Process for the production of polybutadiene having a high cis-1,4-content

A process for the production of polybutadiene having a high cis-1,4-content by the polymerization of 1,3-butadiene in an aliphatic solvent in the presence of a catalyst consisting essentially of PA1 (a) an organoaluminum compound, PA1 (b) water, and PA1 (c) a cobalt compound soluble in the aliphatic solvent, is improved by the combination wherein the 1,3-butadiene is polymerized at a temperature of 0.degree.-100.degree. C., the aliphatic solvent is hexane; the catalyst consists essentially of PA1 (a) diethylaluminum chloride, PA1 (b) water, and PA1 (c) cobalt octoate, cobalt naphthenate or a mixture thereof; and the catalyst components are added to a mixture of the 1,3-butadiene and the hydrocarbon solvent in the sequence of (a), then (b), and then (c), wherein the mixture is homogenized after addition of each catalyst component.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the production of 
polybutadiene having a high cis-1,4-content. 
A process is disclosed in Canadian Pat. No. 934742 for the polymerization 
of conjugated diolefins in the presence of catalysts which are compounds 
of metals of Group VIII and organometallic compounds of metals of Group 
III of the Periodic Table of the Elements to obtain polymers having 
essentially a cis-1,4-content. In this process, homogeneous solutions of 
catalysts consisting of a cobalt compound and an alkyl aluminum halide are 
employed. The polymerizing medium is constituted by cycloaliphatic and 
preferably aromatic hydrocarbons, such as, for example, benzene or 
mixtures made from these solvents and aliphatic hydrocarbons. 
Another process for the production of polybutadiene having a high 
cis1,4-content is known from U.S. Pat. No. 3,066,127. In this process, 
1,3-butadiene is polymerized in a non-aqueous solution with one of several 
compounds of cobalt and/or nickel and one or several organoaluminum 
compounds, preferably alkyl aluminum compounds, as the catalyst in the 
presence of a specified quantity of water. The solvent is preferably 
constituted by aromatic hydrocarbons. The utilization of benzene as the 
sole diluent is a preferred embodiment of the polymerization of butadiene 
with the catalyst claimed. On the other hand, aliphatic hydrocarbons can 
only be used in combination with cyclic or aromatic hydrocarbons. 
As can be seen from these comments on the relevant state of the art 
processes, aromatic hydrocarbons, preferably benzene, are favored as the 
solvent in the production of, for example, polybutadienes having a high 
cis-1,4-content using soluble cobalt- and/or nickel-containing catalysts 
of the Ziegler-Natta type. The reason is that these aromatic hydrocarbons 
support the formation of soluble catalysts as well as being especially 
good solvents for the polymer formed. 
Despite these good properties, however, aromatic hydrocarbons, because of 
their toxicity, and especially benzene, because of its carcinogenic 
effect, pose a great danger to the environment. Consequently, there has 
been an ongoing effort to replace the toxic aromatic solvents with less 
toxic ones. 
Thus, a process is described in U.S. Pat. No. 4,020,255 for the production 
of polybutadiene having a high cis-1,4-content in which the butadiene is 
polymerized in a mixture using an aliphatic or cycloaliphatic solvent. The 
polymerization catalyst therein consists of (a) a trialkyl aluminum 
compound, (b) a nickel-carboxylic acid salt and (c) a boron trifluoride 
etherate. However, such catalysts are very expensive and difficult to 
handle. A process is also described in Canadian Pat. No. 795,860 (Chem. 
Abstr. 62, 6658d) wherein a catalyst of (a) diethylaluminum chloride, (b) 
water and (c) cobalt dioctoate is used to polymerize butadiene. Although 
general aromatic and aliphatic solvents are disclosed, the specific 
solvent utilized is benzene and the catalyst components are employed in 
the sequence (b), (a) and then (c). 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to develop a process 
for the production of polybutadiene having a high cis-1,4-content which 
employs as solvents exclusively aliphatic solvents as well as easy to 
handle and reasonably-priced catalysts. 
It is another object of this invention to provide such a process wherein 
the conversion rate and yield are highly satisfactory. 
Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
These objects have been attained by providing an improved process for the 
production of polybutadiene having a high cis-1,4-content by the 
polymerization of 1,3-butadiene in an aliphatic solvent in the presence of 
a catalyst consisting essentially of 
(a) an organoaluminum compound, 
(b) water, and 
(c) a cobalt compound soluble in the aliphatic solvent, 
wherein the improvement resides in the fact that the 1,3-butadiene is 
polymerized at a temperature of 0.degree.-100.degree. C., the aliphatic 
solvent is hexane; the catalyst consists essentially of 
(a) diethylaluminum chloride, 
(b) water, and 
(c) cobalt octoate, cobalt naphthenate or a mixture thereof; 
and the catalyst components are added to a mixture of the 1,3-butadiene and 
the hydrocarbon solvent in the sequence of (a), then (b), and then (c), 
wherein the mixture is homogenized after addition of each catalyst 
component. 
All features recited above under the improvement are critical in obtaining 
the superior results of this invention. 
DETAILED DISCUSSION 
The superior results achieved by the process of this invention are 
surprising, because the utilization of hexane, especially in the 
large-scale industrial production of polybutadiene having a high 
cis-1,4-content with the aid of Ziegler-Natta catalysts, has heretofore 
only produced insufficient conversion rates and yields (U.S. Pat. No. 
4,020,255). 
According to this invention, hexane is used as the solvent. Hexane is 
utilized because it is an industrially inexpensive product, is especially 
less dangerous to health compared to the aromatic substances and, for 
industrial processes, exhibits especially advantageous physical properties 
such as boiling point and freezing point. Generally, 2-20, preferably 4-9 
wt. parts of the hexane solvent per wt. part of 1,3-butadiene monomer are 
employed. The purity of the hexane is not critical and commercially 
available industrial grade hexane may be employed. 
The catalyst system employed in the process of this invention consists 
essentially of 
(a) diethylaluminum chloride, 
(b) water, and 
(c) cobalt octoate and/or naphthenate. 
The diethylaluminum chloride (DEAC) component (a), preferably in the form 
of a solution in hexane, is added to the mixture made from the hexane 
solvent and 1,3-butadiene. Other organoaluminum compounds can also be 
utilized for the formation of polymerization-active catalysts; however, 
they exhibit disadvantages when compared to DEAC, so that from an 
industrial and economic viewpoint, they are of subordinate importance in 
the utilization of cobalt-containing Ziegler-Natta catalysts. In general, 
the organoaluminum compound is used in quantities of 0.05-1, preferably 
0.1-0.5 percent by weight, based on the amount of 1,3-butadiene. 
The water, catalyst component (b), is generally used in quantities of 
0.1-0.8, preferably 0.3-0.6 mole per mole of organoaluminum compound. The 
water can be introduced into the polymerization system directly in pure 
form; dispersed in neutral carrier media, e.g., paraffin oils; or in 
dissolved form, i.e., as a solution, especially in the reactants 
themselves, e.g., 1,3-butadiene, or in hexane. If the water is introduced 
via a dispersion or via a solution, then the water content of the 
dispersions or solutions is suitably determined by a conventional Karl 
Fischer titration (Karl Fischer in Angew. Chem. 48 (1935), page 394). 
The quantity of catalyst component (c), i.e., cobalt octoate and/or 
naphthenate, used in the process of this invention is 0.0005-0.01 percent 
by weight, preferably 0.001-0.003 percent by weight, calculated as Co, 
based on the amount of 1,3-butadiene used. 
Suitable octoates include those from monocarboxylic acids having 8 carbon 
atoms. The cobalt salt of 2-ethylhexanoic acid is preferred. 
Suitable napthenates include the cobalt salts of acids of the following 
formula R(CH.sub.2).sub.n COOH wherein n is 0-3 and R is a in case 
substituted cyclic aliphatic alkane nucleus having 5 or 6 carbon atoms. 
The sequence and the timing of the addition of the individual catalyst 
components are critical for obtaining the superior results of the process 
of this invention. 
In this connection, the necessary sequence is such that first the DEAC is 
added to the mixture of 1,3 -butadiene and hexane; this mixture is also 
homogenized and the water is added; then the mixture is also homogenized 
and finally the cobalt compound is added, thus commencing the 
polymerization. 
In general, the process of this invention is carried out at temperatures of 
0.degree.-100.degree. C., preferably 15.degree.-50.degree. C. There is no 
limitation on the pressure to be used during polymerization as long as it 
is sufficient to keep the reaction mixture--above all, the monomer that is 
to be polymerized--in a dissolved phase. Typically suitable pressures 
include 1-10 atm. 
The process of this invention can be carried out continuously as well as 
batchwise. The duration of the polymerization varies with the degree of 
conversion of the 1,3-butadiene. In general, the polymerization reaction 
is stopped upon reaching a conversion degree of approximately 80% to 90%, 
typically by the addition of a conventional suitable shortstop compound, 
preferably an alcohol or a ketone, such as methanol, isopropanol or 
acetone. A conventional stabilizer, which protects the polybutadiene from 
the influence of oxygen, is generally also added along with the shortstop 
agent. Suitable such stabilizers include, for example, 
2,2-methylene-bis(6-tert-butyl-p-cresol) and 2,6-di-tert-butyl-p-cresol. 
Prior to or during the polymerization, a conventional, so-called modifier 
can be added to the polymerization medium to attain a determined molecular 
weight. Suitable such compounds which, in general, are added in quantities 
of from 0.01 to 0.5, preferably 0.05 to 0.2 percent by weight based on the 
amount of 1,3-butadiene include, for example, 1,2-butadiene, allene 
(propadiene) and acrylonitrile. 
The shortstop and stabilizer-containing polybutadiene solution is 
subsequently treated in the following manner. The solvent is distilled off 
by the introduction of steam. Expediently, this is performed during 
simultaneous agitation in the aqueous phase, thereby obtaining a 
crumb-like product. This is sieved from the water and dried at 
temperatures of up to approximately 100.degree. C. 
All conditions and features of the butadiene polymerization process of this 
invention which are not discussed herein are fully conventional and are 
disclosed, for example, in U.S. Pat. No. 3,066,127, which is incorporated 
by reference herein. 
The polybutadienes obtained by the process of this invention have a 
cis-1,4-content of greater than 90, preferably greater than 95% 
(determined by IR-spectroscopy). The 1,2-content is generally 1 to 2%. The 
molecular weight, expressed by Mooney value (DIN 53 523), is between 20 
and 120, preferably 40 and 60. Polybutadienes are suited for many 
industrial purposes, especially as a raw material, for example, in the 
manufacture of vehicular tires, sealing profiles and conveyor belts.

Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. In the following 
examples, all temperatures are set forth uncorrected in degrees Celsius; 
unless otherwise indicated, all parts and percentages are by weight. 
COMATIVE EXAMPLE I 
This comparative example shows results for the polymerization of 
1,3-butadiene using benzene as the solvent for comparison with the 
examples according to this invention using hexane as the solvent. 
The following are mixed together: 
benzene--430 g. 
1,3-butadiene--79 g. 
1,2-butadiene--0.1%, calculated on the basis of 1,3-butadiene, as a 
modifier 
water--20 p.p.m. in the reaction mixture 
The water is added to the batch with the aid of a corresponding proportion 
of moistened benzene. Into this batch is mixed 0.3% of DEAC calculated on 
the basis of 1,3-butadiene, as a 20% benzenic solution. The water:DEAC 
proportion corresponds to 0.32:1 mole. The batch is completely clear and 
displays a yellowish-brown color after addition of the DEAC. For starting 
the polymerization, 0.0014% of cobalt (as a benzenic solution of cobalt 
octoate), calculated based on the amount of 1,3-butadiene, is added. (In 
the following examples, the proportion of benzene in the mixture of DEAC 
and cobalt octoate is calculated based on the total amount of benzene 
present therein from all sources. The 1,2-butadiene in the recipe aids the 
ability to produce a defined molecular weight of the polybutadiene which 
is later measured in a rotary shear viscometer in Mooney units. The batch 
is prepared in a pressure bottle, sealed with a crown capsule and is 
shaken in a water bath at 25.degree. C. by vertical rotation of the 
bottle. 
After four hours, the polymerization is interrupted by addition of methanol 
(i.e., to decompose the catalyst) and is stabilized against the influence 
of oxygen by the addition of a stabilizer, i.e., 0.15 g of 
2,2-methylenebis(6-tert-butyl-p-cresol). The solvent is removed from the 
viscous solution obtained by the introduction of steam and the 
disintegrated polymer is dried in a circulating air drying chamber at 
100.degree. C. 
The following polymerization parameters were measured: 
______________________________________ 
Operating time 
Conversion degree 
Mooney value 
of the reaction 
of the 1,3-butadiene 
of the polymer 
______________________________________ 
[h] [%] [ML-4] 
4 88 57 
______________________________________ 
COMATIVE EXAMPLE II 
If the proportion of benzene in the recipe of Comparative Example I is 
replaced by hexane in increasing amounts, it has been found that the 
conversion degree declines drastically. 
Recipe and sequence of the utilization of the components: 
______________________________________ 
(a) (b) (c) (d) 
______________________________________ 
Benzene:hexane proportion 
90:10 50:50 25:75 10:90 
Benzene 387 g 215 g 108 g 43 g 
Hexane 43 g 215 g 322 g 387 g 
1,3-Butadiene 70 g 
Water 18 p.p.m. in the reaction mixture 
1,2-butadiene 0.1% based on the amount of 1,3- 
butadiene 
______________________________________ 
Mixed into the homogenous solution of the above components are: 
0.20% DEAC calculated on the basis of the 1,3-butadiene, corresponding to 
H.sub.2 O:DEAC proportion=0.43:1 mole and then, to start up the 
polymerization 0.0014% cobalt (as cobalt octoate), calculated on the basis 
of the 1,3-butadiene. 
Each of the particular benzene/hexane combinations (a-d) were run in three 
separate experiments, and after four hours operating time at a reaction 
temperature of 25.degree. C., the following conversion degree data 
resulted: 
______________________________________ 
Degree of conversion from 
three single batches 
Combi- Benzene/hexane 
Mean Highest & 
nation Proportion Value (%) Lowest Values (%) 
______________________________________ 
(a) 90:10 93 86-98 
(b) 50:50 33 17-64 
(c) 25:75 4 0-13 
(d) 10:90 0 
______________________________________ 
In preparing the recipes, it is noticed that in the experiments (a) and (b) 
the solution remains clear and takes on a yellowish color, which indicates 
the formation of the polymerization-active, completely dissolved catalyst 
complex; whereas in the batches (c) and (d) no coloration of the solution 
occurs, but instead a turbidity is formed and colorless flakes 
precipitate, which indicates that the catalyst has decomposed. 
COMATIVE EXAMPLE III 
If the order of adding the catalyst components, DEAC and water, in 
Comparative Example II is reversed, then, surprisingly, high conversion 
rates are obtained even with a low benzene/hexane proportion. 
The order of the mixing of the catalyst components is as follows: benzene, 
hexane, 1,3-butadiene and 1,2-butadiene are mixed in a carefully dried 
state and then DEAC is mixed thereto. Thereafter, water in the form of 
moist benzene is added, wherein the quantity of benzene is taken into 
consideration in the respective total benzene/hexane proportion. 
Subsequently, the polymerization is started by the addition of cobalt 
octoate. Except for the procedures discussed herein, the details of 
comparative example II were followed precisely. 
In all the experiments performed, the yellow coloration of the solution 
indicates that the polymerization-active catalyst has formed. 
The conversion degrees obtained are shown in the following table: 
______________________________________ 
Degree of conversion from 
three single batches 
Combi- Benzene/Hexane 
Mean Lowest & 
nation Proportion Value (%) Highest values (%) 
______________________________________ 
(a) 90:10 81 62-96 
(b) 25:75 80 55-85 
(c) 10:90 75 69-83 
______________________________________ 
EXAMPLE 1 
Very good degrees of conversion are obtained when pure hexane is utilized 
as the solvent (benzene content of the utilized hexane is less than 0.001 
wt.%) if the components of the recipe are mixed together according to the 
following procedural method, wherein the metered quantity of DEAC is 0.4 
wt.% calculated on the basis of the amount of 1,3-butadiene used. 
(A) The water in added in the form of moistened 1,3-butadiene. Dry hexane, 
a portion of the 1,3-butadiene, 1,2-butadiene and DEAC are mixed and 
thereafter the remaining 1,3-butadiene provided with the correspondng 
water content is added. The reaction solution takes on a yellow color, the 
sign of the formation of a polymerization-active catalyst. After adding 
cobalt octoate, the butadiene polymerizes within 4 hours at 25.degree. C. 
to a high degree of conversion. In eight single batches the conversion 
degrees are between 80 to 95% with a mean rate of 89%. 
The composition of the recipe is as follows: 
hexane--344 g 
1,3-butadiene--56 g 
1,2-butadiene --0.1% calculated on the basis of the amount of 1,3-butadiene 
water--45 p.p.m. in the reaction mixture 
DEAC--0.4% calculated on the basis of the amount of 1,3-butadiene 
corresponding to a H.sub.2 O:DEAC proportion=0.54:1 mole 
cobalt--0.002% calculated on the basis of the amount of 1,3-butadiene 
(B) The water is added in the form of a dispersion. Dry hexane, 
1,3-butadiene, 1,2-butadiene and DEAC are mixed together and thereafter 
the water is added in the form of a finely divided dispersion in a 
paraffin oil. 
Despite the reduction in the use of DEAC to 0.3 wt.% calculated on the 
basis of the amount of 1,3-butadiene, high conversion degrees are 
obtained, which exhibit the following values in dependence on the 
DEAC:water proportion: 
______________________________________ 
Lowest and Highest 
H.sub.2 O in the Conversion 
Reaction 
Water:DEAC Conversion 
Degrees of the 
Mixture Proportion Degree Prepared Experiments 
[p.p.m.] 
[mole] [%] [%] 
______________________________________ 
27 0.44:1 76 67-81 
31 0.50:1 82 80-83 
35 0.56:1 84 83-85 
38 0.62:1 79 74-82 
______________________________________ 
The recipe used was: 
hexane--344 g 
1,3-butadiene--56 g 
1,2-butadiene--0.08 wt.% calculated on the basis of the amount of 
1,3-butadiene 
water--27, 31, 35 and 38 p.p.m. in the reaction mixture 
DEAC--0.3 wt.% calculated on the basis of the amount of 1,3-butadiene 
cobalt--0.0020% calculated on the basis of the amount of 1,3-butadiene 
(C) The water in liquid form is directly added to the reaction batch. Dry 
hexane, 1,3-butadiene, 1,2-butadiene and DEAC are mixed; the water is 
added to the batch with the aid of an injection syringe; and thereafter it 
is well mixed by shaking. After the addition of the cobalt catalyst, the 
catalyst, the 1,3-butadiene polymerizes at 25.degree. C. within 4 hours at 
conversion rates of 62% on the average and between 54 and 71% as 
individual values in the series of experiments. The recipe data were as 
follows: 
hexane--344 g 
1,3-butadiene--56 g 1,2-butadiene--0.1 wt.% calculated on the basis of the 
amount of 1,3-butadiene 
water--45 p.p.m. in the reaction mixture 
DEAC--0.5 wt.% calculated on the basis of the amount of 1,3-butadiene, 
corresponding to a water/DEAC proportion=0.43:1 mole 
cobalt--0.0020 wt.% calculated for 1,3-butadiene 
COMATIVE EXAMPLE IV 
The water is added to the reaction batch before addition of the DEAC. The 
reaction components are prepared in the following sequence: hexane, 
1,3-butadiene and 1,2-butadiene are mixed together. The water is added via 
moistened 1,3-butadiene. This mixture is brought into rotating movement by 
the shaking of the reaction vessel. Then, the required amount of DEAC is 
injected into the moving solution in a powerful jet from a pipette and is 
mixed in by further shaking. The batch takes on a yellow color and after 
adding the cobalt octoate the polymerization begins. Depending on the 
water content, the following degrees of conversion are attained with a 
DEAC utilization of 0.4% calculated on the basis of the amount of 
1,3-butadiene employed: 
______________________________________ 
Water in the Proportion 
Reaction Mixture 
H.sub.2 O:DEAC 
Conversion Degree 
[p.p.m.] [mole] [%] 
______________________________________ 
41 0.49:1 70 
44 0.53:1 72 
45 0.54:1 83 
47 0.56:1 86 
50 0.60:1 83 
51 0.61:1 80 
______________________________________ 
The composition of the recipe was: 
hexane--344 g 
1,3-butadiene--56 g 
1,2-butadiene--0.12 wt.% calculated on the basis of the amount of 
1,3-butadiene 
water--variation corresponding to the above table 
DEAC--0.4 wt.% calculated on the basis of the amount of 1,3-butadiene 
cobalt--0.002 wt.% calculated on the basis of the amount of 1,3-butadiene 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.