A low entanglement copolymer modified ultra-high molecular weight polyethylene and a method of making the same

Abstract

This invention provides a low-entanglement copolymerized modified ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 1,000,000-1,200,000, a molecular weight distribution of 2-3, a tensile strength of 55-60 MPa, and a ratio of initial elastic modulus to equilibrium elastic modulus of 0.1-0.2. The preparation method includes diluting a metallocene catalyst and a co-catalyst in a solvent (an inert alkane with a boiling point not lower than 145℃) to obtain a catalyst dilution solution; adding the solvent as a bottom liquid to a stirred reactor; and adding the catalyst dilution solution, ethylene, 1-octene, and hydrogen in a stoichiometric ratio to the reactor for polymerization at a temperature of 60-90℃ and a pressure of 0.2-0.8 MPa; the slurry discharged after polymerization is post-treated to obtain the final product. This invention, by copolymerizing ethylene and 1-octene using a long-chain alkane as a solvent, obtains high-performance, low-entanglement copolymerized modified ultra-high molecular weight polyethylene, significantly improving the product's machinability and solving problems such as polymerization difficulties, poor product performance, and low octene polymerization degree in the copolymerization of ethylene and octene.

Description

Technical Field

[0001] This invention relates to the field of polyethylene preparation technology, and in particular to a low-entanglement copolymerized modified ultra-high molecular weight polyethylene and its preparation method. Background Technology

[0002] Polyethylene is a general-purpose polyolefin resin with a wide range of applications, including films, packaging bags, toys, household appliances, automotive parts, adhesives, and engineering plastics. In particular, ultra-high molecular weight polyethylene (UHMWPE) is one of the most resilient plastics with excellent mechanical properties, and it has wide applications in transportation, textiles, mining, agriculture, and chemical industries. It is also widely used in new energy battery separators, artificial joints, and orthopedic surgical parts.

[0003] Because ultra-high molecular weight polyethylene (UHMWPE) has a much larger molecular weight than ordinary polyethylene (UHMWPE), its processing and synthesis are significantly more difficult. Its extremely long polyethylene chains exhibit extensive physical entanglement both between and within the chains, severely restricting chain movement and relaxation, increasing melt viscosity, leading to processing difficulties, and affecting mechanical properties. Compared to entangled UHMWPE, low-entanglement UHMWPE has stronger segment diffusion capabilities, resulting in products with fewer molding defects and superior mechanical properties. Currently, methods to reduce the entanglement density of nascent UHMWPE mainly involve preparing low-entanglement nascent powders based on catalyst technology, blending modification to reduce entanglement, and using solvents and force fields to disentangle during downstream processing. While chain entanglement can be controlled during blending or processing, many industrialization problems remain, such as increased production costs, increased processing difficulty, and reduced product performance. Therefore, the preparation technology of nascent low-entanglement UHMWPE is crucial, and the core lies in controlling the polymerization process.

[0004] Furthermore, in the polyethylene production process, the density and crystallinity can be reduced by adding α-olefins as comonomers (such as 1-butene, 1-hexene, 1-octene, etc.), thereby expanding its physical properties and applications. Among these, the copolymerization of ethylene with 1-butene was the first to be developed and industrialized. Due to market demand, copolymerization of ethylene with 1-hexene and 1-octene has also been developed. However, the copolymerization of ethylene with high-carbon α-olefins is difficult and requires harsh reaction conditions. Existing mature processes struggle to produce qualified products, especially low-entanglement copolymerized modified UHMWPE. Additionally, the removal of residual high-carbon α-olefins after polymerization also presents significant challenges. Therefore, further research is needed on how to prepare low-entanglement copolymerized modified UHMWPE. Summary of the Invention

[0005] The present invention aims to provide a low-entanglement copolymerized modified ultra-high molecular weight polyethylene and a method for preparing the low-entanglement copolymerized modified ultra-high molecular weight polyethylene, so as to solve the above-mentioned defects in the prior art.

[0006] This invention is achieved using the following technical solution:

[0007] A method for preparing low-entanglement copolymerized modified ultra-high molecular weight polyethylene includes the following steps:

[0008] S1. The metallocene catalyst and the co-catalyst are diluted with a solvent to obtain a catalyst dilution solution, wherein the solvent is an inert alkane with a boiling point of not less than 145°C.

[0009] S2. Add a certain amount of solvent to the stirred reactor as the bottom liquid. While maintaining continuous stirring, add the catalyst dilution, ethylene, 1-octene, and hydrogen to the stirred reactor in a metered ratio to carry out the polymerization reaction. The temperature is controlled at 60-90℃ and the pressure inside the reactor is controlled at 0.2-0.8MPa.

[0010] S3. After polymerization, the slurry discharged from the stirred reactor is post-treated to obtain the low entanglement copolymerized modified ultra-high molecular weight polyethylene.

[0011] The solvent includes cycloalkanes and alkanes, preferably cycloalkanes and / or alkanes with a boiling point of not less than 150°C and which are liquid and have low viscosity at room temperature. Long-chain alkanes of C8-C17 are preferred, more preferably long-chain alkanes of C8-C14, and even more preferably long-chain alkanes of C8-C12, such as octane, nonane, undecane, dodecane, etc.

[0012] The metallocene catalyst is a complex with a transition metal as the active center, composed of a transition metal (including iron, cobalt, nickel, titanium, zirconium, hafnium, etc.) and cyclopentadienyl groups (including cyclopentadienyl and its derivatives), such as zirconium catalysts (e.g., Cp₂ZrCl₂), titanocene catalysts (e.g., Cp₂TiCl₂), bridged metallocene catalysts (e.g., [(Cp-Me₂)₂Si]ZrCl₂), mono-cyclopentadienyl metallocene catalysts (e.g., CpZrCl₃), and other commonly used metallocene catalysts in the art. Zirconium is preferred as the transition metal, such as bis(indenylmethylene)bridged zirconium, bis(cyclopentadienyl)zirconium dichloride, and more preferably bis(cyclopentadienyl)zirconium dichloride (CAS No. 1291-32-3).

[0013] The cocatalyst is selected from alkylaluminoxanes, including but not limited to methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, tert-butylaluminoxane, tetrabutylaluminoxane, dimethylethylaluminoxane, triisopropylaluminoxane, and dimethylbutylaluminoxane. At least one of methylaluminoxane and tetrabutylaluminoxane is preferred, and methylaluminoxane is more preferred.

[0014] The molar ratio of the metallocene catalyst to the co-catalyst is 1:50-400, preferably 1:100-200.

[0015] In the catalyst dilution solution, the concentration of the metallocene catalyst in the solvent is 0.1-10 mmol / L, preferably 0.1-5 mmol / L, and more preferably 0.1-1 mmol / L.

[0016] Furthermore, the amount of catalyst diluent added is 1-5% of the volume of the liquid at the bottom of the vessel.

[0017] The amount of 1-octene added, by weight, is 5-30‰ of ethylene, preferably 5-15‰, and more preferably 5-10‰. The amount of hydrogen added is 0.1-5% of the volume of ethylene, preferably 0.1-1%.

[0018] As a preferred technical solution, in step S2, 1-octene is first added to the reactor under continuous stirring, followed by the catalyst dilution solution, and finally ethylene and hydrogen are continuously introduced to carry out the polymerization reaction.

[0019] As a further preferred technical solution, ethylene and hydrogen are added from the bottom of the stirred reactor and enter the bottom liquid.

[0020] The inventors unexpectedly discovered that by using high-boiling-point, liquid-at-room-temperature, low-viscosity cycloalkanes and / or alkanes as solvents in the above copolymerization reaction, low-entanglement copolymerized modified ultra-high molecular weight polyethylene can be obtained. The specific mechanism is not yet fully understood, but it may be due to the low solubility of ethylene in the above-mentioned long-chain alkane solvents. During the reaction, after gaseous ethylene is introduced into the solvent from the bottom of the reactor, the low concentration avoids explosive polymerization. Adjusting the relationship between the crystallization rate and the polymerization rate allows the polymerization process to proceed smoothly, resulting in a more regular polymer structure. This helps to reduce the degree of entanglement of nascent polyethylene chain segments.

[0021] Furthermore, in step S2, the polymerization temperature is preferably 70-80°C, more preferably 70-75°C.

[0022] Furthermore, in step S2, the pressure inside the vessel is preferably controlled at 0.4-0.6 MPa, more preferably at 0.45-0.55 MPa.

[0023] Furthermore, the stirred reactor in step S2 is a stirred reactor with a heat exchange jacket, and the heat exchange jacket is preferably an inner jacket.

[0024] In a further preferred embodiment, the stirred reactor is externally connected to a solvent circulation heat exchange unit, which circulates a portion of the solvent into the stirred reactor after heat exchange via a delivery pump and heat exchange equipment. The stirred reactor is provided with a circulating gas outlet at the top, and the gas is discharged from the circulating gas outlet when the pressure inside the reactor exceeds a set value.

[0025] Since polymerization is a strongly exothermic reaction, timely removal of the heat of reaction is beneficial to the preparation of low-entanglement polyethylene products. This invention effectively removes the heat of reaction and maintains the stability of the reaction temperature in the reactor by using a combination of jacketed heat removal and external circulation heat removal, which is beneficial to the preparation of low-entanglement polyethylene.

[0026] Furthermore, in step S2, the total volume of the liquid at the bottom of the reactor accounts for 1 / 4 to 2 / 3 of the total volume of the stirred reactor, preferably 1 / 3 to 1 / 2. Solvent can be added as needed during the reaction process.

[0027] Further, the post-processing described in step S3 includes the following steps: transferring the reacted slurry to a flash tank for product separation; sending the separated gaseous phase to a recovery unit; and sending the separated solid polymer to a degassing and drying unit. The dried polymer powder is then sieved and homogenized to obtain the low-entanglement copolymerized modified ultra-high molecular weight polyethylene. In the post-polymerization processing stage, due to the high boiling point of the solvent, residual 1-octene is easily separated from the solvent through distillation or flash evaporation, and the separated solvent can be recycled. Simultaneously, low molecular weight polymers are also separated, thereby improving product purity and concentrating the molecular weight distribution.

[0028] The low-entanglement copolymerized modified ultra-high molecular weight polyethylene prepared by this invention has a viscosity-average molecular weight of 1,000,000 to 1,200,000, a molecular weight distribution of 2 to 3, a tensile strength of 55 to 60 MPa, and a ratio of initial elastic modulus to equilibrium elastic modulus GNt (t = 0) of 0.1 to 0.2.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention obtains high-performance, low-entanglement copolymerized ultra-high molecular weight polyethylene by copolymerizing ethylene with 1-octene, significantly improving the product's machinability. A single-active-center metallocene catalyst is used, exhibiting high catalytic activity and increasing the conversion rate of ethylene-1-octene monomer polymerization. Long-chain alkanes are used as solvents; the low solubility of ethylene in long-chain alkane solvents ensures a stable polymerization process, preventing explosive polymerization. This helps reduce the degree of entanglement in the nascent polyethylene chain segments. In the post-polymerization treatment stage, distillation or flash evaporation, due to the high boiling point of the solvent, easily separates the residual 1-octene from the solvent. The separated solvent can be recycled, solving problems such as polymerization difficulties, poor product performance, and low octene polymerization degree in the copolymerization of ethylene and octene. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0032] The following description is provided to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples and are not intended to limit the scope of the invention; other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0033] Unless otherwise specified, all instruments and reagents used in the embodiments of this invention are conventional commercial instruments or reagents. A 2L stirred reactor, made of corrosion-resistant stainless steel, was used in the embodiments. Figure 1 As shown, the typical process flow of this invention is as follows: Solvent is added to a stirred reactor after nitrogen purging as the bottom liquid, followed by the addition of 1-octene and catalyst dilution. Ethylene and hydrogen are continuously introduced under stirring to carry out the polymerization reaction. The stirred reactor has a circulating gas outlet at the top. When the pressure inside the reactor exceeds the set pressure, the gas will be discharged from the circulating gas outlet and collected. The stirred reactor is equipped with a heat exchange jacket. During polymerization, a cooling medium (e.g., cooling water) is introduced to remove the heat of reaction in a timely manner. Additionally, a circulating heat exchange unit is connected to the outside of the stirred reactor. Part of the solvent is circulated back into the stirred reactor after heat exchange via a transfer pump and heat exchange components (e.g., a heat exchanger) to control the temperature inside the reactor. After polymerization, the slurry discharged from the stirred reactor is transferred to a flash tank for product separation, degassing, and drying. The dried polymer powder is then sieved and homogenized to obtain the final product.

[0034] Example 1

[0035] (1) In a catalyst preparation tank, the metallocene catalyst bis(cyclopentadienyl)zirconia, the co-catalyst methylaluminoxane, and the solvent octane are mixed evenly to form a catalyst dilution solution for later use. The molar ratio of bis(cyclopentadienyl)zirconia to methylaluminoxane is 1:150, and the concentration of bis(cyclopentadienyl)zirconia in octane is 0.5 mmol / L.

[0036] (2) Add about 1L of octane as bottom liquid to the stirred reactor after multiple purging with nitrogen, and heat it to about 75°C. Stir the stirred reactor at 300rpm, add about 5.5g of analytical grade 1-octene, and then add about 30ml of catalyst dilution solution. Continuously introduce 856g of ethylene and 1% of the volume of hydrogen into the stirred reactor for 3 hours. Control the pressure inside the stirred reactor at about 0.5MPa. Cooling water is introduced into the heat exchange jacket of the stirred reactor. At the same time, some of the octane is circulated for heat exchange to control the temperature inside the polymerization reactor to be maintained at 75°C.

[0037] (3) After polymerization, the slurry discharged from the stirred reactor is transferred to the flash tank for product separation. The separated light components are sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain ultra-high molecular weight polyethylene sample E1.

[0038] Example 2

[0039] (1) In a catalyst preparation tank, the metallocene catalyst bis(cyclopentadienyl)zirconia, the co-catalyst methylaluminoxane, and the solvent nonane are mixed evenly to form a catalyst dilution solution for later use. The molar ratio of bis(cyclopentadienyl)zirconia to methylaluminoxane is 1:120, and the concentration of bis(cyclopentadienyl)zirconia in nonane is 0.6 mmol / L.

[0040] (2) Add about 1L of undecane as bottom liquid to the stirred reactor after multiple purging with nitrogen, and heat it to about 78°C. Stir the stirred reactor at 300rpm, add about 6.5g of analytical grade 1-octene, and then add about 35ml of catalyst dilution solution. Continuously introduce 870g of ethylene and 1% of the volume of hydrogen into the stirred reactor for 3.5 hours. Control the pressure inside the stirred reactor at about 0.55MPa. Cooling water is introduced into the heat exchange jacket of the stirred reactor. At the same time, some nonane is circulated for heat exchange to control the temperature inside the polymerization reactor to be maintained at 70°C.

[0041] (3) After polymerization, the slurry discharged from the stirred reactor is transferred to the flash tank for product separation. The separated light components are sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain ultra-high molecular weight polyethylene sample E2.

[0042] Example 3

[0043] (1) In a catalyst preparation tank, the metallocene catalyst bis(cyclopentadienyl)zirconia, the co-catalyst methylaluminoxane, and the solvent dodecane are mixed evenly to form a catalyst dilution solution for later use. The molar ratio of bis(cyclopentadienyl)zirconia to methylaluminoxane is 1:200, and the concentration of bis(cyclopentadienyl)zirconia in dodecane is 0.66 mmol / L.

[0044] (2) Add about 0.9 L of dodecane as bottom liquid to the stirred reactor after multiple purging with nitrogen, and heat it to about 80 °C. Stir the stirred reactor at 400 rpm, add about 5.2 g of analytical grade 1-octene, and then add about 32 ml of catalyst dilution solution. Continuously introduce 678 g of ethylene and 1% of the volume of hydrogen into the stirred reactor for 4 hours. Control the pressure inside the stirred reactor at about 0.45 MPa. Cooling water is introduced into the heat exchange jacket of the stirred reactor. At the same time, some of the dodecane is circulated for heat exchange to control the temperature inside the polymerization reactor to be maintained at 80 °C.

[0045] (3) After polymerization, the slurry discharged from the stirred reactor is transferred to the flash tank for product separation. The separated light components are sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain ultra-high molecular weight polyethylene sample E3.

[0046] Example 4

[0047] (1) In a catalyst preparation tank, the metallocene catalyst bis(cyclopentadienyl)zirconia, the co-catalyst methylaluminoxane, and the solvent undecane are mixed evenly to form a catalyst dilution solution for later use. The molar ratio of bis(cyclopentadienyl)zirconia to methylaluminoxane is 1:180, and the concentration of bis(cyclopentadienyl)zirconia in undecane is 0.24 mmol / L.

[0048] (2) Add about 1L of undecane as bottom liquid to the stirred reactor after multiple purging with nitrogen, and heat it to about 78°C. Stir the stirred reactor at 400rpm, add about 5g of analytical grade 1-octene, and then add about 38ml of catalyst dilution solution. Continuously introduce 510g of ethylene and 1% of the volume of hydrogen into the stirred reactor for 2 hours. Control the pressure inside the stirred reactor at about 0.5MPa. Cooling water is introduced into the heat exchange jacket of the stirred reactor. At the same time, some undecane is circulated for heat exchange to control the temperature inside the polymerization reactor to be maintained at 78°C.

[0049] (3) After polymerization, the slurry discharged from the stirred reactor is transferred to the flash tank for product separation. The separated light components are sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain ultra-high molecular weight polyethylene sample E4.

[0050] Example 5

[0051] (1) In the catalyst preparation tank, the metallocene catalyst bis(cyclopentadienyl)zirconia, the co-catalyst methylaluminoxane, and the solvent nonane are mixed evenly to form a catalyst dilution solution for later use. The molar ratio of bis(cyclopentadienyl)zirconia to methylaluminoxane is 1:100, and the concentration of bis(cyclopentadienyl)zirconia in nonane is 1 mmol / L.

[0052] (2) Add about 0.75L of nonane as bottom liquid to the stirred reactor after multiple purging with nitrogen, and heat it to about 74°C. Stir the stirred reactor at 500rpm, add about 5.1g of analytical grade 1-octene, and then add about 42ml of catalyst dilution solution. Continuously introduce 522g of ethylene and 1% of the volume of hydrogen into the stirred reactor for 2.5 hours. Control the pressure inside the stirred reactor at about 0.53MPa. Cooling water is introduced into the heat exchange jacket of the stirred reactor. At the same time, some of the nonane is circulated for heat exchange to control the temperature inside the polymerization reactor to be maintained at 74°C.

[0053] (3) After polymerization, the slurry discharged from the stirred reactor is transferred to the flash tank for product separation. The separated light components are sent to the recovery unit, and the separated solid polymer enters the degassing and drying unit. The dried polymer powder is sieved and homogenized to obtain ultra-high molecular weight polyethylene sample E5.

[0054] Comparative Example 1

[0055] Compared with Example 1, the solvent was replaced with hexane, and the remaining steps and process conditions were the same as in Example 1, resulting in ultra-high molecular weight polyethylene sample D1.

[0056] Comparative Example 2

[0057] Compared with Example 1, 1-octene was not added, and the remaining steps and process conditions were the same as in Example 1, resulting in ultra-high molecular weight polyethylene sample D2.

[0058] Comparative Example 3

[0059] Compared with Example 1, the catalyst was replaced with a Ziegler-Natta catalyst (TiCl4 and triethylaluminum, Ti / Al molar ratio of 1:75, TiCl4 concentration in solvent of 0.12 mmol / L), and the remaining steps and process conditions were the same as in Example 1, to obtain ultra-high molecular weight polyethylene sample D3.

[0060] The molecular weight, mechanical properties, and degree of entanglement of the above-mentioned ultra-high molecular weight polyethylene E1-E5 and ultra-high molecular weight polyethylene D1-D3 were determined according to the following standards / methods, and the specific results are detailed in Table 1.

[0061] 1. Molecular weight determination

[0062] The viscosity-average molecular weight was tested according to standard GB 1632.3-2010 (α=1.49);

[0063] Molecular weight distribution (PDI) was calculated by gel permeation chromatography (GPC).

[0064] The testing method is as follows: Grind the polyethylene sample into a fine powder to ensure uniform dispersion. Weigh 10 mg of the sample and place it in a vial for later use. Filter tetrahydrofuran (THF) or dichloromethane (DCM) solvent to remove impurities, ensuring solvent purity. Add the sample to the solvent and dissolve it in an ultrasonic cleaner to ensure complete dissolution. GPC analysis: Inject the dissolved sample into the GPC instrument for analysis. Use a standard polystyrene calibration curve for molecular weight determination. Record the molecular weight distribution data, calculate the number-average molecular weight (Mn) and weight-average molecular weight (Mw), and finally calculate the PDI.

[0065] 2. Mechanical property testing

[0066] Tensile strength was tested using a universal testing machine in accordance with GB / T528-2009. Standard test specimens for mechanical properties were injection molded using an injection molding machine. The test specimens were then cut into dumbbell-shaped tensile specimens of 25mm × 4mm, with a tensile rate of 20mm / min.

[0067] 3. Determination of entanglement degree

[0068] The degree of entanglement in nascent polyethylene samples was tested using a HAAKE MARS III rheometer. The polyethylene samples were pressed for 30 minutes at 130℃ and 20 MPa using a hot press to obtain small discs with a diameter of 20 mm and a thickness of 2 mm. The rheological tests were conducted under nitrogen protection to prevent sample oxidation. Dynamic time-scan testing was used to observe the entanglement of newly formed UHMWPE at 10 rad·s⁻¹. -1 Entanglement state under 0.5% strain condition. The ratio of initial elastic modulus to equilibrium elastic modulus, GNt (t=0), is used as an indicator of the degree of entanglement.

[0069] Table 1 Sample Test Results

[0070]

[0071] As shown in Table 1, the viscosity-average molecular weight of the products obtained in Examples 1-5 of this invention is between 1 million and 1.2 million, with a molecular weight distribution between 2 and 3, and a tensile strength of 55-60 MPa. Compared with polyethylene without the addition of 1-octene comonomer (Comparative Example 2), the tensile strength of the products is significantly improved. When the solvent type is changed (Comparative Example 1), the entanglement of the products is significantly aggravated, and the tensile strength is significantly worsened. When the catalyst type is changed (Comparative Example 3), the molecular weight of the obtained products decreases, the uniformity deteriorates, the tensile strength decreases, and the entanglement of the products increases.

[0072] Those skilled in the art should understand that the above embodiments are merely examples and do not limit the invention. The objectives of the invention have been fully and effectively achieved. The functions and principles of the invention have been shown and explained in the embodiments, and any variations or modifications can be made to the implementation of the invention without departing from the stated principles.

Claims

1. A method for preparing low-entanglement copolymerized modified ultra-high molecular weight polyethylene, characterized in that, Includes the following steps: S1. The metallocene catalyst and the co-catalyst are diluted with a solvent to obtain a catalyst dilution solution. The solvent is selected from C8-C12 long-chain alkanes. The metallocene catalyst is selected from at least one of bis(indenylmethylene-bridged zirconium) and bis(cyclopentadienyl)zirconium dichloride. The co-catalyst is selected from alkylaluminoxanes. S2. Add a certain amount of solvent to the stirred reactor as the bottom liquid. While maintaining continuous stirring, add the catalyst dilution, ethylene, 1-octene, and hydrogen to the stirred reactor in a metered ratio to carry out the polymerization reaction. The temperature is controlled at 60-90℃, the pressure inside the reactor is controlled at 0.2-0.8MPa, and the amount of 1-octene added is 5-10wt‰ of ethylene. S3. After polymerization, the slurry discharged from the stirred reactor is post-treated to obtain the low entanglement copolymer modified ultra-high molecular weight polyethylene. The stirred reactor described in step S2 is a stirred reactor with a heat exchange jacket. The stirred reactor is externally connected to a solvent circulation heat exchange unit. Part of the solvent is circulated into the stirred reactor after heat exchange through a delivery pump and heat exchange equipment. The stirred reactor is provided with a circulating gas outlet at the top. When the pressure inside the reactor exceeds a set value, the gas is discharged from the circulating gas outlet. The prepared low-entanglement copolymerized modified ultra-high molecular weight polyethylene has a viscosity-average molecular weight of 1,000,000-1,200,000, a molecular weight distribution of 2-3, a tensile strength of 55-60 MPa, and a ratio of initial elastic modulus to equilibrium elastic modulus of 0.1-0.

2.

2. The method as described in claim 1, characterized in that, The co-catalyst is selected from at least one of methylaluminoxane and tetrabutylaluminoxane.

3. The method as described in claim 1, characterized in that, The molar ratio of the metallocene catalyst to the co-catalyst is 1:50-400.

4. The method as described in claim 1, characterized in that, In the catalyst dilution solution, the concentration of the metallocene catalyst in the solvent is 0.1-10 mmol / L, the amount of catalyst dilution solution added is 1-5% of the volume of the bottom liquid in the reactor, and the amount of hydrogen added is 0.1-5% of the volume of ethylene.

5. The method as described in claim 1, characterized in that, The post-processing described in step S3 includes the following steps: the slurry after reaction is transferred to a flash tank for product separation, the separated gas phase is sent to a recovery unit, the separated solid polymer enters a degassing and drying unit, and the dried polymer powder is sieved and homogenized to obtain the low entanglement copolymer modified ultra-high molecular weight polyethylene.

6. The low-entanglement copolymerized modified ultra-high molecular weight polyethylene prepared by the method according to any one of claims 1-5, characterized in that, The low-entanglement copolymerized modified ultra-high molecular weight polyethylene has a viscosity-average molecular weight of 1,000,000 to 1,200,000, a molecular weight distribution of 2 to 3, a tensile strength of 55 to 60 MPa, and a ratio of initial elastic modulus to equilibrium elastic modulus of 0.1 to 0.2.

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