JPH0757769B2 - Solventless polymerization of olefins - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a solventless polymerization method of an olefin. More specifically, the present invention provides an olefin polymer such as a soft polypropylene or an olein-based thermoplastic elastomer having a good powder fluidity, particularly by a gas phase polymerization method, without problems such as formation of an adhesive solidified product, and an efficiency. It relates to a method of manufacturing well.

[Prior Art] Conventionally, an α-olefin polymer is produced using a highly active catalyst system for the purpose of improving the stereoregularity of the produced polymer. At this time, an atactic polyolefin produced as a by-product, particularly Atactic polypropylene has a very low molecular weight and is of poor practical value.

Therefore, the present inventors previously used a novel catalyst system,
A process for producing a high molecular weight atactic polyolefin which is industrially useful has been found (Japanese Patent Laid-Open Nos. 63-243106 and 63-243107). However, in these methods, when the gas phase polymerization of an olefin is carried out using the catalyst, there are problems that the resulting polymer powder has poor fluidity or that an adherent solidified product is formed.

[Problems to be Solved by the Invention] The present invention solves the problems in the conventional method for producing a high molecular weight atactic polyolefin, and provides a flexible polypropylene or olefinic thermoplastic resin containing a certain amount of boiling heptane-soluble components. A method for efficiently producing an olefin polymer such as an elastomer by a solvent-free polymerization method, in particular, a vapor-phase polymerization method for producing a powdery olefin polymer having a very small amount of an adhered solidified product and good powder fluidity It was made for the purpose of doing.

[Means for Solving the Problems] As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that a solid component composed of a crystalline polyolefin and a specific solid catalyst component, an organoaluminum compound and a specific alkoxy compound. It was found that the object can be achieved by using a catalyst system composed of a combination of group-containing aromatic compounds, and the present invention has been completed based on this finding.

That is, the present invention provides a solid catalyst component comprising (A) (a) a crystalline polyolefin and (b) magnesium, titanium, a halogen atom and an electron donor, which comprises a magnesium compound and a general formula Ti (OR ⁴ ) _k X _4-k (wherein R ⁴ is an alkyl group, a cycloalkyl group or a phenyl group, X is a halogen atom such as chlorine or bromine, and k is 0 to 4)
A solid component composed of a titanium compound represented by: and a solid catalyst component prepared by contacting an electron donor, (B) an organoaluminum compound, and (C) a general formula (In the formula, R ¹ is an alkyl group having 1 to 20 carbon atoms, and R ² is 1 carbon atom.
To 10 hydrocarbon groups, m is an integer from 1 to 6, and n is (6-m)
An olefin is polymerized in the presence of a catalyst system comprising a combination of alkoxy group-containing aromatic compounds represented by to produce an olefin polymer having a boiling heptane-soluble content of 30% by weight or more. And a solventless polymerization method for olefins.

Hereinafter, the present invention will be described in detail.

In the method of the present invention, as the component (A) of the catalyst system, that is, the solid component, (a) a crystalline polyolefin and (b)
A solid catalyst component composed of magnesium, titanium, a halogen atom and an electron donor is used.

The solid component (A) may be prepared by, for example, preliminarily polymerizing an olefin in the presence of a combination of the solid component (b), an organoaluminum compound and an electron-donating compound optionally used. ,
(2) The crystalline powder such as crystalline polypropylene or polyethylene having a uniform particle size is mixed with (b) the solid catalyst component, an organoaluminum compound and an electron donating compound (melting point 100 ° C. or higher), which are optionally used. How to disperse,
(3) A method combining the method (1) and the method (2) can be used.

In the method (1) in the method for preparing the solid component (A), an α-olefin having 2 to 10 carbon atoms such as ethylene, propylene, butene-1, and 4-methylpentene-1 is used as the olefin, The prepolymerization is usually carried out at a temperature in the range of 30 to 80 ° C, preferably 55 to 70 ° C to form a crystalline polyolefin having a melting point of 100 ° C or higher. At this time, the aluminum / titanium atomic ratio of the catalyst system is usually selected in the range of 0.1 to 100, preferably 0.5 to 5, and the electron donating compound / titanium molar ratio is 0 to 50.
It is preferably selected in the range of 0.1 to 2.

As the organoaluminum compound used for this prepolymerization, those exemplified later as the organoaluminum compound of the component (B) can be used. Further, the electron-donating compound used as necessary basically has the ability to improve regularity during the polymerization of propylene, such as diphenyldimethoxysilane, diphenyldiethoxysilane, dibenzyldimethoxysilane, tetramethoxy. Organic silicon compounds such as silane, tetraethoxysilane, tetraphenoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriphenoxysilane, phenyltrimethoxysilane and benzyltrimethoxysilane, n-butyl phthalate, diisobutyl phthalate Aromatic dicarboxylic acid ester such as
Carbon number of aromatic monocarboxylic acid such as benzoic acid, p-methoxybenzoic acid, p-ethoxybenzoic acid, toluic acid 1
~ 4 alkyl ester, isopropyl methyl ether, isopropyl ethyl ether, t-butyl methyl ether, t-butyl ethyl ether, t-butyl-n-
Propyl ether, t-butyl-n-butyl ether,
Unsymmetrical ethers such as t-amyl methyl ether and t-amyl ethyl ether, 2,2'-azobis (2-methylpropane), 2,2'-azobis (2-ethylpropane), 2,2'-azobis (2 -Methylpentane), α,
α'-azobisisobutyronitrile, 1,1'-azobis (1-cyclohexanecarboxylic acid), (1-phenylmethyl) -azodiphenylmethane, 2-phenylazo-2,
Examples thereof include an azo compound in which a sterically hindering substituent is bonded to an azo bond such as 4-dimethyl-4-trixypentanenitrile. These may be used alone or in combination of two or more. Good.

The solid catalyst component of the component (b) used in the solid component (A) contains magnesium, titanium, a halogen atom and an electron donor as essential components, and contains a magnesium compound and a titanium compound represented by the above general formula. It can be prepared by contacting with an electron donor.

Examples of the magnesium compound include magnesium dihalides such as magnesium dichloride, magnesium oxide, magnesium hydroxide, hydrotalcite, carboxylates of magnesium, alkoxy magnesium such as diethoxy magnesium, and aryloxy magnesium.
Alkoxy magnesium halides, allyloxy magnesium halides, alkyl magnesiums such as ethylbutyl magnesium, alkyl magnesium halides, or reaction products of organomagnesium compounds with electron donors, halosilanes, alkoxysilanes, silanols, aluminum compounds and the like. However, among these, magnesium halide, alkoxy magnesium, alkyl magnesium, and alkyl magnesium halide are preferable. Moreover, these magnesium compounds may be used alone or in combination of two or more.

In addition, as the titanium compound represented by the above general formula, for example, tetramethoxy titanium, tetraethoxy titanium, tetra-n-propoxy titanium, tetraisopropoxy titanium, tetra-n-butoxy titanium, tetraisobutoxy titanium, tetracyclohexyloxy. Titanium, tetraalkoxytitanium such as tetraphenoxytitanium, titanium tetrachloride, titanium tetrabromide, titanium tetrahalide such as titanium tetraiodide, methoxytitanium trichloride, ethoxytitanium trichloride, propoxytitanium trichloride, n-butoxytitanium trichloride. Trihalogenated alkoxytitanium such as chloride, ethoxytitanium tribromide, dimethoxytitanium dichloride, diethoxytitanium dichloride, dipropoxytitanium dichloride, di Dihalogenated dialkoxytitanium such as n-propoxytitanium dichloride and diethoxytitanium dibromide, monomethoxytrialkoxytitanium such as trimethoxytitanium chloride, triethoxytitanium chloride, tripropoxytitanium chloride and tri-n-butoxytitanium chloride. Among these, a high halogen content titanium compound, particularly titanium tetrachloride is preferable. These titanium compounds may be used alone or in combination of two or more.

Further, as the electron donor, an organic compound containing oxygen, nitrogen, phosphorus, sulfur or the like can be used.
Examples of such electron donors include esters, thioesters, amines, ketones, nitriles, phosphines, ethers, thioethers, acid anhydrides, acid halides, acid amides, aldehydes, and organic compounds. Examples thereof include acids.

Specifically, dimethyl phthalate, diethyl phthalate, dipropyl phthalate, diisobutyl phthalate,
Methyl ethyl phthalate, methyl propyl phthalate,
Methyl isobutyl phthalate, ethyl propyl phthalate, ethyl isobutyl phthalate, propyl isobutyl phthalate, dimethyl terephthalate, diethyl terephthalate, dipropyl terephthalate, diisobutyl terephthalate, methyl ethyl terephthalate, methyl propyl terephthalate, methyl isobutyl terephthalate, ethyl propyl terephthalate, ethyl isobutyl terephthalate, propyl Isobutyl terephthalate,
Aromatic such as dimethylisophthalate, diethylisophthalate, dipropylisophthalate, diisobutylisophthalate, methylethylisophthalate, methylpropylisophthalate, methylisobutylisophthalate, ethylpropylisophthalate, ethylisobutylisophthalate and propylisobutylisophthalate Dicarboxylic acid diester, methyl formate, ethyl acetate,
Vinyl acetate, propyl acetate, octyl acetate, cyclohexyl acetate, ethyl propionate, ethyl butyrate, ethyl valerate, methyl chloroacetate, ethyl dichloroacetate, methyl methacrylate, ethyl crotonate, ethyl pivalate,
Dimethyl maleate, ethyl cyclohexanecarboxylate, ethyl benzoate, propyl benzoate, butyl benzoate, octyl benzoate, cyclohexyl benzoate, phenyl benzoate, benzyl benzoate, ethyl toluate,
Monoesters such as amyl toluate, ethyl anisate, ethyl ethoxybenzoate, ethyl p-butoxybenzoate, ethyl o-chlorobenzoate and ethyl naphthoate,
C2-C18 esters such as r-valerolactone, coumarin, phthalide and ethylene carbonate, organic acids such as benzoic acid and p-oxybenzoic acid, succinic anhydride, benzoic anhydride and p-toluic anhydride C3 to C15 ketones such as acid anhydrides, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzophenone, and benzoquinone, and C2 to C15 aldehydes such as acetaldehyde, octylaldehyde, benzaldehyde, tolualdehyde, and naphthylaldehyde Acids, acetyl chloride, benzyl chloride, toluic acid chloride, anisic acid chloride, and other acid halides having 2 to 15 carbon atoms, methyl ether, ethyl ether, isopropyl ether, n-butyl ether, amyl ether, tetrahydrofuran, aniso , Ethers having 2 to 20 carbon atoms such as diphenyl ether, ethylene glycol butyl ether, acid amides such as acetic acid amide, benzoic acid amide, toluic acid amide, tributylamine, N, N′-dimethylpiperazine, tribenzylamine, aniline, Examples thereof include amines such as pyridine, picoline and tetramethylethylenediamine, nitriles such as acetonitrile, benzonitrile and tolunitrile.

Among these, esters, ethers, ketones and acid anhydrides are preferable, and especially di-n-butyl phthalate,
Aromatic dicarboxylic acid diesters such as diisobutyl phthalate, benzoic acid, p-methoxybenzoic acid, p-ethoxybenzoic acid and alkyl esters of aromatic monocarboxylic acids such as toluic acid having 1 to 4 carbon atoms are preferable. Aromatic dicarboxylic acid diesters are particularly preferred because they improve catalyst activity and activity persistence.

The (b) solid catalyst component can be prepared by a known method (JP-A-53-4309).
4, JP-A-55-135102, JP-A-55-135103
JP, JP-A-56-18606), for example, (1) a magnesium compound or a complex compound of a magnesium compound and an electron donor in the presence of an electron donor and a grinding aid used as desired. Method of pulverizing and reacting with titanium compound, (2) Liquid substance of magnesium compound having no reducing ability and liquid titanium compound are reacted in the presence of electron donor to deposit solid titanium complex Method, (3) a method of reacting a titanium compound with the one obtained in (1) or (2) above, (4) a method obtained by further adding an electron donor to the one obtained in (1) or (2) above. A method of reacting a titanium compound, (5) a magnesium compound or a complex compound of a magnesium compound and an electron donor,
A method of pulverizing in the presence of an electron donor, a titanium compound and optionally a pulverizing aid, and then treating with a halogen or a halogen compound, (6) above (1) to
It can be prepared by a method of treating the compound obtained in (4) with halogen or a halogen compound.

Furthermore, methods other than these (JP-A-56-166205,
JP-A-57-63309, JP-A-57-190004, JP-A-57-300407, JP-A-58-47003) also provides the solid catalyst component (a). You can

Further, oxides of elements belonging to Groups II to IV of the periodic table, for example,
Oxides such as silicon oxide, magnesium oxide, and aluminum oxide, or composite oxides containing at least one oxide of an element belonging to groups II to IV of the periodic table, for example, a solid product obtained by supporting the magnesium compound on silicalumina. Electron donor and titanium compound in a solvent, 0-200
2 minutes to 2 at a temperature in the range of ℃, preferably 10 to 150 ℃
The solid catalyst component can be prepared by contacting for 4 hours.

In preparing the solid catalyst component, an organic solvent inert to magnesium compounds, electron donors and titanium compounds as a solvent, for example, aliphatic hydrocarbons such as hexane and heptane, aromatic carbons such as benzene and toluene. Hydrogen or halogenated hydrocarbons such as saturated or unsaturated aliphatic, alicyclic and aromatic hydrocarbon mono and polyhalogen compounds having 1 to 12 carbon atoms can be used.

Regarding the composition of the (b) solid catalyst component thus prepared, the magnesium / titanium atomic ratio is usually 2 to 10
0, the halogen / titanium atomic ratio is 5 to 200, and the electron donor / titanium molar ratio is 0.1 to 10.

Regarding the ratio of the crystalline polyolefin of (a) to the solid catalyst component of (b) in the solid component of (A),
The weight ratio of component (a) to component (b) is usually 1/30 to 20
It is selected to be 0, preferably 1/10 to 50.

The component (B) of the catalyst system in the present invention, that is, the organoaluminum compound, has the general formula AlR ³ _p X _3-p (II) (wherein R ³ is an alkyl group having 1 to 10 carbon atoms, and X is A halogen atom such as chlorine or bromine, and p is a number of 1 to 3) can be used. Examples of such an aluminum compound include, for example, trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, trialkyl aluminum such as trioctyl aluminum, diethyl aluminum monochloride, diisopropyl aluminum monochloride, diisobutyl aluminum monochloride, dioctyl aluminum. Dialkylaluminum monohalides such as monochloride and alkylaluminum sesquihalides such as ethylaluminum sesquichloride can be preferably used. These aluminum compounds may be used alone or in combination of two or more.

The alkoxy group-containing aromatic compound of the component (C) is
General formula (In the formula, R ¹ , R ² , m and n have the same meanings as described above), such as vinylanisole, p- (1-propenyl) anisole, p-
Monoalkoxy compounds such as allylanisole and 1,3-bis (p-methoxyphenyl) -1-pentene, o
-Dimethoxybenzene, m-dimethoxybenzene, p-
Dimethoxybenzene, 3,4-dimethoxytoluene, 1-
Dialkoxy compounds such as allyl-3,4-dimethoxybenzene and 1,3,5-trimethoxybenzene, 5-allyl-1,2,3-trimethoxybenzene, 5-allyl-1,2,4-
Trimethoxybenzene, 1,2,3-trimethoxy-5-
(1-propenyl) benzene, 1,2,4-trimethoxy-
Examples thereof include trialkoxy compounds such as 5- (1-propenyl) benzene, 1,2,3-trimethoxybenzene, and 1,2,4-trimethoxybenzene. Among these, dialkoxy compounds and trialkoxy compounds are included. Is preferred. These aromatic compounds containing an alkoxy group may be used alone or in combination of two or more.

Regarding the amount of each component of the catalyst system in the present invention,
The solid component of the component (A) is used in an amount of 0.0005 to 1 mmol per reaction volume, calculated as titanium atoms. The organoaluminum compound as the component (B) has an aluminum / titanium atomic ratio of usually 1 to 30.
An amount of 00, preferably 40 to 800 is used, and if the amount deviates from the above range, the catalytic activity may be insufficient. Further, the alkoxy group-containing aromatic compound of the component (C) is used in such a proportion that the molar ratio to the titanium atom in the component (A) is usually 0.01 to 500, preferably 1 to 300. If it is less than 0.01, the physical properties of the produced polymer may be lowered, and if it exceeds 500, the catalytic activity tends to be lowered.

In the method of the present invention, the solid component (A) and the solid component (B)
The α-olefin homopolymer or copolymer is obtained by polymerizing at least one α-olefin in the presence of a catalyst system comprising a combination of an organoaluminum compound of component and an aromatic group-containing aromatic compound of component (C). A polymer is produced. At this time, the component (A), the component (B) and the component (C) are mixed at a predetermined ratio and brought into contact with each other.
The olefin may be introduced immediately to start the polymerization, or the olefin may be introduced after aging for 0.2 to 3 hours after the contact. Furthermore, this catalyst component can be supplied by suspending it in an inert solvent or olefin.

In the method of the present invention, a solventless polymerization method such as gas phase polymerization or bulk polymerization is used as a polymerization mode, and regarding the reaction conditions, the olefin pressure is usually 1 to 50 kg / cm ² G, and the reaction temperature is usually 20. To 200 ° C, preferably 40 to 80 ° C. The molecular weight of the polymer can be adjusted by known means, for example, by adjusting the hydrogen concentration in the polymerization vessel,
It can be carried out. The reaction time depends on the type of olefin as a raw material and the reaction temperature and cannot be determined unconditionally, but 5 minutes to 10 hours is sufficient.

In the method of the present invention, the α-olefin used as a raw material is preferably one having 2 to 10 carbon atoms, such as ethylene, propylene, butene-1, pentene-1, 4
-Methylpentene-1, hexene-1, heptene-1,
Examples include octene-1, nonene-1, decene-1, and the like, which may be used alone or in combination of two or more kinds, or may be used in combination with a non-conjugated diene compound. . Examples of the non-conjugated diene compound include ethylidene norbornene, dicyclopentadiene, 1,4-hexadiene, 4-methyl-1,4-hexadiene and 5-methyl-1,4-hexadiene. As a particularly preferable α-olefin, propylene can be used in the case of homopolymerization, and a combination of ethylene and an α-olefin having 3 to 10 carbon atoms, in particular, propylene can be used in the case of copolymerization. In the case of this copolymerization, the molar ratio of the α-olefin to ethylene is 0.2.
The range of -20 is preferred.

In the present invention, post-treatment after polymerization can be carried out by a conventional method. That is, in the gas phase polymerization method, after the polymerization, a nitrogen stream or the like may be passed through the polymer powder discharged from the polymerization vessel in order to remove the olefin and the like contained therein. If desired, pelletization may be carried out by an extruder, and in this case, a small amount of water, alcohol or the like may be added in order to completely deactivate the catalyst. Further, in the bulk polymerization method, after the polymerization, the monomer can be completely separated from the polymer discharged from the polymerization vessel, and then pelletized.

FIG. 1 is a flow chart showing an example of the embodiment of the present invention.

The olefin polymer thus obtained has a boiling heptane-soluble content of 30% by weight or more, and has excellent properties as a soft olefin polymer.
Therefore, according to the method of the present invention, a soft polypropylene or an olefinic thermoplastic elastomer can be easily obtained.

When the present invention is applied to a gas phase polymerization method, the bulk density is 0.25.
A powdery olefin polymer having a powder fluidity of g / cm ³ or more and having good fluidity can be easily obtained, and an adhered solidified substance is hardly formed.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The invention is in no way limited by these examples.

Example 1 (1) To a glass three-necked flask having an inner volume of 500ml was prepared fully purged with nitrogen of the solid catalyst component (B), purified heptane 2 ml, Mg (OEt) ₂ 4g and phthalate -n- butyl 1.2 g was added, keeping the inside of the system to 90 ° C., then was added dropwise TiCl ₄ 4 ml while stirring, further adding introducing TiCl ₄ 111 ml, heated to 110 ° C., and reacted for 2 hours, then purified 80 ° C. Wash with heptane. Next, 115 ml of TiCl ₄ was added to the obtained solid phase portion, and the mixture was further reacted at 11 g ° C. for 2 hours. After completion of the reaction, the product was washed several times with 110 ml of purified heptane to obtain a solid catalyst component (II).

(2) Preparation of solid component (A) In a pressure-resistant _three- necked glass flask with an internal volume of 2.5, which had been sufficiently replaced with nitrogen, purified heptane 1.7, AlEt ₃ 0.07 mol, diphenyldimethoxysilane (DMDPS) 0.05 mol and the above (1) were obtained. 120 g of the obtained solid catalyst component was added. 30 in the system
Kept at ℃, continuously supplying propylene with stirring,
The internal pressure was maintained at 0.5 kg / cm ² . After the reaction was continued for 1 hour, the solid component (A) was washed 5 times with purified heptane.
[(B) m.p165 ° C.] was obtained.

(3) Polymerization of Propylene In a pressure resistant autoclave made of 5 stainless steel containing 20 g of polypropylene powder, AlEt ₃ 4.0 mmol, 1-allyl-
After adding 20 ml of a heptane solution containing 2.0 mmol of 3,4-dimethoxybenzene and 130 mg of the solid component obtained in (2) above (0.68 mmol of titanium atom), the system was evacuated for 5 minutes and then the temperature was changed.
Polymerization of propylene was carried out for 2 hours under the conditions of 55 ° C. and a polymerization pressure of 20 kg / cm ² . The results are shown in Table 1.

Examples 2 to 4 The same as Example 1 except that the reaction time in the preparation of the solid component (A) of (2) in Example 1 was changed to change the molar ratio of component (a) / component (b). Carried out. The results are shown in Table 1.

Comparative Example 1 In the polymerization of propylene of (3) in Example 1,
Example 1 was repeated except that the solid catalyst component (b) was used instead of the solid component (A). The results are shown in Table 1.

Example 5 It implemented like Example 1 except having changed the preparation method of the solid component (A) of (2) in Example 1 as follows. The results are shown in Table 1.

That is, in a _three- necked flask having an internal volume of 500 ml sufficiently replaced with nitrogen, heptane 400 ml, polypropylene powder (a) 90 g, AlEt ₃ 0.01 mol, diphenyldimethoxysilane 0.005 mol and a solid catalyst component (b) 30 g, while stirring, After stirring for 15 minutes, the upper portion was removed and then vacuum dried to prepare a solid component (A) [m.p 165 ° C. of (a)].

Example 6 In the preparation of the solid component (A) of (2) in Example 1, a solid component (A) [m.p 240 ° C. of (a)] was prepared by using 4-methylpentene-1 instead of propylene. The same procedure as in Example 1 was carried out except the above. The result is first
Shown in the table.

[Effect of the Invention] According to the method of the present invention, a solvent-free polymerization method using a specific catalyst system is industrially useful as a flexible polypropylene or olefinic thermoplastic elastomer having a boiling heptane-soluble content of 30% by weight or more. It is possible to efficiently produce such an olefin polymer. Especially by the gas phase polymerization method,
A powdery olefin polymer having a bulk density of 0.25 g / cm ³ or more and good powder fluidity can be easily produced without the problem of formation of an adherent solidified product.

[Brief description of drawings]

FIG. 1 is a drawing showing the steps for preparing a catalyst used in the method of the present invention.

Claims (2)

[Claims] 1. A crystalline polyolefin (A) (a),
(B) A solid catalyst component composed of magnesium, titanium, a halogen atom and an electron donor, which is a magnesium compound and a general formula Ti (OR ⁴ ) _k X _4-k (wherein R ⁴ is an alkyl group or a cycloalkyl group) Or a phenyl group, X is a halogen atom, k is an integer of 0 to 4), and a solid component composed of a solid catalyst component prepared by contacting the titanium compound with an electron donor, B) an organoaluminum compound and (C) a general formula (In the formula, R ¹ is an alkyl group having 1 to 20 carbon atoms, and R ² is 1 carbon atom.
To 10 hydrocarbon groups, m is an integer from 1 to 6, and n is (6-m)
An olefin is polymerized in the presence of a catalyst system comprising a combination of alkoxy group-containing aromatic compounds represented by to produce an olefin polymer having a boiling heptane-soluble content of 30% by weight or more. Solventless polymerization of olefins characterized by: 2. The solvent-free olefin polymerization method according to claim 1, wherein a powdery olefin polymer having a bulk density of 0.25 g / cm ³ or more is produced by a gas phase polymerization method.