Ethylene / Α-olefin copolymer and use thereof

Abstract

The present application relates to the technical field of olefin polymerization, and in particular relates to an ethylene / α-olefin copolymer and the use thereof. The ethylene / α-olefin copolymer has the following characteristics: (a) as measured by DSC, the melting peak temperature is 35-100°C, and the width of the melting range is 50-70°C; and (b) dH(90) and dH(100) measured by means of successive self-nucleation / annealing (SSA) using a differential scanning calorimeter satisfy 0≤dH(90)≤2 J / g and dH(100)=0. When the copolymer of the present application is used for preparing a photovoltaic adhesive film, the processing efficiency at a relatively low processing temperature is high, the number of crystal spots in a film product is small, and the requirements of most downstream application scenarios, especially the application requirements of a casting section mold, can be met.

Description

Ethylene / α-olefin copolymer and its application Technical Field

[0001] The present application relates to the technical field of olefin polymerization, for example, an ethylene / α-olefin copolymer and its application. Background Art

[0002] Polyolefins, the largest polymer material, boast low cost, light weight, and easy molding and processing, making them widely used in a wide range of fields, including industry, agriculture, the military, and medicine. Polyethylene, a crucial product within the polyolefin industry, is currently the world's largest-volume general-purpose synthetic resin. Copolymers derived from the copolymerization of ethylene and α-olefins possess the plasticity of plastics and the high elasticity of rubber, making them a key area of ​​development for high-end polyolefin materials.

[0003] Downstream applications have high requirements for ethylene / α-olefin copolymers, and their thermal properties have a significant impact on the application scenario. In particular, during the film formation process of ethylene / α-olefin copolymers, downstream companies are particularly concerned about the number of crystal points on the film, especially in the photovoltaic film field.

[0004] When preparing cross-linked photovoltaic films, due to the inclusion of a cross-linking aid in the formulation, high processing temperatures are crucial for preventing the decomposition of the cross-linking aid during film casting or the formation of cross-links during the casting process. Therefore, the casting temperature must be kept relatively low. Lower processing temperatures, on the other hand, limit the processing efficiency of the polymers involved and increase the number of crystals in the resulting film. Therefore, it is crucial to develop ethylene / α-olefin copolymers with specific properties to address the issues of processing efficiency at lower temperatures and control the number of crystals in the resulting film.

[0005] For example, application document CN114466873A discloses an olefin polymer (ethylene / α-olefin copolymer), but it has a highly crystalline region and a high-temperature peak in its SSA, posing challenges to the processing of photovoltaic films. Application document CN109890854A, for example, discloses an ethylene / α-olefin copolymer, but its layered crystals are relatively thick and its thermal properties are not further clarified, potentially limiting its application in areas such as thermal performance and transparency.

[0006] For example, application document WO 2007 / 136497 A2 discloses a method for polymerizing ethylene and optionally one or more α-olefins under continuous solution polymerization conditions to prepare a high molecular weight polymer. The method comprises carrying out the polymerization under conditions that result in a polymerization index Ψ value and in the presence of a catalyst composition comprising a transition metal complex and an activating co-catalyst. This method solves the problem of comonomer insertion, but does not involve research on related issues such as processing efficiency at low temperatures or crystallinity of film products.

[0007] For example, application documents CN111943977A and CN111909196A both use a batch process to prepare polymers. The concentration of the comonomer in the reactor decreases continuously with the reaction time, and a uniform polymer product cannot be obtained. In addition, in the preparation methods disclosed in these two patent documents, ethylene pressure is used to control the total pressure of the reactor. The ethylene concentration in the reactor is the solubility under the pressure. Therefore, the ethylene concentration in the reactor is high and the conversion rate is low, making it difficult to achieve industrial production.

[0008] In view of this, it is very necessary to develop a solution polymerization method for producing ethylene / α-olefin copolymers with specific properties.

[0009] Summary of the Invention

[0010] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0011] In order to solve the problems of excessive crystal points and low processing efficiency in the film forming process of ethylene / α-olefin copolymers, the present application provides an ethylene / α-olefin copolymer and its application. The copolymer has specific properties, high processing efficiency at lower processing temperatures when preparing photovoltaic films, and a small number of crystal points in the film products. It can meet the needs of most downstream application scenarios, especially the application requirements of cast molds, and has good industrial prospects.

[0012] In a first aspect, the present application provides an ethylene / α-olefin copolymer, wherein the ethylene / α-olefin copolymer has the following characteristics:

[0013] (a) a melting peak temperature of 35 to 100°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C, 80°C, 90°C, 95°C) and a melting range of 50 to 70°C (e.g., 52°C, 54°C, 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 65°C, 66°C, 68°C) as measured by DSC;

[0014] (b) dH(90) and dH(100) measured using a differential scanning calorimeter using continuous self-nucleation / annealing (SSA), where 0≤dH(90)≤2 J / g (e.g., 0.01 J / g, 0.05 J / g, 0.1 J / g, 0.2 J / g, 0.4 J / g, 0.5 J / g, 0.8 J / g, 1.0 J / g, 1.2 J / g, 1.5 J / g, 1.8 J / g), and dH(100)=0.

[0015] The melting range of a polymer is a temperature range called the melting range. The two limits are called the initial melting temperature and the final melting temperature. The initial melting temperature is the temperature at which the substance begins to melt, and the final melting temperature is the temperature at which the substance is completely melted. In this text, the melting range width is the difference between the temperature at which the polymer is completely melted and the temperature at which it begins to melt, that is, T endset With T onset The difference.

[0016] In this text, in the results of SSA measurements using a differential scanning calorimeter, when the heat capacity of each segment is graded relative to the total heat capacity by integrating the temperature-heat capacity curve of each segment, dH(90) represents the sum of the melting enthalpies above 90°C, and dH(100) represents the sum of the melting enthalpies above 100°C.

[0017] According to the ethylene / α-olefin copolymer provided herein, in some embodiments, the ethylene / α-olefin copolymer further has the following characteristics:

[0018] (c) Density is 0.855 to 0.910 g / cm 3 ; For example, 0.860g / cm 3 , 0.865g / cm 3 、0.870g / cm 3 、0.875g / cm 3 , 0.880g / cm 3 , 0.885g / cm 3 、0.890g / cm 3 、0.895g / cm 3 , 0.900g / cm 3 、0.905g / cm 3 、0.908g / cm 3 ;

[0019] (d) a weight average molecular weight of 40,000 to 200,000 g / mol (e.g., 42,000 g / mol, 45,000 g / mol, 50,000 g / mol, 55,000 g / mol, 60,000 g / mol, 80,000 g / mol, 90,000 g / mol, 100,000 g / mol, 120,000 g / mol, 140,000 g / mol, 150,000 g / mol, 160,000 g / mol, 180,000 g / mol), and a molecular weight distribution width (PDI) of 2.3 to 3 (e.g., 2.4, 2.5, 2.6, 2.8, 2.9).

[0020] According to the ethylene / α-olefin copolymer provided by the present application, in some embodiments, the melting enthalpy of the ethylene / α-olefin copolymer is 20 to 100 J / g, for example, 22 J / g, 25 J / g, 28 J / g, 30 J / g, 40 J / g, 50 J / g, 60 J / g, 80 J / g, 90 J / g, and 95 J / g.

[0021] In some embodiments, the ethylene / α-olefin copolymer has a melt index (MI) of 0.1 to 30 g / 10 min at 190° C. and a load of 2.16 kg, for example, 0.15 g / 10 min, 0.3 g / 10 min, 0.5 g / 10 min, 1.0 g / 10 min, 2.0 g / 10 min, 5.0 g / 10 min, 8.0 g / 10 min, 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, 18 g / 10 min, 20 g / 10 min, 25 g / 10 min, or 28 g / 10 min.

[0022] In some embodiments, the ethylene / α-olefin copolymer has a glass transition temperature Tg of -65°C to -30°C, for example, -62°C, -60°C, -58°C, -55°C, -50°C, -45°C, -40°C, -35°C, -32°C.

[0023] In some embodiments, in the ethylene / α-olefin copolymer, the α-olefin is a C3-20 olefin or a mixture thereof, optionally selected from one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-eicosene.

[0024] In some embodiments, the ethylene / α-olefin copolymer is a product obtained by solution polymerization of ethylene and one or more α-olefins in the presence of a catalyst and, optionally, hydrogen as a chain transfer agent.

[0025] In some embodiments, in the solution polymerization reaction, the catalyst includes a main catalyst and a co-catalyst.

[0026] In some embodiments, the main catalyst is a homogeneous catalyst selected from a metallocene catalyst or a non-metallocene catalyst.

[0027] The main catalyst can be selected from, but not limited to, methylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dichloride, dimethylsilyl (N-tert-butylamino) (tetramethylcyclopentadienyl) titanium dimethyl, dimethylsilyl (N-tert-butylamino) (fluorenyl) titanium dichloride, (pentamethylcyclopentadienyl) trimethoxytitanium, dibenzylidene (cyclopentadienyl) (9-fluorenyl) zirconium dichloride, dimethyldisilylbis (2-methyl-4-phenyl-1-indenyl) zirconium dichloride, mesodimethylsilylbis (1-indenyl) zirconium dichloride, bis (methylcyclopentadienyl) zirconium dichloride, rac- Ethylenebis(1-indenyl)zirconium dichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, (cyclopentadienyl)(1,2-dimethoxyethane)zirconium trichloride, diphenylsilyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, racemic dimethylsilylbis(2-methyl-1-indenyl)zirconium dichloride, dibenzylidenecyclopentadienyl(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, di-p-toluenedicyclopentadienyl(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, dimethylbis(propylcyclopentadienyl)hafnium, bis(n-butylcyclopentadienyl)hafnium dichloride, dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, and one or more of the compounds represented by the following formulas (I) to (VIII).

[0028] From left to right and from top to bottom, they are Formula (IV) to Formula (VIII).

[0029] In some embodiments, the cocatalyst is one or more of aluminoxane, alkylaluminum compound and alkylaluminum chloride, or a combination of one or more of aluminoxane, alkylaluminum compound, alkylaluminum chloride and one or more organic boron compounds; for example, the cocatalyst is a combination of aluminoxane and organic boron compound, a combination of alkylaluminum compound and organic boron compound, or a combination of alkylaluminum chloride and organic boron compound.

[0030] In some embodiments, the aluminoxane is selected from methylaluminoxane (MAO) and modified methylaluminoxane (MMAO).

[0031] In some embodiments, the alkyl aluminum compound is selected from triethylaluminum, triisobutylaluminum, and trioctylaluminum.

[0032] In some embodiments, the alkylaluminum chloride is selected from ethylaluminum monochloride, ethylaluminum sesquichloride, and ethylaluminum dichloride.

[0033] In some embodiments, the organic boron compound is selected from trityltetrakis(pentafluorophenyl)borate, tris(pentafluorophenyl)boron, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate, dioctadecylmethyltertiaryaminetetrakis(pentafluorophenyl)borate, and dihydrogenated tallow methyltertiaryaminetetrakis(pentafluorophenyl)borate.

[0034] Furthermore, the molar ratio Al / M of the metal aluminum in the co-catalyst to the metal M in the main catalyst is 3 to 1000, for example, it can be 5, 10, 20, 50, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500, 600, 700, 800, 900, and can be optionally 10 to 100.

[0035] Furthermore, the molar ratio B / M of the organic boron compound (measured in boron) in the co-catalyst to the metal M in the main catalyst is 0 to 10, for example, it can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 9.5, etc., and can be optionally 1 to 3.

[0036] In the solution polymerization process, a solvent is also present. The solvent is in a liquid or supercritical state under polymerization conditions. The solvent can be a hydrocarbon solvent. The liquid hydrocarbon solvent used can be a C5-12 hydrocarbon, which can be unsubstituted or substituted with a C1-4 alkyl group (for example, one or more of pentane, methylpentane, hexane, heptane, octane, cyclohexane, C6 mixed alkanes, methylcyclohexane and hydrogenated naphtha). The solvent is more preferably selected from hexane, C6 mixed alkanes, methylcyclohexane, Isopar E, etc.

[0037] In some embodiments, the solution polymerization reaction is carried out in one or more polymerization reactors. Suitable reactors may include, for example, non-stirred or stirred spherical, cylindrical, and tank-shaped vessels, as well as loop reactors and tubular reactors.

[0038] In some embodiments, when the polymerization reactor is stirred or mixed by a circulation pump, the Reynolds number Re is controlled to be 6000-20000 (for example, 6500, 7000, 7500, 8000, 8500, 9000, 10000, 11000, 112000, 14000, 15000, 16000, 18000, 19000), and can be optionally 6000-10000.

[0039] The Reynolds number is a function of the flow rate, viscosity, and density of the reaction liquid within the polymerization reactor. Therefore, by controlling the Reynolds number, the material concentration distribution and temperature distribution within the polymerization reaction system can be comprehensively controlled, and the system flow rate, viscosity, and density can be comprehensively controlled. This allows for the regulation and production of polymers with specific properties (such as melting range width, dH(90), and dH(100)). For example, the Reynolds number can be controlled to adjust the temperature distribution and material concentration distribution within the polymerization system, and to limit the viscosity and flow rate of the polymerization system, thereby achieving the production of polymers with specific properties.

[0040] In some embodiments, the solution polymerization reaction is carried out at 2 to 10 MPa (e.g., 2.2 MPa, 2.5 MPa, 3.0 MPa, 3.5 MPa, 4.0 MPa, 4.5 MPa, 5.0 MPa, 5.5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa), optionally 2 to 5 MPa.

[0041] In some embodiments, the reaction temperature of the solution polymerization reaction is 100-220°C, for example, 110°C, 120°C, 140°C, 150°C, 180°C, 200°C, or 210°C.

[0042] Herein, the ethylene / α-olefin copolymer can be prepared by conventional polymerization processes in the art. For example, using equipment related to solution polymerization is also a conventional choice in the art and will not be described in detail here.

[0043] In a second aspect, the present application provides an application of the ethylene / α-olefin copolymer described above in the field of photovoltaic films.

[0044] The application of the ethylene / α-olefin copolymer in the field of photovoltaic films can be achieved through conventional operations in the art, which will not be described in detail here. For example, the prepared ethylene / α-olefin copolymer can be used to prepare a cast film through a casting process, using conventional casting equipment and processes.

[0045] The ethylene / α-olefin copolymer described in the present application has a wide melting range and 0≤dH(90)≤2J / g, so there is no high crystallization peak in the copolymer system, so it is easier to melt, that is, it is easier to achieve good processing at low temperatures; the melting range of the copolymer becomes wider, and the particles can be partially melted under the conditions of low extruder feeding and early conveying temperatures, and further conveying does not require too high a temperature to fully melt, and there is no gel, so the processing efficiency can be improved, the processing temperature can be reduced, and when some additives need to be added thereto, the decomposition of the additives can also be avoided; in addition, the copolymer has dH(100)=0, indicating that there is no gel in the copolymer system, so there are few or no crystal points in the process of copolymer film casting.

[0046] Compared with related technologies, the excellent effect of the technical solution of the present application lies at least in that: when the ethylene / α-olefin copolymer of the present application is used to prepare photovoltaic adhesive film, the processing efficiency is high at a lower processing temperature and the number of crystal points in the film product is small or almost no crystal points appear, which can meet the needs of most downstream application scenarios, especially the application requirements of cast molds.

[0047] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0048] In order to understand the technical features and content of the present application in detail, the optional embodiments of the present application will be described in more detail below. Although the optional embodiments of the present application are described in the embodiments, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein.

[0049] Unless otherwise specified, the experimental procedures used in the following examples are conventional methods.

[0050] The materials and reagents used in the following examples can all be obtained from commercial sources. The specific information of some raw materials is as follows:

[0051] 8660, ethylene / octene copolymer, available from Dow;

[0052] 8688, ethylene / butene copolymer, available from Dow;

[0053] Isopar E, 100% hydrogenated naphtha, purchased from Mobil;

[0054] Ethylene, polymerization grade, was purchased from Air Liquide;

[0055] 1-Octene, 98%, purchased from INEOS;

[0056] 1-Hexene, 99%, purchased from Lingyan Biotechnology;

[0057] 1-Butene, 99%, purchased from Mingju;

[0058] rac-ethylenebis(1-indenyl)zirconium dichloride, 99%, strem, labeled M1;

[0059] Dimethylsilyl(N-tert-butylamino)(tetramethylcyclopentadienyl)titanium dimethyl, 99%, purchased from Sinotec and marked as M2;

[0060] Dibenzylidenecyclopentadienyl (2,7-di-tert-butyl-fluorenyl) zirconium dichloride, 98%, purchased from Yaodexin Chemical, marked as M3;

[0061] The compound (M4) shown below was synthesized according to Example 16 described in patent document CN202010798198.8 (CN111943977B), and its structural formula is shown below;

[0062] The compound (M5) shown below was synthesized according to Example 4 disclosed in patent document CN202010793023.8 (CN111909196B), and its structural formula is shown below;

[0063] MMAO, 7% aluminum solution, purchased from Nouryon;

[0064] MAO, 15% aluminum solution, purchased from Albemarle;

[0065] Triisobutylaluminum (TIBA) hexane solution, 1 mol / L, purchased from Inokai;

[0066] Trityl tetrakispentafluorophenyl borate, 99%, was purchased from Inochem and dissolved in toluene and labeled as B1.

[0067] <Test Method>

[0068] (1) In the following examples and comparative examples, the melting peak temperature of the obtained polymer is T m The melting enthalpy and melting enthalpy were measured using DSC, using the data obtained from the second heating, with a heating and cooling rate of 10°C / min. The melting range width is the difference between the temperature at which the polymer is completely melted and the temperature at which it begins to melt, that is, T endset With T onset The difference.

[0069] (2) In the following examples and comparative examples, the SSA of the obtained polymers was measured by DSC. Specifically, in the first cycle, the temperature was raised to 150°C, held for 1 minute, and then lowered to -50°C; in the second cycle, the temperature was raised to 120°C, held for 5 minutes, and then lowered to -50°C; in the third cycle, the temperature was raised to 112.5°C, held for 5 minutes, and then lowered to -50°C; the temperature was raised and held for 5 minutes and then lowered according to the above cyclic operation, and the fourth cycle (i.e., in the fourth cycle, the temperature was raised to a maximum of 105°C at intervals of 7.5°C and held for 5 minutes before lowering the temperature to -50°C), the fifth cycle (i.e., in the fifth cycle, the temperature was raised to a maximum of 97.5°C at intervals of 7.5°C and held for 5 minutes before lowering the temperature to -50°C), the sixth cycle, etc., until the rising temperature reached -40°C, thereby crystallizing in each temperature interval. In the final cycle, the temperature was raised to 150°C at 10°C / min and the heat capacity was measured, dH(90) representing the sum of the melting enthalpies above 90°C and dH(100) representing the sum of the melting enthalpies above 100°C.

[0070] (3) In the following examples and comparative examples, the density of the obtained polymer was tested using a densitometer; the sample to be tested was cut from a tabletting plate and the density was tested using a densitometer Mettler XS204, using an immersion method with anhydrous ethanol AR as the immersion liquid; the test ambient temperature was 23°C ± 2°C, and the test temperature required internal calibration; the mass of the sample to be tested was > 1g and free of bubbles; the mass of the sample in air and the mass in the immersion liquid were weighed separately, and the density of the sample to be tested was calculated and derived using the Archimedean principle.

[0071] (4) In the following examples and comparative examples, the molecular weight, molecular weight distribution and insertion rate of α-olefin (such as 1-octene) of the obtained polymers were obtained by GPC-IR testing of polymer char at a test temperature of 150°C, and the product recovery rate exceeded 95%.

[0072] (5) In the following examples and comparative examples, the melt index (MI) of the obtained polymers was tested at 190°C and a load of 2.16 kg: 4-8 g of the pellets to be tested were taken, the temperature was set to 190°C, the load was 2.16 kg, and the inner diameter of the standard die was 2.095 mm. After the pellets were melted in the barrel for 5 minutes, they flowed out of the die under the action of a pressure load, and the time taken for the displacement point to be 46 mm to 20.6 mm was measured and recorded. The specimens were automatically cut and the mass of the specimens was weighed on a balance. The MFR or MVR was calculated in units of g / 10 min and cm 3 / 10min.

[0073] The ethylene / α-olefin copolymers in the various examples and comparative examples were prepared in a continuous reaction platform equipped with reactors of different volumes and types, and the operation steps were as follows:

[0074] The dried solvent is continuously introduced into the reactor for 2 days to remove impurities from the reactor, and then an α-olefin comonomer, a solvent, a primary catalyst, and a co-catalyst are introduced into the reactor in sequence, stirring and mixing is started, the system is heated, and ethylene monomer at 3 to 9 MPa is introduced to carry out a polymerization reaction; wherein:

[0075] The reaction was conducted according to the polymerization reaction conditions shown in Tables 1 to 3 (specific solvent, ethylene, α-olefin comonomer, primary catalyst, and co-catalyst were delivered to the reactor at a specific feed rate, and the reaction pressure, reaction temperature, and mixing Reynolds number were controlled). The resulting reaction solution was subjected to subsequent steps (removal of volatile components, drying, extrusion, and granulation) to obtain specific ethylene / α-olefin copolymer product particles. Wherein:

[0076] The volatile components in the reaction liquid are removed by flash evaporation; extrusion and granulation are carried out by a twin-screw extruder, the extrusion temperature is 80-260° C., and the screw speed is 30-150 rpm.

[0077] The characteristic test results of the products prepared in each embodiment and comparative example are shown in Tables 4-5.

[0078] Table 1 Polymerization conditions of each embodiment and comparative example

[0079] Table 2 Polymerization conditions of each embodiment and comparative example

[0080] Table 3 Polymerization conditions of each embodiment and comparative example

[0081] Table 4 Characteristic test results of polymers obtained in various examples and comparative examples

[0082] Table 5 Characteristic test results of polymers obtained in various examples and comparative examples

[0083] Furthermore, the copolymers of the above-mentioned embodiments and comparative examples were film-cast on a casting machine (equipped with a single-screw extruder, L / D=35, screw diameter 30 mm), the casting processing temperature was 110° C., and the film thickness was controlled to be 0.6 mm.

[0084] After the cast film was obtained, the number of crystal points and film processing efficiency were tested. The number of crystal points was tested according to ASTM D3351, and the processing efficiency was measured by the length of the film processed within 10 minutes. The relevant test results are shown in Table 6.

[0085] Table 6 Test on the number of crystal points and casting efficiency of ethylene / α-olefin copolymer after film casting

[0086] As can be seen from Table 6, after the ethylene / α-olefin copolymers prepared in the examples of the present application are used to prepare cast films, the number of crystal points in the films is significantly less than that of the cast films prepared from the copolymers obtained in Comparative Examples 1 to 2, and the processing efficiency during the casting process is significantly faster than that of Comparative Examples 3 to 4, indicating that the ethylene / α-olefin copolymers of the present application have unique characteristics, which significantly reduce the number of crystal points in the cast films prepared from the copolymers and significantly improve the processing efficiency.

[0087] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those skilled in the art without departing from the spirit of the present invention.

Claims

1. An ethylene / α-olefin copolymer, wherein, the ethylene / α-olefin copolymer has the following characteristics: (a) The melting peak temperature measured by DSC is 35 to 100 °C, and the melting range width is 50 to 70 °C; (b) dH(90) and dH(100) measured by differential scanning calorimetry using successive self-nucleation / annealing (SSA), where 0 ≤ dH(90) ≤ 2 J / g and dH(100) = 0.

2. The ethylene / α-olefin copolymer according to claim 1, wherein, the ethylene / α-olefin copolymer further has the following characteristics: (c) The density is 0.855 to 0.910 g / cm 3 ; (d) The weight-average molecular weight is 40,000 to 200,000 g / mol, and the molecular weight distribution width PDI is 2.3 to 3.

3. The ethylene / α-olefin copolymer according to claim 1, wherein, the melting enthalpy of the ethylene / α-olefin copolymer is 20 to 100 J / g.

4. The ethylene / α-olefin copolymer according to claim 1, wherein, the melt index (MI) of the ethylene / α-olefin copolymer under the conditions of 190 °C and a load of 2.16 kg is 0.1 to 30 g / 10 min.

5. The ethylene / α-olefin copolymer according to claim 1, wherein, the glass transition temperature Tg of the ethylene / α-olefin copolymer is -65 °C to -30 °C.

6. The ethylene / α-olefin copolymer according to claim 1, wherein, in the ethylene / α-olefin copolymer, the α-olefin is an olefin of C3 to 20 or a mixture thereof.

7. The ethylene / α-olefin copolymer according to claim 6, wherein, the α-olefin is selected from one or more of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-eicosene.

8. The ethylene / α-olefin copolymer according to claim 1, wherein, the ethylene / α-olefin copolymer is a product obtained by solution polymerization of ethylene with one or more α-olefins in the presence of a catalyst and optionally a chain transfer agent hydrogen.

9. The ethylene / α-olefin copolymer according to claim 8, wherein, the catalyst includes a main catalyst and a co-catalyst; the main catalyst is a homogeneous catalyst, selected from metallocene catalysts or non-metallocene catalysts; and / or the co-catalyst is one or more of aluminoxane, alkylaluminum compounds, and alkylaluminum chlorides, or a composition of one or more of aluminoxane, alkylaluminum compounds, and alkylaluminum chlorides and one or more organic borides.

10. The ethylene / α-olefin copolymer according to claim 9, wherein, the aluminoxane is selected from methylaluminoxane, modified methylaluminoxane; and / or the alkylaluminum compound is selected from triethylaluminum, triisobutylaluminum, trioctylaluminum; and / or the alkylaluminum chloride is selected from chloroethylaluminum, sesquiethylaluminum, dichloroethylaluminum; and / or The organoboride is selected from trityl tetrakis(pentafluorophenyl)borate, tris(pentafluorophenyl)borane, N,N-dimethylaniline tetrakis(pentafluorophenyl)borate, bis(octadecyl)methyl tertiary amine tetrakis(pentafluorophenyl)borate, and bis(hydrogenated tallow)methyl tertiary amine tetrakis(pentafluorophenyl)borate.

11. The ethylene / α-olefin copolymer according to claim 8, wherein, the solution polymerization reaction is carried out in one or more polymerization reactors; and / or when the polymerization reactor is mixed by stirring or a circulation pump, the Reynolds number Re is controlled to be 6000-20000.

12. The ethylene / α-olefin copolymer according to claim 8, wherein, the solution polymerization reaction is carried out at 2-10 MPa.

13. Use of the ethylene / α-olefin copolymer according to any one of claims 1-12 in the field of photovoltaic adhesive films.

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