A special polyethylene resin for rotational molding with high environmental stress cracking resistance

Abstract

The application discloses a special polyethylene resin for rotational molding with high environmental stress cracking resistance, and relates to the polyethylene field.The polyethylene resin is composed of a high molecular weight polyethylene component and a low molecular weight polyethylene component, the melt index (MI 2.16 ) of which is in the range of 0.3 g / 10 min to 25 g / 10 min, the density is in the range of 0.9292 g / cm 3 to 0.9419 g / cm 3 , the molecular weight distribution is in the range of 0.3 to 24.9, the probability of tie molecule formation is in the range of 0.5 to 6, and the environmental stress cracking time is more than 1000 h.The high molecular weight component is used to improve the tie molecule content and crystalline integrity of the resin, and the low molecular weight component is used to improve the processing fluidity and interchain synergistic effect of the resin.The resin realizes multiple balance of the mechanical properties, cracking resistance and processing adaptability of the rotational molding product.The wide distribution polyethylene resin of the application is suitable for rotational molding and has good processing performance and excellent environmental stress cracking resistance.

Description

Technical Field

[0001] This invention relates to the field of polyethylene, and more specifically to a wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking. Background Technology

[0002] Rotational molding, as a traditional plastic processing technology, is widely used in the manufacture of large storage containers and other fields due to its simple mechanical operation and zero shear characteristics.

[0003] Currently, most rotational molding resins on the market are made of polyethylene, due to its excellent high-temperature resistance, chemical resistance, and low material cost. Considering the physical properties of polyethylene itself and the characteristics of rotational molding, the melt flow index of polyethylene raw materials typically needs to be controlled within the range of 3 g / 10 min to 6 g / 10 min to ensure suitable melt flowability and uniform spreading on the mold surface. Simultaneously, to ensure good mechanical properties of the rotationally molded products, the density of the polyethylene raw material is usually required to be 0.9250 g / cm³. 3 ~0.9380 g / cm 3 Within this range. The application scenarios for rotationally molded products also require excellent resistance to environmental stress cracking.

[0004] To improve the environmental stress cracking resistance of polyethylene, blending materials with different branched structures is commonly used. Short branches influence the properties of polyethylene by regulating its aggregated structure. Too few short branches make it difficult to form stable ligated molecules, while too many short branches reduce crystallinity, resulting in the mechanical properties of polyethylene failing to reach the expected level. Chinese patent CN201980009394.8 describes a polyolefin composition obtained by physically blending high-density polyethylene, polyolefin elastomer, and polypropylene. The polyethylene elastomer or polypropylene synergistically interacts with the high-density polyethylene, introducing different branched structures while maintaining a balance of rigidity and toughness and good processing flowability, thus improving the environmental stress cracking resistance of high-density polyethylene. This composition is suitable for pipeline system components, solar water heaters, hazardous material containers, industrial containers, fuel tanks, caps, or closures. However, this technology involves certain compatibility issues during the blending process of high-density polyethylene, polyolefin elastomer, and polypropylene, leading to potential defects and limiting the reliability of the products during use. In German patent EP13173536.7, extremely high molecular weight (Mz) and long-chain branched structure significantly improve the ESCR and impact resistance of the material while maintaining high density (stiffness). This material is not prone to melt fracture even under high shear rates, exhibiting excellent processing performance. However, this method places extremely stringent requirements on the catalyst system and polymerization process to precisely control such ultra-high molecular weight components and long-chain branched structures. In production applications, it demands extremely high levels of expertise in temperature, pressure, and time control from both the production equipment and the operators, making stable production difficult.

[0005] In addition, the molecular weight of polyethylene directly affects its performance in use and processing. While low molecular weight polyethylene possesses excellent processing properties, it has lower thermal stability and strength; while high molecular weight polyethylene boasts higher strength and excellent resistance to environmental stress cracking, but its poor flowability and high viscosity make it difficult to plasticize and mold. Therefore, improving resistance to environmental stress cracking while meeting requirements for density, melt index, and processing performance is the key challenge in developing high-performance polyethylene specifically for rotational molding. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a rotomolding-specific polyethylene resin with high resistance to environmental stress cracking, which significantly improves ESCR performance while maintaining suitable processing properties.

[0007] The core idea of ​​this invention is to increase the content of ligand molecules by controlling the content of comonomers, hydrogen partial pressure, and the mass ratio of the high molecular weight component during the polymerization process of the high molecular weight and low molecular weight components, while ensuring that the melt index and density meet the requirements of rotational molding. Since ligand molecules are long chains of two or more lamellar structures linked together, connected across the lamellae and supported by covalent bonds, they possess high mechanical strength. Environmental stress cracking mainly occurs due to the slippage of ligand molecules in crystalline regions and the disentanglement in amorphous regions. The more ligand molecules there are, the tighter the entanglement between chain segments, and the stronger the environmental stress cracking resistance of polyethylene. Increasing the content of ligand molecules can be achieved by increasing the content of short branches and increasing the molecular weight. Short branches affect the polymer's properties by altering the aggregated structure of polyethylene. Too few short branches make it difficult to form stable ligand molecules, while too many short branches reduce crystallinity, causing the mechanical properties of polyethylene to fall short of expectations. Furthermore, the molecular weight of polyethylene also directly affects the material's performance in use and processing. While low molecular weight polyethylene (LMWPE) exhibits excellent processing properties, it suffers from low thermal stability and strength. Conversely, high molecular weight polyethylene (HMWPE), despite its superior strength and resistance to environmental stress cracking, suffers from poor flowability, high viscosity, and difficulty in plasticizing and molding. This invention designs a chain structure that simultaneously improves the processing flowability and environmental stress cracking resistance of polyethylene resin.

[0008] This invention first provides a wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking, which is composed of a high molecular weight polyethylene component and a low molecular weight polyethylene component, wherein the weight-average molecular weight of the high molecular weight polyethylene component is in the range of 9 × 10⁻⁶. 5 g / mol to 3×10 6 g / mol; the weight-average molecular weight range of the low molecular weight polyethylene component is 4 × 10⁻⁶ g / mol. 4 g / mol ~ 9 × 10 4 g / mol; the high molecular weight polyethylene component in the polyethylene resin accounts for 8% to 18% by mass; the melt index of the polyethylene resin is in the range of 0.3 to 25 g / 10 min, and the density is 0.9292 g / cm³. 3 ~0.9419g / cm 3 Within the range, the weight-average molecular weight ranges from 6 × 10⁻⁶. 4 g / mol ~ 2 × 10 5 With a molecular weight distribution ranging from 0.3 to 24.9 g / mol and a ligand formation probability ranging from 0.5 to 6.0, it was subjected to environmental stress cracking tests at 50 °C with 10% alkylphenol polyoxyethylene ether (OP-10) surfactant, and its environmental stress cracking resistance time exceeded 1000 h.

[0009] Preferably, the polyethylene resin has a melt flow index in the range of 0.3 to 3.1 g / 10 min and a density of 0.9347 g / cm³. 3 ~0.9364 g / cm 3 Within the range.

[0010] Preferably, the probability of ligation of the polyethylene resin is in the range of 4 to 6.

[0011] Preferably, the mass ratio of high molecular weight polyethylene component to low molecular weight polyethylene component is in the range of 12% to 18%.

[0012] According to a preferred embodiment of the present invention, the high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained by sequential polymerization. The sequential polymerization includes: first synthesizing the high molecular weight polyethylene component in a polymerization reactor by controlling the polymerization conditions, and then switching the polymerization conditions to polymerize the low molecular weight component in situ in the same polymerization reactor, thereby obtaining the wide-distribution rotational molding polyethylene resin with high environmental stress cracking resistance.

[0013] The methods for switching polymerization conditions include: adding a chain transfer agent to the polymerization reactor, adding a comonomer to the polymerization reactor, changing one or more of the following: the temperature or the polymerization pressure of the polymerization reaction.

[0014] Preferably, the polymerization reactor is a batch reactor, and polymer is not discharged when switching polymerization conditions. Preferably, when the polymerization conditions are not switched, polymerization is carried out under a single polymerization condition until the polymerization is completed.

[0015] Calculation of the probability of polymer banding molecule formation: For polydisperse systems, the Huang & Brown statistical method is used to calculate the molecular weight M for each component. i The probability of slices forming ligament molecules P i After simplification: D The chain elongation factor in the molten state is used; the polyolefin resin of this invention is polyethylene. D =6.8; n The number of chain segments is taken from polyethylene. n = M w / 14; l The unit length is 0.153 nm in polyethylene. L The critical distance for the formation of banded molecules between lamellar layers, and the thickness of the crystal region.l c Amorphous region thickness l a Related, and L=2 l c +l a The Gibbs-Thompson equation is used to approximate the calculation. lc : Among them, the crystalline density of polyethylene ρ c =1.006 g / cm 3 amorphous region density ρ a =0.852 g / cm 3 At 1.006 g / cm 3 The melting point value of polyethylene at the specified density The temperature is generally taken as 142.3 ℃. ρ For polymer density, ω c This represents the mass fraction of the crystal region.

[0016] P i The value is considered to be the molecular weight. M i Weighting factors for slices, defining parameters PSP2 i : PSP2 i = P i ×100; for each slice PSP2 i Multiplying the value by the corresponding weight of that slice yields the overall probability of telogen effluvium formation in the polymer: in, M and MWD i It can be obtained directly from GPC testing.

[0017] Note: In this specification, the "probability of ligament formation" refers to the value calculated by the above method.

[0018] Typically, but not limitingly, in a further preferred embodiment of the invention, the polyethylene resin is prepared by the following manner: 1) The catalyst, co-catalyst, and olefin monomer are sequentially added to the reactor. The catalyst is one or more of the following: metallocene catalyst, chromium-based catalyst, FI catalyst, Ziegler-Natta catalyst, and post-transition metal catalyst. The co-catalyst is one or more of the following: triethylaluminum, triisopropylaluminum, trimethylaluminum, diethylaluminum chloride, dichloroethylaluminum, tributylaluminum, trihexylaluminum, and trioctylaluminum. The olefin monomer is one or more of the following: ethylene, propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene. 2) The first stage of polymerization produces a product with a molecular weight of 6×10⁻⁶. 5 g / mol ~5×10 6 In the second stage, a high molecular weight polyethylene component of g / mol was generated by controlling temperature, pressure, and comonomer content to produce a product with a molecular weight of 5 × 10⁻⁶ g / mol. 3 g / mol ~5×10 5 Low molecular weight components (g / mol).

[0019] Depending on the requirements of the target product, different polymeric monomers may or may not be introduced into the reactor, or other comonomers may be added after ensuring that the polymeric monomers remain in the reactor after initial introduction, so as to achieve switching between different homopolymers and different copolymers.

[0020] In a preferred embodiment of the present invention, the olefin monomer is ethylene, and the copolyolefin monomer is one or more of α-olefins. Preferably, the copolyolefin monomer is one or more of propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene.

[0021] In a preferred embodiment of the present invention, the reactor is a batch reactor or a tubular reactor, and polymer is not discharged when switching polymerization conditions.

[0022] In a preferred embodiment of the present invention, the switching point is selected according to the required ratio of high molecular weight polyethylene component and low molecular weight polyethylene component in the target polyethylene resin.

[0023] In a preferred embodiment of the present invention, the chain transfer agent of the polymerization reaction is hydrogen or an alkyl metal, preferably hydrogen.

[0024] In a preferred embodiment of the present invention, the polymerization reaction temperature is -30 to 100 °C, the polymerization pressure is 0.5 to 60 bar, and the reaction time is 0.1 to 10 h.

[0025] Compared with existing technologies, the high environmental stress cracking resistance, wide-distribution rotational molding polyethylene resin of the present invention is composed of high molecular weight polyethylene components and low molecular weight polyethylene components. The high molecular weight component provides more ligand molecules to the polyethylene resin, and by further introducing the low molecular weight component, the overall melt flowability of the resin can be improved, which helps to improve processing performance. Ligand molecules are long chains of two or more lamellar structures linked together, connected across the lamellae and supported by covalent bonds, thus possessing high mechanical strength. Environmental stress cracking mainly occurs due to the slippage of ligand molecules in crystalline regions and the disentanglement in amorphous regions. The more ligand molecules there are, the tighter the entanglement between chain segments, and the stronger the environmental stress cracking resistance of polyethylene.

[0026] The present invention relates to a wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking, exhibiting a melt index ranging from 0.3 to 25 g / 10 min and a density of 0.9292 g / cm³. 3 ~0.9419 g / cm 3 Within the range, the weight-average molecular weight ranges from 6 × 10⁻⁶. 4 g / mol ~ 2 × 10 5 With a molecular weight distribution ranging from 0.3 to 24.9 g / mol, a chalcedony formation probability ranging from 0.5 to 6.0, and an environmental stress cracking time ranging from 12 h to 1000 h, this resin possesses both suitable processing properties and high resistance to environmental stress cracking. Attached Figure Description

[0027] Figure 1 This is a molecular weight distribution diagram of the polyethylene resin for rotational molding prepared in Example 1.

[0028] Figure 2 The time of environmental stress cracking resistance of the rotomolding-specific polyethylene resin prepared in Examples 1-4 and Comparative Examples 1-2 is indicated. Detailed Implementation

[0029] The following examples provide those skilled in the art with guidance on how to manufacture and evaluate the invention. These examples are merely illustrative of the present disclosure and do not limit its scope. While every effort has been made to ensure accuracy regarding numerical values ​​(e.g., quantities, temperatures, etc.), some errors and deviations should be considered. Unless otherwise stated, temperatures are in °C or at ambient temperature, and pressures are at or near atmospheric pressure.

[0030] Characterization methods for polymer structure and properties: (1) Melt flow index: According to GB / T368283, the melt flow rate was measured for 10 min at 190 ℃ and 2.16 kg load.

[0031] (2) Density: determined according to GB / 10331986 method.

[0032] (3) Resistance to environmental stress cracking: determined according to GB / T 1842-2008, wherein the test solvent is 10% alkylphenol polyoxyethylene ether (OP-10) surfactant, and the test is conducted at 50 °C.

[0033] (4) Weight average molecular weight and molecular weight distribution: determined by high temperature permeation gel chromatography.

[0034] (5) Chordination molecules: determined and calculated by HT-GPC high-temperature permeation gel chromatography.

[0035] Example 1 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 20 mg of catalyst (Ziegler-Natta catalyst), 2 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 4 g of co-olefin monomer (1-butene) were added sequentially, followed by 0.8 bar of hydrogen to initiate a preliminary polymerization reaction. The reaction was carried out for 10 min to prepare high molecular weight polyethylene. The ethylene injection was then stopped, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene), 25 g of co-olefin monomer (1-butene), and 1.7 bar of hydrogen were added sequentially. The reaction was carried out for 2 h to prepare low molecular weight polyethylene, with the high molecular weight component accounting for 14 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0036] Figure 1 This diagram shows the molecular weight distribution of the rotomolding-specific polyethylene resin prepared in Example 1 of the present invention. The melt index (MI) of the prepared rotomolding-specific polyethylene resin is also shown. 2.16 The concentration was 3.1 g / 10 min, and the density was 0.9364 g / cm³. 3 The weight-average molecular weight is 1.3 × 10⁻⁶. 5 With a molecular weight distribution of 11 g / mol and a chelate molecular formation probability of 4.9, this resin exhibits an environmental stress cracking resistance time exceeding 1000 h.

[0037] Example 2 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 20 mg of catalyst (Ziegler-Natta catalyst), 2 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 4 g of co-olefin monomer (1-butene) were added sequentially, followed by 0.8 bar of hydrogen to initiate a preliminary polymerization reaction. The reaction was carried out for 15 min to prepare high molecular weight polyethylene. The ethylene injection was then stopped, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene), 25 g of co-olefin monomer (1-butene), and 1.7 bar of hydrogen were added sequentially. The reaction was carried out for 2 h to prepare low molecular weight polyethylene, with the high molecular weight component accounting for 18 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0038] The melt index (MI) of the prepared rotomolding-specific polyethylene resin 2.16 The concentration was 0.3 g / 10 min, and the density was 0.9347 g / cm³. 3 The weight-average molecular weight is 1.6 × 10⁻⁶. 5 With a molecular weight distribution of 12 g / mol and a chalcedony formation probability of 5.5, this resin exhibits an environmental stress cracking resistance time exceeding 1000 h.

[0039] Example 3 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 10 mg of catalyst (Ziegler-Natta catalyst), 1 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 30 mL of co-olefin monomer (1-hexene) were added sequentially, followed by 0.5 bar of hydrogen to initiate a preliminary polymerization reaction. The reaction was carried out for 8 min to prepare high-molecular-weight polyethylene. The ethylene feed was then cut off, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene) and 1.6 bar of hydrogen were added sequentially. The reaction was carried out for 2 h to prepare low-molecular-weight polyethylene, with the high-molecular-weight component accounting for 12 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0040] The melt index (MI) of the prepared rotomolding-specific polyethylene resin 2.16 The concentration was 2.0 g / 10min, and the density was 0.9348 g / cm³. 3 The weight-average molecular weight is 1.4 × 10⁻⁶. 5 With a molecular weight distribution of 11 g / mol and a ligation molecule formation probability of 4.5, this resin exhibits an environmental stress cracking resistance time exceeding 1000 h.

[0041] Example 4 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 10 mg of catalyst (Ziegler-Natta catalyst), 1 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 30 mL of co-olefin monomer (1-hexene) were added sequentially, followed by 0.5 bar of hydrogen to initiate a preliminary polymerization reaction. The reaction was carried out for 12 min to prepare high molecular weight polyethylene. The ethylene injection was then stopped, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene) and 1.6 bar of hydrogen were added. The reaction was continued for 2 h to prepare low molecular weight polyethylene, with the high molecular weight component accounting for 16 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0042] The melt index (MI) of the prepared rotomolding-specific polyethylene resin 2.16 The concentration was 3.8 g / 10min, and the density was 0.9346 g / cm³. 3 The weight-average molecular weight is 1.5 × 10⁻⁶. 5 With a molecular weight distribution of 12 g / mol and a chalcedony formation probability of 5.6, this resin exhibits an environmental stress cracking resistance time exceeding 1000 h.

[0043] Comparative Example 1 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 20 mg of catalyst (Ziegler-Natta catalyst), 2 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 4 g of co-olefin monomer (1-butene) were added sequentially, followed by 0.8 bar of hydrogen for initial polymerization. The reaction was carried out for 8 min to prepare high molecular weight polyethylene. The ethylene injection was then stopped, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene), 25 g of co-olefin monomer (1-butene), and 1.5 bar of hydrogen were added sequentially. The reaction was carried out for 2 h to prepare low molecular weight polyethylene, with the high molecular weight component accounting for 10 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0044] The melt index (MI) of the prepared rotomolding-specific polyethylene resin 2.16 The concentration was 5.7 g / 10min, and the density was 0.9343 g / cm³. 3 The weight-average molecular weight is 6.8 × 10⁻⁶. 4With a molecular weight distribution of 8 g / mol and a chelate molecular formation probability of 2.8, the environmental stress cracking time of this resin is 120 h.

[0045] Comparative Example 2 The reactor was purged with high-purity nitrogen to remove water and oxygen from the batch reactor. The reactor temperature was adjusted to 70 °C, and hexane was added as the polymerization solvent. Then, 10 mg of catalyst (Ziegler-Natta catalyst), 1 mL of co-catalyst (triethylaluminum), 5 bar of olefin monomer (ethylene), and 30 mL of co-olefin monomer (1-hexene) were added sequentially, followed by 0.5 bar of hydrogen to initiate a preliminary polymerization reaction. The reaction was carried out for 6 min to prepare high-molecular-weight polyethylene. The ethylene injection was then stopped, and the pressure inside the reactor was slowly released to a slightly positive pressure. The reactor temperature was increased to 84 °C, and then 5 bar of olefin monomer (ethylene) and 1.6 bar of hydrogen were added sequentially. The reaction was carried out for 2 h to prepare low-molecular-weight polyethylene, with the high-molecular-weight component accounting for 8 wt%, ultimately yielding a rotomolding-specific polyethylene resin.

[0046] The melt index (MI) of the prepared rotomolding-specific polyethylene resin 2.16 The concentration was 1.0 g / 10min, and the density was 0.9356 g / cm³. 3 The weight-average molecular weight is 8.1 × 10⁻⁶. 4 With a molecular weight distribution of 7 g / mol and a chelate formation probability of 2.7, the resin has an environmental stress cracking resistance time of 580 h.

[0047] Figure 2 The figures show the environmental stress cracking resistance times of the rotomolding-specific polyethylene resins prepared in Examples 1-4 and Comparative Examples 1-2. As can be seen from the figures, by controlling the mass percentage of the high molecular weight polyethylene component within the range of 12%~18% and the ligand formation probability within the range of 4~6, a polyethylene resin possessing both good processability and high environmental stress cracking resistance can be obtained. The high molecular weight component provides more ligand molecules to the polyethylene resin, and by further introducing low molecular weight components, the overall melt flowability of the resin can be improved, which helps to improve processability. Ligand molecules are long chains of two or more lamellar structures linked together, connected across the lamellae and supported by covalent bonds, thus possessing high mechanical strength. Environmental stress cracking mainly occurs due to the slippage of ligand molecules in crystalline regions and the disentanglement in amorphous regions. The greater the number of ligand molecules and the tighter the entanglement between chain segments, the stronger the environmental stress cracking resistance of the polyethylene.

[0048] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A wide-distribution polyethylene resin for rotational molding with high resistance to environmental stress cracking, characterized in that, It is composed of high molecular weight polyethylene components and low molecular weight polyethylene components; The weight-average molecular weight range of the high molecular weight polyethylene component is 9 × 10⁻⁶. 5 g / mol to 3×10 6 g / mol; the weight-average molecular weight range of the low molecular weight polyethylene component is 4 × 10 g / mol. 4 g / mol ~ 9 × 10 4 g / mol; the high molecular weight polyethylene component in the polyethylene resin accounts for 8%~18% by mass; The melt flow index (MI) of the polyethylene resin 2.16 Within the range of 0.3~25 g / 10 min, the density is 0.9292 g / cm³. 3 ~0.9419 g / cm 3 Within the range, the weight-average molecular weight ranges from 6 × 10⁻⁶. 4 g / mol ~ 2 × 10 5 g / mol, molecular weight distribution in the range of 0.3 to 24.9, and chelate molecule formation probability in the range of 0.5 to 6. The polyethylene resin was subjected to an environmental stress cracking test at 50 °C with 10% alkylphenol polyoxyethylene ether (OP-10) surfactant, and the environmental stress cracking time exceeded 1000 h.

2. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 1, characterized in that, The high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained through sequential polymerization. The sequential polymerization includes: first synthesizing the high molecular weight polyethylene component by controlling the polymerization conditions, and then switching the polymerization conditions to polymerize the low molecular weight component in situ in the same polymerization reactor, thereby obtaining the wide-distribution rotational molding polyethylene resin with high environmental stress cracking resistance.

3. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 2, characterized in that, The methods for switching polymerization conditions include: adding a chain transfer agent to the polymerization reactor, adding a comonomer to the polymerization reactor, changing one or more of the following: polymerization reaction temperature or polymerization reaction pressure.

4. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 2, characterized in that, The polymerization reactor is either a batch reactor or a tubular reactor. When switching polymerization conditions, the polymer is not discharged.

5. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The high molecular weight polyethylene component and the low molecular weight polyethylene component are obtained by ethylene polymerization in the presence of a polyethylene catalyst and a co-catalyst; the polyethylene catalyst is one or more of metallocene catalysts, chromium-based catalysts, FI catalysts, Ziegler-Natta catalysts, and post-transition metal catalysts; the co-catalyst is one or more of triethylaluminum, triisopropylaluminum, trimethylaluminum, diethylaluminum chloride, dichloroethylaluminum, tributylaluminum, trihexylaluminum, and trioctylaluminum.

6. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The solvent used in the polymerization is selected from one or more of C6-C10 alkanes and C7-C10 aromatics. Preferably, the solvent is one or more of n-hexane, n-heptane, toluene, and xylene.

7. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The olefin monomer being polymerized is ethylene, and the copolyolefin monomer is one or more of propylene, 1-butene, butadiene, 1-hexene, 1-heptene, 1-octene, and 1-decene. More preferably, the polyolefin monomer is 1-butene or 1-hexene.

8. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The polyethylene resin has a crystallinity of 40% to 60% and a crystal melting point of 124 to 132 °C.

9. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The polymerization reaction is one or more of the following: slurry reaction, gas-phase reaction, and gas-liquid two-phase reaction.

10. The wide-distribution rotational molding polyethylene resin with high resistance to environmental stress cracking as described in claim 3, characterized in that, The polymerization reaction temperature is -30 ℃ to 100 ℃, the polymerization reaction pressure is 0.5 to 60 bar, and the reaction time is 0.1 to 10 h.

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