Steric Hindered Ethylene Acenamethanone Nickel Catalysts, Their Preparation Methods and Applications

Abstract

This invention discloses a sterically hindered, biasymmetric (α-diimine) nickel-olefin catalyst based on an ethylene acenaphthoquinone framework, its preparation method, and its applications. The catalyst's structural formula is shown in Formula (I), where X is chlorine or bromine. The catalyst has a simple preparation process and, when used as a co-catalyst, can produce ultra-high molecular weight polyethylene in ethylene polymerization without affecting the degree of branching. Furthermore, this type of catalyst exhibits good thermal stability and polymerization activity, showing promising prospects for industrial applications. Formula (I)

Description

Technical Field

[0001] This invention relates to a sterically hindered ethylene acenaphthene nickel catalyst, its preparation method and application, and more particularly to a sterically hindered ethylene acenaphthene biasymmetric α-diimine nickel catalyst, its preparation method, and its application in catalyzing the polymerization of ethylene or propylene to obtain polyethylene or polypropylene. Background Technology

[0002] Polyolefins, as one of the most widely used synthetic polymers, have been extensively applied in all aspects of daily life. In the process of preparing polyolefins, the development and improvement of new catalysts are crucial factors driving the advancement and improvement of polyolefin production efficiency and product performance.

[0003] While pre-transition metal catalysts play a crucial role in olefin polymerization, the polyethylene structures they produce are almost always linear, making it impossible to prepare non-linear (e.g., branched) polymers. Post-transition metal catalysts, on the other hand, possess unique advantages such as lower oxygen affinity and stronger tolerance to polar groups. In 1995, Brookhart et al. pioneered the development of (α-diimine) nickel / palladium catalysts, the specific structural formula of which is shown in formula (Ⅳ). The "chain-walking" mechanism of this type of catalyst makes it possible to synthesize polymers with high activity and high molecular weight and high degree of branching, thus attracting widespread attention to transition metal catalysts in olefin polymerization. Equation (Ⅳ) Typically, much research has focused on modifying the ortho-position groups of the aryl group (R' in the formula) while maintaining the diimine backbone structure. When R' is a sterically hindered group, the resulting polymer usually has a higher molecular weight and a lower degree of branching. This is mainly because the introduced sterically hindered substituent inhibits the β-H elimination reaction during chain growth, thereby suppressing chain transfer and resulting in a higher molecular weight and lower degree of branching in the final polymer. However, our team previously discovered that when a sterically hindered substituent is introduced, as shown in formula (V), compared to patent CN109956980B, although the degree of branching of the resulting polymer is lower, its molecular weight is also lower. By analogy, when a substituent with even greater steric hindrance is introduced, a polymer with an even lower molecular weight can be obtained. However, the preparation of ultra-high molecular weight products requires sterically hindered and highly stable α-diimine ligands, which involve multiple synthesis steps and have high purification costs. These factors greatly limit its industrial application. Formula (V) Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sterically hindered ethylacenaphthene biasymmetric α-diimine nickel catalyst, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a biasymmetric (α-diimine) nickel olefin catalyst, the chemical structure of which is shown in formula (I): Equation (I) Where X is chlorine or bromine.

[0006] In a second aspect, the present invention provides the above-mentioned biasymmetric (α-diimine) nickel olefin catalyst ligand, the structural formula of which is shown in formula (II): Formula (II) In a third aspect, the present invention also provides a method for preparing the above-mentioned ligand compound, comprising the following steps: 1) Ethylene acenaphthene reacts with aniline containing a sterically hindered substituent via a ketamine condensation reaction to yield the compound shown in formula (III):

[0007] 2) The compound shown in formula (III) reacts with asymmetric 2,4-dimethyl-6-diphenylmethylaniline modified with phenyl group via a ketamine condensation reaction to yield the ligand of formula (II):

[0008] In one embodiment of the present invention, the solvent used in step 1) above is selected from at least one of toluene, acetonitrile, acetic acid and anhydrous ethanol, preferably at least one of toluene and acetonitrile.

[0009] In one embodiment of the present invention, the catalyst used in step 1) above is selected from at least one of p-toluenesulfonic acid and acetic acid.

[0010] In one embodiment of the present invention, the ratio of the catalyst, ethylene acenaphthene, aniline with a large sterically hindered substituent, and solvent in step 1) above is 0.1-0.15 mmol: 1-1.1 mmol: 1-1.4 mmol: 5-10 mL.

[0011] In one embodiment of the present invention, the reaction time of step 1) above is 2-8 hours, preferably 3-6 hours.

[0012] In one embodiment of the present invention, step 1) above further includes the following step: using a mixed solvent of dichloromethane and petroleum ether or a mixed solvent of petroleum ether and ethyl acetate as eluent, the product is subjected to column chromatography in a silica gel column to obtain the product shown in formula (III).

[0013] In one embodiment of the present invention, the solvent used in step 2) is selected from at least one of toluene, acetonitrile, acetic acid and anhydrous ethanol, preferably at least one of toluene and acetonitrile.

[0014] In one embodiment of the present invention, the catalyst used in step 2) is selected from at least one of p-toluenesulfonic acid and acetic acid.

[0015] In one embodiment of the present invention, the ratio of the catalyst, ethylene acenaphthene, aniline with a large sterically hindered substituent, and solvent in step 2) above is 0.2-0.5 mmol: 1-1.1 mmol: 1-1.4 mmol: 30-70 mL.

[0016] In one embodiment of the present invention, the reaction time of step 2) above is 6-16 hours, preferably 8-12 hours.

[0017] In one embodiment of the present invention, step 2) above further includes the following step: using a mixed solvent of dichloromethane and petroleum ether or a mixed solvent of petroleum ether and ethyl acetate as eluent to perform column chromatography on the product in a silica gel column to obtain the product shown in formula (II).

[0018] In a fourth aspect, the present invention also provides a method for preparing the catalyst shown in formula (I), comprising the following steps: under an inert gas atmosphere, complexing the compound shown in formula (II) with one of ethylene glycol dimethyl ether nickel dibromide, ethylene glycol dimethyl ether nickel dichloride, or nickel dichloride hexahydrate to obtain the catalyst of the present invention. In the structural formula of the catalyst of the present invention, X is chlorine or bromine. In one embodiment of the present invention, X is selected as bromine. In another embodiment of the present invention, X is selected as chlorine.

[0019] In one embodiment of the present invention, under a nitrogen atmosphere, the compound shown in formula (II) is used as a ligand, and the nickel-containing compound complexed with the ligand is selected as nickel dimethyl ether dibromide (DME)NiBr2, wherein the molar ratio of the ligand to (DME)NiBr2 is 1:1-1.2, preferably 1:1.1; the solvent is dichloromethane, the reaction temperature is 15-35°C, preferably 25°C, and the reaction time is 8-30 hours, preferably 16-24 hours.

[0020] In a fifth aspect, the present invention also provides a catalyst composition for catalyzing olefin polymerization, the composition comprising a main catalyst and a co-catalyst, the main catalyst being selected from the catalyst shown in formula (I), the co-catalyst being selected from at least one of alkylaluminum chloride, alkylaluminum and aluminoxane, and the olefin being ethylene or propylene.

[0021] In one embodiment of the present invention, the composition comprises a main catalyst and a co-catalyst, wherein the main catalyst is selected from the catalyst shown in formula (I), the co-catalyst is selected from at least one of alkylaluminum chloride, alkylaluminum and aluminoxane, and the olefin is ethylene or propylene.

[0022] Optionally, in the above catalyst composition, the aluminum oxane is methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, or isobutylaluminoxane.

[0023] Optionally, in the above catalyst composition, the alkylaluminum is trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum.

[0024] Optionally, in the above catalyst composition, the alkylaluminum chloride is diethylaluminum chloride, sesqui-diethylaluminum chloride, or ethylaluminum dichloride.

[0025] Considering the effectiveness and cost of the co-catalyst, in a preferred embodiment, the co-catalyst in the above-mentioned catalyst composition is alkyl aluminum chloride.

[0026] In a preferred embodiment, when alkylaluminum chloride is used as a co-catalyst, the molar ratio of metallic aluminum in alkylaluminum chloride to metallic nickel in the catalyst is referred to as the aluminum-nickel ratio, which ranges from 50 to 2000:1.

[0027] In a sixth aspect, the present invention also discloses the application of the catalyst shown in formula (I) in catalyzing the polymerization of ethylene and propylene to prepare polyethylene and polypropylene.

[0028] The beneficial effects of this invention lie in providing a biasymmetric (α-diimine) nickel olefin polymerization catalyst with good thermal stability and polymerization activity. This catalyst, modified with a large sterically hindered group, differs from expectations, enabling the preparation of ultra-high molecular weight polymers without affecting the branching degree of the polymers, and can be used to prepare materials with good mechanical properties. Furthermore, this type of catalyst has a low synthesis threshold, simple ligand synthesis, requires a small amount of co-catalyst, and has significant overall production cost advantages. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0030] Example 1, Preparation of intermediate of formula (III): p-Toluenesulfonic acid (0.34 g, 2 mmol) was added to a toluene (150 mL) solution of 2,6-bis(diphenylmethyl)-4-methylaniline (8.8 g, 20 mmol) and ethylenaclairone (4.16 g, 20 mmol), and the mixture was refluxed for 6 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a 2:1 volume ratio of dichloromethane and petroleum ether to obtain intermediate of formula (III) with a mass of 12.1 g, yield: 96%.

[0031] Example 2, Preparation of ligand (II): A solution of 2,4-dimethyl-6-diphenylmethylaniline (0.43 g, 1.5 mmol) and intermediate (0.629 g, 1 mmol) of formula (III) in toluene (50 mL) was reacted with p-toluenesulfonic acid (0.086 g, 0.5 mmol) under reflux for 12 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 30:1 to obtain ligand (II) with a mass of 0.78 g, yield: 87%.

[0032] Example 3, Preparation of catalyst of formula (I): Under a nitrogen atmosphere, ligand of formula (II) (0.18 g, 0.2 mmol) and (DME)NiBr2 (0.062 g, 0.2 mmol) were dissolved in 20 mL of dichloromethane and stirred at room temperature for 24 hours. The dichloromethane was dried under vacuum, and the solution was washed three times with 20 mL of diethyl ether each time. The diethyl ether was then dried under vacuum to obtain catalyst of formula (I), 0.203 g, with a yield of 91%.

[0033] The following examples illustrate catalytic ethylene polymerization: Example 4: Ethylene pressure polymerization was carried out under anhydrous and oxygen-free conditions. The ethylene pressure was 1 MPa, and the polymerization temperature was 60 °C. 1 L of heptane was poured into a 2000 mL stainless steel reactor, followed by the injection of 1.5 mL of a 2.0 mol / L diethylaluminum chloride toluene solution as a co-catalyst. 2 μmol of catalyst (I) was dissolved in 10 mL of toluene solution and injected. The ethylene pressure was increased to 1.0 MPa, and the mixture was stirred. After reacting for half an hour, the polymer solution was poured into an acidified ethanol solution for sedimentation. The polymer was filtered, washed several times with acidified ethanol, and vacuum dried at 60 °C to constant weight. 12.7 g of polymer was obtained. The catalytic activity was 12.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 242 × 10⁻⁶. 4 g / mol, polydispersity index of 1.96, and branching degree of 60.

[0034] Example 5: The polymerization pressure in Example 4 was adjusted to 1.5 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 16.4 g of polymer was obtained. The catalytic activity was 16.4 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 258 × 10⁻⁶. 4 g / mol, polydispersity index of 2.01, and branching degree of 56.

[0035] Example 6: The polymerization pressure in Example 4 was adjusted to 1.9 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 25.5 g of polymer was obtained. The catalytic activity was 25.5 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 285 × 10⁻⁶. 4 g / mol, polydispersity index of 1.89, and branching degree of 56.

[0036] Example 7: The polymerization pressure in Example 4 was adjusted to 0.7 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 9.7 g of polymer was obtained. The catalytic activity was 9.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 240 × 10⁻⁶. 4 g / mol, polydispersity index of 1.97, and branching degree of 62.

[0037] Example 8: The polymerization temperature in Example 7 was adjusted to 40 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 8.7 g of polymer was obtained. The catalytic activity was 8.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 294 × 10⁻⁶. 4 g / mol, polydispersity index of 2.01, and branching degree of 57.

[0038] Example 9: The polymerization temperature in Example 7 was adjusted to 80 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 7.6 g of polymer was obtained. The catalytic activity was 7.6 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 166 × 10⁻⁶. 4 g / mol, polydispersity index of 1.83, and branching degree of 69.

[0039] Example 10: The polymerization temperature in Example 7 was adjusted to 100 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 3.0 g of polymer was obtained. The catalytic activity was 3.0 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 84.7 × 10⁻⁶. 4 g / mol, polydispersity index of 1.91, and branching degree of 75.

[0040] Example 11: The amount of co-catalyst in Example 4 was adjusted to 1.5 mL with a concentration of 2.0 mol / L, and the amount of catalyst (I) was adjusted to 10 μmol. Other conditions remained unchanged. The polymerization product was vacuum dried at 60°C to constant weight, and 24.0 g of polymer was obtained. The catalytic activity was 4.8 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 91.2 × 10⁻⁶. 4 kg / mol, polydispersity index of 2.03, and branching degree of 72.

[0041] Comparative Example 1: A solution of 3-methyl-[1,1'-biphenyl]-2-amine (0.296 g, 1.5 mmol) and intermediate of formula (III) (0.629 g, 1 mmol) in toluene (50 mL) was reacted with p-toluenesulfonic acid (0.086 g, 0.5 mmol) and refluxed for 12 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a mixture of petroleum ether and ethyl acetate (30:1 v / v) to obtain 0.33 g of ligand of formula (V), yield: 41.5%.

[0042] Comparative Example 2: The formula (V) ligand synthesized in Comparative Example 1 was used instead of the formula (II) ligand in Example 3. Other operations were the same as in Example 3, and 0.200 g of the formula (V) catalyst was obtained with a yield of 98.5%.

[0043] Comparative Example 3: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 4. All other operations were the same as in Example 4. The polymerization product was vacuum dried at 60 °C to constant weight, and 15.4 g of polymer was obtained. The catalytic activity was 15.4 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 51.5 × 10⁻⁶. 4 g / mol, polydispersity index of 1.83, and branching degree of 61.

[0044] Comparative Example 4: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 5. All other operations were the same as in Example 5. The polymerization product was vacuum dried at 60 °C to constant weight, and 22.9 g of polymer was obtained. The catalytic activity was 22.9 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 58.5 × 10⁻⁶. 4 g / mol, polydispersity index of 1.82, and branching degree of 56.

[0045] Comparative Example 5: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 6. All other operations were the same as in Example 6. The polymerization product was vacuum dried at 60 °C to constant weight, and 25.8 g of polymer was obtained. The catalytic activity was 25.8 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 60.5 × 10⁻⁶. 4 g / mol, polydispersity index of 1.85, and branching degree of 64.

[0046] Comparative Example 6: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 7. All other operations were the same as in Example 7. The polymerization product was vacuum dried at 60 °C to constant weight, and 8.5 g of polymer was obtained. The catalytic activity was 8.5 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 51.2 × 10⁻⁶. 4 g / mol, polydispersity index of 1.68, and branching degree of 65.

[0047] Comparative Example 7: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 8. All other operations were the same as in Example 8. The polymerization product was vacuum dried at 60 °C to constant weight, and 13.1 g of polymer was obtained. The catalytic activity was 13.1 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 94.4 × 10⁻⁶. 4 g / mol, polydispersity index of 1.82, and branching degree of 49.

[0048] Comparative Example 8: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 9. All other operations were the same as in Example 9. The polymerization product was vacuum dried at 60 °C to constant weight, and 4.3 g of polymer was obtained. The catalytic activity was 4.3 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 25.6 × 10⁻⁶. 4 g / mol, polydispersity index of 1.76, and branching degree of 74.

[0049] Comparative Example 9: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 10. All other operations were the same as in Example 10. The polymerization product was vacuum dried at 60 °C to constant weight, and 1.3 g of polymer was obtained. The catalytic activity was 1.3 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 16.6 × 10⁻⁶. 4g / mol, polydispersity index of 1.79, and branching degree of 85.

[0050] Comparative Example 10: The catalyst of formula (V) synthesized in Comparative Example 2 was used instead of the catalyst in Example 11. All other operations were the same as in Example 11. The polymerization product was vacuum dried at 60 °C to constant weight, and 26.0 g of polymer was obtained. The catalytic activity was 5.2 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 20.7 × 10⁻⁶. 4 g / mol, polydispersity index of 1.99, and branching degree of 82.

[0051] Comparative Example 11: A solution of 2,6-dimethylaniline (0.18 g, 1.5 mmol) and intermediate of formula (III) (0.629 g, 1 mmol) in toluene (50 mL) was reacted with p-toluenesulfonic acid (0.086 g, 0.5 mmol) and refluxed for 12 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 30:1 to obtain 0.34 g of 2,6-dimethylaniline ligand, yield: 46.1%.

[0052] Comparative Example 12: The ligand of formula (II) in Example 3 was replaced with the 2,6-dimethylaniline ligand synthesized in Comparative Example 11, and the other operations were the same as in Example 3, to obtain 0.169 g of 2,6-dimethylaniline diimine nickel bromide complex, with a yield of 89%.

[0053] Comparative Example 13: The catalyst in Example 4 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 4. The polymerization product was vacuum dried at 60 °C to constant weight, and 15.9 g of polymer was obtained. The catalytic activity was 15.9 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 129 × 10⁻⁶. 4 g / mol, polydispersity index of 1.73, and branching degree of 84.

[0054] Comparative Example 14: The catalyst in Example 5 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 5. The polymerization product was vacuum dried at 60 °C to constant weight, and 18.4 g of polymer was obtained. The catalytic activity was 18.4 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 120 × 10⁻⁶. 4g / mol, polydispersity index of 1.94, and branching degree of 80.

[0055] Comparative Example 15: The catalyst in Example 6 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 6. The polymerization product was vacuum dried at 60 °C to constant weight, and 19.6 g of polymer was obtained. The catalytic activity was 19.6 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 114 × 10⁻⁶. 4 g / mol, polydispersity index of 1.96, and branching degree of 76.

[0056] Comparative Example 16: The catalyst in Example 7 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 7. The polymerization product was vacuum dried at 60 °C to constant weight, and 9.1 g of polymer was obtained. The catalytic activity was 9.1 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 110 × 10⁻⁶. 4 g / mol, polydispersity index of 1.90, and branching degree of 87.

[0057] Comparative Example 17: The catalyst in Example 8 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 8. The polymerization product was vacuum dried at 60 °C to constant weight, and 10.5 g of polymer was obtained. The catalytic activity was 10.5 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 169 × 10⁻⁶. 4 g / mol, polydispersity index of 2.31, and branching degree of 74.

[0058] Comparative Example 18: The catalyst in Example 9 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 9. The polymerization product was vacuum dried at 60 °C to constant weight, and 6.7 g of polymer was obtained. The catalytic activity was 6.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 54.2 × 10⁻⁶. 4 g / mol, polydispersity index of 1.81, and branching degree of 96.

[0059] Comparative Example 19: The catalyst in Example 10 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 10. The polymerization product was vacuum dried at 60 °C to constant weight, and 2.0 g of polymer was obtained. The catalytic activity was 2.0 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 29.9 × 10⁻⁶. 4 g / mol, polydispersity index of 1.85, and branching degree of 103.

[0060] Comparative Example 20: The catalyst in Example 11 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 12. All other operations were the same as in Example 11. The polymerization product was vacuum dried at 60 °C to constant weight, and 30.5 g of polymer was obtained. The catalytic activity was 6.1 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 38.2 × 10⁻⁶. 4 g / mol, polydispersity index of 2.10, and branching degree of 99.

[0061] By comparing Comparative Examples 3-10 with Comparative Examples 13-20, it was found that introducing a benzene ring using the catalyst of formula (V) increases steric hindrance, resulting in polymers with smaller molecular weights. Furthermore, with a significant decrease in molecular weight, the degree of branching also decreases significantly. To obtain polymers with even smaller molecular weights, experiments were conducted in Examples 4-11. Unexpectedly, compared to Comparative Examples 3-10, Examples 4-11 yielded polymers with significantly higher molecular weights, while the degree of branching of the polymers did not change significantly. This indicates that by adjusting the steric hindrance of aniline in the α-diimine nickel catalyst, polymers with significantly different molecular weights but similar degrees of branching can be obtained, making them suitable for various industrial applications. In addition, this type of catalyst has a simple preparation process, high yield, good thermal stability and polymerization activity, and also shows promising prospects for industrial applications.

Claims

1. The biasymmetric (α-diimine) nickel olefin catalyst shown in formula (Ⅰ): Formula (I) wherein X is chlorine or bromine.

2. The compound represented by formula (II): Formula (II).

3. A method for preparing the compound according to claim 2, comprising the following steps: 1) Ethylene acenaphthene reacts with aniline containing a sterically hindered substituent via a ketamine condensation reaction to yield the compound shown in formula (III): 2) The compound shown in formula (III) reacts with a sterically hindered asymmetric aniline via a ketamine condensation reaction to yield the compound shown in formula (II): 。 4. A method for preparing the catalyst according to claim 1, comprising the following steps: under an inert gas protection environment, complexing the compound according to claim 2 with one of ethylene glycol dimethyl ether nickel dibromide, ethylene glycol dimethyl ether nickel dichloride, or nickel dichloride hexahydrate to obtain the catalyst according to claim 1.

5. A catalyst composition for catalyzing the polymerization of olefins, characterized in that, It includes a main catalyst and a co-catalyst, wherein the main catalyst is selected from... According to claim 1, the catalyst is selected from at least one of alkylaluminum chloride, alkylaluminum, or aluminoxane, and the olefin is ethylene or propylene.

6. The application of the (α-diimine) nickel olefin catalyst according to claim 1 in the catalytic polymerization of ethylene to prepare polyethylene.

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