Ethylene / alpha-olefin copolymer, preparation method and application

Abstract

The invention discloses an ethylene / alpha-olefin copolymer as well as a preparation method and application thereof. The N value, calculated according to the following equation, of the copolymer ranges from 1.4 to 2.5; n is equal to NT + NTV, and NT is equal to NV + NV1; in the formula, N, NT, NTV, NV and NV1 respectively represent the total number of vinyl groups, the total number of terminal vinyl groups, 1, 2-disubstituted double bonds, the number of monosubstituted double bonds and the number of 1, 1-disubstituted double bonds in every 1000 carbon atoms through nuclear magnetic co-spectrum analysis. The ethylene / alpha-olefin copolymer provided by the invention has improved crosslinking vulcanization speed and crosslinking degree, also has good melt flowability, and can be widely applied to packaging adhesive films of photovoltaic modules.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to an ethylene / α-olefin copolymer, its preparation method, and its application. Background Technology

[0002] Polyolefins, as the largest category of polymer materials in terms of production volume, have been widely used in many fields such as packaging, building materials, automobiles, and electronics due to their outstanding advantages such as low cost, low density, and excellent molding and processing performance. Among them, polyethylene is one of the most important products in the polyolefin industry and is currently the highest-produced general-purpose synthetic resin globally, with its market demand consistently ranking among the top of all synthetic resins. In the process of developing high-end polyolefin materials, ethylene-α-olefin copolymers, which are prepared by copolymerization of ethylene and α-olefins, have become one of the core development directions of high-end polyolefin materials due to their combination of the plasticity of plastics and the high elasticity of rubber, and have shown broad application prospects in many high-performance application scenarios. Solar cells are the core components for converting solar energy into electrical energy. Module-type solar cells, due to their stable structure and convenient installation, are widely used in outdoor applications such as building rooftops and photovoltaic power stations. In the manufacturing process of crystalline solar cell modules, the typical structure is a stacked arrangement of front glass / solar cell encapsulant / crystalline solar cell device / solar cell encapsulant / rear glass (or rear protective sheet). The solar cell encapsulant, as the core encapsulation material, must possess excellent transparency, flexibility, adhesion, and weather resistance to ensure the long-term stable operation of the solar cell module. Currently, commonly used encapsulants in the photovoltaic field mainly include ethylene-vinyl acetate copolymer (EVA) and ethylene-α-olefin copolymer. Compared to EVA encapsulant, ethylene-α-olefin copolymer has superior resistance to potential-induced degradation (PID), effectively improving the long-term reliability of photovoltaic modules, and has gradually become the mainstream choice and future development direction for photovoltaic cell encapsulation materials.

[0003] However, when ethylene-α-olefin copolymers are used as photovoltaic encapsulants, in order to meet the weather resistance requirements for long-term outdoor use, their mechanical strength, heat resistance, and dimensional stability must be improved through crosslinking reactions to resist the damage to the encapsulant film performance caused by complex outdoor environments (such as high and low temperature cycling and ultraviolet radiation). Currently, the photovoltaic encapsulant film industry commonly uses peroxide crosslinking systems to achieve crosslinking of ethylene-α-olefin copolymers, but the crosslinking efficiency of this system is closely related to the type and content of terminal unsaturated bonds in the copolymer molecular chain itself. In existing technologies, the molecular chain ends of general-purpose ethylene-α-olefin copolymers are mostly saturated structures or internal double bond structures. These structures have low crosslinking reactivity, resulting in significant technical defects in the crosslinking process: First, the degree of crosslinking is difficult to improve, making it impossible for the mechanical strength, heat resistance, and weather resistance of the film to fully meet the requirements of long-term service of photovoltaic modules, thus affecting the service life of the modules; Second, the crosslinking reaction rate is slow, which prolongs the lamination process time of photovoltaic modules, significantly reducing production efficiency and increasing production costs; Third, during the film processing and casting process, due to insufficient crosslinking reactivity, polymer chain segments are prone to over-crystallization, leading to the formation of crystal point defects in the film during low-temperature casting processes. This not only affects the light transmittance of the film and reduces the photoelectric conversion efficiency of the photovoltaic module, but also damages the uniformity of the film's appearance, ultimately threatening the long-term reliability of the photovoltaic modules. In summary, existing general-purpose ethylene-α-olefin copolymers suffer from technical problems when used in photovoltaic films, including insufficient crosslinking activity, slow crosslinking speed, low upper limit of crosslinking degree, and susceptibility to crystal point formation during processing. These issues severely restrict their further application in photovoltaic encapsulation. Therefore, there is an urgent need to develop a novel ethylene-α-olefin copolymer with highly reactive end structures through molecular structure design to fundamentally improve its crosslinking performance and overcome the aforementioned shortcomings of existing technologies. Summary of the Invention

[0004] To address the above technical problems, this invention proposes an ethylene / α-olefin copolymer, its preparation method, and its applications. The ethylene / α-olefin copolymer provided by this invention exhibits improved crosslinking vulcanization speed and degree of crosslinking, while also maintaining good melt flowability. It can be widely used in encapsulation films for photovoltaic modules, resulting in improved module yield.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An ethylene / α-olefin copolymer having an N value between 1.4 and 2.5, for example 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, preferably 1.4-2.0, calculated according to the following equation (1); N = NT + NTV (1) NT = NV + NV1 (2) In the equation, N, NT, NTV, NV, and NV1 represent the total number of vinyl groups, the total number of terminal vinyl groups, the number of 1,2-disubstituted double bonds, the number of monosubstituted double bonds, and the number of 1,1-disubstituted double bonds per 1000 carbon atoms, respectively, as determined by nuclear magnetic resonance spectroscopy.

[0006] Among them, 1,2-disubstituted double bond refers to an unsaturated double bond structure in which both carbon atoms in a carbon-carbon double bond are attached to a non-hydrogen substituent, which can be represented by the following formula: -R-CH=CH-R'-; 1,1-Disubstituted double bond refers to an unsaturated double bond structure in a carbon-carbon double bond in which two non-hydrogen substituents are attached to one carbon atom and two hydrogen atoms are attached to the other carbon atom. It can be represented by the following formula: -R2C=CH2; A monosubstituted double bond is an unsaturated double bond structure in which only one non-hydrogen atom or group is attached to the carbon-carbon double bond, and the remaining three attachment sites are all hydrogen atoms. It can be represented by the following formula: -R-CH=CH2; Terminal vinyl groups refer to the carbon-carbon double bond ends of copolymer segments (including monosubstituted double bonds and 1,1-disubstituted double bonds). The total number of vinyl groups refers to the sum of the carbon-carbon double bond content of all types.

[0007] In some preferred examples, the melt index (MI) of the ethylene / α-olefin copolymer at 190°C and 2.16 kg is 0.5-30 g / min, for example 0.5 g / min, 1 g / min, 3 g / min, 5 g / min, 7 g / min, 10 g / min, 13 g / min, 15 g / min, 17 g / min, 20 g / min, 23 g / min, 25 g / min, 27 g / min, 30 g / min, preferably 1.5-24 g / min, more preferably 3-22 g / min; Preferably, the density of the ethylene / α-olefin copolymer is 0.860-0.880 g / cm³. 3 For example, 0.860 g / cm³ 3 0.865 g / cm 3 0.870 g / cm 3 0.872 g / cm 3 0.877 g / cm 3 0.880 g / cm 3 The preferred concentration is 0.862-0.880 g / cm³. 3 More preferably 0.865-0.877 g / cm³ 3 ; Preferably, the molecular weight distribution index of the ethylene / α-olefin copolymer is 2.0-3.5, for example 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 3.2, more preferably 2.0-3, and more preferably 2.1-2.6.

[0008] In some preferred examples, the weight-average molecular weight Mw of the ethylene / α-olefin copolymer is 40,000-150,000, preferably 45,000-130,000, and more preferably 46,000-90,000; Preferably, the α-olefin insertion rate in the ethylene / α-olefin copolymer is 20-38%. Specifically, the molar insertion rate can be above 22%, above 25%, or above 28%, and can be below 36%, below 34%, or below 30%.

[0009] This invention does not limit the preparation method of the ethylene / α-olefin copolymer described above; the following is merely an example of a feasible solution: The method for preparing the ethylene / α-olefin copolymer includes the following steps: Ethylene is mixed with α-olefin, main catalyst, co-catalyst, solvent and optional chain transfer agent and added to a reactor for solution polymerization to obtain ethylene / α-olefin copolymer; The solution polymerization reaction satisfies the following conditions:

[0010] Among them, F α-烯烃 F is the feed rate for α-olefins, expressed in kg / h. 主催化剂 The catalyst feed rate is expressed in g / h, C. 主催化剂效率 The mass of polymer produced per unit mass of catalyst is expressed in kg / g, F. H2 The hydrogen feed mass is expressed in kg / h, F 乙烯 The value represents the mass of ethylene feed, expressed in kg / h.

[0011] In some preferred embodiments, the solution polymerization reaction is characterized by a reaction temperature of 110-200°C, preferably 120-190°C, and a reaction time of 2-20 minutes, preferably 3-12 minutes. Preferably, the solution polymerization reaction is carried out at 2-10 MPa, and more preferably at 3-7 MPa.

[0012] In some preferred examples, the α-olefin is selected from C3-C4. 20 The α-olefin is preferably 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.

[0013] In some preferred examples, the main catalyst is selected from metallocene catalysts and / or non-metallocene catalysts; preferably rac-ethylene bis(1-indenyl)zirconia, silyl(N-tert-butylamino)(tetramethylcyclopentadienyl)titanium dichloride, disilyl(N-tert-butylamino)(tetramethylcyclopentadienyl)dimethyltitanium, disilyl(N-tert-butylamino)(fluorenyl)titanium dichloride, (pentamethylcyclopentadienyl)trimethoxytitanium, diphenylmethylene(cyclopentadiene)(9-fluorenyl)zirconia, dimethyldimethylsilyl bis(2-methyl-4-phenyl-1-indenyl)zirconia, meso dimethylsilyl bis(1-indenyl)zirconia, (bis(methylcyclopentadiene)zirconia), (bis(1,3-dimethylcyclopentadienyl)zirconia, (cyclopentadienyl)(1 Zirconium trichloride (2-dimethoxyethane), diphenylsilyl(cyclopentadiene)(9-fluorenyl)zirconium dichloride, racemic dimethylsilylbis(2-methyl-1-indene)zirconium dichloride, diphenylmethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, di-p-tolymethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconium dichloride, dimethylbis(propylcyclopentadienyl)hafnium, bis(n-butylcyclopentadiene)hafnium dichloride, dimethylsilylbis(2-methyl-4-phenylindene)zirconium dichloride, and at least one of the following compounds:

[0014]

[0015]

[0016] Preferably, the co-catalyst comprises an aluminum additive selected from one or more of alkylaluminum, aluminum oxane, alkylaluminum chloride and their modifiers, preferably one or more of methylaluminoxane (MAO), modified methylaluminoxane (MMAO), trimethylaluminum, triethylaluminum, tripropylaluminum, tri-n-butylaluminum, triisobutylaluminum, trioctylaluminum, monochloroethylaluminum, sesquiethylaluminum chloride, and dichloroethylaluminum; Preferably, the amount of aluminum additive is 10-1000 based on the molar ratio Al / M of metallic aluminum and metallic M in the main catalyst, for example, it can be 10, 10, 20, 50, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500, 600, 700, 800, 1000, etc., preferably 20-100.

[0017] In some preferred examples, the cocatalyst further includes an organoboride, preferably one or more of triphenylmethyltetra(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, N,N-dimethylanilinetetra(pentafluorophenyl)borate, bis(octadecylmethyl)tertiaryaminetetra(pentafluorophenyl)borate, and dihydrotallowylmethyl)tertiaryaminetetra(pentafluorophenyl)borate. Preferably, the amount of the organoboride used is 0-20 based on the molar ratio of boron to metal M in the main catalyst (B / M), for example, it can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, etc., preferably 1-10.

[0018] In some preferred examples, the solvent is typically and preferably a hydrocarbon solvent, preferably a C5-C12 aliphatic hydrocarbon solvent and / or an aromatic hydrocarbon solvent, preferably selected from one or more of n-butane, isobutane, methylcyclopentane, methylenecyclopentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, n-octane, isoparaffins (IsoparE), benzene, toluene, and xylene. Preferably, the amount of solvent used is such that the mass concentration of the main catalyst is 10-1000 ppm.

[0019] In some preferred examples, the chain transfer agent is selected from one or more of methane, ethane, propane, and hydrogen; Preferably, the amount of chain transfer agent used is 0.014-1.4% of the molar amount of ethylene.

[0020] Application of an ethylene / α-olefin copolymer as described above or an ethylene / α-olefin copolymer prepared by the method described above in photovoltaic encapsulation materials.

[0021] The ethylene / α-olefin copolymer of the present invention can be used to form a resin composition with any one or more of the following additives: crosslinking agent, crosslinking aid, silane coupling agent, light stabilizer, ultraviolet absorber, anti-precipitation aid, anti-PID aid, etc. In addition to the aforementioned components, resin compositions can also be prepared with various other additives known in the art, depending on the intended use of the applicable resin components.

[0022] In addition, the above-mentioned resin composition can be used to prepare photovoltaic encapsulation materials by molding methods such as casting extrusion and twin-screw extrusion. For example, it can be used to make encapsulation films in photovoltaic modules to ensure that the cells have stable power generation performance over a long period of time.

[0023] The beneficial effects of this invention are as follows: This invention designs the amount of various vinyl groups in the ethylene / α-olefin copolymer to make the crosslinking active sites more active under the same or similar insertion rate conditions, and to enable faster vulcanization crosslinking reaction under the same conditions, while also having a higher degree of crosslinking. This results in faster processing speed and higher film strength in photovoltaic encapsulants, while reducing the use of crosslinking aids. This is of great significance for reducing costs and increasing production volume in photovoltaic modules. Detailed Implementation

[0024] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0025] In the various embodiments and comparative examples of this invention, the main raw materials are sourced as follows; unless otherwise specified, other raw materials and reagents were obtained through commercially available channels: Ethylene: Purchased from liquefied air, purity 99.95%; 1-Octenene, 98%, Sinopec INEOS (Tianjin) Petrochemical Co., Ltd.; 1-Butene, 99%, light source; Iospar E isoparaffin, purchased from Jingbo Petrochemical Co., Ltd. rac-ethylenebis(1-indenyl)zirconium dichloride, 99%, strem, denoted as A1; Dimethicone (N-tert-butylamino) (tetramethylcyclopentadienyl)dimethyltitanium, 99%, Xinnoco is A2; Diphenylmethylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconium dichloride, Yaodexin Chemical, 98%, designated as A3; The compounds in the following formula were synthesized according to the scheme in Example 4 disclosed in patent CN111909196B: A4 MAO, a 10wt% hexane solution of Al, was purchased from Akzo, B1; MMAO, a 10wt% hexane solution of Al, purchased from Norinon, B2; Triisobutylaluminum, 10wt% Al in n-hexane solution, purchased from Inokai, B3.

[0026] The copolymer performance testing method involved in the following embodiments of the present invention is as follows: (1) Density: Measured according to ASTM D-792, unit g / cm³ 3 .

[0027] (2) Melt flow index (MI): Measured according to ASTM D-1238 (conditions: 190℃, 2.16Kg load).

[0028] (3) Weight-average molecular weight (Mw), molecular weight distribution (PDI), and comonomer insertion rate can be obtained using gel permeation chromatography (GPC). Specifically, the chromatographic column is an Agilent Olexis; the solvent is trichlorobenzene; the flow rate is 1.0 ml / min; the sample concentration is 1.0 mg / ml; the injection volume is 200 μl; the column temperature is 160 °C; the detector is an Agilent High Temperature RI detector; and the standard is polystyrene (corrected using a cubic function).

[0029] (4) Double bond quantity test The specific steps for NMR analysis are as follows: Approximately 15 mg of the copolymer sample was dissolved in 0.6 mL of deuterated chloroform (containing 0.03% v / v TMS internal standard), and the analysis was performed using a Bruker AVANCE NEO 500 MHz NMR spectrometer. The test temperature was 25°C, a 5 mm BBO probe was used, the relaxation delay time was 5 seconds, and a total of 64 scans were performed. After manual correction of the phase and baseline of the spectrum, the characteristic peak regions, including the internal standard TMS peak (0 ppm) and 1,2-disubstituted double bonds (δ 4.7–5.2 ppm), monosubstituted double bonds (δ 5.4–6.0 ppm), and 1,1-disubstituted double bonds (δ 4.6–5.0 ppm), were integrated. The number of carbon atoms per kilocarbon for each functional group was calculated based on the ratio of its integrated area to the total integrated area of ​​the entire spectrum, taking into account the number of protons represented by each functional group and the average number of carbon and hydrogen atoms in the repeating unit of the polymer. In addition, the total number of terminal vinyl groups is equal to the sum of the number of monosubstituted double bonds and the number of 1,1-disubstituted double bonds, and the total number of vinyl groups is equal to the sum of the number of monosubstituted double bonds, the number of 1,1-disubstituted double bonds and the number of 1,2-disubstituted double bonds.

[0030] The following embodiments of the present invention involve a method for testing the performance of the encapsulating film: (1) Crosslinking degree: The crosslinking degree was determined according to the photovoltaic industry association standard T / CPIA 0006-2017.

[0031] (2) Crosslinking vulcanization time T90: The optimal vulcanization time T90 of the film was measured according to GB / T 16584-1996. T90 is used to characterize the speed of crosslinking. The smaller the T90 time, the faster the crosslinking speed.

[0032] (3) The crystal point test method refers to the industry standard QB / T 4451-2012, which tests the number of crystal points with a diameter ≥ 0.2 micrometers in 1 square meter cast film.

[0033] Example 1 Ethylene / α-olefin copolymers were prepared according to the following method: Hexane solvent (800 kg / h) and α-olefin (150 kg / h) were added to a 250 L autoclave continuous reactor, and the temperature at the top of the reactor was preheated to 145 °C. Simultaneously, the main catalyst A1 (1.668 g / h) and co-catalyst B1 (7.97 g / h) were introduced into the reactor. Subsequently, ethylene (100 kg / h) and hydrogen (0.001 kg / h) were added to the autoclave reactor, and the reaction pressure was maintained at 5 MPa throughout the continuous process. The copolymerization reaction was carried out at 145 °C for 15 minutes to obtain a copolymer solution (relevant reaction conditions are shown in Table 1, where Q represents...). The reaction solution was quenched with methanol and then entered a three-stage devolatilization tank for devolatilization. After removing unreacted solvent, α-olefins and ethylene in the devolatilization tank, copolymer particles were obtained by extrusion granulation. Their properties were tested and are shown in Table 2.

[0034] Examples 2-8, Comparative Examples 1-2 Examples 2-8 show copolymers with different properties prepared by changing the catalyst type, α-olefin type, polymerization temperature, polymerization pressure, ethylene conversion rate, and other parameters in Example 1. The parameters are shown in Table 2.

[0035] Comparative Examples 3-4 Comparative Example 3 was selected from Dow Chemical's 8680 ethylene / α-olefin copolymer; Comparative Example 4 was selected from Dow Chemical's 8688 ethylene / α-olefin copolymer.

[0036] Table 1

[0037] Table 2

[0038] The number of different double bond types in the ethylene / α-olefins prepared in Examples 1-8 and Comparative Examples 1-4 was analyzed, and the results are shown in Table 3: Table 3

[0039] Application examples Photovoltaic encapsulating films were prepared using the ethylene / α-olefin copolymers provided in the respective embodiments and comparative examples as raw materials, according to the following methods: According to the weight parts, 100 parts of ethylene / α-olefin copolymer, 0.8 parts of crosslinking agent (2-ethylhexyl) tert-amyl carbonate peroxide, 0.7 parts of co-crosslinking agent (traceryl isocyanurate), 0.3 parts of silane coupling agent (3-(methacryloyloxy)propyltrimethoxysilane), and 0.2 parts of antioxidant (β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester) are thoroughly mixed. The mixture is added to a single-screw casting extruder, melted and plasticized, and then injected into a T-die. The melting temperature is 90°C. After melt extrusion, casting film formation, cooling, slitting, and winding, the encapsulating film is obtained.

[0040] The performance tests for each encapsulating film were performed as shown in Table 4, and the results are as follows: Table 4

[0041] The test results above show that the encapsulating film prepared using the ethylene / α-olefin copolymer provided in Examples 1-8 of this invention has a higher degree of crosslinking and a faster crosslinking speed, which can significantly shorten the crosslinking time of the material and improve the processing efficiency; at the same time, the encapsulating film has a lower crystal point level.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. An ethylene / α-olefin copolymer, characterized in that, The value of N calculated according to the following equation (1) is between 1.4 and 2.5; N = NT + NTV (1) NT = NV + NV1 (2) In the equation, N, NT, NTV, NV, and NV1 represent the total number of vinyl groups, the total number of terminal vinyl groups, the number of 1,2-disubstituted double bonds, the number of monosubstituted double bonds, and the number of 1,1-disubstituted double bonds per 1000 carbon atoms, respectively, as determined by nuclear magnetic resonance spectroscopy.

2. The ethylene / α-olefin copolymer according to claim 1, characterized in that, The ethylene / α-olefin copolymer has a melt index (MI) of 0.5-30 g / min at 190°C and 2.16 kg; and / or, The density of the ethylene / α-olefin copolymer is 0.860-0.880 g / cm³. 3 ; and / or, The molecular weight distribution index of the ethylene / α-olefin copolymer is 2.0-3.

5.

3. The ethylene / α-olefin copolymer according to claim 1 or 2, characterized in that, The weight-average molecular weight (Mw) of the ethylene / α-olefin copolymer is 40,000-150,000; and / or, The α-olefin insertion rate in the ethylene / α-olefin copolymer is 20-38%.

4. A method for preparing an ethylene / α-olefin copolymer according to any one of claims 1-3, characterized in that, Includes the following steps: Ethylene is mixed with α-olefin, main catalyst, co-catalyst, solvent and optional chain transfer agent and added to a reactor for solution polymerization to obtain ethylene / α-olefin copolymer; The solution polymerization reaction satisfies the following conditions: Among them, F α-烯烃 F is the feed rate for α-olefins, expressed in kg / h. 主催化剂 Main catalyst feed rate, in g / h, C 主催化剂效率 The mass of polymer produced per unit mass of main catalyst, expressed in kg / g, F H2 The hydrogen feed mass is expressed in kg / h, F 乙烯 The value represents the mass of ethylene feed, expressed in kg / h.

5. The method for preparing the ethylene / α-olefin copolymer according to claim 4, characterized in that, The solution polymerization reaction is carried out at a temperature of 110-200℃; the reaction time is 2-20 minutes; and / or, The solution polymerization reaction was carried out at 2-10 MPa.

6. The method for preparing the ethylene / α-olefin copolymer according to claim 4, characterized in that, The main catalyst is selected from metallocene catalysts and / or non-metallocene catalysts; and / or, The cocatalyst includes an aluminum promoter selected from one or more of alkylaluminum, aluminoxane, alkylaluminum chloride, and their modifiers; and / or, The amount of aluminum additive used, calculated as the molar ratio Al / M of metallic aluminum and metallic M in the main catalyst, is 10-1000.

7. The method for preparing the ethylene / α-olefin copolymer according to claim 6, characterized in that, The cocatalyst further includes organoborides; and / or, The amount of the organoboronide used, calculated as the molar ratio of boron to metal M in the main catalyst (B / M), is 0-20.

8. The method for preparing the ethylene / α-olefin copolymer according to any one of claims 4-7, characterized in that, The solvent is selected from aliphatic hydrocarbon solvents and / or aromatic hydrocarbon solvents; and / or, The amount of solvent used is such that the mass concentration of the main catalyst is 10-1000 ppm.

9. The method for preparing the ethylene / α-olefin copolymer according to any one of claims 4-7, characterized in that, The chain transfer agent is selected from one or more of methane, ethane, propane, and hydrogen; and / or, The amount of the chain transfer agent used is 0.014-1.4% of the molar amount of ethylene.

10. The application of an ethylene / α-olefin copolymer as described in any one of claims 1-3 or an ethylene / α-olefin copolymer prepared by the method described in any one of claims 4-9 in photovoltaic encapsulation materials.

Images