A method for preparing bimodal ultra-high molecular weight polyethylene in one pot

Abstract

The application discloses an ONN-Ti / ONN-Cr bimetallic co-loaded heterogeneous catalyst and a method for preparing bimodal ultra-high molecular weight polyethylene (UHMWPE) in one pot. The catalyst uses inorganic oxide pretreated by alkyl aluminum as a carrier, and ONN-Ti catalyst for generating high molecular weight polyethylene components and ONN-Cr catalyst for generating low molecular weight polyethylene components are co-anchored on the surface of the same carrier. The carrier is selected from SiO2, MgO or ZnO, the pretreatment agent is selected from MAO, i Bu3Al or AlEtCl2. By adjusting the loading molar ratio of ONN-Ti and ONN-Cr, bimodal UHMWPE can be prepared in one pot in a single reactor. When the loading molar ratio of ONN-Ti / ONN-Cr is 1 / 1, the obtained polyethylene has a bimodal molecular weight distribution, and the overall weight average molecular weight M w is 1446*10 3 g·mol ‑1 , the molecular weight distribution D is 6.3, the high molecular weight component M w is 2180*10 3 g·mol ‑1 , and the low molecular weight component M w is 179*10 3 g·mol ‑1 ; the tensile strength of the bimodal UHMWPE material can reach 50 MPa, the elongation at break can reach 1400%, and the complex viscosity is lower than that of unimodal UHMWPE. In addition, the application can also improve the reactor fouling in slurry polymerization and control the morphology of the obtained polymer particles by co-loading, and is suitable for efficient preparation of bimodal UHMWPE.

Description

Technical Field

[0001] This invention belongs to the fields of polyolefin catalysts, heterogeneous olefin polymerization and high-performance polyethylene material preparation, specifically relating to an ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst and a one-pot method for preparing bimodal ultra-high molecular weight polyethylene. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) possesses excellent impact resistance, abrasion resistance, and chemical stability, and is widely used in fields such as artificial joints, bulletproof vests, and high-performance fibers. Prog. Polym. Sci. 2020, 109 , 101290; Eur Polym J. 2020, 125 , 109529). However, UHMWPE molecular chains are extremely long and highly entangled, resulting in extremely high melt viscosity, making it difficult to directly mold using traditional thermoplastic processing techniques ( Polym. Test. 2005, 24, 909).

[0003] To improve its processing fluidity, one strategy is to design novel catalysts to prepare low-entanglement UHMWPE ( Macromolecules 2018, 51 , 4541; Angew. Chem., Int. Ed. 2023, 62 Another strategy is to introduce inorganic fillers or low molecular weight polyolefins through physical blending (e202215582); Polymer 2019, 165 , 61; J. Appl. Polym. Sci. 2017, 134 , 26). However, physical blending struggles to significantly improve processing fluidity while maintaining excellent mechanical properties ( J. Catal. 2018, 360 (145). Constructing a bimodal molecular weight distribution is an important method for improving the processing properties of UHMWPE. Bimodal polyethylene contains both high molecular weight components (providing strength) and low molecular weight components (reducing melt viscosity), which can achieve a synergistic improvement in processing and mechanical properties. Chem. Rev. 2016, 116 , 1398; ACS Appl. Polym. Mater. 2024, 21 (13210). Currently, the industrial production of bimodal polyethylene typically employs multi-stage reactors in series or multi-catalyst parallel processes, which are complex and require sophisticated equipment. Furthermore, homogeneous catalysts in slurry polymerization are prone to problems such as reactor sticking, scaling, and uncontrollable polymer morphology.

[0004] In recent years, by using a co-anchoring strategy to co-load two catalysts with different properties onto the same solid support (such as SiO2, MgO, TiO2), bimodal polyethylene can be directly prepared in a single reactor, while simultaneously improving polymer particle morphology and inhibiting reactor scaling. Macromolecules 2018, 51 (49). However, there are no reports on applying such co-anchored supported catalyst systems to UHMWPE and systematically studying the effects of their bimodal structure on mechanical properties, rheological properties and processing properties.

[0005] Therefore, developing a supported bimetallic catalyst system that can directly prepare bimodal UHMWPE in a single reactor while improving reactor scaling and particle morphology, and achieving a balance between high strength, high toughness and excellent processing flowability, has significant scientific and industrial application value. Summary of the Invention

[0006] A heterogeneous catalyst supported on an ONN-Ti / ONN-Cr bimetallic substrate has the catalyst structure shown in formula (I): (I).

[0007] The above-mentioned ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst is characterized in that it comprises an inorganic oxide support, an ONN-Ti catalyst and an ONN-Cr catalyst supported on the surface of the inorganic oxide support.

[0008] The above-mentioned ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst is characterized in that the inorganic oxide support is selected from one or more of SiO2, MgO, and ZnO.

[0009] The above-mentioned ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst is characterized in that the inorganic oxide support needs to be pretreated, the pretreatment comprising: activating the inorganic oxide support at 400-600 °C for 2-8 h, cooling it and reacting it in toluene with alkylaluminum or aluminum oxane in a molar equivalent of 1.0-3.0 molar equivalents relative to the hydroxyl groups on the support surface for 2-8 h, followed by washing with n-hexane and drying; wherein the alkylaluminum or aluminum oxane is selected from one or more of methylaluminoxane, triisobutylaluminum, and diethylaluminum chloride.

[0010] The above-mentioned ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst is characterized in that the total loading of the ONN-Ti catalyst and the ONN-Cr catalyst on the support is 0.1-100% based on the metal content. m The loading molar ratios of ONN-Ti and ONN-Cr were 1 / 1, 1 / 5, 1 / 10, and 1 / 20, respectively, with a carrier loading of mol / g.

[0011] This invention also provides a one-pot method for preparing bimodal ultra-high molecular weight polyethylene, characterized in that, in the presence of a co-catalyst, the above-mentioned ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst is used to catalyze the homopolymerization of ethylene, wherein the ONN-Ti catalyst is used to catalyze the generation of high molecular weight polyethylene components from ethylene, and the ONN-Cr catalyst is used to catalyze the generation of low molecular weight polyethylene components from ethylene, thereby obtaining bimodal ultra-high molecular weight polyethylene.

[0012] The method for preparing bimodal ultra-high molecular weight polyethylene in one pot as described above is characterized in that the polymerization reaction is carried out in hexane, toluene, heptane or a combination thereof; the polymerization temperature is 30-110 °C, the ethylene pressure is 10-40 atm, and the polymerization time is 2-60 min; the co-catalyst is methylaluminoxane.

[0013] The method for preparing bimodal ultra-high molecular weight polyethylene using the above one-pot method is characterized in that the weight-average molecular weight of the obtained bimodal ultra-high molecular weight polyethylene is 184 × 10⁻⁶. 3 ~2743 × 10 3 g·mol -1 The molecular weight distribution is 2.1–20.8; the weight-average molecular weight of the high molecular weight component is 1865 × 10⁻⁶. 3 ~2180 × 10 3 g·mol -1 The weight-average molecular weight of the low molecular weight component is 179 × 10⁻⁶. 3 ~256 × 10 3 g·mol -1 .

[0014] The method for preparing bimodal ultra-high molecular weight polyethylene in one pot as described above is characterized in that the obtained bimodal ultra-high molecular weight polyethylene has a tensile strength of 45-55 MPa, an elongation at break of 1300-1500%, and a lower complex viscosity compared to unimodal ultra-high molecular weight polyethylene.

[0015] The present invention has the following beneficial effects: First, by utilizing the differentiated chain growth behavior of ONN-Ti and ONN-Cr, bimodal UHMWPE can be prepared in a single reactor in one step; Second, carrier loading can significantly inhibit fouling in the reactor and improve the morphology of polymer particles; Third, the Ti / Cr ratio can control the bimodal structure and the content of low molecular weight components; Fourth, when the Ti / Cr ratio is 1 / 1, the material has both high strength and high toughness, with a tensile strength of up to 50 MPa and an elongation at break of up to 1400%; Fifth, after introducing an appropriate amount of low molecular weight components, the complex viscosity is reduced and the processing fluidity is improved. Attached Figure Description

[0016] Figure 1 This is a flowchart of the carrier activation and alkylaluminum / aluminoxane pretreatment process.

[0017] Figure 2 The bimodal UHMWPE peak distribution results are shown for the ONN-Ti / ONN-Cr co-loaded system.

[0018] Figure 3 Stress-strain curves of polyethylene obtained with different Ti / Cr ratios are shown.

[0019] Figure 4 The curves show the comparison of complex viscosity between unimodal and bimodal UHMWPE. Detailed Implementation

[0020] The present invention is further illustrated by examples, but is not limited thereto. These examples will enable those skilled in the art to gain a more comprehensive understanding of the invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0022] Unless otherwise specified, all raw materials and reagents described below are commercially available finished products.

[0023] The synthesis of the ONN-Ti catalyst and ONN-Cr catalyst in this invention is based on the methods described in the literature (Chin. J. Chem. 2022, 2785; Polym. Chem. 2022, 13, 1852; Inorg. Chem. Front. 2024, 11, 613; Inorg. Chem. 2024, 63, 18137).

[0024] The present invention is described below with reference to specific embodiments.

[0025] Example 1 Synthesis of ONN-Ti catalyst Under a nitrogen atmosphere, the ligand (1.1 g, 2.4 mmol) was added to a 100 mL Schlenk flask, dissolved in 40 mL of anhydrous toluene, and then n-butyllithium was added over 5 minutes using a syringe at -78 °C. nBuLi (1.1 mL, 2.7 mmol, 2.5 M hexane solution). The mixture was gradually brought to room temperature and stirred overnight. At -78°C, a TiCl4 solution (0.26 mL, 2.4 mmol) dissolved in toluene (10 mL) was slowly added to the mixture. The resulting mixture was stirred further overnight at room temperature and filtered at room temperature. The filtrate was dried under reduced pressure to give a red solid, which was washed with hexane (3 × 10 mL) to give the desired ONN-Ti, 0.92 g, in 50% yield.

[0026] Example 2 Synthesis of ONN-Cr catalyst 3,5-Di-tert-butylsalicylaldehyde (4.69 g, 20.0 mmol) and p-toluenesulfonic acid (60 mg) were added to a methanol solution of N-(2,6-diisopropylphenyl)phenyl-1,2-diamine (5.37 g, 20.0 mmol). The mixture was stirred at room temperature for 18 h to obtain a yellow suspension. The suspension was concentrated and filtered to obtain a yellow solid (7.56 g, 15.9 mmol, yield 84%).

[0027] Example 3 Inorganic carrier surface treatment and activation SiO2, MgO, or ZnO were placed in a high-temperature resistant crucible and dried and activated at 500 °C for 4 h. After cooling, they were stored in a glove box for later use. Me3SiCH2Li was reacted with the hydroxyl groups on the support surface, with ferrocene as an internal standard. 1 The surface hydroxyl content was determined by ¹H NMR. The measured hydroxyl content of SiO₂ surface was approximately 1.78 × 10⁻⁶. -3 mol·g -1 The amount of MgO is approximately 1.12 × 10⁻⁶. -3 mol·g -1 ZnO is approximately 1.02 × 10⁻⁶. -3 mol·g -1 .

[0028] The activated carrier was immersed in toluene, and MAO with a molar equivalent of 1.5 moles relative to the surface hydroxyl groups was added respectively. i Bu3Al or AlEtCl2 was stirred at room temperature for 5 h. After standing, the supernatant was removed, and the mixture was washed 3-5 times with n-hexane. The solvent was then removed to obtain the carriers MAO@SiO2 and... i Bu3Al@SiO2, EtAlCl2@SiO2.

[0029] Example 4 Preparation of supported ONN-Ti catalyst The ONN-Ti catalyst was weighed according to the aluminum content or the amount of reactive sites on the surface of the support, stirred in toluene with the pretreated support at room temperature for 2 min, filtered and dried to obtain the supported ONN-Ti catalyst.

[0030] Example 5 Preparation of ONN-Ti / ONN-Cr co-supported catalyst MAO@SiO2 was selected as the support. ONN-Ti and ONN-Cr were added to toluene at a predetermined molar ratio and stirred with MAO@SiO2 at room temperature to anchor both catalysts onto the support surface. The Ti / Cr molar ratio could be set to 1 / 1, 1 / 5, or 1 / 10. After filtration and drying, the ONN-Ti / ONN-Cr-MAO@SiO2 bimetallic co-supported catalyst was obtained, which could also be used directly in the form of a suspension for polymerization reactions.

[0031] The following examples [6-7] demonstrate the preparation of ultra-high molecular weight polyethylene using homogeneous ONN-Ti and ONN-Cr catalysts.

[0032] Example 6 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous toluene was added, followed by the injection of methylaluminoxane using a syringe. The Al / Ti ratio was 1000, the ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 2... m 5 mL of anhydrous toluene was added to a sample vial and stirred until dissolved. The toluene solution was then injected into the main catalyst feed tank using a syringe. The main catalyst was forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 120 mg of the obtained polymer was obtained, with a polymerization activity of 1.8 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 2.74 million and a molecular weight distribution of 3.5. The material has a tensile strength of up to 35 MPa and an elongation at break of up to 850%.

[0033] Example 7 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous toluene was added, followed by the injection of methylaluminoxane using a syringe. The Al / Ti ratio was 1000, the ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 2... m5 mL of anhydrous toluene was added to a sample vial and stirred until dissolved. The toluene solution was then injected into the main catalyst feed tank using a syringe. The main catalyst was forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 180 mg of the obtained polymer was observed, with a polymerization activity of 2.7 × 10⁻⁶. 6 g·mol -1 ·h -1 The molecular weight is 180,000, and the molecular weight distribution is 2.1.

[0034] The following examples [8-16] demonstrate the preparation of ultra-high molecular weight polyethylene using heterogeneous ONN-Ti catalysts.

[0035] Example 8 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A mol) ONN-Ti metal catalyst (Ti-MAO@SiO2) was supported on a sample vial. 5 mL of anhydrous n-hexane was added to the vial using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 180 mg of the obtained polymer was obtained, with a polymerization activity of 2.7 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 2.76 million and a molecular weight distribution of 3.5.

[0036] Example 9 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m mol) supported ONN-Ti metal catalyst (Ti- i(Bu3Al@SiO2) Using a syringe, 5 mL of anhydrous n-hexane was added to the sample vial and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feeding vessel using a syringe. The main catalyst was forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 200 mg of the obtained polymer was obtained, with a polymerization activity of 3.0 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 1.63 million and a molecular weight distribution of 3.8.

[0037] Example 10 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A mol) ONN-Ti metal catalyst (Ti-AlEtCl2@SiO2) was supported on a sample vial. 5 mL of anhydrous n-hexane was added to the vial using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 230 mg of the obtained polymer was obtained, with a polymerization activity of 3.4 × 10⁻⁶. 6 g·mol -1 ·h -1 The molecular weight is 1.73 million, and the molecular weight distribution is 3.4.

[0038] Example 11 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. mA mol) ONN-Ti metal catalyst (Ti-MAO@MgO) was supported on a sample vial. 5 mL of anhydrous n-hexane was added to the vial using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 190 mg of the obtained polymer was obtained, with a polymerization activity of 2.8 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 1.4 million and a molecular weight distribution of 3.2.

[0039] Example 12 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m mol) supported ONN-Ti metal catalyst (Ti- i Using a syringe, 5 mL of anhydrous n-hexane was added to a sample vial and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst (total volume 200 mL) was forced in using nitrogen gas at 45 atm. The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 140 mg of the obtained polymer was observed, with a polymerization activity of 2.1 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 1.44 million and a molecular weight distribution of 3.5.

[0040] Example 13 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. mA mol) ONN-Ti metal catalyst (Ti-AlEtCl2@MgO) was supported on a sample vial. 5 mL of anhydrous n-hexane was added to the vial using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 260 mg of the obtained polymer was obtained, with a polymerization activity of 3.9 × 10⁻⁶. 6 g·mol -1 ·h -1 The molecular weight is 1.61 million, and the molecular weight distribution is 3.2.

[0041] Example 14 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A mol) ONN-Ti metal catalyst (Ti-MAO@ZnO) was supported on a sample vial. 5 mL of anhydrous n-hexane was added using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 110 mg of the obtained polymer was obtained, with a polymerization activity of 1.2 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 1.62 million and a molecular weight distribution of 3.6.

[0042] Example 15 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m mol) supported ONN-Ti metal catalyst (Ti- iUsing a syringe, 5 mL of anhydrous n-hexane was added to a sample vial and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst (total volume 200 mL) was forced in using nitrogen gas at 45 atm. The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 120 mg of the obtained polymer was found, with a polymerization activity of 1.8 × 10⁻⁶. 6 g·mol -1 ·h -1 It has a molecular weight of 1.47 million and a molecular weight distribution of 3.4.

[0043] Example 16 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A mol) ONN-Ti metal catalyst (Ti-AlEtCl2@ZnO) was supported on a sample vial. 5 mL of anhydrous n-hexane was added to the vial using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 350 mg of the obtained polymer was obtained, with a polymerization activity of 5.2 × 10⁻⁶. 6 g·mol -1 ·h -1 The molecular weight is 2.05 million, and the molecular weight distribution is 3.5.

[0044] The following examples [17-20] demonstrate the preparation of bimodal ultra-high molecular weight polyethylene using a heterogeneous ONN-Ti / ONN-Cr bimetallic catalyst.

[0045] Example 17 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m5 mL of anhydrous n-hexane was injected into a sample vial using a syringe to form a suspension. The catalyst toluene solution was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 310 mg of the obtained polymer was observed, with a polymerization activity of 4.6 × 10⁻⁶. 6 g·mol -1 ·h -1 The molecular weight is 350,000, and the molecular weight distribution is 2.1.

[0046] Example 18 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A 1 / 10 mol) ONN-Ti / ONN-Cr metal catalyst (Ti / Cr-MAO@SiO2) was supported on a sample vial. 5 mL of anhydrous n-hexane was added using a syringe and stirred to form a suspension. The toluene solution of the catalyst was injected into the main catalyst feeding vessel using a syringe. The main catalyst was then forced in using nitrogen gas at 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 290 mg of the obtained polymer was obtained, with a polymerization activity of 4.3 × 10⁻⁶. 6 g·mol -1 ·h -1 Molecular weight 1.44 million, molecular weight distribution 6.3. High molecular weight component. M w Approximately 2.18 million, with a molecular weight distribution of 1.6; low molecular weight components M w The molecular weight is approximately 170,000, with a molecular weight distribution of 1.8. The tensile strength of the material can reach 50 MPa, and the elongation at break can reach 1400%. The complex viscosity is significantly lower than that of UHMWPE prepared with homogeneous ONN-Ti catalyst.

[0047] Example 19 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A 1 / 5 mol) ONN-Ti / ONN-Cr metal catalyst (Ti / Cr-MAO@SiO2) was supported on a sample vial. 5 mL of anhydrous n-hexane was added using a syringe and stirred to form a suspension. The toluene solution of the catalyst was injected into the main catalyst feeding vessel using a syringe. The main catalyst was then forced in using nitrogen gas at 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 280 mg of the obtained polymer was obtained, with a polymerization activity of 4.2 × 10⁻⁶. 6 g·mol -1 ·h -1 Molecular weight 930,000, molecular weight distribution 17.3. High molecular weight component. M w Approximately 1.99 million, with a molecular weight distribution of 1.4; low molecular weight components M w Approximately 230,000, with a molecular weight distribution of 2.2. The material has a tensile strength of up to 32 MPa and an elongation at break of up to 800%.

[0048] Example 20 The high-pressure reactor was connected to a high-pressure pipeline to remove nitrogen and purge ethylene three times. Under an ethylene atmosphere, 195 mL of anhydrous n-hexane was added, and methylaluminoxane was injected using a syringe to achieve an Al / Ti ratio of 1000. The ethylene pressure was 40 atm, and the temperature was 70 °C. In a glove box, 50 mg (2...) was added to a 10 mL sample vial equipped with a magnetic stirrer. m A 1 / 10 mol) ONN-Ti / ONN-Cr metal catalyst (Ti / Cr-MAO@SiO2) was supported on a sample vial. 5 mL of anhydrous n-hexane was added using a syringe and stirred to form a suspension. The toluene solution of the catalyst was then injected into the main catalyst feed tank using a syringe. The main catalyst was then forced in using nitrogen gas at a pressure of 45 atm (total volume 200 mL). The reaction was carried out at 70 °C with an ethylene pressure of 40 atm and vigorous stirring for 2 min. The reaction solution was neutralized with 10 mL of hydrochloric acid-acidified ethanol solution to obtain a polymer precipitate. The precipitate was washed with ethanol, vacuum dried overnight, and weighed. 250 mg of the obtained polymer was obtained, with a polymerization activity of 3.7 × 10⁻⁶. 6 g·mol -1 ·h-1 Molecular weight 650,000, molecular weight distribution 20.8. High molecular weight component. M w Approximately 1.86 million, with a molecular weight distribution of 1.6; low molecular weight components M w Approximately 250,000, with a molecular weight distribution of 3.6. The material has a tensile strength of up to 25 MPa and an elongation at break of up to 600%. The polymerization performance of each embodiment and the comparative embodiment was tested, and the results are shown in Table 1 and Table 2.

[0049] Table 1. Different reaction conditions in Examples 6-16

[0050] Table 2. Different reaction conditions in Examples 17-20

[0051] Where act. represents polymerization activity, and the unit is 10. 6 g·mol -1 ·h -1 ; M w This indicates molecular weight, with units of 10. 3 g·mol -1 , Ɖ Indicates molecular weight distribution; T m This indicates the melting point of ethylene.

Claims

1. An ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst, the catalyst structure of which is shown in formula (I): （I）。 2. The ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst according to claim 1, characterized in that, It includes an inorganic oxide support, an ONN-Ti catalyst and an ONN-Cr catalyst supported on the surface of the inorganic oxide support.

3. The ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst according to claims 1-2, characterized in that, The inorganic oxide support is selected from one or more of SiO2, MgO, and ZnO.

4. The ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst according to claims 1-2, characterized in that, The inorganic oxide support needs to undergo pretreatment, which includes: activating the inorganic oxide support at 400-600 °C for 2-8 h, cooling it, and then reacting it in toluene with alkylaluminum or aluminum oxane in a molar equivalent of 1.0-3.0 molar equivalents relative to the hydroxyl groups on the support surface for 2-8 h, followed by washing with n-hexane and drying; the alkylaluminum or aluminum oxane is selected from one or more of methylaluminoxane, triisobutylaluminum, and diethylaluminum chloride.

5. The ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst according to claims 1-2, characterized in that, The total loading of ONN-Ti and ONN-Cr catalysts on the support is 0.1-100% based on metal content. μ The loading molar ratios of ONN-Ti and ONN-Cr were 1 / 1, 1 / 5, 1 / 10, and 1 / 20, respectively, with a carrier loading of mol / g.

6. A method for preparing bimodal ultra-high molecular weight polyethylene in a one-pot process, characterized in that, In the presence of a co-catalyst, the ONN-Ti / ONN-Cr bimetallic co-supported heterogeneous catalyst of claim 1 is used to catalyze the homopolymerization of ethylene, wherein the ONN-Ti catalyst is used to catalyze the formation of high molecular weight polyethylene component from ethylene, and the ONN-Cr catalyst is used to catalyze the formation of low molecular weight polyethylene component from ethylene, thereby obtaining bimodal ultra-high molecular weight polyethylene.

7. The method according to claim 6, characterized in that, The polymerization reaction is carried out in hexane, toluene, heptane or a combination thereof; the polymerization temperature is 30-110 °C, the ethylene pressure is 10-40 atm, and the polymerization time is 2-60 min; the co-catalyst is methylaluminoxane.

8. The method according to claim 6, characterized in that, The weight-average molecular weight of the obtained bimodal ultra-high molecular weight polyethylene was 184 × 10⁻⁶. 3 ~2743 × 10 3 g·mol -1 The molecular weight distribution is 2.1–20.8; the weight-average molecular weight of the high molecular weight component is 1865 × 10⁻⁶. 3 ~2180 × 10 3 g·mol -1 The weight-average molecular weight of the low molecular weight component is 179 × 10⁻⁶. 3 ~256 × 10 3 g·mol -1 .

9. The method according to claim 6, characterized in that, The resulting bimodal ultra-high molecular weight polyethylene has a tensile strength of 45-55 MPa, an elongation at break of 1300-1500%, and a lower complex viscosity compared to unimodal ultra-high molecular weight polyethylene.

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