Process of preparing butadiene-styrene copolymer with nickel compound and alkylaluminoxane compound catalysts

A process is provided for preparing butadiene-styrene copolymers having cis-1,4 configuration of at least 80% of butadiene units, bound styrene contents of 2 to 55% and no homopolystyrene. The copolymers are prepared with a new catalyst system having high polymerization activity. The process involves carrying out polymerization of butadiene monomer and styrene monomer in the presence of the new catalyst system which is comprised of a nickel compound and an alkylaluminoxane compound.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel process for copolymerizing 
butadiene and styrene and to a process for preparing improved 
butadiene-styrene copolymers having a high cis-1,4 configuration of the 
butadiene units. 
2. Description of the Related Art 
High cis-1,4 polybutadiene rubber has many excellent properties such as 
high resilience, low heat-built-up and abrasion resistance, and is 
therefore used for tires. 
However, this rubber tends to have undesirable processing characteristics 
such as poor banding on a roll mill, which therefore necessitates a 
multiplation mixing stage. Further, the rubber has poor tear resistance, 
which results in chipping or cutting of the rubber. 
A butadiene-styrene copolymer, which has a high cis-1,4 configuration of 
the butadiene units and the suitable contents of styrene, may be the most 
desirable polymer to solve these drawbacks without adversely affecting the 
above-described excellent characteristic properties of cis-1,4 
polybutadiene. 
Further, it has been known in the prior art that polybutadienes having a 
high cis-1,4 configuration of the butadiene units can be produced with 
high activity catalysts such as a three-component catalyst system 
comprising a nickel compound, a Lewis acid and an organo aluminum 
compound, as described in U.S. Pat. No. 3,170,904 and others. 
The copolymerization of butadiene and styrene was carried out with an 
aforementioned three-component catalyst having acetylacetone nickel 
compound as the nickel compound, titanium tetrachloride as the Lewis acid 
and triethylaluminum as the organo aluminum compound, as described above 
(U.S. Pat. No. 3,639,520 and Kogyo Kagaku Zasshi, Vol.72, p. 2081 (1969)). 
In this case, the polymerization activity of the catalyst system becomes 
markedly lower. Further, resultant copolymers have a high cis-1,4 
configuration of the butadiene units and have a very low content of bound 
styrene of the copolymer. As the resultant copolymers contain 
homopolystyrene, the desirable properties of the copolymer deteriorate. 
Further, there are processes, which are well-known in the industry, for 
producing butadiene-styrene copolymers. 
Main catalyst systems in such processes are as follows: an alkyllithium 
compound system and a radical type catalyst system. Further, in the 
well-known processes mentioned above, the cis-1,4 configuration of the 
butadiene units of the copolymer is less than or equal to about 60%. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide butadiene-styrene 
copolymers having a cis-1,4 configuration of at least 80% of the butadiene 
units, bound styrene contents of 2 to 55% , and no homopolystyrene. 
Another object of the present invention is to provide a process for 
producing the copolymers described above by copolymerization using a new 
catalyst system having high polymerization activity. 
The process involves carrying out polymerization of butadiene monomer and 
styrene monomer in the presence of a catalyst, wherein the catalyst 
comprises of (A) a nickel compound and (B) an alkylaluminoxane compound, 
wherein the amount of the nickel compound is 0.001 to 10 mmole per 100 g 
of total monomers charged, and further, the molar ratio of aluminum in the 
alkylaluminoxane compound to nickel in the nickel compound is 1 to about 
1.times.1O.sup.5, wherein the alkylaluminoxane compound is represented by 
any one of the following formulas (I), (II) and (III): 
______________________________________ 
R.sup.1 [Al(R.sup.2)O]nAl(R.sup.3,R.sup.4) 
(linear structure) 
(I) 
[Al(R.sup.5)O]m (cyclic structure) 
(II) 
mixtures of (I) and (II) (III) 
______________________________________ 
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are selected from 
alkyls having from 1 to about 10 carbon atoms, n is an integer from 1 to 
about 100, and m is an integer from 2 to about 50.

DETAILED DESCRIPTION OF THE INVENTION 
The butadiene-styrene copolymers of the present invention are prepared by 
copolymerization using a catalyst system containing a nickel compound as 
the (A) component and an alkylaluminoxane compound as the (B) component. 
The nickel compound of the catalyst system includes a nickel salt of an 
organic carboxylic acid and an organic complex compound of nickel. 
The nickel salt of an organic carboxylic acid has the following formula: 
EQU (R.sub.6 --CO--O).sub.P Ni 
wherein R.sup.6 is selected from the group consisting of aliphatic-, 
alicyclic- and aromatic-hydrocarbon and p is the valence of nickel. 
These salts are, for example, nickel formate, nickel acetate, nickel 
ethylhexoate, nickel isooctenate, nickel palmitate, nickel stearate, 
nickel benzoate, nickel methylbenzoate, nickel cyclohexylcarboxylate and 
nickel naphthenate. 
The organic complex compound of nickel is a carbonyl nickel complex such as 
tetracarbonyl nickel, a hydroxyaldehyde nickel complex such as 
salicylaldehyde nickel or salicylaldehydeimine nickel, a hydroxyketone 
nickel complex such as acetylacetone nickel, a hydroxyester nickel complex 
such as acetaceticethylester nickel, a diketonedioximo nickel complex such 
as bis (dimethylglyoximo) nickel, an 8-hydroxyquinoline nickel complex 
such as 8-hydroxyquinoline nickel or a .pi.-cyclopentadienyl nickel 
complex such as .pi.-cyclopentadienyl nickel. 
It is preferable to use nickel formate, nickel naphthenate, nickel 
stearate, nickel benzoate, acetylacetone nickel, acetaceticethylester 
nickel, salicylaldehyde nickel or salicylaldehydeimine nickel. 
It should be noted with regard to the alkylaluminoxane compound that the 
structure may basically be either a linear polymer structure or a cyclic 
polymer structure consisting of a -Al(R)O-(alkylaluminoxy) unit, or may be 
a mixture of both structures. 
Thus, the alkylaluminoxane compound of the catalyst system is represented 
by any one of the following formulas (I), (II) and (III): 
______________________________________ 
R.sup.1 [Al(R.sup.2)O]nAl(R.sup.3,R.sup.4) 
(linear structure) 
(I) 
[Al(R.sup.5)O]m (cyclic structure) 
(II) 
mixtures of (I) and (II) (III) 
______________________________________ 
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are selected from 
alkyls having from 1 to about 10 carbon atoms, n is an integer from 1 to 
about 100, and m is an integer from 2 to about 50. The mixtures (III) are 
preferable for alkylaluminoxane compound. 
R.sup.1, R.sup.2, R.sup.3 l , R.sup.4 and R.sup.5 may be the same or 
different and are preferably alkyls having from 1 to 5 carbon atoms. 
Examples of alkyls include methyl, ethyl, propyl, butyl, isobutyl, pentyl 
and the like. 
It is preferable that n is an integer from 10 to 30 and that m is an 
integer from 2 to 10. 
Examples of the alkylaluminoxane compound are methylaluminoxane, 
ethylaluminoxane, propylaluminoxane, isobutylaluminoxane and the like. 
The alkylaluminoxane compound can be prepared in accordance with any of a 
variety of preparation techniques. For example, the compound is prepared 
by reacting a trialkylaluminum in solution in the hydrocarbon solvent with 
water under mild conditions, and reacting also a cupric sulfate hydrate 
(Cu SO.sub.4,5H.sub.2) with an aluminum compound. 
When methylaluminoxane is prepared, the product obtained by reacting a 
trimethylaluminum with water (molar ratio 1.0) contains mixtures of linear 
polymer structure and cyclic polymer structure. 
The copolymerization reaction is usually effected in the presence of an 
inert hydrocarbon solvent. 
Examples of such solvents are aromatic hydrocarbons such as benzene, 
toluene, xylene, and the like; aliphatic hydrocarbons such as butane, 
pentane, hexane, heptane, octane, and the like; alicyclic hydrocarbons 
such as cyclohexane, and the like; and halogenated hydrocarbons such as 
methylenechloride, and the like. 
The amount of the nickel compound is 0.001 to 10 mmole per 100 g of total 
monomers charged, and is preferably 0.01 to 1 mmole. 
Further the molar ratio of aluminum in the alkylaluminoxane compound to 
nickel in the nickel compound is 1 to about 1.times.10.sup.5, and is 
preferably 10 to about 1.times.10.sup.4. 
The relative amounts of butadiene and styrene employed in the copolymers of 
the invention can vary over a wide range. However, in general, the weight 
ratio of butadiene to styrene in the monomer charge is in the range of 
95:5 to 5:95. 
The polymerization process of the invention is effected at temperatures of 
-50.degree. C. to 200.degree. C., with temperatures between -20.degree. C. 
and 100.degree. C. being preferred. 
The usual reaction time for the polymerization of the present invention can 
vary from 1 hour to 10 or more hours depending on the polymerization 
temperature, the solvent, the size of the polymerization reaction mixture, 
and all other conditions. 
In the polymerization process of the present invention, a mixture of 
butadiene and styrene is contacted with a catalyst in the liquid phase, 
and the process is usually effected at pressures sufficient to maintain a 
liquid phase operation under an inert atmosphere. 
All materials used in the polymerization system of this process should be 
essentially free from catalyst poisons. 
The copolymerization reaction can be effected batchwise or in a continuous 
manner. 
The catalyst used in the present invention has high polymerization 
activity, and in particular, high polymerization activity for comonomer 
styrene. 
The copolymers produced by the process of the invention have cis-1,4 
configuration of at least 80% of the butadiene units and bound styrene 
contents of 2 to 55%. These copolymers can be easily obtained by selecting 
catalyst components, catalyst components ratio, monomers ratio and the 
other polymerization conditions. In addition, the product is a true 
copolymer and not a mixture of butadiene-styrene copolymer and 
homopolystyrene. 
The copolymers can be used in various applications in which natural rubber 
and synthetic rubber, e.g., SBR, have been employed heretofore such as in 
the manufacture of tires, tubing, belting, gaskets, hoses and the like. 
The rubber-like copolymers can be compounded by any rubber compounding 
technology. Vulcanization agents, vulcanization accelerators, reinforcing 
agents and fillers, which are used in general-purpose rubbers, can 
similarly be used in compounding the copolymer of the present invention. 
The present invention is described in more detail with reference to the 
following examples, which however should not be construed as limiting the 
scope of the present invention. 
Unless specifically indicated otherwise, parts and percentages are given by 
weight. All reported percentages of "cis", "trans" and "vinyl" are based 
on the butadiene units of the copolymer. 
EXAMPLES 1, 2 AND 3 
19 ml of toluene, 0.1 mmole of nickel compound and 10 mmole of 
methylaluminoxane (produced by Tosoakzo Co.; 2.3 mole/l toluene solution) 
were charged in a 100 ml autoclave equipped with stirrer and maintained 
under a nitrogen atmosphere. After the mixture was stirred at room 
temperature for 10 minutes, a 20 g toluene mixture containing 4 g of 
1,3-butadiene was introduced therein, followed by the addition of 7.8 g of 
styrene. 
Polymerization was carried out at 30.degree. C. for 1 hour while stirring. 
After polymerization, the polymer was precipitated and separated by adding 
the resultant polymer solution to a large amount of methanol containing a 
small amount of hydrochloric acid. Thereafter, the resultant polymer was 
dried in the usual manner. 
Polymer conversion(%) per polymerization time (hour) was used as an index 
of the polymerization activity of the catalyst. 
The polymerization results are shown in Table 1. 
The homopolystyrene was determined as presented in K. Irako et al., "Bull. 
Chem. Soc. Japan", Vol. 41, p. 501 (1968). 
The microstructure of the butadiene units was determined as presented in T. 
Ohtsu et al., Preparative Methods of Polymer, p. 43 (Kagaku Dojin, 1972). 
The bound styrene was determined as presented in V. D. Mochel, "Rub. Chem. 
& Technol.", Vol. 40, p. 1200 (1967). 
EXAMPLES 4, 5 AND 6 
The procedure utilized in Example 1 was repeated in these experiments 
except that 0.2 mmole of acetylacetone nickel and 20 mmole of 
methylaluminoxane were added as a catalyst. In addition, 1,3-butadiene and 
styrene were added in the amounts indicated in Table 2, and polymerization 
was carried out at 50.degree. C. for 1 hour. 
The polymerization results are shown in Table 2. 
TABLE 1 
__________________________________________________________________________ 
Polymerization Microstructure 
activity Bound 
of butadiene 
Experiment conversion (%)/ 
Homopolystyrene 
styrene 
units (%) 
NO. Ni-compound 
polym'n time (hr) 
(g) (%) cis 
trans 
vinyl 
__________________________________________________________________________ 
Example 1 
Ni-acetylacetonate 
41 0.0 39 88 
12 0 
Example 2 
Ni-formate 
50 0.0 39 86 
14 0 
Example 3 
Ni-benzoate 
43 0.0 34 88 
12 0 
Comp. Ni-acetylacetonate 
5.1 0.5 34 75 
20 5 
Example 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Polymerization Microstructure 
activity Bound 
of butadiene 
Experiment 
Monomer conversion (%) 
Homopolystyrene 
styrene 
units (%) 
NO. (g) polym'n time (hr) 
(g) (%) cis 
trans 
vinyl 
__________________________________________________________________________ 
Example 4 
Butadiene 
5.3 
63 0.0 20 90 
10 0 
Styrene 
5.2 
Example 5 
Butadiene 
4.0 
68 0.0 33 90 
10 0 
Styrene 
7.8 
Example 6 
Butadiene 
2.7 
77 0.0 46 90 
10 0 
Styrene 
10.4 
__________________________________________________________________________ 
COMATIVE EXAMPLE 
This experiment was conducted according to Kogyo Kagaku Zasshi, Vol. 72, p. 
2081 (1969). 
19 ml of toluene, 0.06 mmole of acetylacetone nickel and 0.75 mmole of 
titanium tetrachloride were charged in a 100 ml autoclave equipped with 
stirrer and maintained under a nitrogen atmosphere. After the mixture was 
stirred at room temperature for 10 minutes, 0.62 mmole of triethylaluminum 
was added therein. This mixture was then stirred for 10 hours, and thus 
the catalyst was prepared. 
This experiment was carried out utilizing the same procedure described in 
Example 1, with the exception that the above-described catalyst was used. 
The polymerization results are shown in Table 1. 
From the comparison in Tables 1 and 2 of Examples 1 through 6 to the 
Comparative Example, it can be seen that, in the present invention, very 
high polymerization activity can be exhibited and that the copolymers 
obtained in accordance with the present invention are excellent in so far 
as they have a higher content of cis-1,4 configuration of the butadiene 
units and have no homopolystyrene.