Alpha-carboxy-beta-diimine nickel complexes, methods of making and using, and methods of making ethylene-methyl acrylate copolymers

Abstract

The application provides an alpha-carboxyl-beta-diimine nickel complex and a preparation method and application thereof and a preparation method of ethylene-methyl acrylate copolymer. The alpha-carboxyl-beta-diimine nickel complex has a structure shown in general formula (I): in the general formula (I), Ar is selected from 2,6-dialkylphenyl; X is chlorine or bromine; and L is acetonitrile or benzonitrile. The preparation method of the alpha-carboxyl-beta-diimine nickel complex is that acetylacetone is reacted with 2,6-dialkylaniline, then reacted with ammonium formate under the action of alkyl lithium, and then reacted with a halogenated nickel salt in an acetonitrile or benzonitrile solvent to obtain the alpha-carboxyl-beta-diimine nickel complex. The application further provides a preparation method of ethylene-methyl acrylate copolymer, which uses the alpha-carboxyl-beta-diimine nickel complex as a main catalyst. The application improves the copolymer molecular weight and the methyl acrylate insertion rate, and makes the prepared EMA similar to the branched structure of a commercial product prepared by a free radical process.

Description

Technical Field

[0001] This invention relates to an α-carboxy-β-diimine nickel complex, its preparation method and application, and a method for preparing an ethylene-methyl acrylate copolymer, belonging to the field of olefin catalytic polymerization technology. Background Technology

[0002] Polyolefins are high-performance materials widely used in automotive, electronics, piping, medical, and military industries, and are a common polymer in daily life. However, the non-polar nature of polyolefins limits their wider application. Introducing polar groups into the polymer chain can significantly improve the adhesion, dyeability, and compatibility of polyolefin materials. For example, ethylene-methyl acrylate copolymers (EMA) containing 10ω%–30ω% methyl acrylate (MA) have excellent mechanical properties and compatibility, leading to their widespread use in many fields. Industrially, EMA is obtained through free radical copolymerization under harsh conditions of high temperature (150–300℃) and high pressure (150–300MPa), resulting in an uncontrollable branched structure in the copolymer.

[0003] Compared to the harsh conditions of free radical copolymerization, coordination polymerization offers a simple, direct, and effective method for the direct copolymerization of olefins and polar monomers under mild conditions to obtain functionalized polyolefins with controllable branched structures. Polar monomers (MA) typically poison metal catalysts, especially pre-transition metal catalysts, which generally deactivate in the presence of methyl acrylate (MA) and cannot copolymerize. Therefore, directly copolymerizing ethylene-methyl acrylate copolymers via catalytic coordination polymerization presents a significant challenge.

[0004] Post-transition metal nickel-palladium catalysts, due to their weak electrophilic and oxyphilic properties, exhibit better tolerance to polar groups and can catalyze the copolymerization of ethylene and polar monomers. Cationic α-diimine palladium can catalyze the copolymerization of ethylene and MA, typically producing highly branched, amorphous copolymers with MA at the branch ends due to the rapid chain walk process, with a branching degree between 97 and 106 branches / 1000C (J. Am. Chem. Soc. 1998, 120, 888-899). Furthermore, neutral phosphonophenolic nickel catalysts can catalyze the copolymerization of ethylene and MA, yielding highly linear copolymers with MA inserted into the main chain, which differs significantly from the branched structure of EMA prepared industrially using free radicals. Therefore, preparing low-branched EMA copolymers and controlling their microstructure through catalytic coordination polymerization remains a significant challenge and requires further breakthroughs.

[0005] CN105968027A, CN105968027A, CN113651909A, CN113603611A, CN112538098A, etc., have published the latest research results. It can be seen that although the structure of ethylene-methyl acrylate copolymers prepared by the copolymerization of ethylene and methyl acrylate using existing nickel-palladium catalysts can be controlled by catalyst structure, there are still problems such as low copolymer molecular weight and MA monomer insertion rate, and low copolymerization activity. Moreover, compared with EMA copolymers obtained by commercial free radical processes, their branched structures are different. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide an α-carboxy-β-diimine nickel complex, its preparation method, and its applications. The α-carboxy-β-diimine nickel complex provided by this invention can be used as a catalyst in olefin polymerization, particularly suitable for catalyzing the copolymerization of ethylene and methyl acrylate (MA), enabling the product to have a low-branched structure while simultaneously improving copolymerization efficiency.

[0007] Another object of the present invention is to provide a method for preparing ethylene-methyl acrylate copolymer. Using the catalyst provided by the present invention, the efficiency of catalytic copolymerization of ethylene and methyl acrylate (MA) can be improved, the molecular weight of the copolymer and the insertion rate of MA can be increased, and the prepared ethylene-methyl acrylate copolymer (EMA) has a significant melting temperature, similar to the branched structure of commercially available copolymers prepared by free radical processes.

[0008] To achieve the above objectives, the first aspect of the present invention provides an α-carboxy-β-diimine nickel complex having the structure shown in general formula (I):

[0009]

[0010] In general formula (I), the two Ar atoms may be the same or different, and Ar is selected from 2,6-dialkylphenyl; X is a chlorine atom or a bromine atom; L is acetonitrile or benzonitrile.

[0011] In the above-described α-carboxy-β-diimine nickel complex, preferably, in general formula (I), the two Ar atoms are the same or different, and Ar is selected from 2,6-diisopropylphenyl and 2,6-dimethylphenyl. More preferably, in general formula (I), the two Ar atoms are the same, and Ar is 2,6-diisopropylphenyl or 2,6-dimethylphenyl. Particularly preferably, in general formula (I), the two Ar atoms are the same, both being 2,6-diisopropylphenyl.

[0012] In the above-mentioned -β-diimine nickel complex, preferably, in general formula (I), the two Ar are the same, both being 2,6-diisopropylphenyl, X is a bromine atom, and L is acetonitrile.

[0013] This invention introduces carboxyl groups into the framework structure of a cationic β-diimine nickel catalyst, resulting in a novel diimine nickel complex. The α-carboxyl-β-diimine nickel complex of this invention can serve as a catalyst for olefin polymerization, particularly suitable for the copolymerization of ethylene and methyl acrylate (MA). The introduction of carboxyl groups into the framework structure enables the copolymer to achieve a low-branching structure and improve copolymerization efficiency. Specifically, the introduction of carboxyl groups into the framework structure transforms the cationic nickel center into a neutral nickel active center, enhancing its tolerance to methyl acrylate. Furthermore, the active center also reduces chain travel during the copolymerization process, enabling the preparation of low-branching copolymers.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned α-carboxy-β-diimine nickel complex, comprising the following steps:

[0015] (1) React acetylacetone with 2,6-dialkylaniline to give a 2,6-dialkylphenyl-substituted β-diimine compound;

[0016] (2) The β-diimine compound substituted with 2,6-dialkylphenyl is subjected to a substitution reaction with ammonium formate under the action of alkyllithium to obtain α-carboxy-β-diimine lithium salt;

[0017] (3) The α-carboxy-β-diimine lithium salt and the halo nickel salt are subjected to a coordination reaction in acetonitrile or benzonitrile solvent to obtain the α-carboxy-β-diimine nickel complex.

[0018] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, preferably, the 2,6-dialkylaniline comprises 2,6-diisopropylaniline and / or 2,6-dimethylaniline. More preferably, the 2,6-dialkylaniline is 2,6-diisopropylaniline.

[0019] In the above method for preparing the α-carboxy-β-diimine nickel complex, step (1) is a ketamine condensation reaction, and the specific reaction conditions are known in the art; for example, the molar ratio of acetylacetone to 2,6-dialkylaniline can be 1:2; the reaction temperature of acetylacetone and 2,6-dialkylaniline can be 90°C, and the reaction time can be 72h.

[0020] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, preferably, in step (2), the alkyl lithium is butyl lithium, more preferably n-butyl lithium.

[0021] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, preferably, in step (2), the molar ratio of the 2,6-dialkylphenyl-substituted β-diimine compound, the alkyl lithium, and the ammonium formate is 1:(1.0-1.5):(1.2-2.0).

[0022] In the above method for preparing the α-carboxy-β-diimine nickel complex, the substitution reaction in step (2) is a strongly exothermic reaction, and its reaction conditions are related to the reaction scale. Those skilled in the art can adjust the temperature and time of the substitution reaction according to the reaction scale. For example, in the laboratory, a low-heat method can be used, with a reaction temperature of -80 to 40°C and a reaction time of 1 to 10 hours.

[0023] In the above-described method for preparing α-carboxy-β-diimine nickel complex, preferably, in step (3), the nickel halide salt includes nickel bromide and / or nickel chloride, more preferably nickel bromide.

[0024] In the above-described method for preparing the α-hydroxy-β-diimine nickel complex, preferably, in step (3), the α-hydroxy-β-diimine lithium salt and the halonickel salt undergo a coordination reaction in acetonitrile solvent.

[0025] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, preferably, in step (3), the molar ratio of the α-carboxy-β-diimine lithium salt to the nickel halide salt is 1:(1.0 to 1.5).

[0026] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, acetonitrile or benzonitrile is used in step (3) as both a solvent and a coordinating molecule, and therefore its amount is excessive. This invention does not impose specific limitations on its amount; those skilled in the art can make conventional adjustments.

[0027] In the above-described method for preparing the α-carboxy-β-diimine nickel complex, preferably, in step (3), the reaction temperature of the coordination reaction is 0–50°C, and the reaction time is 8–48 h. More preferably, the reaction temperature of the coordination reaction is 20–40°C, and the reaction time is 12–24 h.

[0028] In the preparation method of the α-carboxy-β-diimine nickel complex of the present invention, steps (1) and (2) can both be carried out in an organic solvent. The present invention does not impose any special limitations on the specific organic solvent used, and those skilled in the art can make conventional selections. Furthermore, after obtaining the corresponding products of steps (1), (2), and (3), one or more of the following steps can be performed on the products: separation, crystallization, concentration, washing, and drying. These steps are all conventional operations in the art, and the present invention does not impose any special limitations on them.

[0029] The third aspect of the present invention provides the application of the above-mentioned α-carboxy-β-diimine nickel complex as a catalyst in olefin polymerization reactions.

[0030] In the above applications, preferably, the olefin polymerization includes copolymerization of olefins and polar monomers.

[0031] In the above applications, preferably, the olefin polymerization is a copolymerization of ethylene and acrylate monomers. More preferably, the olefin polymerization is a copolymerization of ethylene and methyl acrylate.

[0032] In the above applications, preferably, the α-carboxy-β-diimine nickel complex is used as the main catalyst in the olefin polymerization reaction, and an organoaluminum compound is used as a co-catalyst.

[0033] In the above applications, preferably, the organoaluminum compound includes one or a combination of several selected from methylaluminoxane (MAO), modified methylaluminoxane (MMAO), isobutylaluminoxane (BAO), triethylaluminum, diethylaluminum chloride, diethylaluminum chloride, and triisobutylaluminum. More preferably, the organoaluminum compound includes one or a combination of several selected from methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and isobutylaluminoxane (BAO).

[0034] In the above applications, preferably, the aluminum-nickel molar ratio of the co-catalyst and the main catalyst is (500-3000):1, more preferably (1000-2000):1.

[0035] The fourth aspect of the present invention provides a method for preparing an ethylene-methyl acrylate copolymer, wherein the preparation method uses the above-mentioned α-carboxy-β-diimine nickel complex as the main catalyst.

[0036] According to a specific embodiment of the present invention, preferably, the preparation method of the ethylene-methyl acrylate copolymer includes the following steps:

[0037] Using the aforementioned α-carboxy-β-diimine nickel complex as the main catalyst and an organoaluminum compound as a co-catalyst, ethylene and methyl acrylate monomers were copolymerized in a solvent. After the reaction was completed, an ethylene-methyl acrylate copolymer was obtained.

[0038] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the reaction temperature of the copolymerization reaction is 0-100°C, more preferably 50-80°C.

[0039] In the above-described method for preparing the ethylene-methyl acrylate copolymer, preferably, the reaction pressure of the copolymerization reaction is 0.5–2.0 MPa. Those skilled in the art should understand that the pressure of the copolymerization reaction in this invention is the ethylene pressure.

[0040] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the reaction time of the copolymerization reaction is 0.5-24 h, more preferably 2-8 h.

[0041] In the above-described method for preparing the ethylene-methyl acrylate copolymer, preferably, the molar ratio of the methyl acrylate monomer to the main catalyst α-carboxy-β-diimine nickel complex is (266–1600):1, more preferably (500–1066):1. The molar ratio of the methyl acrylate monomer to the main catalyst α-carboxy-β-diimine nickel complex is based on a molar amount of nickel in the main catalyst of 1.

[0042] In the above-mentioned method for preparing ethylene-methyl acrylate copolymer, preferably, the organoaluminum compound includes one or a combination of several of methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and isobutylaluminoxane (BAO).

[0043] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the aluminum-nickel molar ratio of the co-catalyst and the main catalyst is (500-3000):1, more preferably (1000-2000):1.

[0044] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the solvent includes one or a combination of several of 1,2-dichloroethane, n-hexane, chlorobenzene, toluene, and xylene.

[0045] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned ethylene-methyl acrylate copolymer further includes the following step: after the reaction is completed, a terminator is added to terminate the reaction, thereby obtaining the ethylene-methyl acrylate copolymer. The specific selection and amount of the terminator can be adjusted by those skilled in the art according to the actual situation.

[0046] In the above-described method for preparing the ethylene-methyl acrylate copolymer, after terminating the reaction with a terminator, the method may further include steps such as washing, filtering, and drying the reaction product to obtain the ethylene-methyl acrylate copolymer. Washing, filtering, and drying are all conventional operations in the art, and this invention does not specifically limit them.

[0047] In the above-mentioned method for preparing ethylene-methyl acrylate copolymer, preferably, the weight-average molecular weight of the prepared ethylene-methyl acrylate copolymer is 13.2 to 100.3 kg / mol.

[0048] In the above-mentioned method for preparing ethylene-methyl acrylate copolymer, preferably, the degree of branching of the prepared ethylene-methyl acrylate copolymer is 25 to 51 branches / 1000C.

[0049] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the methyl acrylate insertion rate of the prepared ethylene-methyl acrylate copolymer is 2.5 to 36.4 ω% (based on the total weight of the ethylene-methyl acrylate copolymer being 100%).

[0050] In the above-mentioned method for preparing ethylene-methyl acrylate copolymer, preferably, the melting temperature of the prepared ethylene-methyl acrylate copolymer is 81.3 to 125.3 °C.

[0051] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the molecular weight distribution index of the prepared ethylene-methyl acrylate copolymer is 1.28-2.63.

[0052] In the above-described method for preparing ethylene-methyl acrylate copolymer, preferably, the catalytic activity of the main catalyst α-carboxy-β-diimine nickel complex is 0.89 × 10⁻⁶. 4 -18.1×10 4 g EMA / (mol Ni·h).

[0053] The preparation methods of the α-carboxy-β-diimine nickel complex and the ethylene-methyl acrylate copolymer provided by this invention include, but are not limited to, the following superior technical effects:

[0054] Beneficial Effect 1: This invention uses an α-carboxy-β-diimine nickel complex as the main catalyst to provide a highly efficient method for the direct copolymerization of ethylene and methyl acrylate to prepare EMA. The α-carboxy-β-diimine nickel complex main catalyst can achieve an MA insertion rate of 36.4 ω and a copolymer molecular weight of 100 kg / mol.

[0055] Beneficial Effect 2: The EMA prepared by the method provided by this invention has low branching and obvious melting temperature characteristics, which are different from the highly branched amorphous and completely linear EMA prepared by previous nickel-palladium catalysts. It has a similar branched structure to commercially available free radical-prepared EMA copolymers and has obvious commercial prospects.

[0056] Beneficial Effect 3: The preparation process of the α-carboxy-β-diimine nickel complex main catalyst provided by the present invention is simple and stable in air; compared with the industrial free radical copolymerization preparation of EMA, the preparation method of ethylene-methyl acrylate copolymer provided by the present invention has the advantages of mild reaction conditions and controllable branching structure.

[0057] In summary, compared with EMA copolymers obtained by commercial free radical processes, ethylene-methyl acrylate (EMA) copolymers prepared by existing nickel-palladium catalysts through copolymerization of ethylene and methyl acrylate (MA) suffer from defects or shortcomings, such as differences in branched structure and lower copolymer molecular weight and MA monomer insertion rate. This invention provides a novel α-carboxy-β-diimine nickel complex main catalyst and a method for preparing ethylene-methyl acrylate copolymers. Using the catalyst of this invention, the efficiency of catalytic copolymerization of ethylene and MA can be significantly improved, the molecular weight of the copolymer and the MA insertion rate can be increased, and the prepared EMA copolymer has a significant melting temperature, similar to the branched structure of commercially available copolymers prepared by free radical processes, thus showing good application prospects. Attached Figure Description

[0058] Figure 1 The image shows the DSC diagram of the EMA copolymer prepared in Example 21.

[0059] Figure 2 The image shows the 1H NMR spectrum of the EMA copolymer prepared in Example 21.

[0060] Figure 3 The image shows the GPC spectrum of the EMA copolymer prepared in Example 21. Detailed Implementation

[0061] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0062] Experimental methods in the following examples, where specific conditions are not specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer. Unless otherwise specified, all raw materials and reagents used are commercially available from conventional markets. Any non-substantial changes and substitutions made by those skilled in the art based on this invention are within the scope of protection claimed by this invention.

[0063] I. Preparation of α-Carboxyl-β-diimine nickel complexes

[0064] Example 1

[0065] This embodiment provides an α-carboxy-β-diimine nickel complex Ni-1, which is prepared by the following steps:

[0066] (1) 2,6-diisopropylaniline (15.1 g, 85.2 mmol), acetylacetone (4.1 g, 41 mmol), hydrochloric acid (12 M, 6 mL), and ethanol (300 mL) were added sequentially to a 500 mL round-bottom flask and heated under reflux for 72 h. The reaction solvent was evaporated under vacuum to obtain a brown solid. 300 mL of dichloromethane and saturated sodium bicarbonate were added to wash the solid and neutralize the excess acid. The organic phase was collected, dried over anhydrous magnesium sulfate, filtered, and the filtrate was collected. The organic phase was evaporated to dryness, and methanol was added for recrystallization to obtain 8.25 g of a white needle-like solid. 1 H NMR (CDCl3, 400MHz) δ (ppm): 12.11 (s, 1H, NH), 7.13 (m, 6H, Ar-H), 4.87 (s, H, α-CH), 3. 08(m,4H,CHMe2),1.72(s,6H,CH3),1.21(d,12H,CH(CH3)2),1.11(d,12H,CH(CH3)2). 13 C10 NMR (CDCl3, 100MHz) δ (ppm): 161.34, 142.62, 140.89, 125.24, 123.15, 93.41, 28.35, 24.35, 23.34, 20.90. It is a 2,6-diisopropylphenyl-substituted β-diimine compound.

[0067] (2) Under a nitrogen atmosphere, the 2,6-diisopropylphenyl-substituted β-diimine compound (3.86 g, 9.24 mmol) synthesized in step (1) was dissolved in 50 mL of anhydrous tetrahydrofuran to form a colorless clear liquid. 4.3 mL of n-butyllithium (2.5 M, 10.75 mmol) was slowly added dropwise at -78 °C, turning into a yellow clear liquid. The reaction was continued at -78 °C for 1 h with stirring. The reaction solution was then transferred to room temperature and allowed to warm for 30 min. 0.698 g of ammonium formate (11.088 mmol) was added at -78 °C, and the mixture was slowly restored to room temperature with stirring overnight. The mixture was filtered, concentrated, and frozen at -30 °C to obtain 4.97 g of white solid ligand lithium salt precipitate. 1 H NMR(DMSO-d6,400MHz)δ(ppm):7.50-7.20(m,6H,Ar-H),2.84(m,4H,CHMe2),2.72(s,1H,α-CH),1.94(s,6H,CH3),1.16(m,24H,CH(CH3)2). 13 C NMR (DMSO-d6, 100MHz) δ (ppm): 175.4, 164.6, 143.2, 136.7, 123.3, 122.3, 56.0, 28.8, 23.3, 22.9, 14.7. It is an α-carboxy-β-diimine lithium salt.

[0068] (3) Under a nitrogen atmosphere, the ligand α-carboxy-β-diimine lithium salt (0.281 g, 0.61 mmol), NiBr2·3H2O (0.216 g, 0.74 mmol), and acetonitrile solvent (40 mL) synthesized in step (2) were mixed and stirred at -40 °C for 30 min. The mixture was then transferred to room temperature and stirred for another 24 h to obtain a suspension. The reaction solution was concentrated, filtered, and a solid was obtained. The solid was washed with n-hexane (3 × 5 mL) to remove the residual ligand. The residual solvent was then removed by vacuum drying, and the solid was dried to obtain a green powder with a yield of 65%. NMR analysis: 1 H NMR(DMSO-d6,400MHz)δ(ppm):7.45-7.15(m,6H,Ar-H),2.81(m,4H,CHMe2),2.70(s,1H,α-CH),1.91(s,6H,CH3),1.13(m,24H,CH(CH3)2). 13 C10 NMR (DMSO-d6, 100MHz) δ (ppm): 175.1, 164.3, 143.0, 136.4, 123.0, 122.0, 55.7, 28.5, 23.0, 22.4, 14.5. Elemental analysis: (C10) 32 H 44 Theoretical values ​​(BrN3NiO2, %): C, 59.93; H, 6.92; N, 6.55. Measured values: C, 59.78; H, 6.78; N, 6.38.

[0069] The α-carboxy-β-diimine nickel complex Ni-1 provided in this embodiment has the structure shown in formula (II):

[0070]

[0071] In formula (II), the two Ars are the same, both being 2,6-diisopropylphenyl.

[0072] Example 2

[0073] This embodiment provides an α-carboxy-β-diimine nickel complex Ni-2, the preparation steps of which are basically the same as those in Example 1, except that NiBr2·3H2O (0.216 g, 0.74 mmol) in step (3) of Example 1 is replaced with NiCl2·6H2O (0.175 g, 0.74 mmol). Yield: 56%. NMR analysis: 1H NMR(DMSO-d6,400MHz)δ(ppm):7.46-7.17(m,6H,Ar-H),2.82(m,4H,CHMe2),2.72(s,1H,α-CH),1.92(s,6H,CH3),1.14(m,24H,CH(CH3)2). 13 C10 NMR (DMSO-d6, 100MHz) δ (ppm): 175.3, 164.4, 143.1, 136.5, 123.1, 122.1, 55.8, 28.6, 23.1, 22.3, 14.6. Elemental analysis: (C10) 32 H 44 ClN3NiO2 (%) Theoretical values: C, 64.39; H, 7.43; N, 7.04. Measured values: C, 64.18; H, 7.18; N, 6.97.

[0074] The α-carboxy-β-diimine nickel complex Ni-2 provided in this embodiment has the structure shown in formula (III):

[0075]

[0076] In formula (III), the two Ars are the same, both being 2,6-diisopropylphenyl.

[0077] Example 3

[0078] This embodiment provides an α-carboxy-β-diimine nickel complex Ni-3, the preparation steps of which are basically the same as those in Example 1, except that the acetonitrile solvent (40 mL) in step (3) of Example 1 is replaced with benzonitrile solvent (40 mL). Yield: 53%. NMR analysis: 1 H NMR(DMSO-d6,400MHz)δ(ppm):7.92(s,2H,PhCN-H),7.62(s,1H,PhCN-H),7.48(s,2H,PhCN-H),7.48- 7.22(m,6H,Ar-H),2.86(m,4H,CHMe2),2.75(s,1H,α-CH),1.95(s,6H,CH3),1.18(m,24H,CH(CH3)2). 13 C10 NMR (DMSO-d6, 100MHz) δ (ppm): 175.5, 164.7, 143.4, 136.8, 132.2, 129.5, 123.4, 122.5, 116.5, 112.6, 55.9, 28.8, 23.5, 22.5, 14.9. Elemental analysis (C10) 37 H 46BrN3NiO2 (%) Theoretical values: C, 63.18; H, 6.59; N, 5.97. Measured values: C, 63.01; H, 6.42; N, 5.73.

[0079] The α-carboxy-β-diimine nickel complex Ni-3 provided in this embodiment has the structure shown in formula (IV):

[0080]

[0081] In formula (IV), the two Ars are identical, both being 2,6-diisopropylphenyl.

[0082] Example 4

[0083] This embodiment provides an α-carboxy-β-diimine nickel complex Ni-4, whose preparation steps are basically the same as those in Example 1, except that: NiBr2·3H2O (0.216 g, 0.74 mmol) in step (3) of Example 1 is replaced with NiCl2·6H2O (0.175 g, 0.74 mmol); and the acetonitrile solvent (40 mL) in step (3) is replaced with benzonitrile solvent (40 mL). The product is a light yellow powder solid with a yield of 52%. NMR analysis: 1 H NMR(DMSO-d6,400MHz)δ(ppm):7.94(s,2H,PhCN-H),7.65(s,1H,PhCN-H),7.49(s,2H,PhCN-H),7.49- 7.23(m,6H,Ar-H),2.85(m,4H,CHMe2),2.74(s,1H,α-CH),1.94(s,6H,CH3),1.17(m,24H,CH(CH3)2). 13 C10 NMR (DMSO-d6, 100MHz) δ (ppm): 175.7, 164.9, 143.6, 136.9, 132.5, 129.8, 123.7, 122.6, 116.7, 112.8, 56.0, 28.9, 23.8, 22.5, 15.1. Elemental analysis (C10) 37 H 46 ClN3NiO2 (%) Theoretical values: C, 67.44; H, 7.04; N, 6.38. Measured values: C, 67.31; H, 7.02; N, 6.15.

[0084] The α-carboxy-β-diimine nickel complex Ni-4 provided in this embodiment has the structure shown in formula (V):

[0085]

[0086] In formula (V), the two Ars are identical, both being 2,6-diisopropylphenyl.

[0087] II. Preparation of ethylene-methyl acrylate copolymer

[0088] In the following examples, the weight-average molecular weight of the prepared copolymers was determined by gel permeation chromatography (GPC chromatogram), the melting temperature of the copolymers was determined by differential scanning calorimetry (DSC chromatogram), and the degree of branching and the methyl acrylate monomer insertion rate of the copolymers were calculated by proton NMR spectroscopy.

[0089] Example 5

[0090] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst, and specifically includes the following steps:

[0091] The autoclave was dried under vacuum and cooled to room temperature. The ethylene was then repeatedly replaced three times. Dry toluene (40 mL), methyl acrylate (0.72 mL, 8 mmol, MA / Ni = 266:1), and co-catalyst methylaluminoxane (MAO, 10 mL, 45 mmol, Al / Ni = 1500:1) were added to the autoclave and stirred at a constant temperature of 50 °C. A toluene solution of the main catalyst Ni-1 (19.5 mg, 30 μmol) was added to the reactor to initiate copolymerization. The copolymerization reaction was carried out at 0.5 MPa ethylene pressure and 50 °C for 4 h. The reaction was terminated with 100 mL of 5% hydrochloric acid-ethanol solution. The copolymer was obtained by filtration, washed three times with ethanol, and dried under vacuum at 50 °C to constant weight.

[0092] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 8.14 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 44.2 kg / mol, a molecular weight distribution index of 1.32, an methyl acrylate insertion rate of 7.8 ω, a melting temperature of 100.1 °C, and a branching degree of 36 / 1000 °C.

[0093] Example 6

[0094] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-2 provided in Example 2 as the main catalyst. The specific steps of this preparation method are the same as those in Example 5.

[0095] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-2 is 6.95 × 10⁻⁶. 4The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 39.1 kg / mol, a molecular weight distribution index of 1.38, an methyl acrylate insertion rate of 7.2 ω, a melting temperature of 98.1 °C, and a branching degree of 37 / 100 °C.

[0096] Example 7

[0097] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-3 provided in Example 3 as the main catalyst. The specific steps of this preparation method are the same as those in Example 5.

[0098] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-3 is 4.75 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 41.1 kg / mol, a molecular weight distribution index of 1.28, an methyl acrylate insertion rate of 6.8 ω, a melting temperature of 97.1 °C, and a branching degree of 35 / 100 °C.

[0099] Example 8

[0100] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-4 provided in Example 4 as the main catalyst. The specific steps of this preparation method are the same as those in Example 5.

[0101] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-4 is 4.35 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 43.1 kg / mol, a molecular weight distribution index of 1.42, an methyl acrylate insertion rate of 6.5 ω, a melting temperature of 100.1 °C, and a branching degree of 36 / 1000 °C.

[0102] Example 9

[0103] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the co-catalyst methylaluminoxane (MAO, 10 mL, 45 mmol, Al / Ni = 1500:1) in Example 5 is replaced with modified methylaluminoxane (MMAO, 10 mL, 45 mmol, Al / Ni = 1500:1).

[0104] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 7.55 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 58.1 kg / mol, a molecular weight distribution index of 1.36, an methyl acrylate insertion rate of 6.2 ω, a melting temperature of 102.1 °C, and a branching degree of 35 / 1000 °C.

[0105] Example 10

[0106] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the co-catalyst methylaluminoxane (MAO, 10 mL, 45 mmol, Al / Ni = 1500:1) in Example 5 is replaced with isobutylaluminoxane (BAO, 10 mL, 45 mmol, Al / Ni = 1500:1).

[0107] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 6.15 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 48.6 kg / mol, a molecular weight distribution index of 1.43, an methyl acrylate insertion rate of 6.1 ω, a melting temperature of 102.1 °C, and a branching degree of 37 / 1000 °C.

[0108] Example 11

[0109] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the molar ratio of aluminum-nickel to co-catalyst in Example 5 is adjusted to 500:1.

[0110] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 2.51 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 18.2 kg / mol, a molecular weight distribution index of 1.45, an methyl acrylate insertion rate of 6.9 ω, a melting temperature of 98.1 °C, and a branching degree of 38 / 100 °C.

[0111] Example 12

[0112] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the molar ratio of aluminum-nickel to co-catalyst in Example 5 is adjusted to 1000:1.

[0113] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 7.72 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 38.2 kg / mol, a molecular weight distribution index of 1.39, an methyl acrylate insertion rate of 7.1 ω, a melting temperature of 96.8 °C, and a branching degree of 39 / 100 °C.

[0114] Example 13

[0115] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the molar ratio of aluminum-nickel to co-catalyst in Example 5 is adjusted to 3000:1.

[0116] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 11.2 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 13.2 kg / mol, a molecular weight distribution index of 1.47, an methyl acrylate insertion rate of 6.7 ω, a melting temperature of 100.8 °C, and a branching degree of 35 / 1000 °C.

[0117] Example 14

[0118] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the temperature of the copolymerization reaction in Example 5 is adjusted from 50°C to 0°C.

[0119] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 2.38 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 22.1 kg / mol, a molecular weight distribution index of 1.53, an methyl acrylate insertion rate of 2.5 ω, a melting temperature of 125.3 °C, and a branching degree of 28 / 1000 °C.

[0120] Example 15

[0121] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the temperature of the copolymerization reaction in Example 5 is adjusted from 50°C to 25°C.

[0122] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 4.21 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 35.3 kg / mol, a molecular weight distribution index of 1.41, an methyl acrylate insertion rate of 5.8 ω, a melting temperature of 120.3 °C, and a branching degree of 33 / 1000 °C.

[0123] Example 16

[0124] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the temperature of the copolymerization reaction in Example 5 is adjusted from 50°C to 80°C.

[0125] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 5.95 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 38.6 kg / mol, a molecular weight distribution index of 1.83, an methyl acrylate insertion rate of 9.6 ω, a melting temperature of 89.3 °C, and a branching degree of 46 / 100 °C.

[0126] Example 17

[0127] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the temperature of the copolymerization reaction in Example 5 is adjusted from 50°C to 100°C.

[0128] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 3.55 × 10⁻⁶. 4The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 19.7 kg / mol, a molecular weight distribution index of 2.63, an methyl acrylate insertion rate of 11.8 ω, a melting temperature of 81.3 °C, and a branching degree of 51 / 1000 °C.

[0129] Example 18

[0130] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the ethylene pressure of the copolymerization reaction in Example 5 is adjusted from 0.5 MPa to 1.0 MPa.

[0131] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 10.2 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 68.7 kg / mol, a molecular weight distribution index of 1.47, an methyl acrylate insertion rate of 4.6 ω, a melting temperature of 106.5 °C, and a branching degree of 31 / 1000 °C.

[0132] Example 19

[0133] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the ethylene pressure of the copolymerization reaction in Example 5 is adjusted from 0.5 MPa to 2.0 MPa.

[0134] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 18.1 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 100.3 kg / mol, a molecular weight distribution index of 1.41, an methyl acrylate insertion rate of 2.8 ω, a melting temperature of 113.3 °C, and a branching degree of 25 / 100 °C.

[0135] Example 20

[0136] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the concentration of methyl acrylate in Example 5 is adjusted to 0.4 mol / L and the molar ratio of methyl acrylate to the main catalyst is 533:1.

[0137] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 4.51 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 42.1 kg / mol, a molecular weight distribution index of 1.36, an methyl acrylate insertion rate of 13.8 ω, a melting temperature of 96.1 °C, and a branching degree of 40 / 100 °C.

[0138] Example 21

[0139] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the concentration of methyl acrylate in Example 5 is adjusted to 0.8 mol / L and the molar ratio of methyl acrylate to the main catalyst is 1066:1.

[0140] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 2.73 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 27.1 kg / mol, a molecular weight distribution index of 1.31, an methyl acrylate insertion rate of 30.5 ω, a melting temperature of 92.5 °C, and a branching degree of 44 / 1000 °C.

[0141] The DSC diagram of the copolymer prepared in this embodiment is shown below. Figure 1 As shown, its hydrogen NMR spectrum is as follows: Figure 2 As shown, its GPC spectrum is as follows Figure 3 As shown.

[0142] Example 22

[0143] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the concentration of methyl acrylate in Example 5 is adjusted to 1.2 mol / L and the molar ratio of methyl acrylate to the main catalyst is 1600:1.

[0144] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 0.89 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 18.6 kg / mol, a molecular weight distribution index of 1.40, an methyl acrylate insertion rate of 36.4 ω, a melting temperature of 94.2 °C, and a branching degree of 46 / 1000 °C.

[0145] Example 23

[0146] This embodiment provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of this preparation method are basically the same as those in Example 5, except that the solvent toluene in Example 5 is replaced with 1,2-dichloroethane, while the amount remains the same.

[0147] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 9.09 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 43.1 kg / mol, a molecular weight distribution index of 1.36, an methyl acrylate insertion rate of 5.8 ω, a melting temperature of 101.1 °C, and a branching degree of 34 / 1000 °C.

[0148] Example 24

[0149] The present invention provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of the preparation method are basically the same as those in Example 5, except that the solvent toluene in Example 5 is replaced with n-hexane, while the amount remains the same.

[0150] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 7.19 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 39.6 kg / mol, a molecular weight distribution index of 1.42, an methyl acrylate insertion rate of 5.5 ω, a melting temperature of 99.1 °C, and a branching degree of 36 / 100 °C.

[0151] Example 25

[0152] The present invention provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of the preparation method are basically the same as those in Example 5, except that the solvent toluene in Example 5 is replaced with chlorobenzene, while the amount remains the same.

[0153] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 9.75 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 46.3 kg / mol, a molecular weight distribution index of 1.36, an methyl acrylate insertion rate of 5.9 ω, a melting temperature of 101.1 °C, and a branching degree of 38 / 1000 °C.

[0154] Example 26

[0155] The present invention provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of the preparation method are basically the same as those in Example 5, except that the solvent toluene in Example 5 is replaced with xylene, while the amount remains the same.

[0156] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 8.03 × 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 56.9 kg / mol, a molecular weight distribution index of 1.35, an methyl acrylate insertion rate of 6.1 ω, a melting temperature of 101.1 °C, and a branching degree of 39 / 1000 °C.

[0157] Example 27

[0158] The present invention provides a method for preparing ethylene-methyl acrylate copolymer. The preparation method uses the α-carboxy-β-diimine nickel complex Ni-1 provided in Example 1 as the main catalyst. The specific steps of the preparation method are basically the same as those in Example 5, except that the solvent toluene in Example 5 is replaced with a mixed solvent of chlorobenzene and toluene (50% v / v), while the amount remains the same.

[0159] In this embodiment, the catalytic activity of the α-carboxy-β-diimine nickel complex Ni-1 is 8.23 ​​× 10⁻⁶. 4 The copolymer prepared by g EMA / (molNi·h) has a weight-average molecular weight of 45.6 kg / mol, a molecular weight distribution index of 1.53, an methyl acrylate insertion rate of 6.8 ω, a melting temperature of 101.1 °C, and a branching degree of 39 / 1000 °C.

[0160] The copolymerization of ethylene and methyl acrylate was carried out using β-diimine nickel catalyst, α-diimine palladium catalyst, and phosphonic acid palladium catalyst as comparative examples.

[0161] Comparative Example 1

[0162] This comparative example provides a method for preparing an ethylene-methyl acrylate copolymer using a β-diimine nickel catalyst having the structure shown in formula (VI), which is prepared according to the method in Organometallics 1997, 16, 1514.

[0163]

[0164] The autoclave was heated to 150°C and evacuated for 2 hours. After cooling to room temperature under vacuum, the ethylene was repeatedly replaced three times. Dry toluene (40 mL), methyl acrylate (2.8 mL, 32 mmol, MA / Ni = 1066:1), and co-catalyst methylaluminoxane (MAO, 10 mL, 45 mmol, Al / Ni = 1500:1) were added to the autoclave and stirred at a constant temperature of 50°C. A toluene solution of a β-diimine-type nickel catalyst (19.2 mg, 30 μmol) with the structure shown in formula (VI) was added to the reactor to initiate copolymerization. The copolymerization reaction was carried out for 4 hours at 0.5 MPa ethylene pressure and 50°C, and the reaction was terminated with 100 mL of 5% hydrochloric acid-ethanol solution. No solid polymer was obtained. The copolymerization activity of the β-diimine-type nickel catalyst in this comparative example was zero.

[0165] Comparative Example 2

[0166] This comparative example provides a method for preparing an ethylene-methyl acrylate copolymer using an α-diimine palladium main catalyst having the structure shown in formula (VII), which is prepared according to the method in J. Am. Chem. Soc. 1996, 118, 267.

[0167]

[0168] The autoclave was heated to 150°C and evacuated for 2 hours. After cooling to room temperature under vacuum, the ethylene was repeatedly replaced three times. Dry toluene (40 mL) and methyl acrylate (2.8 mL, 32 mmol, MA / Pd = 1066:1) were added to the autoclave and stirred at a constant temperature of 50°C. The α-diimine palladium main catalyst (16.9 mg, 30 μmol) with the structure shown in formula (VII) was activated with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (NaBArF, 36 μmol, B / Pd = 1.2:1) and then added to the reactor. The copolymerization reaction was carried out at 0.5 MPa ethylene pressure and 50°C for 4 hours. The reaction was terminated with 100 mL of 5% hydrochloric acid-ethanol solution. The copolymer was obtained by filtration, washed three times with ethanol, and dried under vacuum at 50°C to constant weight.

[0169] In this comparative example, the catalytic activity of the α-diimine palladium main catalyst was 9.4 × 10⁻⁶. 3 The copolymer prepared by g EMA / (mol Pd·h) has a weight-average molecular weight of 10.2 kg / mol, a molecular weight distribution index of 1.52, an methyl acrylate insertion rate of 9.8 ω, a branching degree of 110 / 1000°C, and no obvious melting temperature.

[0170] Comparative Example 3

[0171] This comparative example provides a method for preparing an ethylene-methyl acrylate copolymer using a phosphonic sulfonic acid type palladium main catalyst having the structure shown in formula (VIII). This phosphonic sulfonic acid type palladium main catalyst is prepared according to the method provided in the literature Polym. Chen., 2017, 8, 2405-2409.

[0172]

[0173] The autoclave was heated to 150°C and evacuated for 2 hours. After cooling to room temperature under vacuum, the ethylene was repeatedly replaced three times. Dry toluene (40 mL), methyl acrylate (2.8 mL, 32 mmol, MA / Pd = 1066:1), and co-catalyst methylaluminoxane (MAO, 10 mL, 45 mmol, Al / Pd = 1500:1) were added to the autoclave and stirred at a constant temperature of 50°C. A toluene solution of a phosphonic acid-type palladium main catalyst (19.2 mg, 30 μmol) with the structure shown in formula (VIII) was added to the reactor. The copolymerization reaction was carried out at 0.5 MPa ethylene pressure and 50°C for 4 hours. The reaction was terminated with 100 mL of 5% hydrochloric acid-ethanol solution. The copolymer was obtained by filtration, washed three times with ethanol, and dried under vacuum at 50°C to constant weight.

[0174] In this comparative example, the catalytic activity of the phosphonic acid-type palladium main catalyst was 3.08 × 10⁻⁶.3 The copolymer prepared by g EMA / (mol Pd·h) has a weight-average molecular weight of 5.5 kg / mol, a molecular weight distribution index of 1.81, an methyl acrylate insertion rate of 16.8 ω, a melting temperature of 123.9 °C, and a branching degree of 3 / 1000 °C.

[0175] The results of catalytic copolymerization of ethylene and methyl acrylate in Example 5 are compared with those in Comparative Examples 1-3, as shown in Table 1.

[0176] Table 1 Comparison of copolymerization results of ethylene and methyl acrylate catalyzed by different catalysts.

[0177]

[0178] As shown in Table 1, the α-carboxy-β-diimine nickel complex main catalyst of this invention can catalyze the copolymerization of ethylene and methyl acrylate more efficiently, with significantly improved catalytic copolymerization activity, product molecular weight, and insertion rate. In comparison, the α-diimine palladium catalyst produces a highly branched ethylene-methyl acrylate copolymer with no melting point; while the phosphononsulfonate palladium catalyst produces a completely linear copolymer. The EMA copolymer prepared using the α-carboxy-β-diimine nickel complex of Example 5 of this invention as the main catalyst is a low-branched copolymer with a melting point of 100.1°C and a branching degree of 36 / 1000°C, similar to the branched structure of EMA prepared by commercial free radicals.

Claims

1. An α-carboxy-β-diimine nickel complex having the structure shown in general formula (I): General Formula (I) In general formula (I), the two Ar atoms may be the same or different, and Ar is selected from 2,6-diisopropylphenyl or 2,6-dimethylphenyl; X is a chlorine atom or a bromine atom; L is acetonitrile or benzonitrile.

2. The α-carboxy-β-diimine nickel complex according to claim 1, wherein, In general formula (I), the two Ars are identical, and Ar is 2,6-diisopropylphenyl or 2,6-dimethylphenyl.

3. The α-carboxy-β-diimine nickel complex according to claim 2, wherein, In general formula (I), the two Ars are identical and are both 2,6-diisopropylphenyl.

4. A method for preparing the α-carboxy-β-diimine nickel complex according to any one of claims 1-3, comprising the following steps: (1) Reaction of acetylacetone with 2,6-dialkylaniline to give a 2,6-dialkylphenyl-substituted β-diimine compound; wherein the 2,6-dialkylaniline is selected from 2,6-diisopropylaniline and / or 2,6-dimethylaniline; (2) The β-diimine compound substituted with 2,6-dialkylphenyl is subjected to a substitution reaction with ammonium formate under the action of alkyllithium to obtain α-carboxy-β-diimine lithium salt; (3) The α-carboxy-β-diimine lithium salt and the halonickel salt are subjected to a coordination reaction in acetonitrile or benzonitrile solvent to obtain the α-carboxy-β-diimine nickel complex.

5. The application of the α-carboxy-β-diimine nickel complex according to any one of claims 1-3 as a catalyst in olefin polymerization.

6. The application according to claim 5, wherein, The olefin polymerization includes the copolymerization of olefins with polar monomers.

7. The application according to claim 6, wherein, The olefin polymerization is a copolymerization of ethylene and acrylate monomers.

8. The application according to claim 7, wherein, The olefin polymerization is a copolymerization of ethylene and methyl acrylate.

9. The application according to claim 5, wherein, The α-carboxy-β-diimine nickel complex serves as the main catalyst in olefin polymerization, with an organoaluminum compound used as a co-catalyst.

10. The application according to claim 9, wherein, The organoaluminum compound is selected from one or more of methylaluminoxane, modified methylaluminoxane, isobutylaluminoxane, triethylaluminum, diethylaluminum chloride, diethylaluminum chloride, and triisobutylaluminum.

11. The application according to claim 10, wherein, The organoaluminum compound is selected from one or a combination of several of methylaluminoxane, modified methylaluminoxane, and isobutylaluminoxane.

12. The application according to claim 9, wherein, The molar ratio of aluminum to nickel in the co-catalyst and the main catalyst is (500~3000):

1.

13. The application according to claim 12, wherein, The molar ratio of aluminum to nickel in the co-catalyst and the main catalyst is (1000~2000):

1.

14. A method for preparing an ethylene-methyl acrylate copolymer, wherein the preparation method uses the α-carboxy-β-diimine nickel complex of any one of claims 1-3 as the main catalyst.

15. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The preparation method includes the following steps: Using the aforementioned α-carboxy-β-diimine nickel complex as the main catalyst and an organoaluminum compound as a co-catalyst, ethylene and methyl acrylate monomers were copolymerized in a solvent. After the reaction was completed, an ethylene-methyl acrylate copolymer was obtained.

16. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The reaction temperature for the copolymerization reaction is 0~100℃.

17. The method for preparing the ethylene-methyl acrylate copolymer according to claim 16, wherein, The reaction temperature for the copolymerization reaction is 50~80℃.

18. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The reaction pressure of the copolymerization reaction is 0.5~2.0 MPa.

19. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The reaction time for the copolymerization reaction is 0.5-24 h.

20. The method for preparing the ethylene-methyl acrylate copolymer according to claim 19, wherein, The reaction time for the copolymerization reaction is 2-8 h.

21. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The molar ratio of the methyl acrylate monomer to the main catalyst α-carboxy-β-diimine nickel complex is (266~1600):

1.

22. The method for preparing the ethylene-methyl acrylate copolymer according to claim 21, wherein, The molar ratio of the methyl acrylate monomer to the main catalyst α-carboxy-β-diimine nickel complex is (500~1066):

1.

23. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The organoaluminum compound is selected from one or a combination of several of methylaluminoxane, modified methylaluminoxane, and isobutylaluminoxane.

24. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The molar ratio of aluminum to nickel in the co-catalyst and the main catalyst is (500~3000):

1.

25. The method for preparing the ethylene-methyl acrylate copolymer according to claim 24, wherein, The molar ratio of aluminum to nickel in the co-catalyst and the main catalyst is (1000~2000):

1.

26. The method for preparing the ethylene-methyl acrylate copolymer according to claim 15, wherein, The solvent is selected from one or a combination of several of 1,2-dichloroethane, n-hexane, chlorobenzene, toluene, and xylene.

27. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The weight-average molecular weight of the prepared ethylene-methyl acrylate copolymer was 13.2~100.3 kg / mol.

28. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The degree of branching of the prepared ethylene-methyl acrylate copolymer is 25~51 branches / 1000C.

29. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The methyl acrylate insertion rate of the prepared ethylene-methyl acrylate copolymers ranged from 2.5% to 36.4%. ω %.

30. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The melting temperature of the prepared ethylene-methyl acrylate copolymer is 81.3~125.3℃.

31. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The molecular weight distribution index of the ethylene-methyl acrylate copolymer prepared therefrom is 1.28-2.

63.

32. The method for preparing the ethylene-methyl acrylate copolymer according to claim 14, wherein, The catalytic activity of the main catalyst, the α-carboxy-β-diimine nickel complex, is 0.89 × 10⁻⁶. 4 -18.1×10 4 g EMA / (mol Ni·h).

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