Catalyst and process for producing conjugated diene polymer

Abstract: A catalyst obtained by contacting (A) a compound of a transition metal of the group V of the Periodic Table represented by formula (I): R n M(O) m X p ·L a wherein M represents a transition metal of the group V of the Periodic Table; R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group or a substituted fluorenyl group; O represents an oxygen atom; X represents a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group, an aryloxy group or an amido group; L represents a Lewis basic compound; n, m, and p each represent an integer selected to make a combination of (n=1, m=1, p=2), (n=1, m=0, p=3), (n=2, m=0, p=1) or (n=1, m=0, p=2); and a represents 0, 1 or 2, and (B) at least one of (B1) an ionic compound comprising a non-coordinating anion and a cation and (B2) an aluminoxane, provided that the component (B) is an ionic compound comprising a non-coordinating anion and a cation (B1) when the combination of n, m, and p of the component (A) is (n=2, m=0, p=1) or (n=1, m=0, p=2).

Description: This invention relates to a novel catalyst comprising a compound of a transition metal of the group V of the Periodic Table, a process for producing a conjugated diene polymer using the catalyst, and polybutadiene having a specific structure. BACKGROUND OF THE INVENTION Catalyst systems comprising a metallocene complex of a transition metal, e.g., Ti, Zr or Hf, and an organoaluminum-oxy compound, e.g., methylaluminoxane, have been attracting attention as a catalyst for olefin polymerization. They have high activity particularly in copolymerization of ethylene and an α-olefin to provide excellent polymers having narrow molecular weight distribution and narrow composition distribution. These catalysts are described in detail in, e.g., J.M.S. - Rev. Macromol. Chem. Phys. , C34, No. 3, p. 439 (1994). Catalyst systems containing a compound of a transition metal, e.g., Ti, V, Co, Ni or Nd, are known for catalysis in coordination anionic polymerization of conjugated dienes, such as butadiene and isoprene. For example, a method of using VCl 3 -AlR 3 as a catalyst of conjugated diene polymerization is reported, e.g., in Chim. e Ind., Vol. 40, p. 362 (1958). The result as reported, however, is production of crystalline polybutadiene having nearly 100% of a trans structure, and the catalyst has extremely low polymerization activity. International Rubber Conference Kobe, Preprint, 25C-4 (1995) reports that V(acac)3-methylaluminoxane provides polybutadiene comprising a cis structure, a trans structure, and a 1,2-structure in a proportion of 63%, 14%, and 21%, respectively, but the catalyst activity is still low. Polymerization of conjugated diene by using a metallocene catalyst of the group IV transition metal (e.g., Ti or Zr) is reported in Macromolecular Symposia, Vol. 89, p. 383 (1995), in which a catalyst system containing cyclopentadienyltitanium trichloride [(η 5 C 5 H 5 )TiCl 3 ] is used. The activity of this catalyst system in conjugated diene polymerization is not deemed sufficient because the polymerization activity of (η 5 c 5 H 5 )TiCl 3 -methylaluminoxane, for instance, is, as reported, 100 g/mmol-Ti/hr at the most. Macromolecular Symposia, Vol. 4, p. 103 (1986) reports copolymerization of ethylene and butadiene in the presence of a combination of bis(cyclopentadienyl)zirconium dichloride [(η 5 C 5 H 5 ) 2 ZrCl 2 ]and methylaluminoxane, but the report has no mention of the comonomer composition of the resulting polymer. Neither does the report refer to homopolymerization of butadiene. The reported catalyst activity is very low. With regards to a polymerization catalyst comprising a metallocene compound of vanadium (V), the group V transition metal, JP-64-66216 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") (U.S. Patent 5,204,429), JP-W-63-501962 (the term "JP-W" as used herein means an "unexamined published international patent application") (U.S. Patents 4,752,597 and 4,791,180), and JP-W-1-501633 (U.S. Patents 5,191,052, 4,808,561 and 4,897,455) disclose a combination of a metallocene compound of vanadium and an aluminoxane as a catalyst for copolymerization of an olefin and a diene. These publications refer to bis(cyclopentadienyl)vanadium dichloride [(η 3 C 5 H 5 ) 2 VCl 2 ] as an illustrative example of the vanadium metallocene compounds without giving any working example using this particular compound. JP-B-46-20494 (the term "JP-B" as used herein means an "examined published Japanese patent application") discloses a process for producing polybutadiene using a catalyst system comprising a cyclopentadienyl complex of vanadium, a halogen-containing organoaluminum compound, an oxygen-containing compound. (C 5 H 5 )VCl 3 is mentioned as an example of the cyclopentadienyl complex of vanadium, but its polymerization activity is problematically low. According to the disclosure, it is essential for the organoaluminum compound, which serves as a co-catalyst, to contain a halogen component. For example, a working example using (C 5 H 5 )VCl 3 -Al(i-Bu) 3 /AlCl 3 is given, but the polymerization activity attained in that example is 350 g/mmol-V/hr at the most. Polymer , Vol. 37 (2), p. 363 (1996) describes a process for producing polybutadiene, in which a catalyst comprising a vanadium (III) compound, e.g., (substituted C 5 H 5 )VCl 2 ·(PR 3 ) 2 or (substituted C 5 H 5 ) 2 VCl, and methylaluminoxane is used to obtain polybutadiene of high cis structure having a 1,2-structure content of 10 to 20%. The polymerization activity of the catalyst is low however. It is known that conjugated diene polymers take various microstructure depending on the polymerization catalyst used. While polybutadiene, for instance, is generally prepared by polymerization of 1,3-butadiene, polybutadiene as produced comprises different microstructures in its molecular chain, i.e., a structural unit produced through 1,4-addition (1,4-structure) and a structural unit produced through 1,2-addition (1,2-structure), due to the difference in mode of addition. The 1,4-structure is further divided into a cis-1,4-structure and a trans-1,4-structure. The 1,2-structure has a vinyl group as a side chain and can have an isotactic structure, an syndiotactic structure, and an atactic structure. The above-described macrostructure varies depending on the catalyst of polymerization, and polybutadiene species having different microstructures find their respective uses according to their characteristics. In particular, polybutadiene mainly comprising a cis structure and a moderate proportion of a 1,2-structure is expected as an impact modifier for plastics such as polystyrene. Polybutadiene produced by using a butyllithium catalyst is known for use in high impact polystyrene (HIPS). Since it has a smaller content of a cis structure than the one produced by using a cobalt catalyst, an improvement in viscosity and the like has been demanded in the production of HIPS. Cobalt catalyst systems that provide polybutadiene containing both a cis structure and a 1,2-structure include a catalyst system comprising a phosphate, an organoaluminum compound, water, and a cobalt compound and a catalyst system comprising an organoaluminum compound, water, and a cobalt dithiocarbamate compound as disclosed in JP-A-55-129403 and JP-A-59-232106. These catalysts sometimes provide polybutadiene having a low molecular weight, or they are not deemed to have sufficient catalyst activity. JP-B-62-16201 discloses a process of using a catalyst system comprising a cobalt salt, a dialkylaluminum monohalide, and a dihydric alcohol. According to the disclosure, the resulting polybutadiene comprises 4 to 20% of a 1,2-structure, 75 to 95% of a cis-1,4-structure, and not more than 4% of a trans-1,4-structure, in which the content of 1,2-structures distributed at random is higher than the content of those connected to each other to form blocks, and is suitable for the production of HIPS. For use as an impact modifier, polybutadiene must have a controlled molecular weight. For example, in the preparation of polybutadiene having a high cis content by using the above-described cobalt compound-organoaluminum compound catalyst system, it has been proposed to add a non-conjugated diene compound, such as cyclooctadiene, to the polymerization system as disclosed in JP-B-35-495. However, addition of cyclooctadiene to the polymerization system comprising a metallocene complex of the group V transition metal unsuccessfully produces a sufficient effect for molecular weight reduction, only to lead to reduced polymerization activity. JP-B-52-32912 (U.S. Patent 3,983,183) and JP-B-56-50894 (U.S. Patent 3,966,697) disclose a process for producing polybutadiene having a high 1,2-structure content by using a specific catalyst system. The Examples of the disclosures reveal that an increase in molecular weight of polybutadiene results in an increase in gel content. A polybutadiene production system is liable to suffer from gelation in the polymer or the polymerization vessel. Gelation becomes conspicuous as the molecular weight increases. It is important for high-molecular weight polybutadiene, which is generally used as a mixture with an oil extender or a low-molecular polymer, to have an extremely low gel content formed during polymerization. JP-B-3-57128 shows a process for producing polybutadiene having a cis-1,4-structure content of 50% or higher, a 1,2-structure content of 7 to 50%, an intrinsic viscosity of not less than 1, and a gel content of not more than 0.03%, which comprises using a catalyst system comprising a halogenated organoaluminum compound, a cobalt dithiocarbamate compound, water, and a free radical scavenger. However, the intrinsic viscosity of the polybutadiene obtained in the Examples is 2.5 at the most. SUMMARY OF THE INVENTION An object of the present invention is to provide a polymerization catalyst comprising a compound of a transition metal of the group V of the Periodic Table as defined below. Another object of the invention is to provide a process for producing a controlled conjugated diene polymer using the above catalyst with high activity. A further object of the invention is to provide polybutadiene having a specific structure which is effective as an impact modifier for HIPS. Other objects and effects of the present invention will be apparent from the following description. The present invention relates to a catalyst obtained by contacting (A) a compound of a transition metal of the group V of the Periodic Table represented by formula (I): R n M(O) m x p •L a wherein M represents a transition metal of the group V of the Periodic Table; R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group or a substituted fluorenyl group; O represents an oxygen atom; X represents a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group, an aryloxy group or an amido group; L represents a Lewis basic compound; n, m, and p each represent an integer selected to make a combination of (n=1, m=1, p=2), (n=1, m=0, p=3), (n=2, m=0, p=1) or (n=1, m=0, p=2); and a represents 0, 1 or 2, and (B) at least one ionic compound comprising a non-coordinating anion and a cation. In a preferred embodiment, the catalyst obtained by contacting the components (A) and (B) and (C) an organic compound of the group I, II or III metal of the Periodic Table. The present invention also relates to a catalyst comprising the components (A) and (B), preferably comprising components (A), (B) and (C). The present invention further relates to a process for producing a conjugated diene polymer comprising a step of polymerizing a conjugated diene in the presence of the above-described catalysts. DETAILED DESCRIPTION OF THE INVENTION In formula (I) representing component (A) of the catalyst of the invention, the transition metal of the group V as represented by M represents vanadium (V), niobium (Nb), and tantalum (Ta), with vanadium being preferred. R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group or a substituted fluorenyl group. Examples of substituents in the substituted cyclopentadienyl group, substituted indenyl group or substituted fluorenyl group include hydrocarbon groups which may contain a silicon atom, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a hexyl group, a phenyl group, a benzyl group, and a trimethylsilyl group. A cyclopentadienyl ring as R and part of X may be bonded together via a linking group, such as a dimethylsilyl group, a dimethylmethylene group, a methylphenylmethylene group, a diphenylmethylene group, an ethylene group or a substituted ethylene group. Examples of the substituted cyclopentadienyl group include methylcyclopentadienyl, benzylcyclopentadienyl, vinylcyclopentadienyl, 2-methoxyethylcyclopentadienyl, trimethylsilylcyclopentadienyl, t-butylcyclopentadienyl, ethylcyclopentadienyl, phenylcyclopentadienyl, 1,2-dimethylcyclopentadienyl, 1,3-dimethylcyclopentadienyl, 1,3-di(t-butyl)cyclopentadienyl, 1,2,3-trimethylcyclopentadienyl, 1,2,3,4-tetramethylcyclopentadienyl, pentamethylcyclopentadienyl, 1-ethyl-2,3,4,5-tetramethylcyclopentadienyl, 1-benzyl-2,3,4,5-tetramethylcyclopentadienyl, 1-phenyl-2,3,4,5-tetramethylcyclopentadienyl, 1-trimethylsilyl-2,3,4,5-tetramethylcyclopentadienyl, and 1-trifluoromethyl-2,3,4,5-tetramethylcyclopentadienyl groups. Examples of the substituted indenyl group include 1,2,3-trimethylindenyl, heptamethylindenyl and 1,2,4,5,6,7-hexamethylindenyl groups. R in formula (I) preferably represents a cyclopentadienyl group, a mono-substituted cyclopentadienyl group (e.g., ethylcyclopentadienyl group, a benzylcyclopentadienyl group or a methylcyclopentadienyl group) or an indenyl group. X in formula (I) represents a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group or an amido group. Examples of the halogen includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a chlorine atom being preferred. Examples of the hydrocarbon group having 1 to 20 carbon atoms include straight-chain or branched aliphatic hydrocarbons, such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, neopentyl, hexyl and octyl groups; and aromatic hydrocarbon groups, such as phenyl, tolyl, naphthyl and benzyl groups. Hydrocarbon groups containing a silicon atom, such as trimethylsilylmethyl and bistrimethylsilylmethyl groups, are also included. Preferred of these hydrocarbon groups are methyl, benzyl and trimethylsilylmethyl groups. Examples of the alkoxy group include methoxy, ethoxy, propoxy, butoxy, and t-butoxy groups. Additionally, amyloxy, hexyloxy, octyloxy, 2-ethylhexyloxy and thiomethoxy groups are also included. Examples of the aryloxy group include a phenoxy group. Preferred of these alkoxy groups and aryloxy groups are methoxy, t-butoxy, and phenoxy groups. Examples of the amido group include dimethylamido, diethylamido, and diisopropylamido groups, with a dimethylamido group and a diethylamido group being preferred. L in formula (I) represents a Lewis basic compound, i.e., a general organic or inorganic compound exhibiting Lewis basicity that can coordinate to a metal element with its counter electron. Compounds having no active hydrogen are preferred. Examples of such compounds include ethers, esters, ketones, amines, phosphines, and silyloxy compounds. The compounds represented by formula (I) include RMX 3 , RM(O)X 2 , R 2 MX•L a , RmX 2 •L a , and the like. In particular, vanadium compounds (where M is V), such as RVX 3 , RV(O)X 2 , R 2 VX•La, and RVX 2 •L a , are preferred. Specific examples of RMX 3 include the following compound groups (1) to (17): (1) Cyclopentadienylvanadium trichloride; (2) Mono-substituted cyclopentadienylvanadium trichloride: Methylcyclopentadienylvanadium trichloride, Ethylcyclopentadienylvanadium trichloride, Propylcyclopentadienylvanadium trichloride, Isopropylcyclopentadienylvanadium trichloride, t-Butylcyclopentadienylvanadium trichloride, Benzylcyclopentadienylvanadium trichloride, (1,1-Dimethylpropyl)cyclopentadienylvanadium trichloride, (1,1-Dimethylbenzyl)cyclopentadienylvanadium trichloride, (1-Ethylpropyl)cyclopentadienylvanadium trichloride, (1-Ethyl-1-methylpropyl)cyclopentadienylvanadium trichloride, (Diethylbenzyl)cyclopentadienylvanadium trichloride, (Trimethylsilylcyclopentadienyl)vanadium trichloride, [Bis(trimethylsilyl)cyclopentadienyl]vanadium trichloride; (3) 1,3-Substituted cyclopentadienylvanadium trichloride: (1,3-Dimethylcyclopentadienyl)vanadium trichloride, (1-Methyl-3-ethylcyclopentadienyl)vanadium trichloride, (1-Methyl-3-propylcyclopentadienyl)vanadium trichloride, [1-Methyl-3-bis(trimethylsilyl)silylcyclopentadienyl] vanadium trichloride, (1-Methyl-3-phenylcyclopentadienyl)vanadium trichloride, (1-Methyl-3-tolylcyclopentadienyl)vanadium trichloride, [1-Methyl-3-(2,6-dimethylphenyl)cyclopentadienyl]-vanadium trichloride, (1-Methyl-3-butylcyclopentadienyl)vanadium trichloride; (4) 1,2,3-Trisubstituted cyclopentadienylvanadium trichloride: (1,2,3-Trimethylcyclopentadienyl)vanadium trichloride, (1,2,3-Triethylcyclopentadienyl)vanadium trichloride, (1,2,3-Triphenylcyclopentadienyl)vanadium trichloride; (5) 1,2,4-Trisubstituted cyclopentadienylvanadium trichloride: (1,2,4-Trimethylcyclopentadienyl)vanadium trichloride, (1,2,4-Triethylcyclopentadienyl)vanadium trichloride, (1,2,4-Triphenylcyclopentadienyl)vanadium trichloride; (6) Tetrasubstituted cyclopentadienylvanadium trichloride: (1,2,3,4-Tetramethylcyclopentadienyl)vanadium trichloride, (1,2,3,4-Tetraphenylcyclopentadienyl)vanadium trichloride; (7) Pentasubstituted cyclopentadienylvanadium trichloride: (Pentamethylcyclopentadienyl)vanadium trichloride, (1,2,3,4-Tetramethyl-5-phenylcyclopentadienyl)vanadium trichloride, (1,2,3,4-Tetraphenyl-5-methylcyclopentadienyl)vanadium trichloride, (Pentaphenylcyclopentadienyl)vanadium trichloride; (8) Indenylvanadium trichloride; (9) Substituted indenylvanadium trichloride: (2-Methylindenyl)vanadium trichloride, (2-Trimethylsilylindenyl)vanadium trichloride; (10) The compounds (1) to (9) with one or two of the chlorine atoms displaced with an alkoxy group(s) (i.e., monoalkoxides or dialkoxides): Cyclopentadienylvanadium t-butoxydichloride, Cyclopentadienylvanadium isopropoxydichloride, Cyclopentadienylvanadium dimethoxychloride, Cyclopentadienylvanadium di-isopropoxychloride, Cyclopentadienylvanadium di-t-butoxychloride, Cyclopentadienylvanadium diphenoxychloride, Cyclopentadienylvanadium isopropoxydichloride, Cyclopentadienylvanadium t-butoxydichloride, Cyclopentadienylvanadium phenoxydichloride; (11) The compounds (1) to (10) with the chlorine atom(s) displaced with 1 to 3 methyl groups; (12) Compounds in which R and X are bonded via a hydrocarbon group or a hydrocarbon silyl group: (t-Butylamido)dimethylsilyl(η 5 -cyclopentadienyl)vanadium dichloride, (t-Butylamido)dimethylsilyl(trimethyl-η 5 -cyclopentadienyl)vanadium dichloride, (t-Butylamido)dimethylsilyl(tetramethyl-η 5 -cyclopentadienyl)vanadium dichloride; (13) The compounds (12) with their chlorine atom(s) displaced with 1 or 2 methyl groups; (14) The compounds (12) with their chlorine atoms(s) displaced with 1 or 2 alkoxy groups; (15) The monochloride compounds of the compounds (14) with the chlorine atom displaced with a methyl group; (16) The compounds (1) to (10) with their chlorine atom(s) displaced with an amido group(s): (Cyclopentadienyl)tris(diethylamido)vanadium, (Cyclopentadienyl)tris(isopropylamido)vanadium, (Cyclopentadienyl)tris(n-octylamido)vanadium, (Cyclopentadienyl)bis(diethylamido)vanadium chloride, (Cyclopentadienyl)bis(isopropylamido)vanadium chloride, (Cyclopentadienyl)bis(n-octylamido)vanadium chloride, (Cyclopentadienyl)diethylamidovanadium dichloride, (Cyclopentadienyl)isopropylamidovanadium dichloride, (Cyclopentadienyl)n-octylamidovanadium dichloride; (17) Fluorenylvanadium trichloride, in which the chlorine atom(s) thereof may be displaced with a methyl group(s), an alkoxy group(s) and/or an amido group(s). Specific examples of R n M(O)X 2 include the following compound groups (18) to (25): (18) Cyclopentadienyloxovanadium dichloride; (19) Substituted cyclopentadienyloxyvanadium dichloride: Methylcyclopentadienyloxovanadium dichloride, 1,3-Dimethylcyclopentadienyloxovanadium dichloride, 1-Methyl-3-butylcyclopentadienyloxovanadium dichloride, Pentamethylcyclopentadienyloxovanadium dichloride, Trimethylsilylcyclopentadienyloxovanadium dichloride, 1,3-Di(trimethylsilyl)cyclopentadienyloxovanadium dichloride, Indenyloxovanadium dichloride, 2-Methylindenyloxovanadium dichloride, 2-Trimethylsilylindenyloxovanadium dichloride, Fluorenyloxovanadium dichloride; (20) The compounds (18) to (19) with 1 or 2 of the chlorine atoms displaced with 1 to 2 methyl groups: (21) Compounds in which R and X are bonded via a hydrocarbon group or a hydrocarbon silyl group: Amidochloride compounds, e.g., (t-butylamido)dimethylsilyl(η 5 -cyclopentadienyl)silaneoxovanadium chloride, (t-butylamido)dimethylsilyl(tetramethyl-η 5 -cyclopentadienyl)silaneoxovanadium chloride; and these compounds with their chlorine atom substituted with a methyl group. (22) Compounds in which X is an alkoxy group: Cyclopentadienyloxovanadium dimethoxide, Cyclopentadienyloxovanadium di-isopropoxide, Cyclopentadienyloxovanadium di-t-butoxide, Cyclopentadienyloxovanadium diphenoxide, Cyclopentadienyloxovanadium methoxychloride, Cyclopentadienyloxovanadium isopropoxychloride, Cyclopentadienyloxovanadium t-butoxychloride, Cyclopentadienyloxovanadium phenoxychloride; (23) The compounds (22) with their chlorine atom displaced with a methyl group; (24) Compounds in which X is an amido group: (Cyclopentadienyl)bis(diethylamido)oxovanadium, (Cyclopentadienyl)bis(di-isopropylamido)oxovanadium, (Cyclopentadienyl)bis(di-n-octylamido)oxovanadium; (25) The compounds (24) with their amido group displaced with a methyl group. Specific examples of RMX 2 •L a include the following compound groups (26) to (30): (26) Dichloride compounds, e.g., cyclopentadienylvanadium dichloride, methylcyclopentadienylvanadium dichloride, (1,3-dimethylcyclopentadienyl)vanadium dichloride, (1-methyl-3-butylcyclopentadienyl)vanadium dichloride, (pentamethylcyclopentadienyl)vanadium dichloride, (trimethylsilylcyclopentadienyl)vanadium dichloride, [1,3-di(trimethylsilyl)cyclolpentadienyl)vanadium dichloride, indenylvanadium dichloride, (2-methylindenyl)vanadium dichloride, (2-trimethylsilylindenyl)vanadium dichloride, and fluorenylvanadium dichloride; and compounds derived therefrom by displacing the chlorine atoms with methyl groups. (27) Compounds in which R and X are connected via a hydrocarbon group or a silyl group, such as amidochloride compounds, e.g., (t-butylamido)dimethylsilyl(η 5 -cyclopenta dienyl)vanadium chloride and (t-butylamido)dimethylsilyl-(tetramethyl -η5-cyclopentadienyl)vanadium chloride; and compounds derived therefrom by displacing the chlorine atom with a methyl group. (28) Alkoxide compounds, such as cyclopentadienylvanadium dimethoxide, cyclopentadienylvanadium di-isopropoxide, cyclopentadienylvanadium di-t-butoxide, cyclopentadienylvanadium diphenoxide, cyclopentadienylvanadium methoxychloride, cyclopentadienylvanadium isopropoxychloride, cyclopentadienylvanadium t-butoxychloride, and cyclopentadienylvanadium phenoxychloride; and compounds derived therefrom by displacing the chlorine atom with a methyl group. (29) Bisamide compounds, such as (cyclopentadienyl)bis(diethylamido)vanadium, (cyclopentadienyl)bis(di-isopropylamido)vanadium, and (cyclopentadienyl)bis(di-n-octylamido)vanadium. (30) Phosphine complexes, such as cyclopentadienylvanadium dichloride bistriethylphosphine complex, cyclopentadienylvanadium dichloride bistrimethylphosphine complex, (cyclopentadienyl)bis(di-isopropylamido)vanadium trimethylphosphine complex, and monomethylcyclopentadienylvanadium dichloride bistriethylphosphine complex. Specific examples of R 2 MX•L a include the following compound groups (31) to (33): (31) Chloride compounds, e.g., dicyclopentadienylvanadium chloride, bis(methylcyclopentadienyl)vanadium chloride, bis(1,3-dimethylcyclopentadienyl)vanadium chloride, bis(1-methyl-3-butylcyclopentadienyl)vanadium chloride, bis(pentamethylcyclopentadienyl)vanadium chloride, bis(trimethylsilylcyclopentadienyl)vanadium chloride, bis(1,3-di(trimethylsilyl)cyclopentadienyl)vanadium chloride, diindenylvanadium chloride, bis(2-methylindenyl)vanadium chloride, bis(2-trimethylsilylindenyl)vanadium chloride, and difluorenylvanadium chloride; and compounds derived therefrom by displacing the chlorine atom with a methyl group. (32) Dicyclopentadienylvanadium methoxide, dicyclopentadienylvanadium isopropoxide, dicylopentadienylvanadium t-butoxide, dicyclopentadienylvanadium phenoxide, dicyclopentadienyldiethylamidovanadium, dicyclopentadienyldi(isopropylamido)vanadium, and dicyclopentadienyldi(n-octylamido)vanadium. (33) Compounds in which R and X are connected via a hydrocarbon group or a hydrocarbon silyl group, such as dimethylsilylbis(η 5 -cyclopentadienyl)vanadium chloride and dimethylsilylbis(tetramethyl-η 5 -cyclopentadienyl)vanadium chloride; and compounds derived therefrom by displacing the chlorine atom with a methyl group. The compounds represented by RVCl 3 or RV(O)Cl 2 are synthesized through, for example, the following route. VCl 4 or VCl 3 is reacted with an organometallic compound, e.g., RLi, RNa or RMgCl, to prepare R 2 VCl 2 or R 2 VCl, which is then treated with thionyl chloride SOCl 2 to synthesize RVCl 3 . Treatment of RVCl 3 with oxygen gives RV(O)Cl 2 . Examples of the ionic compound composed of a non-coordinating anion and a cation as component (B) includes ionic compounds capable of reacting with the transition metal compound as component (A) to produce a cationic transition metal compound. Examples of the non-coordinating anion includes tetraphenylborate, tetrakis(monofluorophenyl)borate, tetrakis(difluorophenyl)borate, tetrakis(trifluorophenyl)borate, tetrakis(tetrafluorophenyl)borate, tetrakis(pentafluorophenyl)borate, tetrakis(tetrafluoromethylpheyl)borate, tetratolylborate, tetraxylylborate, triphenyl(pentafluorophenyl)borate, tris(pentafluorophenyl)phenylborate, and tridecahydride 7,8-dicarbaundecaborate. Examples of the cation includes a carbonium cation, an oxonium cation, an ammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, and a ferrocenium cation having a transition metal. Examples of the carbonium cation include tri-substituted carbonium cations, e.g., a triphenylcarbonium cation and a tri(substituted phenyl)carbonium cation (e.g., a tri(methylphenyl)carbonium cation and a tri(dimethylphenyl)carbonium cation. Examples of the ammonium cation include trialkylammonium cations, such as a trimethylammonium cation, a triethylammonium cation, a tripropylammonium cation, a tributylammonium cation, a tri(n-butyl)ammonium cation; N,N-dialkylanilinium cations, such as an N,N-diethylanilinium cation, an N,N-diemthylanilinium cation and an N,N-dimethyl-2,4,6-trimethylanilinium cation; and dialkylammonium cations, such as a diisopropylammonium cation and a dicyclohexylammonium cation. Examples of the phosphonium cation include triarylphosphonium cations, such as a triphenylphosphonium cation, a trimethylphenylphosphonium cation, and a tri(dimethylphenyl)phosphonium cation. These non-coordinating anions and cations are combined arbitrarily to provide an appropriate ionic compound. Of the ionic compounds, preferred are triphenylcarbonium tetrakis(pentafluorophenyl)borate, triphenylcarbonium tetrakis(tetrafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, and 1,1' -dimethylferrocenium tetrakis(pentafluorophenyl)borate. These ionic compounds may be used either individually or as a combination of two or more thereof. In the present invention, polymerization of a conjugated diene can be carried out in the presence of (C) an oganometallic compound of the group I to III element of the Periodic Table in combination with components (A) and (B). Addition of component (C) is effective in increasing the polymerization activity of the catalyst of the invention. Examples of the organometallic compound of the group I to III element includes organoaluminium compounds, organolithium compounds, organomagnesium compounds, organozinc compounds and organoboron compounds. Examples of the organometallic compound as component (C) are methyllithium, butyllithium, phenyllithium, benzyllithium, neopentyl lithium, trimethylsilylmethyl lithium, bistrimethylsilylmethyl lithium, dibutylmagnesium, dihexylmagnesium, diethylzinc, dimethylzinc, trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, and tridecylaluminum. Further, organic metal halides, such as ethylmagnesium chloride, butylmagnesium chloride, dimethylaluminum chloride, diethylaluminum chloride, sesquiethylaluminum chloride, and ethylaluminum dichloride; and organic metal hydrides, such as diethylaluminum hydride and sesquiethylaluminum hydride, are also useful as component (C). These organometallic compounds may be used either individually or as a combination or two or more thereof. Alternatively, an aluminoxane may be used as component (C). Aluminoxane is an organoaluminum-oxy compound obtained by contacting an organoaluminum compound with a condensing agent and includes an acyclic or cyclic aluminoxane represented by formula (-Al(R')O-) n , wherein R' represents a hydrocarbon group having 1 to 10 carbon atoms, part of which may be substituted with a halogen atom and/or an alkoxy group; and n represents a degree of polymerization of 5 or more, (preferably 10 or more). R' preferably represents a methyl, ethyl, propyl or isobutyl group, with a methyl group being preferred. Examples of the organoaluminum compound which can be used as a starting material of the aluminoxane includes trialkylaluminum compounds, e.g., trimethylaluminum, triethylaluminum, and triisobutylaluminum, and mixtures thereof. Trimethylaluminum is particularly preferred. An aluminoxane obtained from a mixture of trimethylaluminum and tributylaluminum can preferably be used. An aluminoxane having satisfactory solubility in aliphatic hydrocarbons is particularly suitable. Typical examples of the condensing agent include water. In addition, arbitrary condensing agents causing condensation of trialkylaluminum compounds, such as adsorbed water of an inorganic substance or a diol, can also be used. While the ratio of the catalyst components varies depending on various conditions, a preferred molar ratio of the transition metal compound as component (A) to the component (B) is 1/0.1 to 1/10, particularly 1/0.2 to 1/5. A preferred molar ratio of the transition metal compound as component (A) to the organometallic compound as component (C) is 1/0.1 to 1/1000, particularly 1/0.2 to 1/500. While not limiting, the catalyst components are added, e.g., in the following order: (1) Component (A) is added to a contact mixture of a conjugated diene monomer to be polymerized and component (B). (2) Component (B) is added to a contact mixture of a conjugated diene monomer to be polymerized and component (C), and component (A) is then added thereto. (3) A transition metal compound as component (A) is added to a contact mixture of a conjugated diene monomer to be polymerized and component (C), and component (B) is then added. The order of addition (3) is preferred. The catalyst of the invention and/or the individual catalyst component(s) thereof can be used as supported on an inorganic compound or an organic high polymeric compound. Examples of inorganic compounds useful as a carrier preferably include inorganic oxides, inorganic chlorides, and inorganic hydroxides. These inorganic compounds may contain a small amount of a carbonate or a sulfate. Inorganic oxides, such as silica, alumina, magnesia, titania, zirconia, and calcia, are particularly preferred. The inorganic compounds are preferably used in the form of fine porous particles having an average particle size of 5 to 150 µm and a specific surface area of 2 to 800 m 2 /g. The inorganic compound particles can be used after heat treatment, e.g., at 100 to 800°C. Examples of the organic high polymeric compounds useful as a carrier preferably include those having an aromatic ring, a substituted aromatic ring or a functional group, e.g., a hydroxyl group, a carboxyl group, an ester group or a halogen atom, in the side chain thereof. Examples of such compounds include α-olefin homo- or copolymers having the functional group obtained by chemical modification of polyethylene, polypropylene, polypolybutene, etc., homo- or copolymers of acrylic acid, methacrylic acid, vinyl chloride, vinyl alcohol, styrene, divinylbenzene, etc., and chemically modified polymers thereof. These organic high polymeric compounds are usually used in the form of spherical fine particles having an average particle size of 5 to 250 µm. The language "a conjugated diene monomer to be polymerized" as used above means the whole amount or a part of a conjugated diene monomer to be polymerized. In the latter case, the "contact mixture" as referred to above can be mixed with the rest of the conjugated diene monomer. Examples of the conjugated diene monomer are 1,3-butadiene, isoprene, 1,3-pentadiene, 2-ethyl-1,3-butadiene, 2,3-dimethylbutadiene, 2-methylpentadiene, 4-methylpentadiene, and 2,4-hexadiene. 1,3-Butadiene is particularly preferred. These conjugated diene monomers may be used either individually or a combination of two or more thereof. The monomer to be polymerized may be a mixture of a conjugated diene and a minor proportion of other monomers. Other monomers that may be present include acyclic monoolefins, e.g., ethylene, propylene, butene-1, butene-2, isobutene, pentene-1, 4-methylpentene-1, hexene-1, and octene-1; cyclic monoolefins, e.g., cyclopentene, cyclohexene, and norbornene; and/or aromatic vinyl compounds, e.g., styrene and α-methylstyrene; and non-conjugated diolefins, e.g., dicyclopentadiene, 5-ethylidene-2-norbornene, and 1,5-hexadiene. The polymerization system is not particularly limited, and bulk polymerization, solution polymerization, gas phase polymerization, and the like can be adopted. Useful solvents for solution polymerization include aromatic hydrocarbons, e.g., toluene, benzene, and xylene; aliphatic hydrocarbons, e.g., n-hexane, butane, heptane, and pentane; alicyclic hydrocarbons, e.g., cyclopentane and cyclohexane; olefinic hydrocarbons, e.g., 1-butene, cis-2-butene, and trans-2-butene; hydrocarbon solvents, such as mineral spirit, solvent naphtha and kerosine; and halogenated hydrocarbons, e.g., methylene chloride. 1,3-Butadiene as a monomer may also serve as a solvent in bulk polymerization. In particular, a mixture mainly comprising toluene, cyclohexane or cis-2-butene or a mixture comprising cis-2-butene and trans-2-butene is a preferred solvent. Bulk polymerization or polymerization using a low-boiling hydrocarbon solvent is advantageous in that great energy for solvent recovery is not required. It is possible to control the molecular weight of a conjugated diene polymer by carrying out the polymerization of a conjugated diene in the presence of hydrogen and the above-described catalyst. Hydrogen is used preferably in an amount of not more than 50 mmol or 1.2 ℓ (at 20°C under atmospheric pressure) per mole of a conjugated diene, particularly 0.05 to 20 mmol or 0.012 to 0.48 ℓ (20°C, atmospheric pressure) per mole of a conjugated diene. The polymerization is preferably carried out at -100 to 150°C, more preferably -100 to 100°C, particularly preferabl -50 to 100°C, still particularly preferably -50 to 60°C, for 10 minutes to 12 hours, particularly 0.5 to 6 hours. After performing polymerization for a prescribed time period, the inner pressure of the reaction vessel is relieved according to necessity, and the polymer produced is worked up by washing, drying, and the like. According to the process of the invention which uses the catalyst of the invention, polybutadiene having a 1,2-structure content of 4 to 30%, preferably 5 to 25%, still preferably 5 to 20%, a cis-1,4-structure content of 65 to 95%, preferably 70 to 95%, and a trans-1,4-structure content of not more than 5%, preferably not more than 4.5%, can be produced. The polybutadiene having the above microstructure is suitable for use as an impact modifier for polystyrene. The 1,2-structure content, cis-1,4-structure content, trans-1,4-structure content, and (1,2-structure)(1,4-structure) diad chain content can be obtained from the 13 C-NMR spectrum in accordance with the analytical method described in Macromoelcules , Vol. 20, p. 2418 (1987). If the 1,2-structure content is less than 4%, the graft efficiency of polybutadiene is reduced, and the effect of improving impact resistance of polystyrene is reduced. If the 1,2-structure content exceeds 30%, grafting of polybutadiene exceeds excessively, also resulting in reduction of the effect of improving impact resistance of polystyrene. If the cis-1,4-structure content is out of the above range, the effect of improving impact resistance of polystyrene is reduced. The present invention also provides polybutadiene having a 1,2-structure content of 4 to 30%, a cis-1,4-structure content of 65 to 95%, and a trans-1,4-structure content of not more than 5%, and whose B value represented by equation (a) is more than 1.0 and not more than 1.43. B = P 1,2-1,4 / (2 × P 1,2 × P 1,4 ) wherein P 1,2 is a 1,2-structure content; P 1,4 is a 1,4-structure content; and P 1,2-1,4 is a (1,2-structure)(1,4-structure) diad chain content in the total diad chains. B value is a parameter calculated from P 1,2 , P 1,4 , and P 1,2-1,4 and indicative of the distribution of (1,2-structure) and (1,4-structure) in a polybutadiene chain. When B is equal to 1, (1,2-structure) and (1,4-structure) are distributed completely at random. When B is larger than 1, diad chains in which (1,2-structure) and (1,4-structure) alternate are present in a larger proportion than in the completely random distribution. When B is smaller than 1, diad chains in which (1,2-structure) and (1,4-structure) are linked in respective blocks are present in a larger proportion than in the completely random distribution. B value of the polybutadiene of the present invention is more than 1.0 and not more than 1.43, preferably more than 1.0 and not more than 1.25. This means that the proportion of diad chains in which (1,2-structure) and (1,4-structure) alternate is larger than that of the diad chains of completely random polybutadiene. The polybutadiene of the invention shows improvement over conventional polybutadiene known for applicability to production of HIPS and exerts a more excellent effect as an impact modifier. The invention further provides polybutadiene having a 1,2-structure content of 4 to 30%, a cis-1,4-structure content of 65 to 95%, a trans-1,4-structure content of not more than 5%, a gel content of not more than 0.1%, and an intrinsic viscosity [η] of 3 to 20 as measured in toluene at 30°C. The above polybutadiene has a 1,2-structure content of 4 to 30%, preferably 5 to 25%, still preferably 7 to 15%, a cis-1,4-structure content of 65 to 95%, preferably 70 to 95%, still preferably 85 to 95%, and a trans-1,4-structure content of not more than 5%, preferably not more than 4.5%. If the 1,2-structure content is less than 4%, the graft efficiency of polybutadiene is reduced, and the effect of improving impact resistance of polystyrene is reduced. If the 1,2-structure content exceeds 30%, grafting of polybutadiene exceeds excessively, also resulting in reduction of the effect of improving impact resistance of polystyrene. If the cis-1,4-structure content is out of the above range, the effect of improving impact resistance of polystyrene is reduced. The cis-1,4-structure, trans-1,4-structure and 1,2-structure are hereinafter sometimes referred to as "cis", "trans" and "vinyl", respectively. The above polybutadiene is characterized by its gel content of not more than 0.1%, preferably not more than 0.05%. If the gel content is out of this range, the physical properties of polybutadiene or appearance of resultant molded articles are adversely affected. The above polybutadiene is also characterized by its intrinsic viscosity [η] of 3 to 20, preferably 3 to 17, still preferably 5 to 15, as measured in toluene at 30°C. The polybutadiene of the invention preferably have a number average molecular weight (Mn) of 300,000 to 2,000,000, particularly 600,000 to 1,500,000, a weight average molecular weight (Mw) of 750,000 to 4,000,000, particularly 1,000,000 to 3,000,000, as measured by gel-permeation chromatography (GPC), and a molecular weight distribution (Mw/Mn ratio) of 1.8 to 3.5, particularly 1.8 to 3.0. The invention will now be illustrated in greater detail with reference to Examples and Comparative Examples, but it should be understood that the invention is not construed as being limited thereto. In the Examples and Comparative Examples, the measurements of the polymers were conducted by the following manners. The microstructure of the polymer was determined by analysis of infrared absorption spectrum. Specifically, the microstructure was determined from the intensity ratio of the absorptions at 740 cm -1 (cis-1,4-structure), 967 cm -1 (trans-1,4-structure) and 911 cm -1 (1,2-structure). The molecular weight was evaluated from results of GPC analysis using the standard polystyrene in terms of weight average molecular weight Mw, number average molecular weight Mn, and molecular weight distribution Mw/Mn. The intrinsic viscosity [η] was measured. The gel content was determined by dissolving about 2 g of a polymer produced in 200 ml of toluene, filtering the polymer solution through a metal net of 250 mesh, thoroughly washing the metal net with toluene, drying the metal net in vacuo at 80°C for 5 hours, and obtaining an increase in weight of the net. The Basic Example, Examples 1 to 13 and Comparative Examples 1 to 4 concern RMX 3 compounds and polymerization using the same. Basic Example (not in accordance with the present invention). Synthesis of Cyclopentadienylvanadium Trichloride The synthesis is in accordance with Z. Anorg. Allg. Chem., Vol. 423, p. 231 (1976). To 134 ml (1.85 mol) of thionyl chloride was added 4.7 g (18.5 mmol) of bis(cyclopentadienyl) vanadium dichloride, followed by stirring at room temperature for 48 hours. Thionyl chloride was removed by evaporation under reduced pressure, and the residue was washed twice with a small amount of n-heptane. The residue was extracted twice with 100 ml portions of boiling chloroform. The extract was concentrated under reduced pressure and allowed to stand at room temperature to crystallize. The black purple crystals thus formed were collected by filtration, washed with toluene, and dried under reduced pressure to give 1.2 g (30%) of the title compound. Elementary Analysis: Found (%) C 26.8; H 2.3; Cl 47.5 Calcd. (%) C 27.00; H 2.27; Cl 47.82 Polymerization of 1,3-Butadiene A 1.5 ℓ autoclave was purged with nitrogen, and 300 ml of toluene and 62 g of 1,3-butadiene were charged therein. To the mixture were added 0.8 ml of a toluene solution containing 2.5 mmol/ml-toluene of methylaluminoxane (MMAO, produced by Tosoh Akzo Corp.) as component (B) and 0.2 ml of a toluene solution containing 0.05 mmol/ml-toluene of cyclopentadienylvanadium trichloride (CpVCl 3 ) as component (A), and polymerization reaction was carried out at 40°C for 60 minutes. After completion of polymerization, unreacted 1,3-butadiene was released from the autoclave, and an antioxidant was added to the reaction mixture. The reaction mixture was poured into ethanol, and the thus precipitated polymer was collected, washed, filtered, and dried. The reaction results are shown in Table 2 below. The values of "catalytic activity" used in this Basic Example and in the following Examples and Comparative Examples were those obtained from calculation of the yielded amount of the polymer, the reaction time and the vanadium amount in the catalyst used. EXAMPLE 1 A 1.5 ℓ autoclave was purged with nitrogen, and 300 ml of toluene and 62 g of 1,3-butadiene were charged therein. To the mixture were added 0.5 ml of toluene solution containing 1 mmol/ml-toluene of triisobutylaluminum (TIBAL) as component (C), 1.5 ml of a toluene solution containing 0.005 mmol/ml-toluene of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ) as component (B), and 0.1 ml of a toluene solution containing 0.05 mmol/ml-toluene of cyclopentadienylvanadium trichloride (CpVCl 3 ) as component (A), and polymerization reaction was conducted at 40°C for 20 minutes. The reaction results are shown in Table 2. EXAMPLE 2 1,3-Butadiene was polymerized in the same manner as in Example 1, except for altering the conditions as shown in Table 1 below. The reaction results are shown in Table 2. EXAMPLE 3 1,3-Butadiene was polymerized under the conditions shown in Table 1 in the same manner as in Example 1, except for using 2 mmol of MMAO as component (C). The reaction results are shown in Table 2. COMPARATIVE EXAMPLE 1 1,3-Butadiene was polymerized in the same manner as in the Basic Example above, except for using acetylacetonatovanadium (III) (V(acac) 3 ) as component (A) and MMAO as component (B) and changing the reaction conditions as shown in Table 3 below. The reaction results are shown in Table 4. COMPARATIVE EXAMPLE 2 1,3-Butadiene was polymerized in the same manner as in the Basic Example above, except for using triethylalumium (TEA) as component (B) and changing the reaction conditions as shown in Table 3 below. The reaction results are shown in Table 4. COMPARATIVE EXAMPLE 3 1,3-Butadiene was polymerized in the same manner as in the Basic Example above, except for using ethylalumium sesquichloride (EASC) as component (B) and changing the reaction conditions as shown in Table 3 below. The reaction results are shown in Table 4. COMPARATIVE EXAMPLE 4 1,3-Butadiene was polymerized in the same manner as in the Basic Example above, except for using bis(cyclopentadienyl) vanadium dichloride (Cp 2 VCl 2 ) as component (A) and changing the reaction conditions as shown in Table 3 below. The reaction results are shown in Table 4. EXAMPLES 4 TO 8 1,3-Butadiene was polymerized in the same manner as in Example 1, except for using 300 ml of cyclohexane as a polymerization solvent (cyclohexane and 1,3-butadiene made 400 ml), CpVCl 3 as component (A), and Ph 3 CB(C 6 F 5 ) 4 as component (B), and triisobutylaluminum as component (C), and changing the reaction conditions as shown in Table 5 below. The reaction results are shown in Table 6. EXAMPLE 9 1,3-Butadiene was polymerized in the same manner as in Example 4, except for using triethylaluminum as component (C) and changing the reaction conditions as shown in Table 5. The reaction results are shown in Table 6. EXAMPLES 10 TO 13 1,3-Butadiene was polymerized in the same manner as in Example 4, except that a mixed solvent of cyclohexane and a cis-2-butene/trans-2-butene mixture (about 80/20 by weight) was used as a polymerization solvent (the mixed solvent and 1,3-butadiene made 400 ml), CpVCl 3 as component (A), and Ph 3 CB(C 6 F 5 ) 4 as component (B), and triisobutylaluminum as component (C), and changing the reaction conditions as shown in Table 7 below. The reaction results are shown in Table 8 below. Example No. Component (A) Component (B) Component (C) Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (°C) (min) Basic 0.01 2 - 40 60 1 0.005 0.0075 0.5 40 20 2 0.005 0.01 0.5 40 20 3 0.01 0.01 2 40 30 Example No. Yield Catalytic Activity Microstructure (%) cis trans vinyl (g) (g/mmol-V.hr) Basic 13.3 1330 90.5 0.6 8.9 1 36.8 22080 88.0 2.0 10.0 2 35.8 21420 88.0 2.0 10.0 3 42.9 8580 88.0 2.0 10.0 Comparative Example No. Component (A) Component (B) Component (C) Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (°C) (min) 1 0.1 40 - 20 60 2 0.1 15 - 40 60 3 0.1 15 - 40 60 4 0.01 10 - 40 60 Comparative Example No. Yield Catalytic Activity Microstructure (%) cis trans vinyl (g) (g/mmol-V.hr) 1 2.3 23 55.5 33.6 10.9 2 0 0 - - - 3 0.8 8 84.0 3.4 12.6 4 1.4 140 90.0 1.4 8.6 Example No. Component (A) Component (B) Component (C) Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (°C) (min) 4 0.005 0.0075 0.25 40 60 5 0.005 0.0075 0.5 40 60 6 0.005 0.01 0.25 40 60 7 0.005 0.0125 0.25 40 60 8 0.005 0.01 0.25 60 60 9 0.005 0.01 0.25 40 60 Example No. Yield Catalytic Activity Microstructure (%) Mw (×10 6 ) Mn (×10 6 ) Mw/Mn cis trans vinyl (g) (g/mmol-V.hr) 4 22.4 4480 86.8 1.1 12.1 2.94 1.42 2.07 5 16.0 3200 87.2 1.0 11.8 2.33 0.96 2.42 6 28.1 5620 86.7 1.3 12.0 3.17 1.58 2.01 7 17.0 3400 86.7 1.2 12.1 2.77 1.43 1.94 8 35.7 7140 86.0 2.0 12.0 1.53 0.72 2.12 9 47.0 9400 86.7 1.6 11.7 2.39 1.02 2.34 Examples 14 to 20 relate to RM(O)X 2 compounds and polymerization using the same. Synthesis of Transition Metal Compound Cyclopentadienyloxovanadium dichloride (VO(Cp)Cl 2 ) used in certain of the Examples below was synthesized in accordance with Organometallics, Vol. 7, pp. 496-502 (1988) in the form of a solution in toluene. EXAMPLE 14 Polymerization of Butadiene To 200 ml of toluene was added a toluene solution containing 0.2 mmol of triisobutylaluminum, and the solution was kept at 40°C. To the solution was added 32 ml of butadiene, and 1.5 µmol of Ph 3 CB(C 6 F 5 ) 4 and a toluene solution of 1.0 µmol of VO(Cp)Cl 2 were added thereto to conduct polymerization for 1 hour. The polymerization reaction was stopped by addition of an HCl-containing ethanol solution, and the reaction mixture was filtered and dried to give white polybutadiene having a cis-structure content of 88.9%, a trans-structure of 1.7%, a vinyl (1,2)-structure of 9.4%, an Mw of 2,917,000, and an Mw/Mn ratio of 2.96. The catalytic activity was 10,200 g/mmol.V.hr. EXAMPLE 15 Polymerization of Butadiene To 200 ml of toluene was added a toluene solution containing 0.2 mmol of triisobutylaluminum, and the solution was kept at 40°C. To the solution was added 32 ml of butadiene, and 1.5 µmol of Ph 3 CB(C 6 F 5 ) 4 was then added thereto. A toluene solution containing 1.0 µmol of VO(Cp)Cl 2 was added to the mixture while feeding hydrogen at a rate of 5 ml/min to conduct polymerization for 1 hour. The polymerization reaction was stopped by addition of an HCl-containing ethanol solution, and the reaction mixture was filtered and dried to give white polybutadiene having a cis-structure content of 87.2%, a trans-structure of 3.6%, a vinyl (1,2)-structure of 9.2%, an Mw of 502,000, and an Mw/Mn ratio of 1.59. The catalytic activity was 8,100 g/mmol.V.hr. EXAMPLE 16 Polymerization of Butadiene Butadiene was polymerized in the same manner as in Example 15, except for feeding hydrogen at a rate of 20 ml/min. The polymerization reaction was stopped by addition of an HCl-containing ethanol solution, and the reaction mixture was filtered and dried to give white polybutadiene having a cis-structure content of 86.7%, a trans-structure of 5.9%, a vinyl (1,2)-structure of 7.4%, an Mw of 19,000, and an Mw/Mn ratio of 2.86. The catalytic activity was 5,200 g/mmol.V.hr. EXAMPLES 17 TO 20 Butadiene was polymerized in the same manner as in Example 1, except for using VO(Cp)Cl 2 was used as component (A) in place of CpVCl 3 , triethylalumium was used as component (C) in place of TIBAL, and the conditions were changed to those shown in Table 9. The reaction results are shown in Table 10. EXAMPLES 21 AND 22 Butadiene was polymerized in the same manner as in Example 9, except for using VO(Cp)Cl 2 was used as component (A) in place of CpVCl 3 and the conditions were changed to those shown in Table 11. The reaction results are shonw in Table 12. Example No. Component (A) Component (B) Component (C) Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (°C) (min) 21 0.005 0.01 0.5 40 60 22 0.005 0.01 0.75 40 60 Example No. Yield Catalytic Activity Microstructure (%) Mw (×10 6 ) Mn (×10 6 ) Mw/Mn cis trans vinyl (g) (g/mmol-V.hr) 21 38.4 7680 87.2 1.1 11.7 2.07 1.07 1.94 22 38.1 7620 87.1 1.3 11.6 1.75 0.84 2.08 EXAMPLE 23 Preparation of Transition Metal Compound (η 5 C 5 H 4 (SiMe 3 )VCl 3 ) In 40 ml of tetrahydrofuran (THF) was dissolved 7.3 g (40 mmol) of C 5 H 5 (SiMe 3 ) in a nitrogen stream, and the solution was cooled to -78°C. To the solution was added dropwise 29.8 ml (48 mmol) of a 1.61M hexane solution of n-BuLi. The reaction mixture was concentrated, and the residue was washed with hexane. The solid was dissolved in 40 ml of THF, and the solution was added dropwise to 20 ml of a toluene solution containing 2.3 ml (22 mmol) of VCl 4 at a THF refluxing temperature, followed by stirring at room temperature for 10 hours. The solvent was removed, and 100 ml of toluene was added to the residue. After stirring, LiCl was removed by filtration. The filtrate was concentrated, and to the residue was added an equivalent weight of hexane, followed by cooling to -78°C. The precipitated deep blue crystals were separated by filtration. To the crystals was added 50 ml of thionyl chloride, and the mixture was stirred at room temperature for 10 hours. After completion of the reaction, thionyl chloride was removed by evaporation under reduced pressure. To the residue was added 100 ml of toluene, followed by filtration. The filtrate was concentrated, 50 ml of hexane was added thereto, and deep purple crystals were obtained at -78°C. The crystals were collected by filtration and dried at room temperature under reduced pressure. The resulting compound was identified by analysis to be η 5 C 5 H 4 ,(SiMe 3 )VCl 3 . Elementary Analysis for C 8 H 13 Cl 3 SiV: Calcd. (%) C 32.62; H 4.45; Cl 36.10 Found (%) C 32.83; H 4.61; Cl 36.20 EXAMPLE 24 Preparation of Transition Metal Compound (η 5 C 5 H 3 (1,3-Me 2 )VCl 3 ) In 110 ml of THF was dissolved 10 g (110 mmol) of C 5 H 4 (1,3-Me 2 ) in a nitrogen stream, and the solution was cooled to -78°C. To the solution was added dropwise 80 ml (130 mmol) of a 1.61M hexane solution of n-BuLi. The reaction mixture was concentrated, and the residue was washed with hexane. The solid was dissolved in 40 ml of THF, and the solution was added dropwise to 20 ml of a toluene solution containing 2.2 ml (20 mmol) of VCl 4 at a THF refluxing temperature, followed by stirring at room temperature for 10 hours. The solvent was removed, and 100 ml of toluene was added to the residue. After stirring, LiCl was removed by filtration. The filtrate was concentrated to dryness to separate a green solid. The solid was dissolved in 20 ml of methylene chloride, 10 ml of toluene. was added thereto, and the system was cooled to -78°C for crystallization. The thus formed green crystals were collected, and 50 ml of thionyl chloride was added to the residue, followed by stirring at room temperature for 10 hours. After the reaction, thionyl chloride was removed by evaporation under reduced pressure. To the residue was added 100 ml of toluene, followed by filtration. The filtrate was concentrated, 50 ml of hexane was added thereto, and deep purple crystals were obtained at -78°C. The crystals were collected by filtration and dried at room temperature under reduced pressure. The resulting compound was identified by analysis to be η 5 C 5 H 3 (1,3-Me 2 )VCl 3 . Elementary Analysis for C 7 H 9 Cl 3 V: Calcd. (%) C 33.57; H 3.62; Cl 42.47 Found (%) C 33.61; H 3.61; Cl 42.80 EXAMPLE 25 Preparation of Transition Metal Compound (η 5 C 5 H 4 (t-Bu)VCl 3 ) In 80 ml of THF was dissolved 10 g (82 mmol) of C 5 H 5 (t-Bu) in a nitrogen stream, and the solution was cooled to -78°C. To the solution was added dropwise 61 ml (98 mmol) of a 1.61M hexane solution of n-BuLi. The reaction mixture was concentrated, and the residue was washed with hexane. The solid was dissolved in 60 ml of THF, and the solution was added dropwise to 20 ml of a toluene solution containing 2.4 ml (23 mmol) of VCl 4 at a THF refluxing temperature, followed by stirring at room temperature for 10 hours. The solvent was removed, and 100 ml of methylene chloride was added to the residue, followed by stirring. LiCl was removed by filtration, and the filtrate was concentrated to dryness. Recrystallization of the solid from hexane gave deep blue crystals. To the crystals was added 50 ml of thionyl chloride, followed by stirring at room temperature for 10 hours. After the reaction, thionyl chloride was removed by evaporation under reduced pressure. To the residue was added 100 ml of toluene, followed by filtration. The filtrate was concentrated, 50 ml of hexane was added thereto, and deep purple crystals were obtained at -78°C. The crystals were collected by filtration and dried at room temperature under reduced pressure. The resulting compound was identified by analysis to be η 5 C 5 H 4 (t-Bu)VCl 3 . Elementary Analysis for C 9 H 13 Cl 3 V: Calcd. (%) C 38.81; H 4.72; Cl 38.19 Found (%) C 38.89; H 4.89; Cl 38.50 EXAMPLE 26 Preparation of Transition Metal Compound (η 5 C 5 H 4 (CH 2 Ph)VCl 3 ) In 20 ml of THF was dissolved 2.6 g (17 mmol) of C 5 H 5 (CH 2 Ph) in a nitrogen stream, and the solution was cooled to -78°C. To the solution was added dropwise 10.4 ml (17 mmol) of a 1.60M hexane solution of n-BuLi. The reaction mixture was concentrated, and the residue was washed with hexane. The solid was dissolved in 40 ml of THF, and the solution was added dropwise to 20 ml of a toluene solution containing 0.8 ml (8 mmol) of VCl 4 at a THF refluxing temperature, followed by stirring at room temperature for 10 hours. The solvent was removed, and 100 ml of methylene chloride was added to the residue. After stirring, LiCl was removed by filtration. The filtrate was concentrated to dryness to obtain a green solid, and 50 ml of thionyl chloride was added thereto, followed by stirring at room temperature for 10 hours. After the reaction, thionyl chloride was removed by evaporation under reduced pressure. To the residue was added 100 ml of toluene, followed by filtration. The filtrate was concentrated, 50 ml of hexane was added thereto, and deep purple crystals were obtained at -78°C. The crystals were collected by filtration and dried at room temperature under reduced pressure. The resulting compound was identified by analysis to be η 5 C 5 H 4 (CH 2 Ph)VCl 3 . Elementary Analysis for C 12 H 11 Cl 3 V: Calcd. (%) C 46.12; H 3.55; Cl 34.03 Found (%) C 46.53; H 3.61; Cl 34.30 EXAMPLE 27 Preparation of Transition Metal Compound (η 5 C 5 H 3 (Sime 3 ) 2 VCl 3 ) In 20 ml of THF was dissolved 2.1 g (10 mmol) of C 5 H 4 (SiMe 3 ) 2 in a nitrogen stream, and the solution was cooled to -78°C. To the solution was added dropwise 6.2 ml (10 mmol) of a 1.61M hexane solution of n-BuLi. The reaction mixture was concentrated, and the residue was washed with hexane. The solid was dissolved in 20 ml of THF, and the solution was added dropwise to 20 ml of a toluene solution containing 0.5 ml (5 mmol) of VCl 4 at a THF refluxing temperature, followed by stirring at room temperature for 10 hours. The solvent was removed, and 50 ml of toluene was added to the residue. After stirring, LiCl was removed by filtration. The filtrate was concentrated, and an equivalent amount of hexane was added thereto, followed by cooling to -78°C. The thus precipitated deep blue crystals were separated by filtration. To the crystals was added 15 ml of thionyl chloride, followed by stirring at room temperature for 10 hours. After the reaction, thionyl chloride was removed by evaporation under reduced pressure. To the residue was added 50 ml of toluene, followed by filtration. The filtrate was concentrated to dryness and recrystallized from hexane to obtain purple crystals. The crystals were collected by filtration and dried at room temperature under reduced pressure. The resulting compound was identified by analysis to be η 5 C 5 H 3 (Sime 3 ) 2 VCl 3 . Elementary Analysis for C 11 H 21 Cl 3 Si 2 V: Calcd. (%) C 36.02; H 5.77; Cl 29.00 Found (%) C 36.83; H 5.91; Cl 29.50 Examples 28 to 32 relate to preparation of RM(O)X 2 having a substituent. EXAMPLE 28 Preparation of Transition Metal Compound (η 5 C 5 H 4 (SiMe 3 )V(O)Cl 2 ) Deep blue trimethylsilylcyclopentadienyloxovanadium dichloride (η 5 C 5 H 4 (SiMe 3 )V(O)Cl 2 ) was synthesized by oxygen treatment of η 5 C 5 H 4 (SiMe 3 )VCl 3 prepared in Example 35 in accordance with Organometallics , Vol. 7, pp. 496-502 (1988). Elementary Analysis for C 8 H 13 Cl 2 OSiV: Calcd. (%) C 34.93; H 4.76; Cl 25.77 Found (%) C 34.73; H 4.61; Cl 25.61 1 H-NMR (CDCl 3 ): 7.01-7.00 (2H, d, Cp-H), 6.90-6.89 (2H, d, Cp-H), 0.38 (9H, s, Me 3 Si) EXAMPLE 29 Preparation of Transition Metal Compound Deep blue 1,3-dimethylcyclopentadienyloxovanadium dichloride (η 5 C 5 H 3 (1,3-Me 2 )V(O)Cl 2 ) was synthesized by oxygen treatment of η 5 C 5 H 3 (1,3-Me 2 )VCl 3 prepared in Example 36 in accordance with Organometallics , Vol. 7, pp. 496-502 (1988). Elementary Analysis for C 7 H 9 Cl 2 OV: Calcd. (%) C 36.40; H 3.93; Cl 30.70 Found (%) C 36.23; H 3.71; Cl 30.61 1 H-NMR (CDCl 3 ): 6.41-6.40 (2H, d, Cp-H), 6.22 (1H, s, Cp-H), 2.52 (6H, s, Me -Cp) EXAMPLE 30 Preparation of Transition Metal Compound Deep blue t-butylcyclopentadienyloxovanadium dichloride (η 5 C 5 H 4 (t-Bu)V(O)Cl 2 ) was synthesized by oxygen treatment of η 5 C 5 H 4 (t-Bu)VCl 3 prepared in Example 37 in accordance with Organometallics , Vol. 7, pp. 496-502 (1988). Elementary Analysis for C 9 H 13 Cl 2 OV: Calcd. (%) C 41.73; H 5.06; Cl 27.37 Found (%) C 41.53; H 4.91; Cl 27.21 1 H-NMR (CDCl 3 ): 6.79-6.78 (2H, d, Cp-H), 6.73-6.72 (2H, d, Cp-H), 1.43 (9H, s, Me 3 C) EXAMPLE 31 Preparation of Transition Metal Deep blue benzylcyclopentadienyloxovanadium dichloride (η 5 C 5 H 4 (CH 2 Ph)V(O)Cl 2 ) was synthesized by oxygen treatment of η 5 C 5 H 4 (CH 2 Ph)VCl 3 prepared in Example 38 in accordance with Organometallics , Vol. 7, pp. 496-502 (1988). Elementary Analysis for C 12 H 11 Cl 2 OV: Calcd. (%) C 49.18; H 3.78; Cl 24.19 Found (%) C 49.01; H 3.70; Cl 24.11 1 H-NMR (CDCl 3 ): 7.37-7.23 (5H, m, Ph), 6.80-6.70 (2H, d, Cp-H), 6.46-6.40 (2H, d, Cp-H), 4.20 (2H, s, CH 2 ) EXAMPLE 32 Preparation of Transition Metal Compound Bis(trimethylsilyl)cyclopentadienyloxovanadium dichloride (η 5 C 5 H 3 (SiMe 3 ) 2 V(O)Cl 2 ) was synthesized by oxygen treatment of η 5 C 5 H 3 (SiMe 3 ) 2 VCl 3 prepared in Example 39 in accordance with Organometallics , Vol. 7, pp. 496-502 (1988). Elementary Analysis for C 11 H 21 Cl 2 OSi 2 V: Calcd. (%) C 38.04; H 6.09; Cl 20.42 Found (%) C 37.89; H 5.97; Cl 20.06 1 H-NMR (CDCl 3 ): 7.24-7.23 (2H, d, Cp-H), 6.87-6.85 (2H, t, Cp-H), 0.42 (18H, s, Si-Me) Examples 45 to 60 offer examples of polymerization using RMX 3 having a substituent. EXAMPLES 33 TO 41 Butadiene was polymerized by using (A) a substituted cyclopentadienylvanadium trichloride shown in Table 9 below, (B) triphenylcarbonium tetrakis(pentafluorophenyl)borate, and (C) triisobutylaluminum under the reaction conditions shown in Table 13. The reaction results are shown in Table 14 below. Example No. Transition Metal Compound Reaction Temp. Reaction Time Kind Amount Ph 3 CB(C 6 F 5 ) 4 Al(i-Bu) 3 (mmol) (mmol) (mmol) (°C) (min) 33 (MeCp)VCl 3 0.0012 0.0018 0.2 30 30 34 (1,3-Me 2 Cp)VCl 3 0.001 0.0015 0.2 30 30 35 (1,3-Me 2 Cp)VCl 3 0.002 0.003 0.2 30 30 36 (Me 5 Cp)VCl 3 0.005 0.0075 0.5 30 30 37 (Me 3 SiCp)VCl 3 0.001 0.0015 0.2 30 30 38 (Me 3 SiCp)VCl 3 0.0012 0.0018 0.2 30 30 39 (t-BuCp)VCl 3 0.001 0.0015 0.2 30 30 40 (t-BuCp)VCl 3 0.0012 0.0018 0.2 30 30 41 (PhCH 2 Cp)VCl 3 0.0012 0.0018 0.2 30 30 Example No. Catalytic Activity Microstructure (%) Mw (×10 6 ) Mw/Mn (g/mmol-V.hr) cis trans vinyl 33 5412 83.4 2.4 14.2 1.60 2.66 34 360 74.2 4.2 21.1 0.37 3.90 35 1546 75.1 4.4 20.5 0.45 3.20 36 87 53.8 7.0 39.2 0.20 2.00 37 214 89.7 3.0 9.8 0.23 2.11 38 178 86.0 4.0 10.0 0.27 2.04 39 1230 86.2 3.3 10.5 0.21 1.92 40 113 83.0 6.5 10.5 0.28 2.04 41 15387 85.6 1.7 12.7 1.72 2.69 Examples 42 to 53 and Comparative Example 5 relate to examples of using an R n MX p •L a compound. EXAMPLE 42 Preparation of Transition Metal Compound (η 5 CH 3 -C 5 H 4 )VCl 2 [P(CH 2 CH 3 ) 3 ] 2 was synthesized in accordance with the process of Journal of Organometallic Chemistry, Vol. 255, p. 193 (1983) in the form of a toluene solution. EXAMPLE 43 Preparation of Transition Metal Compound (η 5 C 5 H 5 ) 2 VCl was synthesized in accordance with the process of Journal of Organometallic Chemistry, Vol. 110, p. 291 (1976) and prepared as a toluene solution. EXAMPLE 44 Polymerization of Butadiene To 200 ml of toluene was added a toluene solution containing 0.2 mmol of triisobutylaluminum as component (C), and the solution was kept at 40°C. To the solution was added 32 ml of butadiene, and 1.5 µmol of (CH 3 ) 2 NH(C 6 H 5 )B(C 6 F 5 ) 4 as component (B) and a toluene solution of 1.0 µmol of the transition metal compound prepared in Example 42 as component (A) were added thereto. Polymerization was carried out for 1 hour. The reaction was stopped by addition of an HCl-containing ethanol solution, and the reaction mixture was filtered. The filter cake was dried to obtain a white butadiene polymer. The reaction results are shown in Table 15 below. EXAMPLES 45 TO 47 Polymerization of Butadiene Butadiene was polymerized in the same manner as in Example 44, except for changing the reaction conditions as shown in Table 15 below. The reaction results are shown in Table 16. EXAMPLES 48 AND 49 Polymerization of Butadiene Butadiene was polymerized in the same manner as in Example 44, except for using the transition metal compound prepared in Example 43 as component (A) and changing the reaction conditions as shown in Table 15. The reaction results are shown in Table 16. EXAMPLES 50 TO 52 Polymerization of Butadiene Butadiene was polymerized in the same manner as in Example 44, except for using the transition metal compound prepared in Example 42 as component (A) and Ph 3 CB(C 6 F 5 ) 4 as component (B) and changing the reaction conditions as shown in Table 15. The reaction results are shown in Table 16. EXAMPLE 53 Polymerization of Butadiene To 200 ml of toluene was added a toluene solution containing 0.2 mmol of triisobutylaluminum, and the solution was maintained at 10°C. To the solution was added 0.5 ml of butadiene, and 1.5 µmol of (CH 3 ) 2 NH(C 6 H 5 )B(C 6 F 5 ) 4 and a toluene solution of 1.0 µmol of the transition metal compound prepared in Example 43 were then added, followed by stirring for 2 hours. The solution was maintained at 40°C, and 32 ml of butadiene was added thereto to commence reaction. Polymerization reaction was continued for 1 hour. The reaction was stopped by addition of an HCl-containing ethanol solution, and the reaction mixture was filtered. The filter cake was dried to obtain a white butadiene polymer. The reaction results are shown in Table 16 below. COMPARATIVE EXAMPLE 5 Polymerization of Butadiene Butadiene was polymerized in the same manner as in Example 44, except for using 1.0 µmol.of the transition metal compound prepared in Example 42 and 0.2 mmol of methylaluminoxane as catalyst components. The reaction results are shown in Table 16. Example No. Component (A) Component (B) Component (C) H 2 (µmol) (µmol) (mmol) (ml/min) 44 1 1.5 0.2 - 45 1 1.5 1.0 - 46 1 1.5 0.2 20 47 1 1.5 0.2 10 48 1 1.5 0.2 - 49 1 1.5 0.2 10 50 1 1.5 0.2 - 51 1 1.5 0.2 20 52 1 1.5 0.2 10 53 1 1.5 0.2 - Example No. Catalytic Activity Microstructure (%) Mw (×10 4 ) Mw/Mn cis trans vinyl (g/mmol-V.hr) 44 1400 84.5 1.3 14.2 242.0 2.3 45 1600 84.2 1.0 14.8 224.4 2.3 46 1200 83.0 2.9 14.1 1.9 1.8 47 900 82.6 3.1 14.3 8.9 2.0 48 500 84.3 1.5 14.2 212.3 2.4 49 400 84.0 2.8 13.2 15.6 2.5 50 1300 82.1 2.1 15.8 236.0 2.2 51 800 82.5 2.4 15.1 2.3 1.8 52 700 81.9 2.6 15.5 21.0 2.1 53 800 82.1 2.1 15.8 216.1 2.2 Comparative Example 5 400 81.4 1.3 17.3 192.2 2.3 Examples 54 to 62 and Comparative Examples 6 to 10 relate to polymerization in the presence of hydrogen. EXAMPLES 54 TO 57 To a 1.5 ℓ autoclave having been purged with nitrogen were charged 300 ml of toluene and 62 g of 1,3-butadiene, and the mixture was stirred. A pressure container having a capacity corresponding to the amount of hydrogen shown in Table 17 below was filled with hydrogen at 20°C and atmospheric pressure, and hydrogen was introduced into the autoclave with nitrogen pressure. To the autoclave were then fed 0.5 ml of a toluene solution containing 0.5 mmol of triisobutylaluminum, 1.5 ml of a toluene solution containing 0.0075 mmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ), and 0.1 ml of a toluene solution containing 0.005 mmol of cyclopentadienylvanadium trichloride (CpVCl 3 ), and polymerization was carried out at 40°C for 20 minutes. After the reaction, ethanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction system, and the thus precipitated polymer was collected by filtration and dried. The reaction results are shown in Table 18 below. EXAMPLES 58 TO 62 To a 1.5 ℓ autoclave having been purged with nitrogen were charged 300 ml of cyclohexane and 62 g of 1,3-butadiene, and the mixture was stirred. A pressure container having a capacity corresponding to the amount of hydrogen shown in Table 19 below was filled with hydrogen at 20°C and atmospheric pressure, and hydrogen was introduced into the autoclave with nitrogen pressure. To the autoclave were then fed 0.25 ml of a toluene solution containing 0.25 mmol of triethylaluminum, 2 ml of a toluene solution containing 0.01 mmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ), and 0.1 ml of a toluene solution containing 0.005 mmol of cyclopentadienylvanadium trichloride (CpVCl 3 ), and polymerization was carried out at 40°C for 60 minutes. After the reaction, ethanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction system, and the thus precipitated polymer was collected by filtration and dried. The reaction results are shown in Table 20 below. COMPARATIVE EXAMPLES 6 TO 8 Butadiene was polymerized in the same manner as in Example 58, except for replacing hydrogen gas with a toluene solution of 1,5-cyclooctadiene, the amount of which is shown in Table 21 below, which was fed by means of a syringe. The reaction results are shown in Table 22. COMPARATIVE EXAMPLES 9 TO 10 Butadiene was polymerized in the same manner as in Example 58, except for replacing hydrogen gas with a toluene solution of 1,2-butadiene, the amount of which is shown in Table 23 below, which was fed by means of a syringe. The reaction results are shown in Table 24. Example No. Hydrogen Gas (20°C, 1 atm) Yield Catalytic Activity (ml) (g) (g/mmol-V.hr) 54 10 36.0 21600 55 30 41.0 24600 56 50 39.2 23520 57 78 35.2 21120 Example No Microstructure (%) [η] Mw (×10 6 ) Mw/Mn cis trans vinyl 54 88.3 2.0 9.7 6.50 1.55 2.21 55 88.3 1.7 10.0 3.51 0.96 2.18 56 87.4 1.9 10.7 2.02 0.46 2.30 57 88.4 1.8 9.8 1.30 0.27 1.93 Example No. Hydrogen Gas (20°C, 1 atm) Yield Catalytic Activity (ml) (g) (g/mmol-V.hr) 58 10 34.4 6880 59 30 39.2 7840 60 50 35.0 7000 61 78 38.2 7640 62 120 37.0 7400 Example No. Microstructure (%) [η] Mw (×10 6 ) Mw/Mn cis trans vinyl 58 87.3 1.2 11.5 5.86 1.48 2.10 59 87.4 1.5 11.1 2.60 0.68 2.27 60 87.3 1.4 11.3 1.67 0.34 2.05 61 87.3 1.4 11.3 1.24 0.22 2.06 62 87.3 1.4 11.3 0.81 0.12 1.89 Comparative Example No. 1,5-Cyclo-octadiene Yield Catalytic Activity (mmol) (g) (g/mmol-V.hr) 6 3 43.6 8720 7 6 44.0 8800 8 10 4.7 940 Comparative Example No. Microstructure (%) [η] Mw (×10 6 ) Mw/Mn cis trans vinyl 6 86.8 1.0 12.2 8.82 2.04 2.13 7 86.9 1.3 11.8 8.01 1.82 1.83 8 86.8 1.2 12.0 5.24 1.30 2.67 Comparative Example No. 1,2-Butadiene Yield Catalytic Activity (mmol) (g) (g/mmol-V.hr) 9 0.3 10.6 2120 10 3.0 0 - Comparative Example No. Microstructure (%) [η] Mw (×10 6 ) Mw/Mn cis trans vinyl 9 87.0 1.0 12.0 9.50 2.11 2.32 10 - - - - - EXAMPLE 63 To 200 ml of toluene was added 0.2 mmol of triisobutylaluminum as a toluene solution, and the resulting solution was maintained at 40°C. To the solution was added 33 ml of butadiene, and then added 1.5 µmol of (CH 3 ) 2 NH(C 6 H 5 )B(C 6 F 5 ) 4 . Polymerization was carried out for 1 hour by adding 1.0 µmol of cyclopentadienyloxovanadium dichloride as a toluene solution, while hydrogen was added at a rate of 5 ml/min. Polmerization was terminated by adding an HCl-containing ethanol solution to the reaction system, and the thus precipitated polymer was collected by filtration and dried to obtain white polybutadiene. The catalyst activity was 8100 g/mmol-V.hr. The microstructure of the polybutadiene was that cis was 87.2%, trans was 3.6%, and vinyl was 9.2%. Mw was 0.502×10 6 and Mw/Mn was 1.59. EXAMPLE 64 Butadiene was polymerized in the same manner as in Example 63, except for changing the addition rate of hydrogen to 20 ml/min. Polmerization was terminated by adding an HCl-containing ethanol solution to the reaction system, and the thus precipitated polymer was collected by filtration and dried to obtain white polybutadiene. The catalyst activity . was 5200 g/mmol-V.hr. The microstructure of the polybutadiene was that cis was 86.7%, trans was 5.9%, and vinyl was 7.4%. Mw was 0.091×10 6 and Mw/Mn was 2.86. Examples 65 to 78 provide examples of bulk polymerization. EXAMPLE 65 To a 1.7 ℓ autoclave having been purged with nitrogen was charged 248 g (400 ml) of 1,3-butadiene, and 0.5 mmol of triethylaluminum, 0.01 mmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ), and 0.005 mmol of cyclopentadienylvanadium trichloride (CpVCl 3 ) were added thereto. Polymerization was carried out at 40°C for 15 minutes. After the reaction, ethanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction system, and the thus precipitated polymer was collected by filtration and dried. The reaction results are shown in Table 26 below. EXAMPLES 66 TO 70 Butadiene was polymerized in the same manner as in Example 65, except for performing the polymerization in the presence of hydrogen as shown in Table 25 and changing the reaction conditions as shown in Table 25. The reaction results are shown in Table 26. EXAMPLE 71 To a 1.7 ℓ autoclave having been purged with nitrogen was charged 248 g (400 ml) of 1,3-butadiene, and hydrogen gas of the amount shown in Table 27 below was introduced into the autoclave. Then, 0.5 mmol of triethylaluminum, 0.005 mmol of cyclopentadienylvanadium trichloride (CpVCl 3 ), and 0.01 mmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ) were added thereto. Polymerization was carried out at 40°C for 15 minutes. After the reaction, ethanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction system, and the thus precipitated polymer was collected by filtration and dried. The reaction results are shown in Table 28 below. EXAMPLES 72 AND 73 Butadiene was polymerized in the same manner as in Example 71, except for changing the reaction conditions as shown in Table 27. The reaction results are shown in Table 28. Example No. CpVCl 3 TEA Ph 3 CB-(C 6 F 5 ) 4 H 2 Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (kgf/cm 2 ; ml) (°C) (min) 65 0.005 0.5 0.01 - 40 15 66 0.005 0.5 0.01 0.06; 78 40 15 67 0.005 0.5 0.01 0.1 ; 128 40 60 68 0.005 0.5 0.01 0.16; 208 40 15 69 0.005 0.5 0.01 0.16; 208 40 60 70 0.005 0.5 0.01 0.2 ; 260 40 60 EXAMPLE 74 A 1.7 ℓ autoclave was purged with nitrogen, and 248 g (400 ml) of 1,3-butadiene was charged therein to a pressure of 0.16 Kgf/cm 2 . To the system were added 0.75 mmol of triethylalminum and 0.01 mmol of N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, and polymerization reaction was carried out at 40°C for 15 minutes. After completion of polymerization, etanol containing a small amount of 2,6-t-butyl-p-cresol was added to the reaction system to precipitate the polymer thus produced, and the polymer was then filtered and dried. The reaction results are shown in Tables 30 and 31. EXAMPLES 75 TO 78 The polymerization of 1,3-butadiene was carried out in the same manner as in Example 74, except for changing the reaction conditions as shown in Table 29. The reaction results are shown in Tables 30 and 31. Example No. CpVCl 3 TEA Me 2 PhNH B(C 6 F 5 ) 4 H 2 Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (kgf/cm 2 ; ml) (°C) (min) 74 0.005 0.75 0.01 - 40 5 75 0.005 0.75 0.01 0.10; 130 40 60 76 0.005 0.75 0.01 0.15; 195 40 60 77 0.005 0.75 0.01 0.20; 260 40 60 78 0.005 0.75 0.01 0.30; 390 40 60 Example No. Yield Catalytic Activity Microstructure (%) (g) (g/mmol-V.hr) cis trans vinyl 74 96.9 232560 75 77.1 15420 88.2 0.6 11.2 76 75.3 15060 88.4 0.6 11.0 77 83.9 16780 88.4 0.7 10.9 78 62.7 12540 88.1 0.9 11.0 Example No. Mw (×10 6 ) Mn (×10 6 ) Mw/Mn [η] Gel Content (%) 74 19.14 75 0.711 0.281 2.54 3.21 0.002 76 0.416 0.174 2.40 2.09 0.003 77 0.254 0.120 2.11 1.44 0.000 78 0.117 0.063 1.85 0.81 0.000 Examples 79 and 80 relate to production of polybutadiene having a specific B value. In these Examples, 13 C-NMR spectra of polybutadiene produced were taken under the following conditions. Equipment: FT-NMR, JEOL Model EX-400 Sample tube: 5 mm in diameter Solvent: o-dichlorobenzene/C 6 D 6 (4/1) Concentration: 10% Temperature: 130°C Standard: TMS Width of observation: 20,000 Hz Method of measurement: proton noise decoupling Data point: 32K Number of integration: 5000 Pulse width: 3 sec (45°) EXAMPLE 79 Polymerization of 1,3-butadiene was carried out in the same manner as in Example 1. The reaction results are shown in Table 32 below. The diad chain contents, microstructure, and B value of the resulting polybutadiene are shown in Table 33. EXAMPLE 80 Polymerization of butadiene was carried out in the same manner as in Example 79, except for using 0.01 mmol of CpVCl 3 , 0.01 mmol of Ph 3 CB(C 6 F 5 ) 4 , and 2 mmol of MMAO. The reaction results are shown in Table 32. The diad chain contents, microstructure, and B value of the resulting polybutadiene are shown in Table 33. Example No. Yield Catalytic Activity (g) (g/mmol-V.hr) 74 36.8 22080 75 42.9 8580 Example 79 Example 80 Microstructure (%): (cis-1,4) 84.6 84.4 (trans-1,4) 4.0 3.6 (1,2) 11.4 12.0 Diad Chain (%): (cis-1,4)(1,2) 10.6 11.1 (1,2)(cis-1,4) 9.7 10.4 (trans-1,4)(1,2) 0.0 0.0 (1,2)(trans-1,4) 0.9 0.7 (cis-1,4)(1,4) 74.0 73.3 (trans-1,4)(1,4) 4.0 3.6 (1,2)(1,2) 0.8 0.9 P 1,2 0.114 0.120 P 1,4 0.886 0.880 P 1,2-1,4 0.212 0.222 B 1.05 1.05 Examples 81 to 86 illustrate production of polybutadiene having a specific intrinsic viscosity and a specific gel content. EXAMPLE 81 A 1.5 ℓ autoclave was purged with nitrogen, and 300 ml of toluene and 62 g of 1,3-butadiene were charged therein. To the mixture were added a toluene solution containing 0.5 mmol of triisobutylaluminum as component (C), a toluene solution containing 0.0075 mmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate (Ph 3 CB(C 6 F 5 ) 4 ) as component (B), and a toluene solution containing 0.005 mmol of cyclopentadienylvanadium trichloride (CpVCl 3 ), and polymerization reaction was carried out at 40°C for 20 minutes. The polymerization conditions and the reaction results are shown in Tables 34 and 35, respectively. The analytical results of the resulting polybutadiene are shown in Table 36. EXAMPLES 82 TO 84 Polymerization was carried out in the same manner as in Example 76, except for using cyclohexane as a polymerization solvent. The polymerization conditions and the reaction results are shown in Tables 34 and 35, respectively. The analytical results of the resulting polybutadiene are shown in Table 36. EXAMPLE 85 Polymerization was carried out in the same manner as in Example 84, except for using triethylaluminum as component (C). The polymerization conditions and the reaction results are shown in Tables 34 and 35, respectively. The analytical results of the resulting polybutadiene are shown in Table 36. EXAMPLE 86 A 1 ℓ autoclave was purged with nitrogen, and 200 ml of toluene and a toluene solution containing 0.2 mmol of triisobutylaluminum as component (C) were charged therein. To the mixture were then added a toluene solution containing 0.0015 mmol of ((CH 3 ) 2 NH(C 6 H 5 )B(C 6 F 5 ) 4 ) as component (B) and a toluene solution containing 0.001 mmol of cyclopentadienyloxovanadium dichloride (CpV(O)Cl 2 ) as component (A). Polymerization reaction was carried out at 40°C for 20 minutes. The polymerization conditions and the reaction results are shown in Tables 34 and 35, respectively. The analytical results of the resulting polybutadiene are shown in Table 36. Example No. Component (A) Component (B) Component (C) Reaction Temp. Reaction Time (mmol) (mmol) (mmol) (°C) (min) 81 0.005 0.0075 0.5 40 20 82 0.005 0.0075 0.25 40 60 83 0.005 0.0075 0.5 40 60 84 0.005 0.01 0.25 40 60 85 0.005 0.01 0.25 40 60 86 0.001 0.0015 0.2 40 60 Example No. Yield Catalytic Activity (g) (g/mmol-V.h) 81 36.8 22080 82 22.4 4480 83 16.0 3200 84 28.1 5620 85 47.0 9400 86 10.2 10200 Example No. Microstructure (%) [η] Mw (×10 6 ) Mn (×10 6 ) Mw/ Mn Gel Content cis trans 1,2- (%) 81 88.4 1.9 9.7 12.00 2.63 1.14 2.31 0.006 82 86.8 1.1 12.1 14.51 2.94 1.42 2.07 0.021 83 87.2 1.0 11.8 10.32 2.33 0.96 2.42 0.022 84 86.7 1.3 12.0 16.20 3.17 1.58 2.01 0.036 85 86.7 1.6 11.7 11.03 2.39 1.02 2.34 0.012 86 88.9 1.7 9.4 14.33 2.92 0.99 2.96 0.008 While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims: A catalyst comprising (A) a compound of vanadium, niobium or tantalum represented by formula (I): R n M(O) m X p ·L a wherein M represents vanadium, niobium or tantalum; R represents a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group, a substituted indenyl group, a fluorenyl group or a substituted fluorenyl group; O represents an oxygen atom; X represents a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group, an aryloxy group or an amido group; L represents a Lewis basic compound; n, m, and p each represent an integer selected to make a combination of (n=1, m=1, p=2), (n=1, m=0, p=3), (n=2, m=0, p=1) or (n=1, m=0, p=2); and a represents 0, 1 or 2, and (B) at least one ionic compound comprising a non-coordinating anion and a cation. A catalyst as claimed in claim 1, wherein said catalyst further comprises (C) an organic compound of a group I, II or III metal of the Periodic Table. A catalyst according to claim 1 or claim 2 wherein said compound of vanadium, niobium or tantalum (A) represented by formula (I) is a compound represented by formula RMX 3 , wherein R, M and X have the same meanings as in claim 1. A catalyst according to claim 3 wherein the compound represented by formula RMX 3 is a vanadium compound represented by formula: RVCl 3 , wherein V is a vanadium metal; Cl is a chlorine atom; and R represents a 1,3-dimethylcyclopentadienyl group, a t-butylcyclopentadienyl group, a trimethylsilylcyclopentadienyl group, a bis (trimethylsilyl) cyclopentadienyl group, or a benzylcyclopentadienyl group. A catalyst as claimed in claim 1 or claim 2 wherein said compound of vanadium, niobium or tantalum (A) represented by formula (I) is a compound represented by formula RM(O)X 2 , wherein R, M, O and X have the same meanings as in claim 1. A catalyst according to claim 5 wherein the compound represented by formula RM(O)X 2 is a vanadium compound represented by formula: RV(O)Cl 2 , wherein V is a vanadium metal; C1 is a chlorine atom; R represents a 1,3-dimethylcyclopentadienyl group, a t-butylcyclopentadienyl group, a trimethylsilylcyclopentadienyl group, a bis(trimethylsilyl)cyclopentadienyl group, or a benzylcyclopentadienyl group; and O is an oxygen atom. A catalyst as claimed in claim 1 or claim 2 wherein said compound of vanadium, niobium or tantalum (A) represented by formula (I) is a compound represented by formula R n MX p ·L a , wherein R, M, X and L have the same meaning as in claim 1; the combination of (n,p) is (n=2, p=1) or (n=1, p=2); and a is 0, 1 or 2. A catalyst as claimed in any of claims 1 to 7 wherein said compound of vanadium, niobium or tantalum (A) is a vanadium compound. A process for producing a conjugated diene polymer comprising a step of polymerizing a conjugated diene in the presence of a catalyst as defined in any of the preceding claims. A process for producing a conjugated diene polymer as claimed in claim 9, wherein said polymerizing step is conducted in the presence of hydrogen. A process for producing a conjugated diene polymer as claimed in claim 9 or 10, wherein said polymerizing step is conducted by bulk polymerization. A process for producing a conjugated diene polymer as claimed in claim 9 or 10, wherein said polymerizing step is conducted in the presence of toluene as a polymerization solvent. A process for producing a conjugated diene polymer as claimed in claim 9 or 10, wherein said polymerization step is conducted in the presence of a solvent mainly comprising 2-butene as a polymerization solvent. A process for producing a conjugated diene polymer as claimed in claim 9 or 10, wherein said conjugated diene mainly comprises 1,3-butadiene. A process for producing a conjugated diene polymer as claimed in claim 14, wherein said conjugated diene polymer has a 1,2-structure content of 4 to 30%, a cis-1,4-structure content of 65 to 95%, and a trans-1,4-structure content of not more than 5%. Polybutadiene obtainable by a process according to any of claims 9 to 15 having a 1,2-structure content of 4 to 30%, a cis-1,4-structure content of 65 to 95%, a trans-1,4-structure content of not more than 5%, and B value of more than 1 and not more than 1.43, said B value being represented by equation (a): B = P 1,2-1,4 /(2 x P 1,2 x P 1,4 ) wherein P 1,2 is a 1,2-structure content; P 1,4 is a 1,4-structure content; and P 1,2-1,4 is a (1,2-structure)(1,4-structure) diad chain content in the total diad chains. Polybutadiene obtainable by a process according to any of claims 9 to 15 having a 1,2-structure content of 4 to 30%, a cis-1,4-structure content of 65 to 95%, a trans-1,4-structure content of not more than 5%, a gel content of not more than 0.1%, and an intrinsic viscosity [η] of 3 to 20 as measured in toluene at 30°C.

Inventors: IKAI SHIGERU, IMAOKA KOJI, KAI YOSHIYUKI, SUZUKI MICHINORI, TSUJIMOTO NOBUHIRO, TSUKAHARA KEI, YAMASHITA JUN, IKAI, SHIGERU, IMAOKA, KOJI, KAI, YOSHIYUKI, SUZUKI, MICHINORI, TSUJIMOTO, NOBUHIRO, TSUKAHARA, KEI, YAMASHITA, JUN, Ikai, Shigeru, c/o Ube Industries, Ltd., Imaoka, Koji, c/o Ube Industries, Ltd., Kai, Yoshiyuki, c/o Ube Industries, Ltd., SUZUKI, MICHINORI, C/O UBE INDUSTRIES, LTD., Tsujimoto, Nobuhiro, c/o Ube Industries, Ltd., Tsukahara, Kei, c/o Ube Industries, Ltd., Yamashita, Jun, c/o Ube Industries, Ltd.
Applicants: UBE INDUSTRIES, UBE INDUSTRIES, LTD.
Application year: 1996
Main classification: C08F4
IPC codes: C07F17, C08F4, C08F36, C08F10