Polyethylene elastomer and preparation method thereof
By copolymerizing α-olefins with an odd number of carbon atoms (greater than 4) with ethylene and combining this with continuous self-nucleating annealing technology, the problem of high copolymer usage in polyethylene elastomer preparation was solved. This resulted in the preparation of polyethylene elastomers with high light transmittance and low cost, thereby increasing the added value and profit of the products.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA YITAI COAL BASED NEW MATERIALS RES INST CO LTD
- Filing Date
- 2025-10-30
- Publication Date
- 2026-05-19
AI Technical Summary
In order to achieve high light transmittance, existing polyethylene elastomers require the addition of a high proportion of expensive comonomers during the preparation process, which increases production costs.
α-olefins with an odd number of carbon atoms (greater than 4) are copolymerized with ethylene. By controlling the insertion rate and distribution of the comonomers, a microstructure with phase separation of amorphous and microcrystalline regions is formed. The thickness of the lamellar crystals is controlled by continuous self-nucleation annealing technology, thereby reducing the amount of comonomers used.
While ensuring high light transmittance, the amount of comonomer used is significantly reduced, thus lowering production costs, while maintaining the material's excellent elasticity and mechanical properties.
Smart Images
Figure CN122060103A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of copolymer technology, and more specifically to a polyethylene elastomer and its preparation method. Background Technology
[0002] Polyethylene (PE), as one of the most widely produced and used general-purpose plastics, accounts for 50% to 60% of total consumption in the film industry, making it one of the most important applications. The optical and mechanical properties of films are key indicators of their quality, mainly including light transmittance, haze, tensile strength, dart impact strength, and puncture resistance.
[0003] Polyethylene elastomers (POEs) have been widely used in recent years in fields such as photovoltaic module encapsulation films due to their excellent flexibility, weather resistance, and electrical insulation properties. In these applications, the light transmittance of the material directly affects the photoelectric conversion efficiency of the solar cell; therefore, POE materials are required to have extremely high transparency, typically exceeding 90% to meet practical application requirements. However, to achieve the desired light transmittance during the preparation of commercially available polyethylene elastomers, 25 wt% to 35 wt% comonomers are often added. The high price of these comonomers significantly increases production costs.
[0004] Therefore, how to effectively reduce the amount of expensive comonomers while ensuring the high light transmittance of polyethylene elastomers has become a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] This disclosure aims to address the problems existing in the prior art by providing a polyethylene elastomer and a method for preparing the same.
[0006] According to a first aspect of this disclosure, a polyethylene elastomer is provided, wherein the polyethylene elastomer is a copolymer of ethylene and a second olefin, the transmittance of the polyethylene elastomer is >91.0%, the insertion rate of the second olefin in the polyethylene elastomer is 1.5-5.0 mol%, the second olefin is an α-olefin with more than 4 carbon atoms and an odd number of carbon atoms, and after continuous self-nucleation annealing, the average lamellar thickness of the copolymer is 2.0-4.0 nm, and the portion with an average lamellar thickness of more than 4.0 nm accounts for no more than 10% of the total amount of copolymer lamellars; the polyethylene elastomer is graded into 5 fractions by heating and washing in the range of 30-105°C, the temperature ranges of the 5 fractions are 30-45°C, 45-60°C, 60-75°C, 75-90°C, and 90-105°C, respectively, and the content of the second olefin in the fraction with a temperature range of 90-105°C is no more than 5 mol%.
[0007] In one embodiment of this disclosure, the second olefin is selected from one of 1-pentene, 1-heptene, 1-nonene, and 1-undecene.
[0008] In one embodiment of this disclosure, the polyethylene elastomer has a weight-average molecular weight of 50,000-270,000 g / mol, a molecular weight distribution of 1.5-6.0, a melting point of 50-100°C, and a density of 0.865-0.895 g / cm³. 3 .
[0009] According to a second aspect of this disclosure, a method for preparing a polyethylene elastomer is provided, comprising the following steps: S1: Add the polymerization solvent, the second olefin and the co-catalyst sequentially into the reactor; S2: After ethylene is introduced into the reactor of S1 until the pressure inside the reactor reaches the predetermined polymerization pressure, the temperature is raised and stabilized at the predetermined polymerization temperature; S3: Inject the catalyst into the reactor of S2 and maintain the pressure inside the reactor at the predetermined polymerization pressure. After reacting for 10-15 minutes, discharge the material, collect the polyethylene elastomer, dry it, and weigh it.
[0010] In one embodiment of this disclosure, the catalyst in S3 is one or more of a metallocene catalyst, a post-transition metal catalyst, and a non-metallocene catalyst.
[0011] In one embodiment of this disclosure, the central metal element of the catalyst is selected from one of Ti, Zr, Hf, Cr, Fe, Co, and Ni.
[0012] In one embodiment of this disclosure, the co-catalyst is selected from one or more of methylaluminoxane, modified methylaluminoxane, tri(pentafluorophenyl)borane, borate, triethylaluminum, triisobutylaluminum, and trihexylaluminum.
[0013] In one embodiment of this disclosure, the polymerization solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, isoalkanes Isopar C, and isoalkanes Isopar E.
[0014] In one embodiment of this disclosure, the predetermined polymerization temperature is 100-180°C, and the predetermined polymerization pressure is 2.0-5.0 MPa.
[0015] This disclosure discloses a polyethylene elastomer and its preparation method. By copolymerizing α-olefins with an odd number of carbon atoms (greater than 4) with ethylene, the odd-numbered carbon α-olefins are inserted into the polyethylene main chain. Due to steric hindrance, the terminal methyl groups are forced to adopt a side-chain conformation close to the main chain, forming a "bent structure." This bent side chain strongly pushes against the main chain, forcing it to locally twist into a side-chain conformation, thus disrupting the continuity of the planar zigzag structure. This main chain conformational distortion prevents effective lattice insertion, reducing crystal perfection. Furthermore, the twisted main chain hinders crystal thickness, resulting in reduced crystal thickness and increased light transmittance.
[0016] In the polyethylene elastomer of the present invention, the insertion rate of the second olefin is 1.5-5.0 mol%, indicating that the present invention has a low requirement for the insertion rate of the second olefin. Therefore, the present application can obtain a polyethylene elastomer with high light transmittance by using a low insertion rate of odd-numbered carbon α-olefin comonomers, which can significantly reduce the cost of raw materials and thus increase the added value and profit of the product.
[0017] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description
[0018] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.
[0019] Figure 1 This is a carbon NMR spectrum of a polyethylene elastomer provided in Embodiment 1 of this disclosure; Figure 2 This is a temperature program diagram for a continuous self-nucleating annealing (SSA) test provided in one embodiment of this disclosure; Figure 3 This is a melting peak curve obtained from the final heating process of the continuous self-nucleation annealing (SSA) of a polyethylene elastomer provided in Embodiment 3 of this disclosure; Figure 4 It is based on Figure 3 The lamellar thickness distribution obtained from the melting peak temperature calculation; Figure 5 This is a flowchart of a method for preparing a polyethylene elastomer provided in one embodiment of the present disclosure. Detailed Implementation
[0020] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.
[0021] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.
[0022] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.
[0023] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.
[0024] First, the nouns and terms used in one or more embodiments will be explained.
[0025] Successive Self-nucleation / Annaling (SSA) is a thermal classification analysis technique commonly used to analyze polyethylene and its copolymers. It uses a series of continuous heating, holding, and cooling cycles to reveal the molecular structure characteristics of the material, particularly the distribution of short-chain branches. SSA results in different melting peaks, and the crystal size can be calculated from the temperatures corresponding to these peaks. Simply put, each heating step melts only the least perfect crystals with the lowest melting point, while retaining the most perfect crystals with the highest melting point as "nucleating agents." It can "classify" molecular chains based on their chemical composition (comonomer content) and sequence length. Each partial melting step in SSA essentially "screens" the molecular chains: at a given Ta temperature, only long chain segments that can form crystals with melting points higher than Ta are retained. Short chain segments containing more comonomers can only crystallize at lower temperatures.
[0026] Isopar C and Isopar E are two types of isoparaffin solvents produced by ExxonMobil, differing primarily in the number of carbon atoms. Isopar C: Carbon number 10-12, distillation range 98-104℃, density 0.698 g / cm³, flash point below 0℃. Isopar E: Carbon number 12-14, distillation range 105-125℃, density 0.78 kg / dm³, flash point 63℃.
[0027] Lamellar crystals are a basic microscopic crystal structure unit in semi-crystalline polymers (such as polyethylene and polypropylene). They are layered structures formed by the folding and arrangement of polymer molecular chains. The thinner the lamellar crystals, the less perfect the crystal development and the lower the crystallinity.
[0028] Polyethylene (PE), as one of the most widely produced and used general-purpose plastics, accounts for 50% to 60% of total consumption in the film industry, making it one of the most important applications. Film products are widely used in packaging, agriculture, construction, and new energy fields. Market demand for high-performance films continues to grow, especially in applications such as outer packaging where aesthetics are paramount. Consumers generally seek products with smooth film surfaces, low haze, and high light transmittance.
[0029] The optical and mechanical properties of thin films are key indicators for evaluating their quality, mainly including light transmittance, haze, tensile strength, dart impact strength, and puncture resistance. Among these, light transmittance, as a core parameter reflecting the clarity and visual effect of the film, directly affects the product's appearance quality and performance. The light transmittance of polyethylene film is mainly affected by the material's crystallization behavior. Specifically, its melt flow index (MFI) and the number of crystal nuclei formed during cooling, grain size, and crystallinity are key factors determining transparency. Larger spherulitic structures or higher crystallinity tend to cause light scattering at the interface between crystalline and amorphous regions, thereby increasing haze and reducing light transmittance.
[0030] Polyethylene elastomers (POEs) have been widely used in recent years in fields such as photovoltaic module encapsulation films due to their excellent flexibility, weather resistance, and electrical insulation properties. In these applications, the light transmittance of the material directly affects the photoelectric conversion efficiency of the solar cell; therefore, POE materials are required to have extremely high transparency, typically exceeding 90% to meet practical application requirements. However, to achieve the desired light transmittance during the preparation of commercially available polyethylene elastomers, 25 wt% to 35 wt% comonomers are often added. The high price of these comonomers significantly increases production costs.
[0031] Through in-depth research, the inventors discovered that when using α-olefins with odd-numbered carbon chains as comonomers, the prepared polyethylene elastomers exhibit weaker crystallinity and can achieve higher light transmittance with lower comonomer content. This discovery provides a novel technical approach and development direction for developing low-cost, high-transparency polyethylene-based film materials, particularly for applications in high-end packaging films, high-transparency films, and photovoltaic encapsulation films.
[0032] This invention discloses a polyethylene elastomer and its preparation method. The polyethylene elastomer obtained by the method is a copolymer of ethylene and a second olefin, wherein the second olefin is selected from 1-pentene, 1-heptene, 1-nonene, and 1-undecene. The obtained polyethylene elastomer has a weight-average molecular weight of 50,000-270,000 g / mol, a molecular weight distribution of 1.5-6.0, a melting point of 50-100℃, and a density of 0.865-0.895 g / cm³. 3 The copolymer has a light transmittance > 91.0%, and the second olefin in the polyethylene elastomer has an insertion rate of 1.5-5.0 mol%. The second olefin is an α-olefin with more than 4 carbon atoms and an odd number of carbon atoms. The polyethylene elastomer is produced by continuous self-nucleation annealing (as shown in the example). Figure 2 After testing the temperature change over time procedure, the following results were obtained: Figure 3 , Figure 3 This is a melt peak curve obtained from the final heating process of continuous self-nucleation annealing (SSA) of polyethylene elastomer, based on... Figure 3 The melting peak temperature was calculated. Figure 4 The diagram shows the lamellar thickness distribution. (Through...) Figure 4 It is known that the average lamellar thickness of the copolymer is 2.0-4.0 nm, and the proportion of the portion with an average lamellar thickness of more than 4.0 nm in the total amount of lamellars in the copolymer is no more than 10%. The polyethylene elastomer is graded into 5 fractions in the range of 30-105℃ after being heated and washed. The temperature ranges of the 5 fractions are 30-45℃, 45-60℃, 60-75℃, 75-90℃, and 90-105℃, respectively. In the fraction with a temperature range of 90-105℃, the content of the second olefin is no more than 5 mol.
[0033] like Figure 5 As shown, this disclosure provides a method for preparing a polyethylene elastomer, comprising the following steps: S1: Add the polymerization solvent, the second olefin and the co-catalyst sequentially into the reactor; S2: After ethylene is introduced into the reactor of S1 until the pressure inside the reactor reaches the predetermined polymerization pressure, the temperature is raised and stabilized at the predetermined polymerization temperature; S3: Inject the catalyst into the reactor of S2 and maintain the pressure inside the reactor at the predetermined polymerization pressure. After reacting for 10-15 minutes, discharge the material, collect the polyethylene elastomer, dry it, and weigh it.
[0034] Specifically, the preparation principle of polyethylene elastomer is to use a single active center catalyst to coordinate copolymerize ethylene and α-olefin. By controlling the content and distribution of comonomers, the distribution and crystallization behavior of short branches in the polymer chain can be regulated, thereby forming a microstructure with phase separation of amorphous and microcrystalline regions. This allows the material to exhibit excellent elasticity and mechanical properties at room temperature by relying on microcrystals as physical crosslinking points, while maintaining good thermoplastic processability.
[0035] In one embodiment of this disclosure, the catalyst in S3 is one or more of a metallocene catalyst, a post-transition metal catalyst, and a non-metallocene catalyst.
[0036] Specifically, metallocene catalysts, post-transition metal catalysts, and non-metallocene catalysts all belong to the category of single-active-site catalysts. They can control the polymerization process at the molecular level, enabling efficient copolymerization of ethylene and α-olefins. Among them, metallocene catalysts are characterized by high activity and a single active site, allowing for the control of molecular weight and copolymer composition; post-transition metal catalysts generally have better tolerance to polar groups and can adapt to a wider range of reaction conditions; and non-metallocene catalysts are low-cost and have excellent activity. Using these catalysts or combinations thereof can effectively control the number and distribution of short branches in copolymers.
[0037] In one embodiment of this disclosure, the central metal element of the catalyst is selected from one of Ti, Zr, Hf, Cr, Fe, Co, and Ni. Different metal centers affect the catalyst's activity, copolymerization ability, molecular weight regulation, and thermal stability. By selecting a suitable metal element, the distribution and crystallization behavior of short branches in the polymer chain can be controlled, thereby forming a microstructure with phase separation of amorphous and microcrystalline regions. This allows the material to exhibit excellent elasticity and mechanical properties at room temperature by relying on microcrystals as physical crosslinking points, while maintaining good thermoplastic processability.
[0038] In one embodiment of this disclosure, the co-catalyst is selected from one or more of methylaluminoxane, modified methylaluminoxane, tri(pentafluorophenyl)borane, borate, triethylaluminum, triisobutylaluminum, and trihexylaluminum.
[0039] Specifically, the main function of these cocatalysts is to activate catalysts with Ti, Zr, Hf, Fe, Ni, etc., as the central metal, generating highly active cationic centers through alkylation and / or anion abstraction, thereby initiating and maintaining the copolymerization reaction of ethylene and α-olefins. The selection of different cocatalysts or their combinations directly affects the catalyst activity, polymerization rate, comonomer insertion efficiency, and the molecular weight and structural uniformity of the final polymer.
[0040] In one embodiment of this disclosure, the polymerization solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, isoalkanes Isopar C, and isoalkanes Isopar E. These solvents are all inert alkane compounds with good chemical stability and will not react with the catalyst or polymer. The main function of the polymerization solvent is to act as a medium for the polymerization reaction, uniformly disperse the catalyst system, dissolve or suspend the monomers (ethylene and α-olefins), and effectively transfer the heat of reaction, preventing localized overheating that could lead to catalyst deactivation or polymer degradation. Simultaneously, these solvents can dissolve the generated polymer, maintain the fluidity of the system, and facilitate subsequent separation and processing.
[0041] In one embodiment of this disclosure, the predetermined polymerization temperature is 100-180°C. Within this temperature range, the polymerization system remains in a solution state, which is conducive to the full dissolution and uniform participation of ethylene and α-olefin monomers in the reaction. The predetermined polymerization pressure is 2.0-5.0 MPa, wherein the predetermined polymerization pressure is mainly determined by the partial pressure of ethylene. The pressure range of 2.0-5.0 MPa can maintain a high ethylene concentration, ensure sufficient polymerization rate and molecular weight, and promote the effective copolymerization of comonomers. This pressure level also matches the high temperature conditions, ensuring that the reaction system remains stable in the liquid phase, preventing gas-liquid phase separation, and facilitating mass transfer and temperature control.
[0042] The embodiments of the present invention will be described in detail below with reference to the examples. All of the following embodiments employ... Figure 5 The sample was prepared using the method shown. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions were applied under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.
[0043] The following methods were used to test the structure or properties of the ethylene and α-olefin copolymers produced in the experimental examples described above: High-temperature gel permeation chromatography (GPC) is used to test the weight-average molecular weight and molecular weight distribution of copolymers.
[0044] Gradient density meters are used to test the density of copolymers.
[0045] A melt indexer is used to test the melt index of copolymers.
[0046] Nuclear magnetic resonance (NMR) spectrometers are used to test the α-olefin insertion rate in copolymers.
[0047] Differential scanning calorimetry (DSC) is used to test the melting point of copolymers.
[0048] A haze meter is used to test the transmittance and haze of copolymers.
[0049] Example 1 2.3 L of n-hexane solvent, 0.7 L of the second olefin 1-heptene, 4 mmol of methylaluminoxane co-catalyst, and 7 µmol of tris(pentafluorophenyl)borane were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 3.2 MPa. The temperature was raised and stabilized at 135 °C. Finally, 6.2 µmol of metallocene catalyst (CAS 135072-61-6) was injected while maintaining the reactor pressure at 3.2 MPa. After reacting for 15 min, the product was discharged, copolymer A was collected, dried, and weighed. The physical properties of copolymer A are shown in Table 1, and its carbon NMR spectrum is shown in [Table 1]. Figure 1 , Figure 1 The image shows the carbon NMR spectrum of polyethylene elastomer. The insertion rate of the comonomer can be calculated based on the peak positions and peak areas of the spectrum.
[0050] Example 2 2.7 L of cyclohexane solvent, 1.0 L of the second olefin 1-heptene, and 4 mmol of modified methylaluminoxane co-catalyst were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 3.5 MPa. The temperature was raised and stabilized at 155 °C. Finally, 7 µmol of metallocene catalyst (CAS 132510-07-7) was injected while maintaining the reactor pressure at 3.5 MPa. After reacting for 10 min, the product was discharged, copolymer B was collected, dried, and weighed. The physical properties of copolymer B are shown in Table 1.
[0051] Example 3 2.0 L of isoparaffin Isopar E solvent, 1.2 L of the second olefin 1-heptene, and 4 mmol of modified methylaluminoxane co-catalyst were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 3.9 MPa. The temperature was raised and stabilized at 125 °C. Finally, 7 µmol of metallocene catalyst (CAS 100163-29-9) was injected while maintaining the reactor pressure at 3.9 MPa. After reacting for 15 min, the product was discharged, copolymer C was collected, dried, and weighed. The physical properties of copolymer C are shown in Table 1.
[0052] Example 4 2.5 L of n-hexane solvent, 0.9 L of the second olefin 1-pentene, 0.5 mmol of triisobutylaluminum co-catalyst, and 9 µmol of tris(pentafluorophenyl)borane were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 2.9 MPa. The temperature was raised and stabilized at 140 °C. Finally, 7 µmol of metallocene catalyst (CAS 135072-61-6) was injected while maintaining the reactor pressure at 2.9 MPa. After reacting for 15 min, the product was discharged, copolymer D was collected, dried, and weighed. The physical properties of copolymer D are shown in Table 1.
[0053] Comparative Example 1 2.5 L of n-hexane solvent, 0.7 L of 1-octene, 5 mmol of methylaluminoxane co-catalyst, and 9 µmol of tris(pentafluorophenyl)borane were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 3.2 MPa. The temperature was raised and stabilized at 135 °C. Finally, 8 µmol of metallocene catalyst (CAS 135072-61-6) was injected while maintaining the reactor pressure at 3.2 MPa. After reacting for 15 min, the product was discharged, copolymer E was collected, dried, and weighed. The physical properties of copolymer E are shown in Table 1.
[0054] Comparative Example 2 2.5 L of n-hexane solvent, 0.7 L of 1-heptene, and 15 mmol of triethylaluminum co-catalyst were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 2.9 MPa. The temperature was raised and stabilized at 110 °C. Finally, 0.6 g of supported Ziegler-Natta catalyst A (prepared according to the method described below) was added, and the reactor pressure was maintained at 2.9 MPa. After reacting for 15 min, the product was discharged, copolymer F was collected, dried, and weighed. The physical properties of copolymer F are shown in Table 1.
[0055] The preparation method of supported Ziegler-Natta catalyst A is as follows: In a 250 mL flask equipped with a reflux condenser and a stirrer, 2 g of magnesium chloride with a total water content of 1.5% (w / w) was suspended in 60 mL of highly purified hexane. A 1:1 molar mixture of 4 mL of dipentyl ether and ethanol was added to the flask, and the mixture was stirred under reflux for 3 hours. The mixture was cooled to ambient temperature, and 10 g of triethylaluminum was added dropwise to avoid excessive heat of formation. The resulting slurry was cooled to room temperature under stirring, and then washed 12 times with 50 mL of hexane each time to obtain a slurry containing the activated support.
[0056] Add 2 mL of a 1:1 molar mixture of ethanol and 1-nonanol to the slurry containing the activated carrier, and stir the slurry at ambient temperature for 3 hours. Then add 15 mL of TiCl4, and stir the mixture under reflux for 2 hours. After cooling, wash the slurry 10 times with 50 mL of hexane each time, and then dry it.
[0057] Comparative Example 3 2.0 L of isoparaffin Isopar E solvent, 1.5 L of the second olefin 1-octene, and 4 mmol of modified methylaluminoxane co-catalyst were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 3.9 MPa. The temperature was raised and stabilized at 125 °C. Finally, 7 µmol of metallocene catalyst (CAS 100163-29-9) was injected while maintaining the reactor pressure at 3.9 MPa. After reacting for 15 min, the product was discharged, copolymer G was collected, dried, and weighed. The physical properties of copolymer G are shown in Table 1.
[0058] Comparative Example 4 The commercially available POE material SK Chemicals Solumer 8605L is copolymer H, and the comonomer of copolymer H is 1-octene. Its physical property characterization results are shown in Table 1.
[0059] Comparative Example 5 2.5 L of n-hexane solvent, 0.4 L of 1-pentene, 0.5 L of 1-heptene, 0.5 mmol of triisobutylaluminum co-catalyst, and 9 µmol of tris(pentafluorophenyl)borane were added sequentially to a 5 L reactor. Ethylene was then introduced until the reactor pressure reached 2.9 MPa. The temperature was raised and stabilized at 140 °C. Finally, 7 µmol of metallocene catalyst (CAS 135072-61-6) was injected while maintaining the reactor pressure at 2.9 MPa. After reacting for 15 min, the product was discharged, copolymer I was collected, dried, and weighed. The physical properties of copolymer I are shown in Table 1.
[0060] Table 1
[0061] As shown in Table 1, compared to copolymer A in Example 1, copolymer E in Comparative Example 1, which uses even-numbered carbon 1-octene as a comonomer, has a higher melting point, indicating that polyethylene chains with odd-numbered carbon 1-heptene comonomer insertion are less prone to crystallization. Furthermore, the table shows that copolymer A has a higher transmittance, reaching 91.1%, while copolymer E has only 89.9%. Based on carbon NMR calculations, the comonomer insertion rate of copolymer A is only 3.45 mol%, yet its transmittance reaches 91.1%, while copolymer E has a 1-octene insertion rate of 3.41 mol%, and its transmittance is only 89.9%.
[0062] It's important to note that ordinary polyethylene generally has low light transmittance. To increase the transmittance of polyethylene to over 85%, it requires the individual or combined effects of catalysts, optimized polymerization processes, nucleating agents, and rapid quenching processes. Further increasing transmittance beyond 85% becomes significantly more difficult. Firstly, this is already close to the theoretical transmittance limit of polyethylene, determined by its intrinsic absorption and ideally achievable scattering. For polyethylene, intrinsic absorption in the visible light region is very low, with a theoretical limit that is very high (possibly exceeding 95%). However, 85% transmittance means it's very close to this "engineerably achievable" limit. Secondly, at the 85% level, the remaining light loss mainly comes from the smallest and most difficult-to-eliminate scattering centers. These may be a very small number of remaining large spherulites, nanoscale impurities, trace amounts of catalyst residue, or tiny defects at the ends of molecular chains. Therefore, above 85% transmittance, each 1% increase is extremely difficult and already approaches the theoretical limit of polyethylene transmittance.
[0063] A comparison of copolymers C and G reveals that copolymer G, using 1-octene as an even-numbered carbon α-olefin comonomer, has a higher comonomer insertion rate of 7.08 mol%, but its transmittance is only 91.0%, far lower than copolymer C, which uses 1-heptene as an odd-numbered carbon α-olefin comonomer, with an insertion rate of only 4.92 mol% but a transmittance of 91.9%. Comparing this to commercial POE copolymer H, we can see that its comonomer is 1-octene, with a transmittance of 92.0%, but the insertion rate of 1-octene is as high as 12.62 mol%, far exceeding the range of odd-numbered carbon α-olefin comonomer insertion rates in the copolymers described in this invention. The lower insertion rate indicates that fewer corresponding α-olefins need to be added during the reaction.
[0064] Taking copolymer C as an example, its transmittance is as high as 91.9%. Continuous self-nucleation annealing (SSA) testing results show that... Figure 4 As shown, the average lamellar thickness is 3.48 nm, with 17.44% of lamellars having a thickness of 2-3 nm, 77.40% having a thickness of 3-4 nm, and 5.16% having a thickness of 4-5 nm. This data indicates that the lamellar thickness of copolymer C after crystallization is mostly distributed in the 2-4 nm range, with a relatively low proportion of lamellars thicker than 4-5 nm. In contrast, copolymer G has a transmittance of 91.0%. Continuous self-nucleation annealing (SSA) testing results show that its average lamellar thickness is 3.89 nm, with 10.29% of lamellars having a thickness greater than 4 nm. The comparison of lamellar thickness distribution between copolymers C and G shows that a higher proportion of thicker lamellars (>4 nm) affects light transmission, resulting in reduced transmittance.
[0065] As shown in Table 1, comparing copolymers D and I, it can be observed that the amount of comonomer added during preparation was the same, 0.9 L. However, copolymer D, using only one second olefin, 1-pentene, as a comonomer, exhibited higher transmittance (91.5%), while copolymer I, using two second olefins, 1-pentene and 1-heptene, had lower transmittance, at only 91.0%. Furthermore, when achieving the same transmittance, the insertion rate of the second olefin in the copolymer was 2.0-5.0 mol%, which was 40-90% lower than that in copolymers using even-numbered carbon α-olefins as comonomers.
[0066] Furthermore, by comparing the characterization results of copolymer A and copolymer F, it can be concluded that, when preparing copolymers, using a metallocene catalyst compared to using a supported Ziegler-Natta catalyst A can produce copolymer A with higher second olefin content, lower melting point, higher transmittance, lower haze, and smaller lamellar thickness. Copolymer F, limited by the weak copolymerization properties of Ziegler-Natta catalyst A, has even lower second olefin content, higher melting point, lower transmittance, higher haze, and larger lamellar thickness. Therefore, it is difficult to prepare copolymers with the performance characteristics described in this invention using Ziegler-Natta catalyst A.
[0067] This disclosure discloses a polyethylene elastomer and its preparation method. By copolymerizing α-olefins with an odd number of carbon atoms (greater than 4) with ethylene, the odd-numbered carbon α-olefins are inserted into the polyethylene main chain. Due to steric hindrance, the terminal methyl groups are forced to adopt a side-chain conformation close to the main chain, forming a "bent structure." This bent side chain strongly pushes against the main chain, forcing it to locally twist into a side-chain conformation, thus disrupting the continuity of the planar zigzag structure. This main chain conformational distortion prevents effective lattice insertion, reducing crystal perfection. Furthermore, the twisted main chain hinders crystal thickness, resulting in reduced crystal thickness and increased light transmittance.
[0068] In the polyethylene elastomer of the present invention, the insertion rate of the second olefin is 1.5-5.0 mol%, indicating that the present invention has a low requirement for the insertion rate of the second olefin. Therefore, the present application can obtain a polyethylene elastomer with high light transmittance by using a low insertion rate of odd-numbered carbon α-olefin comonomers, which can significantly reduce the cost of raw materials and thus increase the added value and profit of the product.
[0069] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the invention is defined by the appended claims.
Claims
1. A polyethylene elastomer, wherein the polyethylene elastomer is a copolymer of ethylene and a second olefin, characterized in that, The transmittance of the polyethylene elastomer is >91.0%, and the insertion rate of the second olefin in the polyethylene elastomer is 1.5-5.0 mol%. The second olefin is an α-olefin with more than 4 carbon atoms and an odd number of carbon atoms. After continuous self-nucleation annealing, the average lamellar thickness of the copolymer is 2.0-4.0 nm, and the portion with an average lamellar thickness of more than 4.0 nm accounts for no more than 10% of the total amount of copolymer lamellars. The polyethylene elastomer is graded into 5 fractions in the range of 30-105℃ by heating and washing. The temperature ranges of the 5 fractions are 30-45℃, 45-60℃, 60-75℃, 75-90℃, and 90-105℃, respectively. In the fraction with a temperature range of 90-105℃, the content of the second olefin is no more than 5 mol%.
2. The polyethylene elastomer according to claim 1, characterized in that, The second olefin is selected from one of 1-pentene, 1-heptene, 1-nonene, and 1-undecene.
3. The polyethylene elastomer according to claim 2, characterized in that, The polyethylene elastomer has a weight-average molecular weight of 50,000-270,000 g / mol, a molecular weight distribution of 1.5-6.0, a melting point of 50-100℃, and a density of 0.865-0.895 g / cm³. 3 .
4. The polyethylene elastomer according to claim 3, characterized in that, The melt index of the polyethylene elastomer is 0.05-10.0 g / 10 min.
5. A method for preparing a polyethylene elastomer according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Add the polymerization solvent, the second olefin and the co-catalyst sequentially into the reactor; S2: After ethylene is introduced into the reactor of S1 until the pressure inside the reactor reaches the predetermined polymerization pressure, the temperature is raised and stabilized at the predetermined polymerization temperature; S3: Inject the catalyst into the reactor of S2 and maintain the pressure inside the reactor at the predetermined polymerization pressure. After reacting for 10-15 minutes, discharge the material, collect the polyethylene elastomer, dry it, and weigh it.
6. The preparation method according to claim 5, characterized in that, The catalyst in S3 is one or more of the following: metallocene catalyst, post-transition metal catalyst, and non-metallocene catalyst.
7. The preparation method according to claim 6, characterized in that, The central metal element of the catalyst is selected from one of Ti, Zr, Hf, Cr, Fe, Co, and Ni.
8. The preparation method according to claim 5, characterized in that, The co-catalyst is selected from one or more of methylaluminoxane, modified methylaluminoxane, tris(pentafluorophenyl)borane, borate, triethylaluminum, triisobutylaluminum, and trihexylaluminum.
9. The preparation method according to claim 5, characterized in that, The polymerization solvent is selected from one or more of n-hexane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, isoalkanes Isopar C, and isoalkanes Isopar E.
10. The preparation method according to claim 6, characterized in that, The predetermined polymerization temperature is 100-180℃, and the predetermined polymerization pressure is 2.0-5.0MPa.