Ethylene with alpha-olefin copolymers and process for their preparation, insulating sheaths for cables

Abstract

The present application relates to a kind of ethylene and alpha-olefin copolymer and its preparation method, the insulating sheath for cable.The branched chain distribution index BDI of the ethylene and alpha-olefin copolymer is 1.05~1.5;Wherein, BDI=AWD / BWD, AWD is the weight average branched chain content of the ethylene and alpha-olefin copolymer, BWD is the number average branched chain content of the ethylene and alpha-olefin copolymer.The ethylene and alpha-olefin copolymer can have high toughness and excellent long-term heat aging retention rate.

Description

Technical Field

[0001] This invention relates to the field of polyolefin elastomer technology, and in particular to a copolymer of ethylene and α-olefin, a method for preparing the copolymer, and an insulating sheath for cables. Background Technology

[0002] The performance of the insulation sheath material in cables directly determines the service life and operational safety of the cables. Especially in application scenarios such as power cables, photovoltaic cables, communication cables, and high-voltage cables for new energy vehicles, the materials not only need to have excellent initial mechanical properties, such as high elongation at break and tensile strength, but also need to have excellent long-term aging resistance to resist performance degradation under long-term hot and oxygen environments.

[0003] Currently, the insulation sheath materials for medium and high voltage power cables and cables used in special environments mostly employ peroxide-crosslinked polyethylene (XLPE), ethylene-vinyl acetate copolymer (EVA), or ethylene propylene diene monomer (EPDM). However, these traditional material systems all have inherent performance limitations. For example, while XLPE has excellent electrical insulation properties, it suffers from poor flexibility, insufficient impact resistance, and crack resistance; EVA, due to the presence of polar groups, is prone to hydrolysis in high-temperature and high-humidity environments, leading to a decrease in insulation resistance; and EPDM struggles to fully meet increasingly stringent industrial requirements in terms of weather resistance and tear resistance.

[0004] In recent years, polyolefin elastomers (POEs), especially random copolymers of ethylene and α-olefins, have been increasingly widely used in the cable industry due to their excellent flexibility, low-temperature resistance, impact resistance, and superior electrical insulation properties. However, traditional polyolefin elastomers struggle to simultaneously possess both high toughness and excellent long-term thermo-oxidative aging retention. Summary of the Invention

[0005] Based on this, the present invention provides a copolymer of ethylene and α-olefin that can have both high toughness and excellent long-term thermo-oxidative aging retention rate, a method for preparing the same, and an insulating sheath for cables.

[0006] In a first aspect, the present invention provides a copolymer of ethylene and α-olefin, wherein the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.05 to 1.5.

[0007] Wherein, BDI = AWD / BWD, AWD is the weight-average branched content of the copolymer of ethylene and α-olefin, and BWD is the number-average branched content of the copolymer of ethylene and α-olefin.

[0008] In one embodiment, the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.1 to 1.25.

[0009] In one embodiment, the weight-average branching (AWD) of the copolymer of ethylene and α-olefin is 70 to 110 branched carbon atoms per 1000 carbon atoms; or,

[0010] The number-average branching content (BWD) of the copolymer of ethylene and α-olefin is 70 to 100 carbon atoms per 1000 carbon atoms.

[0011] In one embodiment, the weight-average branching (AWD) of the copolymer of ethylene and α-olefin is 88 to 100 branches per 1000 carbon atoms; or,

[0012] The number-average branching content (BWD) of the copolymer of ethylene and α-olefin is 80 to 90 carbon atoms per 1000 carbon atoms.

[0013] In one embodiment, the copolymer of ethylene and α-olefin has one or more of the following characteristics:

[0014] (1) The molecular weight distribution index (PDI) is 2 to 4.5;

[0015] (2) The melt index (MI) at 190℃ and 2.16kg is 0.5g / 10min to 15g / 10min;

[0016] (3) The density is 0.865 g / cm³ 3 ~0.9g / cm 3 ;

[0017] (4) The mass percentage of structural units derived from α-olefins in the copolymer of ethylene and α-olefins is 15% to 40%.

[0018] A second aspect of the present invention provides a method for preparing a copolymer of ethylene and α-olefin, comprising the following steps:

[0019] The copolymer of ethylene and α-olefin is prepared by polymerizing ethylene and α-olefin in the presence of a catalyst.

[0020] The reactor for the polymerization reaction includes a first temperature zone and a second temperature zone, with a temperature difference of ΔT between the first temperature zone and the second temperature zone, where ΔT is 40℃~115℃.

[0021] In one embodiment, the temperature of the first temperature zone is 120°C to 190°C; or,

[0022] The temperature in the second temperature zone is 30℃~120℃.

[0023] In one embodiment, the preparation method has one or more of the following features:

[0024] (1) The pressure of the polymerization reaction is 2MPa~10MPa;

[0025] (2) The polymerization reaction time is 3 min to 25 min;

[0026] (3) The catalyst includes a main catalyst and a co-catalyst; the main catalyst includes a transition metal catalyst; the co-catalyst is an organoaluminum compound, or a combination of an organoaluminum compound and an organoboride;

[0027] (4) The polymerization reaction is carried out in the presence of a chain transfer agent, which includes one or more of methane, ethane, propane and hydrogen.

[0028] (5) The α-olefin includes one or more of the α-olefins of C3 to C20.

[0029] A third aspect of the present invention provides an insulating sheath for cables, comprising the copolymer of ethylene and α-olefins as described in the first aspect or the copolymer of ethylene and α-olefins prepared by the preparation method described in the second aspect.

[0030] In one embodiment, the insulating sheath for the cable comprises, by weight, the following:

[0031] 80-99 parts of matrix resin

[0032] The copolymer of ethylene and α-olefin is 1 to 20 parts.

[0033] Crosslinking agent 0.1 to 3 parts

[0034] 0.5 to 2 parts of crosslinking agent, and

[0035] Antioxidant 0.1 to 1 part.

[0036] The beneficial effects of this invention include:

[0037] The properties of polyolefin elastomers (POEs) are closely related to the distribution of their comonomers (α-olefins) within the molecular chains. In traditional POEs, the insertion of comonomers typically exhibits a random distribution or a distribution where the insertion rate of low-molecular-weight segments is higher than that of high-molecular-weight segments. Specifically, excessively high branching content in low-molecular-weight segments can excessively weaken their crystallinity, leading to a decrease in the material's mechanical properties; conversely, excessively low branching content in high-molecular-weight segments results in excessively high crystallinity, leading to poor compatibility with other components in cable formulations and a tendency for phase separation. This not only impairs long-term thermal stability and mechanical toughness but also affects the elongation at break and its retention rate after aging. This distribution defect creates a performance bottleneck for traditional POEs in cable applications that require both high toughness and excellent long-term thermo-oxidative aging retention.

[0038] To address the aforementioned issues, this invention controls the branch distribution index (BDI) of the ethylene-α-olefin copolymer within the range of 1.05 to 1.5, ensuring that the branch content on high molecular weight segments is moderately higher than that on low molecular weight segments at a specific ratio. This non-uniform yet ordered distribution allows a suitable amount of crystallizable high molecular weight segments to act as physical crosslinking points and a heat-resistant framework, forming a synergistic effect with the highly amorphous low molecular weight segments. This results in excellent initial toughness while significantly delaying segment thermal motion and oxidative chain breakage during thermo-oxidative aging, achieving excellent long-term thermo-oxidative aging retention. This is particularly suitable for applications with stringent requirements for insulation sheath materials, such as power cables, communication cables, and photovoltaic cables. Detailed Implementation

[0039] The following detailed description, with reference to specific embodiments, illustrates the copolymer of ethylene and α-olefins of the present invention, its preparation method, and its use as an insulating sheath for cables. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0041] In this article, "one or more" refers to any one, two or more of the listed items.

[0042] In this invention, terms such as "first aspect," "second aspect," and "third aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," and "third" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0043] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0044] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0045] Unless otherwise specified, the percentage content involved in this invention refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0046] Unless otherwise specified, all percentage concentrations mentioned in this invention refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0047] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.

[0048] In this invention, room temperature generally refers to 4℃~30℃, and preferably 20±5℃.

[0049] In this invention, "high molecular weight segment" and "low molecular weight segment" are relative concepts. The division method is as follows: the molecular weight distribution of the copolymer of ethylene and α-olefin generally conforms to the Flory distribution, the high molecular weight part refers to the right half of the distribution, and the low molecular weight part refers to the left half of the distribution.

[0050] In this invention, "weight-average branching content" is a short-chain / branching density obtained by weighted averaging based on molecular weight (weight), which indicates that the higher the proportion of high molecular weight segments, the greater the weight of the overall branching content; "number-average branching content" is a short-chain / branching density obtained by weighted averaging based on the number of molecular chains, which indicates that the higher the proportion of low molecular weight segments, the greater the impact on the overall branching content.

[0051] Some embodiments of the present invention provide a copolymer of ethylene and α-olefin, wherein the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.05 to 1.5; wherein, BDI = AWD / BWD, AWD is the weight-average branching content of the copolymer of ethylene and α-olefin, and BWD is the number-average branching content of the copolymer of ethylene and α-olefin.

[0052] Specifically, the BDI includes, but is not limited to, 1.05, 1.08, 1.09, 1.10, 1.12, 1.14, 1.15, 1.16, 1.18, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.5, or any range between the foregoing. Further, the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.1 to 1.25. Even further, the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.12 to 1.2. Even more further, the branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.12 to 1.16.

[0053] Without limitation, the units for weight-average branching content (AWD) and number-average branching content (BWD) can be atoms per 1000 carbon atoms.

[0054] In some embodiments, the weight-average branching (AWD) of the copolymer of ethylene and α-olefin is 70 to 110 carbon atoms per 1000 carbon atoms. Specifically, the weight-average branching (AWD) includes, but is not limited to (unit: atoms per 1000 carbon atoms): 70, 72, 75, 78, 80, 82, 85, 88, 90, 92, 95, 98, 100, 102, 105, 108, 110, or any range between the foregoing. Further, the weight-average branching (AWD) is 88 to 100 carbon atoms per 1000 carbon atoms. Even further, the weight-average branching (AWD) is 90 to 100 carbon atoms per 1000 carbon atoms. Furthermore, the weight-average branching content (AWD) is 90 to 95 carbon atoms per 1000 carbon atoms.

[0055] In some embodiments, the number-average branching content (BWD) of the copolymer of ethylene and α-olefin is 70 to 100 branching atoms per 1000 carbon atoms. Specifically, the number-average branching content (BWD) includes, but is not limited to (all in terms of branches per 1000 carbon atoms): 70, 72, 75, 78, 80, 80.5, 81, 81.5, 82, 85, 88, 90, 92, 95, 98, 100, or any range between the foregoing. Further, the number-average branching content (BWD) is 80 to 90 branching atoms per 1000 carbon atoms. Even further, the number-average branching content (BWD) is 80.5 to 83 branching atoms per 1000 carbon atoms. Furthermore, the number-average branching content (BWD) is 80.5 to 81.5 per 1000 carbon atoms.

[0056] In some embodiments, the molecular weight distribution index (PDI) of the ethylene-α-olefin copolymer is 2 to 4.5. Specifically, the PDI includes, but is not limited to, 2, 2.2, 2.4, 2.48, 2.5, 2.6, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.4, 4.5, or any range between the foregoing. Further, the PDI of the ethylene-α-olefin copolymer is 2 to 3.5.

[0057] In some embodiments, the melt index (MI) of the copolymer of ethylene and α-olefin at 190°C and 2.16 kg is 0.5 g / 10 min to 15 g / 10 min. Specifically, the melt index (MI) includes, but is not limited to: 0.5 g / 10 min, 0.8 g / 10 min, 1.0 g / 10 min, 2.0 g / 10 min, 2.8 g / 10 min, 3.0 g / 10 min, 3.2 g / 10 min, 4.0 g / 10 min, 4.9 g / 10 min, 5.0 g / 10 min, 5.1 g / 10 min, 6.0 g / 10 min, 7.0 g / 10 min, 8.0 g / 10 min, 9.0 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, 15 g / 10 min, or any range between the two. Furthermore, the melt index (MI) of the copolymer of ethylene and α-olefin at 190°C and 2.16 kg is 0.5 g / 10 min to 10 g / 10 min.

[0058] In some embodiments, the density of the ethylene-α-olefin copolymer is 0.865 g / cm³. 3 ~0.9g / cm 3Specifically, the density includes, but is not limited to: 0.865 g / cm³ 3 0.867 g / cm 3 0.868 g / cm 3 0.870 g / cm 3 0.872 g / cm 3 0.874 g / cm 3 0.875g / cm 3 0.876 g / cm 3 0.878g / cm 3 0.880 g / cm 3 0.882 g / cm 3 0.885g / cm 3 0.888g / cm 3 0.890 g / cm 3 0.892 g / cm 3 0.895g / cm 3 0.898g / cm 3 0.9g / cm 3 Or the range between any two of the aforementioned.

[0059] In some embodiments, the mass percentage of structural units derived from α-olefins in the copolymer of ethylene and α-olefins is 15% to 40%. Specifically, the mass percentage of structural units derived from α-olefins includes, but is not limited to: 15%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 38%, 40%, or any range between the foregoing.

[0060] Understandably, this invention controls the branching distribution index (BDI) of the ethylene-α-olefin copolymer within the range of 1.05 to 1.5, ensuring that the branching content on the high molecular weight segments is moderately higher than that on the low molecular weight segments. This allows the ethylene-α-olefin copolymer to maintain a high initial elongation at break while significantly improving its elongation at break retention after long-term thermo-oxidative aging. Based on this, those skilled in the art can use conventional methods to adjust the preparation method of the ethylene-α-olefin copolymer to obtain the aforementioned ethylene-α-olefin copolymer within the specific BDI range.

[0061] As an example, some other embodiments of the present invention provide a method for preparing a copolymer of ethylene and α-olefin, comprising the following steps:

[0062] The copolymer of ethylene and α-olefin is prepared by polymerizing ethylene and α-olefin in the presence of a catalyst.

[0063] The reactor for the polymerization reaction includes a first temperature zone and a second temperature zone, with a temperature difference of ΔT between the first temperature zone and the second temperature zone, where ΔT is 40℃~115℃.

[0064] In the above preparation method, by controlling the temperature difference ΔT between the first and second temperature zones in the polymerization reactor to be 40℃~115℃, the BDI of the ethylene-α-olefin copolymer can be precisely controlled to the target range. The mechanism is that the same catalyst exhibits drastically different comonomer insertion behaviors at different temperatures: the higher temperature zone tends to generate low molecular weight, low branched chain segments, while the lower temperature zone is conducive to generating high molecular weight, high branched chain segments. By setting a specific temperature difference range, a higher branched chain content is retained on the high molecular weight segments, and a lower branched chain content is formed on the low molecular weight segments, and finally the BDI of the ethylene-α-olefin copolymer is controlled at 1.05~1.5, thereby enabling the ethylene-α-olefin copolymer to significantly improve its long-term heat and oxygen aging resistance while ensuring the initial toughness of the material.

[0065] Without limitation, those skilled in the art can also control the branching distribution index (BDI) of ethylene-α-olefin copolymers within the range of 1.05 to 1.5 by other means, such as catalyst modification.

[0066] Without limitation, the temperature difference between the first and second temperature zones, or their respective temperatures, can be achieved through measures such as zoned temperature control jackets, installation of asymmetric cooling components, optimization of stirring and mixing mechanisms, and construction of novel reactor structures.

[0067] Specifically, the temperature difference ΔT between the first temperature zone and the second temperature zone includes, but is not limited to: 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or any two of the foregoing.

[0068] In some embodiments, the temperature of the first temperature zone is 120°C to 190°C. Specifically, the temperature of the first temperature zone includes, but is not limited to: 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, or any range between the foregoing.

[0069] In some embodiments, the temperature of the second temperature zone is 30°C to 120°C. Specifically, the temperature of the second temperature zone is 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, or a range between any two of the foregoing.

[0070] In some embodiments, the polymerization pressure is 2 MPa to 10 MPa. Specifically, the polymerization pressure includes, but is not limited to, 2 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, 4.5 MPa, 5.0 MPa, 6.0 MPa, 7.0 MPa, 8.0 MPa, 9.0 MPa, 10 MPa, or any range between the foregoing. Further, the polymerization pressure is 3 MPa to 7 MPa.

[0071] In some embodiments, the polymerization reaction time is 3 min to 25 min. Specifically, the polymerization reaction time includes, but is not limited to: 3 min, 4 min, 5 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 25 min, or any range between the foregoing. Further, the polymerization reaction time is 5 min to 18 min.

[0072] In some embodiments, the catalyst includes a main catalyst and a co-catalyst; the main catalyst includes a transition metal catalyst; and the co-catalyst is an organoaluminum compound, or a combination of an organoaluminum compound and an organoboride.

[0073] Without limitation, the main catalyst includes a metallocene catalyst, and may further include one or more of rac-ethylenebis(1-indenyl)zirconia, dimethicyl(N-tert-butylamino)(tetramethylcyclopentadienyl)dimethyltitanium, diphenylmethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconia and dimethylsilicylbis(2-methyl-4-phenylindenyl)zirconia.

[0074] Without limitation, the organoaluminum compound includes one or more of aluminum oxanes, alkylaluminum compounds, and alkylaluminum chlorides. As an example, the aluminum oxane includes one or more of methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, and butylaluminoxane; the alkylaluminum compound includes one or more of triethylaluminum, triisobutylaluminum, trioctylaluminum, trimethylaluminum, tripropylaluminum, tri-n-butylaluminum, and trisec-butylaluminum; and the alkylaluminum chloride includes one or more of monochloroethylaluminum, sesquiethylaluminum chloride, and dichloroethylaluminum.

[0075] In some embodiments, the molar ratio of Al in the organoaluminum compound to the transition metal in the main catalyst is (5~1000):1. Specifically, this molar ratio includes, but is not limited to: 5:1, 8:1, 10:1, 15:1, 18.7:1, 20:1, 30:1, 50:1, 80:1, 100:1, 150:1, 200:1, 300:1, 500:1, 800:1, 1000:1, or any range between the foregoing. Further, the molar ratio of Al in the organoaluminum compound to the transition metal in the main catalyst is (10~100):1.

[0076] Without limitation, the organoborides include one or more of triphenylmethyltetra(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, N,N-dimethylanilinetetra(pentafluorophenyl)borate, dioctadecylmethyltertiaryaminetetra(pentafluorophenyl)borate, and dihydrotallowylmethyltertiaryaminetetra(pentafluorophenyl)borate.

[0077] In some embodiments, the molar ratio of boron in the organoboride to the transition metal in the main catalyst is (0.8~10):1. Specifically, this molar ratio includes, but is not limited to: 0.8:1, 1:1, 1.2:1, 1.37:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or any range between the foregoing. Further, the molar ratio of boron in the organoboride to the transition metal in the main catalyst is (1~5):1.

[0078] In some embodiments, the polymerization reaction is carried out in the presence of a chain transfer agent, which includes one or more of methane, ethane, propane, and hydrogen. Further, the chain transfer agent includes hydrogen.

[0079] In some embodiments, the polymerization reaction is carried out in the presence of a solvent, which includes one or more of pentane, methylpentane, n-butane, isobutane, methylcyclopentane, methylenecyclopentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, isoalkanes, hydrogenated naphtha, benzene, toluene, and xylene.

[0080] In some embodiments, the α-olefin includes one or more of C3-C20 α-olefins. Further, the α-olefin includes one or more of C3-C12 α-olefins. As an example, the α-olefin includes one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-decene.

[0081] In other embodiments of the present invention, an insulating sheath for cables is provided, comprising a copolymer of ethylene and α-olefin as described above or a copolymer of ethylene and α-olefin prepared by the preparation method described above.

[0082] Without limitation, other components of the insulating sheath for cables may employ compositions conventional in the art. In some embodiments, the insulating sheath for cables, by weight, comprises:

[0083] 80-99 parts of matrix resin

[0084] The copolymer of ethylene and α-olefin is 1 to 20 parts.

[0085] Crosslinking agent 0.1 to 3 parts

[0086] 0.5 to 2 parts of crosslinking agent, and

[0087] Antioxidant 0.1 to 1 part.

[0088] Additionally, as an example, the matrix resin may include one or more of low-density polyethylene, linear low-density polyethylene, ethylene-acrylate copolymer, and ethylene-vinyl acetate copolymer. The crosslinking agent may include organic peroxides. The co-crosslinking agent may include one or more of triallyl isocyanurate and triallyl cyanurate. The antioxidant may include hindered phenolic or thioester antioxidants. Without limitation, the composition of the insulating sheath for cables may also include one or more of other additives, such as flame retardants, lubricants, copper inhibitors, colorants, and light stabilizers; wherein the flame retardant may be a halogen-free flame retardant.

[0089] For experimental parameters not specified in the following specific embodiments, please refer to the guidelines given in this invention document first, or refer to experimental manuals or other experimental methods known in the art, or refer to the experimental conditions recommended by the manufacturer.

[0090] The raw materials and reagents used in the following specific embodiments can be obtained commercially or prepared by those skilled in the art using known methods. Information on the main raw materials in the embodiments and comparative examples is shown in Table 1 below:

[0091] Table 1

[0092]

[0093] Example 1

[0094] This embodiment describes a copolymer of ethylene and α-olefin, and its preparation method is as follows:

[0095] In a continuous stirred tank reactor (volume 2L), a temperature gradient is constructed by a zoned temperature control jacket, so that the temperature in the high-temperature zone is 135℃, the temperature in the low-temperature zone is 85℃, and the temperature gradient ΔT is 50℃.

[0096] The purified solvent n-hexane was continuously injected into the reactor at a flow rate of 10 kg / h, and the α-olefin 1-octene was continuously injected at a flow rate of 2.2 kg / h. Simultaneously, ethylene gas was continuously introduced at a feed rate of 1.5 kg / h to maintain the total reactor pressure at 3.5 MPa. The chain transfer agent hydrogen was continuously fed at a flow rate of 0.03 g / h.

[0097] The main catalyst CAT1 (rac-ethylene bis(1-indenyl)zirconia) was continuously injected into the reactor at a flow rate of 0.01 g / h (based on the feed mass rate of pure catalyst, the same below), the co-catalyst alkylaluminum A1 (methylaluminoxane, prepared as a 10 wt% hexane solution with Al element content) at a flow rate of 0.12 g / h, and the organoboronide B1 (triphenylmethyltetra(pentafluorophenyl)borate, prepared as a 10 wt% hexane solution) at a flow rate of 0.30 g / h. The average residence time of the materials in the reactor was controlled to be approximately 8 min to 12 min. The polymer solution flowing out of the reactor outlet was deashed, extruded, granulated, and dried to obtain ethylene / 1-octene copolymer. The polymer yield was 1.65 kg / h, and the polymer activity was 165 kg / g cat, i.e., the number of kilograms of polymer produced per gram of catalyst.

[0098] The copolymers of ethylene and α-olefins provided in Examples 2-4 and Comparative Examples 1-2 were prepared using the same method as in Example 1, with the main difference being the change of the corresponding preparation parameters, as shown in Table 2 below:

[0099] Table 2

[0100]

[0101] Comparative Examples 3 and 4 used Dow Chemical's commercial POE products Engage 7467 (ethylene / 1-butene copolymer) and Engage 8200 (ethylene / 1-octene copolymer), respectively.

[0102] Test Example 1

[0103] The basic properties and branching characteristics of the ethylene-α-olefin copolymers in the test examples and comparative examples were examined.

[0104] (1) Melt index (MI):

[0105] The mass of the extrudate was measured using a melt flow indexer (CEAST melt flow indexer, Italy) and in accordance with the method of GB / T 3682.1-2018. At 190℃ and 2.16kg load, the mass of the extrudate was weighed every 6 seconds. Five parallel operations were performed, and the average value was taken and converted into the mass of the extrudate every 10 minutes, expressed in g / 10min.

[0106] (2) Density: Tested according to the method in standard ASTM D-792.

[0107] (3) Molecular weight (weight-average molecular weight Mw, number-average molecular weight Mn) and molecular weight distribution (PDI, Mw / Mn) can be obtained by gel permeation chromatography (GPC). The main parameters are: column: Agilent Olexis; solvent: 1,2,4-trichlorobenzene; flow rate: 1.0 mL / min; sample concentration: 1.0 mg / mL; injection volume: 200 μL; column temperature: 160 °C; detector: Agilent High Temperature RI detector; standard: polystyrene (PS) corrected with a cubic function.

[0108] (4) Branch Distribution Index (BDI):

[0109] a) Fractionation: The samples were fractionated using analytical temperature-elution fractionation-gel permeation chromatography (aTREF-GPC). The specific steps are as follows:

[0110] The polymer sample was completely dissolved in 1,2,4-trichlorobenzene at 150 °C to prepare a dilute solution (2 mg / mL). The solution was then slowly cooled to room temperature, allowing the polymer to precipitate and chromatographically deposited on an inert support according to its crystallinity (i.e., branching content), from highly crystalline (low branching content) to low crystalline (high branching content). Subsequently, multiple fractions with different branching contents were collected by gradually increasing the temperature.

[0111] b) Testing and calculation: The molecular weight (Mi) and branching content (Bi, in units of atoms per 1000 carbon atoms) of each fraction were determined online.

[0112] c) Calculate AWD and BWD:

[0113] The number-average branched content BWD = Σ(Bi*Ni) / ΣNi, where Ni is the number of moles in the i-th fraction.

[0114] The weight-average branched content AWD = Σ(Bi*Mi*Ni) / Σ(Mi*Ni) = Σ(Bi*Wi) / ΣWi, where Wi is the mass of the i-th fraction.

[0115] d) Calculate BDI: BDI = AWD / BWD.

[0116] The test results are shown in Tables 3 and 4 below.

[0117] Table 3

[0118]

[0119] Table 4

[0120]

[0121] Test Example 2

[0122] The copolymers of ethylene and α-olefins used in the examples and comparative examples were applied to cable insulation sheaths. The formulation, by weight, was: linear low-density polyethylene (LLDPE, MI=2.0 g / 10 min, density 0.920 g / cm³). 3 85 parts of the mixture, 15 parts of the copolymer to be tested, 1.5 parts of the crosslinking agent dicumyl peroxide (DCP), 1.0 part of the co-crosslinking agent triallyl isocyanurate (TAIC), and 0.5 parts of the antioxidant 1010. All components were melt-blended and granulated in a twin-screw extruder at 160°C, then molded into 1 mm thick test pieces, and crosslinked at 180°C for 15 minutes.

[0123] Toughness and long-term thermo-oxidative aging retention rate were tested on each specimen:

[0124] (1) Initial elongation at break: Tested according to GB / T 1040.3-2006 standard, with a tensile rate of 250 mm / min.

[0125] (2) Retention rate of elongation at break after thermo-oxidative aging: The test piece was placed in an aging oven at 136℃ for 168 hours and then taken out and tested again for elongation at break, i.e. elongation at break after aging.

[0126] Retention rate = (Elongation at break after aging / Initial elongation at break) × 100%.

[0127] The test results are shown in Table 5 below.

[0128] Table 5

[0129]

[0130] As shown in Tables 4 and 5, the examples demonstrate that by constructing ethylene-α-olefin copolymers with a branching distribution index (BDI) within a specific range, the materials effectively balance initial elongation at break and retention of elongation at break after aging. In contrast, the copolymers provided in Comparative Examples 1-4 have either excessively high or low BDI. Excessively high BDI indicates significant variations in branching distribution, which impairs the long-term thermal stability of the material. Conversely, excessively low BDI indicates a near-uniform distribution of α-olefins among the molecular chains, which also significantly reduces long-term thermal stability. This confirms that a specific non-uniform branching distribution based on a specific BDI plays a crucial role in effectively improving the long-term heat aging resistance of ethylene-α-olefin copolymers while maintaining a high initial elongation at break.

[0131] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0132] The embodiments described above are merely illustrative of several implementations of the present invention, designed to facilitate a detailed understanding of the technical solutions of the present invention, but should not be construed as limiting the scope of patent protection. It should be noted that 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 copolymer of ethylene and α-olefin, characterized in that, The branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.05~1.5; where BDI = AWD / BWD, AWD is the weight-average branching content of the copolymer of ethylene and α-olefin, and BWD is the number-average branching content of the copolymer of ethylene and α-olefin. The weight-average branching content (AWD) of the copolymer of ethylene and α-olefin is 70 to 110 carbon atoms per 1000 carbon atoms; the number-average branching content (BWD) of the copolymer of ethylene and α-olefin is 70 to 100 carbon atoms per 1000 carbon atoms.

2. The copolymer of ethylene and α-olefin according to claim 1, characterized in that, The branching distribution index (BDI) of the copolymer of ethylene and α-olefin is 1.1 to 1.

25.

3. The copolymer of ethylene and α-olefin according to claim 1, characterized in that, The weight-average branching (AWD) of the copolymer of ethylene and α-olefin is 88 to 100 carbon atoms per 1000 carbon atoms.

4. The copolymer of ethylene and α-olefin according to claim 1, characterized in that, The number-average branching content (BWD) of the copolymer of ethylene and α-olefin is 80 to 90 carbon atoms per 1000 carbon atoms.

5. The copolymer of ethylene and α-olefin according to any one of claims 1 to 4, characterized in that, The copolymer of ethylene and α-olefin has one or more of the following characteristics: (1) The molecular weight distribution index (PDI) is 2 to 4.5; (2) The melt index (MI) at 190℃ and 2.16kg is 0.5g / 10min to 15g / 10min; (3) The density is 0.865 g / cm³ 3 ~0.9g / cm 3 ; (4) The mass percentage of structural units derived from α-olefins in the copolymer of ethylene and α-olefins is 15% to 40%.

6. A method for preparing a copolymer of ethylene and α-olefin, characterized in that, Includes the following steps: The copolymer of ethylene and α-olefin is prepared by polymerizing ethylene and α-olefin in the presence of a catalyst. The polymerization reaction is carried out in the same reactor, which includes a first temperature zone and a second temperature zone. The temperature difference between the first temperature zone and the second temperature zone is ΔT, where ΔT is 40℃~115℃. The temperature in the first temperature zone is 135℃~165℃; The temperature in the second temperature zone is 30℃~120℃.

7. The method for preparing the copolymer of ethylene and α-olefin according to claim 6, characterized in that, The preparation method has one or more of the following characteristics: (1) The pressure of the polymerization reaction is 2MPa~10MPa; (2) The polymerization reaction time is 3 min to 25 min; (3) The catalyst includes a main catalyst and a co-catalyst; the main catalyst includes a transition metal catalyst; the co-catalyst is an organoaluminum compound, or a combination of an organoaluminum compound and an organoboride; (4) The polymerization reaction is carried out in the presence of a chain transfer agent, which includes one or more of methane, ethane, propane and hydrogen.

8. The method for preparing the copolymer of ethylene and α-olefin according to claim 6, characterized in that, The α-olefin includes one or more of the C3 to C20 α-olefins.

9. An insulating sheath for cables, characterized in that, Its composition includes the copolymer of ethylene and α-olefin as described in any one of claims 1 to 5 or the copolymer of ethylene and α-olefin prepared by the preparation method described in any one of claims 6 to 8.

10. The insulating sheath for cables according to claim 9, characterized in that, Its composition, by weight, includes: 80-99 parts of matrix resin The copolymer of ethylene and α-olefin is 1 to 20 parts. Crosslinking agent 0.1 to 3 parts 0.5 to 2 parts of crosslinking agent, and Antioxidant 0.1 to 1 part.

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