A method for preparing polyolefin plastomer

Abstract

The present invention provides a method for preparing a polyolefin plastomer. The preparation method comprises the following steps: oligomerizing ethylene in the presence of an oligomerization catalyst and an oligomerization co-catalyst to produce an alpha-olefin; adding a copolymerization catalyst and a copolymerization co-catalyst to a reaction system, and copolymerizing the alpha-olefin to produce a polyolefin plastomer; wherein the oligomerization catalyst is a phosphine nitrogen ligand-chromium salt complex. The copolymer prepared using the catalyst combination is a polyolefin plastomer having an alpha-olefin insertion rate greater than 13 wt%, a high molecular weight, and excellent mechanical properties.

Description

Technical Field

[0001] The invention belongs to the field of ethylene polymerization and relates to a method for preparing a polyolefin plastomer. Background Art

[0002] Polyolefins, or olefin polymers, are polymers derived from ethylene and propylene homopolymers or their copolymerization with α-olefins such as 1-butene, 1-hexene, and 1-octene, as well as cycloolefins. Key examples include polypropylene, polyethylene, ethylene-propylene rubber, and random or block copolymers of ethylene and α-olefins. Polyolefins offer excellent chemical stability, processing and mechanical properties, and a relatively low cost, making them widely used in various fields, including industrial and consumer goods. While my country's polyolefin industry is currently substantial, many high-end products remain subject to foreign production.

[0003] The properties of ethylene / α-olefin copolymers are primarily influenced by the α-olefin content. As the α-olefin content increases, the polymer's density, melting point, and crystallinity decrease, transforming the product from a thermoplastic to an elastomer. Typically, the comonomer mass fraction of polyolefin elastomers is greater than 20%, while the comonomer mass fraction of polyolefin plastomers is less than 20%. Compared to linear low-density polyethylene (LLDPE), polyolefin plastomers no longer form spherulites; instead, the copolymer contains only mixed lamellae and microcrystals, resulting in a wide melting range, from microcrystal melting at room temperature to lamellar melting at higher temperatures. Polymers with a density less than 0.89 g / cm³ are polyolefin elastomers, with a crystallinity of less than 25%, consisting only of clustered microcrystals. Polyolefin elastomers are primarily used in fields such as modification and photovoltaic films, while plastomers have good melt strength, excellent bonding strength, tear resistance, and transparency, and are primarily used in film preparation.

[0004] The production process for polyolefin elastomers / plastomers primarily relies on solution polymerization, employing copolymerization of ethylene and α-olefins (such as 1-octene, 1-hexene, and 1-butene). Copolymers based on 1-hexene and 1-octene offer excellent performance and high added value, attracting significant market attention. High-carbon olefins such as 1-hexene and 1-octene are expensive in the market and are primarily produced by ethylene oligomerization, which carries high subsequent separation costs. Cascade catalytic technology uses ethylene as the sole monomer feedstock. An oligomerization catalyst and a copolymerization catalyst are introduced into the reactor. The oligomerization catalyst is used to in situ prepare the comonomer—a higher α-olefin—and the copolymerization catalyst is used to copolymerize the α-olefin with ethylene, resulting in the production of ethylene / α-olefin copolymers. Compared to traditional polymerization processes, this process eliminates the costs associated with comonomer production, transportation, and storage. Patent CN113248643A discloses a cascade catalytic technology that uses two connected reactors. Ethylene is oligomerized in the first reactor to produce α-olefins (primarily 1-octene and 1-hexene), which are then transferred to the second reactor to produce polyolefin elastomers under the action of a copolymerization catalyst. The polymerization process is relatively complex. Patent application publication WO2004056480 uses a homogeneous complex of Cr to catalyze the tetramerization of ethylene to produce 1-octene, and then uses a later transition metal catalyst as a copolymerization catalyst to produce a copolymer with 1-octene as a comonomer. Although many cascade catalytic systems have been reported in the literature, most of them are not directed to the ethylene / α-olefin copolymer production equipment and polymerization conditions currently being used in industry.

[0005] A good cascade catalytic system requires that the catalysts do not interfere with each other and that the cocatalyst is well-matched with both catalysts. Conventional copolymerization catalysts significantly reduce polymer molecular weight upon addition of comonomers, affecting the polymer's mechanical properties. To address this issue, the catalyst combination proposed in this invention can produce high-molecular-weight polyolefin plastomers, a product with promising application prospects. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a method for preparing a polyolefin plastomer. This method uses ethylene as a single raw material and employs a cascaded oligomerization and copolymerization catalytic system to produce the plastomer in a single reactor. The oligomerization and copolymerization catalysts have excellent compatibility, and the co-catalyst is well compatible with both catalysts. The resulting plastomer has excellent market application prospects.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] A method for preparing a polyolefin plastomer, comprising the following steps:

[0009] S1: oligomerization of ethylene in the presence of an oligomerization catalyst and an oligomerization cocatalyst to produce α-olefins;

[0010] S2: adding a copolymerization catalyst and a copolymerization co-catalyst to the reaction system to copolymerize α-olefins to form a polyolefin plastomer;

[0011] Wherein, the oligomerization catalyst described in S1 is a phosphine nitrogen ligand-chromium salt complex of formula I:

[0012]

[0013] Wherein, R1, R2, R3, and R4 are each independently selected from one of alkyl, aryl, substituted alkyl, and substituted aryl; preferably, R1, R2, R3, and R4 are each independently selected from one of C2-C9 alkyl, aryl, substituted alkyl, and substituted aryl; more preferably, R1, R2, R3, and R4 are each independently selected from phenyl, benzyl, biphenyl, naphthyl, anthracenyl, vinyl, propenyl, isopropyl, tert-butyl, cyclohexyl, 4-methylcyclohexyl, 4-ethylcyclohexyl, 4-isopropylcyclohexyl, 2-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl , 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 4-methoxyphenyl, o-methoxyphenyl, 4-ethoxyphenyl, o-ethoxyphenyl, 2-(trimethylsilyl)phenyl, 3-(trimethylsilyl)phenyl, 4-(trimethylsilyl)phenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 4-(trifluoromethyl)phenyl, 3,5-bis(trifluoromethyl)phenyl, 2-(tri-n-butylsilyl)phenyl, 3-(tri-n-butylsilyl)phenyl, 4-(tri-n-butylsilyl)phenyl.

[0014] The oligomerization catalyst can generate α-olefins. The present invention uses a phosphine nitrogen ligand-chromium salt complex as the oligomerization catalyst. After the oligomerization reaction is completed, it exists in the form of a stable PN-Cr complex. It does not contain strong electron-withdrawing groups such as halogenated groups and has minimal effect on the active center of the copolymerization catalyst. The metallocene catalyst or post-metallocene catalyst can stably catalyze polymerization to generate a high-molecular-weight plastomer.

[0015] In one embodiment of the present invention, the amount of the oligomerization catalyst added to S1 is 0.5 μmol / L-100 μmol / L, preferably 1 μmol / L-50 μmol / L.

[0016] In one embodiment of the present invention, the oligomerization co-catalyst described in S1 is one or more of alkyl aluminum, aluminoxane, and organic boron compounds, preferably one or more of methyl aluminoxane, ethyl aluminoxane, propyl aluminoxane, butyl aluminoxane, isobutyl aluminoxane, and modified methyl aluminoxane; preferably, the molar ratio of the oligomerization catalyst to the oligomerization co-catalyst is 1:(100-1500).

[0017] In one embodiment of the present invention, the reaction of S1 is carried out in a solvent; preferably, the solvent is selected from aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents, preferably C2-C9 aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents; more preferably, the aliphatic hydrocarbon solvent is selected from one or more of methylcyclohexane, cyclohexane, n-butane, isobutane, n-pentane, cyclopentane, methylcyclopentane, methylenecyclopentane, Isopar E, Isopar H, n-hexane, ethylcyclohexane, n-heptane, n-octane and n-nonane; more preferably, the aromatic hydrocarbon solvent is selected from one or more of benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene and dichlorotoluene.

[0018] In one embodiment of the present invention, the oligomerization reaction temperature of S1 is 30°C-90°C, and the reaction time is 10-80 min.

[0019] In one embodiment of the present invention, the ethylene pressure in the reaction of S1 is 1 to 10 MPa.

[0020] In one embodiment of the present invention, the α-olefin in S1 comprises C4-C10 α-olefin, preferably one or more of 1-hexene, 1-octene, and 1-butene.

[0021] In one embodiment of the present invention, the copolymerization catalyst of S2 is a metallocene catalyst and / or a post-metallocene catalyst with a single active site, preferably one or more selected from titanium, zirconium, and hafnium metallocene catalysts and / or post-metallocene catalysts, more preferably dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) trimethoxytitanium, dimethylbis (propylcyclopentadienyl) hafnium, bis (n-butylcyclopentadiene) hafnium dichloride, racemic dimethylsilylbis (2-methyl-1-indenyl) zirconium dichloride, dibenzylidenecyclopentadiene (2,7-di-tert-butyl) -fluorenyl) zirconium dichloride, di-p-toluenediaminecyclopentadiene (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, dibenzylidene (cyclopentadiene) (9-fluorenyl) zirconium dichloride, dimethyldisilylbis (2-methyl-4-phenyl-1-indenyl) zirconium dichloride), mesodimethylsilylbis (1-indenyl) zirconium dichloride, (bis (methylcyclopentadiene) zirconium dichloride), (bis (1,3-dimethylcyclopentadienyl) zirconium dichloride, (cyclopentadienyl) (1,2-dimethoxyethane) zirconium trichloride, diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride one or more; preferably, the molar ratio of the oligomerization catalyst to the copolymerization catalyst is 1: (0.03 to 10), preferably 1: (0.1 to 5).

[0022] In one embodiment of the present invention, the S2 copolymerization co-catalyst is one or more of alkyl aluminum, alkyl aluminoxane, and organic boron compound, preferably one or more of methyl aluminoxane, modified methyl aluminoxane, ethyl aluminoxane, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trioctylaluminum, tris(pentafluorophenyl) borate compound, and tetrakis(pentafluorophenyl) borate compound; preferably, in the copolymerization reaction, when the co-catalyst contains aluminum, the molar ratio of metal atoms in the copolymerization catalyst to aluminum in the copolymerization co-catalyst is 1:(50~1000), and when the co-catalyst contains boron, the molar ratio of metal atoms in the copolymerization catalyst to boron in the copolymerization co-catalyst is 1:(1~5).

[0023] In one embodiment of the present invention, the copolymerization reaction temperature of S2 is 90° C.-230° C., and the reaction time is 5-20 min.

[0024] In one embodiment of the present invention, the polyolefin plastomer prepared by S2 has a melting point of 45°C-120°C, preferably 55°C to 105°C; a weight average molecular weight of 20,000-180,000, preferably 30,000-150,000; and a molecular weight distribution index ≤4, preferably 1.2 to 3.5.

[0025] Another object of the present invention is to provide a catalyst composition for preparing polyolefin plastomers.

[0026] A catalyst composition for preparing a polyolefin plastomer, the composition being the catalyst composition used in the above-mentioned preparation method, the composition comprising an oligomerization catalyst, an oligomerization co-catalyst, a copolymerization catalyst, and a copolymerization co-catalyst;

[0027] Wherein, the oligomerization catalyst is a phosphine nitrogen ligand-chromium salt complex of formula I:

[0028]

[0029] Wherein, R1, R2, R3, and R4 are each independently selected from one of alkyl, aryl, substituted alkyl, and substituted aryl; preferably, R1, R2, R3, and R4 are each independently selected from one of C2-C9 alkyl, aryl, substituted alkyl, and substituted aryl; more preferably, R1, R2, R3, and R4 are each independently selected from phenyl, benzyl, biphenyl, naphthyl, anthracenyl, vinyl, propenyl, isopropyl, tert-butyl, cyclohexyl, 4-methylcyclohexyl, 4-ethylcyclohexyl, 4-isopropylcyclohexyl, 2-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl , 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 4-methoxyphenyl, o-methoxyphenyl, 4-ethoxyphenyl, o-ethoxyphenyl, 2-(trimethylsilyl)phenyl, 3-(trimethylsilyl)phenyl, 4-(trimethylsilyl)phenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 4-(trifluoromethyl)phenyl, 3,5-bis(trifluoromethyl)phenyl, 2-(tri-n-butylsilyl)phenyl, 3-(tri-n-butylsilyl)phenyl, 4-(tri-n-butylsilyl)phenyl.

[0030] In one embodiment of the present invention, the co-catalyst for oligomerization is one or more of alkyl aluminum, aluminoxane, and organic boron compound, preferably one or more of methyl aluminoxane, ethyl aluminoxane, propyl aluminoxane, butyl aluminoxane, isobutyl aluminoxane, and modified methyl aluminoxane; preferably, the molar ratio of the oligomerization catalyst to the co-catalyst is 1:(100-1500).

[0031] In one embodiment of the present invention, the copolymerization catalyst is a metallocene catalyst and / or a post-metallocene catalyst with a single active site, preferably one or more selected from titanium, zirconium, and hafnium metallocene catalysts and / or post-metallocene catalysts, more preferably dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) trimethoxytitanium, dimethylbis (propylcyclopentadienyl) hafnium, bis (n-butylcyclopentadienyl) hafnium dichloride, racemic dimethylsilylbis (2-methyl-1-indenyl) zirconium dichloride, dibenzylidenecyclopentadiene (2,7-di-tert-butyl-fluorenyl) ) zirconium dichloride, di-p-toluenediaminecyclopentadiene (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, dibenzylidene (cyclopentadiene) (9-fluorenyl) zirconium dichloride, dimethyldisilylbis (2-methyl-4-phenyl-1-indenyl) zirconium dichloride), mesodimethylsilylbis (1-indenyl) zirconium dichloride, (bis (methylcyclopentadiene) zirconium dichloride), (bis (1,3-dimethylcyclopentadienyl) zirconium dichloride, (cyclopentadienyl) (1,2-dimethoxyethane) zirconium trichloride, diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride or more; preferably, the molar ratio of the oligomerization catalyst to the copolymerization catalyst is 1: (0.03 to 10), preferably 1: (0.1 to 5).

[0032] In one embodiment of the present invention, the copolymerization co-catalyst is one or more of alkyl aluminum, alkyl aluminoxane, and organic boron compound, preferably one or more of methyl aluminoxane, modified methyl aluminoxane, ethyl aluminoxane, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trioctylaluminum, tris(pentafluorophenyl) borate compound, and tetrakis(pentafluorophenyl) borate compound; preferably, in the copolymerization reaction, when the co-catalyst contains aluminum, the molar ratio of the metal atoms in the copolymerization catalyst to the aluminum in the copolymerization co-catalyst is 1:(50-1000), and when the co-catalyst contains boron, the molar ratio of the metal atoms in the copolymerization catalyst to the boron in the copolymerization co-catalyst is 1:(1-5).

[0033] Unless otherwise specified in the present invention, all pressures involved are gauge pressures.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) In a single reactor, by adjusting the catalyst combination, a polyolefin plastomer comprising a copolymer of ethylene and α-olefin is directly produced using ethylene as a single raw material without the need for additional addition of 1-octene or 1-hexene;

[0036] (2) The process for preparing the polyolefin plastomer of the present invention is simple, and the molecular weight and degree of branching of the product can be adjusted by simply changing the reaction time and the ratio of the oligomerization catalyst to the copolymerization catalyst;

[0037] (3) The produced polyolefin plastomers have high α-olefin insertion rate, small molecular weight distribution index, excellent performance and good application prospects. DETAILED DESCRIPTION

[0038] The following specific examples are only used to illustrate the present invention, but these examples are only part of the present invention and do not limit the application of the present invention in other fields. The raw materials used in the examples are all conventional raw materials in the field, and the purity specifications used are analytically pure or chemically pure.

[0039] Raw material source information:

[0040] N1,N3-dimethylbenzene-1,3-diamine: 98%, Shanghai Xinkai Pharmaceutical Technology Co., Ltd.

[0041] Triethylamine: ≥99.5% (GC), Shanghai Aladdin Biochemical Technology Co., Ltd.

[0042] Tripropylamine: ≥99.5% (GC), Shanghai Aladdin Biochemical Technology Co., Ltd.

[0043] Diphenylphosphine chloride: 97%, Alfa Aesar (China) Chemicals Co., Ltd.

[0044] Dichloromethane: 99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0045] Acetonitrile: 99.5%, Beijing Bailingwei Technology Co., Ltd.

[0046] Chlorobis[4-(trifluoromethyl)phenyl]phosphine: 97%, San Chemical Technology (China) Co., Ltd.

[0047] Chloro(2-fluorophenyl)(phenyl)phosphine: 97%, Shanghai Xinkai Pharmaceutical Technology Co., Ltd.

[0048] Chlorobis(4-methylphenyl)phosphine: >97%, Jiangsu Sino-K Catalyst Co., Ltd.

[0049] 4-(Tri-n-butylsilyl)phenylphosphine chloride: 97%, Jiangsu Sinoco Catalyst Co., Ltd.

[0050] Diisopropylphosphine chloride: 98%, Beijing Bailingwei Technology Co., Ltd.

[0051] Ethyl acetate: 99.9%, Bailingwei Technology Co., Ltd.

[0052] Ethanol: analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0053] MMAO-3a (modified methylaluminoxane): 7 wt% Al, n-heptane solvent, Nouryon Chemicals (Ningbo) Co., Ltd.

[0054] MMAO-7 (modified methylaluminoxane): 7 wt% Al, Isopar E solvent, Nouryon Chemicals (Ningbo) Co., Ltd.

[0055] MAO (methylaluminoxane), concentration 10 wt%, toluene solvent, Nouryon Chemicals (Ningbo) Co., Ltd.

[0056] [Ph3C][B(C6F5)4]:>97%, Jiangsu Sinocatalyst Co., Ltd.

[0057] iPr-PNP (CAS: 60981-68-20): >97%, Jiangsu Sinoco Catalyst Co., Ltd.

[0058] Melting point test: A DSC analyzer is used to characterize the melting point (Tm) of the polymer product. The instrument model used is MettleDSC1. Weigh about 5 mg of sample into an aluminum sample dish and seal it with a lid. Use tweezers to place the prepared sample into the sample cell and cover the furnace. Enter the sample mass in the control software. The heating program first increases the temperature from 40°C to 160°C at a heating rate of 10°C / min, and maintains a constant temperature of 160°C for 5 minutes to eliminate the thermal history. Then cool it to 40°C at a cooling rate of 10°C / min, and collect the crystallization curve of the sample. Finally, heat it to 160°C at a heating rate of 10°C / min, collect the thermal melting curve of the sample, and record the thermal enthalpy change and melting point in this process.

[0059] Weight-average molecular weight, comonomer insertion rate and molecular weight distribution index test: GPC-IR is used to determine the molecular weight, molecular weight distribution and branching degree of the polymer product. The instrument model used is Agilent 7870, equipped with two PLgel-Olexis chromatographic columns. About 7 mg of sample is weighed and placed in a 20 mL sample bottle. 10 mL of 1,2,4-trichlorobenzene (TCB) solution containing a small amount of antioxidant is added with a syringe. Oscillate and dissolve at 160 ° C for 4 hours, then use a filter gun to filter the dissolved sample solution into the injection bottle and place it in the injection tray. The test temperature is 160 ° C, the solvent flow rate is 1.0 mL / min, and the automatic injection test is started after the instrument runs stably. Polystyrene (PS) is used as the standard sample to obtain the molecular weight calibration curve.

[0060] Qualitative characterization of the product, NMR model: BRUKERAVANCE 400, manufacturer: Bruker, Switzerland.

[0061] Gas chromatography (GC) was used to qualitatively and quantitatively analyze the components in the polymerization reaction solution. The GC analysis instrument used was as follows: Shimadzu GC2010; Column: DB-5 (30 m, 0.25 mm, 0.25 μm); Column temperature program: 35°C for 10 min, then increased to 250°C at a rate of 10°C / min and maintained at this temperature for 10 min. Detector temperature: 300°C; Carrier gas: 1 bar; Air: 0.3 bar; Gas (H2): 0.3 bar.

[0062] Sample quality analysis is performed using the internal standard method.

[0063]

[0064] Where m1 is the mass of a product, m is the mass of the internal standard, a1 is the peak area of ​​the product detected in the gas chromatograph, and a is the peak area of ​​the internal standard. k is a correction factor related to the substance being measured and the test conditions.

[0065] Preparation of oligomerization catalyst:

[0066] (1) Under anhydrous and oxygen-free conditions, 50 mmol of N1,N3-dimethylbenzene-1,3-diamine was dissolved in 200 ml of dichloromethane. 110 mmol of tripropylamine was added dropwise to the reaction solution under stirring at -8°C. 55 mmol of diphenylphosphine chloride was first slowly added thereto. After the solution stabilized and no longer released heat, another 55 mmol of diphenylphosphine chloride was added. The reaction was stirred for 2 hours, and then the low-temperature constant temperature reaction bath was removed. The reaction solution was stirred at room temperature for 12 hours. The reaction solution was purified by column chromatography (tetrahydrofuran elution, height-to-diameter ratio of 2), and then recrystallized at 76°C (solvent: ethanol:ethyl acetate = 5:1) to obtain the phosphine-nitrogen ligand P1.

[0067]

[0068] The NMR data of ligand P1 are as follows: 1 HNMR (400MHz, CDCl3): 7.11-7.39(m,21H), 5.83-6.12(m,3H), 2.75(s,6H).

[0069] 1 mmol of phosphine-nitrogen ligand P1 and 1 mmol of tetrahydrofuran chromium chloride were added to 100 ml of toluene and heated to 80°C with stirring for 12 hours to produce a blue powdery precipitate. After cooling to room temperature, the toluene was filtered off. The crude product was washed twice with petroleum ether (20 ml) and dried under vacuum to obtain the phosphine-nitrogen ligand-chromium complex L1.

[0070] (2) Under anhydrous and oxygen-free conditions, 100 mmol of N1,N3-dimethylbenzene-1,3-diamine was dissolved in 200 ml of dichloromethane. 200 mmol of triethylamine was added dropwise to the reaction solution at -5°C with stirring. 115 mmol of chloro(2-fluorophenyl)(phenyl)phosphine was first slowly added thereto. After the solution stabilized and no longer released heat, 115 mmol of chloro(2-fluorophenyl)(phenyl)phosphine was added. The reaction was stirred for 5 hours, and then the low-temperature constant temperature reaction bath was removed. The reaction solution was stirred at room temperature for 15 hours. The reaction solution was purified by column chromatography (tetrahydrofuran elution, height-to-diameter ratio of 2), and then recrystallized at 76°C (solvent: ethanol:ethyl acetate = 5:1) to obtain phosphine-nitrogen ligand P3. Phosphine-nitrogen ligand-chromium complex L2 was obtained by referring to the preparation of L1.

[0071]

[0072] The NMR data of ligand L2 are as follows: 1 HNMR (400MHz, CDCl3): 7.14-7.65(m,19H), 5.78-6.15(m,3H), 2.68(s,6H).

[0073] (3) Under anhydrous and oxygen-free conditions, 100 mmol of N1,N3-dimethylbenzene-1,3-diamine was dissolved in 200 ml of dichloromethane. 160 mmol of triethylamine was added dropwise to the reaction solution at -8°C with stirring. 140 mmol of chlorobis[4-(trifluoromethyl)phenyl]phosphine was first slowly added thereto. After the solution stabilized and no longer released heat, 140 mmol of chlorobis[4-(trifluoromethyl)phenyl]phosphine was added. The reaction was stirred for 3.5 hours, and then the low-temperature constant temperature reaction bath was removed. The reaction solution was stirred at room temperature for 19 hours. The reaction solution was purified by column chromatography (tetrahydrofuran elution, height-to-diameter ratio of 2), and then recrystallized at 76°C (solvent: ethanol:ethyl acetate = 5:1) to obtain phosphine-nitrogen ligand P3. Phosphine-nitrogen ligand-chromium complex L3 was obtained by referring to the preparation of L1.

[0074]

[0075] The NMR data of ligand P3 are as follows: 1 H NMR (400MHz, CDCl3): 7.05-7.43 (m, 17H), 5.71 ~ 6.02 (m, 3H), 2.78 (s, 6H).

[0076] (4) Under anhydrous and oxygen-free conditions, 100 mmol of N1,N3-dimethylbenzene-1,3-diamine was dissolved in 200 ml of dichloromethane. 170 mmol of triethylamine was added dropwise to the reaction solution at -9°C with stirring. 150 mmol of chlorobis(4-methylphenyl)phosphine was first slowly added thereto. After the solution stabilized and no longer released heat, 150 mmol of chlorobis(4-methylphenyl)phosphine was added. The reaction was stirred for 4.5 hours, and then the low-temperature constant temperature reaction bath was removed. The reaction solution was stirred at room temperature for 14 hours. The reaction solution was purified by column chromatography (tetrahydrofuran elution, height-to-diameter ratio of 2), and then recrystallized at 76°C (solvent: ethanol:ethyl acetate = 5:1) to obtain phosphine-nitrogen ligand P4. Phosphine-nitrogen ligand-chromium complex L4 was obtained by referring to the preparation of L1.

[0077]

[0078] The NMR data of ligand P4 are as follows: 1 H NMR (400MHz, CDCl3): 7.08-7.15 (m, 17H), 5.88~6.16 (m, 3H), 2.81 (s, 6H), 2.39 (s, 12H).

[0079] (5) Under anhydrous and oxygen-free conditions, 100 mmol of N1,N3-dimethylbenzene-1,3-diamine was dissolved in 200 ml of dichloromethane. 230 mmol of triethylamine was added dropwise to the reaction solution at -3°C with stirring. 160 mmol of 4-(tri-n-butylsilyl)phenylphosphine chloride was first slowly added. After the solution stabilized and no longer released heat, 160 mmol of 4-(tri-n-butylsilyl)phenylphosphine chloride was added. The reaction was stirred for 3.9 hours, and then the low-temperature constant temperature reaction bath was removed. The reaction solution was stirred at room temperature for 13 hours. The reaction solution was purified by column chromatography (tetrahydrofuran elution, height-to-diameter ratio of 2), and then recrystallized at 76°C (solvent: ethanol:ethyl acetate = 5:1) to obtain phosphine-nitrogen ligand P5. Phosphine-nitrogen ligand-chromium complex L5 was obtained by referring to the preparation of L1.

[0080]

[0081] The NMR data of ligand P5 are as follows: 1 H NMR (400MHz, CDCl3): 7.09-7.43 (m, 17H), 5.81~6.01 (m, 3H), 2.75 (s, 6H), 0.28 (s, 36H).

[0082] Example 1

[0083] Oligomerization catalyst: phosphine-nitrogen ligand-chromium complex L1.

[0084]

[0085] Copolymerization catalyst: Dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) dimethyltitanium (T1)

[0086] Oligomerization co-catalyst system: MMAO-7 (7wt% Al)

[0087] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0088] Polymerization experiment: A 300ml reactor was heated to 150°C, evacuated for 2 hours, and replaced with nitrogen. After cooling to room temperature, the atmosphere was replaced with ethylene three times. At a reaction temperature of 45°C and an ethylene pressure of 3.5 MPa, 100ml of dehydrated and deoxygenated methylcyclohexane and 300μmol of MMAO-7 were added to the reactor in sequence. The mixture was stirred for 2 minutes, and 3μmol of oligomerization catalyst L1 was added and reacted for 30 minutes. (GC analysis of the reaction mixture revealed a molar ratio of 1-octene:1-hexene:1-butene of 78.5:12.7:1.) The ethylene pressure was then maintained constant, the reactor temperature was raised to 100°C, and 1μmol of copolymerization catalyst T1 and 60μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After completion of the reaction, the polymer solution was poured into 10ml of a 30% (v / v) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 6.22g of polymer. The properties of the polymers are shown in Table 2.

[0089] Example 2

[0090] Oligomerization catalyst: phosphine-nitrogen ligand-chromium complex L2.

[0091]

[0092] Copolymerization catalyst: Dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) dimethyltitanium (T1)

[0093] Oligomerization co-catalyst system: MMAO-7 (7wt% Al)

[0094] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0095] Polymerization experiment: Heat a 300 ml reactor to 120°C, evacuate for 3 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 55°C and an ethylene pressure of 3.5 MPa, 100 ml of dehydrated and deoxygenated n-hexane and 800 μmol of MMAO-7 were added to the reactor in sequence. The mixture was stirred for 2 minutes, and then 3 μmol of oligomerization catalyst L2 was added and allowed to react for 20 minutes. (GC analysis of the reaction mixture revealed a molar ratio of 1-octene:1-hexene:1-butene of 77.2:14.9:1.) The ethylene pressure was then maintained constant (some ethylene was purged as needed), and the reactor temperature was raised to 150°C. 0.5 μmol of copolymerization catalyst T1 and 70 μmol of MMAO-7 were added, and the reaction continued for 10 minutes. After the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / n-octanol solution to terminate the reaction. The product was washed with ethanol and dried under vacuum to yield 5.27 g of the polymer. The polymer properties are shown in Table 2.

[0096] Example 3

[0097] Oligomerization catalyst: phosphine-nitrogen ligand-chromium complex L3.

[0098]

[0099] Copolymerization catalyst: Dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl

[0100] Oligomerization co-catalyst system: MMAO-7 (7wt% Al)

[0101] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0102] Polymerization experiment: Heat a 500ml reactor to 130°C, evacuate for 3 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 65°C and an ethylene pressure of 3.5 MPa, 200 ml of dehydrated and deoxygenated cyclohexane and 550 μmol of MMAO-7 were added to the reactor in sequence. The mixture was stirred for 2 minutes, and then 3 μmol of oligomerization catalyst L3 was added and allowed to react for 20 minutes. (GC analysis of the reaction mixture revealed a molar ratio of 1-octene:1-hexene:1-butene of 65.1:15.4:1.) The ethylene pressure was then maintained constant (with some ethylene removed). The reactor temperature was then raised to 130°C, and 5 μmol of copolymerization catalyst T1 and 100 μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After the reaction was completed, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / 2-ethylhexanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 10.91 g of the polymer. The polymer properties are shown in Table 2.

[0103] Example 4

[0104] Oligomerization catalyst: phosphine-nitrogen ligand-chromium complex L4.

[0105]

[0106] Copolymerization catalyst: diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride (Zr1)

[0107] Oligomerization promoter system: MAO (10wt% Al)

[0108] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0109] Polymerization experiment: A 300ml reactor was heated to 160°C, evacuated for 2 hours, and replaced with nitrogen. After cooling to room temperature, ethylene replacement was performed. At a reaction temperature of 75°C and an ethylene pressure of 3.5 MPa, 100ml of dehydrated and deoxygenated methylcyclohexane and 150μmol MAO were added to the reactor in sequence. The mixture was stirred for 2 minutes, and 3μmol of oligomerization catalyst L4 was added and reacted for 20 minutes. (GC analysis of the reaction mixture revealed a molar ratio of 1-octene:1-hexene:1-butene of 63.5:17.3:1.) The ethylene pressure was then maintained constant (some ethylene was removed as needed). The reactor temperature was then raised to 160°C, and 1μmol of copolymerization catalyst Zr1 and 300μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After the reaction, the polymer solution was poured into 10ml of a 30% (v / v) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 15.99g of polymer. The product was collected and dried. The properties of the polymers are shown in Table 2.

[0110] Example 5

[0111] Oligomerization catalyst: phosphine-nitrogen ligand-chromium complex L5.

[0112]

[0113] Copolymerization catalyst: diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride (Zr1)

[0114] Oligomerization co-catalyst system: MMAO-3 (7wt% Al)

[0115] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0116] Polymerization experiment: Heat a 300 ml reactor to 150°C, evacuate for 2 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 50°C and an ethylene pressure of 3.5 MPa, 100 ml of dehydrated and deoxygenated Isopar E and 900 μmol of MMAO-7 were added to the reactor, stirred for 2 minutes, and then 3 μmol of oligomerization catalyst L5 was added and allowed to react for 20 minutes. (GC analysis of the reaction solution revealed a molar ratio of 1-octene:1-hexene:1-butene of 80.2:12.1:1.) The ethylene pressure was then maintained constant (with some ethylene removed). The reactor temperature was raised to 180°C, and 1 μmol of copolymerization catalyst Zr1 and 60 μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 20.43 g of the polymer. The polymer properties are shown in Table 2.

[0117] Example 6

[0118] Oligomerization catalyst: Phosphine-nitrogen ligand-chromium complex L5

[0119] Copolymerization catalyst: diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride (Zr1)

[0120] Oligomerization promoter system: MAO (10wt% Al)

[0121] Copolymerization co-catalyst system: MMAO-7 (7wt% Al), [Ph3C][B(C6F5)4]

[0122] Polymerization experiment: Heat a 300 ml reactor to 150°C, evacuate for 2 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 50°C and an ethylene pressure of 3.5 MPa, 100 ml of dehydrated and deoxygenated Isopar E and 1500 μmol of MAO were added to the reactor in sequence. The mixture was stirred for 2 minutes, and then 3 μmol of oligomerization catalyst L5 was added and allowed to react for 20 minutes. (GC analysis of the reaction mixture revealed a molar ratio of 1-octene:1-hexene:1-butene of 77.5:13.4:1.) The ethylene pressure was then maintained constant (some ethylene was purged as needed). The reactor temperature was then raised to 140°C, and 1 μmol of copolymerization catalyst Zr1, 1 μmol of [Ph3C][B(C6F5)4], and 60 μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 14.86 g of polymer. The polymer properties are shown in Table 2.

[0123] Example 7

[0124] Oligomerization catalyst: Phosphine-nitrogen ligand-chromium complex L5

[0125] Copolymerization catalyst: diphenylsilyl (cyclopentadiene) (9-fluorenyl) zirconium dichloride (Zr1)

[0126] Oligomerization promoter system: MAO (10wt% Al)

[0127] Copolymerization co-catalyst system: MMAO-7 (7wt% Al), [Ph3C][B(C6F5)4]

[0128] Polymerization experiment: Heat a 300 ml reactor to 150°C, evacuate for 2 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 75°C and an ethylene pressure of 3.5 MPa, 100 ml of dehydrated and deoxygenated Isopar E and 2000 μmol of MAO were added to the reactor, stirred for 2 minutes, and then 3 μmol of oligomerization catalyst L5 was added and allowed to react for 20 minutes. (GC analysis of the reaction solution revealed a molar ratio of 1-octene:1-hexene:1-butene of 19.5:58.2:1.) The ethylene pressure was then maintained constant (some ethylene was purged as needed), and the reactor temperature was raised to 100°C. 3 μmol of copolymerization catalyst Zr1, 3.3 μmol of [Ph3C][B(C6F5)4], and 300 μmol of MMAO-7 were added. The reaction was continued for 10 minutes. After the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 22.47 g of polymer. The polymer properties are shown in Table 2.

[0129] Example 8

[0130] Oligomerization catalyst: Phosphine-nitrogen ligand-chromium complex L2

[0131] Copolymerization catalyst: dibenzylidene (cyclopentadiene) (9-fluorenyl) zirconium dichloride (Zr2)

[0132] Oligomerization promoter system: MAO (10wt% Al)

[0133] Copolymerization promoter system: Al i Bu3, [Ph3C][B(C6F5)4]

[0134] Polymerization experiment: Heat a 300ml reactor to 150°C, evacuate for 2h, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 65°C and an ethylene pressure of 4.5MPa, add 100ml of dehydrated and deoxygenated Isopar E and 500μmol MMAO-7 to the reactor in sequence, stir for 2min, add 2μmol of oligomerization catalyst L2 and react for 50min (sampling GC test shows that the molar ratio of 1-octene: 1-hexene: 1-butene in the reaction liquid is 57.2:13.7:1). Then, control the ethylene pressure to be constant (discharge some ethylene appropriately), raise the reactor temperature to 100°C, add 1μmol of copolymerization catalyst Zr2, 1μmol [Ph3C][B(C6F5)4] and 500μmol Al i Bu3 was added and the reaction was continued for 5 minutes. After the reaction, the polymer solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to obtain 6.54 g of polymer. The properties of the polymer are shown in Table 2.

[0135] Example 9

[0136] Oligomerization catalyst: Phosphine-nitrogen ligand-chromium complex L3

[0137] Copolymerization catalyst: dimethyldisilylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride)(Zr3)

[0138] Oligomerization promoter system: MAO (10wt% Al)

[0139] Copolymerization co-catalyst system: MMAO-7 (7wt% Al), [Ph3C][B(C6F5)4]

[0140] Polymerization experiment: Heat a 300 ml reactor to 150°C, evacuate for 2 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 55°C and an ethylene pressure of 1 MPa, 100 ml of dehydrated and deoxygenated Isopar E and 900 μmol of MAO were added to the reactor, stirred for 2 minutes, and then 6 μmol of oligomerization catalyst L3 was added and allowed to react for 30 minutes. (GC analysis of the reaction solution revealed a molar ratio of 1-octene:1-hexene:1-butene of 39.8:45.2:1.) The ethylene pressure was then maintained constant (some ethylene was purged as needed), and the reactor temperature was raised to 200°C. 1 μmol of copolymerization catalyst Zr3 and 200 μmol of MMAO-7 (7 wt% Al) were added, and the reaction continued for 5 minutes. After the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 12.11 g of polymer. The polymer properties are shown in Table 2.

[0141] Example 10

[0142] Oligomerization catalyst: Phosphine-nitrogen ligand-chromium complex L4

[0143] Copolymerization catalyst: di-p-toluene methylene cyclopentadiene (2,7-di-tert-butyl-fluorenyl) zirconium dichloride (Zr4)

[0144] Oligomerization co-catalyst system: MMAO-7 (7wt% Al)

[0145] Copolymerization promoter system: MMAO-7 (7wt% Al)

[0146] Polymerization experiment: Heat a 300 ml reactor to 150°C, evacuate for 2 hours, replace with nitrogen, cool to room temperature, and replace with ethylene. At a reaction temperature of 65°C and an ethylene pressure of 5 MPa, 100 ml of dehydrated and deoxygenated Isopar E and 600 μmol of MMAO-7 were added to the reactor, stirred for 2 minutes, and then 5 μmol of oligomerization catalyst L4 was added and allowed to react for 30 minutes. (GC analysis of the reaction solution revealed a molar ratio of 1-octene:1-hexene:1-butene of 66.9:13.7:1.) The ethylene pressure was then maintained constant (some ethylene was purged as needed), and the reactor temperature was raised to 150°C. 1 μmol of copolymerization catalyst Zr4 and 150 μmol of MMAO-7 (7 wt% Al) were added, and the reaction continued for 15 minutes. After completion of the reaction, the polymerization solution was poured into 10 ml of a 30% (volume ratio) hydrochloric acid / ethanol solution to terminate the reaction. The polymer product was washed with ethanol and dried under vacuum to yield 10.39 g of the polymer. The polymer properties are shown in Table 2.

[0147] Comparative Example 1

[0148] The purchased ligand iPr-PNP was used. The preparation method was the same as in Example 1 to obtain the catalyst phosphine-nitrogen ligand-chromium complex La.

[0149]

[0150] The polymerization experiment was conducted as in Example 1, yielding 4.31 g of polymer. A comparison revealed that the phosphine-nitrogen ligand-chromium complex prepared by the existing PNP system for the cascade preparation of polyolefin plastomers exhibited relatively low overall selectivity for octene, hexene, and butene in the oligomerization product, and an even lower monomer insertion rate in the prepared copolymer.

[0151] Table 1 Reaction conditions of each embodiment and comparative example

[0152]

[0153] Table 2 Test results

[0154]

[0155]

Claims

1. A method for preparing a polyolefin plastomer, characterized in that: The preparation method comprises the following steps: S1: oligomerization of ethylene in the presence of an oligomerization catalyst and an oligomerization cocatalyst to produce α-olefins; S2: adding a copolymerization catalyst and a copolymerization co-catalyst to the reaction system to copolymerize α-olefins to form a polyolefin plastomer; Wherein, the oligomerization catalyst described in S1 is a phosphine nitrogen ligand-chromium salt complex of formula I: Wherein, R1, R2, R3, and R4 are each independently selected from one of aryl groups and substituted aryl groups.

2. The preparation method according to claim 1, characterized in that R1, R2, R3, and R4 are each independently selected from phenyl, benzyl, biphenyl, naphthyl, anthracenyl, 2-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl, 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl, 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 2- One of oxyphenyl, o-methoxyphenyl, 4-ethoxyphenyl, o-ethoxyphenyl, 2-(trimethylsilyl)phenyl, 3-(trimethylsilyl)phenyl, 4-(trimethylsilyl)phenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 4-(trifluoromethyl)phenyl, 3,5-bis(trifluoromethyl)phenyl, 2-(tri-n-butylsilyl)phenyl, 3-(tri-n-butylsilyl)phenyl, and 4-(tri-n-butylsilyl)phenyl.

3. The preparation method according to claim 1 or 2, characterized in that The amount of the oligomerization catalyst added in S1 is 0.5 μmol / L-100 μmol / L; and / or, the oligomerization cocatalyst in S1 is one or more of alkyl aluminum, aluminoxane, and organic boron compound; And / or, the reaction of S1 is carried out in a solvent; and / or, the oligomerization reaction temperature of S1 is 30° C.-90° C., and the reaction time is 10-80 min; And / or, the ethylene pressure in the reaction of S1 is 1 to 10 MPa gauge pressure.

4. The preparation method according to claim 3, characterized in that The amount of the oligomerization catalyst added in S1 is 1 μmol / L-50 μmol / L; And / or, the oligomerization cocatalyst in S1 is one or more of methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, and modified methylaluminoxane; The molar ratio of the oligomerization catalyst to the oligomerization co-catalyst in S1 is 1:(100-1500); The solvent in S1 is selected from aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents.

5. The preparation method according to claim 4, characterized in that The solvent in S1 is selected from C2-C9 aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents.

6. The preparation method according to claim 5, characterized in that In S1, the aliphatic hydrocarbon solvent is selected from one or more of methylcyclohexane, cyclohexane, n-butane, isobutane, n-pentane, cyclopentane, methylcyclopentane, methylenecyclopentane, Isopar E, Isopar H, n-hexane, ethylcyclohexane, n-heptane, n-octane, and n-nonane; and the aromatic hydrocarbon solvent is selected from one or more of benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene, and dichlorotoluene.

7. The preparation method according to claim 1 or 2, characterized in that The α-olefins in S1 include C4-C10 α-olefins.

8. The preparation method according to claim 7, characterized in that The α-olefins in S1 include one or more of 1-hexene, 1-octene, and 1-butene.

9. The preparation method according to claim 1 or 2, characterized in that: The copolymerization catalyst of S2 is a single-active-center metallocene catalyst and / or a post-metallocene catalyst; and / or, the S2 copolymerization co-catalyst is one or more of alkyl aluminum, alkyl aluminoxane, and organic boron compound; And / or, the copolymerization reaction temperature of S2 is 90° C.-230° C., and the reaction time is 5-20 min.

10. The preparation method according to claim 9, characterized in that The copolymerization catalyst of S2 is selected from one or more of titanium, zirconium, and hafnium-based metallocene catalysts and / or post-metallocene catalysts; The molar ratio of the oligomerization catalyst to the copolymerization catalyst in S2 is 1:(0.03-10); And / or, the S2 copolymerization cocatalyst is one or more of methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, tris(pentafluorophenyl)borate compounds, and tetrakis(pentafluorophenyl)borate compounds; In the copolymerization reaction described in S2, when the co-catalyst contains aluminum, the molar ratio of the metal atoms in the copolymerization catalyst to the aluminum in the copolymerization co-catalyst is 1:(50-1000); when the co-catalyst contains boron, the molar ratio of the metal atoms in the copolymerization catalyst to the boron in the copolymerization co-catalyst is 1:(1-5); And / or, the copolymerization reaction temperature of S2 is 90° C.-230° C., and the reaction time is 5-20 min.

11. The preparation method according to claim 10, characterized in that: The copolymerization catalyst of S2 is dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) trimethoxytitanium, dimethylbis (propylcyclopentadienyl) hafnium, bis (n-butylcyclopentadienyl) hafnium dichloride, racemic dimethylsilyl bis (2-methyl-1-indenyl) zirconium dichloride, dibenzylidenecyclopentadienyl (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, di-p-methyl One or more of benzhydrylidenecyclopentadienyl(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, dibenzylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, dimethyldisilylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride), mesodimethylsilylbis(1-indenyl)zirconium dichloride, bis(methylcyclopentadienyl)zirconium dichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, (cyclopentadienyl)(1,2-dimethoxyethane)zirconium trichloride, and diphenylsilyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride; The molar ratio of the oligomerization catalyst to the copolymerization catalyst in S2 is 1:(0.1-5).

12. The preparation method according to claim 1 or 2, characterized in that: The polyolefin plastomer prepared in S2 has a melting point of 45° C.-120° C., a weight-average molecular weight of 20,000-180,000, and a molecular weight distribution index of ≤4.

13. The preparation method according to claim 12, characterized in that The polyolefin plastomer prepared in S2 has a melting point of 55° C. to 105° C., a weight-average molecular weight of 30,000-150,000, and a molecular weight distribution index of 1.2 to 3.

5.

14. A catalyst composition for preparing a polyolefin plastomer, wherein the composition is the catalyst composition used in the preparation method according to any one of claims 1 to 13, characterized in that: The composition comprises an oligomerization catalyst, an oligomerization co-catalyst, a copolymerization catalyst, and a copolymerization co-catalyst; Wherein, the oligomerization catalyst is a phosphine nitrogen ligand-chromium salt complex of formula I: Wherein, R1, R2, R3, and R4 are each independently selected from one of aryl groups and substituted aryl groups.

15. The catalyst composition according to claim 14, characterized in that R1, R2, R3, and R4 are each independently selected from phenyl, benzyl, biphenyl, naphthyl, anthracenyl, 2-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl, 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2-ethylphenyl, 4-ethylphenyl, 2,4-diethylphenyl, 2,6-diethylphenyl, 2-isopropylphenyl, 4-isopropylphenyl, 2,4-diisopropylphenyl, 2,6-diisopropylphenyl, 2-butylphenyl, 4-butylphenyl, 2,4-dibutylphenyl, 2,6-dibutylphenyl, 2- One of oxyphenyl, o-methoxyphenyl, 4-ethoxyphenyl, o-ethoxyphenyl, 2-(trimethylsilyl)phenyl, 3-(trimethylsilyl)phenyl, 4-(trimethylsilyl)phenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2-(trifluoromethyl)phenyl, 3-(trifluoromethyl)phenyl, 4-(trifluoromethyl)phenyl, 3,5-bis(trifluoromethyl)phenyl, 2-(tri-n-butylsilyl)phenyl, 3-(tri-n-butylsilyl)phenyl, and 4-(tri-n-butylsilyl)phenyl.

16. The catalyst composition according to claim 14, characterized in that The oligomerization co-catalyst is one or more of alkyl aluminum, aluminoxane, and organic boron compound; And / or, the copolymerization catalyst is a single-active-site metallocene catalyst and / or a post-metallocene catalyst; And / or, the copolymerization co-catalyst is one or more of alkyl aluminum, alkyl aluminoxane, and organic boron compound.

17. The catalyst composition according to claim 16, characterized in that The oligomerization cocatalyst is one or more of methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, and modified methylaluminoxane; The molar ratio of the oligomerization catalyst to the oligomerization co-catalyst is 1:(100-1500); and / or, the copolymerization catalyst is one or more of titanium, zirconium, and hafnium-based metallocene catalysts and / or post-metallocene catalysts; The molar ratio of the oligomerization catalyst to the copolymerization catalyst is 1:(0.03-10); And / or, the copolymerization cocatalyst is one or more of methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, tris(pentafluorophenyl)borate compounds, and tetrakis(pentafluorophenyl)borate compounds; In the copolymerization reaction, when the co-catalyst contains aluminum, the molar ratio of the metal atoms in the copolymerization catalyst to the aluminum in the copolymerization co-catalyst is 1:(50-1000); when the co-catalyst contains boron, the molar ratio of the metal atoms in the copolymerization catalyst to the boron in the copolymerization co-catalyst is 1:(1-5).

18. The catalyst composition according to claim 17, characterized in that The copolymerization catalyst is dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) trimethoxytitanium, dimethylbis (propylcyclopentadienyl) hafnium, bis (n-butylcyclopentadienyl) hafnium dichloride, racemic dimethylsilyl bis (2-methyl-1-indenyl) zirconium dichloride, dibenzylidenecyclopentadienyl (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, di-p-toluene One or more of methylenecyclopentadienyl(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, dibenzylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, dimethyldisilylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride), mesodimethylsilylbis(1-indenyl)zirconium dichloride, bis(methylcyclopentadienyl)zirconium dichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, (cyclopentadienyl)(1,2-dimethoxyethane)zirconium trichloride, and diphenylsilyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride; The molar ratio of the oligomerization catalyst to the copolymerization catalyst is 1:(0.1-5).

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