A one-pot method for synthesizing bimodal polyethylene

Abstract

The present invention reports a one-pot method for synthesizing bimodal polyethylene. The present invention is characterized in that phenolic hydrogen is selectively removed by NaH, while amino hydrogen is retained, thereby synthesizing a trichlorometallic catalyst containing H atoms on the N atom. During the polymerization process, the H atom has two forms, namely, retention and removal, so that two active centers can be generated in situ, thereby synthesizing bimodal polyethylene. The bimodal polyethylene reported in the present invention has adjustable molecular weight and distribution, is obtained by one-step polymerization in a single reactor, has high efficiency and low cost, and has an activity of up to 6.3×10 8 g(PE)·mol ‑1 (Ti) h ‑1 Therefore, the present invention is original and innovative and can enhance the competitiveness of my country's polyolefin polymer material technology market.

Description

Technical Field

[0001] The invention relates to a method for synthesizing bimodal polyethylene in one pot. Background Art

[0002] With the gradual increase in the domestic ethylene consumption, more and more polyethylene products have been developed, resulting in people's requirements for the performance of polyethylene materials, such as processing performance, mechanical properties, etc. People are trying to improve the performance of polyethylene, gradually improving its mechanical properties and thermal stability, but often lead to deterioration of processing performance. The emergence of bimodal polyethylene (Bimodal PE) solves this problem. It takes into account the advantages of low molecular weight and high molecular weight polyethylene resins, improves the performance of polyethylene materials, and thus meets people's requirements for the polyethylene market (Angew Chem, Int Ed, 2003, 42 (41): 5010-5030).

[0003] Bimodal polyethylene (Bimodal PE) is a molecular weight distribution that presents two peaks with different properties, including low molecular weight and high molecular weight components. In general, the microstructure of a polymer determines the performance, especially the molecular weight and molecular weight distribution play a key role in the mechanical properties of a polymer. High molecular weight polyethylene with a narrow distribution has advantages such as high mechanical strength (J.Polym.Sci., Part A:Polym.Chem, 2011, 49 (17): 3739-3750). For polyethylene, the higher the molecular weight, the better its mechanical properties, but high molecular weight polyethylene has a poor processability due to increased melt viscosity, and is more difficult to apply. In order to overcome these limitations, the molecular weight distribution must be broadened. Bimodal PE with a bimodal molecular weight distribution has many side chains in its high molecular weight component, which ensures the stability of mechanical properties such as toughness and strength. The low molecular weight component with fewer side chains has a low viscosity and can crystallize faster, which plays a role in lubrication and improves the processing properties of Bimodal PE, thereby making it have good mechanical properties and processing properties at the same time.

[0004] There are two main methods for producing bimodal polyethylene, namely, melt blending and reactor method. The melt blending method is to produce high and low molecular weight polyethylene resins in two reactors respectively, and physically melt and mix to form a uniform mixture. The disadvantages are high cost and miscibility problems. The reactor method includes a series reactor (Macromolecular Symposia, 2001, 163 (1): 135-144) and a single reactor method. The series connection is to obtain a bimodal polyethylene with a desired molecular weight by adjusting the hydrogen concentration, catalyst, pressure, etc. in each reactor. A special catalytic system that produces different active centers is added to a single reactor, and an ethylene mixture is obtained by one-step polymerization. Although the series connection process is commonly used in industry, the single reactor method is low in cost and simple in process, making it more attractive. This requires advanced catalyst technology support. The catalyst used in the single reactor method can be divided into a composite catalyst and a single component catalyst according to the catalytic system. Composite catalyst (J.Polym.Sci., Part A:Polym.Chem, 2010, 48(17):3722-3728) refers to the combination of Ziegler-Natta catalyst, cyclopentadienyl catalyst, chromium catalyst and late transition metal catalyst in pairs, which can form bimodal polyethylene by using co-catalyst or loading. However, since this system requires different combinations for different polyethylenes, uniform mixing is a problem. In comparison, single-component catalysts (Macromolecules, 2019, 52(7):2701-2711) are more popular because they can achieve the synthesis of bimodal polyethylene by simply adjusting the ligand structure and reaction conditions.

[0005] Combining bidentate salicylaldimine ligands with NN-bidentate imine-amine ligands is an effective way to develop high-performance polyolefin catalysts (Angew Chem, Int Ed, 1999, 38 (4): 428-447). Recently, we reported a series of salicylaldimine titanium dichloride catalysts (L-TiCl2) and achieved good polymerization results. It is worth noting that these titanium complexes have high thermal stability and activity and can be used to synthesize monodisperse and narrowly distributed polyethylene (Chin. J. Chem. 2022, 40, 2785-2793).

[0006]

[0007] The present invention reports a one-pot method for synthesizing bimodal polyethylene. The present invention is characterized in that phenolic hydrogen is selectively removed by NaH, while amino hydrogen is retained, thereby synthesizing a trichlorometallic catalyst containing H atoms on the N atom. During the polymerization process, the H atom has two forms, namely, retention and removal, so that two active centers can be generated in situ, thereby synthesizing bimodal polyethylene. The bimodal polyethylene reported in the present invention has adjustable molecular weight and distribution, is obtained by one-step polymerization in a single reactor, has high efficiency and low cost, and has an activity of up to 6.3×10 8 g(PE)·mol -1 (Ti) h -1 Therefore, the present invention is original and innovative and can enhance the competitiveness of my country's polyolefin polymer material technology market. Summary of the invention

[0008] The object of the present invention is to provide a method for synthesizing bimodal polyethylene in one pot.

[0009] In the above one-pot method for synthesizing bimodal polyethylene, the catalyst used is a metal catalyst represented by formula (I):

[0010]

[0011] The preparation method of the metal catalyst, as shown in formula (II), comprises the following steps: under a nitrogen atmosphere, stirring 1 molar equivalent of 1-L or 2-L or 3-L or 4-L ligand and 1 molar equivalent of NaH in toluene at room temperature overnight, then adding 1 molar equivalent of TiCl4, continuing to stir at 110°C for 72 hours, and filtering after returning to room temperature, and after draining the solvent from the filtrate, washing with 5 mL of anhydrous n-hexane to obtain the metal catalyst,

[0012]

[0013] In the one-pot method for synthesizing bimodal polyethylene, a co-catalyst is also added, and the co-catalyst is one or more of tripentafluorophenyl boron, triphenylcarbonium tetrakis(pentafluorophenyl)borate, aluminoxane, alkyl aluminum and alkyl aluminum chloride. The aluminoxane is methylaluminoxane, ethylaluminoxane or isobutylaluminoxane; the alkyl aluminum is trimethyl aluminum, triethyl aluminum, triisobutyl aluminum or tri-n-hexyl aluminum; the alkyl aluminum chloride is diethyl aluminum monochloride, diethyl aluminum sesquichloride or ethyl aluminum dichloride.

[0014] In the above one-pot method for synthesizing bimodal polyethylene, the polymerization temperature is 0-180° C., the polymerization pressure is 0.1-5 MPa, and the polymerization solvent is one or more of toluene, hexane, and heptane.

[0015] The present invention reports a one-pot method for synthesizing bimodal polyethylene. The present invention is characterized in that phenolic hydrogen is selectively removed by NaH, while amino hydrogen is retained, thereby synthesizing a trichlorometallic catalyst containing H atoms on the N atom. During the polymerization process, the H atom has two forms, namely, retention and removal, so that two active centers can be generated in situ, thereby synthesizing bimodal polyethylene. The bimodal polyethylene reported in the present invention has adjustable molecular weight and distribution, is obtained by one-step polymerization in a single reactor, has high efficiency and low cost, and has an activity of up to 6.3×10 8 g(PE)·mol -1 (Ti) h -1 Therefore, the present invention is original and innovative and can enhance the competitiveness of my country's polyolefin polymer material technology market. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the crystal structure diagram of the metal catalyst 3-TiCl3.

[0017] Figure 2 This is the crystal structure diagram of the metal catalyst 4-ZrCl3.

[0018] Figure 3 This is the GPC chart of the bimodal polyethylene prepared in Example 9.

[0019] Figure 4 This is the GPC chart of the bimodal polyethylene prepared in Example 19.

[0020] Figure 5 This is the GPC chart of the bimodal polyethylene prepared in Example 20.

[0021] Figure 6 This is the GPC chart of the bimodal polyethylene prepared in Example 21.

[0022] Figure 7 This is the GPC chart of the unimodal polyethylene prepared in Control Experiment 1.

[0023] Figure 8 This is the GPC chart of the unimodal polyethylene prepared in Control Experiment 2.

[0024] Fig. 9 This is the GPC chart of the unimodal polyethylene prepared in Control Experiment 3. DETAILED DESCRIPTION

[0025] The present invention is further described by way of examples, but the present invention is not limited thereto. The examples of the present invention can enable those skilled in the art to understand the present invention more comprehensively.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0027] In the present invention, 2,6- i Pr-C6H3-NH-C6H4-N=CH-C6H2-3,5- t Bu-2-OH(1-L),2,6-Me-C6H3-NH-C6H4-N=CH-C6H2-3,5- t Bu-2-OH(2-L),C6H5-NH-C6H4-N=CH-C6H2-3,5- t Bu-2-OH(3-L),2,6-F-C6H3-NH-C6H4-N=CH-C6H2-3,5- t Bu-2-OH (4-L) was synthesized according to the method reported in Chin. J. Chem. 2022, 40, 2785-2793.

[0028] The present invention is described below with reference to specific embodiments.

[0029] Example 1. Preparation of Metal Catalyst 1-TiCl3

[0030] Under a nitrogen atmosphere, 1-L ligand (0.97 g, 2.00 mmol) and 1 molar equivalent of NaH were stirred in toluene at room temperature overnight, and then 1 molar equivalent of TiCl4 was added and stirred at 110°C for 72 hours. After returning to room temperature, the mixture was filtered first, and the filtrate was drained of the solvent and washed with 5 mL of anhydrous n-hexane to obtain the metal catalyst 1-TiCl3 (1.02 g, 1.60 mmol, yield 80%). 1 H NMR(C6D6): δ8.22(s,1H,N=CH),8.06(s,1H,NH),7.71(d,J=2.4Hz,1H,Ar-H),7.35–7.25(m,3H,A r-H),6.98(d,J=2.3Hz,1H,Ar-H),6.82(d,J=8.1Hz,1H,Ar-H),6.76(t,J=7.2Hz,1H,Ar-H),6.61( t,J=7.2Hz,1H,Ar-H),5.96(dd,J=8.2,0.8Hz,1H,Ar-H),3.54(sept,J=6.8Hz,2H,CHMe2),1.61(d ,J=6.8Hz,6H,CHCH3CH3),1.57(s,9H,CMe3),1.27(s,9H,CMe3),1.10(d,J=6.8Hz,6H,CHCH3CH3). 13CNMR (100MHz, C6D6): δ166.17 (N=CH),157.97,155.04,152.35,144.70,142.02,139.07,138.37,131.72,129.55,129 .35,128.56,124.84,123.22,121.21,114.98,112.97,35.52,34.60,31.34,29.57,28.92,25.24,24.70.Anal.Calcd for C 33 H 43 Cl3N2OTi:C,62.13;H,6.79;N,4.39.Found:C,62.03;H,6.83;N,4.32.

[0031] Example 2. Preparation of Metal Catalyst 2-TiCl3

[0032] The experimental steps were the same as those in Example 1, and 2-L ligand was used as the raw material to obtain compound 2-TiCl3 as a reddish brown solid (0.940 g, 1.62 mmol, yield 81%). 1 H NMR (400MHz, C6D6): δ8.20(s,1H,N=CH),8.07(s,1H,NH),7.71(d,J=2.4Hz,1H,Ar-H),7.15–7.07(m,3H,Ar-H),6.98(d,J=2.4Hz,1H,Ar-H),6.75– 6.71(m,2H,Ar-H),6.57(ddd,J=8.3,7.2,1.2Hz,1H,Ar-H),5.84(d,J=8.1Hz,1H,Ar-H),2.44(s,6H,Ar-Me),1.56(s,9H,CMe3),1.27(s,9H,CMe3). 13 C NMR (100MHz, C6D6): δ165.81 (N=CH), 158.28, 154.70, 153.14, 144.77, 139.72, 138.36, 132.08, 130.16, 128. 64,128.17,127.93,127.53,123.26,121.17,114.98,111.26,35.50,34.60,31.33,29.65,19.12.Anal.Calcd for C 29 H 35 Cl3N2OTi:C,59.86;H,6.05;N,4.80.Found:C,59.80;H,6.00;N,4.74.

[0033] Example 3. Preparation of Metal Catalyst 3-TiCl3

[0034] The experimental steps were the same as those in Example 1, and 3-L ligand was used as the raw material to obtain compound 3-TiCl3 as a reddish brown solid powder (0.89 g, 1.60 mmol, yield 80%). 1 H NMR (400MHz, CDCl3) δ8.87(s,1H,N=CH),8.70(s,1H,NH),7.71(d,J=2.3Hz,1H,Ar-H),7.63(dd,J=6.0,2.2Hz,2H,Ar-H),7.52(d,J=2 .3Hz,1H,Ar-H),7.49–7.32(m,5H,Ar-H),7.33–7.28(m,1H,Ar-H),7.19(d,J=8.0Hz,1H,Ar-H),1.52(s,9H,CMe3),1.37(s,9H,CMe3). 13 C NMR (100MHz, CDCl3) δ160.18 (N=CH),159.91,148.01,144.66,144.05,140.51,136.81,132.80,130.73,1 30.39,129.21,127.07,126.79,126.23,123.83,123.78,117.07,35.55,34.94,31.35,29.87.Anal.Calcd for C 27 H 31 Cl3N2OTi· 1 / 2CH2Cl2:C,55.40;H,5.41;N,4.70.Found:C,55.81;H,5.81;N,4.50.

[0035] Example 4. Preparation of Metal Catalyst 3-ZrCl3

[0036] Weigh 3-L ligand containing aniline (0.80g, 2.00mmol) and add it to a 100mL Shrek bottle. After vacuuming on a double-row tube for 1 hour, transfer it to a glove box. Add NaH (0.054g, 2.25mmol) to the glove box, add 30mL of anhydrous toluene under a nitrogen atmosphere, the solution changes from yellow to reddish brown, and the reaction mixture is stirred at 25°C overnight. The next day, weigh 0.466g ZrCl4 (2.00mmol) in the glove box and add it to a prepared 250mL solvent storage bottle. Add 20mL of anhydrous and oxygen-free toluene under a nitrogen atmosphere, then introduce the mixed solution in the Shrek bottle into the solvent storage bottle, and continue to stir the reaction at 110°C for 48h. After the reaction solution was cooled to room temperature, the reaction mixture was transferred to a 100 mL Shrek bottle with a double needle. After filtering with a single needle, the filtrate was drained, anhydrous n-hexane (about 5 mL×3) was added for washing, filtered, and vacuum dried to obtain a reddish-brown solid 3-ZrCl3 (1.03 g, 1.72 mmol, yield 86%). 1 H NMR (400MHz, CDCl3) δ8.87(s,1H,N=CH),8.07(s,1H,,NH),7.74(d,J=2.4Hz,1H,Ar-H),7.63–7.58(m,3H,Ar-H),7.51(t,J=7.9Hz,2H,Ar-H), 7.45(dd,J=4.9,2.0Hz,2H,Ar-H),7.38(dt,J=8.6,4.4Hz,2H,Ar-H),7.23(dd,J=8.0,1.2Hz,1H,Ar-H),1.51(s,9H,CMe3),1.37(s,9H,CMe3). 13 C NMR (100MHz, CDCl3) δ164.94 (N=CH),157.05,145.27,144.34,138.83,138.71,138.59,133.71,130.88,1 30.21,129.67,129.24,127.78,124.44,124.03,123.66,118.27,35.47,34.70,31.44,29.77.Anal.Calcd forC 27 H 31 Cl3N2OZr·CH2Cl2:C,49.31;H,4.88;N,4.11.Found:C,50.02;H,5.06;N,3.97.

[0037] Example 5. Preparation of Metal Catalyst 4-ZrCl3

[0038] The experimental steps were the same as those in Example 4, and 4-L ligand was used as the raw material to obtain compound 4-ZrCl3 as a reddish brown solid powder (1.11 g, 1.76 mmol, yield 88%). 1 H NMR (400MHz, CDCl3) δ8.95(s,1H,N=CH),8.28(s,1H,,NH),7.74(d,J=2.4Hz,1H, Ar-H),7.67(d,J=7.8Hz,1H,Ar-H),7.50(dd,J=15.1,4.9Hz,2H,Ar-H),7.40(t,J =8.2Hz,1H,Ar-H),7.30(ddd,J=8.8,6.1,2.7Hz,1H,Ar-H),7.17(dd,J=6.3,1.7 Hz,1H,Ar-H),7.07(t,J=7.8Hz,2H,Ar-H),1.51(s,9H,CMe3),1.36(s,9H,CMe3). 13 C NMR (100MHz, CDCl3) δ164.76 (N=CH),157.52,145.30,143.44,138.60,138.03,136.98,134.00,131.37,1 29.97,129.86,129.19,128.38,125.45,125.26,124.04,117.96,35.50,34.71,31.43,29.83.Anal.Calcd for C 27 H 29 Cl3F2N2OZr· 1 / 6Tol 1 / 6C6H 14 :C,52.85;H,4.97;N,4.23. Found:C,52.88;H,4.89;N,4.16.

[0039] Example 6. Preparation of Metal Catalyst 3-HfCl3

[0040] The experimental steps were the same as those in Example 4, using 3-L ligand and HfCl4 as raw materials to obtain compound 3-HfCl3 as a yellow solid powder (1.16 g, 1.70 mmol, yield 85%). 1H NMR (400MHz, CDCl3) δ8.88(s,1H,N=CH),7.90(s,1H,,NH),7.77(d,J=2.4Hz,1H,Ar-H),7.61(d,J=8.0Hz,1H,Ar-H),7.55(d,J=8.0Hz,2H,Ar-H),7.4 8(t,J=7.7Hz,3H,Ar-H),7.44(d,J=7.1Hz,1H,Ar-H),7.38(t,J=7.4Hz,2H,Ar-H),7.21(d,J=7.9Hz,1H,Ar-H),1.50(s,9H,CMe3),1.36(s,9H,CMe3). 13 C NMR (100MHz, CDCl3) δ165.33 (N=CH),157.45,144.70,144.15,139.54,139.11,138.68,134.06,130.76,1 30.07,129.73,129.41,127.67,124.97,123.91,123.80,118.31,35.39,34.60,31.45,29.72.Anal.Calcd for C 27 H 31 Cl3N2OHf·CH2Cl2:C,43.71;H,4.32;N,3.64.Found:C,44.17;H,4.65;N,3.41.

[0041] Example 7: 1-TiCl3 catalyzed ethylene polymerization

[0042] The autoclave was connected to a high-pressure pipeline to remove nitrogen and replace ethylene three times. 195 mL of toluene was added under ethylene atmosphere, and 3.4 mL of co-catalyst was injected with a syringe to make Al / Ti=2500, ethylene pressure 40 atm, and temperature 50°C. In a glove box, 1.2 mg (2 μmol) of 1-TiCl3 complex was added to a 10 mL sample bottle equipped with a magnetic stirrer, 5 mL of anhydrous toluene was taken with a syringe, added to the sample bottle and stirred for 5 minutes to dissolve it, and the above catalyst toluene solution was injected into the main catalyst feed tank with a syringe, and the main catalyst was pressed in with a nitrogen pressure of 45 atm (total volume 200 mL), and the ethylene pressure of 40 atm was maintained at 50°C, and the reaction was stirred vigorously for 2 minutes. The reaction solution was neutralized with 10 mL of ethanol solution acidified with hydrochloric acid to obtain a polymer precipitate, which was washed with ethanol, and the polymer was vacuum dried overnight and weighed. Polymerization activity: 4.6×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 340 kg·mol -1, Mw / Mn=4.1, bimodal distribution.

[0043] Example 8: Ethylene polymerization catalyzed by 2-TiCl3

[0044] The polymerization process and reaction conditions were the same as in Example 7, and the catalyst used was 2-TiCl3. Polymerization activity: 71×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 260 kg·mol -1 , Mw / Mn=4.2, bimodal distribution.

[0045] Example 9: Ethylene polymerization catalyzed by 3-TiCl3

[0046] The polymerization process and reaction conditions were the same as in Example 7, and the catalyst used was 3-TiCl3. Polymerization activity: 165×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 86 kg·mol -1 , Mw / Mn=4.1, bimodal distribution.

[0047] Example 10: Ethylene polymerization catalyzed by 3-ZrCl3

[0048] The polymerization process and reaction conditions were the same as in Example 7, and the catalyst used was 3-ZrCl3. Polymerization activity: 630x10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 19 kg·mol -1 , Mw / Mn=28.9, bimodal distribution.

[0049] Example 11: Ethylene polymerization catalyzed by 4-ZrCl3

[0050] The polymerization process and reaction conditions were the same as in Example 7, and the catalyst used was 4-ZrCl3. Polymerization activity: 360x10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 129 kg·mol -1 , Mw / Mn=59.1, bimodal distribution.

[0051] Example 12: Ethylene polymerization catalyzed by 3-HfCl3

[0052] The polymerization process and reaction conditions were the same as in Example 7, and the catalyst used was 3-HfCl3. Polymerization activity: 60x10 6 g·mol -1 (Ti) h-1 .Polymer Mw = 315 kg·mol -1 , Mw / Mn=66.0, bimodal distribution.

[0053] Example 14: Ethylene polymerization catalyzed by 3-TiCl3

[0054] The polymerization process and reaction conditions were the same as in Example 7, the catalyst used was 3-TiCl3, and the polymerization temperature was 70°C. Polymerization activity: 69×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 111 kg·mol -1 , Mw / Mn=2.9, bimodal distribution.

[0055] Example 15: Ethylene polymerization catalyzed by 3-TiCl3

[0056] The polymerization process and reaction conditions were the same as in Example 7, the catalyst used was 3-TiCl3, and the polymerization temperature was 90°C. Polymerization activity: 57×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 128 kg·mol -1 , Mw / Mn=6.1, bimodal distribution.

[0057] Example 16: Ethylene polymerization catalyzed by 3-TiCl3

[0058] The polymerization process and reaction conditions were the same as in Example 7, the catalyst used was 3-TiCl3, and the polymerization temperature was 110°C. Polymerization activity: 48.6×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 197 kg·mol -1 , Mw / Mn=4.1, bimodal distribution.

[0059] Example 17: Ethylene polymerization catalyzed by 3-TiCl3

[0060] The polymerization process and reaction conditions were the same as in Example 7, the catalyst used was 3-TiCl3, and the polymerization temperature was 130°C. Polymerization activity: 39.8×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 238 kg·mol -1 , Mw / Mn=4.2, bimodal distribution.

[0061] Example 18: Ethylene polymerization catalyzed by 3-TiCl3

[0062] The polymerization process and reaction conditions were the same as in Example 7, the catalyst used was 3-TiCl3, and the polymerization temperature was 150°C. Polymerization activity: 32.0×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 270 kg·mol -1 , Mw / Mn=4.2, bimodal distribution.

[0063] Example 19: Ethylene polymerization catalyzed by 3-TiCl3

[0064] The polymerization process and reaction conditions were the same as in Example 9, and the polymerization time was 10 min. Polymerization activity: 60.3×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 377 kg·mol -1 , Mw / Mn=5.3, bimodal distribution.

[0065] Example 20: Ethylene polymerization catalyzed by 3-TiCl3

[0066] The polymerization process and reaction conditions were the same as in Example 9, and the polymerization time was 20 min. Polymerization activity: 45.3×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 520 kg·mol -1 , Mw / Mn=4.8, bimodal distribution.

[0067] Example 21: Ethylene polymerization catalyzed by 3-TiCl3

[0068] The polymerization process and reaction conditions were the same as in Example 9, and the polymerization time was 30 min. Polymerization activity: 39.4×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 723 kg·mol -1 , Mw / Mn=4.6, bimodal distribution.

[0069] A control experiment was carried out using the catalyst shown in formula (III) to synthesize unimodal polyethylene.

[0070]

[0071] Control experiment 1, 3-TiCl2 catalyzed ethylene polymerization

[0072] The polymerization process and reaction conditions were the same as in Example 9, and the catalyst used was 3-TiCl2. Polymerization activity: 132×10 6 g·mol-1 (Ti) h -1 . Polymer Mw = 439 kg·mol -1 , Mw / Mn=1.8, unimodal distribution.

[0073] Control experiment 2, 3-TiCl2 catalyzed ethylene polymerization

[0074] The polymerization process and reaction conditions were the same as in Example 19, and the catalyst used was 3-TiCl2. Polymerization activity: 69.3×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 759 kg·mol -1 , Mw / Mn=1.2, unimodal distribution.

[0075] Control experiment 3, 3-TiCl2 catalyzed ethylene polymerization

[0076] The polymerization process and reaction conditions were the same as in Example 20, and the catalyst used was 3-TiCl2. Polymerization activity: 51.0×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 1160 kg·mol -1 , Mw / Mn=1.2, unimodal distribution.

[0077] Control experiment 4: Ethylene polymerization catalyzed by 1-TiCl2

[0078] The polymerization process and reaction conditions were the same as in Example 9, and the catalyst used was 1-TiCl2. Polymerization activity: 30×10 6 g·mol -1 (Ti) h -1 . Polymer Mw = 1020 kg·mol -1 , Mw / Mn=1.2, unimodal distribution.

[0079] Control experiment 5: Ethylene polymerization catalyzed by 2-TiCl2

[0080] The polymerization process and reaction conditions were the same as in Example 9, and the catalyst used was 2-TiCl2. Polymerization activity: 35×10 6 g·mol -1 (Ti) h -1 .Polymer Mw = 424 kg·mol -1 , Mw / Mn=1.3, unimodal distribution.

Claims

1. A method for synthesizing bimodal polyethylene in one pot, characterized in that: The method for synthesizing bimodal polyethylene requires the use of a metal catalyst represented by formula (I), 2. The method according to claim 1, characterized in that: The method for synthesizing bimodal polyethylene further comprises adding a co-catalyst, which is one or more of tripentafluorophenyl boron, triphenylcarbonium tetrakis(pentafluorophenyl)borate, aluminoxane, alkylaluminum and alkylaluminum chloride.

3. The method according to claim 2, characterized in that: The aluminoxane is methylaluminoxane, ethylaluminoxane or isobutylaluminoxane; the alkylaluminum is trimethylaluminum, triethylaluminum, triisobutylaluminum or tri-n-hexylaluminum; and the alkylaluminum chloride is diethylaluminum monochloride, diethylaluminum sesquichloride or ethylaluminum dichloride.

4. The method according to claim 1, characterized in that: The polymerization temperature is 0-180° C., the polymerization pressure is 0.1-5 MPa, and the polymerization solvent is one or more of toluene, hexane, and heptane.

5. The method for preparing the catalyst according to claim 1, as shown in formula (II), comprises the following steps: Under a nitrogen atmosphere, 1 molar equivalent of 1-L or 2-L or 3-L or 4-L ligand and 1 molar equivalent of NaH were stirred in toluene at room temperature overnight, and then 1 molar equivalent of MCl4 was added, and stirring was continued at 110°C for 72 hours. After returning to room temperature, the mixture was filtered, and the filtrate was drained of the solvent and washed with 5 mL of anhydrous n-hexane to obtain the metal catalyst.

Images