High density polyethylene copolymer, process for its preparation and use thereof

Abstract

The application provides an HDPE copolymer and a preparation method and application thereof. The HDPE copolymer is obtained by using ethylene and alpha-olefin as monomers and using catalyst component A and catalyst component B to catalyze polymerization of the monomers; the catalyst component A comprises a reaction product of a magnesium compound, an organic boron compound, a titanium compound and a vanadium compound; and the catalyst B comprises an organic aluminum compound. The preparation method of the HDPE copolymer comprises the following steps: adding a second organic solvent, the catalyst component A and the catalyst component B into a reactor, introducing ethylene, performing a first polymerization reaction to obtain a polyethylene homopolymer; introducing ethylene and alpha-olefin into the reactor, performing a second polymerization reaction to obtain a copolymer intermediate; introducing ethylene and alpha-olefin into the reactor, performing a third polymerization reaction to obtain the multimodal structure HDPE copolymer. The application further provides a polyethylene copolymer pipe prepared from the HDPE copolymer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ethylene polymerization, in particular to a HDPE copolymer with a multimodal distribution structure of molecular weight and a preparation method and application thereof. BACKGROUND

[0002] High-density polyethylene has good mechanical strength at high temperature, but poor long-term creep resistance. In recent years, with the research on the relationship between the molecular structure and performance of polyethylene, great progress has been made. By improving the polymerization process and developing new catalyst systems, the distribution of comonomers in the polymer chain can be controlled, and the crystallization of the polymer can be more accurately controlled, making it possible for polyethylene to have good high-temperature resistance and long-term creep resistance.

[0003] The preparation method of high-efficiency titanium-based Ziegler-Natta catalyst for ethylene polymerization is well known, mainly composed of MgCl2 or SiO2 supported titanium halide. However, the current Ziegler-Natta catalyst has the following problems: 1. The solid catalyst particle morphology is poor, the bulk density is low, and the thickness is uneven, so the polymer morphology is also poor, with more fine powder, easy to produce static electricity and easily block the pipeline, and the catalyst has more oligomers in the solvent during polymerization, which brings great trouble to the post-treatment; 2. Some catalyst systems have low catalyst activity and poor hydrogen regulation performance when used for ethylene polymerization, which are not suitable for preparing bimodal polymers; 3. Some catalysts used for ethylene polymerization have long induction time, large catalyst activity fluctuation and low oligomer content; 4. It is difficult to obtain a wide molecular weight distribution of the polymer. Although researchers can control the particle size, morphology and distribution of the catalyst through emulsification technology, and control the activity of the catalyst through the components and electron donor compounds of the catalyst. But the control of the copolymerization performance, hydrogen regulation sensitivity and oligomer generation amount of the catalyst has always been a difficult problem, which is very important for the development of bimodal polyethylene products.

[0004] Heat-resistant polyethylene pipe resin first requires that the molecular weight of the polymer has a bimodal or multimodal distribution. The high molecular weight part provides the product with good environmental stress cracking resistance, slow crack growth resistance, high creep resistance, high tensile strength and high impact strength; the low molecular weight part can effectively reduce its melt viscosity at high shear rate, improve the flowability in processing, and ensure a high crystallinity, so that the product has good rigidity. Only when the high molecular weight part and the low molecular weight part reach a certain proportion, can the processing performance of the pipe be considered while the final strength and service life of the pipe are improved.

[0005] The current method for preparing heat-resistant polyethylene copolymer generally has one or more of the following defects: (1) the polyethylene prepared using metallocene catalyst has narrow molecular weight distribution and poor processability; (2) the reaction steps of two-kettle or multi-kettle series polymerization are more, and the process condition control is difficult; and (3) the heat performance and mechanical performance of the polyethylene copolymer cannot meet the performance requirements of hot water pipe material under long-term high temperature. SUMMARY

[0006] In order to solve the above problems, the present application aims to provide a HDPE (high density polyethylene) copolymer and a preparation method and application thereof. The HDPE copolymer provided by the present application has wide molecular weight distribution and multi-modal structure, and has excellent heat resistance and pressure resistance, and is suitable for extrusion molding as heat-resistant pipe material.

[0007] In order to achieve the above-mentioned purpose, the present application provides a HDPE copolymer, which is obtained by polymerizing ethylene and α-olefin as monomers using catalyst component A and catalyst component B; wherein the catalyst component A comprises the reaction product of magnesium compound, organic boron compound, titanium compound and vanadium compound; and the catalyst component B comprises organic aluminum compound.

[0008] In the specific embodiments of the present application, the catalyst component A and the catalyst component B form a Ziegler-Natta catalyst, which is used to catalyze the homopolymerization of ethylene and the multi-stage copolymerization of ethylene and α-olefin, thereby obtaining a HDPE copolymer with multi-modal molecular weight distribution (i.e. three or more peaks or three or more intervals in the molecular weight distribution) and wide molecular weight distribution. In some specific embodiments, the Mw / Mn of the HDPE copolymer can reach 12-20.

[0009] In the specific embodiments of the present application, the mass content of the HDPE copolymer with a weight average molecular weight less than 50,000 can be 40-50%, the mass content of the HDPE copolymer with a weight average molecular weight of 50,000-1,000,000 can be 50-60%, and the mass content of the HDPE copolymer with a weight average molecular weight greater than 1,000,000 can be 0-5%, based on the total mass of the HDPE copolymer being 100%.

[0010] In the specific embodiments of the present application, when the weight average molecular weight of the HDPE copolymer is less than 50,000, the crystallinity of the HDPE copolymer is generally 65-75%, and the lamella thickness of the HDPE copolymer is generally 35-45 nm.

[0011] In the specific embodiments of the present application, when the weight average molecular weight of the HDPE copolymer is 50,000-1,000,000, the crystallinity of the HDPE copolymer is generally 45-55%, and the lamella thickness of the HDPE copolymer is generally 20-30 nm.

[0012] In the specific embodiments of the present application, when the weight average molecular weight of the HDPE copolymer is greater than 1 million, the crystallinity of the HDPE copolymer is generally 30-40%, and the lamella thickness of the HDPE copolymer is generally 10-20 nm.

[0013] The wide molecular weight distribution of the polymer can make the HDPE copolymer maintain good strength and processability, which is beneficial to the extrusion molding into pipes. The low molecular weight part provides a higher lamella thickness, which is beneficial to improve the mechanical properties and heat distortion temperature of the polymer; the high molecular weight part has a suitable lamella thickness, which means that it can contribute to part of the mechanical properties and contain a certain amount of tie molecular chain structure to resist crack propagation; the ultra-high molecular weight part has a thinner lamella thickness, which means that it has more branched chain structures, which can form a large number of tie molecules to resist crack propagation and improve the melt strength, so that the copolymer can be applied to heat-resistant pipes.

[0014] In the specific embodiments of the present application, the density of the HDPE copolymer is generally 0.940-0.955 / cm 3 .

[0015] In the specific embodiments of the present application, the melt index (190℃, 5Kg) of the HDPE copolymer can reach 0.1-1.0 g / 10 min.

[0016] In the specific embodiments of the present application, the branching degree of the HDPE copolymer is generally 2.5-4.5 / 1000 carbon atoms.

[0017] In the specific embodiments of the present application, the structure of the magnesium compound includes: n MgR 2-n wherein n is an integer of 0-2; R is one or a combination of two or more of hydrogen, alkyl, alkoxy, carboxyl, aryl and cycloalkyl, and X is halogen. Among them, the carbon number of the alkyl is preferably 1-20, the carbon number of the alkoxy is preferably 1-20, the carbon number of the aryl is preferably 6-20, and the carbon number of the cycloalkyl is preferably 3-20.

[0018] In the specific embodiments of the present application, the above-mentioned organic magnesium compound can include one or a combination of two or more of alkyl magnesium, alkyl magnesium halide, alkyl magnesium alkoxy compound, magnesium halide, alkoxy magnesium halide, aryloxy magnesium halide, aryloxy magnesium, carboxylate of magnesium, metallic magnesium, magnesium hydride, and monohydrogen alkyl magnesium. Among them:

[0019] The alkyl magnesium can include one or a combination of two or more of dimethyl magnesium, diethyl magnesium, dipropyl magnesium, dibutyl magnesium, dipentyl magnesium, dihexyl magnesium, didecyl magnesium, octyl butyl magnesium, and ethyl butyl magnesium;

[0020] The alkyl magnesium halide can include one or more than two combinations of ethyl magnesium chloride, propyl magnesium chloride, butyl magnesium chloride, pentyl magnesium chloride, hexyl magnesium chloride, and the like;

[0021] The alkyl magnesium alkoxide can include one or more than two combinations of butyl ethyl magnesium alkoxide, ethyl butyl magnesium alkoxide, octyl butyl magnesium alkoxide, and the like;

[0022] The magnesium halide can include one or more than two combinations of magnesium chloride, magnesium bromide, magnesium iodide, magnesium fluoride, and the like;

[0023] The alkoxy magnesium halide can include one or more than two combinations of methoxy magnesium chloride, ethoxy magnesium chloride, isopropoxy magnesium chloride, butoxy magnesium chloride, octyloxy magnesium chloride, and the like;

[0024] The aryloxy magnesium halide can include one or more than two combinations of phenoxy magnesium chloride, methyl phenoxy magnesium chloride; alkoxy magnesium, such as ethoxy magnesium, isopropoxy magnesium, butoxy magnesium, n-octyl magnesium, 2-ethyl hexyl magnesium, and the like;

[0025] The aryloxy magnesium can include phenoxy magnesium, di(methyl phenoxy) magnesium, and the like;

[0026] The carboxylate of magnesium can include magnesium laurate, magnesium stearate, and the like.

[0027] Preferably, the magnesium compound includes one or more than two combinations of magnesium chloride, alkoxy magnesium chloride, and aryloxy magnesium chloride.

[0028] In specific embodiments of the present application, the catalyst component A is a solid catalyst, the particles of which are spheroidal, have a narrow particle size distribution, little fine powder, good copolymerization performance, and good hydrogen sensitivity, and can more effectively adjust the molecular weight distribution of the polymer and the distribution of the comonomer on the polymer molecular chain. Moreover, the production process is simple, and the production cost is low.

[0029] In some specific embodiments, the above-mentioned catalyst component A is obtained by adding a multifunctional organic boron compound as a modifier to a magnesium compound, and then reacting with a titanium compound and a vanadium compound to obtain a spheroidal catalyst component A solid by precipitation. Specifically, the preparation method of the catalyst component A can include: mixing a magnesium compound, an organic boron compound, a titanium compound, and a vanadium compound in a protective atmosphere (such as nitrogen), reacting, filtering, and washing to obtain the catalyst component A; the reaction temperature is generally controlled to be 50-120°C, and the reaction time is generally controlled to be 0.5-4h, for example, 2h.

[0030] In a specific embodiment of the present application, the magnesium compound is generally involved in the preparation of the catalyst component A in the form of a microemulsion to facilitate the precipitation of spherical catalyst particles; the microemulsion comprises a first organic solvent and a diluent (i.e., the microemulsion of the magnesium compound comprises a magnesium compound-first organic solvent-diluent form).

[0031] In some specific embodiments, the method for preparing the microemulsion of the magnesium compound can comprise mixing the magnesium compound with a first organic solvent and a diluent to obtain the microemulsion of the magnesium compound. In the above process, the magnesium compound is complexed with the first organic solvent such as alcohol, and the resulting complex is dissolved in the diluent to form the microemulsion.

[0032] In the above method for preparing the microemulsion of the magnesium compound, the temperature of the mixing can be 50-150°C.

[0033] In a specific embodiment of the present application, the method for preparing the catalyst component A can be: dissolving the solid magnesium compound in a first solvent and a diluent at a temperature of 50-150°C to form a uniform microemulsion, adding an organic acid compound during or after the formation of the microemulsion, and then performing a contact reaction with a titanium compound and a vanadium compound, slowly increasing the temperature to 50-120°C, at which time the solid gradually precipitates and forms particles, removing the reactants and solvents after a period of reaction, washing with a diluent until no titanium compound and vanadium compound are detected in the washing liquid, thereby obtaining the catalyst component A.

[0034] In the above method for preparing the microemulsion of the magnesium compound, the first organic solvent can include one or a combination of two or more of alcohol, phenol, carboxylic acid, aldehyde, amine, ester, and metal acid ester.

[0035] In the above first solvent, the alcohol can include one or a combination of two or more of aliphatic alcohol, alicyclic alcohol, aromatic alcohol, alkoxyl-containing alcohol, halogen-containing alcohol. Among them, the aliphatic alcohol can include one or a combination of two or more of methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, 2-methylpentanol, 2-ethylbutanol, heptanol, 2-ethylhexanol, octanol, decanol, dodecanol, tetradecanol, octadecanol, undecanol, oleyl alcohol, and ethylene glycol; the alicyclic alcohol can include cyclohexanol and / or methylcyclohexanol; the aromatic alcohol can include one or a combination of two or more of benzyl alcohol, methylbenzyl alcohol, isopropylbenzyl alcohol, α-methylbenzyl alcohol, α,α'-dimethylbenzyl alcohol, phenethyl alcohol, and cumyl alcohol; the alkoxyl-containing alcohol can include one or a combination of two or more of ethylene glycol-n-butyl ether, ethylene glycol-ethyl ether, and 1-butoxy-2-propanol; the halogen-containing alcohol can include one or a combination of two or more of trichloromethyl alcohol, trichloroethanol, and trichlorohexanol.

[0036] According to a specific embodiment of the present application, the alcohol has a carbon number of preferably 6 or more.

[0037] According to a specific embodiment of the present application, when an alcohol having a carbon number of 6 or more is used as the first solvent, the molar ratio of the alcohol to magnesium in the magnesium compound is usually 1 or more, preferably 1 to 40, and more preferably 1 to 10.

[0038] When an alcohol having a carbon number of 5 or less is used as the first solvent, the molar ratio of the alcohol to magnesium in the magnesium compound is usually 1 or more.

[0039] In the above first solvent, the phenol can include one or a combination of two or more of phenol, cresol, xylenol, ethyl phenol, propyl phenol, nonyl phenol, and naphthol.

[0040] In the above first solvent, the carboxylic acid has a carbon number of usually 7 or more. Specifically, the carboxylic acid can include one or a combination of two or more of octanoic acid, 2-ethylhexanoic acid, nonanoic acid, and undecylenic acid.

[0041] In the above first solvent, the aldehyde has a carbon number of usually 7 or more. Specifically, the aldehyde can include one or a combination of two or more of octanal, 2-ethylhexanal, undecanal, benzaldehyde, toluic aldehyde, and naphthaldehyde.

[0042] In the above first solvent, the amine has a carbon number of usually 6 or more. Specifically, the amine can include one or a combination of two or more of heptylamine, octylamine, 2-ethylhexylamine, nonylamine, decylamine, undecylamine, and dodecylamine.

[0043] In a specific embodiment of the present application, a diluent is generally used in combination with the first solvent to dissolve the solid magnesium compound. Specifically, the diluent can include a hydrocarbon solvent and / or an ionic liquid.

[0044] In a specific embodiment of the present application, the hydrocarbon solvent includes one or a combination of two or more of an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, and a halogenated hydrocarbon. Among them, the aliphatic hydrocarbon can include one or a combination of two or more of pentane, hexane, heptane, octane, decane, dodecane, tetradecane, and kerosene; the alicyclic hydrocarbon can include one or a combination of two or more of cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and cyclooctane; the aromatic hydrocarbon can include one or a combination of two or more of benzene, toluene, xylene, ethylbenzene, cumene, and methylisopropylbenzene; and the halogenated hydrocarbon can include one or a combination of two or more of carbon tetrachloride, dichloroethane, dichloropropane, trichloroethylene, and chlorobenzene.

[0045] When the first solvent comprises an alcohol and the diluent comprises an aromatic hydrocarbon, the molar ratio of alcohol to magnesium in the magnesium compound is usually 1 or more, preferably 1 to 40, more preferably 1 to 10. In this case, an alcohol having any carbon number can be used to sufficiently dissolve the desired compound.

[0046] When the first solvent comprises an alcohol and the diluent comprises an aliphatic and / or alicyclic hydrocarbon, if the carbon number of the alcohol is 6 or more, the molar ratio of alcohol to magnesium in the magnesium compound is usually 1 or more, preferably 1 to 40, more preferably 1 to 10; if the carbon number of the alcohol is 5 or less, the molar ratio of alcohol to magnesium in the magnesium compound is usually 1 or more.

[0047] In a specific embodiment of the present application, when an alcohol is used as the first solvent and a hydrocarbon solvent is used as the diluent, the solid magnesium compound is generally contacted with the alcohol in the hydrocarbon solvent to achieve dissolution of the magnesium compound, and preferably, the process can be carried out under heating and stirring, the heating temperature is usually 0 to 300°C, preferably 20 to 180°C, and the contact time is generally 15 minutes to 5 hours, preferably 30 minutes to 3 hours.

[0048] In a specific embodiment of the present application, when an alcohol is used as the first solvent and an ionic liquid is used as the diluent, the solid magnesium compound is generally contacted with the alcohol in the presence of the ionic liquid under heating and stirring to achieve dissolution of the magnesium compound, the heating temperature is usually 0 to 300°C, preferably 20 to 180°C, and the contact time is generally 15 minutes to 5 hours, preferably 30 minutes to 3 hours.

[0049] In a specific embodiment of the present application, the organic boron compound without active hydrogen not only acts as a precipitant and a co-precipitant, but also improves the particle morphology of the catalyst, increases the catalytic activity of the catalyst, makes the bulk density of the polymer and the particle size distribution of the polymer more concentrated, and further improves the particle morphology of the polymer. Specifically, the organic boron compound generally uses an organic boron compound without active hydrogen, such as an organic borate, etc. Compared with an organic boron compound with active hydrogen, the organic boron compound without active hydrogen has a more obvious effect on improving the particle morphology of the catalyst and the polymer. Specifically, the above-mentioned organic borate can include triethylene glycol methyl ether borate triester. Triethylene glycol methyl ether borate triester participates in the coordination of active centers, affects the chemical environment of active centers, and makes the catalyst exhibit good hydrogen regulation sensitivity.

[0050] In a specific embodiment of the present application, the structure of the titanium compound comprises: Ti(OR) a X b ; wherein R comprises one or a combination of two or more of an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or an aromatic group, X is a halogen, a is an integer of 0 to 3, and b is an integer of 1 to 4; preferably, the sum of a and b is 3 or 4.

[0051] Preferably, the aliphatic hydrocarbon group has a carbon number of 1-10, the alicyclic hydrocarbon group has a carbon number of 3-10, and the aromatic group has a carbon number of 6-10.

[0052] Preferably, the titanium compound includes one or more than two combinations of titanium tetrachloride, titanium tetrabromide, and titanium tetraiodide.

[0053] In a specific embodiment of the present application, the catalyst component A has a dual active center structure by adding the vanadium compound and the titanium compound, which further improves the copolymerization performance of the polymerized monomers catalyzed by the catalyst component A, is more beneficial to the preparation of the multimodal structure polymer, finally improves the comonomer content in the copolymer product, and expands the molecular weight distribution width of the copolymer product.

[0054] In a specific embodiment of the present application, the addition of the vanadium compound makes the catalyst form a second active center, and the main feature of the vanadium active component is that the molecular weight of the ethylene polymer product is high and the insertion amount of the comonomer is high. Specifically, the structure of the vanadium compound can include: V(OR) a X b ; wherein R includes one or more than two combinations of aliphatic hydrocarbon group, alicyclic hydrocarbon group, or aromatic group, X is halogen, a is an integer of 0-3, and b is an integer of 1-4; preferably, the sum of a and b is 3 or 4.

[0055] Preferably, the aliphatic hydrocarbon group has a carbon number of 1-10, the alicyclic hydrocarbon group has a carbon number of 3-10, and the aromatic group has a carbon number of 6-10.

[0056] Preferably, the vanadium compound includes vanadium tetrachloride, such as VCl4, VBr4, and VI4.

[0057] In a specific embodiment of the present application, the molar ratio of Ti in the titanium compound to V in the vanadium compound is generally controlled to be 1-10:1.

[0058] In a specific embodiment of the present application, the structure of the organic aluminum compound includes: AlR n X 3-n ; wherein R is a hydrocarbon group, X is halogen, and n is an integer of 0-3. Preferably, the carbon number of R is 1-20; the hydrocarbon group can include one or more than two combinations of alkyl group, aralkyl group, and aromatic group; and the halogen includes chlorine and / or bromine.

[0059] Preferably, the organic aluminum compound includes one or more than two combinations of alkyl aluminum halide, more preferably, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trioctyl aluminum, monochlorodiethyl aluminum, monochlorodiisobutyl aluminum, and diethyl aluminum chloride.

[0060] In the specific embodiments of the present application, the molar ratio of Al in the organoaluminum compound to Ti in the titanium compound is generally controlled to be 5-500:1, for example, 20-200:1.

[0061] In the specific embodiments of the present application, the polymerization process includes one or a combination of two or more of solution polymerization, slurry polymerization, and gas phase polymerization. In the slurry polymerization, the medium used can include inert solvents, such as saturated aliphatic hydrocarbons and / or aromatic hydrocarbons. Specifically, the saturated aliphatic hydrocarbons can include one or a combination of two or more of propane, isobutane, hexane, heptane, cyclohexane, naphtha, raffinate, hydrogas oil, kerosene, benzene, toluene, and xylene.

[0062] In the specific embodiments of the present application, the polymerization mode can be batch, semi-continuous, or continuous, single-kettle or multi-kettle in series.

[0063] In the specific embodiments of the present application, the polymerization temperature is generally controlled to be 0-150℃, for example, 40-100℃.

[0064] In the specific embodiments of the present application, the α-olefin as the monomer is generally aliphatic, with a carbon number generally being 4-12.

[0065] Specifically, the α-olefin can include one or a combination of two or more of propylene, butene, pentene, hexene, octene, and 4-methyl-1-pentene.

[0066] The present application also provides a preparation method of the HDPE copolymer as described above, to solve the problems of complex process, difficult control of polymer molecular structure and performance, and poor processing performance in the prior art method. The preparation method includes:

[0067] S1, adding a second organic solvent, a catalyst component A, and a catalyst component B into a reactor, introducing ethylene, and performing a first polymerization reaction to obtain a polyethylene homopolymer;

[0068] S2, introducing ethylene and α-olefin into the above reactor, and performing a second polymerization reaction to obtain a copolymer intermediate;

[0069] S3, introducing ethylene and α-olefin into the reactor of S2, and performing a third polymerization reaction to obtain the HDPE copolymer.

[0070] The preparation method as described above provided by the present application can simulate the process of the existing ethylene preparation process using two or more polymerization kettles in series by using one polymerization kettle to perform multi-stage polymerization.

[0071] In the above method for preparing the HDPE copolymer, S1 produces an ethylene homopolymer with a higher density and a higher MI value, S2 produces a low-density and low-MI-value polyethylene copolymer, and S3 produces a polyethylene copolymer product with a multimodal molecular weight distribution.

[0072] In the above method for preparing the HDPE copolymer, S1 produces a low-molecular-weight polymerization product, S2 produces a high-molecular-weight polymerization product, and S3 produces an ultrahigh-molecular-weight polymerization product. By adjusting the reaction conditions in each polymerization reaction, the proportion of the low-molecular-weight polymerization product in S1 and the high-molecular-weight polymerization product in S2 participating in the next polymerization reaction can be controlled. For example, the reaction pressure in S3 is generally controlled to be lower than that in S2, and the amount of the molecular weight regulator added in S3 is controlled to be lower than that in S2, so that the low-molecular-weight polymerization product produced in S1 and part of the high-molecular-weight polymerization product produced in S2 participate in further polymerization in S2 and S3, and the unreacted low-molecular-weight polymerization product and high-molecular-weight polymerization product are retained in the final product, thereby making the molecular weight of the final polymer product exhibit a multimodal distribution.

[0073] In the above method for preparing the HDPE copolymer, in S1, the temperature of the first polymerization reaction is generally controlled to be 50-100°C, for example, 70-90°C; the pressure of the first polymerization reaction is generally controlled to be 0.5-1 MPa; and the time of the first polymerization reaction is generally controlled to be 0.1-5 h. In the above method for preparing the HDPE copolymer, in S2, the temperature of the second polymerization reaction is generally controlled to be 50-100°C; the pressure of the second polymerization reaction is generally controlled to be 0.1-0.5 MPa, for example, 0.2-0.4 MPa, and specifically can be 0.3 MPa or 0.4 MPa; and the time of the second polymerization reaction is generally controlled to be 0.1-2 h.

[0074] In the above method for preparing the HDPE copolymer, in S2, the partial pressure ratio of the α-olefin to ethylene is generally controlled to be 0.01-1.

[0075] In the above method for preparing the HDPE copolymer, in S3, the temperature of the third polymerization reaction is generally controlled to be 50-100°C; the pressure of the third polymerization reaction is generally lower than that of the second polymerization reaction, and can be controlled to be 0.1-0.5 MPa, preferably 0.1-0.3 MPa, and is generally selected to be 0.1 MPa or 0.2 MPa; and the time of the third polymerization reaction is generally controlled to be 0.1-2 h.

[0076] In the above method for preparing the HDPE copolymer, in S3, the partial pressure ratio of the α-olefin to ethylene is generally controlled to be 0.01-1.

[0077] In the above-mentioned method for preparing the HDPE copolymer, the second organic solvent used is generally an inert solvent, such as one or a combination of two or more of alkanes, arenes, and halogenated hydrocarbons.

[0078] Preferably, the second organic solvent comprises one or a combination of two or more of toluene, isopentane, n-hexane, cyclohexane, and heptane.

[0079] In the above-mentioned method for preparing the HDPE copolymer, in S1, the ratio of the second organic solvent to Ti in the catalyst component A is generally controlled to be 1 L: 0.001-0.06 mmol.

[0080] In the above-mentioned method for preparing the HDPE copolymer, in S1, the ratio of the second organic solvent to Al in the catalyst component B is generally controlled to be 1 L: 0.02-10 mmol.

[0081] In a specific embodiment of the present application, the above-mentioned method further comprises the operation of introducing a molecular weight regulator before the first, second, and third polymerization reactions are carried out, so as to realize the stepwise ethylene homopolymerization and multistage copolymerization through a single reactor. Specifically, the molecular weight regulator can be hydrogen or the like.

[0082] In a specific embodiment of the present application, in S1, the pressure ratio of the molecular weight regulator to ethylene is generally controlled to be 1-10, for example, 3-6.

[0083] In a specific embodiment of the present application, in S2, the partial pressure ratio of the molecular weight regulator to the mixed gas of ethylene and α-olefins is generally controlled to be 0-1, for example, 0.01-1, 0.01-0.5, 0.1-0.5, or the like.

[0084] In a specific embodiment of the present application, in S3, the amount of the molecular weight regulator is generally lower than that in S2, and the partial pressure ratio of the molecular weight regulator to the mixed gas of ethylene and α-olefins is generally controlled to be 0-0.2, for example, 0.01-0.1.

[0085] The present application further provides a polyethylene copolymer pipe material, which comprises the above-mentioned HDPE copolymer. The HDPE copolymer provided by the present application has excellent heat resistance and pressure resistance, and the pipe material formed by extruding the HDPE copolymer can be used as a heat-resistant pipe material.

[0086] The present application has the following advantages:

[0087] 1. The catalyst component A used in the present application is a spherical catalyst particle, which contains an organic boron compound without active hydrogen. The organic boron compound not only plays the role of precipitant and co-precipitant, but also participates in the coordination of active center, affects the chemical environment of active center, and promotes the catalyst to exhibit good hydrogen regulation sensitivity. The vanadium compound can form a second active center, so that the molecular weight of the ethylene polymerization product is high and the insertion amount of comonomer is high. The above characteristics enable the catalyst component A and the catalyst component B to effectively improve the molecular weight and molecular weight distribution of the polymerization product, and the short chain content and short chain distribution when they are used together in ethylene polymerization, thereby improving the comonomer distribution and long chain branching structure of high-density polyethylene, and ultimately producing polyethylene with wide relative molecular mass distribution and adjustable comonomer distribution through single-pot or multi-pot series polymerization.

[0088] 2. The preparation method provided by the present application uses a solid Ziegler-Natta catalyst (composed of catalyst component A and catalyst component B) suitable for ethylene polymerization or copolymerization to catalyze the copolymerization of ethylene and low-cost α-olefin under mild conditions. By adjusting the polymerization process, the molecular weight of the polymer produces a multimodal distribution. The method has a short process flow, flexible operation, and easy-to-control product performance and structure. The prepared copolymer has a wide molecular weight distribution and a multimodal distribution, and different molecular weight components and copolymers correspond to different properties of the material, thereby meeting the performance requirements of heat-resistant polyethylene pipe materials and being suitable for extrusion molding as heat-resistant pipe materials. BRIEF DESCRIPTION OF DRAWINGS

[0089] Figure 1 Performance test and characterization data of the polymers prepared for Examples 1 to 6 and Comparative Examples 1 to 3.

[0090] Figure 2 SEM photograph of the catalyst component A prepared for Example 1.

[0091] Figure 3 SEM photograph of the catalyst component A prepared for Example 3.

[0092] Figure 4 SEM photograph of the catalyst component A prepared for Comparative Example 1.

[0093] Figure 5 SEM photograph of the catalyst component A prepared for Comparative Example 3. DETAILED DESCRIPTION

[0094] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application will be described in detail below, but it should not be understood as limiting the scope of the present application. The scope of the present application is set forth in the claims.

[0095] Polymer density was determined in accordance with standard GB / T 1033-86 "Test Methods for Density and Relative Density of Plastics".

[0096] The polymer melt flow rate was determined in accordance with the standard GB / T 3682-2000 "Determination of melt mass flow rate and melt volume flow rate of thermoplastics".

[0097] Melting point and crystallinity were determined using differential scanning calorimetry in accordance with the standard ASTM D 3418-03 (the Chinese name of the standard is: Thermal Analysis Method for Polymer Transition Temperature Test).

[0098] Molecular weight and molecular weight distribution were determined using high-temperature gel permeation chromatography (GPC). A PL220 GPC column packed with a mix-B column was used. The sample was prepared by dissolving 10 mg of resin in 10 mL of 1,2,4-trichlorobenzene. The nominal flow rate of the mobile phase was 1.0 mL / min, and the temperature was 155 °C. Molecular weight was calculated using a narrow-distribution polystyrene calibration curve.

[0099] Branching degree was tested according to JY / T007-1996 "General Rules for Superconducting Pulse Fourier Transform Nuclear Magnetic Resonance Spectroscopy". 50-100 mg of sample was weighed into a 5 mm diameter NMR tube, 0.5 mL of deuterated o-dichlorobenzene was added, the sample was heated to dissolve and air bubbles were removed, and the carbon NMR spectrum of the sample was tested at 120 °C. 13 C-NMR). Spectral width 22123.895 Hz, pulse width 45°, sampling time 0.741 s, decoupling method was combined pulse decoupling, pulse interval was 3 s, and calibration was performed using an isolated methylene peak with a chemical shift of 30.00.

[0100] The method for calculating polymerization activity is shown in Equation 1:

[0101]

[0102] In the formula:

[0103] P – Catalytic efficiency of the catalyst, expressed as gPE / gCat;

[0104] M – Mass of the polymer obtained by polymerization, in grams (g);

[0105] m – Catalyst dosage.

[0106] The test method for tensile yield stress shall be in accordance with GB / T1040 "Determination of tensile properties of plastics - Part 1: General Rules", and the test method for cantilever beam impact strength shall be in accordance with GB / T1843-2008 "Determination of impact strength of plastic cantilever beams".

[0107] Example 1

[0108] The present example provides a HDPE copolymer with a multimodal molecular weight distribution structure, and a preparation method thereof, comprising:

[0109] 1. Preparation of catalyst component A:

[0110] 1) Under nitrogen protection, 4.76 grams (50 mmol) of anhydrous magnesium chloride, 75 milliliters of decane and 16.3 grams (125 mmol) of isooctanol were mixed, heated to 130°C, and stirred for 3 hours to obtain a microemulsion of a homogeneous magnesium compound.

[0111] 2) 2.5 mmol of triethylene glycol methyl ether borate triester was added to the microemulsion and stirred at 50°C for 2 hours until dissolved, cooled to room temperature, and then the above microemulsion containing triethylene glycol methyl ether borate triester was added dropwise into a mixture of 150 mL of titanium tetrachloride and vanadium tetrachloride with a molar ratio of titanium and vanadium of 3:1 at a temperature of 0°C within 1 hour. After the dropwise addition, the temperature of the mixture was maintained at 0°C for 1 hour, and then the temperature was raised to 120°C within 2 hours under stirring, and the temperature was maintained for 2 hours. After 2 hours of reaction, the generated solid was separated by hot filtration. The solid catalyst was washed with decane and hexane until no titanium compound and vanadium compound was detected in the washing liquid, and then dried to obtain the solid catalyst component A.

[0112] 2. Preparation of HDPE copolymer:

[0113] In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum as catalyst component B, 20mg of the above prepared catalyst component A were sequentially added, heated to 70°C, hydrogen was introduced at 0.48MPa, heated to 85°C, and then ethylene was introduced, the pressure was maintained at 0.8MPa, and the reaction was carried out for 3 hours. After that, the temperature of the reactor was lowered to 30°C, and then the hydrogen was replaced by nitrogen, the temperature was raised to 70°C, hydrogen was introduced at 0.06MPa, and then a mixture of 1-butene and ethylene was introduced at 80°C, the gas partial pressure ratio of 1-butene to ethylene was 0.3, the pressure was maintained at 0.35MPa, and the reaction was carried out for 1 hour. Then the temperature of the reactor was lowered to 30°C, the hydrogen was replaced by nitrogen, the temperature was raised to 70°C, hydrogen was introduced at 0.01MPa, and then a mixture of 1-butene and ethylene was introduced at 75°C, the gas partial pressure ratio of 1-butene to ethylene was 0.02, the pressure was maintained at 0.25MPa, and the reaction was carried out for 0.5 hours, thereby obtaining an ethylene copolymer, i.e. a HDPE copolymer.

[0114] The polymerization activity, polymer bulk density and particle size distribution were measured and the results are shown in Table 1. The polymer performance test results are shown in Figure 1 .

[0115] Example 2

[0116] The present example provides a HDPE copolymer with a multimodal molecular weight distribution structure, and a preparation method thereof, which comprises:

[0117] 1. Preparation of catalyst component A:

[0118] 1) 4.76 g (50 mmol) of anhydrous magnesium chloride, 75 mL of decane and 16.3 g (125 mmol) of isooctanol were heated to 130°C for 3 hours to obtain a microemulsion of a magnesium compound.

[0119] 2) The microemulsion of the magnesium compound obtained above was cooled to room temperature, and then was added dropwise into a mixture of 150 mL of titanium tetrachloride and vanadium tetrachloride with a molar ratio of titanium to vanadium of 5:1 at 0°C for 1 hour. After the dropwise addition, the mixture was kept at 0°C for 1 hour, and then 2.5 mmol of triethylene glycol methyl ether borate triester was added to the solution, and was kept for 1 hour to dissolve the triethylene glycol methyl ether borate triester in the solution system. Then the temperature was raised to 120°C for 2 hours under stirring, and was kept at this temperature for 2 hours. After the 2-hour reaction, the generated solid was separated by hot filtration. The solid catalyst was washed with hexane and decane respectively until no titanium compound and vanadium compound were detected in the washing liquid, and was dried to obtain a solid catalyst component A.

[0120] 2. Preparation of the HDPE copolymer:

[0121] In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum as catalyst component B, 20mg of catalyst component A were sequentially added, the temperature was raised to 70°C, hydrogen was introduced at 0.48MPa, the temperature was raised to 85°C, ethylene was introduced, the pressure was kept at 0.8MPa, and the reaction was carried out for 3 hours. Then the temperature of the reactor was lowered to 30°C, the reactor was vented, replaced with nitrogen, the temperature was raised to 70°C, hydrogen was introduced at 0.06MPa, the mixture gas of 1-butene and ethylene was introduced at 80°C, the partial pressure ratio of 1-butene to ethylene was 0.3, the pressure was kept at 0.35MPa, and the reaction was carried out for 1 hour. Then the temperature of the reactor was lowered to 30°C, the reactor was vented, replaced with nitrogen, the temperature was raised to 70°C, hydrogen was introduced at 0.01MPa, the mixture gas of 1-butene and ethylene was introduced at 75°C, the partial pressure ratio of 1-butene to ethylene was 0.02, the pressure was kept at 0.25MPa, and the reaction was carried out for 0.5 hours to obtain the ethylene copolymer, i.e. the HDPE copolymer.

[0122] The polymerization activity, the polymer bulk density and the particle size distribution were determined, and the results are shown in Table 1. The polymer performance test results are shown in Table 2. Figure 1

[0123] Example 3​

[0124] This example provides a HDPE copolymer with a multimodal molecular weight distribution structure, which is prepared according to the method of Example 1, except that:

[0125] This example adds 5.0 mmol of triethylene glycol methyl ether borate triester to the mixture of titanium tetrachloride and vanadium tetrachloride, wherein the molar ratio of metal titanium to vanadium is 1:1.

[0126] The polymerization activity and polymer bulk density, particle size distribution results are shown in Table 1. The polymer performance test results are shown in Figure 1 .

[0127] Example 4

[0128] This example provides a HDPE copolymer with a multimodal molecular weight distribution structure, which is prepared according to the method of Example 2, except that:

[0129] This example adds an active hydrogen-free organic boron compound, triethylene glycol methyl ether borate triester, to the mixture of titanium tetrachloride and vanadium tetrachloride, wherein the molar ratio of metal titanium to vanadium is 10:1.

[0130] The polymerization activity and polymer bulk density, particle size distribution results are shown in Table 1. The polymer performance test results are shown in Figure 1 .

[0131] Example 5

[0132] This example provides a HDPE copolymer with a multimodal molecular weight distribution structure, which is prepared according to the method comprising:

[0133] 1. Preparation of catalyst component A: same as step 1 of Example 1;

[0134] 2. Preparation of HDPE copolymer:

[0135] In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum as catalyst component B, 20mg of catalyst component A were added in sequence, heated to 70°C, hydrogen was added at 0.6MPa, heated to 85°C, ethylene was introduced, the pressure was kept at 0.8MPa, and the reaction was carried out for 3 hours. Then the reactor was cooled to 30°C, vented, replaced by nitrogen, heated to 70°C, hydrogen was added at 0.12MPa, 1-butene / ethylene mixed gas was introduced at 80°C, the 1-butene / ethylene gas partial pressure ratio was 0.7, the pressure was kept at 0.35MPa, and the reaction was carried out for 1 hour. The reaction temperature was cooled to 30°C, vented, replaced by nitrogen, heated to 70°C, hydrogen was added at 0.005MPa, 1-butene / ethylene mixed gas was introduced at 75°C, the 1-butene / ethylene gas partial pressure ratio was 0.1, the pressure was kept at 0.25MPa, and the reaction was carried out for 0.5 hour. An ethylene copolymer, i.e. HDPE copolymer, was prepared.

[0136] The polymer performance test results are shown in Table 1.

[0137] Example 6

[0138] The present example provides a HDPE copolymer with a multimodal distribution structure of molecular weight, and a preparation method thereof comprises the following steps:

[0139] 1. Preparation of catalyst component A: same as step 1 of Example 2;

[0140] 2. Preparation of HDPE copolymer:

[0141] In a 5L polymerization reactor, 2.5L of n-hexane, 5mmol of triethylaluminum, 20mg of catalyst component A were added in sequence, heated to 70°C, hydrogen was added at 0.48MPa, heated to 85°C, ethylene was introduced, the pressure was kept at 0.8MPa, and the reaction was carried out for 3 hours. Then the reactor was cooled to 30°C, vented, replaced by nitrogen, heated to 70°C, hydrogen was added at 0.06MPa, 1-butene / ethylene mixed gas was introduced at 80°C, the 1-butene / ethylene gas partial pressure ratio was 0.1, the pressure was kept at 0.35MPa, and the reaction was carried out for 1 hour. The reaction temperature was cooled to 30°C, vented, replaced by nitrogen, heated to 70°C, hydrogen was added at 0.01MPa, 1-butene / ethylene mixed gas was introduced at 75°C, the 1-butene / ethylene gas partial pressure ratio was 0.01, the pressure was kept at 0.25MPa, and the reaction was carried out for 0.5 hour. An ethylene copolymer, i.e. HDPE copolymer, was prepared.

[0142] Comparative Example 1

[0143] The present comparative example provides an ethylene copolymer, and the preparation method is the same as Example 1, except that:

[0144] In Step 1, the comparative example added the microemulsion of magnesium compound into 150 mL titanium tetrachloride, but did not add vanadium tetrachloride.

[0145] The polymerization activity and the polymer bulk density and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2. Figure 1 .

[0146] Comparative Example 2

[0147] The comparative example provided an ethylene copolymer, which was prepared by the method of Example 1, except that:

[0148] In Step 1, the comparative example added the microemulsion of magnesium compound into 150 mL titanium tetrachloride, but did not add vanadium tetrachloride.

[0149] The polymerization activity and the polymer bulk density and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2. Figure 1 .

[0150] Comparative Example 3

[0151] The comparative example provided an ethylene copolymer, which was prepared by the method comprising:

[0152] 1. Preparation of catalyst component A: The preparation method was the same as that of the catalyst in Example 1 of CN1229092A (application number 98101108.X, invention name: catalyst for ethylene polymerization or copolymerization and its preparation method). The specific method was as follows:

[0153] In a reactor which was sufficiently replaced by high-purity nitrogen, 0.042 mol of anhydrous MgCl2 (about 4 g), 60 mL of toluene, 0.032 mol of epichlorohydrin, 0.022 mol of tributyl phosphate, and 0.017 mol of ethanol were sequentially added. The temperature was increased to 80°C under stirring, and the solid was completely dissolved for 15 minutes to form a uniform solution. Then, 0.0074 mol of phthalic anhydride was added, and the solution was maintained for 1 hour. The solution was cooled to -25°C, and then 0.5 mol of titanium tetrachloride (about 55 mL) was added dropwise. Then, the temperature was slowly increased to 80°C, and the reaction was performed for 3 hours. After filtration, the solid catalyst was washed with toluene and hexane for 3 times, and then dried in vacuum to obtain a solid catalyst.

[0154] 2. Preparation of HDPE copolymer, which was prepared by the method of Example 1.

[0155] The polymerization activity and the polymer bulk density and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Table 2. Figure 1 .

[0156] Comparative Example 4

[0157] The comparative example provided an ethylene copolymer, which was prepared by the method comprising:

[0158] 1. Preparation of catalyst component A: the preparation method is the same as the preparation method of catalyst in the example of JP4951378 (application number JP2007073493, invention name: Waveform generator and test device, publication date: 20120613), and the specific method is as follows:

[0159] In a reactor which is sufficiently replaced by high-purity nitrogen, 10 mol of commercially available anhydrous MgCl2 is suspended in 10 L of hexane, 60 mol of ethanol is added dropwise at room temperature, and stirred for 30 minutes. 31 mol of diethylaluminum chloride is added dropwise while maintaining the temperature of the system at no more than 40°C, and stirred for 30 minutes. 5 mol of TiCl4 is added, the system is maintained at 60°C, and stirred for 6 hours. After filtration and hexane washing, a solid catalyst is obtained.

[0160] 2. Preparation of HDPE copolymer, the preparation method is the same as example 1.

[0161] The polymerization activity and the polymer bulk density and particle size distribution results are shown in Table 1. The polymer performance test results are shown in Figure 1 .

[0162] Table 1 Polymerization activity, polymer bulk density and particle size distribution results

[0163]

[0164] From Table 1 and Figure 1 It can be seen that: compared with the existing olefin catalyst, the catalyst component A has higher polymerization activity, the prepared polymer has higher bulk density, the particle size distribution of the polymer is more concentrated, the molecular weight distribution of the polymer is concentrated in the medium and high molecular weight region, and the polymer has better mechanical properties and heat resistance.

[0165] Figures 2 to 5 The SEM photos of catalyst component A prepared in example 1, example 3, comparative example 1 and comparative example 3 are shown in the order of example 1, example 3, comparative example 1, comparative example 3. From Figures 2 to 5 It can be seen that, compared with the existing ethylene polymerization catalyst, the catalyst component A prepared by the method provided by the application has a regular morphology, which is a spherical particle with uniform particle size; and without vanadium compounds, the regularity of the particle morphology will decrease, and there will be obvious irregular particles with uneven particle size. According to the above results, it can be seen that the catalyst component A provided by the application has a regular spherical structure, and when the catalyst is used to catalyze ethylene polymerization, the particle morphology of the polymer can be effectively improved, the bulk density of the polymer is improved, and the particle size distribution of the polymer is more concentrated.

[0166] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes should all belong to the protection scope of the claims of the present application.

Claims

1. An HDPE copolymer obtained by polymerizing ethylene and α-olefins as monomers using catalyst component A and catalyst component B; in, Catalyst component A comprises reaction products of magnesium compounds, organoboron compounds, titanium compounds, and vanadium compounds; catalyst component B comprises organoaluminum compounds; the organoboron compounds comprise organoboroesters, and the organoboroesters comprise triethylene glycol methyl ether borate triester. The molecular weight of the HDPE copolymer exhibits a multi-peak distribution, with three or more peaks or three or more intervals in the molecular weight distribution; the Mw / Mn ratio of the HDPE copolymer is 12-20. Based on the total mass of HDPE copolymers as 100%, the mass content of HDPE copolymers with a weight average molecular weight of less than 50,000 is 40-50%, the mass content of HDPE copolymers with a weight average molecular weight of 50,000-1,000,000 is 50-60%, and the mass content of HDPE copolymers with a weight average molecular weight of greater than 1,000,000 is 0-5% and not 0. When the weight-average molecular weight of the HDPE copolymer is less than 50,000, the crystallinity of the HDPE copolymer is 65-75% and the wafer thickness is 35-45 nm. When the weight-average molecular weight of the HDPE copolymer is 50,000 to 1,000,000, the crystallinity of the HDPE copolymer is 45-55% and the wafer thickness is 20-30 nm. When the weight-average molecular weight of the HDPE copolymer is greater than 1 million, the crystallinity of the HDPE copolymer is 30-40% and the wafer thickness is 10-16.45 nm.

2. The HDPE copolymer according to claim 1, wherein, The density of the HDPE copolymer is 0.940-0.955 g / cm³. 3 .

3. The HDPE copolymer according to claim 1, wherein, The melt index of the HDPE copolymer is 0.1-1.0 g / 10 min.

4. The HDPE copolymer according to claim 1, wherein, The degree of branching of the HDPE copolymer is 2.5-4.5 / 1000 carbon atoms.

5. The HDPE copolymer according to claim 1, wherein, The structure of the magnesium compound includes: X n MgR 2-n Where n is an integer from 0 to 2; R is one or more combinations of hydrogen, alkyl, alkoxy, carboxyl, aryl and cycloalkyl, and X is a halogen.

6. The HDPE copolymer according to claim 5, wherein, X n MgR 2-n In R, the alkyl group has 1-20 carbon atoms, the alkoxy group has 1-20 carbon atoms, the aryl group has 6-20 carbon atoms, and the cycloalkyl group has 3-20 carbon atoms.

7. The HDPE copolymer according to claim 5, wherein, The magnesium compound includes one or more of the following: alkyl magnesium, alkyl magnesium halide, alkyl magnesium alkoxy compound, magnesium halide, alkoxy magnesium halide, aryloxy magnesium halide, aryloxy magnesium, magnesium carboxylate, magnesium hydride, and monohydroalkyl magnesium.

8. The HDPE copolymer according to claim 5, wherein, The magnesium compound participates in the preparation of catalyst component A in the form of a microemulsion; the microemulsion contains a first organic solvent and a diluent.

9. The HDPE copolymer according to claim 8, wherein, The droplet diameter of the microemulsion is 5nm-100nm.

10. The HDPE copolymer according to claim 8, wherein, The method for preparing the magnesium compound microemulsion includes: mixing the magnesium compound with a first organic solvent and a diluent, reacting to obtain the magnesium compound microemulsion, wherein the reaction temperature is 50-150℃.

11. The HDPE copolymer according to claim 8, wherein, The diluent includes hydrocarbon solvents and / or ionic liquids.

12. The HDPE copolymer according to claim 11, wherein, The hydrocarbon solvents include one or more of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons.

13. The HDPE copolymer according to claim 8, wherein, The first organic solvent includes one or more of alcohols, phenols, carboxylic acids, aldehydes, amines, esters, and metal esters.

14. The HDPE copolymer according to claim 13, wherein, The alcohols include one or more of the following: fatty alcohols, alicyclic alcohols, aromatic alcohols, alkoxyl alcohols, and halogenated alcohols.

15. The HDPE copolymer according to claim 14, wherein, The alcohol has 6 or more carbon atoms.

16. The HDPE copolymer according to claim 13, wherein, When the alcohol has 6 or more carbon atoms, the molar ratio of the alcohol to Mg in the magnesium compound is 1 or more; when the alcohol has 5 or fewer carbon atoms, the molar ratio of the alcohol to Mg in the magnesium compound is 1 or more.

17. The HDPE copolymer according to claim 16, wherein, When the alcohol has 6 or more carbon atoms, the molar ratio of the alcohol to Mg in the magnesium compound is 1-40.

18. The HDPE copolymer according to claim 16, wherein, When the alcohol has 6 or more carbon atoms, the molar ratio of the alcohol to Mg in the magnesium compound is 1-10.

19. The HDPE copolymer according to claim 1, wherein, The structure of the titanium compound includes: Ti(OR) a X b Wherein, R includes one or more combinations of aliphatic hydrocarbon group, alicyclic hydrocarbon group or aryl group, X is a halogen, a is an integer from 0 to 3, and b is an integer from 1 to 4.

20. The HDPE copolymer according to claim 19, wherein, The sum of a and b is 3 or 4.

21. The HDPE copolymer according to claim 19, wherein, The aliphatic hydrocarbon group has 1-10 carbon atoms, the alicyclic hydrocarbon group has 3-10 carbon atoms, and the aryl group has 6-10 carbon atoms.

22. The HDPE copolymer according to claim 19, wherein, The titanium compound includes titanium tetrahalide.

23. The HDPE copolymer according to claim 19, wherein, The titanium compound includes one or more of TiCl4, TiBr4, and TiI4.

24. The HDPE copolymer according to claim 1, wherein, The structure of the vanadium compound includes: V(OR) a X b Wherein, R includes one or more combinations of aliphatic hydrocarbon group, alicyclic hydrocarbon group or aryl group, X is a halogen, a is an integer from 0 to 3, and b is an integer from 1 to 4.

25. The HDPE copolymer according to claim 24, wherein, The sum of a and b is 3 or 4.

26. The HDPE copolymer according to claim 24, wherein, The aliphatic hydrocarbon group has 1-10 carbon atoms, the alicyclic hydrocarbon group has 3-10 carbon atoms, and the aryl group has 6-10 carbon atoms.

27. The HDPE copolymer according to claim 24, wherein, The vanadium compounds include vanadium tetrahalides.

28. The HDPE copolymer according to claim 24, wherein, The vanadium compounds include VCl4, VBr4, and VI4.

29. The HDPE copolymer according to claim 24, wherein, The molar ratio of Ti in the titanium compound to V in the vanadium compound is 1-10:

1.

30. The HDPE copolymer according to any one of claims 1-29, wherein, The preparation method of catalyst component A includes: Magnesium compounds, organoboron compounds, titanium compounds, and vanadium compounds are mixed and reacted in a protective atmosphere, then filtered and washed to obtain catalyst component A; the reaction temperature is 50-120℃ and the reaction time is 0.5h-4h.

31. The HDPE copolymer according to claim 30, wherein, The reaction time is 2 hours.

32. The HDPE copolymer according to claim 1, wherein, The structure of the organoaluminum compound includes: AlR n X 3-n , where R is a hydrocarbon group, X is a halogen, and n is an integer from 0 to 3.

33. The HDPE copolymer according to claim 32, wherein, The number of carbons in R is 1-20.

34. The HDPE copolymer according to claim 32, wherein, The hydrocarbon group includes one or more combinations of alkyl, aralkyl, and aryl groups.

35. The HDPE copolymer according to claim 32, wherein, The halogens include chlorine and / or bromine.

36. The HDPE copolymer according to claim 32, wherein, The organoaluminum compounds include alkyl aluminum halides.

37. The HDPE copolymer according to claim 32, wherein, The organoaluminum compounds include one or more of the following: trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, diethylaluminum chloride, diisobutylaluminum chloride, sesquiethylaluminum chloride, and diethylaluminum chloride.

38. The HDPE copolymer according to claim 32, wherein, The molar ratio of Al in organoaluminum compounds to Ti in titanium compounds is 5-500:

1.

39. The HDPE copolymer according to claim 32, wherein, The molar ratio of Al in organoaluminum compounds to Ti in titanium compounds is 20-200:

1.

40. The HDPE copolymer according to claim 1, wherein, The polymerization process includes one or more of solution polymerization, slurry polymerization, and gas-phase polymerization.

41. The HDPE copolymer according to claim 40, wherein, The polymerization temperature is 0-150℃.

42. The HDPE copolymer according to claim 40, wherein, The polymerization temperature is 40-100℃.

43. The HDPE copolymer according to claim 1, wherein, The α-olefin has 4-12 carbon atoms.

44. The HDPE copolymer according to claim 43, wherein, The α-olefins include one or more of propylene, butene, pentene, hexene, octene, and 4-methyl-1-pentene.

45. A method for preparing the HDPE copolymer according to any one of claims 1-44, comprising: S1. Add the second organic solvent, catalyst component A and catalyst component B to the reactor, and introduce ethylene to carry out the first polymerization reaction to obtain polyethylene homopolymer. S2. Ethylene and α-olefin are introduced into the above reactor to carry out a second polymerization reaction, and a copolymer intermediate is obtained. S3. Ethylene and α-olefin are introduced into the reactor of S2 to carry out a third polymerization reaction, thereby obtaining the HDPE copolymer.

46. ​​The HDPE copolymer according to claim 45, wherein, The temperature of the first polymerization reaction is 50-100℃, the pressure of the first polymerization reaction is 0.5-1 MPa, and the time of the first polymerization reaction is 0.1-5 hours.

47. The HDPE copolymer according to claim 45, wherein, The temperature of the first polymerization reaction is 70-90℃.

48. The HDPE copolymer according to claim 45, wherein, The temperature of the second polymerization reaction is 50-100℃, the pressure of the second polymerization reaction is 0.1-0.5MPa, and the time of the second polymerization reaction is 0.1-2h.

49. The HDPE copolymer according to claim 45, wherein, The pressure of the second polymerization reaction is 0.2-0.4 MPa.

50. The HDPE copolymer according to claim 45, wherein, The temperature of the third polymerization reaction is 50-100℃, the pressure of the third polymerization reaction is 0.1-0.5MPa, and the time of the third polymerization reaction is 0.1-2h.

51. The HDPE copolymer according to claim 45, wherein, The pressure of the third polymerization reaction is 0.1-0.3 MPa.

52. The method for preparing the HDPE copolymer according to claim 45, wherein, The second organic solvent is an inert solvent.

53. The method for preparing the HDPE copolymer according to claim 52, wherein, The inert solvent includes one or more of alkanes, aromatics, and halogenated hydrocarbons.

54. The method for preparing the HDPE copolymer according to claim 52, wherein, The second organic solvent includes one or more of toluene, isopentane, n-hexane, cyclohexane, and heptane.

55. The method for preparing the HDPE copolymer according to claim 45, wherein, The above preparation method also includes the operation of introducing a molecular weight regulator before carrying out the first polymerization reaction, the second polymerization reaction and the third polymerization reaction.

56. The method for preparing the HDPE copolymer according to claim 55, wherein, The molecular weight regulator includes hydrogen.

57. The method for preparing the HDPE copolymer according to claim 55, wherein, In S1, the pressure ratio of the molecular weight regulator to ethylene is 1 to 10.

58. The method for preparing the HDPE copolymer according to claim 55, wherein, In S1, the pressure ratio of the molecular weight regulator to ethylene is 3-6.

59. The method for preparing the HDPE copolymer according to claim 55, wherein, In S2, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0-1.

60. The method for preparing the HDPE copolymer according to claim 55, wherein, In S2, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0.01-1.

61. The method for preparing the HDPE copolymer according to claim 55, wherein, In S2, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0.01-0.

5.

62. The method for preparing the HDPE copolymer according to claim 55, wherein, In S2, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0.1-0.

5.

63. The method for preparing the HDPE copolymer according to claim 55, wherein, In S3, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0-0.

2.

64. The method for preparing the HDPE copolymer according to claim 55, wherein, In S3, the partial pressure ratio of the molecular weight regulator to the mixture of ethylene and α-olefin is 0.01-0.

1.

65. The method for preparing the HDPE copolymer according to claim 45, wherein: In S2, the partial pressure ratio of α-olefin to ethylene is 0.01-1; In S3, the partial pressure ratio of α-olefin to ethylene is 0.01-1; In S1, the ratio of the second organic solvent to Ti in the catalyst component A is 1L:0.001-0.06mmol; The ratio of the second organic solvent to Al in catalyst component B is 1L:0.02-10mmol.

66. A polyethylene copolymer pipe, wherein the raw material comprises the HDPE copolymer as described in any one of claims 1-44.

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