above. The amount of branched polyethylene relative to the total amount of the composition is 1 wt%-50 wt%, preferably 3 wt%-30 wt%, more preferably 5 wt%-25%, and particularly preferably 5 wt%-20 wt%. If the content of branched polyethylene is too low, the toughening effect cannot be fully realized; if the content of branched polyethylene is too high, it will have a certain adverse effect on the tensile strength of the polyolefin.

[0099] By adding the branched polyethylene of the present invention as an additive to polyolefins, particularly polypropylene, the low-temperature impact strength of polyolefins can be significantly improved while maintaining or further increasing tensile strength.

[0100] The present invention also provides an application of the branched polyethylene of the present invention for improving the low-temperature impact properties of polyolefins, particularly polypropylene.

[0101] Examples

[0102] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0103] In this invention, the methyl content in the branched chain is determined by carbon NMR spectroscopy. 13 The C NMR spectroscopy was performed at 120°C. The polymer sample was dissolved in deuterated o-dichlorobenzene to prepare a 20 wt% solution, and the sample was scanned 3000 times at 120°C to obtain the sample's fluorescence. 13 CNMR spectrum. (Through) 13 The peaks in C NMR determine the content of methyl branches in branched polyethylene.

[0104] The polypropylene composition was prepared by mixing branched polyethylene and polypropylene in a specific ratio, and adding 0.05 wt% antioxidant 1010 and 0.05 wt% antioxidant 168 to the total composition, wherein both 1010 and 168 are commercially available products. The homogeneous mixture was granulated by twin-screw extrusion, and the tensile strength and Izod notched low-temperature impact strength of the granules were measured.

[0105] Impact performance testing

[0106] The Izod notched impact strength of all samples was tested using an impact testing machine.

[0107] Polypropylene compositions were fabricated into 80×10×4mm specimens with a notch depth of 2mm. All samples were tested at -30℃, and five sets of data were collected for each sample, with the average value taken.

[0108] Tensile strength test

[0109] The tensile strength of the samples was measured using a universal tensile testing machine. The samples were measured at room temperature and a tensile speed of 50 mm / min⁻¹. The samples were dumbbell-shaped with a gauge length of 25 mm and average dimensions of 50 × 5 × 2 mm. Five sets of data were tested for each sample, and the average value was taken.

[0110] In the application examples and comparative examples, the catalyst shown in the following formula is used. The catalyst is synthesized using conventional methods in the art, for example, the method in CN201710919796.4.

[0111]

[0112] Application Example 1

[0113] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.2 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 73.44 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0114] Application Example 2

[0115] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (10 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.4 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 72.05 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0116] Application Example 3

[0117] In a glove box, M1 (16.04 μmol), 1,2-dichloroethane (8 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 85.81 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0118] Application Example 4

[0119] In a glove box, M1 (14.25 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.9 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 71.04 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0120] Application Example 5

[0121] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 2.3 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 65.19 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0122] Application Example 6

[0123] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (7 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 2.5 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. The polymer was filtered, washed, and then vacuum dried at 50 °C to constant weight to obtain 59.11 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0124] Application Example 7

[0125] In a glove box, M1 (16.04 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 65 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 81.16 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0126] Application Example 8

[0127] In a glove box, M1 (16.04 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 70 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 50.69 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0128] Application Example 9

[0129] In a glove box, M1 (16.04 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 75 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 47.16 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0130] Application Example 10

[0131] In a glove box, M1 (16.04 μmol), dichloromethane (50 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 80 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 24.78 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0132] Application Example 11

[0133] In a glove box, M1 (16.04 μmol), dichloromethane (15 ml), and dichloroethylaluminum (2.32 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 76.91 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0134] Application Example 12

[0135] In a glove box, M2 (16.04 μmol), dichloromethane (5 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.5 MPa at 65 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 68.09 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0136] Application Example 13

[0137] In a glove box, M2 (16.04 μmol), o-dichlorobenzene (20 ml), and dichloroethylaluminum (3.22 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 2.5 MPa at 75 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 52.29 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0138] Comparative Example 1

[0139] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 0.75 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 36.58 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0140] Comparative Example 2

[0141] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 3.5 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 40.29 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0142] Comparative Example 3

[0143] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 2.3 MPa at 30 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 56.45 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0144] Comparative Example 4

[0145] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 2.3 MPa at 90 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. The polymer was filtered, washed, and then vacuum dried at 50 °C to constant weight to obtain 12.8 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0146] Comparative Example 5

[0147] The vulcanization characteristics of EPDM4045 were determined according to the above method.

[0148] Comparative Example 6

[0149] In a glove box, M1 (13.99 μmol), toluene (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.4 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 67.5 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0150] Comparative Example 7

[0151] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (250 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.4 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 hr. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 67.08 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0152] Comparative Example 8

[0153] In a glove box, M1 (13.99 μmol), 1,2-dichloroethane (0.5 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.4 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was vacuum dried at 50 °C to constant weight to obtain 67.29 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0154] Comparative Example 9

[0155] In a glove box, M3 (13.99 μmol), 1,2-dichloroethane (15 ml), and dichloroethylaluminum (3.96 mmol) were sequentially added to a 50 ml Erlenmeyer flask and mixed to prepare a catalyst solution. Hexane (1 L) and the prepared catalyst solution were added sequentially to a 2 L high-pressure polymerization reactor purged with nitrogen. Ethylene was introduced at 1.4 MPa at 60 °C, and the polymerization reaction was carried out with stirring at 300 rpm for 0.5 h. The polymerization was terminated with ethanol containing 5% hydrochloric acid. After filtration and washing, the polymer was dried under vacuum at 50 °C to constant weight to obtain 56.59 g of polymer. The obtained polymer was used to prepare a composition according to the method for preparing polypropylene compositions, and its properties were measured.

[0156] Table 1 Summary of Results

[0157]

[0158]

[0159] ①PP is YPM-2203T, and PE is the branched polyethylene used in each example and comparative example;

[0160] ②The Izod notched impact strength of PP / PE = 100 at -30℃ is 8.23 ​​KJ / m. 2 (Add 0.05 wt% of antioxidant 1010 and 0.05 wt% of antioxidant 168 to the total composition);

[0161] ③When PP / PE = 100 / 0, the tensile strength is 29.81 MPa (0.05 wt% antioxidant 1010 and 0.05 wt% antioxidant 168 are added to the total composition).

[0162] The results of the above examples and comparative examples sufficiently demonstrate that, through the specific polymerization method of the present invention, not only does the catalyst system exhibit excellent catalytic activity, but the branched polyethylene obtained also significantly improves the impact strength of polypropylene.

[0163] In contrast, when the specific polymerization method of the present invention is not satisfied, the catalyst system exhibits poor catalytic activity, and the resulting branched polyethylene has a limited effect on improving the impact strength of polypropylene.

[0164] While the specific embodiments of the present invention have been described in detail above, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the appended claims. Those skilled in the art can make appropriate modifications to these embodiments without departing from the technical concept and spirit of the present invention, and these modified embodiments are obviously also included within the scope of protection of the present invention.

Claims

1. A method for preparing branched polyethylene, characterized in that, Includes the following steps: Using the α-diimine nickel catalyst shown in formula (1) as the main catalyst; and using at least one selected from aluminoxanes, modified aluminoxanes, alkylaluminum, alkylaluminum hydrolysates, haloalkylaluminum, arylboron, alkylboron, and borates as a co-catalyst, ethylene is polymerized using a polymerization solvent containing a halogenated organic solvent at a polymerization temperature of 60-85°C and a polymerization pressure of 1.2-3.0 MPa to obtain branched polyethylene. The halogenated organic solvent is 0.005-0.05 parts by volume relative to the polymerization solvent. In equation (1), R1 and R2 are each independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon groups, or R1 and R2 together with their bonded carbon atoms to form a 5-6 membered ring; R3, R5, R7, R8, R 10 R 12 Each is independently selected from C 3-10 Straight-chain or branched hydrocarbon groups, R4, R6, R9, R 11 Each is independently selected from hydrogen and C. 1-4 Straight-chain or branched hydrocarbon group, where X is a halogen.

2. The preparation method according to claim 1, characterized in that, In formula (1), R1 and R2 are each independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, or R1 and R2 together with the carbon atoms they are bonded to form a 5-membered ring; R4, R6, R9, R 11 Each is independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl; R3, R5, R7, R8, R 10 R 12 Each is independently selected from propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl and its isomers, hexyl and its isomers, heptyl and its isomers, octyl and its isomers, nonyl and its isomers, decyl and its isomers.

3. The preparation method according to claim 1 or 2, characterized in that, The α-diimine nickel catalyst shown in formula (1) is selected from at least one of the compounds shown in formula (2) or formula (3): 。 4. The preparation method according to claim 1, characterized in that, The aluminoxane is a linear aluminoxane represented by general formula (I) or a cyclic aluminoxane represented by general formula (II). In general formulas (I) and (II), the groups R are the same or different from each other and are each independently selected from C1-C8 alkyl groups.

5. The preparation method according to claim 1, characterized in that, The alkylaluminum is a compound represented by the following general formula (III): Al(R)3 (III) In general formula (III), the groups R are the same or different from each other, and each is independently selected from C1-C8 alkyl groups.

6. The preparation method according to claim 1, characterized in that, The haloalkylaluminum is a compound represented by the following general formula (IV): Al(R) n X 3-n (IV) In general formula (IV), the groups R are the same or different from each other and are each independently selected from C1-C8 alkyl groups; X represents fluorine, chlorine, bromine or iodine; n represents 1 or 2.

7. The preparation method according to claim 1, characterized in that, The alkylboron and arylboron are compounds represented by general formula (V): B(R')3 (V) In general formula (V), each of the three R' groups may be the same as or different from the others, and each R' is independently selected from C. 1-6 Straight-chain or branched alkyl groups and C 6-10 aryl groups, each optionally bonded by one or more halogen atoms or halogenated carbons. 1-6 Straight-chain or branched alkyl or phenoxy substitution.

8. The preparation method according to claim 1, characterized in that, The borate is a compound represented by the following general formula (VI): [L] + [BE4] m - (WE) In general formula (VI), L is a cationic group, and each E can be the same or different, and each is independently selected from halogen atoms, C 6-10 aryl group, wherein the aryl group is optionally surrounded by one or more halogen atoms, C 1-6 Straight-chain or branched alkyl, halogenated C 1-6 Straight-chain or branched alkyl groups, C 1-6 The group is substituted with a straight-chain or branched alkoxy or phenoxy group, m represents the numerical value of the valence of the group in the L part, and E is selected from fluorine, phenyl, trifluoromethylphenyl and pentafluorophenyl.

9. The preparation method according to claim 1, characterized in that, The halogenated organic solvent is selected from halogenated C. 1-10 Alkanes, Halogenated C 6-10 At least one of the aromatic hydrocarbons.

10. The preparation method according to claim 1, characterized in that, The polymerization solvent is selected from C. 4-10 Alkanes and C 6-10 At least one of aromatic hydrocarbon solvents.

11. The preparation method according to claim 1, characterized in that, Further steps include: The α-diimine nickel catalyst shown in formula (1) is dissolved in a halogenated organic solvent with at least one selected from aluminum oxane, modified aluminum oxane, alkyl aluminum, alkyl aluminum hydrolysate, haloalkyl aluminum, aryl boron, alkyl boron and borate, and then a polymerization solvent is added to carry out ethylene polymerization.

12. The preparation method according to claim 1, wherein it satisfies at least one of the following conditions: Ethylene is polymerized using a polymerization solvent containing halogenated organic solvents at a polymerization temperature of 65-70℃ and a polymerization pressure of 1.4-2.3MPa. The aluminum oxane is at least one selected from methyl aluminum oxane, ethyl aluminum oxane, isobutyl aluminum oxane and n-butyl aluminum oxane; The alkylaluminum is selected from trimethylaluminum (Al(CH3)3), triethylaluminum (Al(CH3CH2)3), tri-n-propylaluminum (Al(C3H7)3), triisopropylaluminum (Al(i-C3H7)3), triisobutylaluminum (Al(i-C4H9)3), tri-n-butylaluminum (Al(C4H9)3), and triisopentylaluminum (Al(i-C5H)3). 11 )3) Tri-n-pentyl aluminum (Al(C5H) 11 )3) Tri-n-hexyl aluminum (Al(C6H) 13 )3) Triisohexylaluminum (Al(i-C6H) 13 )3) At least one of diethylmethylaluminum (Al(CH3)(CH3CH2)2) and dimethylethylaluminum (Al(CH3CH2)(CH3)2); The alkyl halogenated aluminum is selected from dichlorodimethylaluminum (Al(CH3)2Cl), dichloromethylaluminum (Al(CH3)Cl2), dichlorodiethylaluminum (Al(CH3CH2)2Cl), dichloroethylaluminum (Al(CH3CH2)Cl2), dichlorodipropylaluminum (Al(C3H7)2Cl), dichloropropylaluminum (Al(C3H7)Cl2), dichlorodi-n-butylaluminum (Al(C4H9)2Cl), dichlorodi-n-butylaluminum (Al(C4H9)Cl2), dichlorodiisobutylaluminum (Al(i-C4H9)2Cl), dichloroisobutylaluminum (Al(i-C4H9)Cl2), dichlorodi-n-pentylaluminum (Al(C5H9)Cl2), and dichlorodi-n-pentylaluminum (Al(C5H9)Cl2). 11 )2Cl), dichloro-n-pentyl aluminum (Al(C5H) 11 Cl2), diisopentylaluminum chloride (Al(i-C5H) 11 )2Cl), dichloroisopentylaluminum (Al(i-C5H) 11 Cl2), di-n-hexyl aluminum chloride (Al(C6H) 13 )2Cl), dichloro-n-hexyl aluminum (Al(C6H) 13 Cl2), aluminum monochlorodiisohexyl (Al(i-C6H) 13 )2Cl), dichloroisohexylaluminum (Al(i-C6H) 13 At least one of the following: methyl ethyl aluminum (Al(CH3)(CH3CH2)Cl), methyl propyl aluminum (Al(CH3)(C3H7)Cl), methyl n-butyl aluminum (Al(CH3)(C4H9)Cl), methyl isobutyl aluminum (Al(CH3)(i-C4H9)Cl), ethyl propyl aluminum (Al(CH2CH3)(C3H7)Cl), ethyl n-butyl aluminum (AlCH2CH3)(C4H9)Cl), and ethyl isobutyl aluminum (Al(CH2CH3)(i-C4H9)Cl); The alkyl boron is at least one selected from trimethylboron, triethylboron, triisobutylboron, tripropylboron, or tributylboron; The arylborane is at least one selected from triphenylborane, tris(pentafluorophenyl)borane, and tris[3,5-bis(trifluoromethyl)phenyl]borane; The borate is selected from at least one of the following: trimethylammonium tetraphenylborate, triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tributylammonium tetraphenylborate, trimethylammonium tetra(p-tolyl)borate, tripropylammonium tetra(p-tolyl)borate, trimethylammonium tetra(o-,p-dimethylphenyl)borate, triethylammonium tetra(o-,p-dimethylphenyl)borate, trimethylammonium tetra(p-trifluoromethylphenyl)borate, tributylammonium tetra(p-trifluoromethylphenyl)borate, tributylammonium tetra(pentafluorophenyl)borate, N,N-diethylphenylammonium tetraphenylborate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, N,N-diethylphenylammonium tetra(pentafluorophenyl)borate, triethylammonium tetra(pentafluorophenyl)borate, triphenylcarbon tetra(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium tetrafluoroborate, and ferrocene tetrafluoroborate. The halogenated organic solvent is selected from at least one of chloromethane, dichloromethane, trichloromethane, chloroethane, dichloroethane and its isomers, trichloroethane and its isomers, chlorobenzene, dichlorobenzene and its isomers, and chlorotoluene. The polymerization solvent is at least one selected from hexaane, heptane, and toluene.

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