JPH06298823A - Polymerization catalyst and production of ethylene-alpha-olefin copolymer using the same - Google Patents

Abstract

PURPOSE:To obtain a polymn. catalyst which effectively gives a high-mol.-wt. ethylene-alpha-olefin copolymer by combining a specific org. zirconium or hafnium compd. with an organoaluminum compd. CONSTITUTION:A polymn. catalyst is obtd. by combining a compd. of formula I (wherein R<1> and R<2> are each a 1-30C hydrocarbon group; M is zorconium or hafnium; Y is alkoxy; and 0<=m<=3 and 0<=n<=3 provided 0<=m+n<=3)(e.g. dimethylamidozirconium trichloride) with an organoaluminum compd. of formula II (wherein R<3>, R<4>, and R<5> are each a 1-6C hydrocarbon group; Z is H or alkoxy; and a, b, and c are each 0-3 provided a+b+c is 1-3)(e.g. triethylaluminum). The catalyst is used to copolymerize ethylene with an alpha-olefin (e.g. propylene) to produce a copolymer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymerization catalyst and a method for producing an ethylene-α-olefin copolymer using the polymerization catalyst.

[0002]

2. Description of the Related Art Generally, as a method for producing an ethylene-α-olefin copolymer, a transition metal compound of Group IV to VI and I to III of the periodic table is used.
A method of using a so-called Ziegler-Natta catalyst comprising a group-organic metal compound is widely known. As a method of using a homogeneous catalyst system composed of a zirconium compound or a hafnium compound and an organic aluminum compound, for example, a method of using a catalyst system composed of a metallocene compound of zirconium or hafnium and an aluminoxane has been proposed (JP-A-62- No. 121709, Japanese Patent Publication No. 1-503788, etc.). However, these methods require the use of a large amount of expensive aluminoxane, which is not preferable industrially and economically.

As a method of polymerizing an olefin by using a catalyst component composed of a compound having a zirconium-nitrogen bond, for example, a catalyst system composed of a zirconium amide compound and an organoaluminum compound having at least one halogen-aluminum bond is used. A method of polymerizing ethylene (Japanese Examined Patent Publication No. 50-30042) is disclosed.
However, in this method, the organoaluminum compound in the catalyst system needs to contain a halogen, and the product of the polymerization is a mixture containing a linear oligomer having 4 to 40 carbon atoms as a main component and having a high molecular weight. For polyethylene, it remains in a negligible range.

[0004]

SUMMARY OF THE INVENTION In view of the present situation, the present inventors have found that a compound having a zirconium-nitrogen bond,
As a result of extensive studies on a catalyst system comprising a halogen-free organoaluminum compound, a new catalyst system was found, a method for producing an ethylene-α-olefin copolymer using the catalyst was found, and the present invention was completed. It was

That is, the present invention provides (A) the general formula (R ¹
R ² N) _{4- (m + n)} MX _m Y _n (wherein R ¹ and R ² are hydrocarbon groups having 1 to 30 carbon atoms and may be the same or different. M is zirconium or hafnium. , X is a halogen, Y is an alkoxy group, m is 0 ≦ m ≦ 3, and n is 0.
≦ n ≦ 3, (m + n) is a number 0 ≦ (m + n) ≦ 3. ) And (B) the general formula R ³ _a R ⁴ _b
R ⁵ _c AlZ _{3- (a + b + c)} (provided that R ³ , R ⁴ and R ⁵ are hydrocarbon groups having 1 to 6 carbon atoms and may be the same or different. Z is a hydrogen atom) Alternatively, it is an alkoxy group.
a, b, and c are 0 ≦ a, b, c ≦ 3, and 1 ≦ a + b, respectively.
+ C ≦ 3. And a method of producing an ethylene-α-olefin copolymer using the polymerization catalyst, which comprises an organoaluminum compound represented by the formula (1).

The present invention will be described in detail below. In the present invention
The catalyst component (A) used has the general formula (R¹R²N)
_{4- (m + n)}MX_mY _n(However, R¹And R²Has 1 to 1 carbon atoms
30 hydrocarbon groups, which may be the same or different
Yes. M is zirconium or hafnium, X is halogen
, Y is an alkoxy group, m is 0 ≦ m ≦ 3, and n is 0 ≦ n ≦
3, (m + n) is a number 0 ≦ (m + n) ≦ 3. )
It is a nitrogen-containing compound represented by. R¹And R²Is preferably a hydrocarbon having 1 to 10 carbon atoms
A group, more preferably a hydrocarbon group having 1 to 8 carbon atoms.
Examples of the halogen represented by X include chlorine, bromine, and yo
Examples of this include chlorine, but from the viewpoint of catalytic activity, chlorine is used.
Is preferred. Further, as the alkoxy group, for example, meth
Xy, ethoxy, propoxy, butoxy, 2-ethyl
Xyloxy group and the like can be mentioned, but from the viewpoint of catalytic performance,
There is no particular limitation.

Specific examples of such suitable zirconium compounds include dimethylamide zirconium trichloride, bis (dimethylamide) zirconium dichloride, tris (dimethylamide) zirconium chloride, tetrakis (dimethylamide) zirconium, diethylamide zirconium trichloride. , Bis (diethylamide) zirconium dichloride, tris (diethylamide) zirconium chloride, tetrakis (diethylamide) zirconium, diisopropylamide zirconium trichloride, bis (diisopropylamide) zirconium dichloride, tris (diisopropylamide) zirconium chloride, tetrakis (diisopropylamide) zirconium, Di-n-propylamide zirconium tri Lolide, bis (di-n-propylamido) zirconium dichloride, tris (di-n-propylamido) zirconium chloride, tetrakis (di-n-propylamido) zirconium, diisobutylamide zirconium trichloride, bis (diisobutylamido) zirconium dichloride, tris ( Diisobutylamide) zirconium chloride, tetrakis (diisobutylamide) zirconium, ditert-butylamide zirconium trichloride, bis (dite
rt-Butylamido) zirconium dichloride, tris (ditert-butylamido) zirconium chloride, tetrakis (ditert-butylamido) zirconium, di-n-butylamide zirconium trichloride, bis (di-n-butylamido) zirconium dichloride, tris (di-n-). Butylamide) zirconium chloride, tetrakis (di-n-butylamide) zirconium, dihexylamide zirconium trichloride, bis (dihexylamide) zirconium dichloride, tris (dihexylamide) zirconium chloride, tetrakis (dihexylamide) zirconium, dioctylamide zirconium trichloride, bis (Dioctylamide) zirconium dichloride, tris (dioctylamide) zirco Umium chloride, tetrakis (dioctylamide) zirconium, didecylamide zirconium trichloride, bis (didecylamide) zirconium dichloride, tris (didecylamide) zirconium chloride, tetrakis (didecylamide) zirconium, dioctadecylamide zirconium trichloride, bis (dioctadecylamide) Zirconium dichloride, tris (dioctadecylamide) zirconium chloride, tetrakis (dioctadecylamide)
Zirconium, diphenylamide zirconium trichloride, bis (diphenylamide) zirconium dichloride, tris (diphenylamide) zirconium chloride, tetrakis (diphenylamide) zirconium, ethoxy (dimethylamide) zirconium dichloride, ethoxy (diethylamide) zirconium dichloride, ethoxy (di n -Propylamido) zirconium dichloride, ethoxy (diisopropylamido) zirconium dichloride, ethoxy (diisobutylamido) zirconium dichloride, ethoxy (di-n-butylamido) zirconium dichloride, ethoxy (dit)
ert-butylamide) zirconium dichloride, ethoxy (dihexylamide) zirconium dichloride, ethoxy (dioctylamide) zirconium dichloride, ethoxy (diphenylamide) zirconium dichloride, propoxy (dimethylamide) zirconium dichloride, propoxy (diethylamide) zirconium dichloride, propoxy (din). -Propylamide) zirconium dichloride, propoxy (diisopropylamide) zirconium dichloride, propoxy (diisobutylamide) zirconium dichloride, propoxy (di-n-butylamide) zirconium dichloride, propoxy (ditert-butylamide) zirconium dichloride, propoxy (dihexylamide)
Zirconium dichloride, propoxy (dioctylamide) zirconium dichloride, propoxy (diphenylamide) zirconium dichloride, butoxy (dimethylamide) zirconium dichloride, butoxy (diethylamide) zirconium dichloride, butoxy (di-n-propylamide) zirconium dichloride, butoxy (diisopropylamide) Zirconium dichloride, butoxy (diisobutylamide) zirconium dichloride, butoxy (di-n-butylamide) zirconium dichloride, butoxy (ditert-butylamide) zirconium dichloride, butoxy (dihexylamide) zirconium dichloride, butoxy (dioctylamide) zirconium dichloride, butoxy (diphenyl) Amide Zirconium dichloride,
Hexyloxy (dimethylamido) zirconium dichloride, hexyloxy (diethylamido) zirconium dichloride, hexyloxy (di-n-propylamido) zirconium dichloride, hexyloxy (diisopropylamido) zirconium dichloride, hexyloxy (diisobutylamido) zirconium dichloride, hexyloxy (di-n-butylamido) zirconium Examples thereof include dichloride, hexyloxy (ditert-butylamide) zirconium dichloride, hexyloxy (dihexylamide) zirconium dichloride, hexyloxy (dioctylamide) zirconium dichloride, hexyloxy (diphenylamide) zirconium dichloride. Among these zirconium compounds, more preferably tetrakis (dimethylamide) zirconium, tetrakis (diethylamide) zirconium, tetrakis (diisopropylamide) zirconium, tetrakis (di-n-propylamide) zirconium, tetrakis (diisobutylamide) zirconium, tetrakis (diisodiamide). tetrakis (dialkylamido) zirconium such as tert-butylamido) zirconium, tetrakis (di-n-butylamido) zirconium, tetrakis (dihexylamido) zirconium and tetrakis (dioctylamido) zirconium.

Specific examples of such a suitable hafnium compound include dimethylamido hafnium trichloride, bis (dimethylamido) hafnium dichloride,
Tris (dimethylamido) hafnium chloride, tetrakis (dimethylamido) hafnium, diethylamido hafnium trichloride, bis (diethylamido) hafnium dichloride, tris (diethylamido) hafnium chloride, tetrakis (diethylamido) hafnium, diisopropylamide hafnium trichloride, bis (diisopropylamide) ) Hafnium dichloride, tris (diisopropylamide) hafnium chloride, tetrakis (diisopropylamide) hafnium, di-n-propylamide hafnium trichloride,
Bis (di-n-propylamido) hafnium dichloride, tris (di-n-propylamido) hafnium chloride, tetrakis (di-n-propylamido) hafnium, diisobutylamide hafnium trichloride, bis (diisobutylamido) hafnium dichloride, tris (diisobutylamide) ) Hafnium chloride, tetrakis (diisobutyramide) hafnium, ditert
-Butylamido hafnium trichloride, bis (di-t
ert-butylamido) hafnium dichloride, tris (ditert-butylamido) hafnium chloride, tetrakis (ditert-butylamido) hafnium, di-n-butylamido hafnium trichloride, bis (di-n-butylamido) hafnium dichloride, tris (di-n-). Butylamide) hafnium chloride, tetrakis (di-n-butylamido) hafnium, dihexylamide hafnium trichloride, bis (dihexylamide) hafnium dichloride, tris (dihexylamide) hafnium chloride, tetrakis (dihexylamide) hafnium, dioctylamide hafnium trichloride, bis (Dioctylamide) hafnium dichloride, Tris (dioctylamide) hafnium chloride, Tetraki Su (dioctylamide) hafnium, didecylamide hafnium trichloride, bis (didecylamide) hafnium dichloride, tris (didecylamide) hafnium chloride, tetrakis (didecylamide) hafnium, dioctadecylamide hafnium trichloride, bis (dioctadecylamide) hafnium dichloride, Tris (dioctadecylamide) hafnium chloride, tetrakis (dioctadecylamide) hafnium, diphenylamide hafnium trichloride, bis (diphenylamide) hafnium dichloride, tris (diphenylamide) hafnium chloride, tetrakis (diphenylamide) hafnium, ethoxy (dimethylamide) ) Hafnium dichloride, ethoxy (diethylamide) hafni Mujikuroraido, ethoxy (di-n- propyl amide) hafnium dichloride, ethoxy (diisopropylamide) hafnium dichloride, ethoxy (diisobutyl amide) hafnium dichloride, ethoxy (di n- butylamide)
Hafnium dichloride, ethoxy (ditert-butylamide) hafnium dichloride, ethoxy (dihexylamide) hafnium dichloride, ethoxy (dioctylamide) hafnium dichloride, ethoxy (diphenylamide) hafnium dichloride, propoxy (dimethylamide) hafnium dichloride, propoxy (diethylamide) hafnium Dichloride, propoxy (di-n-propylamide) hafnium dichloride, propoxy (diisopropylamide) hafnium dichloride, propoxy (diisobutyramide) hafnium dichloride, propoxy (di-n-butylamide)
Hafnium dichloride, propoxy (ditert-butylamide) hafnium dichloride, propoxy (dihexylamide) hafnium dichloride, propoxy (dioctylamide) hafnium dichloride, propoxy (diphenylamide) hafnium dichloride, butoxy (dimethylamido) hafnium dichloride, butoxy (diethylamide) hafnium Dichloride, butoxy (di-n-propylamide) hafnium dichloride, butoxy (diisopropylamide) hafnium dichloride, butoxy (diisobutylamide) hafnium dichloride, butoxy (di-n-butylamide) hafnium dichloride, butoxy (ditert-butylamide) hafnium dichloride, butoxy (Dihexylamide) hafnium Chloride, butoxy (dioctylamide) hafnium dichloride, butoxy (diphenylamide) hafnium dichloride, hexyloxy (dimethylamide) hafnium dichloride, hexyloxy (diethylamide) hafnium dichloride, hexyloxy (di-n-propylamide) hafnium dichloride, hexyloxy (diisopropylamide) hafnium Dichloride, hexyloxy (diisobutylamide) hafnium dichloride, hexyloxy (di-n-butylamide) hafnium dichloride, hexyloxy (di te
rt-butylamide) hafnium dichloride, hexyloxy (dihexylamide) hafnium dichloride,
Hexyloxy (dioctylamide) hafnium dichloride, hexyloxy (diphenylamide) hafnium dichloride and the like can be mentioned. Among these hafnium compounds, more preferably tetrakis (dimethylamido) hafnium, tetrakis (diethylamido) hafnium, tetrakis (diisopropylamido) hafnium, tetrakis (di-n-propylamido) hafnium,
And tetrakis (diisobutylamido) hafnium, tetrakis (ditert-butylamido) hafnium, tetrakis (di-n-butylamido) hafnium, tetrakis (dihexylamido) hafnium and tetrakis (dioctylamido) hafnium.

As a method for synthesizing the above zirconium compound or hafnium compound, for example, DC Bradley & IMTh
The method described in omas, J. Chem. Soc (1960) 3857-3861 can be used. In the present invention, according to these methods, (1) the general formula R ⁶ M (where R ⁶ is a carbon number of 1 to
30 is a hydrocarbon group, and M is an alkali metal such as Li. ) And an organic alkali metal compound represented by the general formula R
¹ R ² NH (provided that R ¹ and R ² are hydrocarbon groups having 1 to 30 carbon atoms and may be the same or different), and are reacted with a dialkylamine to form an alkali metal amide. A compound is synthesized and then represented by the alkali metal compound and (2) the general formula MX ₄ (wherein M is zirconium or hafnium, X is halogen such as chlorine, bromine and iodine, preferably chlorine). Synthesis was performed by reacting the metal tetrahalide.

The organoaluminum compound of the catalyst component (B) used in the present invention has the general formula R ³ _a R ⁴ _b R ⁵ _c AlZ.
_{3- (a + b + c)} (provided that R ³ , R ⁴ and R ⁵ are hydrocarbon groups having 1 to 6 carbon atoms and may be the same or different. Z
Is a hydrogen atom or an alkoxy group. a, b, and c are numbers 0 ≦ a, b, c ≦ 3, and 1 ≦ a + b + c ≦ 3, respectively. ) Is an organoaluminum compound.

Specific examples of the organoaluminum compound include trialkylaluminums such as trimethylaluminum, triethylaluminum, tripropylaluminum, triisobutylaluminum, trihexylaluminum, dimethylaluminum hydride, diethylaluminum hydride, dipropylaluminum hydride and diisobutyl. Aluminum hydride, dialkyl aluminum hydride such as dihexyl aluminum hydride, dimethyl aluminum methoxide, methyl aluminum dimethoxide, diethyl aluminum methoxide, ethyl aluminum dimethoxide, diisobutyl aluminum methoxide, isobutyl aluminum dimethoxide, dihexyl aluminum methoxide, hex Le aluminum dimethoxide, dimethyl aluminum ethoxide, methyl aluminum diethoxide, diethylaluminum ethoxide, ethylaluminum ethoxide, diisobutylaluminum ethoxide, alkyl aluminum alkoxides such as isobutyl aluminum diethoxide. Among these organoaluminum compounds, trialkylaluminums such as triethylaluminum and triisobutylaluminum are preferable.

The component (B) is the metal atom 1 in the component (A).
It can be used in a wide range such as 1 to 100 with respect to mol, but is preferably used in the range of 1 to 50, more preferably 1 to 10.

The monomers constituting the copolymer in the present invention are ethylene and one or more kinds of α-olefins.
Specific examples of the α-olefin include propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, decene-1, octadecene-.
1, α-olefins having 3 to 20 carbon atoms such as eicosene-1.

In the present invention, the method for supplying the polymerization catalyst to the polymerization tank may be, for example, in an inert gas such as nitrogen or argon without water. Catalyst component (A)
The materials (B) and (B) may be supplied individually, or may be supplied by contacting the two in advance.

The polymerization temperature in the present invention is -30 to 30.
It can be carried out at 0 ° C., but preferably 2
It is 0 to 200 ° C, more preferably 70 to 180 ° C.
The polymerization pressure in the present invention is not particularly limited, but is usually 3 to 1 from the viewpoint of being industrial and economical.
It is about 500 atm.

The polymerization method may be either continuous or batch. Also, propane, butane, pentane,
Slurry polymerization with an inert hydrocarbon solvent such as hexane, heptane or toluene, liquid phase polymerization without solvent, or gas phase polymerization is also possible. Further, in the present invention, a chain transfer agent such as hydrogen may be added to adjust the molecular weight of the copolymer.

[0017]

As described above in detail, according to the present invention,
To provide a novel polymerization catalyst comprising a specific zirconium compound having at least one zirconium-nitrogen bond or a specific hafnium compound having at least one hafnium-nitrogen bond, and a specific organoaluminum compound containing no halogen. As well as
By using the polymerization catalyst, high molecular weight ethylene-
The α-olefin copolymer can be efficiently produced.

[0018]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The properties of the polymers in the examples were measured by the following methods. The intrinsic viscosity [η] was measured in a tetralin solution at 130 ° C using an Ubbelohde viscometer. The α-olefin content was determined from the characteristic absorption of ethylene and α-olefin using an infrared spectrophotometer (IR-810 manufactured by JASCO Corporation).

Example 1 (1) Synthesis of zirconium amide complex compound 50 equipped with a stirrer, a dropping funnel, a Dimroth, and a thermometer
After replacing the 0 ml four-necked flask with argon, 6.1 g (21 mmol) of diethylamine and 200 ml of hexane were charged. Next, n-butyllithium (1
36 g (84 mmol) (5% by weight) was added dropwise from a dropping funnel while maintaining the temperature of the solution in the flask at 5 ° C or lower. After completion of dropping, the mixture was stirred at 5 ° C or lower for 2 hours. Next, 5 g (21 mmol) of zirconium tetrachloride was added to the mixed solution obtained in the above reaction while keeping the temperature below 5 ° C. After charging, the mixture was stirred at 5 ° C or lower for 2 hours, the temperature of the solution was heated to about 65 ° C, and the reaction was further performed for 2 hours. After removing solids such as lithium chloride and the solvent in the reaction solution and distilling, a zirconium amide complex compound represented by the composition formula [(C ₂ H ₅ ) ₂ N] ₄ Zr was obtained. (2) Polymerization of ethylene An autoclave equipped with a stirrer and having an internal volume of 400 ml was vacuum-dried and replaced with argon.
-100 ml of hexene-1 was charged as an olefin, and the temperature of the reactor was raised to 180 ° C. After heating, increase ethylene pressure to 25
After feeding while adjusting to kg / cm ² , the system was stabilized, and then 1 mmol of triethylaluminum as an organoaluminum compound was added, and subsequently 0.2 mmol of the amide complex synthesized in the above (1) was added. Polymerization was carried out for 2 minutes while controlling the temperature at 180 ° C. As a result of the polymerization, [η] = 0.
39, comonomer content 8.7% by weight, transition metal 1 mol
2,500g of copolymer (2500g-copoly / mol
・ Zr) was obtained.

Example 2 Polymerization was carried out in the same manner as in Example 1 (2) except that the polymerization temperature of 180 ° C. in Example 1 was changed to 120 ° C. As a result, [η] = 1.06, the comonomer content was 6.9% by weight, and 1500 g of the copolymer (15
00 g-copoly / mol.Zr) was obtained.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 (2) except that triethylaluminum in Example 1 was replaced with diethylaluminum dichloride. As a result, the amount of the copolymer was 0 g and could not be obtained.

Comparative Example 2 Example 1 except that the zirconium compound of Example 1 was replaced with dicyclopentadienyl zirconium dichloride.
Polymerization was performed in the same manner as in (2). As a result, the amount of the copolymer was 0 g and could not be obtained.

Comparative Example 3 Example 2 except that the zirconium compound of Example 2 was replaced with dicyclopentadienyl zirconium dichloride.
Polymerization was performed in the same manner as in. As a result, the copolymer is 0
g and could not be obtained.

Example 3 (1) Synthesis of zirconium amide complex compound 50 equipped with stirrer, dropping funnel, Dimroth, thermometer
After replacing the 0 ml four-necked flask with argon, 6.4 g (63 mmol) of diisopropylamine and 200 ml of tetrahydrofuran were charged. Next, 27 g (63 mmol) of n-butyllithium (15 wt%) diluted with hexane was added dropwise from a dropping funnel while maintaining the temperature of the solution in the flask at 5 ° C or lower. After completion of dropping, the mixture was stirred at 5 ° C or lower for 2 hours. Next, a solution of 5 g (21 mmol) of zirconium tetrachloride in 100 ml of tetrahydrofuran was added to the mixed solution obtained in the above reaction while maintaining the temperature at 5 ° C or lower. After charging, the mixture was stirred at 5 ° C or lower for 2 hours, the temperature of the solution was heated to about 65 ° C, and the reaction was further performed for 2 hours. After the reaction, solids such as lithium chloride and the solvent are removed and then recrystallized to prepare a compositional formula [(C
A zirconium amide complex compound represented by ₃ H ₇ ) ₂ N] ₃ ZrCl was obtained. (2) Polymerization of ethylene Polymerization was performed in the same manner as in Example 1 (2) except that the zirconium compound of Example 1 was replaced with the zirconium compound of (1) above. As a result, [η] = 0.94, comonomer content of 5.7% by weight, and 25 per 1 mol of transition metal.
0 g of copolymer (250 g-copoly / mol.Zr) was obtained.

[Brief description of drawings]

FIG. 1 is a flow chart diagram to assist in understanding the present invention. This flowchart is a representative example of the embodiment of the present invention, and the present invention is not limited to this.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiko Shimizu 1-5 Anezaki Kaigan, Ichihara City, Chiba Sumitomo Chemical Co., Ltd.

Claims (2)

[Claims] 1. (A) General formula (R ¹ R ² N) _{4- (m + n)} MX
_m Y _n (provided that R ¹ and R ² are hydrocarbon groups having 1 to 30 carbon atoms and may be the same or different. M is zirconium or hafnium, X is halogen, Y is an alkoxy group, and m is 0 ≦ m ≦ 3, n is 0 ≦ n ≦ 3, (m + n)
Is a number 0 ≦ (m + n) ≦ 3. ) And (B) the general formula R ³ _a R ⁴ _b R ⁵ _c AlZ
_{3- (a + b + c)} (provided that R ³ , R ⁴ and R ⁵ are hydrocarbon groups having 1 to 6 carbon atoms and may be the same or different. Z
Is a hydrogen atom or an alkoxy group. a, b, and c are numbers 0 ≦ a, b, c ≦ 3, and 1 ≦ a + b + c ≦ 3, respectively. ) A polymerization catalyst comprising an organoaluminum compound represented by 2. A method for producing an ethylene-α-olefin copolymer, which comprises using the polymerization catalyst according to claim 1.