Polybutadiene having high 1,2 and cis-1,4 microstructure contents
This invention relates to a process for producing polybutadiene of a high degree of polymerization having a high cis-1,4 microstructure content and a high 1,2 microstructure content and a low trans-1,4 microstructure content, polybutadiene having a very low gel content in addition to the aforesaid properties, a tire tread containing such polybutadiene as a rubber component, and to high-impact polystyrene. 
     It is well known that the reduction of the fuel cost and the increase of safety are important problems to be solved in the automobile industry, and various studies have been conducted on the improvement of automobile tires as means for solving these problems. 
     Generally, styrene butadiene rubber (SBR) and butadiene rubber (BR) are mainly used as a rubber material for automobile tire treads. The styrene butadiene rubber has rebound characteristics and a glass transition temperature which are satisfactory for practical application, and also possesses high wet skid resistance which is the resistance to slippage on a road surface wetted with water, etc. For these properties, SBR has been used in large quantities as a rubber material for treads. The butadiene rubber, on the other hand, has a much lower glass transition temperature (Tg) and higher rebound, i.e. lower rolling resistance than SBR. Because of the low rolling resistance, BR has been studied, and actually used, as a rubber material that contribute to a reduction in fuel cost. 
     The butadiene rubber, however, has the defect of inferior wet skid resistance. Accordingly, when the butadiene rubber is used as a rubber material for treads in order to realize the reduction of the fuel cost, the resulting tires have reduced wet skid resistance which leads to a decrease in the safety of automobiles. On the other hand, the styrene butadiene rubber has sufficiently high wet skid resistance but is limited in rebound and therefore cannot contribute to the reduction of the fuel cost. An attempt has been made to use these rubbers as a mixture in order to utilize the advantages of the respective rubbers and compensate for their shortcomings. In this case, however, there can only be obtained characteristics corresponding to the mixing ratio of the two. 
     A copolymer obtained by the radical polymerization of a styrene monomer in the presence of polybutadiene has improved impact strength in addition to the excellent properties of polystyrene, and is widely marketed as a high impact polystyrene resin. 
     Polybutadiene used to produce this high impact polystyrene resin is generally known to be obtained by a method involving using an alkyl lithium as a catalyst (see Japanese Patent Publications Nos. 38263/1970 and 38264/1970) or a method involving using a cobalt- or nickel-type catalyst (see Japanese Patent Publications Nos. 3894/1961, 8193/1962, 1243/1963 and 5474/1966). The former method gives polybutadiene having a cis-1,4 microstructure content of 30 to 35%, a trans-1,4 microstructure content of 50 to 60% and a 1,2 microstructure content of 10 to 20% (low cis polybutadiene), and the latter method gives polybutadiene having a cis-1,4 microstructure content of 96 to 98%, a trans-1,4 microstructure content of 1 to 2% and a 1,2 microstructure content of 1 to 2% (high cis polybutadiene). 
     Since the low cis polybutadiene is composed mainly of the trans-1,4 microstructure, its rubbery characteristics cannot be said to be sufficient. A polystyrene resin obtained by using the low cis polybutadiene and a styrene monomer is not entirely satisfactory in regard to impact strength. 
     The high cis polybutadiene has low reactivity (graft reactivity) with the styrene monomer because its 1,2 microstructure content is as low as 1 to 2%. A polystyrene resin obtained by using the high cis polybutadiene and the styrene monomer is neither entirely satisfactory in regard to impact strength. 
     Polybutadiene used as a material for a high impact polystyrene resin should have a high 1,2 microstructure content and a high cis-1,4 microstructure content. 
     It is also important that polybutadiene used as a material for the high impact polystyrene resin should have a high molecular weight in addition to the high 1,2 microstructure content and cis-1,4 microstructure content. Low-molecular-weight polybutadiene gives a polystyrene resin which is difficult of exhibiting the rubbery properties of polybutadiene and is not entirely satisfactory in regard to impact strength. 
     It is an object of this invention therefore to provide a process for producing polybutadiene of a high degree of polymerization having high 1,2 and cis-1,4 microstructure contents and a low trans-1,4 microstructure content by using a novel catalyst system. 
     Another object of this invention is to provide polybutadine of a high degree of polymerization having a low gel content produced by using a novel catalyst system. 
     Still another object of this invention is to provide polybutadiene for tire treads capable of giving a tire which has high wet skid resistance and rebound and therefore has high safety and contributes to the saving of the fuel cost. 
     Yet another object of this invention is to provide polybutadiene for high-impact polystyrene having excellent Izod impact strength and markedly improved Du Pont impact strength. 
     Further objects and advantages of this invention will become apparent from the following description. 
     According to this invention, these objects and advantage of the invention are achieved by a process for producing polybutadiene of a high degree of polymerization having high 1,2 and cis-1,4 microstructure contents and a low trans-1,4 microstructure content, which comprises polymerizing 1,3-butadiene in the presence of a catalyst system composed of 
     (1) a halogen-containing organoaluminum compound, 
     (2) (a) a cobalt dithiocarbamate compound or (b) the reaction product of carbon disulfide, a secondary amine and a cobalt compound, and 
     (3) water, 
     to form polybutadiene having 
     (A) a 1,2 microstructure content of 7 to 50%, 
     (B) a cis-1,4 microstructure content of at least 50%, 
     (C) a trans-1,4-microstructure content of at most 5%, and 
     (D) an inherent viscosity, measured in toluene at 30° C., of at least 1. 
     The catalyst system used in this invention is composed of (1) a halogen-containing organoaluminum compound, (2) (a) a cobalt dithiocarbamate compound or (b) the reaction product of carbon disulfide, a secondary amine and a cobalt compound, and water. 
     Examples of preferred halogen-containing organoaluminum compounds are those represented by the following general formula (I) 
     
         AlR.sub.n X.sub.3-n                                        (I) 
    
     wherein R represents an alkyl group having 1 to 8 carbon atom, a cycloalkyl group, or a phenyl group, X represents a halogen atom, and n is a number of 1.5 to 2. 
     The alkyl group having 1 to 8 carbon atoms in formula (I) may be linear or branched, and includes, for example, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, n-pentyl, n-hexyl and n-octyl. 
     Examples of the cycloalkyl group are cyclopentyl and cyclohexyl groups. 
     X represents a halogen atom such as chlorine or bromine. 
     Examples of the halogen-containing organoaluminum compound of formula (I), therefore, include dialkyl aluminum halides such as diethyl aluminum monochloride, diethyl aluminum monobromide and diisobutyl aluminum monochloride; and alkyl aluminum sesquihalides such as ethyl aluminum sesquichloride. 
     A preferred example of the cobalt dithiocarbamate compound (a) is a compound repesented by the following general formula (II) ##STR1## wherein R 1  and R 2  are identical or different and each represents an alkyl group having 1 to 20 carbon atoms, a phenyl group or a cycloalkyl group, or R 1  and R 2  may be bonded to each other to form a heterocyclic ring together with the nitrogen atom to which they are bonded, and m is a number of 2 to 3. 
     In formula (II), the alkyl group having 1 to 20 carbon atoms may be linear or branched, and includes, for example, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, n-dodecyl, n-pentadecyl, n-octadecyl and n-eicosyl. 
     Cyclopentyl and cyclohexyl groups may be cited as examples of the cycloalkyl group. 
     Examples of the heterocyclic ring formed by the bonding of R 1  and R 2  together with the nitrogen atom are piperidine or pipecoline. 
     The cobalt in formula (II) may be divalent or trivalent. 
     In formula (II), R 1  and R 2  are identical or different, and preferably represent an alkyl group having 1 to 12 carbon atoms, especially preferably an alkyl group having 1 to 6 carbon atoms. Preferably, the compound of formula (II) is cobalt dithiocarbamate in which cobalt is trivalent, or a mixture of cobalt dithiocarbamates in which cobalt is trivalent as a main component and cobalt dithiocarbamate in which cobalt is divalent. 
     The cobalt dithiocarbamate compound of formula (II) is a compound known per se, and can be produced by reacting a sodium dialkyldithiocarbamate with cobalt chloride. 
     Detailed methods of producing the cobalt dithiocarbamate compounds are described, for example in M. Delepine, Bull. Soc. Chim., [4], 3, 643-652 (C.A. 2, 2691), L. Compin, Bull. Soc. Chim., 27, 464-469 (1920) (C.A. 14, 3025), and &#34;Shin Jikken Kagaku Koza 8&#34; (New Lecture on Experimental Chemistry), page 1582, published by Maruzen Co. (especially in regard to the production of cobalt (III) dithiocarbamate). 
     Examples of the cobalt dithiocarbamate compound of formula (II) that can be used preferably in this invention include cobalt dimethyldithiocarbamate, cobalt diethyldithiocarbamate, cobalt dipropyldithiocarbamate, cobalt dibutyldithiocarbamate, cobalt dicyclohexyldithiocarbamate, cobalt pentamethylenedithiocarbamate and cobalt pipecolyldithiocarbamate (cobalt methylpentamethylenedithiocarbamate). 
     The reaction product (b) of carbon disulfide, a secondary amine and a cobalt compound may be used as the component (2) of the catalyst system used in this invention instead of the above cobalt dithiocarbamate compound (a). The reaction product (b) can be obtained by intimately contacting carbon disulfide, the secondary amine and the cobalt compound in the presence of an organic reaction medium. 
     The secondary amine is preferably a compound represented by the following formula (III) ##STR2## 
     Examples of the compound of formula (III) are dimethylamine, diethylamine, dipropylamine, dibutylamine, dihexylamine, dioctylamine, piperidine and pipecoline. 
     Examples of the cobalt compound which can be used include organic acid salts such as cobalt acetate, cobalt octenate, cobalt naphthenate and cobalt stearate; complexes such as cobalt tris-acetylacetonate and cobalt bis-acetylacetonate; and inorganic acid salts such as cobalt chloride, cobalt bromide, cobalt iodide, cobalt nitrate and cobalt carbonate. 
     Examples of preferred organic reaction media used in the reaction of carbon disulfide, the secondary amine and the cobalt compound are aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, and halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride and chlorobenzene. Diene monomers, olefin monomers, or aromatic vinyl monomers may be present in the reaction system. 
     The cobalt compound is used preferably in a concentration of not more than 0.2 mole/liter, more preferably not more than 0.1 mole/liter. 
     The mole ratio of the cobalt compound to the secondary amine is preferably from 1:1 to 1:6, more preferably from 1:1 to 1:4. The mole ratio of the secondary amine to carbon disulfide is preferably at least 1:0.5, more preferably from 1:0.5 to 1:5. By changing the ratios of the secondary amine and carbon disulfide to the cobalt compound, the 1,2 microstructure content of the resulting polybutadiene can be changed. 
     In performing the reaction, there is no particular restriction on the sequence of adding the cobalt compound, carbon disulfide and the secondary amine. Preferably, the reaction temperature is usually 10° to 40° C. The reaction time is neither restricted in particular. However, when the cobalt compound is insoluble in the solvent used in the reaction, a slightly longer period of time is required for the cobalt compound to react and dissolve in it. 
     In the polymerization of 1,3-butadiene in the presence of the catalyst system of this invention, the cobalt dithiocarbamate compound (a) or the reaction product (b) of carbon disulfide, the secondary amine and the cobalt compound is used preferably in an amount of 0.001 to 0.5 millimoles, as cobalt, per mole of 1,3-butadiene. The mole ratio of cobalt of the cobalt dithiocarbamate compound (a) or the reaction product (b) to the halogen-containing organoaluminum compound (1) is preferably from 1:5 to 1:2000, more preferably from 1:5 to 1:1000, especially preferably from 1:10 to 1:350. 
     In the catalyst system of this invention, water is an essential component for the smooth proceeding of the polymerization reaction. The mole ratio of water to the halogen-containing organoaluminum compound (H 2  O/Al mole ratio) is preferably from 0.01:1 to 0.7:1, especially preferably from 0.1:1 to 0.6:1. The 1,2 microstructure content of the resulting polybutadiene can be increased by increasing the H 2  O/Al mole ratio of the catalyst system. 
     As a polymerization solvent, there may be used an aromatic hydrocarbon such as benzene, toluene or xylene, an aliphatic hydrocarbon such as butane, butene, n-hexane or n-heptane, an alicyclic hydrocarbon such as cyclohexane or methyl cyclohexane and a halogenated hydrocarbon such as methylene chloride or chlorobenzene. 
     In performing the polymerization, a molecular weight controlling agent, a radical scavenger, etc. may be used. The molecular weight controlling agent is, for example, cyclooctadiene, 1,2-butadiene or allene, and 1,4-benzoquinone may be used as the radical scavenger. The preferred amount of the radical scavenger is 0.2 to 20 moles, especially 0.5 to 10 moles, per mole of the cobalt component. Polybutadiene obtained by using the radical scavenger has an increased content of 1,2 microstructure or is obtained in a larger amount than polybutadiene having the same 1,2-microstructure content but obtained without using the radical scavenger. 
     Preferably, the polymerization of 1,3-butadiene is carried out at a temperature of 5° to 80° C., especially 20° to 70° C. The polymerization time is usually 10 minutes to 10 hours. 
     In the preparation of the catalyst system used in this invention, the contacting of the cobalt dithiocarbamate compound (a) or the reaction product (b) with the halogen-containing organoaluminum compound is desirably effected in the presence of 1,3-butadiene. 
     When the contacting of the components (a) or (b) with the halogen-containing organoaluminum compound is carried out in the absence of 1,3-butadiene, it is desirably carried out under conditions in which the aging of the two components does not so much proceed, for example at a temperature of not more than 50° C. with a contact time of within 5 minutes in the absence of 1,3-butadiene. 
     Preferably, the process of this invention is carried out, for example, by dissolving water in a mixture of 1,3-butadiene and the solvent, and initiating the polymerization of 1,3-butadiene by simultaneously adding the cobalt dithiocarbamate compound (a) or the reaction product (b) and the halogen-containing organoaluminum compound; or by initiating the polymerization of 1,3-butadiene by adding the halogen-containing organoaluminum compound or the cobalt dithiocarbamate compound (a) or the reaction product (b) in the last place. 
     Except for the aforesaid points, the polymerization reaction in accordance with this invention can be performed by conventional known reaction operations for the polymerization of 1,3-butadiene. 
     Generally, the 1,2 microstructure content of the resulting polybutadiene becomes higher as the polymerization temperature is lower or the mole ratio of the halogen-containing organoaluminum compound to the cobalt dithiocarbamate compound (a) or the reaction product (b) (Al/Co) is lower. By adjusting the polymerization temperature and the Al/Co mole ratio, polybutadiene having a high 1,2 microstructure content can be easily obtained. 
     With the catalyst system containing the reaction product (b), the 1,2 microstructure content of the resulting polybutadiene can be changed also by changing the ratio of the cobalt compound, carbon disulfide and the secondary amine in the reaction product (b). For example, the 1,2 microstructure content can be increased by adjusting the mole ratio of carbon disulfide to the secondary amine to 1:1 and increasing the amounts of these compounds over the cobalt compound. 
     Furthermore, the 1,2 microstructure content of polybutadiene can be increased by increasing the mole ratio of water to the halogen-containing organoaluminum compound (H 2  O/Al mole ratio). 
     After the polymerization, an antioxidant may be added as desired to the reaction mixture. Then, polybutadiene can be taken out from the reaction mixture by using known methods, for example by treating the reaction mixture with alcohols, hot water or cold water. 
     Thus, the process of this invention can easily give polybutadiene having 
     (A) a 1,2 microsructure content of 7 to 50%, especially 10 to 50%, 
     (B) a cis-1,4 microstructure content of at least 50%, especially 50 to 88%, 
     (C) a trans-1,4 microstructure content of at most 5%, especially not more than 2%, and 
     (D) an inherent viscosity, measured in toluene at 30° C., of at least 1, especially 1 to 10. 
     In addition to the aforesaid characteristics (A) to (D), polybutadiene produced by the process of this invention has (E) a gel content of at most 0.3%, especially not more than 0.03%. 
     Since the polybutadiene obtained by this invention has excellent wet skid resistance and rebound, a rubber material suitable for automobile tire treads can be produced by adding suitable compounding chemicals and additives to it or to a blend of it with styrene butadiene rubber, and vulcanizing the composition. 
     A superior high-impact polystyrene resin can be produced, for example, by radical polymerization of a mixture composed of 2 to 25 parts by weight, preferably 2 to 20 parts by weight, of the polybutadiene of this invention particularly having a 1,2 microstructure content of 10 to 25% and 75 to 98 parts by weight (preferably 80 to 98 parts by weight) of styrene by a bulk method (continuous method) or a bulk-suspension method (batch method). Methods for production of high-impact polystyrene resin are known per se, and reference may be made to the methods described, for example, in Japanese Patent Publications Nos. 16185/1966 and 447/1969. 
     The 1,2 microstructure content, cis-1,4 microstructure content and trans-1,4 microstructure content (these are inclusively referred to as the microstructure content) are values calculated from the IR spectrum and NMR spectrum of polybutadiene. The inherent viscosity [η] is a value measured in toluene at 30° C. 
     The gel content of the polymer is determined as follows: About 4 g of the polymer is dissolved in 200 ml of toluene at 25° C., and the solution is filtered through a 400-mesh wire gauze. The wire gauze is washed with fresh toluene and dried in vacuum at 80° C. for 5 hours. The gel content is calculated from the weight increase of the wire gauze. 
     The following Examples and Comparative Examples illustrate the present invention more specifically. 
    
    
     EXAMPLES 1-3 
     The air inside a 1-liter autoclave was replaced by dry nitrogen gas, and 200 ml of dehydrated benzene and 62 g of 1,3-butadiene were put in the autoclave. Furthermore, a predetermined amount (indicated in Table 1) of water was added. The mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 0.78 millimole of diethyl aluminum monochloride was added, and 0.007 millimole of cobalt diethyldithiocarbamate was also introduced at 60° C. to initiate the polymerization of 1,3-butadiene. The polymerization was carried out by stirring the reaction mixture at 60° C. for 30 minutes. 
     The cobalt diethyldithiocarbamate had been obtained by reacting sodium diethyldithiocarbamate with cobalt chloride, drying the resulting precipitate and recovering a benzene-soluble portion of the precipitate. The elemental analysis values of the benzene-soluble portion were as follows: C 36.99%, H 6.00%, N 8.26%. Cobalt in the compound was trivalent. 
     After the polymerization, 5 ml of methanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction mixture to stop the polymerization reaction. Methanol (300 ml) was further added to precipitate the resulting polymer. The polymer was dried under reduced pressure at room temperature for 24 hours. 
     The microstructure content, inherent viscosity and gel content of the polymer were measured, and the results are given in Table 1. 
     
                       TABLE 1                                                     
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                           Microstructure                                 
                                        Gel                               
Water     Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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1     0.15    24.3     5.27  89.0 1.0    10.0 0.104                       
2     0.30    24.0     5.29  83.2 0.8    16.0 0.140                       
3     0.39    22.5     5.39  80.1 0.6    19.3 0.252                       
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     In Table 1 and other tables, cis-1,4, trans-1,4 and 1,2 respectively mean cis-1,4 microstructure content, trans-1,4 microstructure content and 1,2 microstructure content. 
     EXAMPLE 4 
     Water was dissolved in a mixture of benzene and butadiene in accordance with the procedure of Example 2, and then cobalt diethyldithiocarbamate was added. Then, diethyl aluminum monochloride was added at 60° C., and the same polymerization as in Example 2 was carried out, and the resulting polymer was taken out. The microstructure content, inherent viscosity and gel content of the polymer are shown in Table 2. 
     EXAMPLE 5 
     Water was dissolved in a mixture of benzene and butadiene in accordance with the procedure of Example 2, and cobalt diethyldithiocarbamate and diethyl aluminum monochloride were simultaneously added at 60° C. Then, the same polymerization reaction as in Example 2 was carried out, and the resulting polymer was taken out. The microstructure content, inherent viscosity and gel content of the resulting polymer are shown in Table 2. 
     
                       TABLE 2                                                     
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                           Microstructure                                 
                                        Gel                               
Water     Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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4     0.30    17.6     4.85  86.8 0.5    12.7 0.265                       
5     0.30    15.2     4.20  87.7 1.0    11.3 0.260                       
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     EXAMPLES 6-8 
     1,3-Butadiene was polymerized in the same way as in Example 2 except that the amount of the cobalt diethyldithiocarbamate was changed as shown in Table 3. The resulting polymer was taken out and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 3. For easy reference, the data obtained in Example 2 are also given in Table 3. 
     
                       TABLE 3                                                     
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                           Microstructure                                 
                                        Gel                               
Co        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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6     0.0035  17.0     6.83  87.6 0.8    11.6 0.132                       
2     0.007   24.0     5.29  83.2 0.8    16.0 0.141                       
7     0.014   24.5     3.17  75.5 0.5    24.0 0.100                       
8     0.021   24.9     3.10  70.4 0.5    29.1 0.105                       
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     EXAMPLES 9-10 
     1,3-Butadiene was polymerized in the same way as in Example 2 except that the amount of dehydrated benzene was changed to 250 ml, the amount of 1,3-butadiene was changed to 31 g, and the amount of cobalt diethyldithiocarbamate was changed as shown in Table 4. The resulting polymer was taken out, and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 4. 
     
                       TABLE 4                                                     
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                           Microstructure                                 
                                        Gel                               
Co        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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 9    0.007    9.7     3.05  75.2 0.5    24.3 0.030                       
10    0.021   14.5     2.29  68.0 0.2    31.8 0.025                       
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     EXAMPLES 11-14 
     1,3-Butadiene was polymerized in the same way as in Example 2 except that the kind of the cobalt dithiocarbamate compound was changed as shown in Table 5. The resulting polymer was taken out, and its microstructure, inherent viscosity and gel content were measured. The results are shown in Table 5. 
     
                       TABLE 5                                                     
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                       Microstructure                                     
        Amount         content (%)    Gel                                 
Ex-   Kind    yielded        cis- trans-      con-                        
ample of Co   (g)      [η]                                            
                             1,4  1,4    1,2  tent                        
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11    A       11.7     4.53  80.4 0.8    18.8 0.080                       
12    B       23.8     4.07  78.5 0.6    20.9 0.121                       
13    C       17.0     4.68  80.3 0.7    19.0 0.101                       
14    D       21.6     4.52  81.5 0.5    18.0 0.110                       
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     The kinds of Co represented by A, B, C and D were as follows: 
     A: Cobalt dimethyldithiocarbamate 
     B: Cobalt di-n-butyldithiocarbamate 
     C: Cobalt pentamethylenedithiocarbamate 
     D: Cobalt pipecolyldithiocarbamate 
     These compounds were synthesized in the same way as in the preceding Examples, and the benzene-soluble portions were used. 
     EXAMPLES 15-17 
     1,3-Butadiene was polymerized in the same way as in Examples 1 to 3 except that the amount of water added was changed as indicated in Table 6, the amount of diethyl aluminum monochloride was changed to 1.56 millimoles, cobalt diethyldithiocarbamate was added at 30° C., and the polymerization temperature was changed to 30° C. The resulting polymer was taken out, and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 6. 
     
                       TABLE 6                                                     
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                           Microstructure                                 
                                        Gel                               
Water     Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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15    0.15    18.5     6.18  67.5 0.0    32.5 0.005                       
16    0.30    18.2     6.12  63.1 0.2    36.7 0.005                       
17    0.45    11.0     6.22  60.4 1.1    38.5 0.021                       
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     EXAMPLES 18-19 
     1,3-Butadiene was polymerized in the same way as in Example 16 except that the amount of diethylaluminum monochloride was changed as indicated in Table 7. The resulting polymer was taken out, and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 7. 
     
                       TABLE 7                                                     
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                           Microstructure                                 
                                        Gel                               
Al        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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18    0.78    11.0     6.63  58.6 0.0    41.4 0.001                       
19    7.80    14.1     6.31  79.3 0.5    20.2 0.009                       
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     Al in this and other tables means diethylaluminum monochloride. 
     EXAMPLE 20 
     1,3-Butadiene was polymerized in the same way as in Example 19 except that the amount of water was changed to 0.90 millimole. The resulting polymer was taken out, and its microstructure, inherent viscosity and gel content were measured. The results are shown in Table 8. 
     
                       TABLE 8                                                     
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                           Microstructure                                 
                                        Gel                               
Water     Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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20    0.90    14.2     5.79  64.5 0.6    34.9 0.010                       
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     EXAMPLE 21 
     The air inside a 5-liter autoclave was replaced by dry nitrogen gas, and 1300 ml of dehydrated benzene and 420 g of 1,3-butadiene were put into it. Water (1.4 millimoles) was added, and the mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 5.2 millimoles of diethyl aluminum monochloride and 56.0 millimoles of 1,5-cyclooctadiene were added, and further 0.2 millimole of cobalt diethyldithiocarbamate was added at 50° C. to initiate the polymerization of 1,3-butadiene. The polymerization reaction was carried out by stirring the reaction mixture at 50° C. for 30 minutes. 
     After the polymerization, 30 ml of methanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to stop the polymerization reaction. Furthermore, 2 liters of methanol was added to precipitate the resulting polymer. The polymer was dried under reduced pressure at room temperature for 24 hours. The microstructure content, inherent viscosity and gel content of the resulting polymer were measured, and the results are shown in Table 9. 
     
                       TABLE 9                                                     
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                           Microstructure                                 
                                        Gel                               
Al        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
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21    5.2     137      2.50  59.7 0.6    39.7 0.040                       
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     EXAMPLES 22-23 
     1,3-Butadiene was polymerized in the same way as in Example 21 except that the temperature at which cobalt diethyldithiocarbamate was added and the polymerization temperature were changed to 60° C., and the amount of cobalt diethyldithiocarbamate was changed as indicated in Table 10. 
     The resulting polymer was taken out, and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 10. 
     
                       TABLE 10                                                    
______________________________________                                    
                           Microstructure                                 
                                        Gel                               
Co        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
______________________________________                                    
22    0.094   135      2.35  73.3 0.7    26.0 0.075                       
23    0.047   123      2.11  83.0 0.8    16.2 0.062                       
______________________________________                                    
 
    
     EXAMPLES 24-25 
     1,3-Butadiene was polymerized in the same way as in Example 21 except that the amount of diethylaluminum monochloride was changed to 6.0 millimoles, the temperature at which cobalt diethyldithiocarbamate was added and the polymerization temperature were changed to 60° C., and the amount of cobalt diethyldithiocarbamate was changed as indicated in Table 11. The resulting polymer was taken out and its microstructure content, inherenet viscosity and gel content were measured. The results are shown in Table 11. 
     
                       TABLE 11                                                    
______________________________________                                    
                           Microstructure                                 
                                        Gel                               
Co        Amount           content (%)  con-                              
Ex-   (milli- yielded        cis- trans-      tent                        
ample moles)  (g)      [η]                                            
                             1,4  1,4    1,2  (%)                         
______________________________________                                    
24    0.094   142      2.13  79.2 0.6    20.2 0.074                       
25    0.047   132      1.87  86.7 0.8    12.5 0.070                       
______________________________________                                    
 
    
     EXAMPLES 26-28 AND COMPARATIVE EXAMPLES 1-2 
     Each of the polybutadienes produced in Examples 21 to 23 was vulcanized at 150° C. for 30 minutes in accordance with the following recipe. The various properties of the vulcanizate were measured. 
     For comparison, commercial high cis polybutadiene rubber (high cis BR: cis-1,4 microstructure content 97.0%, trans-1,4 microstructure content 1.0%, 1,2 microstructure content 2.0%, [η]=2.0) and commercial styrene butadiene rubber (SBR: styrene monomer unit content=23.5%) were vulcanized in the same way as above (the vulcanization time for SBR was 60 minutes). The properties of the vulcanizates were also measured. 
     
         ______________________________________                                    
Vulcanization recipe                                                      
                  Parts by weight                                         
______________________________________                                    
Rubber            100                                                     
HAF carbon        50                                                      
High aromatic oil 10                                                      
Zinc oxide        5                                                       
Stearic acid      2                                                       
Antioxidant       1                                                       
Vulcanization accelerator                                                 
                  1                                                       
Sulfur            1.5                                                     
______________________________________                                    
 
    
     The antioxidant used was Antigen AS made by Sumitomo Chemical Co., Ltd. The vulcanization accelerator was N-cyclohexyl-2-benzothiazole sulfenamide. 
     The results of the measurement are shown in Table 12. 
     
                       TABLE 12                                                    
______________________________________                                    
                   Wet skid                                               
                   resistance                                             
                             Rebound                                      
         Rubber    (relative (relative                                    
Example  used      value)    value) Hardness                              
______________________________________                                    
26       Example 21                                                       
                   50 (152)  59 (95)                                      
                                    62                                    
27       Example 22                                                       
                   42 (127)  60 (97)                                      
                                    60                                    
28       Example 23                                                       
                   39 (118)  61 (98)                                      
                                    58                                    
Comp.    High cis  33 (100)  62 (100)                                     
                                    59                                    
Ex. 1    BR                                                               
Comp.    SBR       51 (155)  47 (76)                                      
                                    60                                    
Ex. 2                                                                     
______________________________________                                    
 
    
     The properties given in Table 12 were measured by the following methods. 
     (1) Wet skid resistance 
     Measured on a wet ground glass surface at room temperature (25° C.) by means of a portable skid tester made by Stanley Co., Britain. 
     (2) Rebound 
     Measured at room temperature (25° C.) in accordance with JIS K-6301. 
     (3) Hardness 
     Measured by means of a JIS hardness tester (Shore A). 
     The relative values given in Table 12 were based on the measured values of a rubber obtained by using high cis BR as a material which were each taken as 100. 
     EXAMPLES 29-31 AND COMPARATIVE EXAMPLES 3-4 
     Using each of the polybutadienes produced in Examples 23 to 25, a high-impact polystyrene resin was produced by the method described below, and its impact strength was tested. 
     For comparison, high-impact polystyrene resins were produced by the same method using commercial high cis polybutadiene (high cis BR: cis-1,4 microstructure content 95.9%, trans-1,4 microstructure content 2.0%, 1,2 microstructure content 2.1%, [η]=1.8) and commercial low cis polybutadiene rubber (low cis BR: cis-1,4 microstructure colntent 34.0%, trans-1,4 microstructure conent 54.0%, 1,2 microstructure 12.0%, [η]=1.9), and their impact strnegths were also tested. 
     Production of the high-impact polystyrene resin: 
     The air inside a 1-liter separable flask was replaced by nitrogen gas, and 570 g of styrene and 30 g (5% by weight) of polybutadiene were added and dissolved. Then, 0.3 g of n-dodecylmercaptan and 11.4 g of n-butyl stearate were added. The mixture was stirred at 120° C. until the polymerization conversion of styrene reached 30%. The reaction mixture was added to 600 ml of a 0.5% by weight aqueous solution of polyvinyl alcohol, and the mixture was injected into an autoclave. Benzoyl peroxide (0.93 g) and 0.93 g of dicumyl peroxide were added, and the mixture was stirred at 100° C. for 2 hours, then at 125° C. for 3 hours and further at 140° C. for 2 hours to perform the polymerization. The resulting polymer in the form of beads were collected from the reaction mixture by filtration, washed with water, dried, and then pelletized in an extruder to give 500 g of a polystyrene resin. 
     The properties of the polystyrene were measured, and the results are shown in Table 13. 
     
                       TABLE 13                                                    
______________________________________                                    
                      Izod imapct                                         
                                Du Pont                                   
                      strength  impact                                    
                      (notched) strength                                  
Example   Rubber used (kg-cm/cm)                                          
                                (kg-cm)                                   
______________________________________                                    
29        Example 23  8.9       25                                        
30        Example 24  8.5       24                                        
31        Example 25  8.8       23                                        
Comp.     High cis BR 8.5       19                                        
Ex. 3                                                                     
Comp.     Low cis BR  7.5       20                                        
Ex. 4                                                                     
______________________________________                                    
 
    
     The impact strengths in these and other examples were measured by the following methods. 
     (1) Izod impact strength 
     Measured in accordance with ASTM D256. 
     (2) Du Pont impact strength 
     A 2 mm thick sheet was press-formed and a test sample was taken from it. Its Du Pont impact strength was measured under the following conditions. 
     Falling impact rod diameter: 1/2 inch 
     Bearer diameter: 1/2 inch 
     Load: 500 g 
     EXAMPLES 32-35 
     The air inside a 1.5-liter autoclave was replaced by dry nitrogen gas, and then 717 ml of dehydrated benzene and 176 g of 1,3-butadiene were put into it. Water (1.33 millimoles) was added and the mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 4.0 millimoles of diethyl aluminum monochloride and 49 millimoles of 1,5-cyclooctadiene were added. The temperature was raised to 60° C., and 0.07 millimole of cobalt diethyldithiocarbamate was added. One minute later, a predetermined amount (given in Table 14) of 1,4-benzoquinone was added, and the mixture was stirred at 60° C. for a predetermined polymerization time (indicated in Table 14). 
     After the polymerization, 15 ml of methanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction solution to stop the polymerization. The solution was added to 1 liter of methanol to precipitate the resulting polymer. The polymer was dried under reduced pressure for 24 hours, and its microstructure content, inherent viscosity and gel content were measured. The results are shown in Table 14. 
     
                       TABLE 14                                                    
______________________________________                                    
     1,4-    Poly-                                                        
     Benzo-  meri-              Microstructure                            
                                            Gel                           
Ex-  qui-    zation  Amount     content (%) con-                          
am-  none    time    yielded    cis- trans-     tent                      
ple  (mM)    (min.)  (g)   [η]                                        
                                1,4  1,4   1,2  (%)                       
______________________________________                                    
32   0.035    30     48    2.42 72.7 0.4   26.8 0.010                     
33   0.035   300     74    2.47 71.7 0.6   27.7 0.013                     
34   0.070    30     58    2.24 74.1 0.5   25.4 0.008                     
35   0.070   300     82    2.19 74.0 0.9   25.1 0.010                     
______________________________________                                    
 
    
     EXAMPLES 36-37 
     A 1,3-butadiene solution having the following composition by weight was polymerized. 
     1,3-Butadiene--24.0% 
     cis-2-Butene--19.5% 
     trans-2-Butene--6.3% 
     iso-Butene--0.5% 
     1-Butene--0.2% 
     Ethane--0.1% 
     Benzene--49.4% 
     The air inside a 1.5-liter autoclave was replaced by dry nitrogen gas, and 1000 ml of the above 1,3-butadiene solution was put into it. Water (1.5 millimoles) was added, and the mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 3.3 millimoles of diethyl aluminum monochloride and 20 millimoles of 1,5-cyclooctadiene were added. The temperature was raised to 60° C., and a predetermined amount described in Table 15 of cobalt diethyldithiocarbamate was added. One minute later, 0.074 mM of 1,4-benzoquinone was added, and the mixture was stirred at 60° C. for 62 minutes. 
     After the polymerization, the reaction mixture was worked up in the same way as in Examples 32-35. 
     The results are shown in Table 15. 
     
                       TABLE 15                                                    
______________________________________                                    
     1,4-                                                                 
     Benzo-          A-         Microstructure                            
                                            Gel                           
Ex-  qui-            mount      content (%) con-                          
am-  none    Cobalt  yielded    cis- trans-     tent                      
ple  (mM)    (mM)    (g)   [η]                                        
                                1,4  1,4   1,2  (%)                       
______________________________________                                    
36   0.074   0.035   60    2.20 84.1 0.9   15.0 0.005                     
37   0.074   0.070   72    2.24 79.4 1.0   19.6 0.015                     
______________________________________                                    
 
    
     EXAMPLES 38-40 
     (1) To 20 ml of a benzene solution of cobalt octenate (0.035 mole/liter) was added 2.2 ml of a benzene solution of carbon disulfide (0.7 mole/liter). Then, 2.2 ml of a benzene solution of diethylamine (0.7 mole/liter) was added with stirring. The mixture was stirred at room temperature (25° C.) for 1 day. Then, 24.4 ml of the resulting solution was diluted with 175.6 ml of benzene to prepare a solution of catalyst component (b) (0.0035 mole/liter; mole ratio 1:2.2:2.2). 
     (2) The air inside a 1-liter autoclave was replaced by dry nitrogen gas, and 213 ml of dehydrated benzene and 54 g of 1,3-butadiene were added. Then, a predetermined amount (indicated in Table 16) of water was added. The mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 0.9 millimole of diethylaluminum monochloride was added, and the temperature was raised to 60° C. Three milliliters (0.0105 millimole based on cobalt octenate) of the above catalyst component (b) solution was added, and the mixture was stirred at 60° C. for 30 minutes to perform polymerization. 
     After the polymerization, 5 ml of methanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to stop the polymerization reaction. Further, 300 ml of methanol was added to precipitate the resulting polymer. The polymer was dried at room temperature under reduced pressure for 24 hours. 
     The microstructure, inherent viscosity and gel content of the resulting polymer were measured, and the results are shown in Table 16. 
     
                       TABLE 16                                                    
______________________________________                                    
                            Microstructure                                
                                        Gel                               
Water     Amount            content (%) con-                              
Ex-   (milli- yielded         cis- trans-                                 
                                         1,2  tent                        
ample moles)  (g)      [η]                                            
                              1,4  1,4   1,2  (%)                         
______________________________________                                    
38    0.3     27.7     4.70   83.5 0.8   15.7 0.092                       
39    0.36    27.6     5.50   80.3 0.7   19.0 0.115                       
40    0.45    11.0     4.77   76.7 1.0   22.3 0.230                       
______________________________________                                    
 
    
     EXAMPLES 41-49 
     1,3-Butadiene was polymerized in the same way as in Example 39 except that the mole ratio of the ingredients of the catalyst component (b) were changed as indicated in Table 17. The results are shown in Table 17. 
     
                                           TABLE 17                                
__________________________________________________________________________
Mole ratio of the                                                         
ingredient of the                                                         
catalyst component (b)                                                    
                 Carbon                                                   
                 disul-     Microstructure                                
Cobalt  Carbon   fide/      content (%)                                   
                                      Gel                                 
Ex- octe-                                                                 
        di- Diethyl                                                       
                 diethyl                                                  
                     Yield  cis-                                          
                               trans- content                             
ample                                                                     
    nate                                                                  
        sulfide                                                           
            amine                                                         
                 amine                                                    
                     (g) [η]                                          
                            1,4                                           
                               1,4 1,2                                    
                                      (%)                                 
__________________________________________________________________________
41  1   1.5 1.5  1   27.0                                                 
                         4.38                                             
                            87.7                                          
                               0.8 11.5                                   
                                      0.153                               
42  1   2   2    1   29.7                                                 
                         5.56                                             
                            82.4                                          
                               0.9 16.7                                   
                                      0.141                               
43  1   2.5 2.5  1   26.1                                                 
                         4.11                                             
                            77.8                                          
                               0.7 21.5                                   
                                      0.111                               
44  1   3   3    1   21.0                                                 
                         3.93                                             
                            71.5                                          
                               0.8 27.7                                   
                                      0.087                               
45  1   3.5 3.5  1   12.0                                                 
                         3.58                                             
                            69.9                                          
                               0.6 29.5                                   
                                      0.050                               
46  1   1.5 2    0.75                                                     
                     26.2                                                 
                         4.40                                             
                            84.1                                          
                               1.2 14.7                                   
                                      0.110                               
47  1   2.5 2    1.25                                                     
                     33.0                                                 
                         5.66                                             
                            84.4                                          
                               0.8 14.8                                   
                                      0.200                               
48  1   2   1.5  1.33                                                     
                     30.0                                                 
                         5.03                                             
                            88.7                                          
                               0.8 10.5                                   
                                      0.272                               
49  1   2   2.5  0.8 25.3                                                 
                         4.22                                             
                            80.0                                          
                               0.7 19.3                                   
                                      0.126                               
__________________________________________________________________________
 
    
     EXAMPLES 50-54 
     1,3-Butadiene was polymerized in the same way as in Example 39 except that the mole ratio of cobalt octenate, carbon disulfide and diethylamine of the catalyst component (b) was changed to 1:3:3, and the time spent for reacting the ingredients of the catalyst component (b) was changed as indicated in Table 18. The results are shown in Table 18. 
     
                       TABLE 18                                                    
______________________________________                                    
Reaction                                                                  
time for                                                                  
the cat-                    Microstructure                                
                                        Gel                               
alyst      Amount           content (%) con-                              
Ex-   compo-   yielded        cis- trans-     tent                        
ample nent (b) (g)      [η]                                           
                              1,4  1,4   1,2  (%)                         
______________________________________                                    
50    15 min.  21.0     3.60  74.8 1.2   24.0 0.145                       
51    4 hrs.   20.8     3.67  71.5 0.5   28.0 0.092                       
52    24 hrs.  21.0     3.93  71.5 0.8   27.7 0.080                       
53    3 days   22.5     5.16  74.3 0.7   25.0 0.151                       
54    6 days   20.2     4.80  78.0 1.0   21.0 0.101                       
______________________________________                                    
 
    
     EXAMPLE 55 
     1,3-Butadiene was polymerized in the same way as in Example 44 except that the catalyst component (b) was added at 30° C. and the polymerization temperature was changed to 30° C. There was obtained 10.3 g of polybutadidne having an [η] of 6.32, a cis-1,4 microstructure content of 58.2, a trans-1,4 microstructure content of 0.5% and a 1,2 microstructure content of 41.3%. 
     EXAMPLE 56 
     1,3-Butadiene was polymerized in the same way as in Example 39 except that in the preparation of the catalyst component (b), cobalt tris-acetylacetonate was used instead of cobalt octenate. There was obtained 24.6 g of polybutadiene having an [η] of 4.50, a cis-1,4 microstructure content of 84.1%, a trans-1,4 microstructure content of 1.1% and a 1,2 microstructure content of 14.8%. 
     EXAMPLE 57 
     1,3-Polybutadiene was polymerized in the same way as in Example 44 except that in the preparation of the catalyst component (b), anhydrous cobalt chloride in powder form was used instead of cobalt octenate. There was obtained 19.3 g of polybutadiene having an [η] of 3.55, a cis-1,4 microstructure content of 78.9%, a trans-1,4 microstructure content of 0.9% and a 1,2 microstructure content of 20.2%. 
     EXAMPLE 58 
     1,3-Butadiene was polymerized in the same way as in Example 39 except that in the preparation of the catalyst component (b), di-n-butylamine was used instead of diethylamine. There was obtained 29.0 g of polybutadiene having an [η] of 4.42, a cis-1,4 microstructure content of 78.2%, a trans-1,4 microstructure content of 0.7% and a 1,2 microstructure content of 21.1%. 
     COMPARATIVE EXAMPLE 5 
     (1) To 20 ml of benzene were added 3 ml of a benzene solution of carbon disulfide (0.7 mole/liter) and 3 ml of a benzene solution of diethylamine (0.7 mole/liter). They were reacted with stirring at room temperature (25° C.) for 1 day with stirring to obtain 26 ml of a solution. 
     (2) The air inside a 1-liter autoclave was replaced by dry nitrogen gas, and 213 ml of dehydrated benzene and 54 g of 1,3-butadiene were put into it. Water (0.36 millimole) was added, and the mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 0.9 millimole of diethyl aluminum monochloride was added. The temperature was raised to 60° C., and 0.39 ml of the above catalyst solution was added. Finally, 0.0105 millimole of cobalt octenate was added, and the mixture was stirred at 60° C. for 10 minutes to perform polymerization. There was obtained 32.7 g of polybutadiene having an [η] of 6.21, a cis-1,4 microstructure content of 96.3%, a trans-1,4 microstructure content of 1.4% and a 1,2 microstructure content of 2.3%. 
     EXAMPLES 59-60 
     The air inside a 1.5-liter autoclave was replaced by dry nitrogen gas, and 710 ml of dehydrated benzene and 180 g of 1,3-butadiene were put into it. A predetermined amount (indicated in Table 19) of water was added, and the mixture was stirred at 30° C. for 30 minutes to dissolve water. Then, 4 millimoles of diethylaluminum monochloride and 46 millimoles of 1,5-cyclooctadiene were added. The temperature was raised to 60° C., and 20 ml (0.070 millimole based on cobalt octenate) of the catalyst component (b) solution used in Examples 38 to 40 was added, and the mixture was stirred at 60° C. for 30 minutes. 
     After the polymerization, 15 ml of methanol containing a small amount of 2,6-di-t-butyl-p-cresol was added to the reaction mixture to stop the polymerization. The solution was added to 1 liter of methanol to precipitate the resulting polymer. The polymer was dried at room temperature under reduced pressure for 24 hours. 
     The microstructure content, inherent viscosity and gel content of the resulting polymer were measured, and the results are shown in Table 19. 
     
                       TABLE 19                                                    
______________________________________                                    
                            Microstructure                                
                                        Gel                               
Water     Amount            content (%) con-                              
Ex-   (milli- yielded         cis- trans-     tent                        
ample moles)  (g)      [η]                                            
                              1,4  1,4   1,2  (%)                         
______________________________________                                    
59    1.00    49.5     2.22   84.0 0.8   15.2 0.060                       
60    1.33    52.1     2.40   78.3 0.7   21.0 0.085                       
______________________________________                                    
 
    
     EXAMPLES 61-62 AND COMPARATIVE EXAMPLES 6-7 
     Using the polybutadienes produced in Examples 36 and 37, high-impact polystyrene resins were produced and tested by the same methods as in Examples 29-31. 
     For comparison, high-impact polystyrene resins were also produced and tested by using commercial high cis polybutadiene rubber (high cis BR: cis-1,4 microstructure content 95.1%, trans-1,4 microstructure content 2.5%, 1,2 microstructure content 2.4%, [η]=2.0) and commercial low cis polybutadiene rubber (low cis BR: cis-1,4-microstructure content 31.7%, trans-1,4 microstructure 54.9%, 1,2 microstrucure content 13.4%, [η]=1.9). 
     The results are shown in Table 20. 
     
                       TABLE 20                                                    
______________________________________                                    
                       Izod impact                                        
                                 Du Pont                                  
                       strength  impact                                   
                       (notched) strength                                 
Example   Rubber used  (kg-cm/cm)                                         
                                 (kg-cm)                                  
______________________________________                                    
61        Example 36   8.9       26                                       
62        Example 37   8.6       25                                       
Comp.     High cis BR  8.6       19                                       
Ex. 6                                                                     
Comp.     Low cis BR   7.8       20                                       
Ex. 7                                                                     
______________________________________                                    
 
    
     All of the above molded articles had a good appearance. 
     EXAMPLES 63-64 AND COMPARATIVE EXAMPLES 8-9 
     A high-impact polystyrene resin was produced by a continuous bulk method from the polybutadiene obtained by this invention, and then tested for impact strength. 
     First-stage polymerization was carried out continuously in a 300 ml polymerization vessel equipped with a stirrer, thermometer, reflux condenser, ribbon heater, gas introducing inlet, styrene solution supply opening and polymer solution withdrawing opening. Specifically, the polymerization vessel was purged with nitrogen gas, and fed with a styrene solution containing 6% by weight of each of the rubbers indicated in Table 21 and 0.02% by weight of laurylmercaptan at a rate of 1 ml/ml. While the polymerization was performed at a temperature of 110° C., the polymer solution was extruded at a rate of 1 ml/min. and pooled in a reservoir. When the residence time was adjusted to 3 to 3.5 hours, the conversion was about 30 to 35%. 
     Three hundred grams of the first-stage polymer solution was transferred to a bottle (360 ml). The inside of the bottle was purged with nitrogen gas, and the polymerization was carried out at 125° C. for 2 hours, at 135° C. for 2 hours, at 145° C. for 2 hours, at 160° C. for 2 hours, and finally at 180° C. for 2 hours. 
     The final polymer was molded into a sheet by a hot press, dried in a vacuum dryer to remove the volatile matter, and pelletized. The pelletized sample was tested for impact strengths, and the results are shown in Table 21. 
     
                                           TABLE 21                                
__________________________________________________________________________
Rubber used                 Izod impact                                   
         Microstructure Gel impact strength                               
                                    Du Pont                               
         content (%)    content                                           
                            (notched;                                     
                                    impact strength                       
Example                                                                   
     Type                                                                 
         cis-1,4                                                          
             trans-1,4                                                    
                  1,2                                                     
                     [η]                                              
                        (%) kg-cm/cm)                                     
                                    (kg-cm)                               
__________________________________________________________________________
63   HVP-1                                                                
         86.6                                                             
             0.9  12.5                                                    
                     2.2                                                  
                        0.013                                             
                            10.8    33                                    
64   HVP-2                                                                
         82.5                                                             
             0.7  16.8                                                    
                     2.0                                                  
                        0.010                                             
                            10.5    33                                    
CEx. High                                                                 
         95.1                                                             
             2.5   2.4                                                    
                     2.0                                                  
                        0.010                                             
                            10.9    28                                    
8    cis                                                                  
     BR                                                                   
CEx. Low 32.3                                                             
             55.7 12.0                                                    
                     1.9                                                  
                        0.020                                             
                             9.4    31                                    
9    cis                                                                  
     BR                                                                   
__________________________________________________________________________