Ethylene / alpha-olefin copolymer as well as preparation method and application thereof

Abstract

The invention discloses an ethylene / alpha-olefin copolymer as well as a preparation method and application thereof. The ethylene / alpha-olefin copolymer is a copolymer obtained by polymerizing ethylene and alpha-olefin, and has the following characteristics of a, b and c: a, the weight-average molecular weight is 40000-120000, and the molecular weight distribution width PDI range is 1.5-3; b, the density is 0.855 to 0.910 g / cm < 3 >; and c, the molar percentage content of the sequence EEXEXEE measured by a nuclear magnetic resonance carbon spectrum is 10-20%, the kilocarbon branching number is 30-80, E represents an ethylene unit, and X represents an alpha-olefin unit. The crosslinking degree of the ethylene / alpha-olefin copolymer provided by the invention is remarkably improved, and when the ethylene / alpha-olefin copolymer is applied to a photovoltaic adhesive film, the number of crystal points is small or almost no crystal point exists, so that the ethylene / alpha-olefin copolymer shows relatively high water vapor barrier property.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyolefin materials, and particularly relates to an ethylene / alpha-olefin copolymer and a preparation method and application thereof. BACKGROUND

[0002] As a key material for solar cell modules, photovoltaic encapsulant films need to have high light transmittance, excellent weather resistance, low water vapor permeability, and good mechanical properties to ensure the reliability of the modules in long-term outdoor use. Ethylene / alpha-olefin copolymers, such as ethylene-octene / butene copolymers (POE), have gradually become a substitute for traditional EVA (ethylene-vinyl acetate) encapsulant films due to their excellent flexibility, UV aging resistance, and low-temperature toughness. However, existing ethylene / alpha-olefin copolymers still face two key problems in photovoltaic encapsulation applications: a large number of crystallization points and low crosslinking degree, which seriously affect the water vapor barrier and long-term performance of photovoltaic modules.

[0003] POE is a non-polar polyolefin with a dense arrangement of molecular chains, making it difficult for water molecules to penetrate. Therefore, its intrinsic water vapor transmission rate is much lower than that of polar EVA. During the production of photovoltaic encapsulant films, the presence of crystallization points creates local defects. Instead of improving the overall transmission rate of the film, they create "weak points" and "fast channels" for water vapor intrusion. Crystallization points are hard particles, and their compatibility and bonding force with the surrounding film matrix may be poor. During the lamination process, the crystallization point area cannot form a complete and dense fusion like the surrounding film. This creates small gaps or voids at the interface between the crystallization point and the film. As a hard foreign object, crystallization points cause stress concentration in the film. When the module undergoes thermal expansion and contraction (thermal cycling) in outdoor conditions day and night throughout the year, these stress concentration points are more prone to microcracks. These microcracks extend from the crystallization points, and these interface gaps and microcracks become the preferred path for water vapor intrusion. Water molecules can penetrate more quickly along these defects and directly attack the cell, grid lines, and solder strips, causing corrosion, oxidation, delamination, and exacerbation of PID. The formation of crystallization points is mainly due to uneven sequence distribution of copolymer molecular chains, resulting in excessively high local crystallinity. Ethylene / alpha-olefin copolymers synthesized using traditional Ziegler-Natta catalysts tend to form long ethylene block sequences (EEE) due to their multi-active center characteristics, which leads to high crystalline regions in the film. In addition, if the insertion rate of alpha-olefin is insufficient, such as less than 8wt%, the crystallinity of the copolymer is difficult to effectively reduce, further exacerbating the crystallization point problem. To solve this problem, existing technologies usually use metallocene catalysts to improve the randomness of alpha-olefin insertion or adjust the type of comonomer to reduce crystallinity. However, these methods can reduce crystallization points to some extent, but often result in a decrease in the crosslinking degree of the copolymer, affecting the thermal stability and mechanical strength of the film.

[0004] Crosslinking degree is another key performance indicator of photovoltaic packaging adhesive film, which directly affects the heat resistance (such as PID resistance) and long-term weather resistance of the adhesive film. Photovoltaic adhesive film usually uses peroxide as a crosslinking agent to form a three-dimensional network structure through free radical reaction. However, the crosslinking efficiency of ethylene / alpha-olefin copolymer, especially POE with high alpha-olefin content, is generally lower than that of EVA. The main reasons include the steric hindrance effect of the branched structure of long-chain alpha-olefin on free radical diffusion, and the reduction of crosslinking active sites (tertiary carbon hydrogen) in high random sequence distribution. In order to improve the crosslinking degree, the prior art usually uses multi-functional monomer grafting or composite crosslinking system. However, these methods may introduce new problems, such as graft modification may cause the adhesive film to yellow, and silane crosslinking system may affect long-term weather resistance due to hydrolysis by-products. Patent document CN119285815B discloses a method for improving the light transmittance of polyolefin elastomer by using a modified catalyst in a gas phase polymerization process, which solves the problem of low light transmittance in the prior art and improves the application quality and proportion of the polyolefin elastomer in photovoltaic adhesive film, but does not involve research on problems such as processing efficiency at low temperature and film product crystallization point.

[0005] In summary, the prior art has not effectively solved the problems of too many crystallization points and low crosslinking degree of ethylene / alpha-olefin copolymer in photovoltaic packaging adhesive film. Therefore, it is urgent to develop a new structure design strategy for ethylene / alpha-olefin copolymer to precisely control the sequence distribution and crosslinking active sites in the molecular chain, so as to realize the synergistic optimization of few crystallization points and high crosslinking degree, and meet the stringent requirements of photovoltaic modules for high-performance packaging materials. SUMMARY

[0006] The present application provides an ethylene / alpha-olefin copolymer, its preparation method and application, to solve the problems of too many crystallization points and low crosslinking degree of ethylene / alpha-olefin copolymer in the film forming process. The ethylene / alpha-olefin copolymer has a specific sequence, which precisely controls the sequence distribution and crosslinking active sites in the molecular chain, so as to realize the synergistic optimization of few crystallization points and high crosslinking degree, and meet the requirements of photovoltaic modules for high-performance packaging materials.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] An ethylene / alpha-olefin copolymer is a copolymer obtained by polymerization of ethylene and alpha-olefin, which includes the following characteristics a, b and c:

[0009] a) Weight-average molecular weight is 40,000-120,000 (e.g., 42,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 105,000, 110,000, 115,000, etc.), and molecular weight distribution width (PDI) ranges from 1.5 to 3 (e.g., 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, etc.);

[0010] b. Density is 0.855-0.910 g / cm³ 3 (For example, 0.860 g / cm) 3 0.865g / cm 3 0.870 g / cm 3 0.875g / cm 3 0.880 g / cm 3 0.885g / cm 3 0.890 g / cm 3 0.895g / cm 3 0.900g / cm 3 0.905g / cm 3 0.909 g / cm 3 wait);

[0011] c. The molar percentage of the sequence EEXEXEE, as determined by carbon NMR spectroscopy, is 10-20% (e.g., 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and specific values ​​between the above values; for space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range), and the number of branching per thousand carbons is 30-80 (e.g., 32, 34, 36, 38, 40, 42, 45, 48, 50, 52, 54, 56, 60, 65, 70, 75, 78, etc.), where E represents an ethylene unit and X represents an α-olefin unit.

[0012] As some preferred examples, the ethylene / α-olefin copolymer was analyzed by carbon NMR spectroscopy (…). 13 The molar percentage of the sequence EEXXEE obtained by C-NMR is 3-13.5% (e.g., 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, and specific point values ​​between the above points).

[0013] As some preferred examples, the melt index of the ethylene / α-olefin copolymer at 190°C and a load of 2.16 kg is 0.5-30 g / 10 min (e.g., 0.6 g / min, 0.8 g / min, 1.0 g / min, 2.0 g / min, 5.0 g / min, 8.0 g / min, 10.0 g / min, 12.0 g / min, 14.0 g / min, 15.0 g / min, 17.0 g / min, 20.0 g / min, 25.0 g / min, 28.0 g / min, etc.).

[0014] Preferably, the melting temperature Tm of the ethylene / α-olefin copolymer is 40-90℃ (e.g., 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc.).

[0015] Preferably, the glass transition temperature (Tg) of the ethylene / α-olefin copolymer is -65°C to -30°C (e.g., -63°C, -60°C, -57°C, -55°C, -50°C, -45°C, -40°C, -35°C, -32°C, etc.).

[0016] As some preferred examples, the α-olefin structural units in the ethylene / α-olefin copolymer have a mass content of 20-40% (e.g., 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, etc.).

[0017] Preferably, 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.

[0018] A method for preparing an ethylene / α-olefin copolymer as described above includes a continuous solution polymerization reaction of ethylene and α-olefin in the presence of a main catalyst, a co-catalyst, a hydrocarbon solvent, and a chain transfer agent, hydrogen, to generate a copolymer.

[0019] The reaction conditions for the continuous solution polymerization reaction satisfy the following equation:

[0020]

[0021] Among them, F 氢气 This represents the hydrogen feed rate, expressed in g / h.

[0022] F 主催化剂The feed rate of the catalyst is expressed in kg / h.

[0023] C 催化剂效率 The value represents the mass of copolymer produced per unit mass of main catalyst per hour, expressed in kg / g·h.

[0024] Hydrogen participates in chain transfer reactions during polymerization, causing premature termination of growing polymer chains and the formation of new active centers to reignite polymerization. This results in a decrease in polymer molecular weight, shorter chain segments, an increased statistical probability of α-olefin insertion in the shorter chains, and a more uniform distribution of α-olefin units within the chain. Since ethylene is more reactive, hydrogen is generally more efficient at terminating ethylene chain growth than α-olefins. Therefore, at high hydrogen concentrations, more ethylene segments (EEE) are broken, leading to an increased relative α-olefin insertion rate, an increased apparent comonomer content, a more randomized sequence distribution, reduced crystallinity, and improved light transmittance.

[0025] As some preferred examples, the main catalyst is a metallocene catalyst and / or a post-transition metal catalyst, 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, dimethyldimethylsilylbis(2-methyl-4-phenyl-1-indenyl)zirconia, meso dimethylsilylbis(1-indenyl)zirconia, (bis(methylcyclopentadiene)zirconia) Zirconium, (bis(1,3-dimethylcyclopentadienyl)zirconium chloride, (cyclopentadienyl)(1,2-dimethoxyethane)zirconium trichloride, diphenylsilyl(cyclopentadiene)(9-fluorenyl)zirconium chloride, racemic dimethylsilylbis(2-methyl-1-indene)zirconium chloride, diphenylmethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconium chloride, di-p-tolymethylenecyclopentadiene(2,7-di-tert-butyl-fluorenyl)zirconium chloride, dimethylbis(propylcyclopentadienyl)hafnium, bis(n-butylcyclopentadiene)hafnium chloride, dimethylsilylbis(2-methyl-4-phenylindene)zirconium chloride, and any one or a combination of at least two of the compounds represented by the following formula;

[0026]

[0027]

[0028] The amount of the main catalyst, expressed as the molar concentration of the metal element in the organic solvent, is 0.1-10 μmol / L.

[0029] The cocatalyst includes an aluminum additive selected from one or more of alkylaluminum, aluminum oxanes and their modifiers, preferably one or more of methylaluminoxane, modified methylaluminoxane, trimethylaluminum, triethylaluminum, tripropylaluminum, tri-n-butylaluminum, triisobutylaluminum, trioctylaluminum, monochloroethylaluminum, sesquiethylaluminum chloride, and dichloroethylaluminum.

[0030] Preferably, the amount of aluminum additive is 1-1000 (e.g., 10, 20, 50, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500, 600, 700, 800, 900, etc.) based on the molar ratio Al / M of metallic aluminum and metal M in the main catalyst, and more preferably 10-100.

[0031] As 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;

[0032] Preferably, the amount of the organoboride used is 0-20 (e.g., it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 19, etc.) based on the molar ratio of boron to metal M in the main catalyst B / M, and more preferably 1-10.

[0033] As some preferred examples, the hydrocarbon solvent is selected from C5-C64. 12 The alkane is preferably one or more of the following: pentane, methylpentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, isoheptane, n-octane, isooctane, n-decane, C6 mixed alkanes, and IsoparE.

[0034] As some preferred examples, the reaction temperature of the continuous solution polymerization reaction is 100-190°C, preferably 130-180°C, and the pressure is 2-10 MPa, preferably 2-9 MPa.

[0035] As some preferred examples, after the continuous solution polymerization reaction is completed, the reaction solution is quenched with an alcohol-water mixture and filtered to obtain an ethylene / α-olefin copolymer;

[0036] Preferably, the alcohol-water mixture is water and a mixture selected from C2-C4. 10 A mixture of alcohols, wherein the weight ratio of water to alcohol is 0.1-10;

[0037] Preferably, the alcohol is selected from one or more of ethanol, propanol, butanol, 2-methylpropanol, pentanol, 2-methylbutanol, 3-methylbutanol, 2-ethylpropanol, hexanol, 2-methylpentanol, 3-methylpentanol, 4-methylbutanol, 3-ethylbutanol, heptanol, 2-methylhexanol, 3-methylhexanol, 4-methylhexanol, 5-methylhexanol, 3-ethylpentanol, 4-ethylpentanol, octanol, isooctanol, nonanol, isononol, and decanol.

[0038] Application of an ethylene / α-olefin copolymer as described above or an ethylene / α-olefin copolymer prepared by the method described above in the field of photovoltaic films.

[0039] In this invention, the specific steps for preparing the photovoltaic encapsulating film from the ethylene / α-olefin copolymer described above are conventional operations in the art and will not be elaborated here. For example, the ethylene / α-olefin copolymer can be mixed with additives to form a photovoltaic encapsulating film composition, and then the composition can be processed into a photovoltaic encapsulating film using conventional processing techniques in the art. The additives can be commonly used types of additives in the art, such as crosslinking agents, crosslinking aids, antioxidants, etc.

[0040] The beneficial effects of this invention are as follows: In the ethylene / α-olefin copolymer provided by this invention, through precise design of the chain segment sequence structure, long ethylene sequences are reduced, the dispersion and uniformity of α-olefin units are increased, and the EEXEXEE and EEXXEE sequences are controlled within a reasonable range, significantly improving the degree of crosslinking. This significantly enhances the strength of the encapsulant film without altering the crosslinking process. The prepared photovoltaic encapsulant film exhibits few or almost no crystal points, thus demonstrating high water vapor barrier properties, meeting the needs of most downstream applications, especially the requirements of cast films. Detailed Implementation

[0041] 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.

[0042] 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 term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Locational terms such as top and bottom, mentioned or possibly used in this specification, are relative concepts and may therefore vary depending on their location and usage.

[0043] Main raw material sources

[0044] The materials and reagents used in the following embodiments are all commercially available. Specific information on some of the raw materials is as follows:

[0045] IsoparE, purchased from Mobil;

[0046] Ethylene, polymer grade, 99.95% purity, purchased from liquefied air;

[0047] 1-Octenene, 98% purity, purchased from INEOS;

[0048] 1-Butene, 99% pure, purchased from liquefied air;

[0049] rac-ethylenebis(1-indenyl)zirconium dichloride, 99%, Ström, denoted as M1;

[0050] Dimethicone (N-tert-butylamino) (tetramethylcyclopentadienyl) dimethyltitanium, 99%, purchased from Xinnoco, designated as M2;

[0051] Diphenylmethylenecyclopentadiene (2,7-di-tert-butyl-fluorenyl)zirconium dichloride, 98%, purchased from Yaodexin Chemical, marked as M3;

[0052] The compounds in the following formula were synthesized according to the scheme in Example 4 disclosed in patent CN111909196B:

[0053]

[0054] MAO, a 10wt% hexane solution of Al, was purchased from Akzo, M5.

[0055] MMAO, a 10wt% hexane solution of Al, purchased from Norinon, M6;

[0056] Triisobutylaluminum (TIBA), a 10 wt% Al solution in n-hexane, was purchased from Inokai, M7.

[0057] Triphenylmethyltetra(pentafluorophenyl)borate, 99%, prepared as a 10wt% hexane solution of element B, purchased from Inokai, M8.

[0058] Main testing methods

[0059] (1) In the following examples and comparative examples, the molecular weight, molecular weight distribution and α-olefin insertion rate of the obtained copolymers were obtained by GPC-IR test of polymer char, the test temperature was 150℃ and the test solvent was 1,2,4-trichlorobenzene.

[0060] (2) In the following examples and comparative examples, the density of the obtained copolymers was tested using a densitometer (impregnation method METTLER).

[0061] (3) In the following examples and comparative examples, the melt index of the obtained copolymers under the conditions of 190°C and 2.16kg load was tested by a melt indexer (MI-4), and the unit was g / 10min.

[0062] (4) In the following examples and comparative examples, the ethylene segment sequence distribution of the obtained copolymers can be obtained by nuclear magnetic resonance carbon spectroscopy (NMR spectroscopy). 13 The NMR was obtained using C1NMR. Specifically, 2.74 g of sample and tetrachloroethane-d2 containing 0.025 mol / L Cr(AcAc)3 were added to a Nore II 1001-710 mm NMR tube. The tube was manually purged with nitrogen for 1 minute using a Pasteur pipette to remove oxygen. The tube and its contents were heated to 150 °C using a heating plate, with minimal use of a heating gun, to dissolve and homogenize the sample. The sample was thoroughly mixed immediately before analysis and should not be cooled before insertion into the heated NMR probe. This is necessary to ensure that the sample is homogeneous and representative of the whole sample. Data were collected using a Bruker 400 MHz spectrometer equipped with a Bruker cryopreservation probe. Data were acquired using 160 scans, a 6-second pulse repetition delay, and a sample temperature of 120 °C. All measurements were performed on a non-spin sample in locked mode, allowing the sample to equilibrate for 7 minutes before data acquisition. The acquired data were synthesized using the randall and Seger methods to calculate the sequence distribution of the polymer.

[0063] (5) In the following examples and comparative examples, the degree of crosslinking of the obtained copolymer samples was tested by xylene-soluble content, and the crosslinking rate was characterized by vulcanization characteristics; the specific steps are as follows:

[0064] According to the mass ratio, 100 parts of copolymer particles obtained from each example and comparative example were mixed with 0.9 parts of crosslinking agent 2-ethylhexyl carbonate tert-butyl peroxide, 0.6 parts of co-crosslinking agent triallyl isocyanurate, 0.2 parts of silane coupling agent 3-(methacryloyloxy)propyltrimethoxysilane, 0.1 parts of light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, 0.1 parts of antioxidant β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol, 0.1 parts of ultraviolet absorber 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and 0.1 parts of anti-PID additive ethoxylated trimethylolpropane triacrylate to obtain a photovoltaic film mixture.

[0065] First, a portion of the mixture is processed into a photovoltaic film with a thickness of 500-700μm using a casting machine. Then, it is pressed for 5 minutes under negative pressure at 70℃ using a laminator. Crosslinking occurs during this process. Finally, the crosslinked photovoltaic film is removed, and the degree of crosslinking is obtained by testing the xylene-soluble content.

[0066] Another portion of the mixture was placed into a completely sealed mold cavity, and the crosslinking rate was measured using a rotorless vulcanizer. The test temperature was maintained at 145℃, and the vulcanization time was 15 minutes.

[0067] Examples and Comparative Examples

[0068] The ethylene / α-olefin copolymers in the various examples and comparative examples were prepared in a continuous reaction platform, and the operation steps were as follows:

[0069] The reactor was continuously circulated with dried solvent for 2 days to remove impurities. Then, according to the polymerization reaction conditions shown in Table 1, the solvent, α-olefin, main catalyst, aluminum auxiliaries and optional organoborides were introduced into the reactor by controlling the feed flow rate. Stirring was started and the system was heated. Ethylene monomer and hydrogen were introduced to carry out the polymerization reaction.

[0070] The resulting reaction solution was quenched by a water-alcohol mixture (molar ratio of 12), and the total molar amount of the water-alcohol mixture was 6 times the molar ratio of the co-catalyst metal Al.

[0071] After flash evaporation to remove volatile components and drying, ethylene / α-olefin copolymer is obtained.

[0072] Table 1

[0073]

[0074] The characteristic test results of the products obtained in each embodiment and comparative example are shown in Table 2.

[0075] Table 2

[0076]

[0077] The crosslinking degree and crosslinking rate test results of the products prepared in each embodiment and comparative example are shown in Table 3.

[0078] Table 3

[0079] Crosslinking degree (%) Crosslinking speed (min) Example 1 83.6 11.72 Example 2 84.9 11.62 Example 3 86.5 11.91 Example 4 86.6 12.01 Example 5 82.3 11.82 Example 6 83.5 11.92 Example 7 85.1 11.97 Example 8 86.1 12.29 Comparative Example 1 79 12.59 Comparative Example 2 76 13.50

[0080] The copolymer products obtained in each example and comparative example were cast into films on a casting machine (equipped with a single-screw extruder, L / D = 35, screw diameter 30 mm). The casting temperature was 110°C, and the film thickness was controlled at 0.6 mm. After obtaining the cast film, the number of crystal points on the cast film was tested according to ASTM D3351 standard. The water vapor transmission rate was tested according to ASTM F1249 standard, and the test conditions were 38°C and 100% relative humidity. The test results are shown in Table 4.

[0081] Table 4

[0082] Number of crystal points (pieces) Water vapor transmission rate (g / m 2 ·day) Example 1 0 2.8 Example 2 0 2.7 Example 3 0 2.8 Example 4 0 2.9 Example 5 0 2.8 Example 6 0 2.8 Example 7 0 2.9 Example 8 0 2.7 Comparative Example 1 2 3.3 Comparative Example 2 1 3.2

[0083] The test results show that the ethylene / α-olefin copolymers prepared in the various embodiments of the present invention have a higher degree of crosslinking. After being prepared into cast films, the number of crystal points is significantly less than that of the cast films prepared from the copolymers obtained in the comparative examples, and the water vapor permeability is lower. This indicates that the ethylene / α-olefin copolymers of the present invention have unique characteristics, which significantly reduces the number of crystal points in the cast films prepared from the copolymers and provides excellent water vapor barrier performance.

Claims

1. An ethylene / α-olefin copolymer, characterized in that, It is a copolymer obtained by polymerization of ethylene and α-olefin, including the following characteristics a, b, and c: a. The weight-average molecular weight is 40,000-120,000, and the molecular weight distribution width (PDI) ranges from 1.5 to 3. b. Density is 0.855-0.910 g / cm³ 3 ; c. The molar percentage of the sequence EEXEXEE obtained by nuclear magnetic resonance carbon spectroscopy is 10-20%, and the number of branching per thousand carbons is 30-80, where E represents the ethylene unit and X represents the α-olefin unit.

2. The ethylene / α-olefin copolymer according to claim 1, characterized in that, The molar percentage of the ethylene / α-olefin copolymer with the sequence EEXXEE, as determined by carbon NMR spectroscopy, is 3-13.5%.

3. The ethylene / α-olefin copolymer according to claim 1, characterized in that, The ethylene / α-olefin copolymer has a melt index of 0.5-30 g / 10 min at 190°C and a load of 2.16 kg.

4. The ethylene / α-olefin copolymer according to any one of claims 1-3, characterized in that, The α-olefin structural unit content in the ethylene / α-olefin copolymer is 20-40% by mass; Preferably, 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.

5. A method for preparing an ethylene / α-olefin copolymer as described in any one of claims 1-4, characterized in that, This includes the continuous solution polymerization of ethylene and α-olefins in the presence of a main catalyst, a co-catalyst, a hydrocarbon solvent, and the chain transfer agent hydrogen, to generate copolymers; The reaction conditions for the continuous solution polymerization reaction satisfy the following equation: Among them, F 氢气 This represents the hydrogen feed rate, expressed in g / h. F 主催化剂 The feed rate of the catalyst is expressed in kg / h. C 催化剂效率 The value represents the mass of copolymer produced per unit mass of main catalyst per hour, expressed in kg / g·h.

6. The method for preparing the ethylene / α-olefin copolymer according to claim 5, characterized in that, The main catalyst is a metallocene catalyst and / or a post-transition metal catalyst; The cocatalyst includes an aluminum additive selected from one or more of alkylaluminum, aluminum oxanes and their modifiers, preferably one or more of methylaluminoxane, modified methylaluminoxane, trimethylaluminum, triethylaluminum, tripropylaluminum, tri-n-butylaluminum, triisobutylaluminum, trioctylaluminum, monochloroethylaluminum, sesquiethylaluminum chloride, and dichloroethylaluminum. Preferably, the amount of aluminum additive used, based on the molar ratio Al / M of metallic aluminum and metallic M in the main catalyst, is 1-1000, more preferably 10-100.

7. The method for preparing the ethylene / α-olefin copolymer according to claim 5, characterized in that, The cocatalyst also includes organoborides, preferably one or more of the following: triphenylmethyltetra(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, N,N-dimethylanilinetetra(pentafluorophenyl)borate, bis(octadecylmethyl)tertiaryaminetetra(pentafluorophenyl)borate, and dihydrogenated tallowylmethyl)tertiaryaminetetra(pentafluorophenyl)borate. Preferably, the amount of the organoboride used, based on the molar ratio of boron to metal M in the main catalyst (B / M), is 0-20, more preferably 1-10.

8. The method for preparing the ethylene / α-olefin copolymer according to any one of claims 5-7, characterized in that, The reaction temperature of the continuous solution polymerization reaction is 100-190℃, and the pressure is 2-10MPa.

9. The method for preparing the ethylene / α-olefin copolymer according to any one of claims 5-7, characterized in that, After the continuous solution polymerization reaction is completed, the reaction solution is quenched with an alcohol-water mixture and filtered to obtain an ethylene / α-olefin copolymer; Preferably, the alcohol-water mixture is water and a mixture selected from C2-C4. 10 A mixture of alcohols, wherein the weight ratio of water to alcohol is 0.1-10.

10. The application of an ethylene / α-olefin copolymer as described in any one of claims 1-4 or an ethylene / α-olefin copolymer prepared by the method described in any one of claims 5-9 in the field of photovoltaic films.

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