A method for preparing a low melt index terpolymer

Abstract

The present invention provides a method for preparing a low melt index terpolymer, comprising the following steps: ethylene, α-olefin, and non-conjugated diene are ternarily copolymerized in a saturated alkane solvent in the presence of a primary catalyst and a co-catalyst to obtain a low melt index terpolymer; the primary catalyst is a complex containing a metal atom; the temperature of the ternary copolymerization is 80°C to 200°C, and the pressure is 1MPa to 6MPa. Compared with the prior art, the preparation method provided by the present invention adopts specific process steps, conditions and parameters to achieve overall better interaction, and realizes obtaining a low melt index ethylene / α-olefin / non-conjugated diene terpolymer by high temperature solution polymerization, with the characteristics of high polymerization activity and controllable polymer structure, while low production cost and low polymer metal residue.

Description

Technical Field

[0001] The present invention relates to the technical field of olefin solution polymerization, and more particularly to a method for preparing a low melt index terpolymer. Background Art

[0002] Polyolefins are currently the most popular resin materials due to their low raw material costs, ease of processing and production, and superior performance. Polyolefins account for a significant portion of current chemical production, and their preparation methods are attracting increasing attention.

[0003] In general, conducting solution polymerization under high-temperature conditions is highly preferred because it is closely associated with improved productivity. Specifically, the viscosity of the polymerization solution containing the produced olefin polymer decreases at high temperatures, allowing the concentration of the olefin polymer within the polymerization vessel to be increased compared to low-temperature polymerization, resulting in improved productivity per polymerization vessel. Furthermore, since olefin polymerization is an exothermic reaction, heat removal is generally required to maintain the desired polymerization temperature. High-temperature polymerization requires less heat removal than low-temperature polymerization, thus offering the advantage of reduced heat removal costs. On the other hand, the decrease in molecular weight of the produced olefin polymer with increasing polymerization temperature is well known to those skilled in the art. Consequently, the production of olefin polymers of the desired molecular weight often results in a disadvantageous situation, which limits the upper limit of the polymerization temperature. To address this disadvantage, polymerization catalysts that produce high-molecular-weight olefin polymers are in high demand. Using such olefin polymerization catalysts allows the molecular weight of the produced olefin polymer to be maintained at a desired high value during high-temperature polymerization, resulting in advantages such as improved productivity and reduced production costs.

[0004] However, high-temperature solution polymerization conditions can easily lead to catalyst deactivation, resulting in low polymerization activity. Furthermore, during the ethylene / α-olefin / non-conjugated diene polymerization process, the non-conjugated diene-induced chain transfer tendency increases, resulting in low polymer molecular weight. This makes it difficult to prepare low-melt-index ethylene / α-olefin / non-conjugated diene terpolymers under high-temperature solution polymerization conditions. Furthermore, when used to prepare polymers containing ethylene, α-olefins, and non-conjugated dienes, particularly those containing ethylene, propylene, and the sterically hindered ethylidene norbornene, the resulting polymers exhibit high melt indexes and low ethylidene norbornene insertion rates. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preparing a low melt index terpolymer, wherein a low melt index ethylene / α-olefin / non-conjugated diene terpolymer is obtained by high-temperature solution polymerization, which has the characteristics of high polymerization activity and controllable polymer structure, while having low production cost and low polymer metal residue.

[0006] The present invention provides a method for preparing a low melt index terpolymer, comprising the following steps:

[0007] The ethylene, α-olefin and non-conjugated diene are ternary copolymerized in a saturated alkane solvent in the presence of a main catalyst and a co-catalyst to obtain a low melt index ternary copolymer;

[0008] The main catalyst is a complex containing metal atoms;

[0009] The temperature of the ternary copolymerization is 80° C. to 200° C., and the pressure is 1 MPa to 6 MPa.

[0010] Preferably, the α-olefin is selected from one or more of propylene, 1-butene, 1-hexene, 1-octene and 1-decene;

[0011] The non-conjugated diene is selected from one or more of 1,5-hexadiene, 1,7-octadiene, 3,6-dimethyl-1,7-octadiene, 4,5-dimethyl-1,7-octadiene, 5-methyl-1,8-nonadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene and 2,5-norbornadiene.

[0012] Preferably, the molar ratio of the α-olefin to the non-conjugated diene is (2-15):1.

[0013] Preferably, the saturated alkane solvent is selected from one or more of n-pentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane and isooctane.

[0014] Preferably, the main catalyst is a [NOON] complex having the following structure:

[0015]

[0016] In the formula, R1 is selected from substituted or unsubstituted C1 to C 10 Alkyl, substituted or unsubstituted C6~C 15 Aryl, C6~C containing N 15 The fused ring;

[0017] R2 is selected from substituted or unsubstituted C1 to C 10 Alkyl;

[0018] R3 is selected from substituted or unsubstituted C1-C 10 Alkyl;

[0019] A is biphenyl or binaphthyl;

[0020] X is halogen, alkyl or aryl;

[0021] M is a fourth subgroup transition metal element.

[0022] Preferably, M is titanium, zirconium or hafnium.

[0023] Preferably, the co-catalyst is composed of one or more of triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, and one or more of perfluorophenylboron, triphenylcarbonium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dicetylanilinium tetrakis(pentafluorophenyl)borate.

[0024] Preferably, the molar ratio of aluminum atoms and boron atoms in the co-catalyst to metal atoms in the main catalyst is (50-3000): (1-5):1.

[0025] Preferably, the temperature of the ternary copolymerization is 135° C. to 155° C., and the pressure is 3 MPa to 5 MPa; and the time of the ternary copolymerization is 5 min to 15 min.

[0026] Preferably, the molar insertion rate of α-olefin in the low melt index terpolymer is 5.3% to 19.8%, the molar insertion rate of non-conjugated diene is 0.8% to 3.7%, and the melt index is 0.20 to 7.3 g / 10 min.

[0027] The present invention provides a method for preparing a low-melt index terpolymer, comprising the following steps: terpolymerizing ethylene, an α-olefin, and a non-conjugated diene in a saturated alkane solvent in the presence of a primary catalyst and a co-catalyst to obtain the low-melt index terpolymer; the primary catalyst being a complex containing a metal atom; and the terpolymerization temperature being 80°C to 200°C and the pressure being 1 MPa to 6 MPa. Compared to the prior art, the preparation method provided by the present invention utilizes specific process steps, conditions, and parameters to achieve better overall interaction, resulting in a low-melt index ethylene / α-olefin / non-conjugated diene terpolymer obtained through high-temperature solution polymerization. The terpolymer exhibits high polymerization activity and controllable polymer structure, while also having low production costs and low metal residue in the polymer. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The present invention provides a method for preparing a low melt index terpolymer, comprising the following steps:

[0030] The ethylene, α-olefin and non-conjugated diene are ternary copolymerized in a saturated alkane solvent in the presence of a main catalyst and a co-catalyst to obtain a low melt index ternary copolymer;

[0031] The main catalyst is a complex containing metal atoms;

[0032] The temperature of the ternary copolymerization is 80° C. to 200° C., and the pressure is 1 MPa to 6 MPa.

[0033] The present invention provides a high-temperature solution polymerization method for preparing a low-melt index terpolymer of ethylene, α-olefin, and non-conjugated diene. The method has the characteristics of high polymerization activity and controllable polymer structure, and can prepare terpolymers with low metal residue and low melt index having different structures. The method mainly comprises a method for catalyzing the terpolymerization of ethylene, α-olefin, and non-conjugated diene in a saturated alkane solvent under the combined action of a main catalyst and a co-catalyst at a polymerization temperature of 80°C to 200°C and a polymerization pressure of 1MPa to 6MPa.

[0034] In the present invention, the α-olefin is preferably selected from one or more of propylene, 1-butene, 1-hexene, 1-octene and 1-decene, more preferably 1-butene, 1-hexene or 1-octene; the non-conjugated diene is preferably selected from one or more of 1,5-hexadiene, 1,7-octadiene, 3,6-dimethyl-1,7-octadiene, 4,5-dimethyl-1,7-octadiene, 5-methyl-1,8-nonadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene and 2,5-norbornadiene, more preferably 1,7-octadiene, 5-ethylidene-2-norbornene (5-ethylidene-2-norbornene) or 5-vinyl-2-norbornene.

[0035] The present invention has no particular limitation on the sources of the ethylene, α-olefin, and non-conjugated diene, and commercially available products known to those skilled in the art may be used.

[0036] In the present invention, the molar ratio of the α-olefin to the non-conjugated diene is preferably (2-15):1, more preferably (4-8):1.

[0037] In the present invention, the saturated alkane solvent is preferably selected from one or more of n-pentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane, and isooctane, and more preferably n-hexane or n-heptane. The present invention has no particular limitation on the source of the saturated alkane solvent, and commercially available products known to those skilled in the art may be used.

[0038] In the present invention, the main catalyst is a complex containing a metal atom, preferably a [NOON] complex having the following structure:

[0039]

[0040] In the formula, R1 is selected from substituted or unsubstituted C1 to C 10 Alkyl, substituted or unsubstituted C6~C 15 Aryl, C6~C containing N 15 The fused ring;

[0041] R2 is selected from substituted or unsubstituted C1 to C 10 Alkyl;

[0042] R3 is selected from substituted or unsubstituted C1-C 10 Alkyl;

[0043] A is biphenyl or binaphthyl;

[0044] X is halogen, alkyl or aryl;

[0045] M is a fourth subgroup transition metal element, preferably titanium, zirconium or hafnium.

[0046] In a preferred embodiment of the present invention, the main catalyst is specifically N3 to N6, and the structure is as follows:

[0047] N3: R1 = tert-butyl, R2 = tert-butyl, R3 = cyclopentyl, A = biphenyl, M = Zr, X = Cl;

[0048] N4: R1 = tert-butyl, R2 = 3,5-di-tert-butylphenyl, R3 = cyclohexyl, A = biphenyl, M = Zr, X = Cl;

[0049] N5: R1 = methyl, R2 = carbazole, R3 = phenyl, A = biphenyl, M = Zr, X = Cl;

[0050] N6: R1 = methyl, R2 = cumyl, R3 = benzyl, A = biphenyl, M = Hf, X = Cl.

[0051] In the present invention, the main catalyst can be obtained by using the preparation method disclosed in the applicant's earlier patent application CN103936909A, and the present invention has no special limitation on this.

[0052] In the present invention, the co-catalyst is preferably composed of one or more of triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, and one or more of perfluorophenylboron, triphenylcarbonium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, and N,N-dicetylanilinium tetrakis(pentafluorophenyl)borate, more preferably composed of triisobutylaluminum and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, or composed of triisobutylaluminum and triphenylcarbonium tetrakis(pentafluorophenyl)borate.

[0053] In the present invention, the molar ratio of aluminum atoms and boron atoms in the co-catalyst to metal atoms in the main catalyst is preferably (50-3000):(1-5):1.

[0054] In the present invention, the ternary copolymerization process can be achieved by performing intermittent polymerization in a reactor well known to those skilled in the art; the temperature of the ternary copolymerization is 80°C to 200°C, preferably 100°C to 160°C, more preferably 135°C to 155°C, and the pressure is 1MPa to 6MPa, preferably 3MPa to 5MPa; the time of the ternary copolymerization is preferably 5min to 15min.

[0055] The present invention prepares a low melt index terpolymer of ethylene, α-olefin and non-conjugated diene; the molar insertion rate of α-olefin in the low melt index terpolymer is preferably 5.3% to 19.8%, the molar insertion rate of non-conjugated diene is preferably 0.8% to 3.7%, and the melt index is preferably 0.20 to 7.3 g / 10 min (190° C., 2.16 kg).

[0056] In a preferred embodiment of the present invention, a low melt index ethylene / α-olefin / non-conjugated diene terpolymer is prepared under high temperature solution polymerization conditions using the applicant's earlier invented [NOON] catalyst. Experimental results show that the use of alkyl aluminum and boron agents as co-catalysts can achieve higher polymerization activity and controllable polymer structure. This not only avoids the use of expensive MAO and MMAO, but also greatly reduces the amount of aluminum agent used (by more than 80% compared to the amount used in traditional methods), which is beneficial to improving the optical and electrical properties of the ethylene / α-olefin / non-conjugated diene terpolymer.

[0057] The present invention provides a method for preparing a low-melt index terpolymer, comprising the following steps: terpolymerizing ethylene, an α-olefin, and a non-conjugated diene in a saturated alkane solvent in the presence of a primary catalyst and a co-catalyst to obtain the low-melt index terpolymer; the primary catalyst being a complex containing a metal atom; and the terpolymerization temperature being 80°C to 200°C and the pressure being 1 MPa to 6 MPa. Compared to the prior art, the preparation method provided by the present invention utilizes specific process steps, conditions, and parameters to achieve better overall interaction, resulting in a low-melt index ethylene / α-olefin / non-conjugated diene terpolymer obtained through high-temperature solution polymerization. The terpolymer exhibits high polymerization activity and controllable polymer structure, while also having low production costs and low metal residue in the polymer.

[0058] To further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available; wherein the main catalyst used is a [NOON] complex having the following structure:

[0059]

[0060] In the formula, R1 is selected from substituted or unsubstituted C1 to C 10 Alkyl, substituted or unsubstituted C6~C 15 Aryl, C6~C containing N 15 The fused ring;

[0061] R2 is selected from substituted or unsubstituted C1 to C 10 Alkyl;

[0062] R3 is selected from substituted or unsubstituted C1 to C 10 Alkyl;

[0063] A is biphenyl or binaphthyl;

[0064] X is halogen, alkyl or aryl;

[0065] M is a fourth subgroup transition metal element;

[0066] The specific structures of N3 to N6 are as follows:

[0067] N3: R1 = tert-butyl, R2 = tert-butyl, R3 = cyclopentyl, A = biphenyl, M = Zr, X = Cl;

[0068] N4: R1 = tert-butyl, R2 = 3,5-di-tert-butylphenyl, R3 = cyclohexyl, A = biphenyl, M = Zr, X = Cl;

[0069] N5: R1 = methyl, R2 = carbazole, R3 = phenyl, A = biphenyl, M = Zr, X = Cl;

[0070] N6: R1 = methyl, R2 = cumyl, R3 = benzyl, A = biphenyl, M = Hf, X = Cl.

[0071] Example 1

[0072] The ethylene / α-olefin / non-conjugated diene terpolymerization was carried out batchwise in a 2L autoclave:

[0073] 1. Batch polymerization operation:

[0074] (1) Reactor drying: The polymerization kettle was heated to 140°C and vacuum dried for more than 1 hour. During the heating period, nitrogen was replaced 3 times to ensure that the water and oxygen contents in the reactor met the polymerization requirements.

[0075] (2) Monomer and solvent addition: Operate the comonomer and solvent addition on the computer, and add the set amount of monomer and less than the set amount of solvent to the reactor (reserve 40g of solvent to flush the auxiliary catalyst tank and the main catalyst tank).

[0076] (3) Adding the co-catalyst: Take a set amount of the co-catalyst solution with a syringe in the glove box, add the co-catalyst to the co-catalyst tank under a nitrogen atmosphere, open the valve at the bottom of the co-catalyst tank, and add the co-catalyst to the reactor; then close the valve at the bottom of the tank, add 20g of n-hexane with a high-pressure pump, and then open the valve at the bottom of the tank to flush the remaining co-catalyst into the reactor.

[0077] (4) Temperature and pressure increase: Operate the polymerization kettle temperature control system on the computer to start heating. When the temperature in the reactor reaches 10-20°C below the set polymerization temperature (predict the exothermic situation of the polymerization reaction based on the existing data, and appropriately change the initial feeding temperature), start adjusting the ethylene pressure to 0.3-0.5MPa below the set polymerization pressure (appropriately adjust according to the difference between the feeding temperature and the set polymerization temperature), and then start adding the main catalyst.

[0078] (5) Adding the main catalyst: Use a syringe to take a set amount of the main catalyst solution (freshly prepared and used) in the glove box, add the auxiliary catalyst tank to the main catalyst tank under a nitrogen atmosphere, then use a high-pressure pump to add 20g of solvent (n-hexane), and then open the valve at the bottom of the tank to add the main catalyst to the reactor to start the polymerization reaction; quickly switch to a low-temperature oil bath to cool down to prevent temperature overshoot (the polymerization reaction is highly exothermic within 1 to 3 minutes), and record the changes in temperature, pressure, and ethylene flow rate.

[0079] (6) Polymer discharge: After the reaction reaches the set time, turn off the stirring, quickly reduce the temperature in the reactor to below 80°C, slowly release the pressure, replace with nitrogen three times, and use negative pressure to add about 1L of E solution (mixed isoparaffins, the solvent is resistant to high temperature, has a high boiling point, and is cleaned to be Ispoar E solvent); then heat to 140°C, heat for 10 minutes, then slowly start stirring, continue heating and stirring for 1 hour, then cool to 100°C and discharge the material through the bottom valve of the reactor.

[0080] (7) Cleaning the kettle: After the discharge is completed, add 1.5L E solution to the reactor, heat and stir at 140 °C for 1 h, cool to below 100 °C, drain the E solution, and replace with nitrogen three times.

[0081] (8) Cleaning the kettle: Cool the reactor to below 50°C, open the kettle, and manually clean the polymer remaining on the reactor wall and stirring paddle; then open the kettle and maintain the pressure of 3MPa nitrogen for 30min (leak test).

[0082] (9) Cleaning the reactor: Add 1.5 L of purified n-hexane to the reactor, heat and stir at 140 °C for 1 h, cool to below 60 °C, drain the n-hexane, and replace with nitrogen three times.

[0083] 2. Polymerization conditions:

[0084] The solvent is n-hexane (600 g), the α-olefin is 1-butene (150 g), the non-conjugated diene is 5-ethylidene-2-norbornene (30 g), the main catalyst is N3 (1.0 μmol), the co-catalyst is triisobutylaluminum (0.6 mmol) and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate (2.0 μmol), the polymerization temperature is 135°C, the polymerization pressure is 3.5 MPa, and the polymerization time is 10 min.

[0085] 3. Sample processing: Pour the polymer solution dissolved in solution E in (6) into a beaker and add more than 1L of industrial ethanol. Stir rapidly and the polymer will quickly agglomerate. Take out the polymer and dry it in a fume hood. Then, vacuum dry it in a vacuum drying oven at 120-140°C for more than 4 hours to remove unreacted monomers and solvents. The sample is obtained, weighed and recorded, and various tests are performed.

[0086] (1) Monomer insertion rate test method:

[0087] The amount of α-olefin and non-conjugated binding was measured using a NICOLET MAGNA 560 SPECTROMETER. Thin films of the calibration material with a thickness of 0.05 to 0.14 mm were prepared by compression molding 8 to 10 mg of polymer sample between TEFLON-coated sheets or aluminum foil at 190°C and 20,000 psi for 1 minute. The absorbance of each film was collected using 32 scans in the background. A 4 cm -1 Sample spectra were collected with a resolution of 100 nm or less, zero padding of 1 order of magnitude, and a Happ-Genzel apodization function. The spectra (standard) were obtained at 2450 cm -1 Baseline correction. The second derivatization of the normalized absorbance spectrum was performed at 4000-400 cm -1 To generate the calibration curve, the -1 The "peak to peak value" of the second derivative spectrum of the control sample is calculated, recorded, and plotted against the weight percentage of α-olefin and non-conjugated in each polymer control by 13 The α-olefin and non-conjugated contents in the polymers prepared in the present invention were calculated using a calibration curve.

[0088] (2) Test method for melt index of terpolymer:

[0089] Melt index (I2: 190℃ / 2.16kg) is based on GB / T 3682.1-2018, measurement of thermoplastic melt mass flow rate (MFR) and melt volume flow rate (MVR).

[0090] After testing, 25.6 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 13.7%, the molar insertion rate of 5-ethylidene-2-norbornene was 1.5%, and the melt index of the polymer was 1.7 g / 10 min (190° C., 2.16 kg).

[0091] Example 2

[0092] The preparation method provided in Example 1 was adopted, except that the main catalyst was N5 (1.0 μmol); and a low melt index terpolymer was obtained.

[0093] After testing, 37.1 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 11.2%, the molar insertion rate of 5-ethylidene-2-norbornene was 1.3%, and the melt index of the polymer was 0.8 g / 10 min (190° C., 2.16 kg).

[0094] Example 3

[0095] The preparation method provided in Example 1 was adopted, except that the cocatalysts were triisobutylaluminum (0.6 mmol) and triphenylcarbonium tetrakis(pentafluorophenyl)borate (2.0 μmol); and a low melt index terpolymer was obtained.

[0096] After testing, 21.3 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 9.6%, the molar insertion rate of 5-ethylidene-2-norbornene was 1.5%, and the melt index of the polymer was 0.5 g / 10 min (190° C., 2.16 kg).

[0097] Example 4

[0098] The preparation method provided in Example 1 was adopted, except that the non-conjugated diene was 1,7-octadiene (30 g); and a low melt index terpolymer was obtained.

[0099] After testing, 26.9 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 14.1%, the molar insertion rate of 1,7-octadiene was 1.1%, and the melt index of the polymer was 0.7 g / 10 min (190° C., 2.16 kg).

[0100] Example 5

[0101] The preparation method provided in Example 1 was adopted, except that the polymerization temperature was 155° C.; and a low melt index terpolymer was obtained.

[0102] After testing, 23.4 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 17.8%, the molar insertion rate of 5-ethylidene-2-norbornene was 1.3%, and the melt index of the polymer was 2.1 g / 10 min (190° C., 2.16 kg).

[0103] Example 6

[0104] The preparation method provided in Example 4 was adopted, except that the solvent was n-heptane; and a low melt index terpolymer was obtained.

[0105] After testing, 30.2 g of polymer was obtained after drying, the molar insertion rate of 1-butene was 15.3%, the molar insertion rate of 1,7-octadiene was 1.3%, and the melt index of the polymer was 1.0 g / 10 min (190° C., 2.16 kg).

[0106] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low melt index terpolymer, characterized in that: The following steps are involved: The ethylene, α-olefin and non-conjugated diene are ternary copolymerized in a saturated alkane solvent in the presence of a main catalyst and a co-catalyst to obtain a low melt index ternary copolymer; The main catalyst is a [NOON] complex having the following structure: Its specific structure is N5: N5: R1 = methyl, R2 = carbazole, R3 = phenyl, A = biphenyl, M = Zr, X = Cl; The co-catalyst is composed of triisobutylaluminum and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, or triisobutylaluminum and triphenylcarbonium tetrakis(pentafluorophenyl)borate; the molar ratio of aluminum atoms and boron atoms in the co-catalyst to metal atoms in the main catalyst is (50-3000):(1-5):1; The temperature of the ternary copolymerization is 80° C. to 200° C., and the pressure is 1 MPa to 6 MPa.

2. The preparation method according to claim 1, characterized in that The α-olefin is selected from one or more of propylene, 1-butene, 1-hexene, 1-octene and 1-decene; The non-conjugated diene is selected from one or more of 1,5-hexadiene, 1,7-octadiene, 3,6-dimethyl-1,7-octadiene, 4,5-dimethyl-1,7-octadiene, 5-methyl-1,8-nonadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene and 2,5-norbornadiene.

3. The preparation method according to claim 1, characterized in that The molar ratio of the α-olefin to the non-conjugated diene is (2-15):

1.

4. The preparation method according to claim 1, characterized in that The saturated alkane solvent is selected from one or more of n-pentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane, n-octane and isooctane.

5. The preparation method according to claim 1, characterized in that The temperature of the ternary copolymerization is 135° C. to 155° C., and the pressure is 3 MPa to 5 MPa; and the time of the ternary copolymerization is 5 min to 15 min.

6. The preparation method according to claim 1, characterized in that The molar insertion rate of alpha-olefin in the low melt index terpolymer is 5.3% to 19.8%, the molar insertion rate of non-conjugated diene is 0.8% to 3.7%, and the melt index is 0.20 to 7.3 g / 10 min.

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