JP2720392B2 - Olefin polymerization catalyst and olefin polymerization method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst for olefin polymerization and a method for polymerizing olefin. More specifically, the present invention relates to a catalyst for olefin polymerization and a method for polymerizing olefins, which can polymerize olefins with excellent polymerization activity and can produce an olefin polymer having a large molecular weight even when the amount of aluminoxane used is reduced. More specifically, when applied to copolymerization of two or more olefins having a narrow molecular weight distribution, an olefin copolymer capable of polymerizing an olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution with excellent polymerization activity. The present invention relates to a catalyst for use and a method for polymerizing an olefin.

Technical Background of the Invention and Problems Thereof Conventionally, as a method for producing an α-olefin polymer, particularly an ethylene polymer or an ethylene / α-olefin copolymer, a titanium-based catalyst or a vanadium compound comprising a titanium compound and an organoaluminum compound is used. There is known a method of copolymerizing ethylene or ethylene and an α-olefin in the presence of a vanadium-based catalyst composed of an organic aluminum compound. In general, an ethylene / α-olefin copolymer obtained with a titanium-based catalyst has a wide molecular weight distribution and composition distribution, and is inferior in transparency, surface non-adhesion, and mechanical properties. In addition, the ethylene / α-olefin copolymer obtained with a vanadium-based catalyst has a narrower molecular weight distribution and composition distribution than those obtained with a titanium-based catalyst, and has significantly improved transparency, surface non-adhesion, and mechanical properties. However, these properties are still insufficient for applications requiring these properties, and α-olefin polymers with improved properties, especially ethylene / α-olefin copolymers, are required.

On the other hand, a catalyst comprising a zirconium compound and an aluminoxane has recently been proposed as a new Ziegler-type olefin polymerization catalyst.

JP-A-58-19309 discloses that the following formula (cyclopentadienyl) ₂ MeRHal wherein R is cyclopentadienyl, C ₁ -C ₆ alkyl and halogen, and Me is a transition metal , Hal is a halogen], and a compound represented by the following formula: Al ₂ OR ₄ (Al (R) —O) _n [where R is methyl or ethyl, and n is a number of 4 to 20] Or a linear aluminoxane represented by the following formula: In the presence of a catalyst comprising a cyclic aluminoxane represented by the formula: wherein R and n are the same as defined above, one or more of ethylene and a C _{3 to} C ₁₂ α-olefin may be used. A method of polymerizing at a temperature of -50C to 200C is described. The publication states that in order to control the density of the resulting polyethylene, the polymerization of ethylene should be carried out in the presence of small amounts of up to 10% by weight of somewhat longer-chain α-olefins or mixtures. .

JP-A-59-95292 discloses the following formula: [Where n is 2 to 40, R is a linear aluminoxane represented by C _{1 to} C ₆ and the following formula: [Wherein the definitions of n and R are the same as described above], the invention relating to a method for producing a cyclic aluminoxane represented by the formula: According to the same publication, for example, when methylaluminoxane and a bis (cyclopentadienyl) compound of titanium or zirconium produced by the same production method are mixed and olefin is polymerized, 1 g of transition metal and It is stated that over 25 million g of polyethylene are obtained per hour.

JP-A-60-35005 discloses the following formula: Wherein R ¹ is C ₁ -C ₁₀ alkyl, R ⁰ is R ¹ or is bonded to and represents —O—, and the aluminoxane compound represented by Then, a method is disclosed in which the reaction product is chlorinated and further treated with a compound of Ti, V, Zr or Cr to produce a polymerization catalyst for olefins. The same publication, the catalyst is described as being particularly suitable for the copolymerization of mixtures of α- olefins of ethylene and C ₃ -C _12.

JP-A-60-35006 discloses, as a catalyst system for producing a reactor blend polymer, mono-, di- or tri-cyclopentadienyl of two or more different transition metals or a derivative (a) thereof and alumino. Combinations of xane (b) are disclosed. In Example 1 of the publication, ethylene and propylene were polymerized using bis (pentamethylcyclopentadienyl) zirconium dimethyl and aluminoxane as catalysts to obtain a number average molecular weight of 15,300 and a weight average molecular weight of 3
It is disclosed that a polyethylene containing 6,400 and 3.4% of a propylene component was obtained. In Example 2, ethylene (propylene) was polymerized using bis (pentamethylcyclopentadienyl) zirconium dichloride, bis (methylcyclopentadienyl) zirconium dichloride and aluminoxane as catalysts, and had a number average molecular weight of 2,200 and a weight average molecular weight of 2,200. A toluene-soluble portion containing a propylene component having a molecular weight of 11,900 and 30 mol% and a number average molecular weight of 3,00
0, a number average molecular weight of 2,000 consisting of a toluene insoluble part containing a propylene component having a weight average molecular weight of 7,400 and 4.8 mol%
A blend of polyethylene and an ethylene / propylene copolymer containing a propylene component having a weight average molecular weight of 8,300 and 7.1 mol% is obtained. Similarly, in Example 3, a blend of LLDPE and an ethylene-propylene copolymer comprising a soluble portion having a molecular weight distribution (w / n) of 4.57 and a propylene component of 20.6% and a molecular weight distribution of 3.04 and a propylene component of 2.9 mol% was insoluble. Is described.

JP-A-60-35007 discloses ethylene alone or together with an α-olefin having 3 or more carbon atoms, a metallocene and a compound represented by the following formula: [Where R is an alkyl group having 1 to 5 carbon atoms, and the definition of n is the same as described above]. A method of polymerizing in the presence of a catalyst system containing a linear aluminoxane represented by the formula: ing. According to the publication, the polymer obtained by the method has a weight average molecular weight of about 500 to about 1.4 million and a molecular weight distribution of 1.5 to 4.0.

Further, in JP-A-60-35008, by using a catalyst system comprising at least two metallocenes and aluminoxane, polyethylene or ethylene and C ₃ -C ₁₀ having a width wider molecular weight distribution α- olefin Is described as being produced. The publication describes that the copolymer has a molecular weight distribution (w / n) of 2 to 50. Further, a transition metal compound having a cyclopentadienyl group as a ligand, an aluminoxane and an organoaluminum JP-A-60-260602 and JP-A-60-130604 propose a method of polymerizing an olefin using a catalyst formed from a mixed organoaluminum compound comprising a compound and an organoaluminum compound. It is described that the polymerization activity per unit transition metal is improved by doing so. However, these methods have a problem that the amount of aluminoxane used is large and the activity per aluminoxane is still low. further,
When an α-olefin such as ethylene and propylene is copolymerized using a catalyst formed from these conventionally known transition metal compounds and aluminoxane, a polymer having a sufficiently large molecular weight can be obtained. There is a drawback that it is difficult.

JP-A-61-130314 discloses that, when propylene is polymerized in the presence of a catalyst system comprising a sterically fixed zircon-chelate compound and aluminoxane, a polypropylene having a high isotacticity can be obtained. Have been described. However, in this method, polymerization must be performed at a low temperature in order to use a large amount of aluminoxane and obtain a polymer having a high molecular weight.

The present inventors have found that, when the present invention is applied to copolymerization of two or more olefins having a narrow molecular weight distribution, an olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution has excellent polymerization activity in the use of aluminoxane with a small amount. As a result of examining an olefin polymerization catalyst and an olefin polymerization method which can be produced by the method described above and which can easily produce an olefin polymer having a large molecular weight, [A] a specific hafnium compound [B] aluminoxane and [ C] It has been found that the above object is achieved by using a catalyst formed from a specific organoaluminum compound, and the present invention has been achieved.

Object of the Invention The present invention provides a polymer having a narrow molecular weight distribution and, when applied to copolymerization of two or more types of olefins, is excellent in the use of aluminoxane with a small olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution. It is an object of the present invention to provide an olefin polymerization catalyst and an olefin polymerization method which can be produced with high activity and can easily produce an olefin polymer having a large molecular weight.

SUMMARY OF THE INVENTION According to the present invention, [A] a polydentate compound in which at least two groups selected from the group consisting of an indenyl group, a substituted indenyl group and a partially hydride thereof are bonded via a lower alkylene group [B] aluminoxane, and [C] (i) an organoaluminum compound having a hydrocarbon group selected from an alkyl group, a cycloalkyl group, and an aryl group having a branched chain; and (ii) ) general formula _{(i-C 4 H 9)} x Al y (C 5 H 10) z ( wherein, x, y, z are positive integers, isoprenyl aluminum represented by z ≧ 2x a) An organoaluminum compound selected from the group consisting of olefin polymerization catalyst formed from is further provided, characterized in that olefin is polymerized or copolymerized in the presence of the olefin polymerization catalyst. Polymerization of olefins is provided.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the olefin polymerization catalyst and the olefin polymerization method according to the present invention will be specifically described.

In the present invention, the term "polymerization" may be used to mean not only homopolymerization but also copolymerization, and the term "polymer" is used to mean not only homopolymer but also copolymer. May be used.

The catalyst used in the present invention is formed from three catalyst components [A], [B] and [C].

FIG. 1 shows a flowchart of a method for preparing the catalyst of the present invention.

The catalyst component [A] used in the present invention is a polydentate compound in which at least two groups selected from the group consisting of an indenyl group, a substituted indenyl group and a partially hydride thereof are bonded via a lower alkylene group. It is a hafnium compound used as a ligand. The following compounds can be exemplified as the hafnium compound.

Ethylene bis (indenyl) dimethyl hafnium, ethylene bis (indenyl) diethyl hafnium, ethylene bis (indenyl) diphenyl hafnium, ethylene bis (indenyl) methyl hafnium monochloride, ethylene bis (indenyl) ethyl hafnium monochloride, ethylene bis (indenyl) methyl Hafnium monobromide, ethylenebis (indenyl) hafnium dichloride, ethylenebis (indenyl) hafnium dibromide, ethylenebis (4,5,6,7-tetrahydro-1-indenyl) dimethylhafnium, ethylenebis (4,5,6, 7-tetrahydro-1-indenyl) methylhafnium monochloride, ethylenebis (4,5,6,7-tetrahydro-1-indenyl) hafnium dichloride, ethylenebis (4,5,6,7-tetrahydride -1-indenyl) hafnium dibromide, ethylenebis (4-methyl-1-indenyl) hafnium dichloride, ethylenebis (5-methyl-1-indenyl) hafnium dichloride, ethylenebis (6-methyl-1-indenyl) hafnium dichloride Ethylenebis (7-methyl-1-indenyl) hafnium dichloride, ethylenebis (5-methoxy-1-indenyl) hafnium dichloride, ethylenebis (2,3-dimethyl-1-indenyl) hafnium dichloride, ethylenebis (4, 7-dimethyl-1-indenyl) hafnium dichloride, ethylenebis (4,7-dimethoxy-1-indenyl)
Hafnium dichloride.

The catalyst component [B] used in the method of the present invention is aluminoxane. The aluminoxane used as a catalyst component has the general formula (I) and Can be exemplified. In the aluminoxane, R is a hydrocarbon group such as a methyl group, an ethyl group, a propyl group, and a butyl group, preferably a methyl group, an ethyl group, particularly preferably a methyl group, and m is 2 or more, preferably It is an integer of 5 or more. As a method for producing the aluminoxane, for example, the following method can be exemplified.

(1) Compounds containing adsorbed water, salts containing water of crystallization, such as magnesium chloride hydrate, copper sulfate hydrate, aluminum sulfate hydrate, nickel sulfate hydrate, primary chloride
A method in which a trialkylaluminum is added to a suspension of a hydrocarbon medium such as cerium hydrate to cause a reaction.

(2) A method in which water is allowed to directly act on trialkylaluminum in a medium such as benzene, toluene, ethyl ether, and tetrahydrofuran.

Among these methods, it is preferable to adopt the method (1). The aluminoxane may contain a small amount of an organic metal component.

As the organoaluminum compound [C] used as a catalyst component in the present invention, a compound having at least one Al-C bond in a molecule can be used, and examples thereof include the following types of compounds.

(I) The general formula (R ¹ ) _m Al (OR ² ) _n H _p X _q (where R ¹ and R ² are hydrocarbon groups containing usually 1 to 15, preferably 1 to 10 carbon atoms, and X is halogen, m is 1 ≦ m ≦ 3,
n is 0 ≦ n ≦ 2, p is 0 ≦ p ≦ 2, and q is a number satisfying 0 ≦ q ≦ 2, and m + n + p + q = 3), (ii) a general formula M ¹ Al (R ¹ ) ₄ (where M ¹ is Li, Na or K, and R ¹ is the same as described above), may be a complex alkylated product of a Group 1 metal and aluminum.

Among the above organoaluminum compounds, an organoaluminum compound having a hydrocarbon group other than an n-alkyl group is particularly suitable. Examples of the hydrocarbon group other than the n-alkyl group include an alkyl group having a branched chain such as isoalkyl, a cycloalkyl group, and an aryl group. Specific examples of the organoaluminum compound include triisopropylaluminum, triisobutylaluminum, tri2-methylbutylaluminum, tri3-methylbutylaluminum, tri2-methylpentylaluminum, tri3-methylpentylaluminum, and tri4-aluminum.
Trialkyl aluminum such as methylpentyl aluminum, tri-2-methylhexyl aluminum, tri-3-methylhexyl aluminum and tri-2-ethylhexyl aluminum; tricycloalkyl aluminum such as tricyclohexyl aluminum; triphenyl aluminum such as triphenyl aluminum and tritolyl aluminum Examples thereof include dialkylaluminum hydrides such as reel aluminum and diisobutylaluminum hydride, and alkylaluminum alkoxides such as isobutylaluminum methoxide, isobutylaluminum ethoxide, and isobutylaluminum isopropoxide. Among these organic aluminum compounds, an aluminum compound having a branched alkyl group is preferable, and a trialkylaluminum compound is particularly preferable. In general formula _{(i-C 4 H 9)} x Al y (C 5 H 10) z (x, y, z are positive integers and z ≧ 2x) isoprenylaluminum represented by is preferable. In addition, a compound that forms the above-mentioned organoaluminum compound in the polymerization system, for example, an aluminum halide and an alkyl lithium or an aluminum halide and an alkyl magnesium may be added.

In the present invention, the catalyst components [A], [B] and [C]
May be supplied to the reaction system. Alternatively, two catalyst components may be premixed and the remaining one catalyst component may be supplied to the reaction system. Alternatively, after all the catalyst components are preliminarily mixed, the reaction system May be supplied.

The ratio of the hafnium compound used in carrying out the method of the present invention is usually 10 ⁻⁸ to 10 ⁻² gram atom / preferably, preferably 10 ⁻⁷ , as the concentration of the hafnium atom in the polymerization reaction system.
To 10 ^-3 gram atom /.

In the method of the present invention, the amount of aluminoxane used is preferably 3 mg atom / or less, more preferably 0.01 to 2 mg atom /, particularly preferably 0.02 to 1 mg, in terms of aluminum atom in the reaction system. Range of atoms /. The ratio of the aluminum atom of the aluminoxane component [B] to the total aluminum atom of the aluminoxane component [B] and the organoaluminum compound component [C] in the reaction system is usually 1 to 80%, preferably 1 to 80%. Is 2 to 75
%, Particularly preferably in the range of 5 to 70%. Similarly, the aluminum atom ratio of the organoaluminum compound component [C] is usually 20 to 99%, preferably 25 to 98%.
%, Particularly preferably in the range from 30 to 95%. In the method of the present invention, the ratio of the total amount of aluminum atoms of the aluminoxane component [B] and the organoaluminum compound component [C] to the hafnium atoms in the reaction system is usually 20 to 10,000, preferably 50 to 5000, It is particularly preferably in the range of 100 to 2000.

The process of the present invention is effective for producing olefin polymerization couples, especially α-olefin polymers and copolymers of ethylene and α-olefins. Examples of olefins that can be used in the present invention include ethylene and α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, Examples thereof include -decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. If necessary, a polyene such as a diene can be copolymerized.

In the method of the present invention, the polymerization of the olefin
It is carried out in the gas phase or in the liquid phase. In liquid phase polymerization, an inert hydrocarbon may be used as a solvent, or an olefin itself may be used as a solvent.

Specific examples of the hydrocarbon medium include aliphatic hydrocarbons such as butane, isobutane, pentane, hexane, octane, decane, dodecane, hexadecane, and octadecane; alicyclics such as cyclopentane, methylcyclopentane, cyclohexane, and cyclooctane. Hydrocarbons, aromatic hydrocarbons such as benzene, toluene, and xylene, and petroleum fractions such as gasoline, kerosene, and light oil.

In the method of the present invention, the polymerization temperature is usually -50 to 20.
It is in the range of 0 ° C, preferably 0 to 120 ° C. The polymerization pressure is usually normal pressure to 100 kg / cm ² , preferably normal pressure to 50 k
g / cm ² , and the polymerization can be carried out by any of batch, semi-continuous, and continuous methods. Further, the polymerization can be performed in two or more stages under different reaction conditions. The molecular weight of the polymer can be adjusted by hydrogen and / or polymerization temperature.

Effect of the Invention When applied to the olefin polymerization of the present invention, especially α-olefin polymerization or copolymerization of ethylene and α-olefin, the activity is remarkably high even in the use of less aluminoxane than the conventional method. There is an effect that a polymer having a large molecular weight can be obtained.
In addition, when applied to copolymerization of two or more olefins, there is an effect that an olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution can be obtained.

[Examples] Next, the present invention will be specifically described with reference to Examples. The measurement of w / n is performed as follows according to "Gel Permeation Chromatography" by Takeuchi and published by Maruzen.

(1) Using standard polystyrene having a known molecular weight (monodisperse polystyrene, manufactured by Toyo Soda Co., Ltd.)
And its GPC (Gel Permeation Chromatograph) count are measured, and a correlation curve calibration curve between the molecular weight M and the EV (Elution Volume) is prepared. The concentration at this time is 0.02% by weight.

(2) GPC chromatograph of the sample by GPC measurement,
According to the above (1), the number average molecular weight n and the weight average molecular weight w in terms of polystyrene are calculated, and the w / n value is obtained. The sample preparation conditions and GPC measurement conditions at that time are as follows.

[Sample Preparation] (a) A sample is dispersed in an Erlenmeyer flask together with an o-dichlorobenzene solvent so as to be 0.1% by weight.

(B) Heat the Erlenmeyer flask to 140 ° C, stir for about 30 minutes, and dissolve.

(C) Apply the solution to GPC.

[GPC Measurement Conditions] The measurement was performed under the following conditions.

(B) Equipment Waters (150C-ALC / GPC) (b) Column Toyo Soda (GMH type) (c) Sample amount 400μ (d) Temperature 140 ° C (e) Flow rate 1ml / min Example 1 Aluminoxane Preparation of Al ₂ (SO ₄ ) ₃ in a 400 ml flask purged with nitrogen
· 14H was charged with ₂ O 37 g and toluene 125 ml, cooled to 0 ° C., was added dropwise trimethyl aluminum 500mmol diluted with toluene 125 ml. Next, the temperature was raised to 40 ° C., and the reaction was continued at that temperature for 10 hours. After the reaction, solid-liquid separation was performed by filtration, and toluene was further removed from the liquid to obtain 13 g of aluminoxane as a white solid. The molecular weight determined by freezing point depression in benzene was 930, and the m value shown in the catalyst component [B] was 14.

Synthesis of ethylene bis (indenyl) hafnium dichloride A nitrogen-substituted 200 ml glass flask was charged with 5.4 g of bis (indenyl) ethane (synthesized based on Bull. Soc. Chim., 2954 (1967)) and 50 ml of THF, and stirred. -30
Cooled to 4040 ° C. N-BuLi (1.6M solution) 31.5
Then, after stirring at −30 ° C. for 1 hour, the mixture was spontaneously heated to room temperature to anionize bis (indenyl) ethane. 60 ml of THF was charged into another 200 ml glass flask purged with nitrogen, cooled to −60 ° C. or lower, and HfCl ₄
6.7 g was added slowly. Thereafter, the temperature was raised to 60 ° C., and the mixture was stirred for 1 hour. The anionized ligand is added dropwise to this, and 60
After stirring at 2 ° C. for 2 hours, the mixture was passed through a glass filter.
The liquid was concentrated at room temperature to about the first 1/5 volume. By this operation, a solid precipitates. The precipitated solid was passed through a glass filter, washed with hexane / ethanol, and dried under reduced pressure to obtain the target compound.

(Polymerization) 500 ml of toluene was charged into a stainless steel autoclave having an internal volume of 2 and purged with nitrogen, and then the system was purged with propylene gas. Subsequently, 1 mmol of triisobutylaluminum, 1 mg atom of aluminoxane in terms of Al atom, and 1 × 10 ^-3 mmol of ethylenebis (indenyl) hafnium dichloride were added, and the temperature was raised to 45 ° C. Thereafter, polymerization was carried out at 50 ° C. for 1 hour while supplying propylene gas so that the total pressure became 7 kg / cm ² G, and measured in decalin at 135 ° C. [η] = 2.5 dl / g, w / n = 2.2 45.0 g of isotactic polypropylene was obtained.

Comparative Example 1 In the same manner as in Example 1 except that triisobutylaluminum was not used in the polymerization of Example 1, 5.1 g of isotactic polypropylene having [η] = 1.9 dl / g and w / n = 2.1 was obtained. Was.

Comparative Example 2 The procedure of Example 1 was repeated, except that trimethylaluminum was used instead of triisobutylaluminum in the polymerization of Example 1, to obtain 29.6 g of isotactic polypropylene.

Example 2 Polymerization was performed in the same manner as in Example 1 except that 1 mmol of tri-2-ethylhexylaluminum and 0.5 mg of aluminoxane were converted to Al atoms instead of triisobutylaluminum in Example 1 [η]. = 2.3 dl / g, w / n = 2.4, 38.2 g of isotactic polypropylene was obtained.

Example 3 335 ml of toluene and 15 ml of 1-octene were charged into a nitrogen-purged glass autoclave having an internal volume of 1, and the system was heated to 70 ° C. while blowing ethylene gas. Subsequently, 0.4 mmol of triisobutylaluminum, 0.2 mg atom of aluminoxane in terms of Al atom, and 3 × 10 3 of ethylenebis (indenyl) zirconium dichloride.
^-3 mmol was added to initiate polymerization. Polymerization was performed at 70 ° C for 30 minutes while continuously supplying ethylene gas, and MFR 0.0
16.8 g of an ethylene / 1-octene copolymer having a density of 0.879 g / cm ³ at 9 g / 10 min was obtained.

Example 4 (Synthesis of ethylenebis (4,5,6,7-tetrahydro-1-indenyl) hafnium dichloride) 15 g of ethylenebis (indenyl) hafnium dichloride synthesized in the same manner as in Example 1 was suspended in 700 ml of dichloromethane. Cloudy, add 500 mg of PtO for 48 hours at 35 ° C.
The hydrogenation was performed at 30-35 atm. After filtration of the product, ethylenebis (4,
5,6,7-Tetrahydro-1-indenyl) hafnium dichloride was obtained.

(Polymerization) After 500 ml of toluene was charged into a 2 stainless steel autoclave sufficiently purged with nitrogen, the system was purged with propylene gas. Subsequently, 1 mmol of triisobutylaluminum, 0.75 mg atom of aluminoxane in terms of Al atom, and 1.0 × 10 ⁻³ mmol of the hafnium compound synthesized above were added, and the temperature was raised to 45 ° C. After that, the total pressure is 7kg /
cm ² -G while supplying propylene gas.
As a result of carrying out the polymerization at 1 ° C. for 1 hour, 36.0 g of isotactic polypropylene having [η] of 2.4 dl / g and w / n of 2.4 was obtained.

[Brief description of the drawings]

 FIG. 1 is a flowchart of the catalyst of the present invention.

Claims (2)

(57) [Claims] 1. A polydentate compound in which at least two groups selected from the group consisting of an indenyl group, a substituted indenyl group and a partially hydride thereof are bonded via a lower alkylene group to a ligand. [B] aluminoxane, and [C] (i) an organoaluminum compound having a hydrocarbon group selected from an alkyl group having a branched chain, a cycloalkyl group, and an aryl group; and (ii) a general formula ( i-C ₄ H ₉ ) _x Al _y (C ₅ H ₁₀ ) _z (where x, y, and z are positive integers and z ≧ 2x) An olefin polymerization catalyst formed from the selected organoaluminum compound. 2. A polydentate compound in which at least two groups selected from the group consisting of an indenyl group, a substituted indenyl group and a partially hydride thereof are bonded via a lower alkylene group to a ligand. [B] aluminoxane, and [C] (i) an organoaluminum compound having a hydrocarbon group selected from an alkyl group having a branched chain, a cycloalkyl group, and an aryl group; and (ii) a general formula ( i-C ₄ H ₉ ) _x Al _y (C ₅ H ₁₀ ) _z (where x, y, and z are positive integers and z ≧ 2x) An olefin polymerization method comprising polymerizing or copolymerizing an olefin in the presence of a catalyst formed from a selected organoaluminum compound.