Cascade polymerization preparation method of branched polyethylene without inert medium, branched polyethylene and application

Abstract

The invention belongs to the technical field of polyolefin, olefin products and olefin cascade polymerization reaction, and particularly relates to a cascade polymerization preparation method of branched polyethylene without inert media, the branched polyethylene and application. The invention provides a preparation method of cascade polymerization branched polyethylene without existence of an inert medium, which comprises the following steps: under the catalysis of an oligomerization-copolymerization cascade catalytic system, ethylene is oligomerized to generate even-carbon olefin, and ethylene and even-carbon olefin are copolymerized to prepare branched polyethylene, the even-number carbon olefins comprise C4 or above even-number carbon olefins; the oligomerization-copolymerization cascade catalytic system comprises an oligomerization catalyst and a copolymerization catalyst. According to the method disclosed by the embodiment of the invention, an inert medium does not need to be used, the concentration of the comonomer even-carbon olefin is high, the improvement of the insertion rate of the even-carbon olefin is facilitated, a part of oligomerization products can be simultaneously produced in the process of preparing the branched polyethylene, and the operation efficiency of a device is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyolefins, olefin products and olefin cascade polymerization reactions, and specifically relates to a method for preparing branched polyethylene by cascade polymerization without the presence of an inert medium, the branched polyethylene and its application. Background Art

[0002] Linear low-density polyethylene (LLDPE) is a type of vinyl copolymer with 1-butene, 1-hexene or 1-octene as the main comonomer. Compared with 1-butene, LLDPE with 1-hexene or 1-octene as the comonomer has better mechanical properties. my country's polyolefin industry started late. Although 1-hexene can be produced on a large scale, the production of 1-octene has just started, which seriously restricts the development of my country's industrial production of high-performance LLDPE technology. At present, the main LLDPE production processes in China are based on 1-butene and 1-hexene as comonomers. Therefore, there is an urgent need for the emergence of technologies that can produce higher performance LLDPE.

[0003] Polyolefin elastomer, referred to as POE, refers to a random copolymer of ethylene and long-chain α-olefin with an α-olefin content greater than 20%. Most of them are produced by copolymerization of 1-butene, 1-hexene and 1-octene, and the mass fraction of the comonomer is between 10% and 30%. It is one of the subcategories of new thermoplastic elastomers. Polyolefin elastomers have the characteristics of low density, high strength, large bending, strong impact resistance, good processability, long service life, and good aging resistance. They are mainly used in automobiles, cables, packaging, electronics, photovoltaics, building materials, home appliances, seals and other fields. As the country's "dual carbon" strategy continues to advance in depth, strategic emerging industries such as photovoltaics and new energy vehicles are developing rapidly, and the chemical new materials industry has ushered in new development opportunities. As a new generation of thermoplastic elastomers, POE is a star product among high-end polyolefin new materials. It has high technical barriers and is difficult to produce. Previously, it was basically entirely dependent on imports, which became an important bottleneck restricting the development of China's new materials industry.

[0004] With the continuous development of the polyolefin industry, the demand for α-olefins has grown rapidly worldwide. Linear α-olefins are an important class of chemical intermediates, which are widely used in the fields of ethylene comonomers, surfactant synthesis intermediates, plasticizer alcohols, synthetic lubricants, oil additives, oilfield chemicals, etc. Polymerization-grade high-carbon α-olefins such as 1-butene, 1-hexene and 1-octene are important raw materials for the production of high-grade polyolefin products, which can significantly improve the tear strength and breaking strength of LLDPE. At present, the α-olefin preparation equipment and LLDPE and polyolefin elastomer preparation equipment are invested and constructed separately, facing problems such as large investment and high operating costs. The comonomers are produced by independent devices, stored in tanks and transported to downstream manufacturers for purification before use, which limits the production and development speed of the above products.

[0005] On the other hand, the highly branched polyethylene (currently the industry has different names for such products such as PEE or EPOE) prepared by polymerization of a single ethylene monomer catalyzed by a late transition metal complex catalyst is gradually gaining attention. Compared with conventional POE with uniform branch length obtained by solution copolymerization of ethylene and α-olefins, the highly branched polyethylene (PEE) has branches of different lengths, generally containing methyl, ethyl, propyl, butyl and longer branches, of which methyl accounts for the vast majority, usually up to 70% to 80%. As the length of the branch increases, the content of the branch decreases rapidly. The content of C2 to C6 branches, which are more effective in reducing crystallinity and increasing transparency, and C6 and above long branches, which are more effective in improving mechanical properties, are both low, so it is necessary to carry out targeted copolymerization modification. Therefore, there is an urgent need for a process that can improve the branch distribution of highly branched polyethylene products, enhance product performance, and facilitate industrial scale-up.

[0006] Thirdly, although the polymerization of single ethylene monomer to produce highly branched polyethylene catalyzed by late transition metal complex catalysts has the advantages of cheap raw materials, extremely simple process and low cost, the activity of late transition metal complex catalysts at high temperatures is still not ideal. Generally, polymerization can only be carried out at temperatures below 80°C or even lower, and industrialization is economically meaningful. However, this kind of medium and low temperature polymerization is prone to cause the problem of sticking kettle, affecting the long-term operation of the device, and the prospects for industrialization are still unclear. Improving the high-temperature activity of late transition metal catalysts is a long process, and it is difficult to make major breakthroughs in a short period of time. Therefore, there is an urgent need for a solution in this regard.

[0007] The concept of preparing ethylene-α-olefin copolymers by a polymerization-copolymerization cascade catalytic system was proposed by scientists as early as the 1970s (K. Fischer, K. Jonas, P. Misbach, G. Wilke. Angew. Chem. Int. Ed. Engl. 1973, 12, 943-953). This method is characterized in that only ethylene is needed as a single raw material, and the polymerization catalyst is used to catalyze the polymerization of ethylene in situ to generate comonomers, and the copolymerization catalyst is responsible for catalyzing the copolymerization of ethylene and the comonomers generated in situ. Using this method can save the costs of comonomer production, storage, transportation, etc. Although many manufacturers have applied for patents for preparing ethylene copolymers with cascade catalytic systems, such as Phillips Petroleum's patent US5331070, which introduces the use of a supported Cr catalyst combined with pyrrole and alkyl aluminum to prepare LLDPE; Sasol Technology's patent WO2004056480 introduces the use of a Cr homogeneous complex as a tetramerization catalyst combined with a copolymerization catalyst to prepare a copolymer with octene as the main comonomer; BP Chemicals' patent WO200204119 introduces a P-containing Cr complex as a trimerization catalyst combined with a copolymerization catalyst to prepare an ethylene copolymer in a cascade method. Traditional copolymerization catalysts have the defect of reducing the molecular weight of the comonomer after addition. Increasing the molecular weight can make the polymer have more superior mechanical properties, but there is currently no mature cascade catalytic process that can prepare highly branched polyethylene elastomers.

[0008] Guo Song et al. from Zhejiang University disclosed a cascade polymerization process using an inert solvent in CN201410612198.9. Since the pre-addition technology of the comonomer as the copolymerization product is not adopted, in order to control the polymer composition, it is necessary to pre-polymerize for a certain period of time and then add the copolymerization catalyst to start the copolymerization. Therefore, it is generally operated in an intermittent manner in a single reactor.

[0009] The patent application of Beiouyi (Shandong) New Materials Co., Ltd. also uses a cascade polymerization process with an inert solvent. In CN202410449401.9, polymerization and copolymerization belong to different reaction systems. The polymerization reaction system provides comonomers to the copolymerization reaction system, and during the period, part of the ethylene needs to be distilled off, the polymerization catalyst needs to be deactivated and removed, etc. It is actually a simple coupling of two systems. Although the solvent and ethylene purification system are reused, the device composition and operation control are still complicated, and there is still a separation and purification process of by-product olefins and a large amount of solvents. The same problem exists in another patent of the company, CN202410124694.3, and it is more complicated because polymerization and copolymerization may use different solvents. The company's other patent CN202410357863.8 uses a two-reactor series continuous device, which has the same problem as CN201410612198.9: the polymerization reaction occurs in the first and second reactors, and the copolymerization only occurs in the second reactor, which is equivalent to a single-reactor continuous process for the copolymerization. The utilization rate of the copolymerization catalytic activity is low and the efficiency of the device is low.

[0010] On the other hand, the polyolefin solution polymerization process needs to control the solution viscosity not to be too high, so the solid content is often very low, generally 6 to 13%, and no more than 15%. As a result, a large amount of solvent is circulated internally, and the operating efficiency of the device is low. Therefore, how to improve the operating efficiency of the solution polymerization device is also a problem that needs to be solved urgently.

[0011] Therefore, how to overcome the above-mentioned technical defects is a problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0012] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the embodiment of the present invention provides a method for preparing branched polyethylene without the presence of an inert medium. Compared with the traditional polymerization process with an inert medium, no inert medium is required, the concentration of the comonomer even-numbered carbon olefin is high, which is conducive to improving the insertion rate of the even-numbered carbon olefin, and in the process of preparing the branched polyethylene, part of the oligomerization product can be produced at the same time, thereby improving the operation efficiency of the device.

[0013] The method for preparing polyethylene by cascade polymerization without the presence of an inert medium according to the embodiment of the present invention comprises the following steps: ethylene is polymerized to generate even-numbered carbon olefins under the catalysis of an oligomerization-copolymerization cascade catalytic system, and ethylene and the even-numbered carbon olefins are copolymerized to obtain branched polyethylene;

[0014] The even-numbered carbon olefins include even-numbered carbon olefins of C4 or above;

[0015] The oligomerization-copolymerization cascade catalytic system comprises an oligomerization catalyst and a copolymerization catalyst.

[0016] The advantages and technical effects brought by the cascade polymerization preparation method of branched polyethylene without the presence of an inert medium in the embodiment of the present invention are as follows: 1. The method of the embodiment of the present invention does not need to add an inert medium, and the even-numbered carbon olefins serve as comonomers and also serve as reaction media. The concentration of the comonomer even-numbered carbon olefins is high, which is beneficial to improving the insertion rate of the comonomer, and some catalysts with low copolymerization ability such as late transition metal catalysts can also be used; 2. The method of the embodiment of the present invention has simple polymerization control, and only requires accurate temperature and pressure control, so that the concentration ratio of ethylene / comonomer is maintained constant throughout the process, and the polymer composition and branching degree are maintained constant; 3. The method of the embodiment of the present invention, the polymerization process and the copolymerization process are carried out simultaneously, and no prepolymerization process is required. It is produced on a continuous device, and the catalyst activity utilization rate is high; 4. The method of the embodiment of the present invention In a medium of even-numbered olefins, under the catalysis of a polymerization-copolymerization cascade catalytic system, ethylene is polymerized to generate even-numbered olefins of C4 or above, and at the same time, ethylene is further copolymerized with even-numbered olefins of C4 or above in situ to form branched polyethylene, so that the output of two products can be achieved on a set of equipment, thereby improving the operating efficiency of the equipment and saving production costs; and the process is flexible and adjustable, and the ratio of the polymerization product to the copolymerization product can be adjusted within a range of 0 to 10 or even larger, and only the relative amount of the polymerization-copolymerization catalytic system needs to be changed, without affecting other process controls at all; 5. The method of the embodiment of the present invention, in a system for preparing branched polyethylene by catalyzing ethylene homopolymerization, a comonomer is added and / or generated in situ to form a copolymerization system, and the comonomer participates in the reaction, which can improve the branch distribution and / or increase the branching degree of the chain-walking polymerized branched polyethylene.

[0017] In some embodiments, C4 or even-numbered carbon olefins above C4 are flexibly co-produced while preparing the branched polyethylene.

[0018] In some embodiments, the even-numbered carbon olefins include at least one of C4 to C30 olefins;

[0019] And / or, the molar ratio of the ethylene to the even-numbered olefin is 1:(0.5-50).

[0020] And / or, the even-numbered olefins are pre-added and / or obtained in situ from ethylene by oligomerization.

[0021] In some embodiments, the oligomerization-copolymerization cascade catalytic system further includes an oligomerization co-catalyst and / or a copolymerization co-catalyst.

[0022] In some embodiments, the oligomerization catalyst includes at least one of a titanium-based oligomerization catalyst, a pyridine diimine iron complex catalyst, a pyridine diimine cobalt complex catalyst, a phenanthroline iron complex catalyst, a PNP coordinated chromium catalyst, a SNS coordinated chromium catalyst, or a late transition metal catalyst;

[0023] And / or, the copolymerization catalyst comprises at least one of a ZN catalyst, a metallocene catalyst, a non-metallocene catalyst, an early transition metal catalyst, and a late transition metal catalyst;

[0024] and / or, the oligomerization cocatalyst comprises at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, and organic boron compound;

[0025] And / or, the copolymerization co-catalyst includes at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, alkylaluminum chloride, and organic boron compound.

[0026] In some embodiments, the oligomerization catalyst includes at least one of a PNP coordinated chromium catalyst or a SNS coordinated chromium catalyst;

[0027] And / or, the copolymerization catalyst is at least one of a late transition metal catalyst or a metallocene catalyst.

[0028] In some embodiments, the molar ratio of the metal element of the oligomerization catalyst to the metal element of the copolymerization catalyst is 1 / 100 to 100 / 1; the molar ratio of the oligomerization catalyst to ethylene is 1 / 10000000 to 1 / 1000, and the molar ratio of the copolymerization catalyst to ethylene is 1 / 10000000 to 1 / 1000;

[0029] and / or, the molar ratio of the metal element of the oligomerization promoter to the metal element of the oligomerization catalyst is 0 to 5000:1;

[0030] And / or, the molar ratio of the metal element of the copolymerization promoter to the metal element of the copolymerization catalyst is 0 to 5000:1.

[0031] In some embodiments, the oligomerization-copolymerization reaction comprises at least one of batch polymerization, semi-continuous polymerization, or continuous polymerization;

[0032] And / or, the temperature of the polymerization-copolymerization reaction is 0-250° C., the pressure of the polymerization-copolymerization reaction is 0.1-5 MPa, and the time of the polymerization-copolymerization reaction is 5-120 min.

[0033] In some embodiments, the preparation method further comprises post-treatment: the post-treatment comprises separating the comonomer and the branched polyethylene.

[0034] The embodiment of the present invention further provides a branched polyethylene, which is prepared by the above-mentioned preparation method.

[0035] In some embodiments, the number average molecular weight of the branched polyethylene is 1000 to 3000000 g / mol, and the molecular weight distribution index of the branched polyethylene is 1.2 to 15.0;

[0036] And / or, the total branching degree of the branched polyethylene is 10 to 300 / C;

[0037] And / or, the branched polyethylene has a melt index of 0 to 50 g / 10 min;

[0038] And / or, the transparency of the branched polyethylene after film pressing is 88-92%, and the haze of the branched polyethylene after film pressing is 1-10%;

[0039] And / or, the melting point of the branched polyethylene is -30 to 130°C.

[0040] The embodiments of the present invention also provide the branched polyethylene prepared by the above preparation method or the application of the branched polyethylene in the fields of photovoltaic film, rubber, polymer modifier and elastomer. DETAILED DESCRIPTION

[0041] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0042] The method for preparing branched polyethylene by cascade polymerization without the presence of an inert medium according to an embodiment of the present invention is characterized in that it comprises the following steps: under the catalysis of the oligomerization-copolymerization cascade catalyst system, ethylene is polymerized to generate even-numbered carbon olefins, and ethylene and the even-numbered carbon olefins are copolymerized to obtain branched polyethylene;

[0043] The even-numbered carbon olefins include even-numbered carbon olefins of C4 or above;

[0044] The oligomerization-copolymerization cascade catalytic system comprises an oligomerization catalyst and a copolymerization catalyst.

[0045] The cascade polymerization preparation method of branched polyethylene without the presence of an inert medium in the embodiment of the present invention does not require the addition of an inert medium, and even-numbered olefins are used as comonomers and also serve as reaction media. The concentration of the comonomer even-numbered olefins is high, which is beneficial to improving the insertion rate of the comonomer, and some catalysts with low copolymerization ability such as late transition metal catalysts can also be used; the method of the embodiment of the present invention is simple to control the polymerization, and only requires accurate temperature and pressure control, so that the concentration ratio of ethylene / comonomer is maintained constant throughout the whole process, and the polymer composition and degree of branching are maintained constant; the method of the embodiment of the present invention, the polymerization process and the copolymerization process are carried out simultaneously, and no prepolymerization process is required. The production is carried out on a continuous device, and the catalyst activity utilization rate is high; the method of the embodiment of the present invention, in the medium of even-numbered olefins, under the catalysis of the oligomerization-copolymerization cascade catalytic system, ethylene is polymerized to generate even-numbered olefins above C4, and ethylene is further The method is characterized in that the copolymerization step is carried out by in-situ copolymerization with even-numbered carbon olefins above C4 to form branched polyethylene, and the output of two products can be achieved on a set of equipment, thereby improving the operation efficiency of the equipment and saving production costs. The process is flexible and adjustable, and the ratio of the oligomerization product to the copolymerization product can be adjusted within a range of 0 to 10 or even larger, and only the relative amount of the oligomerization-copolymerization catalytic system needs to be changed, without affecting other process controls at all. In the method of the embodiment of the present invention, a copolymerization system is formed by adding and / or in-situ generating a comonomer in a system for preparing branched polyethylene by catalyzing ethylene homopolymerization, and the comonomer participates in the reaction, which can improve the branch distribution and / or increase the branching degree of the branched polyethylene polymerized by chain walking. In the method of the embodiment of the present invention, no inert medium is used, which overcomes the problems of the complication of polymerization control caused by the need for an inert medium in the prior art and the complication of the post-treatment process caused by the need for a separation step of the oligomerization product and the inert medium.

[0046] It should be noted that no inert medium includes one or more of the following situations: no inert medium at all, a small amount of inert solvent or diluent is inevitably used to meet the needs of the catalyst or co-catalyst, and a small amount of inert medium produced as a by-product of polymerization.

[0047] The preparation of branched polyethylene includes the following three situations: the C4 or C4 even-numbered carbon olefins generated by polymerization are greater than the C4 or C4 even-numbered carbon olefins consumed in copolymerization, and there is a net output of C4 or C4 even-numbered carbon olefins; the C4 or C4 even-numbered carbon olefins generated by polymerization are equal to the C4 or C4 even-numbered carbon olefins consumed in copolymerization, there is no net output of C4 or C4 even-numbered carbon olefins and no need to purchase them externally; the C4 or C4 even-numbered carbon olefins generated by polymerization are less than the C4 or C4 even-numbered carbon olefins consumed in copolymerization, but the purchase amount of C4 or C4 even-numbered carbon olefins can be reduced.

[0048] In some embodiments, preferably, C4 or C4 or higher even-numbered carbon olefins are flexibly co-produced while preparing the branched polyethylene. The flexible co-production means that the ratio of the output of the co-produced C4 or C4 or higher even-numbered carbon olefins to the output of the branched polyethylene can be adjusted within a wide range of 0 to 10 without affecting the copolymerization reaction.

[0049] In some embodiments, preferably, the even-numbered carbon olefin includes at least one of C4 to C30 olefins. Further preferably, the even-numbered carbon olefin includes at least one of 1-butene, 1-hexene, 1-octene, and 1-decene. More preferably, the even-numbered carbon olefin includes at least one of 1-hexene or 1-octene.

[0050] In the embodiment of the present invention, the even-numbered olefin can participate in the polymerization process of the branched polyethylene as a comonomer on the one hand, and act as a medium for the oligomerization-copolymerization reaction on the other hand, thereby avoiding the use of an inert medium in the preparation process. If the even-numbered olefin is a solvent for the polymer, the copolymerization process is a solution polymerization; if the even-numbered olefin is a non-solvent for the polymer, the copolymerization process is a precipitation polymerization or a slurry polymerization. When C4 olefin is used as a polymerization medium and a comonomer, C4 olefin can also serve as a heat carrier to strengthen the gas phase condensation and heat removal in industry, thereby obtaining a branched polyethylene product with improved application performance and facilitating large-scale industrial continuous production.

[0051] In some embodiments, preferably, the molar ratio of the ethylene to the even-numbered olefin is 1:(0.5-50), such as 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:5.5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:20, 1:35, 1:50, etc. Further preferably, the molar fraction of the even-numbered olefin in the liquid phase is 75-95%, and the liquid phase refers to the even-numbered olefin and the ethylene monomer dissolved therein.

[0052] In some embodiments, preferably, the even-numbered olefin is pre-added and / or obtained in situ from ethylene through oligomerization reaction.

[0053] In some embodiments, preferably, the oligomerization catalyst includes at least one of a titanium-based oligomerization catalyst, a pyridine diimine iron complex catalyst, a pyridine diimine cobalt complex catalyst, a phenanthroline iron complex catalyst, a PNP coordinated chromium catalyst, a SNS coordinated chromium catalyst, or a late transition metal complex catalyst. Further preferably, the oligomerization catalyst includes at least one of a PNP coordinated chromium catalyst or a SNS coordinated chromium catalyst.

[0054] In some embodiments, preferably, the copolymerization catalyst comprises at least one of a ZN catalyst, a metallocene catalyst, a non-metallocene catalyst, an early transition metal catalyst, and a late transition metal catalyst; the metallocene catalyst comprises at least one of a restricted geometry catalyst, a non-bridged metallocene, a half-sandwich metallocene, a methyl-bridged metallocene, an ethyl-bridged metallocene, and a silyl-bridged metallocene. Further preferably, the copolymerization catalyst comprises at least one of a late transition metal complex catalyst or a metallocene catalyst, and the late transition metal complex catalyst is at least one of a complex catalyst comprising nickel, a complex catalyst comprising palladium, or a complex catalyst comprising iron. More preferably, the copolymerization catalyst comprises at least one of a diimine nickel complex or a diimine palladium complex. More preferably, the copolymerization catalyst comprises a diimine nickel complex. Among them, the diimine nickel complex is prepared according to the method disclosed in CN116239494A. In a preferred case, the diimine nickel complex is a complex Ni2, Ni3, Ni4, the complex Ni2 is prepared by Example 2 in CN116239494A, the complex Ni3 is prepared by Example 3 in CN116239494A, and the complex Ni4 is prepared by Example 4 in CN116239494A.

[0055] It should be noted that when the oligomerization catalyst and copolymerization catalyst are both selected from late transition metal complexes, it is preferred to use the same late transition metal and different ligands. Preferably, the oligomerization catalyst and copolymerization catalyst both include nickel complex catalysts.

[0056] In some embodiments, preferably, the oligomerization cocatalyst comprises at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, and organic boron compound;

[0057] And / or, the copolymerization cocatalyst includes at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, alkylaluminum chloride, and organic boron compound. Further preferably, the alkylaluminoxane includes at least one of methylaluminoxane (MAO), ethylaluminoxane (EAO) and isobutylaluminoxane; the modified alkylaluminoxane includes modified methylaluminoxane, and the modified methylaluminoxane contains isobutyl and / or 7-octyl; the alkylaluminum includes at least one of trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), trihexylaluminum, and tri-n-octylaluminum; the organic boron compound includes cycloboroxane, NaBH, triethylborane, tributyl borate, perfluorophenylborane, tri(pentafluorophenyl)borane B(C 6 F 5 ) 3, triphenylcarbon tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-dioctadecylmethyl tertiary amine tetrakis(pentafluorophenyl)borate, dihydrogenated tallow methyl tertiary amine tetrakis(pentafluorophenyl)borate, N,N-diethylanilinium tetrakis(pentafluorophenyl)borate or N,N-dihexadecylanilinium tetrakis(pentafluorophenyl)borate; the alkylaluminum chloride includes at least one of dichloromethylaluminum, dimethylaluminum chloride, trimethylaluminum trichloride, diethylaluminum chloride, triethylaluminum trichloride and ethylaluminum dichloride.

[0058] In the embodiments of the present invention, the copolymerization promoter can activate the late transition metal catalyst and remove impurities such as water in the system.

[0059] In some embodiments, preferably, the molar ratio of the metal element of the oligomerization catalyst to the metal element of the copolymerization catalyst is 1 / 100 to 100 / 1; the molar ratio of the oligomerization catalyst to ethylene is 1 / 10000000 to 1 / 1000, and the molar ratio of the copolymerization catalyst to ethylene is 1 / 10000000 to 1 / 1000;

[0060] And / or, the molar ratio of the metal element of the oligomerization co-catalyst to the metal element of the oligomerization catalyst is 0-5000:1, and the molar ratio of the metal element of the copolymerization co-catalyst to the metal element of the copolymerization catalyst is 0-5000:1.

[0061] In some embodiments, preferably, the polymerization catalyst and copolymerization catalyst are both selected from late transition metal complexes, the polymerization cocatalyst includes at least one of alkylaluminoxane, modified alkylaluminoxane, and alkylaluminum, and the copolymerization cocatalyst includes at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, and alkylaluminum chloride. The dosage ratio of the late transition metal catalyst and the cocatalyst is calculated based on the metal element contained in the late transition metal catalyst and the aluminum element contained in the cocatalyst. The molar ratio of the aluminum element in the cocatalyst to the metal element in the late transition metal catalyst is (100-5000):1, preferably (400-1000):1. For example, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1 or 1000:1, etc.

[0062] In some embodiments, preferably, the copolymerization catalytic activity ratio is 1000-20000, such as 1000, 2000, 5000, 10000, 15000 or 20000, etc. The copolymerization catalytic activity ratio is the ratio of the yield of branched polyethylene to the weight of the copolymerization catalyst used.

[0063] In some embodiments, preferably, the oligomerization-copolymerization cascade catalyst system is supported on a carrier material. Further preferably, the carrier material comprises at least one of an inorganic material or a polymer material, and the inorganic material comprises silica, alumina, MgCl 2 , zirconium oxide, artificial hectorite or montmorillonite clay, and the polymer material includes at least one of polyethylene, polypropylene, polystyrene or poly(aminostyrene). The oligomerization-copolymerization cascade catalytic system is formed in situ in the presence of a carrier material, or the carrier material is pre-impregnated or pre-mixed with the oligomerization catalyst, copolymerization catalyst, oligomerization co-catalyst and copolymerization co-catalyst simultaneously or sequentially, and the carrier material can serve as an activator or play a chemical function similar to that of the catalyst.

[0064] In some embodiments, preferably, the oligomerization-copolymerization reaction comprises at least one of batch polymerization, semi-continuous polymerization or continuous polymerization.

[0065] In some embodiments, preferably, the temperature of the oligomerization-copolymerization reaction is 0-250°C, the pressure of the oligomerization-copolymerization reaction is 0.1-5MPa, and the time of the oligomerization-copolymerization reaction is 5-120min. Further preferably, the temperature of the oligomerization-copolymerization reaction is 50-120°C; the pressure of the oligomerization-copolymerization reaction is 0.5-4.5MPa, such as 0.5MPa, 0.8MPa, 1.0MPa, 1.2MPa, 1.5MPa, 2.0MPa, 2.5MPa, 3.0MPa, 3.5MPa, 4.0MPa, 4.5MPa, etc. More preferably, the temperature of the oligomerization-copolymerization reaction is 60-110°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 90°C, 100°C or 110°C, etc. It is understood that the time of the oligomerization-copolymerization reaction refers to the reaction time required for intermittent polymerization.

[0066] In the embodiment of the present invention, the polymerization and copolymerization are carried out in situ and simultaneously under the same medium, temperature and pressure, and no adjustment is required during the preparation process, thereby reducing the difficulty of the process flow.

[0067] In some embodiments, the oligomerization-copolymerization reaction can be carried out in an apparatus comprising any type of reactor, preferably, the apparatus comprises: (a) a reactor, (b) at least one inlet pipeline system for olefin reactants and catalysts entering the reactor, (c) an outflow pipeline from the reactor for polymerization products and (d) at least one separator to separate the desired polymerization products, wherein the reactor comprises at least one of a batch reactor, a semi-batch reactor and a continuous reactor. Further preferably, the reactor comprises a first reactor and a second reactor, wherein the first reactor comprises a continuous stirred tank reactor, and the second reactor comprises at least one of a continuous stirred tank reactor or a batch continuous stirred tank reactor or a plug flow reactor.

[0068] In some embodiments, preferably, the oligomerization-copolymerization reaction is carried out in a polymerization kettle, and before the oligomerization-copolymerization reaction is carried out, the polymerization kettle is subjected to anhydrous and oxygen-free treatment and then evacuated.

[0069] In some embodiments, preferably, the preparation method further comprises post-treatment: the post-treatment comprises separating the comonomer and the branched polyethylene. Further preferably, the post-treatment comprises: ethylene monomer removal, washing, impurity removal, deashing, liquid-liquid phase separation, polymerization medium (i.e., comonomer)-polymer separation (desolventization, devolatilization), polymerization medium (i.e., comonomer) purification, recycling and reuse, polymer drying, granulation, and briquetting. More preferably, the process used for the polymerization medium (i.e., comonomer)-polymer separation comprises at least one of a wet condensation process, a dry devolatilization process or a precipitation separation process; the wet condensation process is to pass the reaction solution and water vapor into hot water with high-speed stirring to complete the removal of the comonomer, and the polymer is granulated and suspended in water; the dry devolatilization process refers to the direct removal of the comonomer and the extrusion granulation or flake formation of the polymer by a special devolatilization extruder with or without multi-stage flash evaporation; the precipitation separation process refers to the addition of a precipitant to the polymerization solution to precipitate the polymer to achieve separation. More preferably, the polymerization medium (i.e., comonomer)-polymer separation is first performed by liquid-liquid phase separation to achieve partial separation and polymer concentration.

[0070] The embodiment of the present invention further provides a branched polyethylene, which is prepared by the above-mentioned preparation method.

[0071] In some embodiments, preferably, the number average molecular weight of the branched polyethylene is 1000 to 3000000 g / mol, for example, 2000, 20000, 200000, 2000000 or 3000000 g / mol.

[0072] In some embodiments, preferably, the molecular weight distribution index of the branched polyethylene is 1.2 to 15.0, such as 1.2, 1.5, 2, 2.5, 3.0, 5.0, 10.0, 15.0, etc.

[0073] In some embodiments, preferably, the total branching degree of the branched polyethylene is 10 to 300 / C, such as 10 / 1000C, 50 / 1000C, 100 / 1000C, 200 / 1000C or 300 / 1000C.

[0074] In some embodiments, preferably, the branched polyethylene has a melt index of 0 to 50 g / 10 min, such as 0, 10 g / 10 min, 20 g / 10 min, 30 g / 10 min, 40 g / 10 min or 50 g / 10 min.

[0075] In some embodiments, preferably, the transparency of the branched polyethylene after film pressing is 88-92%, such as 88%, 90%, 91% or 92%, etc.; the haze of the branched polyethylene after film pressing is 1-10%, such as 1%, 2%, 4%, 6%, 8% or 10%, etc.

[0076] In some embodiments, preferably, the melting point of the branched polyethylene is -30 to 130° C. When the highly branched polyethylene is nearly completely amorphous, the highly branched polyethylene has no obvious melting point.

[0077] The embodiments of the present invention also provide the branched polyethylene prepared by the above preparation method or the application of the branched polyethylene in the fields of photovoltaic film, rubber, polymer modifier and elastomer.

[0078] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0079] Example 1

[0080] This embodiment is a batch cascade slurry polymerization process.

[0081] After the 5L polymerization kettle was treated to be anhydrous and oxygen-free, it was evacuated, and then 3L of liquid 1-butene was pressed into the polymerization kettle. The temperature was raised to 70°C, and then ethylene was introduced into the polymerization kettle to raise the pressure in the polymerization kettle to 2.0Mpa. Then, 0.72g (3mmol) of polymerization catalyst Ti(OiC) was added into the polymerization kettle. 3 H 7 ) 4 30 ml of a hexane solution of 1 M triethylaluminum (TEA) and 0.6 g (corresponding to 0.48 mmol Ti) of a copolymerization catalyst TiCl 4 / MgCl 2 / PE, after the reaction is started, ethylene is continuously introduced into the polymerization kettle, and the ethylene flow rate is recorded. The ethylene feed rate is controlled to keep the pressure in the polymerization kettle at 2.0MPa, the reaction temperature is 70°C, the reaction time is 120min, and a total of 1179g of ethylene is introduced. The gas phase is taken for chromatographic analysis. The reaction is terminated, the polymerization kettle is vented, and the tail gas is compressed and condensed by a compression condensation device to recover butene, and a small amount of ethylene is vented. The dry pellets in the polymerization kettle are taken out, the primary product is washed with ethanol several times, and the branched polyethylene P1 is obtained after drying. The chromatogram shows a small amount of cis-2-butene, trans-2-butene, isomeric hexene, and a trace amount of high melting point PE.

[0082] Example 2

[0083] This embodiment is an intermittent cascade solution polymerization process.

[0084] The preparation method is the same as that of Example 1, except that the copolymerization catalytic system uses 10 ml (0.02 g, 24 μmol) of toluene solution of the complex Ni4 (prepared by Example 4 in CN116239494A) with a concentration of 2 mg / mL and 1 M triethylaluminum trichloride (Et 3 Al 2 Cl 3 ) was added with 4.0 mL of hexane solution (Al / Ni=333), the polymerization temperature was adjusted to 85°C, the reaction time was 60 min, and the polymerization pressure was 2.0 MPa.

[0085] A total of 304 g of ethylene was introduced, and the gas phase was taken for chromatographic analysis to terminate the reaction. The solution in the polymerization kettle was pressed through a 25 μm filter to remove trace high-melting-point PE particles, and then the pressure was released to precipitate the high polymer product. The tail gas was compressed and condensed by a compression condensation device to recover butene, and a small amount of ethylene was vented. The polymer product was repeatedly washed with ethanol and dried to obtain highly branched polyethylene P2. A small amount of cis-2-butene, trans-2-butene, and isomeric hexene were found in the chromatogram.

[0086] Example 3

[0087] This example is an intermittent inert solvent-free solution polymerization process of a high-selectivity trimerization catalyzed by a SNS-Cr catalyst and a copolymerization cascade system catalyzed by a CGC-Ti catalyst.

[0088] Oligomerization catalyst SNS-Cr: Bis(2-dodecylsulfanyl-ethyl)amine-chromium trichloride 3 ), molecular weight: 631.6 g / mol, structural formula:

[0089]

[0090] The polymerization auxiliary catalyst is MMAO;

[0091] The copolymerization catalyst is: CGC-Ti restricted geometry catalyst, N-tert-butylamido)(tetramethylcycloptadienyl)titanium dichloride, i.e.: dimethylsilyl(N-tert-butylamido)(tetramethylcyclopentadienyl)titanium dichloride, molecular weight: 369.2 g / mol, structural formula is as follows:

[0092]

[0093] After the 5L polymerization kettle was treated to be anhydrous and oxygen-free, it was evacuated, and then 3L of 1-hexene was added to the polymerization kettle, and the temperature was raised to 110°C. Then, ethylene was introduced into the polymerization kettle to raise the pressure in the polymerization kettle to 3.0MPa (the molar concentrations of liquid ethylene and 1-hexene were approximately 1.9mol / L and 5.7mol / L, respectively (ethylene / 1-hexene≈1:), and then 0.063g (100μmol) of a toluene solution of a polymerization catalyst SNS-Cr and 150ml of a 1M modified methylaluminoxane (MMAO) 1-hexene solution (containing Al 150mmol) and 18.5ml (0.037g, 100μmol) of toluene solution of copolymerization catalyst CGC-Ti with a concentration of 2mg / mL. After the reaction is started, ethylene is continuously introduced into the polymerization kettle, and the ethylene flow rate is detected. The ethylene feed rate is controlled to keep the pressure in the polymerization kettle at 3.0MPa, the reaction temperature is 110°C, the reaction time is 30min, and a total of 548g of ethylene is introduced to terminate the reaction. The glue in the polymerization kettle is released, washed with ethanol aqueous solution, and finally devolatilized and recovered to obtain the comonomer 1-hexene, and the polymer is dried to obtain branched polyethylene P3.

[0094] Example 4

[0095] The process is basically the same as Example 3, except that the amount of SNS-Cr oligomerization catalyst is reduced to 0.032 g (50 μmol), and the rest remain unchanged. A total of 450 g of ethylene is introduced to obtain polymer P4.

[0096] Example 5

[0097] The process was basically the same as Example 3, except that the polymerization temperature was 90°C, the polymerization pressure was 1.0 MPa, and the rest remained unchanged. A total of 430 g of ethylene was introduced to obtain polymer P5.

[0098] Example 6

[0099] This embodiment is an intermittent solution polymerization process of a high-selectivity trimerization-chain walking copolymerization cascade system.

[0100] The oligomerization catalyst SNS-Cr is the same as that in Example 3; the oligomerization co-catalyst is MMAO / TEA.

[0101] After the 5L polymerization kettle was treated to be anhydrous and oxygen-free, it was evacuated, and then 3L 1-hexene was added into the polymerization kettle. The temperature was raised to 75°C, and then ethylene was introduced into the polymerization kettle to raise the pressure in the polymerization kettle to 1.0 MPa (the molar concentrations of liquid ethylene and 1-hexene were approximately 0.87 mol / L and 6.8 mol / L, respectively (ethylene / 1-hexene≈1:7.8). Then, 0.04g (64 μmol) of a toluene solution of the polymerization catalyst A and 16ml (16mmolAl) of a 1M modified methylaluminoxane (MMAO) in 1-hexene solution, 13ml (13mmolAl) of a 1M triethylaluminum (TEA) in 1-hexene solution, 10ml (0.02g, 24μmol) of a toluene solution of a copolymerization catalyst complex Ni3 with a concentration of 2mg / mL and 1M triethylaluminum trichloride (Et 3 Al 2 Cl 3 ) 4.0mL of 1-hexene solution (Al / Ni=333) was added to the polymerization kettle. After the reaction was started, ethylene was continuously introduced into the polymerization kettle, and the ethylene flow rate was detected. The ethylene feed rate was controlled to keep the pressure in the polymerization kettle at 1.0MPa, the reaction temperature was 75°C, the reaction time was 30min, and 326g of ethylene was introduced cumulatively. The gas phase was taken for chromatographic analysis, and the reaction was terminated. The glue in the polymerization kettle was released, washed with ethanol aqueous solution, and finally devolatilized and recovered to obtain the comonomer 1-hexene. The polymer was dried to obtain branched polyethylene P6.

[0102] Example 7

[0103] This embodiment is a high-selectivity trimerization-chain walking copolymerization cascade system and a continuous solution polymerization process.

[0104] The catalytic system is the same as that in Example 6.

[0105] In this embodiment, highly branched polyethylene and 1-hexene are co-produced in a 10,000 ton / year pilot plant. The pilot plant is a kettle-type continuous polymerization polyethylene process plant, which has two series-connected 10m 3The polymerization kettle has a height-to-diameter ratio H / D=1.50. 4.0 t of 1-hexene was pre-added to each polymerization kettle, the temperature was raised to a reaction temperature of 75°C, ethylene was introduced to increase the pressure to a reaction pressure of 1.0 MPa, and 100 L / h of a toluene solution of a polymerization catalyst A (concentration was 2 g / L, the amount of pure A added was 200 g / h) and 80 L / h of a 1M modified methylaluminoxane (MMAO) 1-hexene solution, 64 L / h of a 1M triethylaluminum (TEA) 1-hexene solution, and 2 g / L The complex Ni3 toluene solution was 100 L / h (the amount of pure catalyst added was 200 g / h) and 1M trichlorotriethylaluminum 1-hexene solution was 40 L / h. After the reaction was started, ethylene was continuously introduced into the two kettles, and the reaction pressure was maintained at 1.0 MPa. 1-hexene was continuously introduced into the first kettle at 16 t / h. The charging factor of the two kettles was maintained at 60%. The total residence time was 30 min. The total ethylene consumption rate after deducting the return amount was 2 .6t / h, the solid content of the glue at the outlet of the second kettle is 9.8wt%. A small amount of water is injected into the glue discharged from the polymerization kettle to deactivate the catalyst. The glue is pressurized and transported by a booster pump, and after being heated by a two-stage heat exchanger, it enters a gas-liquid-liquid separation decanter with a temperature of 225°C and a pressure of 3.5Mpa. Phase separation occurs in the glue in the gas-liquid-liquid separator decanter, and ethylene gas flows out from the upper outlet of the separator, and is directly returned to the polymerization reactor after being cooled by the heat exchanger and dehydrated by a molecular sieve drying tower; the polymer-poor phase (containing polymer <0.1%) flows out from the middle outlet of the separator, and is directly returned to the polymerization reactor after being cooled by the heat exchanger and dehydrated by a molecular sieve drying tower; the polymer-rich phase (containing 30-40% of polymer) flows out from the bottom of the separator, and the glue is filtered to remove trace high-melting-point polyethylene particles, and then passes through a silica gel adsorption tower to remove catalyst residues, and then dry devolatilization and extrusion granulation are performed to obtain branched polyethylene P7. The 1-hexene recovered by devolatilization is returned to the polymerization reactor after dehydration, and the other part is sold as a product after distillation purification and dehydration. The output of branched polyethylene is 1.6t / h (8000 times), and the net output of 1-hexene is 0.37t / h.

[0106] It can be seen that since the system has no inert medium and the polymerization reaction has an ultra-high selectivity for 1-hexene, most of the 1-hexene can be directly returned to the polymerization reactor for reuse without distillation and purification, and the ethylene / 1-hexene concentration ratio is easy to control. Distilling a small amount of 1-hexene as a product is sufficient to remove trace amounts of inert additives and by-products, preventing the continuous accumulation of inert additives and by-products.

[0107] Comparative Example 1

[0108] This comparative example is a cascade slurry polymerization process with an inert medium.

[0109] The method of this comparative example is the same as that of Example 1, except that: in Comparative Example 1, 2.0L of n-hexane + 1.0L of 1-butene are used as a mixed medium, and the reaction pressure is adjusted to 1.5MPa. As a result, a total of 1140g of ethylene is introduced to obtain branched polyethylene D1. A small amount of cis-2-butene, trans-2-butene, isomeric hexene, and a trace amount of high-melting-point PE are found in the chromatogram.

[0110] It can be seen that due to the use of an inert medium, the 1-butene concentration is low. At basically the same effective ethylene concentration, the 1-butene insertion rate is low and the degree of branching is low.

[0111] Comparative Example 2

[0112] The catalytic system and reaction conditions of this comparative example are the same as those of Example 3, except that 3 L of toluene is used as solvent, 1-hexene is not pre-added, 1-hexene is completely derived from polymerization, and a process of pre-polymerization for a certain period of time is adopted. Specific steps:

[0113] After the 5L polymerization kettle was treated with anhydrous and oxygen-free treatment, it was evacuated, and then 3L toluene was added to the polymerization kettle, and the temperature was raised to 110°C. Then, ethylene was introduced into the polymerization kettle to raise the pressure in the polymerization kettle to 3.0MPa. Then, 0.063g (100μmol) of a toluene solution of a polymerization catalyst SNS-Cr and 150ml (containing 150mmol Al) of a toluene solution of a 1M modified methylaluminoxane (MAO) were added into the polymerization kettle. The polymerization reaction was started, ethylene was continuously introduced into the polymerization kettle, and the ethylene flow rate was detected, and the cumulative flow rate of ethylene was recorded. After 1 minute, 18.5ml (0.037g, 100μmol) of a toluene solution of a copolymerization catalyst CGC-Ti with a concentration of 2mg / mL was added. The copolymerization reaction was started, and ethylene was continuously introduced into the polymerization kettle, and the flow rate was detected. The ethylene feed rate was controlled to keep the pressure in the polymerization kettle at 3.0MPa. The reaction temperature was 110°C, the reaction time was 30min, and 532g of ethylene was introduced cumulatively to terminate the reaction. The rubber liquid in the polymerization kettle is released, washed with ethanol aqueous solution, and finally devolatilized and recovered to obtain the comonomer 1-hexene. The polymer is dried to obtain branched polyethylene D2.

[0114] From the comparison between Comparative Example 2 and Example 3, it can be seen that since Comparative Example 2 uses an inert medium, the concentration of 1-hexene is low. At substantially the same effective ethylene concentration, the insertion rate of 1-hexene is low, the degree of branching is low, and the melting point is high. And from the comparison between Example 3 and the chain walking polymerization process catalyzed by a late transition metal, it can be seen that the cascade catalytic system without an inert solvent can also prepare branched polyethylene from a single ethylene monomer, without the need to purchase α-olefins, and can be polymerized at high temperature. The process control is also simple, and α-olefins can be produced flexibly as a by-product.

[0115] Example 4: The amount of the oligomerization catalyst is reduced, and the amount of the oligomerization product is reduced to just enough to offset the copolymerization consumption, so that the comprehensive catalytic activity ratio (polymer amount / (oligomerization catalyst amount + copolymerization catalyst amount)) reaches more than 6000.

[0116] In Example 5, polymerization is carried out at a suitably low temperature and pressure, and the amount of the oligomerization product is similarly controlled to be just enough to offset the copolymerization consumption, so that the degree of branching reaches 62 / 1000C, reaching the level of commercially available POE, and the comprehensive catalytic activity ratio reaches more than 4250.

[0117] Therefore, before the high-temperature activity of late transition metal catalysts is further improved, the cascade catalytic process without inert solvents is still a strong competitor to the chain-walking polymerization process catalyzed by late transition metals.

[0118] Comparative Example 3

[0119] This comparative example is a cascade solution polymerization process with an inert solvent.

[0120] The method of this comparative example is the same as that of Example 6, except that: in Comparative Example 3, 2L of n-hexane and 1L of 1-hexene are used as a mixed solvent, the reaction pressure is 1.0 MPa, and finally branched polyethylene D3 is obtained.

[0121] It can be seen that due to the use of inert solvents, the 1-hexene concentration is low. At basically the same effective ethylene concentration, the 1-hexene insertion rate is low, the branching degree is low, and there is a problem of difficulty in separating n-hexane and 1-hexene when used in industrialization.

[0122] More operating details of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1:

[0123]

[0124]

[0125] The branched polyethylenes P1-P7 prepared in Examples 1-7 and the branched polyethylenes D1-D3 prepared in Comparative Examples 1-3 were tested.

[0126] (1) Degree of branching and branch distribution:

[0127] The degree of branching of branched polyethylene P1 to P7 and D1 to D3 is 13 C NMR determination: The branched polyethylene was dissolved in 1,2-o-dichlorobenzene, TMS was used as the internal standard, and the measurement was performed on a Bruker AVANCE III 500 MHz. The temperature was set to 100 °C, the number of scans was 3000, the spectrum width was 18.8324 kHz, the data acquisition time was 0.87 s, and the delay time was 2 s. The results are shown in Table 2.

[0128] Table 2

[0129]

[0130] (2) Melting point:

[0131] The melting points of branched polyethylenes P1-P7 and D1-D3 were tested by DSC, with a temperature range of 0-150°C and a temperature change process as follows:

[0132] The first stage: from room temperature (25°C) to 150°C, the heating rate is 10°C / min, and the temperature is maintained at 150°C for 2 minutes;

[0133] The second stage: from 150℃ to -60℃, the cooling rate is 10 / min, and the temperature is kept at -60℃ for 2min;

[0134] The third stage: the temperature rises from -60℃ to 150℃ at a rate of 10℃ / min; then drops to 40℃ at a rate of 10℃ / min, and the test ends;

[0135] The melting point was obtained from the melting peak of the third stage heating curve. The results are shown in Table 3.

[0136] Table 3

[0137]

[0138]

[0139] (3) Melt flow rate (melt index):

[0140] The melt flow rates (melt indexes) of the branched polyethylenes P1-P7 and D1-D3 were tested according to the standard ASTM D 1238 test method (190°C and 2.16 kg). The results are shown in Table 4.

[0141] Table 4

[0142] Branched Polyethylene Melt index (g / 10min) Example 1 P1 0 Example 2 P2 1.2 Example 3 P3 6.0 Example 4 P4 5.9 Example 5 P5 10 Example 6 P6 1.5 Example 7 P7 1.6 Comparative Example 1 D 1 0 Comparative Example 2 D 2 4.5 Comparative Example 3 D 3 1.4

[0143] (4) Film transparency and haze:

[0144] The transparency and haze of the films of highly branched polyethylene P2-P7 and D2-D3 were measured according to GBT 2410-2008 Transparent Plastic Transmittance and Haze Test Method Standard, and the results are shown in Table 5. The transparency and haze of the films of branched polyethylene P1-P5 are comparable to the photovoltaic-grade POE indicators on the market, and can be used to prepare photovoltaic films.

[0145] Table 5

[0146]

[0147] (5) Catalytic activity ratio: The catalytic activity ratio is the ratio of the yield of branched polyethylene to the weight of the copolymerization catalyst used. The results are shown in Table 6.

[0148] Table 6

[0149] Example Copolymerization catalytic activity ratio Example 1 1200 Example 2 12500 Example 3 12160 Example 4 12000 Example 5 11300 Example 6 10000 Example 7 9000 Comparative Example 1 1100 Comparative Example 2 10800 Comparative Example 3 8000

[0150] (6) Weight average molecular weight:

[0151] The weight average molecular weight and molecular weight distribution index of branched polyethylenes P1-P7 and D1-D3 were determined by high temperature gel permeation chromatography (PL-GPC220) at 150°C with 1,2,4-trichlorobenzene as the mobile phase and polystyrene as the standard.

[0152] The results are shown in Table 7.

[0153] Table 7

[0154]

[0155] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0156] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium, characterized in that: The following steps are involved: Under the catalysis of the oligomerization-copolymerization cascade catalytic system, ethylene is polymerized to generate even-numbered olefins, and ethylene and even-numbered olefins are copolymerized at the same time to obtain branched polyethylene; The even-numbered carbon olefins include even-numbered carbon olefins of C4 or above; The oligomerization-copolymerization cascade catalytic system comprises an oligomerization catalyst and a copolymerization catalyst.

2. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1, characterized in that: While preparing the branched polyethylene, C4 or even-numbered carbon olefins above C4 can be flexibly co-produced.

3. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1, characterized in that: The even-numbered carbon olefins include at least one of C4 to C30 olefins; and / or, the molar ratio of the ethylene to the even-numbered olefin is 1:(0.5-50); And / or, the even-numbered olefin is pre-added and / or obtained in situ from ethylene by oligomerization.

4. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1, characterized in that: The oligomerization-copolymerization cascade catalytic system further comprises an oligomerization cocatalyst and / or a copolymerization cocatalyst.

5. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 4, characterized in that: The oligomerization catalyst comprises at least one of a titanium-based oligomerization catalyst, a pyridine diimine iron complex catalyst, a pyridine diimine cobalt complex catalyst, a phenanthroline iron complex catalyst, a PNP coordinated chromium catalyst, a SNS coordinated chromium catalyst or a late transition metal catalyst; And / or, the copolymerization catalyst comprises at least one of a ZN catalyst, a metallocene catalyst, a non-metallocene catalyst, an early transition metal catalyst, and a late transition metal catalyst; and / or, the oligomerization cocatalyst comprises at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, and organic boron compound; And / or, the copolymerization co-catalyst includes at least one of alkylaluminoxane, modified alkylaluminoxane, alkylaluminum, alkylaluminum chloride, and organic boron compound.

6. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1 or 5, characterized in that: The oligomerization catalyst includes at least one of a PNP coordinated chromium catalyst or a SNS coordinated chromium catalyst; And / or, the copolymerization catalyst is at least one of a late transition metal catalyst or a metallocene catalyst.

7. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to any one of claims 4 to 6, characterized in that: The molar ratio of the metal element of the oligomerization catalyst to the metal element of the copolymerization catalyst is 1 / 100 to 100 / 1; the molar ratio of the oligomerization catalyst to ethylene is 1 / 10000000 to 1 / 1000, and the molar ratio of the copolymerization catalyst to ethylene is 1 / 10000000 to 1 / 1000; and / or, the molar ratio of the metal element of the oligomerization promoter to the metal element of the oligomerization catalyst is 0 to 5000:1; And / or, the molar ratio of the metal element of the copolymerization promoter to the metal element of the copolymerization catalyst is 0 to 5000:

1.

8. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1, characterized in that: The oligomerization-copolymerization reaction comprises at least one of batch polymerization, semi-continuous polymerization or continuous polymerization; And / or, the temperature of the polymerization-copolymerization reaction is 0-250° C., the pressure of the polymerization-copolymerization reaction is 0.1-5 MPa, and the time of the polymerization-copolymerization reaction is 5-120 min.

9. The method for preparing branched polyethylene by cascade polymerization in the absence of an inert medium according to claim 1, characterized in that: The preparation method further comprises post-processing: the post-processing comprises separating the comonomer and the branched polyethylene.

10. A branched polyethylene, characterized in that Prepared according to the preparation method according to any one of claims 1 to 9.

11. The branched polyethylene according to claim 10, characterized in that The number average molecular weight of the branched polyethylene is 1000 to 3000000 g / mol, and the molecular weight distribution index of the branched polyethylene is 1.2 to 15.0; And / or, the total branching degree of the branched polyethylene is 10 to 300 / C; And / or, the branched polyethylene has a melt index of 0 to 50 g / 10 min; And / or, the transparency of the branched polyethylene after film pressing is 88-92%, and the haze of the branched polyethylene after film pressing is 1-10%; And / or, the melting point of the branched polyethylene is -30 to 130°C.

12. Use of the branched polyethylene obtained by the preparation method according to any one of claims 1 to 9 or the branched polyethylene according to claim 10 or 11 in the fields of photovoltaic films, rubber, polymer modifiers and elastomers.

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