Branching polyethylene with adjustable and controllable degree of branching and method for preparing the same

Abstract

The application discloses branched polyethylene with adjustable and controllable branching degree and a preparation method thereof. The branched polyethylene has a crystallinity less than 25%, a weight average molecular weight between 100,000 g / mol and 1,200,000 g / mol, a molecular weight distribution between 1.5 and 3.5, and an adjustable and controllable branching degree between 60 / 1000C and 200 / 1000C. In the preparation method, an alpha-diimine nickel metal complex is mixed with at least one organic boron compound selected from aryl boron, alkyl boron and borate, and then is contacted with at least one organic aluminum compound selected from alkyl aluminum, aluminoxane and halogenated alkyl aluminum to perform solution polymerization of ethylene. The polymerization method has the advantages of high polymerization activity, no use of a second polymerization monomer, simple process and low cost, and is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to an ethylene polymer and a preparation method thereof, in particular to a branched polyethylene with controllable and adjustable branching degree, and a preparation method for obtaining the branched polyethylene by polymerizing ethylene under the joint action of a post-transition metal nickel complex and an organic boron compound under solution polymerization conditions. BACKGROUND

[0002] The branching degree, type and distribution of polyethylene have a significant impact on the performance and application of polyethylene. Branched polyethylene has low crystallinity, low density, good solubility, low viscosity in solution and melt state, and other characteristics, and has more superior film-forming property, transparency, toughness, and mechanical processing performance compared with conventional linear polyethylene. Generally, branched polyethylene is mainly prepared by copolymerization of ethylene and a small amount of high-carbon α-olefin (1-butene, 1-hexene or 1-octene), but due to the much lower reactivity of α-olefin than ethylene, the branching degree of the polyethylene obtained by this method is usually low, and it is difficult to obtain high-branched polyethylene. Moreover, high-carbon α-olefin is relatively expensive, resulting in an increase in the cost of the copolymer. Subsequently, scientists found that using α-diimine nickel catalyst can catalyze ethylene homopolymerization to prepare branched polyethylene with high molecular weight, but the α-diimine nickel catalyst has poor temperature resistance, and the branching degree of the branched polyethylene obtained by this method is generally low (branching degree < 80 / 1000C) and difficult to control, thereby limiting the application range of the branched polyethylene.

[0003] Brookhart and Guan et al. obtained polyethylene with different branching degrees by changing the temperature or polymerization pressure of the polymerization reaction (Macromolecules, 2000, 33(7):2320-2334; Chem. Eur. J. 2002, 8(14):3086-3092), but adjusting the reaction temperature and pressure by a large margin is difficult to achieve on an industrial scale.

[0004] In Chinese patent CN110590980A, an α-diimine nickel catalyst with a large steric skeleton is designed and synthesized, which changes the electronic distribution and spatial effect around the metal center of the catalyst, thereby realizing the preparation of a polymer target with high molecular weight and a wide range of controllable branching degree at high temperature. However, the ligand structure of this α-diimine nickel catalyst is relatively complex, the synthesis process is complicated, and the preparation cost is high, which is not conducive to industrial application. SUMMARY

[0005] On the basis of the prior art, the present inventors have found, through a large number of experiments, analysis and in-depth research, that, without changing the conditions of the polymerization reaction, by using a catalytic system prepared in a specific manner from an α-diimine nickel catalyst and at least one boron compound selected from alkyl boron, aryl boron and borate, and using the catalytic system for the preparation of branched polyethylene, the degree of branching of the polyethylene can be controlled, without the need for complex catalyst structure design and synthesis, with a large degree of control of the degree of branching, flexible production mode, without harsh reaction conditions, and being very suitable for industrial production, thereby solving the problems in the prior art.

[0006] The present application aims to solve the technical problems of the prior art, i.e. the degree of branching of the branched polymer obtained by the catalysis of the catalyst on ethylene is too low, and the degree of branching is not easy to control, while ensuring the thermal stability of the nickel catalyst and the ability of the catalyst to catalyze the polymerization of ethylene to obtain high molecular weight branched polyethylene, thereby providing a branched polyethylene with adjustable and controllable degree of branching and a preparation method thereof.

[0007] Specifically, the present application provides a preparation method of branched polyethylene with adjustable and controllable degree of branching, comprising the following steps:

[0008] (1) mixing and contacting an α-diimine nickel metal complex represented by formula (I) with at least one organic boron compound selected from aryl boron, alkyl boron and borate in a first organic solvent to obtain a mixture;

[0009] (2) in the presence of the mixture, at least one organic aluminum compound selected from alkyl aluminum, aluminoxane and halogenated alkyl aluminum, performing ethylene polymerization to obtain branched polyethylene,

[0010]

[0011] In formula (I), R1-R6 are the same or different, each independently hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C1-C6 haloalkyl, optionally substituted C2-C6 alkenyl, halogen, optionally substituted C1-C6 alkoxy or optionally substituted C6-C 10 aryl, or, adjacent two groups among R1-R6 are bonded to each other, together with the carbon atoms to which they are connected, to form an optionally substituted C4-C8 ring; R7, R 11 , R 12 , R 16 are the same or different, each independently optionally substituted C1-C6 alkyl, optionally substituted C3-C8 cycloalkyl, optionally substituted phenyl; R8, R9, R 10 , R 13 , R 14 , R 15the same or different, each independently is hydrogen, optionally substituted C1-C6alkyl, optionally substituted C3-C8cycloalkyl, optionally substituted phenyl, halogen, optionally substituted C1-C6alkoxy, nitro, amino, mercapto; X is halogen, wherein the substituents in the "optionally substituted" are selected from the group consisting of halogen, C1-C4alkyl, C1-C4haloalkyl, phenyl.

[0012] The present application also provides a branched polyethylene (also referred to as "polyethylene" or "branched ethylene polymer" in the present application) prepared by the preparation method of the branched polyethylene with adjustable and controllable branching degree.

[0013] Technical effects

[0014] Compared with the prior art, in the present application, by using the catalyst system prepared in a specific way, the branching degree of the polyethylene can be adjusted and improved when the catalyst system is used for ethylene polymerization, and the polymerization activity of the catalyst system can also be effectively improved, so that the purpose of the present application can be achieved without complex catalyst structure, harsh reaction conditions, or significant changes in polymerization conditions.

[0015] The preparation method of the present application has the advantages of simple operation, large adjustable space, flexibility, low production cost, etc., which is very beneficial to realize industrialized production

[0016] In addition, in the preparation method of the branched polyethylene of the present application, ethylene is used as the only polymerization monomer, so that the branched polyethylene containing branches can be obtained, and the expensive high-carbon α-olefin does not need to be used as a comonomer, so that the branching degree of the branched polyethylene can be improved, and the preparation method also has the advantages of low production cost and simple polymerization process.

[0017] The preparation method of the present application has a large adjustable range for the branching degree of the branched polyethylene, and can obtain polyethylene with adjustable and controllable performance in a wide range from amorphous polyethylene to polyethylene with a certain crystallinity, so that the branching degree of the polyethylene can be conveniently adjusted according to the needs, and the application range of the polyethylene is further enriched. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The nuclear magnetic resonance carbon spectrum of the polyethylene obtained in Example 3 of the present application.

[0019] Figure 2 The nuclear magnetic resonance carbon spectrum of the polyethylene obtained in Comparative Example 3 of the present application.

[0020] Figure 3 The GPC spectrum of the polyethylene obtained in Example 3 of the present application.

[0021] Figure 4DSC spectrum of the polyethylene obtained in Example 3 of the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application are described in detail below, but it should be noted that the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims attached to the appendix.

[0023] In the context of the present specification, unless explicitly stated otherwise, any matter or item not mentioned is directly applicable without any change to those known in the art. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, whereby the technical solutions or technical ideas formed thereby are considered to be part of the original disclosure or original description of the present application, and should not be considered to be new content not disclosed or anticipated herein, unless the combination is considered to be obviously unreasonable by those skilled in the art.

[0024] In the context of the present specification, unless explicitly stated otherwise, all percentages, parts, ratios, etc. mentioned therein are based on weight, unless it is not in accordance with the general understanding of those skilled in the art when based on weight.

[0025] The specific embodiments of the present application are described in detail below, but it should be noted that the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims attached to the appendix

[0026] In the context of the present application, unless otherwise specifically stated, the physical property values (such as boiling point) of a substance are measured at normal temperature (25°C) and normal pressure (101325 Pa).

[0027] [α-DIIMINE NICKEL METAL COMPLEX]

[0028] In the present application, the catalyst used for the preparation of branched polyethylene is an α-diimine nickel metal complex represented by the following formula (I),

[0029]

[0030] In formula (I), R1-R6 are the same or different, each independently hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C1-C6 haloalkyl, optionally substituted C2-C6 alkenyl, halogen, optionally substituted C1-C6 alkoxy or optionally substituted C6-C 10 aryl, or, two adjacent groups of R1-R6 are bonded to each other to form an optionally substituted C4-C8 ring together with the carbon atom to which they are attached; R7, R 11 , R 12 , R 16Whether identical or different, each independently represents an optionally substituted C1-C6 alkyl, optionally substituted C3-C8 cycloalkyl, or optionally substituted phenyl; R8, R9, R 10 R 13 R 14 R 15 The same or different, each independently being hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C3-C8 cycloalkyl, optionally substituted phenyl, halogen, optionally substituted C1-C6 alkoxy, nitro, amino, mercapto; X is halogen, wherein the substituent in "optionally substituted" is a substituent selected from the group consisting of: halogen, C1-C4 alkyl, C1-C4 haloalkyl, phenyl.

[0031] In this invention, "C1-C6 alkyl" refers to a straight-chain or branched alkyl group having 1-6 carbon atoms. For example, it can be methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl and its isomers, hexyl and its isomers. In this invention, "C1-C6 alkyl" is preferably "C1-C4 straight-chain branched alkyl".

[0032] In this invention, "C1-C6 haloalkyl" refers to a group obtained by substituting at least one hydrogen atom of the aforementioned C1-C6 alkyl group with a halogen group, wherein the halogen group is selected from fluorine, chlorine, bromine, and iodine. The upper limit of the number of halogen groups in the haloalkyl group is the upper limit of the number of hydrogen atoms that can be substituted in the C1-C6 alkyl group, and can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, or can be 1-8, 1-6, 1-4, or 1-2. When multiple halogen groups are present, the halogen groups can be the same or different. The halogen group in "C1-C6 haloalkyl" is preferably fluorine, chlorine, or bromine, and more preferably fluorine or chlorine.

[0033] In this invention, "C2-C6 alkenyl" refers to a straight-chain or branched alkenyl group having 2-6 carbon atoms, wherein it may have 1, 2, or 3 double bonds, preferably 1 double bond. Examples of "C2-C6 alkenyl" include vinyl, 1-propenyl, 2-propenyl, 1-butenyl and its isomers, 1-pentenyl and its isomers, and 1-hexenyl and its isomers. In this invention, "C2-C6 alkenyl" is preferably "C2-C4 straight-chain branched alkenyl".

[0034] In this invention, "C1-C6 alkoxy" refers to a group formed by bonding the aforementioned C1-C6 alkyl group with an oxygen atom. For example, it can be methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy and its isomers, hexoxy and its isomers. In this invention, "C1-C6 alkoxy" is preferably "C1-C4 straight-chain branched alkoxy".

[0035] In the present application, "C6-C 10 In the present application, "aryl" means a hydrocarbon group having 6 to 10 carbon atoms having aromaticity, and specifically, it can be phenyl or naphthyl.

[0036] In the present application, "C3-C8 cycloalkyl" means a cyclic alkyl group having 3 to 8 carbon atoms, and for example, it can be cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, or cyclooctyl.

[0037] In the present application, "C4-C8 ring" means a cyclic group having 4 to 8 ring-forming carbon atoms, and it can be an unsaturated ring or a saturated ring, and it can have aromaticity or can not have aromaticity. As an unsaturated ring, it can have 1, 2, or 3 double bonds. As an aromatic ring, it can be a benzene ring.

[0038] In the present application, "adjacent two groups among R1 to R6 are bonded to each other to form an optionally substituted C4-C8 ring together with the carbon atom to which they are attached" means that two groups among R4 and R3, R3 and R1, R1 and R2, R2 and R5, and R5 and R6 in any one of the five groups are bonded to each other to form an optionally substituted C4-C8 ring together with the carbon atom to which they are attached.

[0039] In the present application, as a substituent in "optionally substituted", it is at least one group selected from halogen, C1-C4 alkyl, C1-C4 haloalkyl, and phenyl. The upper limit of the number of the substituents is the upper limit of the number of substitutable positions on the group to be substituted, and the number of the substituents can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. For example, it can be 1 to 8, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2. When there are a plurality of substituents, each substituent can be the same or different.

[0040] In the present application, "halogen" means fluorine, chlorine, bromine, or iodine, and preferably, it is fluorine, chlorine, or bromine.

[0041] In the present application, "halo" means being substituted with at least one selected from halogen, and the upper limit of the halo is the upper limit of the number of substitutable positions on the group to be substituted, and it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. For example, it can be 1 to 8, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2. When there are a plurality of halogen groups, each substituent can be the same or different.

[0042] In the present application, the upper limit of the number of substituents in "optionally substituted" is the upper limit of the number of substitutable positions on the group being substituted, and the number of substituents can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. For example, it can be 1 to 8, 1 to 6, 1 to 5, 1 to 4, 1 to 3, 1 to 2. When there are multiple substituents, each substituent can be the same or different.

[0043] In one embodiment of the present application, in formula (I), R1 to R6 are the same or different, and each is independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, fluorine, chlorine, bromine, halomethyl, haloethyl, halopropyl, haloisopropyl, halobutyl, haloisobutyl, halosec-butyl, halotert-butyl, methoxy, ethoxy, propyloxy, isopropyloxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, phenyl, pentafluorophenyl, pentachlorophenyl, or benzhydryl.

[0044] In one embodiment of the present application, in formula (I), R1 to R6 are the same or different, and each is independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, fluorine, chlorine, bromine, halomethyl, haloethyl, halopropyl, haloisopropyl, halobutyl, haloisobutyl, halosec-butyl, halotert-butyl, phenyl, or pentafluorophenyl.

[0045] In one embodiment of the present application, in formula (I), at least one of R4 and R3, R3 and R1, R1 and R2, R2 and R5, and R5 and R6 are bonded to each other, and form, together with the carbon atom to which they are attached, a benzene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, a cyclopentene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, or a cyclopentadiene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl.

[0046] In one embodiment of the present application, in formula (I), R1 and R2 are bonded to each other, and form, together with the carbon atom to which they are attached, a benzene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, a cyclopentene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, or a cyclopentadiene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl.

[0047] In one embodiment of the present application, in formula (I), R4 and R3 are bonded to each other, and form, together with the carbon atom to which they are attached, a benzene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, a cyclopentene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl, or a cyclopentadiene ring optionally substituted with at least one selected from the group consisting of halogen and C1-C4 alkyl.

[0048] In one embodiment of the present application, in formula (I), R5and R6are bonded to each other to form a benzene ring optionally substituted with at least one selected from the group consisting of halogen, C1-C4 alkyl, a cyclopentene ring optionally substituted with at least one selected from the group consisting of halogen, C1-C4 alkyl, or a cyclopentadiene ring optionally substituted with at least one selected from the group consisting of halogen, C1-C4 alkyl.

[0049] In one embodiment of the present application, in formula (I), R7, R 11 , R 12 , R 16 are the same or different, each independently selected from the group consisting of hydrogen, optionally substituted methyl, optionally substituted ethyl, optionally substituted propyl, optionally substituted isopropyl, optionally substituted butyl, optionally substituted isobutyl, optionally substituted sec-butyl, optionally substituted t-butyl, optionally substituted phenyl, pentafluorophenyl, pentachlorophenyl.

[0050] In one embodiment of the present application, in formula (I), R7, R 11 , R 12 , R 16 are the same or different, each independently selected from the group consisting of hydrogen, methyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, ethyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, propyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, isopropyl optionally substituted with halogen, phenyl, butyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, isobutyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, sec-butyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, t-butyl optionally substituted with at least one selected from the group consisting of halogen, phenyl, phenyl optionally substituted with at least one selected from the group consisting of halogen, phenyl.

[0051] In one embodiment of the present application, in formula (I), R8, R9, R 10 , R 13 , R 14 , R 15 are the same or different, each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, fluorine, chlorine, bromine, phenyl, or pentafluorophenyl.

[0052] In one embodiment of the present application, in formula (I), R8, R9, R 10 , R 13 , R 14 , R 15 are the same or different, each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl.

[0053] In one embodiment of the present application, in formula (I), R8, R 10 , R 13 , R 15 are the same or different, each independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl.

[0054] In one embodiment of the present application, in formula (I), R9, R 14 are the same or different, each independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl.

[0055] In one embodiment of the present application, in formula (I), X is chlorine or bromine.

[0056] In one embodiment of the present application, as the α-diimine nickel metal complex represented by formula (I), the following metal complexes can also be listed.

[0057]

[0058]

[0059] Note that, in the present application, as the "α-diimine nickel metal complex" as a catalyst, one kind can be used alone, or two or more kinds can be used in combination.

[0060] Note that, in the present application, when the "α-diimine nickel metal complex" is measured, unless otherwise specified, the content of nickel element (Ni) contained therein is indicated.

[0061] [Organoboron compound]

[0062] In the present application, as the organoboron compound, at least one kind selected from aryl boron, alkyl boron, and borate is used. That is, in the present application, the organoboron compound can be used alone, or two or more kinds can be used in combination.

[0063] In the present application, the alkyl boron and aryl boron can be a compound having the following general formula (B-1):

[0064] B(R)3(B-1)

[0065] wherein each of the three R groups can be the same as or different from each other, and each R is independently selected from C 1-6 linear or branched alkyl, and C 6-10 aryl, each of which is optionally substituted with one or more halogen atoms, halogenated C 1-6 linear or branched alkyl, or phenoxy.

[0066] In one embodiment of the present application, R is preferably selected from the group consisting of methyl, ethyl, propyl, butyl, isobutyl, phenyl, tolyl, trifluoromethylphenyl and pentafluorophenyl.

[0067] In one embodiment of the present application, as specific examples of the alkyl boron, there can be mentioned trimethylboron, triethylboron, triisobutylboron, tripropylboron or tributylboron. As specific examples of the aryl boron, there can be mentioned triphenylboron, tri(pentafluorophenyl)boron, tri[3,5-bis(trifluoromethyl)phenyl]boron.

[0068] In the present application, the borate can be a compound having the following general formula (B-2):

[0069] [L] + [BE4] m - (B-2)

[0070] wherein L is a cationic group, each E can be the same or different, and each is independently selected from the group consisting of a halogen atom, a C 6-10 aryl group optionally substituted with one or more halogen atoms, C 1-6 linear or branched alkyl, halogenated C 1-6 linear or branched alkyl, C 1-6 linear or branched alkoxy or phenoxy.

[0071] In one embodiment of the present application, E is preferably selected from the group consisting of fluorine, phenyl, trifluoromethylphenyl and pentafluorophenyl. m represents the number of valence of the group of the L moiety.

[0072] In the general formula (B-2), the [L] + moiety can be a cation commonly found in borates, and for example, there can be mentioned Li + , Na + , K + , Ca 2+ , Mg 2+ , [Fe(C5H5)2] + (ferrocenyl group) and the like. In addition, the L moiety can also be an organic amine, in which case the L moiety can be represented by N(R')3, each R' being independently selected from the group consisting of H, C 1-6 linear or branched alkyl and C 6-10 aryl, but not H at the same time; or two R' and N can be bonded to each other to form a 5- to 7-membered nitrogen-containing heterocycle optionally substituted with C 1-6 linear or branched alkyl, preferably each R' is independently selected from the group consisting of H, C 1-4 linear or branched alkyl and phenyl, but not H at the same time; or two R' and N can be bonded to each other to form a 5- to 7-membered nitrogen-containing heterocycle optionally substituted with C 1-4A straight-chain or branched alkyl-substituted 5- to 7-membered nitrogen-containing heteroaromatic ring or heterocyclic hydrocarbon. For example, as the L moiety, there can be mentioned methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, N,N-dimethylaniline, N,N-diethylaniline, imidazole, 1-butyl-3-methylimidazole, pyridine, piperidine, and the like.[L] + The moiety can also be a carbonium ion-carrying group such as triphenylmethyl carbonium ion.

[0073] In one embodiment of the present application, as specific examples of the borate salt, there can be mentioned trimethylammonium tetraphenylborate, triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tributylammonium tetraphenylborate, trimethylammonium tetra(p-methylphenyl)borate, tripropylammonium tetra(p-methylphenyl)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, triphenylcarbenium tetra(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium tetrafluoroborate, ferrocenium tetrafluoroborate.

[0074] In one embodiment of the present application, as the organoaluminum compound, at least one selected from the group consisting of tri(pentafluorophenyl)boron, triphenylcarbenium tetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, and triethylammonium tetra(pentafluorophenyl)borate is preferred.

[0075] Note that, in the present application, when the organoaluminum compound is measured, the content of boron (B) element contained in the organoaluminum compound is used unless otherwise specified.

[0076] [Organic aluminum compound]

[0077] In the present application, the organic aluminum compound is at least one selected from the group consisting of alkylaluminum, aluminoxane, and halogenated alkylaluminum.

[0078] In the present application, as the alkylaluminum, there can be mentioned a compound represented by the following formula (D):

[0079] Al(R 11 )3(D)

[0080] In the formula (D), the groups R 11 are the same or different from each other and are each independently selected from the group consisting of C 1-6alkyl, preferably selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl and isohexyl.

[0081] In one embodiment of the present application, as the alkylaluminum, trimethylaluminum (Al(CH3)3), triethylaluminum (Al(CH2CH3)3), tri-n-propylaluminum (Al(C3H7)3), triisobutylaluminum (Al(i-C4H9)3), tri-n-butylaluminum (Al(C4H9)3), triisopentylaluminum (Al(i-C5H 11 )3), tri-n-pentylaluminum (Al(C5H 11 )3), tri-n-hexylaluminum (Al(C6H 13 )3), triisohexylaluminum (Al(i-C6H 13 )3), diethylmethylaluminum (Al(CH3)(CH3CH2)2) and dimethylethylaluminum (Al(CH3CH2)(CH3)2), etc., more preferably trimethylaluminum, triethylaluminum, tri-n-propylaluminum and triisobutylaluminum, further preferably triethylaluminum and triisobutylaluminum, and most preferably triisobutylaluminum.

[0082] In the present application, as the halogenated alkylaluminum, for example, a compound represented by the following formula (E) can be mentioned:

[0083] Al(R 11 ) n X 3-n (E)

[0084] In the formula (E), the groups R 11 are the same as or different from each other, and each is independently selected from the group consisting of C 1-6 alkyl, wherein preferably selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl and isohexyl, and most preferably methyl or ethyl; the group X is halogen, for example, fluorine, chlorine, bromine, iodine, and preferably chlorine. n is an integer of 1 or 2.

[0085] In one embodiment of the present application, as the halogenated alkylaluminum, for example, monochlorodimethylaluminum (Al(CH3)2Cl), dichloromethylaluminum (Al(CH3)Cl2), monochlorodiethylaluminum (Al(CH3CH2)2Cl), dichloroethylaluminum (Al(CH3CH2)Cl2), monochlorodipropylaluminum (Al(C3H7)2Cl), dichloropropylaluminum (Al(C3H7)Cl2), monochlorodi-n-butylaluminum (Al(C4H9)2Cl), dichloro-n-butylaluminum (Al(C4H9)Cl2), monochlorodiisobutylaluminum (Al(i-C4H9)2Cl), dichloroisobutylaluminum (Al(i-C4H9)Cl2), monochlorodi-n-pentylaluminum (Al(C5H 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 The preferred materials are diethylaluminum chloride (Al(CH3)(CH3CH2)Cl), diethylaluminum chloride (Al(CH3)(C3H7)Cl), diethylaluminum chloride (Al(CH3)(C4H9)Cl), diethylaluminum chloride (Al(CH3)(i-C4H9)Cl), diethylaluminum chloride (Al(CH2CH3)(C3H7)Cl), diethylaluminum chloride (Al(CH2CH3)(C4H9)Cl), and diethylaluminum chloride (Al(CH2CH3)(i-C4H9)Cl), among which diethylaluminum chloride, diethylaluminum chloride, diethylaluminum chloride, diethylaluminum chloride, diisobutylaluminum chloride, diisobutylaluminum chloride, diethylaluminum chloride, and diethylaluminum chloride are preferred, diethylaluminum chloride, diethylaluminum chloride, and diethylaluminum chloride are further preferred, and diethylaluminum chloride is the most preferred.

[0086] In this invention, the aluminum oxane can be exemplified by the linear aluminum oxane represented by the following formula (F): (R)(R)Al-(Al(R)-O) n -O-Al(R)(R), and cyclic aluminum oxanes represented by the following formula (G): -(Al(R)-O-) n+2 -

[0087]

[0088] In the aforementioned formulas (F) and (G), the plurality of groups R may be the same or different from each other, and each is independently selected from C1-C6 alkyl groups, wherein methyl, ethyl, n-propyl, isopropyl, n-butyl and isobutyl are preferred, and methyl, ethyl and isobutyl are more preferred. n is any integer in the range of 1-50, preferably any integer in the range of 10-30.

[0089] In one embodiment of the present invention, the preferred aluminum oxane is methyl aluminum oxane, ethyl aluminum oxane, isobutyl aluminum oxane, n-butyl aluminum oxane, modified methyl aluminum oxane, or modified ethyl aluminum oxane, and more preferably methyl aluminum oxane or modified methyl aluminum oxane.

[0090] Note that, in the present application, the amount of the organic aluminum compound is measured based on the content of aluminum (Al) contained in the organic aluminum compound, unless otherwise specified.

[0091] [Method for producing branched polyethylene]

[0092] The present application provides a method for producing branched polyethylene, which comprises the following steps:

[0093] (1) mixing and contacting an α-diimine nickel metal complex represented by the above formula (I) of the present application and at least one organic boron compound of the present application selected from aryl boron, alkyl boron and borate in a first organic solvent to obtain a mixture;

[0094] (2) performing ethylene polymerization in the presence of at least one organic aluminum compound of the present application selected from alkyl aluminum, aluminoxane and halogenated alkyl aluminum in the above mixture to obtain branched polyethylene.

[0095] In the present application, the first step of the method for producing branched polyethylene of the present application is mixing and contacting an α-diimine nickel metal complex represented by the above formula (I) of the present application and at least one organic boron compound of the present application selected from aryl boron, alkyl boron and borate in a first organic solvent to obtain a mixture. The present inventors have surprisingly found that, by mixing and contacting an α-diimine nickel metal complex represented by formula (I) of the present application and an organic boron compound of the present application in advance before performing ethylene polymerization, and then combining with an organic aluminum compound, the catalytic performance of the catalyst system can be better exerted in the ethylene polymerization reaction, and branched polyethylene with excellent performance can be obtained. Without being bound by any existing theory, the present inventors speculate that the reason may be that, by contacting the organic boron compound with the α-diimine nickel metal complex, the organic boron compound can interact with the complex, and thereafter, when the ethylene polymerization reaction is performed and the organic aluminum compound is added, competition between the organic aluminum compound and the organic boron compound is avoided, and the catalytic performance of the catalyst is improved.

[0096] In the present application, the first organic solvent in the above first step is not limited as long as it can disperse / dissolve the α-diimine nickel metal complex represented by formula (I) of the present application and the organic boron compound of the present application, and mix and contact them.

[0097] In one embodiment of the present application, as the first organic solvent, there are included, but not limited to, C 4-10 alkanes (e.g., butane, pentane, hexane, heptane, octane, nonane or decane, etc.), halogenated C 1-10 alkanes (e.g., dichloromethane, trichloromethane, monochloroethane, dichloroethane, trichloroethane and its isomers), C 6-10Aromatic hydrocarbon solvents (such as toluene and xylene and their isomers), halogenated C 6-10 Aromatic hydrocarbon solvents (e.g., chlorobenzene, dichlorobenzene and its isomers, chlorotoluene), etc. C is preferred. 6-10 Aromatic hydrocarbon solvents, halogenated C 1-10 Alkanes, Halogenated C 6-10 Aromatic hydrocarbon solvents, more preferably selected from one or more of toluene, p-xylene, m-xylene, o-xylene, mesitylene, o-dichlorobenzene, dichloromethane, 1,2-dichloroethane, and trichloroethane, and even more preferably selected from one or more of dichloromethane, toluene, p-xylene, or 1,2-dichloroethane.

[0098] In one embodiment of the present invention, in step (1), the molar ratio of the α-diimine nickel metal complex to the organoboron compound, based on the boron (B) element in the organoboron compound and the active metal nickel (Ni) element in the metal complex, is 0.5-50:1, preferably 1-20:1, and more preferably 1-10:1.

[0099] In one embodiment of the present invention, in step (1), the contact time between the α-diimine metal complex and the organoboron compound in the first organic solvent is preferably 5 to 30 minutes, more preferably 10 to 20 minutes. If the contact time is too short, the α-diimine metal complex and the organoboron compound cannot interact sufficiently, thereby affecting the catalytic effect of the final catalytic system. On the other hand, if the contact time is too long, the active center formed by the complex and the organoboron compound may be affected by prolonged contact with the outside environment, thus affecting its activity.

[0100] In this invention, there is no particular limitation on the contact temperature in step (1), as long as it does not affect the structure of the α-diimine metal complex, it can be 0℃-60℃, preferably 10℃-50℃, and more preferably 20℃-40℃.

[0101] In step (2) of the present invention, ethylene polymerization is carried out in the presence of the mixture obtained in step (1) above and at least one organoaluminum compound selected from alkylaluminum, aluminoxane and haloalkylaluminum of the present invention.

[0102] In one embodiment of the present invention, in step (2), ethylene polymerization is carried out in a second organic solvent.

[0103] In one embodiment of the present invention, in step (2), the mixture obtained in step (1) above, at least one organoaluminum compound selected from alkylaluminum, aluminoxane and haloalkylaluminum of the present invention is added to a second organic solvent, and then ethylene is introduced into the solvent to carry out ethylene polymerization.

[0104] In one embodiment of the present application, as the second organic solvent, it can be a polymerization solvent commonly used in the polymerization of polyethylene, for example, including but not limited to C 4-10 paraffin or cycloparaffin (for example, isopropane, butane, pentane, hexane, heptane, octane, nonane, decane, cyclohexane, cycloheptane, etc.), aromatic hydrocarbon solvent (for example, toluene and xylene and isomers thereof), etc. Among them, hexane, isopropane, cyclohexane, toluene or a mixture thereof is preferably used as the second organic solvent.

[0105] In one embodiment of the present application, for the mixture obtained in the first step, the addition order of the above-mentioned organic aluminum compound of the present application in the second organic solvent is not particularly limited, the mixture obtained in the first step can be added first, and then the above-mentioned organic aluminum compound of the present application is added; or the above-mentioned organic aluminum compound of the present application can be added first, and then the mixture obtained in the first step is added; or the mixture obtained in the first step and the above-mentioned organic aluminum compound of the present application can be added at the same time.

[0106] In one embodiment of the present application, for the addition form of the organic aluminum compound, there is no particular limitation, it can be added directly in the second organic solvent, or it can be added in the form of a solution. Generally, it is added in the form of a solution dispersed in a solvent. As the solvent for dispersing the organic aluminum compound, there is no particular limitation, as long as it can disperse the organic aluminum compound, generally it can be an alkane solvent, such as n-hexane, n-pentane, isopentane, cyclopentane, neopentane, etc., or an aromatic hydrocarbon solvent, such as toluene, ethylbenzene, xylene, etc. According to the present application, in order to facilitate subsequent separation, it is preferred that the same solvent as the first solvent and / or the second solvent is used; or the same solvent as at least one of the mixed solvents used in the polymerization system is used.

[0107] In one embodiment of the present application, for the amount of the organic aluminum compound, there is no particular limitation, as long as it is the conventional amount of the organic aluminum compound used in the polymerization of ethylene.

[0108] In one embodiment of the present application, for the ratio of the organic aluminum compound to the α-diimine nickel metal complex, the molar ratio of Al to Ni is 10-2000:1, preferably 100-1500:1, and more preferably 150-1000:1, based on the total aluminum (Al) element in the organic aluminum compound and the active metal nickel (Ni) element in the metal complex.

[0109] In the preparation of the branched polyethylene of the present application, a chain transfer agent can be used, or a chain transfer agent can not be used.

[0110] In one embodiment of the present application, as the chain transfer agent, other metal alkyl compounds than the organoaluminum compound and the organoboron compound of the present application can be exemplified, for example, one or more of n-butyllithium, diethylzinc, dipropylzinc, dibutylzinc, diisobutylzinc, diethylmagnesium, dibutylmagnesium or n-butyethylmagnesium can be exemplified. In one embodiment of the present application, when the chain transfer agent is used, the amount of the chain transfer agent is in a molar ratio of 5 to 300: 1, preferably 10 to 200: 1, of the metal content of the chain transfer agent to the α-diimine nickel metal complex based on the Ni metal content.

[0111] In the present application, the amount of the α-diimine metal complex is not particularly limited, and it is only required to be a conventional amount of the catalyst used in the preparation of the branched polyethylene. In one embodiment of the present application, the α-diimine metal complex is added in an amount of (0.1 to 100) x 10 -6 mol / L, preferably (0.5 to 50) x 10 -6 mol / L, based on the Ni molar content of the complex, relative to the total amount of the solvent in the polymerization process (typically, the sum of the first organic solvent and the second organic solvent and the subsequent optional other solvent) in a volume ratio of (0.1 to 100) x 10

[0112] In the present application, the conditions for the polymerization of ethylene are not particularly limited, and it is only required to be a conventional condition for the preparation of the branched polyethylene. In one embodiment of the present application, the conditions for the polymerization reaction are as follows: the polymerization temperature is 0 to 90°C, preferably 20 to 80°C; and the polymerization pressure is 0.1 to 4.0 MPa, preferably 0.5 to 3.0 MPa.

[0113] In the present application, the time for the polymerization of ethylene is not particularly limited, and it can be arbitrarily adjusted as needed by the person skilled in the art depending on the amount of the catalyst system used, the amount of ethylene, and the polymerization temperature. For example, it can be 10 minutes to 2 hours, 20 minutes to 90 minutes, 30 minutes to 1 hour, etc.

[0114] The method for the preparation of the branched polyethylene of the present application can be performed in a continuous polymerization mode or in a batch polymerization mode.

[0115] The method for the preparation of the branched polyethylene of the present application is preferably performed in a solution polymerization mode.

[0116] The solvent in the solution polymerization of the present application is the mixed solvent of the first solvent and the second solvent described above. In one embodiment of the present application, other solvents can be further added as needed. The other solvents are not particularly limited, and it is only required that they do not affect the polyethylene reaction of the present application. In one embodiment of the present application, the addition of the other solvents is not preferred.

[0117] In the present application, the ethylene polymerization is carried out in the absence of other comonomers. That is, in the present application, the branched polyethylene is prepared by carrying out the homopolymerization of ethylene in the presence of a specific catalyst system.

[0118] In the present application, after the completion of the polymerization reaction, the reaction can be terminated by means known in the art. For example, the polymerization reaction can be terminated by adding hydrochloric acid-acidified ethanol into the polymerization solution, or the polymerization reaction solution can be poured into a hydrochloric acid-acidified ethanol solution to terminate the polymerization reaction.

[0119] In the present application, after the completion of the polymerization reaction, the branched polyethylene can be separated by means conventional in the art.

[0120] [branched polyethylene]

[0121] By the preparation method of the present application, the branched polyethylene of the present application can be prepared by catalyzing the homopolymerization of ethylene under solution polymerization conditions.

[0122] The branched polyethylene of the present application can have branched chains of various lengths.

[0123] In one embodiment of the present application, the branched polyethylene has a crystallinity of less than 25%.

[0124] In one embodiment of the present application, the branched polyethylene has a weight average molecular weight of between 100,000 g / mol and 1,200,000 g / mol.

[0125] In one embodiment of the present application, the branched polyethylene has a molecular weight distribution of between 1.5 and 3.5.

[0126] In one embodiment of the present application, the branched polyethylene has a branching degree of between 60 / 1000C and 200 / 1000C (i.e., 60-200 branches per 1000 carbon main chains), preferably between 70 / 1000C and 150 / 1000C (i.e., 70-150 branches per 1000 carbon main chains).

[0127] Examples

[0128] In order to make the objects, technical solutions and advantages of the present application more clear, the present application will be further described in detail by way of examples. However, the scope of the present application is not limited to these examples.

[0129] The raw materials used in the following examples and comparative examples are all commercially available products, unless otherwise specified.

[0130] The testing method of the molecular weight of the polyethylene obtained in the following examples and comparative examples is as follows: the molecular weight of the polymer is determined by using a PL-220 gel permeation chromatograph of Polymer Laboratories. The mobile phase is 1,2,4-trichlorobenzene, polystyrene is used as a standard sample, a differential detector is used, the flow rate is 1.0 mL / min, the determination temperature is 150°C, and the sample concentration is 2.0 mg / mL.

[0131] The branching degree of the polyethylene obtained in the following examples and comparative examples is calculated according to nuclear magnetic resonance carbon spectrum, and the specific method is as follows: the microstructure of the polyethylene sample is determined by using a Bruker Avance 600M nuclear magnetic resonance spectrometer. The sample is dissolved in deuterated o-dichlorobenzene to form a solution, the test temperature is 120°C, and the nuclear magnetic resonance hydrogen spectrum (H-NMR) and the nuclear magnetic resonance carbon spectrum (C-NMR) are obtained by scanning 2000 times and 6000 times, respectively. 1 13 C-NMR).

[0132] Example 1

[0133] In a glove box, nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl)borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL triangular flask, and after being fully stirred and mixed at 30°C for 10 minutes, a catalyst solution was prepared and used as a catalyst solution. In a 2L high-pressure polymerization kettle purged with nitrogen, hexane (1L) and a cocatalyst triethylaluminum (3.3 mmol) were sequentially added, and the above prepared catalyst solution was transferred into the polymerization kettle, 1.5 MPa of ethylene was introduced at 60°C, and the polymerization reaction was carried out at a stirring speed of 200 rpm for 30 min. After the reaction was completed, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer, the polymer was filtered, washed, and dried at 60°C under vacuum to a constant weight, and the weight of the polymer was measured to be 22.2 g. The polymerization activity was 40.4 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 260.4 kg / mol, and the branching degree was 107.8 / 1000 carbon atoms.

[0134] Example 2

[0135] ​Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst triisobutylaluminum (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 18.2 g. The polymerization activity was 33.1 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 277.0 kg / mol, and the branching degree was 97.5 / 1000 carbon atoms.

[0136] Example 3

[0137] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst triisobutylaluminum (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 18.2 g. The polymerization activity was 33.1 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 277.0 kg / mol, and the branching degree was 97.5 / 1000 carbon atoms. Figure 1 The GPC spectrum is shown in Figure 3 The DSC spectrum is shown in Figure 4

[0138] Example 4

[0139] ​Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst methylaluminoxane (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 39.0 g. The polymerization activity was 70.9 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 497.0 kg / mol, and the branching degree was 90.2 / 1000 carbon atoms.

[0140] Example 5

[0141] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst methylaluminoxane (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 39.0 g. The polymerization activity was 70.9 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 497.0 kg / mol, and the branching degree was 90.2 / 1000 carbon atoms.

[0142] Example 6

[0143] Nickel catalyst C5 (0.011 mmol), N,N-dimethylanilinium tetra(pentafluorophenyl)borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min to prepare a catalyst solution. A 2 L autoclave was purged with nitrogen, and hexane (1 L) and co-catalyst triisobutylaluminum (3.3 mmol) were sequentially added into the autoclave. The catalyst solution was transferred into the autoclave, and 1.5 MPa of ethylene was introduced at 60 °C. The polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 21.3 g. The polymerization activity was 38.7 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 344.0 kg / mol, and the degree of branching was 105.2 / 1000 carbon atoms.

[0144] Example 7

[0145] Nickel catalyst C5 (0.011 mmol), tris(pentafluorophenyl)borane (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min to prepare a catalyst solution. A 2 L autoclave was purged with nitrogen, and hexane (1 L) and co-catalyst triisobutylaluminum (3.3 mmol) were sequentially added into the autoclave. The catalyst solution was transferred into the autoclave, and 1.5 MPa of ethylene was introduced at 60 °C. The polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 19.2 g. The polymerization activity was 34.9 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 316.3 kg / mol, and the degree of branching was 94.8 / 1000 carbon atoms.

[0146] Example 8

[0147] In a glove box, nickel catalyst C5 (0.011 mmol), triethylammonium tetra(pentafluorophenyl)borate (0.022 mmol), and dichloromethane (10 mL) were sequentially added to a 50 mL Erlenmeyer flask. The mixture was stirred thoroughly at 30 °C for 10 minutes to obtain the catalyst solution. In a 2 L high-pressure polymerization reactor purged with nitrogen, hexane (1 L) and triisobutylaluminum co-catalyst (3.3 mmol) were added sequentially. The prepared catalyst solution was then transferred to the polymerization reactor. Ethylene was introduced at 1.5 MPa at 60 °C, and polymerization was carried out at 200 rpm for 30 minutes with stirring. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate solid polymer. The polymer was filtered, washed, and vacuum dried at 60 °C to constant weight, yielding 16.4 g of polymer. The polymerization activity was 29.8 × 10⁻⁶. 5 The polymer has a weight-average molecular weight of 253.7 kg / mol and a branching degree of 87.7 / 1000 carbon atoms.

[0148] Example 9

[0149] In a glove box, nickel catalyst C1 (0.011 mmol), triphenylcarbontetra(pentafluorophenyl)borate (0.022 mmol), and dichloromethane (10 mL) were sequentially added to a 50 mL Erlenmeyer flask. The mixture was stirred thoroughly at 30 °C for 10 minutes to obtain the catalyst solution. In a 2 L high-pressure polymerization reactor purged with nitrogen, hexane (1 L) and co-catalyst dichloroethylaluminum (3.3 mmol) were added sequentially. The prepared catalyst solution was then transferred to the polymerization reactor. Ethylene was introduced at 1.5 MPa at 60 °C, and polymerization was carried out at 200 rpm for 30 minutes with stirring. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate solid polymer. The polymer was filtered, washed, and then vacuum dried at 60 °C to constant weight, yielding 57.5 g of polymer. The polymerization activity was 104.5 × 10⁻⁶. 5 The polymer has a weight-average molecular weight of 215.7 kg / mol and a branching degree of 118.7 / 1000 carbon atoms.

[0150] Example 10

[0151] Nickel catalyst C7 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and the mixture was stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst dichloroethylaluminum (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 65.8 g. The polymerization activity was 119.6 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 174.2 kg / mol, and the branching degree was 90.8 / 1000 carbon atoms.

[0152] Example 11

[0153] Nickel catalyst C8 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and the mixture was stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst dichloroethylaluminum (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 80.3 g. The polymerization activity was 146.0 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 247.0 kg / mol, and the branching degree was 149.2 / 1000 carbon atoms.

[0154] Example 12

[0155] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.011 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 60.1 g. The polymerization activity was 109.3 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 252.8 kg / mol, and the branching degree was 100.8 / 1000 carbon atoms.

[0156] Example 13

[0157] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.044 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 74.4 g. The polymerization activity was 135.3 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 206.2 kg / mol, and the branching degree was 133.4 / 1000 carbon atoms.

[0158] Example 14

[0159] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (1.65 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 32.3 g. The polymerization activity was 58.7 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 374.3 kg / mol, and the branching degree was 95.2 / 1000 carbon atoms.

[0160] Example 15

[0161] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (5.5 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, which was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 76.4 g. The polymerization activity was 138.9 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 237.0 kg / mol, and the branching degree was 131.5 / 1000 carbon atoms.

[0162] Example 16

[0163] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 10 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (11 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 68.1 g. The polymerization activity was 136.2 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 185.2 kg / mol, and the branching degree was 146.6 / 1000 carbon atoms.

[0164] Example 17

[0165] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and stirred at 30 °C for 5 min, then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out for 30 min at 200 rpm. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 70.3 g. The polymerization activity was 127.8 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 238.1 kg / mol, and the branching degree was 119.4 / 1000 carbon atoms.

[0166] Example 18

[0167] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetra(pentafluorophenyl) borate (0.022 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and the mixture was stirred at 30 °C for 40 min, and then used as catalyst solution. Hexane (1 L) and co-catalyst diethylaluminum chloride (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was weighed to be 53.2 g. The polymerization activity was 96.7 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 200.5 kg / mol, and the branching degree was 94.3 / 1000 carbon atoms.

[0168] Comparative Example 1

[0169] Nickel catalyst C5 (0.011 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and the mixture was stirred at 30 °C for 10 min, and then used as catalyst solution. Hexane (1 L) and co-catalyst triethylaluminum (3.3 mmol) were sequentially added into a 2 L high pressure polymerization reactor purged with nitrogen, and the above catalyst solution was transferred into the reactor. The reactor was purged with 1.5 MPa ethylene at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was weighed to be 3.5 g. The polymerization activity was 6.36 x 10 5 gPE / (mol Ni h), the weight average molecular weight of the polymer was 341.8 kg / mol, and the branching degree was 85.3 / 1000 carbon atoms.

[0170] Comparative Example 2

[0171] Nickel catalyst C5 (0.011 mmol) and dichloromethane (10 mL) were added into a 50 mL flask, respectively, in a glove box, and stirred at 30 °C for 10 min, as catalyst solution. A 2 L high pressure polymerization reactor was purged with nitrogen, and hexane (1 L) and co-catalyst triisobutyl aluminum (3.3 mmol) were added into the reactor, and the above catalyst solution was transferred into the reactor. The reactor was purged with ethylene at 1.5 MPa at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, and the polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was 1.9 g. The polymerization activity was 3.45 x 10 5 gPE / (mol Ni h), the weight average molecular weight of the polymer was 532.4 kg / mol, and the branching degree was 67.7 / 1000 carbon atoms.

[0172] Comparative Example 3

[0173] Nickel catalyst C5 (0.011 mmol) and dichloromethane (10 mL) were added into a 50 mL flask, respectively, in a glove box, and stirred at 30 °C for 10 min, as catalyst solution. A 2 L high pressure polymerization reactor was purged with nitrogen, and hexane (1 L) and co-catalyst triisobutyl aluminum (3.3 mmol) were added into the reactor, and the above catalyst solution was transferred into the reactor. The reactor was purged with ethylene at 1.5 MPa at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, and the polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was 1.9 g. The polymerization activity was 3.45 x 10 5 gPE / (mol Ni h), the weight average molecular weight of the polymer was 532.4 kg / mol, and the branching degree was 67.7 / 1000 carbon atoms. Figure 2

[0174] Comparative Example 4

[0175] ​Nickel catalyst C5 (0.011 mmol) and dichloromethane (10 mL) were added into a 50 mL flask, respectively, in a glove box, and stirred at 30 °C for 10 min, as catalyst solution. A 2 L high pressure polymerization reactor was purged with nitrogen, and hexane (1 L) and co-catalyst methylaluminoxane (3.3 mmol) were added into the reactor, and the above catalyst solution was transferred into the reactor. The reactor was purged with ethylene at 1.5 MPa at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, and the polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 20.0 g. The polymerization activity was 36.4 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 524.0 kg / mol, and the branching degree was 65.0 / 1000 carbon atoms.

[0176] Comparative Example 5

[0177] Nickel catalyst C5 (0.011 mmol) and dichloromethane (10 mL) were added into a 50 mL flask, respectively, in a glove box, and stirred at 30 °C for 10 min, as catalyst solution. A 2 L high pressure polymerization reactor was purged with nitrogen, and hexane (1 L) and co-catalyst methylaluminoxane (3.3 mmol) were added into the reactor, and the above catalyst solution was transferred into the reactor. The reactor was purged with ethylene at 1.5 MPa at 60 °C, and the polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into acidified ethanol solution to precipitate the solid polymer, and the polymer was filtered, washed, and dried at 60 °C under vacuum to constant weight. The polymer was obtained in 20.0 g. The polymerization activity was 36.4 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 524.0 kg / mol, and the branching degree was 65.0 / 1000 carbon atoms.

[0178] Comparative Example 6

[0179] Nickel catalyst C5 (0.011 mmol), triphenylcarbenium tetrakis(pentafluorophenyl)borate (0.022 mmol), co-catalyst dichloroethylaluminum (3.3 mmol) and dichloromethane (10 mL) were sequentially added into a 50 mL flask in a glove box, and the mixture was stirred at 30 °C for 10 min to prepare a catalyst solution. A 2 L autoclave was purged with nitrogen, and hexane (1 L) and the catalyst solution were sequentially added into the autoclave. The autoclave was purged with nitrogen for 3 times, and then 1.5 MPa of ethylene was introduced into the autoclave at 60 °C. The polymerization was carried out at 200 rpm for 30 min. After the reaction, the polymerization solution was poured into an acidified ethanol solution to precipitate the solid polymer. The polymer was filtered, washed and dried at 60 °C under vacuum until the weight was constant. The polymer was weighed to be 38.1 g. The polymerization activity was 69.3 x 10 5 g / (mol Ni h), the weight average molecular weight of the polymer was 206.4 kg / mol, and the branching degree was 83.0 / 1000 carbon atoms.

[0180] The results of the examples and the comparative examples are summarized as follows.

[0181] Table 1: Results of the polymerization test

[0182]

[0183]

[0184] As can be fully demonstrated by the above examples and comparative examples, by using the specific polymerization method of the present application, not only the polymerization activity of the catalyst can be significantly improved, but also the branching degree of the obtained polyethylene is obviously improved. Therefore, the preparation method of such a specific polymerization system of the present application is an effective means to regulate the branching degree of polyethylene, and thus the branching degree of polyethylene can be adjusted and controlled in a larger range.

[0185] Meanwhile, compared with the method of regulating the branching degree of polyethylene by changing the structure of the catalyst or substantially adjusting the polymerization temperature and pressure in the prior art, the method of the present application is more feasible, simple and easy to operate, and has a lower cost, which is very beneficial to industrial application.

[0186] In addition, as can be known from the comparison of Example 3, Comparative Example 3 and Comparative Example 6, if the organic aluminum compound and the organic phosphorus compound are mixed with the nickel metal complex at the same time, the polymerization activity and the branching degree of the obtained polymer will be obviously reduced.

[0187] Although the specific embodiments of the present application have been described in detail above, it should be pointed out that the scope of protection of the present application is not limited by the specific embodiments, but is defined by the claims attached hereto. Those skilled in the art can make appropriate changes to the embodiments without departing from the technical idea and the main points of the present application, and the changed embodiments are obviously included in the scope of protection of the present application.

Claims

1. A method for preparing branched polyethylene, comprising the steps of: (1) contacting an α-diimine nickel metal complex represented by formula (I) with at least one boron compound selected from aryl boron, alkyl boron and borate in a first organic solvent to obtain a mixture; (2) performing ethylene polymerization in the presence of the mixture, at least one organoaluminum compound selected from alkyl aluminum, aluminoxane and halogenated alkyl aluminum to obtain branched polyethylene, In formula (I), R1-R6 are the same or different, each independently hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C1-C6 haloalkyl, optionally substituted C2-C6 alkenyl, halogen, optionally substituted C1-C6 alkoxy, or optionally substituted C6-C 10 aryl, or, two adjacent groups from R1-R6 are bonded to each other to form, together with the carbon atoms to which they are attached, an optionally substituted C4-C8 ring; R7, R 11 , R 12 , R 16 are the same or different, each independently hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C3-C8 cycloalkyl, optionally substituted phenyl; R8, R9, R 10 , R 13 , R 14 , R 15 are the same or different, each independently hydrogen, optionally substituted C1-C6 alkyl, optionally substituted C3-C8 cycloalkyl, optionally substituted phenyl, halogen, optionally substituted C1-C6 alkoxy, nitro, amino, thiol; X is halogen, wherein the substituents in "optionally substituted" are selected from the group consisting of halogen, C1-C4 alkyl, C1-C4 haloalkyl, phenyl.

2. The production method according to claim 1, characterized by, in formula (I), R1-R6 are the same or different, each independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, fluorine, chlorine, bromine, halogenated methyl, halogenated ethyl, halogenated propyl, halogenated isopropyl, halogenated butyl, halogenated isobutyl, halogenated sec-butyl, halogenated tert-butyl, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, phenyl, pentafluorophenyl, pentachlorophenyl or benzhydryl, or, at least one group of R4 and R3, R3 and R1, R1 and R2, R2 and R5, R5 and R6, are bonded to each other to form, together with the carbon atoms to which they are connected, a benzene ring optionally substituted with at least one selected from halogen, C1-C4 alkyl, a cyclopentene ring optionally substituted with at least one selected from halogen, C1-C4 alkyl, or a cyclopentadiene ring optionally substituted with at least one selected from halogen, C1-C4 alkyl.

3. The production method according to claim 1 or 2, characterized by, In formula (I), R7, R 11 , R 12 , R 16 are each independently selected from the group consisting of hydrogen, optionally substituted methyl, optionally substituted ethyl, optionally substituted propyl, optionally substituted isopropyl, optionally substituted butyl, optionally substituted isobutyl, optionally substituted sec-butyl, optionally substituted t-butyl, optionally substituted phenyl.

4. The production method according to claim 1 or 2, characterized by, R8, R9, R 10 , R 13 , R 14 , R 15 are each independently selected from any one of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, fluorine, chlorine, bromine, phenyl, or pentafluorophenyl.

5. The production method according to claim 1 or 2, characterized by, the α-diimine nickel metal complex represented by formula (I) is at least one metal complex selected from 6. The production method according to claim 1 or 2, characterized by, the alkyl boron, aryl boron is a compound represented by the following general formula (B-1): B(R)3 (B-1) wherein each of the three R groups can be the same as or different from one another, each R is independently selected from C 1-6 linear or branched alkyl and C 6-10 aryl, each group optionally substituted with one or more halogen atoms, haloC 1-6 linear or branched alkyl or phenoxy; the borate is a compound represented by the following general formula (B-2): [L] + [BE4] m - (B-2) wherein L is a cationic group, each E can be the same or different, each being independently selected from a halogen atom, a C 6-10 aryl group, which aryl group is optionally substituted with one or more halogen atoms, C 1-6 straight-chain or branched alkyl, halogenated C 1-6 straight-chain or branched alkyl, C 1-6 straight-chain or branched alkoxy or phenoxy.

7. The production method according to claim 1 or 2, characterized in that, the alkyl aluminum is a compound represented by the following formula (D): Al(R') 11 )3(D) In the formula (D), the group R' 11 each independently of one another, is selected from the group consisting of C 1-6 alkyl; the halogenated alkyl aluminum is a compound represented by the following formula (E): Al(R' 11 ) n X 3-n (E) In this formula (E), the group R' 11 each independently of one another, is selected from C 1-6 alkyl; the group X is halogen, n is an integer of 1 or 2; the aluminoxane is linear aluminoxane represented by the following formula (F) or cyclic aluminoxane represented by the following formula (G): in the aforementioned formula (F) and formula (G), a plurality of groups R are the same or different, each independently selected from C1-C6 alkyl, and n is any integer in the range of 1-50.

8. The production method according to claim 1 or 2, characterized by, The first organic solvent is at least one selected from the group consisting of C 4-10 alkanes, halogenated C 1-10 alkanes, C 6-10 aromatic solvents, halogenated C 6-10 aromatic solvents.

9. The production method according to claim 1 or 2, characterized by, in step (1), for the ratio of the α-diimine nickel metal complex to the boron compound, the molar ratio of B to Ni is 0.5-50:1, calculated based on boron (B) elements in the boron compound and active metal nickel (Ni) elements in the metal complex.

10. The production method according to claim 1 or 2, characterized by, in step (1), the contact time of the α-diimine nickel metal complex and the boron compound in the first organic solvent is 5-30 minutes.

11. The production method according to claim 1 or 2, characterized by, In step (2), ethylene polymerization is performed in a second organic solvent, wherein the second organic solvent is at least one selected from the group consisting of a paraffin or cycloparaffin, aromatic hydrocarbon solvent. 4-10 a paraffin or cycloparaffin, aromatic hydrocarbon solvent.

12. The production method according to claim 1 or 2, characterized by, for the ratio of the organoaluminum compound to the α-diimine nickel metal complex, the molar ratio of Al to Ni is 10-2000:1, calculated based on total aluminum (Al) elements in the organoaluminum compound and active metal nickel (Ni) elements in the metal complex.

13. The production method according to claim 1 or 2, characterized by, in step (2), the conditions of the polymerization reaction are: the polymerization temperature is 0-90℃; and the polymerization pressure is 0.1-4.0 Mpa.

14. The production method according to claim 1 or 2, characterized by, at least one of the following characteristics is satisfied: R7, R 11 , R 12 , R 16 are each independently selected from the group consisting of hydrogen, methyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, ethyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, propyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, isopropyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, butyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, isobutyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, sec-butyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, t-butyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl, phenyl optionally substituted with at least one member selected from the group consisting of halogen, phenyl; the alkyl boron is at least one selected from trimethyl boron, triethyl boron, triisobutyl boron, tripropyl boron and tributyl boron; the aryl boron is at least one selected from the group consisting of triphenyl boron, tris(pentafluorophenyl)boron and tris[3,5-bis(trifluoromethyl)phenyl]boron; the borate salt is at least one selected from the group consisting of 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-diethylbenzenammonium tetraphenylborate, N,N-dimethylbenzenammonium tetra(pentafluorophenyl)borate, N,N-diethylbenzenammonium tetra(pentafluorophenyl)borate, triethylammonium tetra(pentafluorophenyl)borate, triphenylcarbenium tetra(pentafluorophenyl)borate, 1-butyl-3-methylimidazolium tetrafluoroborate and ferrocenium tetrafluoroborate; the alkyl aluminum is at least one selected from the group consisting of trimethyl aluminum (Al(CH3)3), triethyl aluminum (Al(CH2CH3)3), tri-n-propyl aluminum (Al(n-C3H7)3), triisobutyl aluminum (Al(i-C4H9)3), tri-n-butyl aluminum (Al(n-C4H9)3), triisopentyl aluminum (Al(i-C5H 11 )3), tri-n-pentyl aluminum (Al(n-C5H 11 )3), tri-n-hexyl aluminum (Al(n-C6H 13 )3), triisohexyl aluminum (Al(i-C6H 13 )3), diethylmethyl aluminum (Al(CH3)(CH3CH2)2), and dimethylethyl aluminum (Al(CH3CH2)(CH3)2); The halogenated aluminum alkyl is at least one selected from the group consisting of monochlorodimethylaluminum (Al(CH3)2Cl), dichloromethylaluminum (Al(CH3)Cl2), monochlorodiethylaluminum (Al(CH3CH2)2Cl), dichloroethylaluminum (Al(CH3CH2)Cl2), monochlorodipropylaluminum (Al(C3H7)2Cl), dichloropropylaluminum (Al(C3H7)Cl2), monochlorodi-n-butylaluminum (Al(n-C4H9)2Cl), dichloro-n-butylaluminum (Al(n-C4H9)Cl2), monochlorodi-i-butylaluminum (Al(i-C4H9)2Cl), dichloro-i-butylaluminum (Al(i-C4H9)Cl2), monochlorodi-n-pentylaluminum (Al(n-C5H 11 )2Cl), dichloro-n-pentylaluminum (Al(n-C5H 11 )Cl2), monochlorodi-i-pentylaluminum (Al(i-C5H 11 )2Cl), dichloro-i-pentylaluminum (Al(i-C5H 11 )Cl2), monochlorodi-n-hexylaluminum (Al(n-C6H 13 )2Cl), dichloro-n-hexylaluminum (Al(n-C6H 13 )Cl2), monochlorodi-i-hexylaluminum (Al(i-C6H 13 )2Cl), dichloro-i-hexylaluminum (Al(i-C6H 13 )Cl2), monochloromethylethylaluminum (Al(CH3)(CH3CH2)Cl), monochloromethylpropylaluminum (Al(CH3)(C3H7)Cl), monochloromethyl-n-butylaluminum (Al(CH3)(n-C4H9)Cl), monochloromethyl-i-butylaluminum (Al(CH3)(i-C4H9)Cl), monochloroethylpropylaluminum (Al(CH2CH3)(C3H7)Cl), monochloroethyl-n-butylaluminum (Al(CH2CH3)(n-C4H9)Cl), and monochloroethyl-i-butylaluminum (Al(CH2CH3)(i-C4H9)Cl). the aluminoxane is at least one selected from the group consisting of methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, n-butylaluminoxane, modified methylaluminoxane or modified ethylaluminoxane; the first organic solvent is one or more selected from the group consisting of butane, pentane, hexane, heptane, octane, nonane, decane, dichloromethane, trichloromethane, monochloroethane, dichloroethane, trichloroethane, toluene, p-xylene, m-xylene, o-xylene, mesitylene and o-dichlorobenzene; in step (1), the molar ratio of B to Ni is 1-10:1, based on the boron (B) element in the boron compound and the active metal nickel (Ni) element in the metal complex; in step (1), the contact time of the α-diimine metal complex and the boron compound in the first organic solvent is 10-20 minutes; in step (2), ethylene polymerization is carried out in a second organic solvent, wherein the second organic solvent is at least one selected from the group consisting of isopropane, butane, pentane, hexane, heptane, octane, nonane, decane, cyclohexane and cycloheptane; for the ratio of the organoaluminum compound to the α-diimine nickel metal complex, the molar ratio of Al to Ni is 150-1000:1, based on the total aluminum (Al) element in the organoaluminum compound and the active metal nickel (Ni) element in the metal complex; in step (2), the polymerization conditions are: the polymerization temperature is 0-90°C; and the polymerization pressure is 0.1-4.0 Mpa.

15. The branched polyethylene obtained by the preparation method according to any one of claims 1-14, which satisfies at least one of the following characteristics: 1) the crystallinity of the branched polyethylene is less than 25%; 2) the weight average molecular weight of the branched polyethylene is between 100,000 g / mol and 1,200,000 g / mol; 3) the molecular weight distribution of the branched polyethylene is between 1.5 and 3.5; 4) the branching degree of the branched polyethylene is between 60 / 1000C and 200 / 1000C.

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