Process for making diene copolymer rubbers

A process for making a diene copolymer rubber having improved rebound, which comprises polymerizing a conjugated diene monomer with an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal and/or alkaline earth metal initiator, to form a dienyl-metal terminated, conjugated diene-aromatic vinyl copolymer rubber, and thereafter reacting the copolymer rubber with at least one reactant selected from the group consisting of aminoaldehydes, aminoketones, aminothioaldehydes and aminothioketones.

This invention relates to a process for making diene copolymer rubbers 
having improved rebound. More particularly the invention relates to a 
process for making diene copolymer rubbers which comprises reacting active 
diene copolymer rubbers having dienyl-metal terminals with specific amino 
compounds. 
Recently the demand for a rubber material for tire tread of autombobiles, 
which has a low rolling resistance and a high wet skid resistance is very 
strong, to meet the requirements for reducing the fuel cost and improving 
running safety of automobiles. In order for reducing the rolling 
resistance, the rebound of the rubber material must be increased. However, 
those two properties are incompatible, and various proposals have been 
made to improve the polymers to bring about the favorable balance between 
the two properties. For example, there have been proposed a method in 
which the vinyl content and styrene content of a styrene-butadiene 
copolymer are adjusted to a specific ratio (Japanese Laid-open Patent 
Publication No. 62248/1979), a method in which specific styrene chain 
distribution is given to such a copolymer (Japanese Laid-open Patent 
Publication No. 143209/1981), a method in which specific vinyl linkage 
chain distribution is given to such a copolymer (Japanese Laid-open Patent 
Publication No. 149413/1981), and a method of introducing butadienyl-tin 
bond into the main chain of such a copolymer by coupling reaction 
(Japanese Laid-open Patent Publication No. 87407/1982). 
An object of the present invention is to develop a rubber material which 
exhibits excellently balanced rolling resistance (rebound) and wet skid 
resistance, by a method other than those above-mentioned. 
With the view to accomplish the above object, the present inventors 
measured physical properties of vulcanizates of the hydroxyl-terminated 
SBR (styrenebutadiene copolymer rubbers) disclosed in U.S. Pat. No. 
3,109,871 which are obtained by reacting alkali metal-terminated polymers 
with N,N-disubstituted aminoketones, and also those of the vulcanizates of 
mercaptanterminated SBR disclosed in U.S. Pat. No. 3,755,269 which are 
obtained by reacting metal-terminated polymers with aromatic thioketones, 
to discover that the vulcanizates of such functional group-terminated 
SBR's exhibit markedly improved rebound over the vulcanizates of SBR's 
containing no functional groups bonded at the terminals of their polymer 
chains. 
The present inventors made various studies for improving the method for 
introducing above specific atomic groups, in the attempt to develop 
copolymers of conjugated diene monomers and aromatic vinyl monomers having 
further improved rebound, and as the result discovered that by reacting 
the dienyl-alkali metal and/or alkaline earth metal-terminated copolymers 
with specific compounds, diene copolymer rubbers exhibiting excellently 
balanced rolling resistance (rebound) and wet skid resistance can be 
obtained. Whereupon the present invention was completed. 
Thus, according to the present invention, a process for making a diene 
copolymer rubber is provided, which comprises polymerizing a conjugated 
diene monomer with an aromatic vinyl monomer in a hydrocarbon solvent in 
the presence of an alkali metal and/or alkaline earth metal initiator, to 
form a dienyl- metal-terminated, conjugated diene-aromatic vinyl copolymer 
rubber, and thereafter reacting said copolymer rubber with at least one 
compound selected from aminoaldehydes, aminothioaldehydes, aminoketones 
and aminothioketones (hereinafter the "reactant"). 
The characteristics of the present invention resides in that first a 
dienyl- metal-terminated, conjugated diene-aromatic vinyl copolymer rubber 
is formed, and then it is reacted with the specific reactant. As the 
consequence, the product's rebound is markedly improved over that of the 
similar polymer having aromatic vinyl-metal terminals. 
Generally when a conjugated diene monomer and aromatic vinyl monomer are 
copolymerized in a hydrocarbon solvent in the presence of an organic 
alkali metal initiator, the former exhibits definitely higher 
copolymerization reactivity than the latter. For example, it is described 
in M. Morton, J. Polym. Sci., vol. 61, 25 (1962) that in benzene solvent, 
r.sub.1 (butadiene)=4.5 and r.sub.2 (styrene)=0.08-0.41. Such significant 
differences in the copolymerization reactivity causes the conjugated diene 
monomer to be consumed during the earlier half of the polymerization 
period, and therefore more of the aromatic vinyl monomer remains in the 
system at the final stage of polymerization to increase the active 
aromatic vinyl-alkali metal terminals. This is also apparent from the 
phenomenon observed during the polymerization of butadiene and styrene in 
a hydrocarbon solvent in the presence of n-butyllithium catalyst, i.e., 
when the conversion is yet low, the color of polymerization system is 
light yellow characteristic to butadienyl anions, but as the conversion 
rises and the butadiene is substantially consumed to leave in the system 
mostly styrene, the color of the system changes to reddish orange 
characteristic to styryl anions, and also the rate of polymerization 
increases. 
In the dienyl- metal-terminated, conjugated diene-aromatic vinyl copolymer 
rubber of this invention, the monomer units adjacent to said terminal 
groups may be either conjugated diene or aromatic vinyl. Also the method 
of rendering the copolymer rubber dienyl- metal-terminated is not 
particularly limited as long as the terminals of polymer chains can be 
made dienes. For example, a method of adding conjugated diene to the 
system after completion of the copolymerization (normally the addition of 
at least equivalent amount of conjugated diene monomer to the active metal 
terminals being sufficient, preferably about 10-100 molar times that of 
the active terminals is used), or a method of carrying out the 
copolymerization in a polymerization reactor equipped with a reflux 
condenser can be employed. 
Examples of conjugated diene monomers useful in the present invention 
include 1,3-butadiene, isoprene, 1,3-pentadiene, 
2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, etc., and aromatic vinyl 
monomers include slyrene, .alpha.-methylstyrene, p-methylstyrene, 
vinyltoluene and vinylnaphthalene. 
The conjugated diene monomer and aromatic vinyl monomer are normally used 
at the weight ratios of 95-50:5-50, preferably 95-65:5-35. 
The copolymer rubbers having the dienyl-alkali metal and/or alkaline earth 
metal terminals to be used in this invention can be obtained by 
polymerizing conjugated diene monomers with aromatic vinyl monomers, in 
the presence of alkali metal initiators (e.g., those disclosed in Japanese 
Patent Application, Publication No. 4996/69) or of alkaline earth metal 
catalysts composed chiefly of such compounds as barium, strontium, calcium 
or the like, which are normally employed for solution polymerization. 
As the alkali metal initiators useful for the present invention, the most 
typical are organolithium initiators such as methyllithium, ethyllithium, 
n-propyllithium, i-propyllithium, n-butyllithium, secbutyllithium, 
t-butyllithium, octyllithium, n-decyllithium, phenyllithium, 
2-naphthyllithium, 2-butylphenyllithium, 4-phenyl-butyllithium, 
cyclohexyllithium, 4-cyclopentyllithium, 1,4-dilithio-butene-2, etc., but 
the initiators are not limited to the above. As the alkaline earth metal 
initiators, for example, (1) the complexes composed of Ba-tertiary 
alkoxide/dibutyl Mg, disclosed in Japanese Laid-open Patent Publication 
No. 48910/77, (2) the complexes composed of organic Li and 
##STR1## 
[in which at least one of R"s stands for methyl or cyclohexyl group, the 
rest of R"(s) standing for C.sub.1 -C.sub.6 alkyl group(s), and 
x:y=99.5-88:0.5-12 (mol ratio)], 
disclosed in Japanese Laid-open Patent Publication No. 9090/77, (3) the 
composite initiators composed of an alcoholate or phenolate of Ba or 
Mg/organic Li or organic Al, disclosed in Japanese Laid-open Patent 
Publication No. 112916/81, and (4) those disclosed in Japanese Laid-open 
Patent Publication Nos. 17591/77, 30543/77, 98077/77, 112916/81, 98077/82, 
etc. may be used. 
The amount of the initiator to be used is normally within the range of 
0.2-20 millimoles per 100 g of the monomers. 
Together with the said metal initiator, a polar compound such as an ether 
compound, amine compound, phosphine compound or the like may be used as 
the randomizer or for the purpose of controlling the vinyl content in the 
conjugated diene monomer units. 
The hydrocarbon solvent useful for the present invention may be any of 
aliphatic, aromatic or alicyclic hydrocarbons, including, for example, 
propane, n-butane, i-butane, n-pentane, i-pentane, n-hexane, cyclohexane, 
propene, 1-butene, i-butene, trans-2-butene, cis-2-butene, 1-pentene, 
2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, and ethylbenzene. 
Those are preferred examples. More than one of such hydrocarbons may be 
mixed to serve as the solvent. The ratio of the monomers to the solvent is 
determined according to the viscosity of polymer solution, and agitation 
power and heat-removing capacity of the polymerization reactor. Generally 
it is 1:10 to 1:1, by weight. 
Polymerization temperature normally ranges -20.degree. C.-150.degree. C., 
preferably 40.degree.-120.degree. C. The polymerization is practiceable 
either under rising temperatures or under a constant temperature. 
The reactants useful in the present invention, i.e., aminoaldehydes, 
aminoketones, aminothioaldehydes and aminothioketones are aromatic or 
aliphatic. When aromatic, they should have 1 to 4 amino groups per 
aromatic ring. The amino group is that represented by the general formula 
##STR2## 
in which R and R' may be same or different, and are selected from hydrogen 
and such substituent groups as C.sub.1 -C.sub.12 alkyl groups, cycloalkyl 
groups, aryl groups, aralkyl groups and alkoxyalkylene groups. When 
di-substituted, the substituent groups may be same or different. The 
aromatic ring may contain up to four substituent groups other than above 
amino groups. 
Examples of aromatic reactants include 4,4'-diaminobenzophenone, 
4,4'-bis(dimethylamino)-benzophenone, 4,4'-bis(diethylamino)-benzophenone, 
3-diethylaminobenzophenone, 3,3',5,5'-tetra(dinonylamino)benzophenone, 
aminoanthraquinone, N,N-dimethylaminoanthraquinone, 
1,4-diaminoanthraquinone, 1,4-N,N-dimethyldiaminoanthraquinone, 
1,4-N,N,N',N'-tetramethyldiaminoanthraquinone, phenoxazine, 
N-methylphenoxazine, 10-butylphenoxazine, 
3,7-diamino-10-acetylphenoxazine, acrydone, N-methylacrydone, 
4-aminobenzaldehyde, 4-dimethylaminobenzaldehyde, 
3,5-bis(dihexylamino)benzaldehyde, 2,4,6-tris(diethylamino)-benzaldehyde, 
4-dicyclopentylaminobenzaldehyde, 4,5-bis(diethylamino)-1-naphthaldehyde, 
and the corresponding thioketones and thioaldehydes. 
As the aliphatic reactants may be named for example are 
3-dimethylaminopropionaldehyde, 3-diethylaminopropionaldehyde, 
2-dimethylaminoacetaldehyde, dimethylaminopivalaldehyde, 
1,5-bis(di-n-propylamino)-3-pentanone, 5-dodecylamino-n-heptaldehyde, 
1,3-bis(diheptylamino)-2-propanone, 1,7-bis(methylethylamino)-4-heptanone, 
and the corresponding thioaldehydes and thioketones. 
Particularly preferred reactants are N,N-disubstituted amino compounds. 
The amount of use of the reactant is selected within the range of 0.5-1.0 
mol per mol of the active dienyl- metal-terminated diene copolymer rubber. 
When it is less than 0.5 mol, the improvement in rebound is insufficient. 
Whereas, use of more than 1.0 mol does not bring about the corresponding 
improvement in the rebound. The reaction temperature and time are variable 
over wide ranges, but generally the former ranges from room temperature to 
100.degree. C., and the latter, from several seconds to several hours. 
After termination of the reaction, the modified diene polymer rubber is 
coagulated from the reaction system. The coagulation is effected by the 
methods ordinarily practiced in the production of rubber by solution 
polymerization, such as the addition of a coagulating agent such as 
alcohol e.g., methanol or ethanol) to the reaction system, or steam 
stripping. The coagulation temperature neither is limited. The crumbs 
separated from the reaction system can be dried with the devices 
conventionally employed in production of synthetic rubber, such as a band 
dryer, extrusion-type dryer, etc. The drying temperature is subject to no 
specific limitation. 
Thus obtained diene polymer rubber is excellent in the balance of rebound 
and wet skid resistance, and hence is useful as a rubber material for tire 
treads.

Hereinafter the present invention will be more specifically explained with 
reference to working examples. 
EXAMPLE 1 
(1) A 2-liter stainless steel polymerization reactor was washed and dried, 
and its inside air was substituted with dry nitrogen. Thereafter the 
reactor was charged with 120 g of 1,3-butadiene, 40 g of styrene, 840 g of 
cyclohexane, 0.4 millimole of tetramethylethylenediamine and 1.0 millimole 
of n-butyllithium (n-hexane solution). The polymerization was performed at 
45.degree. C. for 5 hours under stirring of the content. Thereafter 50 g 
of a liquid butadiene-cyclohexane mixture containing 1% by weight of 
butadiene was added to the system, followed by 15 minute's reaction at 
45.degree. C. Then 1 millimole of the reactant as specified in Table 1 was 
added, and the addition reaction was performed for 30 minutes. Whereupon 
the reaction was terminated by the addition of 5 ml of methanol, and the 
polymer solution was poured into a 1.5 weight percent methanol solution of 
2,6-di-t-butyl-p-cresol (BHT) to coagulate the formed copolymer rubber, 
which was dried under reduced pressure at 60.degree. C. for 24 hours to 
provide the rubber samples No. A through No. J. 
(2) Also rubber samples No. K through No. M were obtained through the same 
procedures as in (1) above, except that the addition of butadiene after 
termination of the butadiene-styrene copolymerization reaction was omitted 
and the reactants specified in Table 1 were immediately added to the 
respective systems. 
The vinyl contents and styrene contents of thus obtained copolymer rubbers 
were determined by infrared spectroscopy [Hampton, Anal. Chem., 21, 923 
(1949)]. The analysis results and Mooney viscosities of the copolymer 
rubbers are also shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Amount of 
Reactant later- 
Amount 
added Vinyl 
Styrene 
added butadiene 
content 
Content 
Mooney 
Rubber No. 
Compound (millimole) 
(g) (%) (%) viscosity 
__________________________________________________________________________ 
Examples 
A 4,4'-bis(dimethylamino)benzophenone 
1.0 5 42.3 25.1 38 
of this 
B 4,4'-bis(dimethylamino)thiobenzo- 
1.0 5 42.0 25.1 37 
invention 
phenone 
C 4,4'-bis(diethylamino)benzophenone 
1.0 5 42.0 24.8 41 
D 4,4'-diaminobenzophenone 
1.0 5 43.1 24.6 40 
E 4-dimethylaminobenzaldehyde 
1.0 5 43.3 25.3 38 
F 3,5-bis(diethylamino)benzaldehyde 
1.0 5 42.4 25.0 39 
G 4-diethylaminobenzophenone 
1.0 5 42.4 25.1 41 
H 4-dimethylaminobenzthioaldehyde 
1.0 5 42.0 24.9 40 
I dimethylaminopivalaldehyde 
1.0 5 42.3 25.0 38 
J 1,5-bis(di-n-propylamino)-3- 
1.0 5 42.0 24.89 
39 
pentanone 
Control 
K 4,4'-bis(dimethylamino)benzophenone 
1.0 0 42.7 24.9 43 
examples 
L 4,4'-bis(dimethylamino)- 
1.0 0 43.0 25.0 39 
thiobenzophenone 
M -- 0 5 42.4 24.7 39 
__________________________________________________________________________ 
Those copolymer rubbers were kneaded in a 250 ml. Bravender-type mixer 
following the compounding recipe of Table 2, to provide rubber 
compositions, which were press-cured at 160.degree. C. for 25 minutes to 
provide test specimens. The rebound of vulcanized rubbers was measured at 
50.degree. C. using Dunlop tripsometer. Wet skid resistance was measured 
at 23.degree. C., with a portable skid tester made by Stanley Co., on the 
road surface (ASTM E-303-74, outside type B, black, safety walk made by 
MMM Co.). The results are shown in Table 3. 
TABLE 2 
______________________________________ 
Compounding Recipe 
______________________________________ 
Polymer rubber 100 parts by weight 
Zinc oxide No. 3 3 " 
Stearic acid 2 " 
Sulfur 1.75 " 
N--cyclohexyl-2-benzo- 
1.1 " 
thiazole sulphenamide 
HAF carbon black 50 " 
Aromatic process oil 
5 " 
______________________________________ 
TABLE 3 
______________________________________ 
West Skid 
Rubber No. Rebound (%) 
Resistance 
______________________________________ 
Examples A 68 77 
of this B 68 77 
Invention C 68 77 
D 66 76 
E 66 77 
F 67 76 
G 67 77 
H 67 77 
I 67 77 
J 67 77 
Control K 63 77 
Examples L 63 77 
M 56 77 
______________________________________ 
From the results of Table 3, it could be understood that the vulcanizates 
of butadiene-styrene copolymer rubbers obtained through the present 
process show very high rebound, and the tires using the same rubbers at 
the treads excel in the balance of rolling resistance and wet skid 
resistance. 
EXAMPLE 2 
(1) The copolymerization and the polymerization with later added butadiene 
were performed under identical conditions with those of Example 1-(1), 
except that the feed amounts of butadiene and styrene were changed to 
those specified in Table 4. Thereafter 1.0 millimole of 
4,4'-bis(dimethylamino)benzophenone was added, followed by the procedures 
same to those of Example 1-(1), to provide rubber samples No. N and No. O. 
(2) The procedures under the conditions identical with above (1) were 
repeated except that the amount of tetramethylethylenediamine was changed 
to that indicated in Table 4, to provide rubber samples No. P and No. Q. 
Those copolymer rubbers were formulated into the compositions following the 
same compounding recipe as given in Example 1, and the resulting 
vulcanizates were measured of their rebound and wet skid resistance. The 
results were as shown in Table 5. 
TABLE 4 
__________________________________________________________________________ 
Tetramethyl- Vinyl 
Styrene 
Mooney 
ethylenediamine 
Styrene 
Butadiene 
Content 
Content 
Vis- 
Rubber No. 
(millimole) 
(g) (g) (%) (%) cosity 
__________________________________________________________________________ 
Examples 
N 0.4 16 144 44.5 10.1 38 
of this 
O 0.4 48 112 41.2 30.2 37 
Invention 
P 1.0 40 120 80.0 25.0 40 
Q 0.2 40 120 25.0 24.9 38 
__________________________________________________________________________ 
TABLE 5 
______________________________________ 
West Skid 
Rubber No. Rebound (%) 
Resistance 
______________________________________ 
Examples N 70 70 
of this O 66 79 
Invention P 64 85 
Q 70 74 
______________________________________ 
EXAMPLE 3 
A 50-liter polymerization reactor equipped with a reflux condenser was 
washed and dried, substituted with dry nitrogen, and charged with 2.4 kg 
of 1,3-butadiene, 0.8 kg of styrene, 12.8 kg of cyclohexane, 4.0 kg of 
n-butane and 8 millimoles of tetramethylethylenediamine. The mixture was 
given a temperature of 45.degree. C., and to which 20 millimoles of 
n-butyllithium (n-hexane solution) was added. The polymerization 
temperature was controlled at 45.degree. C., with the latent heat of 
evaporation of 1,3-butadiene and n-butane. The evaporated 1,3-butadiene 
and n-butane were condensed at the ammonia-cooled condenser installed at 
the upper part of the reactor and recirculated into the reactor. After 5 
hours' polymerization, 100% conversion was confirmed. Whereupon 20 
millimoles of 4,4'-bis(dimethylamino)benzophenone was added, followed by 
30 minutes' reaction at 45.degree. C. under stirring. Thereafter 300 ml of 
methanol containing 64 g of 2,6-di-t-butyl-p-cresol (BHT) was added to 
stop the reaction. Thus formed copolymer solution was removed of the 
solvent by steam stripping, and the resulting coagulated rubber was rolled 
into a sheet, which was hot air-dried at 60.degree. C. for 24 hours. 
The properties of the formed copolymer and the rebound and wet skid 
resistance of the vulcanized rubber prepared therefrom, measured as in 
Example 1, were as follows: 
______________________________________ 
Vinyl content 42.3% 
Styrene content 25.3% 
Mooney viscosity 40 
Rebound 68 
Wet skid resistance 
77 
______________________________________ 
When a polymerization reactor equipped with a reflux condenser was used, 
dienyl-lithium was formed without the additional supply of 1,3-butadiene 
after completion of the polymerization reaction, and consequently the 
rebound-improving effect achieved by the addition of 
4,4'-bis(dimethylamino)benzophenone was recognizable. 
The formation of dienyl-lithium could be inferred from the observation that 
the color of the copolymer solution after completion of the polymerization 
reaction was still light yellow characteristic to butadienyl anions, not 
the orange color characteristic to styryl anions. 
EXAMPLE 4 
The same polymerization reactor employed in Example 3 was charged with 14.4 
kg of n-hexane, 2.92 g of butadiene and 0.68 kg of styrene, and the system 
was heated to 70.degree. C. under stirring. Then the polymerization was 
initiated by addition of 13.6 millimoles of barium dinonyl phenoxide, 20 
millimoles of lithium-magnesium tributyl and 26.8 millimoles of 
triethylaluminum, and the reaction was continued for 2 hours. The maximum 
temperature of the polymerization system reached 85.degree. C. Then 30 
millimoles of 4,4'-bis(dimethylamino)benzophenone was added to the 
polymerization system and reacted for 30 minutes. Thus formed copolymer 
was recovered in the manner similar to Example 3 (rubber sample No. R). 
Another copolymer was prepared under idential conditions with above, except 
no reflux condenser was used (rubber sample No. S). 
The properties of the formed copolymers and the rebound and wet skid 
resistance of the vulcanized rubbers prepared therefrom, measured as in 
Example 1, were as in Tables 6 and 7 below, respectively. 
TABLE 6 
______________________________________ 
Styrene Vinyl Trans-1,4 
Cis-1,4 
Rubber 
Mooney content content content 
content 
No. viscosity (%) (%) (%) (%) 
______________________________________ 
R 47 15.1 4.2 79.6 16.2 
S (*) 45 14.8 4.0 80.0 16.0 
______________________________________ 
TABLE 7 
______________________________________ 
Wet skid 
Rubber No. Rebound (%) 
resistance 
______________________________________ 
R 73 65 
S (*) 70 65 
______________________________________ 
Note: 
(*) Control