SBR for asphalt cement modification

It has been determined that a specific type of emulsion SBR can be used to modify asphalt cement to greatly enhance the resistance to shoving, rutting and low temperature cracking of asphalt concretes made therewith. It has further been determined that this emulsion SBR is compatible with virtually all types of asphalt and that modified asphalt cements made therewith have extremely high levels of force ductility, tenacity and toughness. The SBR used to modify asphalt cement in the practice of this invention is a blend of (i) a high molecular weight styrene-butadiene rubber having a weight average molecular weight of at least about 300,000 and (ii) a low molecular weight styrene-butadiene rubber having a weight average molecular weight of less than about 280,000; wherein the ratio of the high molecular weight styrene-butadiene rubber to the low molecular weight styrene-butadiene rubber is within the range of about 80:20 to about 25:75; and wherein the bound styrene content of the high molecular weight styrene-butadiene rubber differs from the bound styrene content of the low molecular weight styrene-butadiene rubber by at least 5 percentage points. These SBR compositions are comprised of repeat units which are derived from styrene and 1,3-butadiene, wherein the styrene-butadiene rubber composition has a number average molecular weight as determined by field flow fractionation which is within the range of about 50,000 to 150,000 and wherein the styrene-butadiene rubber has a light scattering to refractive index ratio which is within the range of 1.8 to 3.9.

BACKGROUND OF THE INVENTION 
The importance of roads and highways has been appreciated since the time of 
the Roman Empire. By about 300 B.C., the first section of the Appian Way 
extending from Rome to Capua was built. Some of the more than 50,000 miles 
of roadway ultimately built in the Roman Empire was constructed with heavy 
stone. However, not much progress was made in the art of road construction 
from the era of the Roman Empire until the development of the motor 
vehicles, such as automobiles and trucks. 
For centuries, stone blocks, wood blocks, vitrified brick and natural 
asphalt (bitumen) have been used to pave roads and highways. However, at 
the beginning of the automobile era, most rural roadway surfacing 
consisted of broken stone or gravel. Such roads were often rough, dusty 
and clearly inadequate for modern automobile and truck traffic. 
Today, the United States has the most extensive highway system in the world 
with about 2,000,000 miles of paved road. Napoleon realized the importance 
of roadway systems and built such a system in France which today has the 
second most extensive system of paved roadways in the world covering about 
500,000 miles. Germany, Japan, Great Britain, India, and Australia also 
currently have systems of paved roads which extend well over 100,000 
miles. In addition to these public roadways, there are countless paved 
driveways and parking lots all over the world. 
Today, roads, highways, driveways and parking lots are often paved with 
asphalt concrete. Pavement can be made with asphalt concretes which are 
dust-free, smooth and which offer the strength required for modern 
automobile and heavy truck traffic. Asphalt concrete is generally made by 
mixing aggregate (sand and gravel or crushed stone) with the proper 
quantity of an asphalt cement at an elevated temperature. The hot asphalt 
concrete is then placed by a layering machine or paver on the surface 
being paved and thoroughly rolled before the asphalt concrete mixture 
cools. The asphalt concrete is normally applied at a thickness varying 
from about 25 to about 100 millimeters. 
Asphalt concrete pavements can be made to be very smooth which offers 
outstanding frictional resistance for vehicles operating thereon. Such 
asphalt concrete pavement can also be repaired simply by adding additional 
hot asphalt concrete to holes and other types of defects which develop in 
the surface. Asphalt concrete pavements can also be upgraded easily by 
adding additional layers of hot asphalt concrete to old surfaces which are 
in need of repair. 
Even though asphalt concrete offers numerous benefits as a paving material, 
its use is not trouble-free. One major problem encountered with asphalt 
concrete pavements is the loss of the adhesive bond between the aggregate 
surface and the asphalt cement. This breaking of the adhesive bond between 
the asphalt cement and the aggregate surface is known as "stripping." The 
stripping of asphalt binder from aggregate surfaces results in shorter 
pavement life and many millions of dollars of maintenance work on American 
highways each year. Reduction of this stripping tendency is of great 
interest when trying to improve conditions of roads and lowering these 
maintenance costs. 
Over the years, various methods have been developed to reduce stripping 
tendencies. For instance, amines and lime are known to act as 
anti-stripping agents and are frequently applied to the surface of the 
aggregate prior to mixing it with the asphalt cement in making asphalt 
concrete. U.S. Pat. No. 5,219,901 discloses a technique for reducing 
stripping tendencies which involves coating the aggregate with a thin 
continuous film of a water-insoluble high molecular weight organic 
polymer, such as an acrylic polymer or a styrene-acrylic polymer. 
U.S. Pat. No. 5,262,240 discloses a technique for providing aggregate with 
a high level of resistance to stripping by water, which comprises: (1) 
mixing the aggregate with latex to form a latex/aggregate mixture which is 
comprised of from about 0.005 weight percent to about 0.5 weight percent 
dry polymer; (2) heating the latex/aggregate mixture to a temperature 
which is within the range of about 66.degree. C. to about 232.degree. C.; 
(3) maintaining the latex/aggregate mixture at said elevated temperature 
for a time which is sufficient to reduce the moisture content of the 
latex/aggregate mixture below about 0.7 weight percent and to allow the 
polymer in the latex to crosslink on the surface of the aggregate to 
produce the coated aggregate. 
At high service temperatures, such as those experienced on hot summer days, 
asphalt concrete can experience rutting and shoving. On the other hand, at 
low service temperatures, such as those experienced during cold winter 
nights, asphalt concrete can also experience low temperature cracking. To 
combat these problems, it is known in the art to modify asphalt cements 
with rubbery polymers, such as styrene-butadiene rubber latex. Such 
modification techniques can greatly improve resistance to rutting, shoving 
and low temperature cracking. However, the rubbery polymers used in such 
applications have a tendency to phase-separate from hot asphalt cements 
due to poor compatibility. A solution to the problem of poor compatibility 
is offered by the technique disclosed in U.S. Pat. No. 5,002,987. 
U.S. Pat. No. 5,002,987 relates to a modified asphalt cement containing 
from about 90 to about 99 parts by dry weight of an asphalt cement and 
from about 1 to about 10 parts by dry weight of a rubber latex having a 
weight average molecular weight of less than 250,000 and a Mooney 
viscosity of less than 50. The latex is a random polymer comprising from 
about 60 to 100 weight percent of at least one conjugated diolefin 
containing from 4 to 6 carbon atoms and from about 0 to 40 weight percent 
styrene. This latex polymer is highly compatible with the asphalt and 
provides good ductility which results in good resistance to low 
temperature cracking. However, the utilization of the rubbery polymers 
described in U.S. Pat. No. 5,002,987 in asphalt cements provide little 
improvement in elastic recovery or toughness. Thus, their use results in 
compromised rutting and shoving characteristics. There accordingly is a 
current need for a modifier which is compatible with asphalt cement and 
which improves the resistance of asphalt concrete made therewith to 
rutting, shoving and low temperature cracking. 
U.S. Pat. No. 5,534,568 reveals an asphalt concrete which is comprised of 
(A) from about 90 weight percent to about 99 weight percent of an 
aggregate and (B) from about 1 weight percent to about 10 weight percent 
of a modified asphalt cement which is comprised of (1) from about 90 
weight percent to about 99 weight percent of asphalt and (2) from about 1 
weight percent to about 10 weight percent of a rubbery polymer which is 
comprised of repeat units which are derived from (a) about 64 weight 
percent to about 84.9 weight percent of a conjugated diolefin monomer, (b) 
about 15 weight percent to about 33 weight percent of a vinyl aromatic 
monomer and (c) about 0.1 weight percent to about 3 weight percent of 
isobutoxymethyl acrylamide. 
U.S. Pat. No. 4,145,322 discloses a process for making a bitumen-polymer 
composition which consists of contacting with each other, at a temperature 
between 130.degree. C. and 230.degree. C., 80 to 98 weight percent of a 
bitumen exhibiting a penetration value between 30 and 220 and 2 to 20 
weight percent of a block copolymer, with an average molecular weight 
between 30,000 and 330,000 having the theoretical formula S.sub.x -B.sub.y 
in which S corresponds to the styrene structure groups, B corresponds to 
the conjugated diene structure groups and x and y are integers, stirring 
the obtained mixture for at least two hours, then adding 0.1 to 3 percent 
by weight of elemental sulfur with respect to the bitumen and maintaining 
the mixture thus obtained under agitation for at least 20 minutes. 
Batch polymerization techniques are normally used in synthesizing block 
copolymers which are utilized in modifying asphalt in order to attain 
desired performance characteristics. However, it would be highly desirable 
from a cost standpoint to be capable of synthesizing such polymers by 
utilizing continuous polymerization techniques. It would also be highly 
desirable to increase the force ductility, elastic recovery, toughness and 
tenacity of asphalt which is modified with such polymers. 
U.S. Pat. No. 5,837,756 discloses an asphalt concrete which is comprised of 
(A) from about 90 weight percent to about 99 weight percent of an 
aggregate and (B) from about 1 weight percent to about 10 weight percent 
of a modified asphalt cement which is comprised of (i) from about 90 
weight percent to about 99 weight percent asphalt; (ii) from about 1 
weight percent to about 10 weight percent of a styrene-butadiene polymer 
made by a process which is comprised of the steps of: (1) continuously 
charging 1,3-butadiene monomer, an organo lithium compound, a polar 
modifier and an organic solvent into a first polymerization zone, (2) 
allowing the 1,3-butadiene monomer to polymerize in said first 
polymerization zone to a conversion of at least about 90 percent to 
produce a living polymer solution which is comprised of said organic 
solvent and living polybutadiene chains having a number average molecular 
weight which is within the range of about 20,000 to about 60,000, (3) 
continuously withdrawing said living polymer solution from said first 
reaction zone, (4) continuously charging styrene monomer, divinyl benzene 
and the living polymer solution being withdrawn from the first 
polymerization zone into a second polymerization zone, (5) allowing the 
styrene monomer and divinyl benzene monomer to polymerize in said second 
polymerization zone to produce a solution of styrene-butadiene polymer 
having a number average molecular weight which is within the range of 
about 30,000 to about 85,000 and (6) continuously withdrawing the solution 
of said styrene-butadiene polymer from the second polymerization zone; and 
(iii) from about 0.1 weight percent to about 5 parts by weight of sulfur 
per 100 parts by weight of the styrene-butadiene polymer. 
SUMMARY OF THE INVENTION 
It has been determined that a specific type of emulsion styrene-butadiene 
rubber can be used to modify asphalt cement to greatly enhance the 
resistance to shoving, rutting and low temperature cracking of asphalt 
concretes made therewith. It has further been determined that this 
styrene-butadiene rubber (SBR) is compatible with virtually all types of 
asphalt and that modified asphalt cements made therewith have extremely 
high levels of force ductility, tenacity and toughness. 
The SBR used to modify asphalt cement in the practice of this invention is 
a blend of (i) a high molecular weight styrene-butadiene rubber having a 
weight average molecular weight of at least about 300,000 and (ii) a low 
molecular weight styrene-butadiene rubber having a weight average 
molecular weight of less than about 280,000; wherein the ratio of the high 
molecular weight styrene-butadiene rubber to the low molecular weight 
styrene-butadiene rubber is within the range of about 80:20 to about 
25:75; and wherein the bound styrene content of the high molecular weight 
styrene-butadiene rubber differs from the bound styrene content of the low 
molecular weight styrene-butadiene rubber by at least 5 percentage points. 
These SBR compositions are comprised of repeat units which are derived 
from styrene and 1,3-butadiene, wherein the styrene-butadiene rubber 
composition has a number average molecular weight as determined by field 
flow fractionation which is within the range of about 50,000 to 150,000 
and wherein the styrene-butadiene rubber has a light scattering to 
refractive index ratio which is within the range of 1.8 to 3.9. 
The present invention discloses an asphalt concrete which is comprised of 
(A) from about 90 weight percent to about 99 weight percent of an 
aggregate and (B) from about 1 weight percent to about 10 weight percent 
of a modified asphalt cement which is comprised of (1) from about 90 
weight percent to about 99 weight percent of asphalt; and (2) from about 1 
weight percent to about 10 weight percent of a rubbery polymer which is 
comprised of repeat units which are derived from styrene and 
1,3-butadiene, wherein the styrene-butadiene rubber composition has a 
number average molecular weight as determined by field flow fractionation 
which is within the range of about 50,000 to 150,000 and wherein the 
styrene-butadiene rubber has a light scattering to refractive index ratio 
which is within the range of 1.8 to 3.9. 
The subject invention also reveals an asphalt concrete which is comprised 
of (A) from about 90 weight percent to about 99 weight percent of an 
aggregate and (B) from about 1 weight percent to about 10 weight percent 
of a modified asphalt cement which is comprised of (1) from about 90 
weight percent to about 99 weight percent of asphalt; and (2) from about 1 
weight percent to about 10 weight percent of a rubbery polymer which is 
comprised of repeat units which are derived from styrene and 
1,3-butadiene, wherein a plot of log frequency versus elastic modulus of 
the styrene-butadiene rubber composition crosses over a plot of log 
frequency versus loss modulus of the styrene-butadiene rubber composition 
at a frequency within the range of 0.001 radians per second to 100 radians 
per second when conducted at 90.degree. C. to 120.degree. C. using 
parallel plate geometry in the dynamic oscillation frequency sweep of the 
styrene-butadiene rubber. 
The subject invention further discloses an asphalt concrete which is 
comprised of (A) from about 90 weight percent to about 99 weight percent 
of an aggregate and (B) from about 1 weight percent to about 10 weight 
percent of a modified asphalt cement which is comprised of (1) from about 
90 weight percent to about 99 weight percent of asphalt; and (2) from 
about 1 weight percent to about 10 weight percent of a rubbery polymer 
which is comprised of a blend of (i) a high molecular weight 
styrene-butadiene rubber having a weight average molecular weight of at 
least about 300,000 and (ii) a low molecular weight styrene-butadiene 
rubber having a weight average molecular weight of less than about 
280,000; wherein the ratio of the high molecular weight styrene-butadiene 
rubber to the low molecular weight styrene-butadiene rubber is within the 
range of about 80:20 to about 25:75; and wherein the bound styrene content 
of the high molecular weight styrene-butadiene rubber differs from the 
bound styrene content of the low molecular weight styrene-butadiene rubber 
by at least 5 percentage points. 
The present invention also discloses a modified asphalt cement which is 
comprised of (1) from about 90 weight percent to about 99 weight percent 
of asphalt; and (2) from about 1 weight percent to about 10 weight percent 
of a rubbery polymer which is comprised of repeat units which are derived 
from styrene and 1,3-butadiene, wherein the styrene-butadiene rubber 
composition has a number average molecular weight as determined by field 
flow fractionation which is within the range of about 50,000 to 150,000 
and wherein the styrene-butadiene rubber has a light scattering to 
refractive index ratio which is within the range of 1.8 to 3.9. 
The subject invention further reveals a modified asphalt cement which is 
comprised of (1) from about 90 weight percent to about 99 weight percent 
of asphalt; and (2) from about 1 weight percent to about 10 weight percent 
of a rubbery polymer which is comprised of repeat units which are derived 
from styrene and 1,3-butadiene, wherein a plot of log frequency versus 
elastic modulus of the styrene-butadiene rubber composition crosses over a 
plot of log frequency versus loss modulus of the styrene-butadiene rubber 
composition at a frequency within the range of 0.001 radians per second to 
100 radians per second when conducted at 90.degree. C. to 120.degree. C. 
using parallel plate geometry in the dynamic oscillation frequency sweep 
of the styrene-butadiene rubber. 
The present invention also reveals a modified asphalt cement which is 
comprised of (1) from about 90 weight percent to about 99 weight percent 
of asphalt; and (2) from about 1 weight percent to about 10 weight percent 
of a blend of (i) a high molecular weight styrene-butadiene rubber having 
a weight average molecular weight of at least about 300,000 and (ii) a low 
molecular weight styrene-butadiene rubber having a weight average 
molecular weight of less than about 280,000; wherein the ratio of the high 
molecular weight styrene-butadiene rubber to the low molecular weight 
styrene-butadiene rubber is within the range of about 80:20 to about 
25:75; and wherein the bound styrene content of the high molecular weight 
styrene-butadiene rubber differs from the bound styrene content of the low 
molecular weight styrene-butadiene rubber by at least 5 percentage points. 
DETAILED DESCRIPTION OF THE INVENTION 
The styrene-butadiene rubber composition which is used to modify asphalt 
cement in accordance with this invention is made by emulsion 
polymerization using a free radical emulsion polymerization technique. The 
styrene-butadiene rubber composition is made by synthesizing a high 
molecular weight SBR latex and a low molecular weight SBR latex and then 
blending the two latices. The styrene-butadiene rubber of this invention 
is preferably made by synthesizing a high molecular weight SBR latex and a 
low molecular weight SBR latex utilizing the general free radical emulsion 
polymerization technique described in U.S. Pat. No. 5,583,173. This 
polymerization technique is known as the FIM process 
(feed-injection-monomer). The latex of the high molecular weight SBR and 
the latex of the low molecular weight SBR are then blended. 
The FIM process is carried out by adding styrene monomer, 1,3-butadiene 
monomer, water, a free radical generator and a soap system to a first 
polymerization zone to form an aqueous polymerization medium. The first 
polymerization zone will normally be a reactor or series of two or more 
reactors. Copolymerization of the monomers is initiated with the free 
radical generator. This copolymerization reaction results in the formation 
of a low conversion polymerization medium. 
At the point where the low conversion polymerization medium reaches a 
monomer conversion which is within the range of about 15 percent to about 
40 percent, the low conversion polymerization medium is charged into a 
second polymerization zone. The second polymerization zone can be a 
reactor or a series of two or more reactors. In any case, the second 
polymerization zone is subsequent to the first polymerization zone. The 
low conversion polymerization medium will normally be charged into the 
second polymerization zone at a monomer conversion level which is within 
the range of about 17 percent to about 35 percent. It will more preferably 
be charged into the second polymerization zone at a level of monomer 
conversion which is within the range of 20 percent to 30 percent. 
Additional styrene monomer and butadiene monomer are charged into the 
second polymerization zone. Normally, from about 20 percent to about 50 
percent of the total amount of styrene monomer and 1,3-butadiene monomer 
will be charged into the second polymerization zone (from 50 percent to 80 
percent of the total monomers are charged into the first polymerization 
zone). It is normally preferred to charge from about 30 weight percent to 
about 45 weight percent of the total quantity of monomers charged into the 
second polymerization zone (from 55 percent to 70 percent of the total 
monomers charged will be charged into the first polymerization zone). It 
is generally most preferred to charge from about 35 weight percent to 
about 42 weight percent of the total quantity of monomers charged into the 
second polymerization zone (from 58 percent to 65 percent of the total 
monomers charged will be charged into the first polymerization zone). By 
splitting the monomer charge between the first polymerization zone and the 
second polymerization zone, the total quantity of soap required to provide 
a stable latex is reduced by at least about 30 percent. 
The copolymerization in the second polymerization zone is allowed to 
continue until a monomer conversion of at least 50 percent is attained. 
The copolymerization will preferably be allowed to continue until a total 
monomer conversion which is within the range of 50 percent to 68 percent 
is realized. More preferably, the copolymerization in the second reaction 
zone will be allowed to continue until a monomer conversion of 58 percent 
to 65 percent is reached. 
In synthesizing the SBR latex, generally from about 1 weight percent to 
about 50 weight percent styrene and from about 50 weight percent to about 
99 weight percent 1,3-butadiene are copolymerized. However, it is 
contemplated that various other vinyl aromatic monomers can be substituted 
for the styrene in the SBR. For instance, some representative examples of 
vinyl aromatic monomers that can be substituted for styrene and 
copolymerized with 1,3-butadiene in accordance with this invention include 
1-vinylnaphthalene, 3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene, 
2,4,6-trimethylstyrene, 4-dodecylstyrene, 3-methyl-5-normal-hexylstyrene, 
4-phenylstyrene, 2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 
2,3,4,5-tetraethyl-styrene, 3-ethyl-1-vinylnaphthalene, 
6-isopropyl-1-vinylnaphthalene, 6-cyclohexyl-1-vinylnaphthalene, 
7-dodecyl-2-vinylnaphthalene, a-methylstyrene, and the like. The high 
molecular weight SBR will typically contain from about 5 weight percent to 
about 50 weight percent bound styrene and from about 50 weight percent to 
about 95 weight percent bound butadiene. It is typically preferred for the 
high molecular weight SBR to contain from about 20 weight percent to about 
30 weight percent styrene and from about 70 weight percent to about 80 
weight percent 1,3-butadiene. It is normally most preferred for high 
molecular weight SBR to contain from about 22 weight percent to about 28 
weight percent styrene and from about 72 weight percent to about 78 weight 
percent 1,3-butadiene. Like ratios of styrene, monomer and butadiene 
monomer will accordingly be charged into the first polymerization zone and 
the second polymerization zone. 
The low molecular weight SBR will normally contain from about 1 weight 
percent to about 50 weight percent styrene and from about 50 weight 
percent to about 99 weight percent 1,3-butadiene. In some cases, for 
instance, where low rolling resistance and excellent treadwear 
characteristics are desired, it will be desirable for the low molecular 
weight SBR to contain a relatively small amount of styrene which is within 
the range of about 3 weight percent to about 10 weight percent with the 
amount of 1,3-butadiene in the SBR being within the range of about 90 
weight percent to about 97 weight percent. Even lower amounts of bound 
styrene can be included in the low molecular weight polymer. For instance, 
the low molecular weight rubbery polymer can contain from 0 weight percent 
to 3 weight percent bound styrene and from 97 weight percent to 100 weight 
percent bound butadiene. Thus, in the most extreme case, polybutadiene can 
be used as one of the polymeric components of the blend. In other cases, 
for instance, in situations where high traction characteristics are 
desired, a much higher level of styrene will be incorporated into the low 
molecular weight SBR. In such cases, it is preferred for low molecular 
weight SBR to contain from about 40 weight percent to about 50 weight 
percent styrene and from about 50 weight percent to about 60 weight 
percent 1,3-butadiene. Like ratios of styrene monomer and butadiene 
monomer will accordingly be charged into the first polymerization zone and 
the second polymerization zone. 
It is critical for the high molecular weight SBR to have a bound styrene 
content which differs from the bound styrene content of the low molecular 
weight SBR by at least 5 percentage points. The high molecular weight SBR 
will normally have a bound styrene content which differs from the bound 
styrene content of the low molecular weight SBR by 5 to 40 percentage 
points. The high molecular weight SBR will typically have a bound styrene 
content which differs from the bound styrene content of the low molecular 
weight SBR by at least 10 percentage points. In most cases, the high 
molecular weight SBR will have a bound styrene content which differs from 
the bound styrene content of the low molecular weight SBR by 10 to 30 
percentage points with a difference of 15 to 25 percentage points being 
most typical. It is normally preferred for the high molecular weight SBR 
to have a bound styrene content which differs from the bound styrene 
content of the low molecular weight SBR by at least 15 percentage points 
with a difference of at least 20 percentage points being most preferred. 
It should be understood that either the high molecular weight or the low 
molecular weight SBR can have the higher bound styrene content. In other 
words, the SBR in the blend having the higher bound styrene content can be 
either the low or the high molecular weight polymer in the blend. It 
should also be understood that polybutadiene (which contains 0 percent 
bound styrene) can be used as one of the polymers in the blend. In such 
cases, the polybutadiene can be either the high or the low molecular 
weight polymer. In cases where polybutadiene is used as one of the rubbery 
polymers in the blend, the SBR in the blend will typically have a bound 
styrene content of at least about 10 weight percent. In such cases, the 
SBR in the blend will more typically have a bound styrene content of at 
least about 15 weight percent and will most preferably have a bound 
styrene content of at least about 20 weight percent. 
Essentially any type of free radical generator can be used to initiate such 
free radical emulsion polymerizations. For example, free radical 
generating chemical compounds, ultra-violet light or radiation can be 
used. In order to ensure a satisfactory polymerization rate, uniformity 
and a controllable polymerization, free radical generating chemical agents 
which are water- or oil-soluble under the polymerization conditions are 
generally used with good results. 
Some representative examples of free radical initiators which are commonly 
used include the various peroxygen compounds such as potassium persulfate, 
ammonium persulfate, benzoyl peroxide, hydrogen peroxide, di-t-butyl 
peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, decanoyl 
peroxide, lauryl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, 
t-butyl hydroperoxide, acetyl acetone peroxide, dicetyl peroxydicarbonate, 
t-butyl peroxyacetate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, 
acetyl cyclohexyl sulfonyl peroxide, and the like; the various azo 
compounds such as 2-t-butylazo-2-cyanopropane, dimethyl azodiisobutyrate, 
azodiisobutyronitrile, 2-t-butylazo-1-cyanocyclohexane, 
1-t-amylazo-1-cyanocyclohexane, and the like, the various alkyl perketals, 
such as 2,2-bis-(t-butylperoxy)butane, ethyl 
3,3-bis(t-butylperoxy)butyrate, 1,1-di-(t-butylperoxy) cyclohexane, and 
the like. Persulfate initiators, such as potassium persulfate and ammonium 
persulfate, are especially useful in such aqueous emulsion 
polymerizations. 
The amount of initiator employed will vary with the desired molecular 
weight of the SBR being synthesized. Higher molecular weights are achieved 
by utilizing smaller quantities of the initiator and lower molecular 
weights are attained by employing larger quantities of the initiator. 
However, as a general rule, from 0.005 to 1 phm (parts by weight per 100 
parts by weight of monomer) of the initiator will be included in the 
reaction mixture. In the case of metal persulfate initiators, typically 
from 0.1 phm to 0.5 phm of the initiator will be employed in the 
polymerization medium. The molecular weight of the SBR produced is, of 
course, also dependent upon the amount of chain transfer agent, such as 
t-dodecyl mercaptan, present during the polymerization. For instance, low 
molecular weight SBR can be synthesized by simply increasing the level of 
chain transfer agent. As a specific example, in the synthesis of high 
molecular weight SBR, the amount of t-dodecyl mercaptan used can be within 
the range of about 0.125 phm to about 0.150 phm. Low molecular weight SBR 
can be produced by simply increasing the level of t-dodecyl mercaptan 
present during the polymerization. For instance, the presence of 0.38 phm 
to 0.40 phm of t-dodecyl mercaptan will typically result in the synthesis 
of a low molecular weight SBR. 
Unless indicated otherwise, molecular weights are determined by gel 
permeation chromatography (GPC). A traditional GPC system is used with 
both light scattering (Wyatt Technologies Inc, model Mini DAWN) and 
refractive index for detection. Samples are filtered through a 1.0 micron 
syringe filter. In some cases, number average molecular weights are 
determined by thermal field flow fractionation. Number average molecular 
weight that is determined by thermal field flow fractionation is sometimes 
abbreviated as M.sub.n3F. In determining M.sub.n3F, a thermal field flow 
fractionation system that consists of an FFFractionation, LLC (Salt Lake 
City, Utah) model T-100 Polymer Fractionator with a model T-005 channel 
spacer, a Hewlett Packard (Palo Alto, Calif.) model 1047A refractive index 
detector and a Wyatt Technologies Corporation (Santa Barbara, Calif.) 
model DAWN DSP laser photometer detector is used. In the test procedure, 
degassed tetrahydrofuran is used as the carrier solvent which is pumped 
through the system at a flow rate of 0.6 mL/minute. The cold wall 
temperature in the thermal field flow fractionation is controlled by an 
FTS Systems model RC150 recirculating chiller. 
Polymer fractionation is accomplished using a Power Programmed Method in 
FFFractionation, LLC software (TEMP, version 1.30 beta 7). The program 
conditions are as follows: Initial Delta T is 60.degree. C., equilibration 
time is 0.5 minutes, t1 is 5.0 minutes, ta is -6.0, hold time is 30 
minutes and final Delta T is 0.degree. C. The temperature set point for 
the cold wall chiller is 25.degree. C. However, at the initial delta T of 
60.degree. C., the cold wall temperature is typically around 40.degree. C. 
Polymer samples are dissolved in a solvent and then injected unfiltered 
into the thermal field flow fractionation system. The sample mass injected 
is typically about 0.12 mg. 
The raw data is collected and processed in Wyatt Technologies Corporation 
software (ASTRA, version 4.70.07). The data collection period is 25 
minutes. Baselines for the peaks are typically set from 1.5 minutes to 25 
minutes for the light scattering detectors and from 1.5 minutes to 20 
minutes for the refractive index detector. For the data processing, the 
DAWN light scattering detectors used include 5 through 16 (representing 
angles from 39.degree. to 139.degree. in THF). The angular dependence of 
the light scattering is fit using a first order equation in the Zimm 
formalism. A refractive index increment (dn/dc) of 0.154 is used for all 
emulsion polymer samples and 0.140 is used for solution polymer samples. 
The sensitivity of the refractive index detector (Aux 1 Constant) is 
determined according to Wyatt Technologies procedures using a monodisperse 
30,000 molecular weight polystyrene standard. 
Average molecular weights and root mean square radii for the samples are 
calculated using slice data fit to a first order polynomial. The light 
scattering to refractive index ratio (LS/RI) is calculated using the 
baseline corrected, normalized voltages from the DAWN 90.degree. detector 
(d11) and the Hewlett Packard model 1047A refractive index detector. The 
area under each peak was estimated as the sum of the voltages within the 
defined integration limits. 
The high molecular weight SBR will typically have a number average 
molecular weight (by GPC) which is within the range of about 200,000 to 
about 1,000,000, a weight average molecular weight (by GPC) which is 
within the range of about 300,000 to about 2,000,000 and a Mooney ML 1+4 
viscosity which is within the range of about 80 to about 160. The high 
molecular weight SBR will preferably have a number average molecular 
weight which is within the range of about 300,000 to about 970,000, a 
weight average molecular weight which is within the range of about 400,000 
to about 1,750,000 and a Mooney ML 1+4 viscosity which is within the range 
of about 90 to about 150. The high molecular weight SBR will more 
preferably have a number average molecular weight which is within the 
range of about 650,000 to about 930,000, a weight average molecular weight 
which is within the range of about 1,000,000 to about 1,500,000 and a 
Mooney ML 1+4 viscosity which is within the range of about 95 to about 
130. 
The low molecular weight SBR will typically have a number average molecular 
weight (by GPC) which is within the range of about 20,000 to about 
150,000, a weight average molecular weight (by GPC) which is within the 
range of about 40,000 to about 280,000 and a Mooney ML 1+4 viscosity which 
is within the range of about 2 to about 40. The low molecular weight SBR 
will preferably have a number average molecular weight which is within the 
range of about 50,000 to about 120,000, a weight average molecular weight 
which is within the range of about 70,000 to about 270,000 and a Mooney ML 
1+4 viscosity which is within the range of about 3 to about 30. The low 
molecular weight SBR will more preferably have a number average molecular 
weight which is within the range of about 70,000 to about 110,000, a 
weight average molecular weight which is within the range of about 120,000 
to about 260,000 and a Mooney ML 1+4 viscosity which is within the range 
of about 5 to about 20. The low molecular weight SBR will usually have a 
Mooney ML 1+4 viscosity which is within the range of 12-18. 
The low molecular weight SBR will have a Mooney ML 1+4 viscosity that 
differs from the Mooney ML 1+4 viscosity of the high molecular weight SBR 
by at least 50 Mooney points. The high molecular weight SBR will normally 
have a Mooney ML 1+4 viscosity that is at least 70 Mooney points higher 
than the Mooney ML 1+4 viscosity of the low molecular weight SBR. The high 
molecular weight SBR will preferably have a Mooney ML 1+4 viscosity that 
is at least 80 Mooney points higher than the Mooney ML 1+4 viscosity of 
the low molecular weight SBR. 
The soap systems used in the emulsion polymerization process contain a 
combination of rosin acid and fatty acid emulsifiers. The weight ratio of 
fatty acid soaps to rosin acid soaps will be within the range of about 
50:50 to 90:10. It is normally preferred for the weight ratio of fatty 
acid soaps to rosin acid soaps to be within the range of 60:40 to 85:15. 
It is normally more preferred for the weight ratio of fatty acid soaps to 
rosin acid soaps to be within the range of 75:25 to 82:18. All of the soap 
is charged into the first polymerization zone. The total amount of soap 
employed will be less than 3.5 phm. The quantity of soap employed will 
normally be within the range of about 2.5 phm to 3.2 phm. It is typically 
preferred to utilize a level of soap which is within the range of about 
2.6 phm to about 3.0 phm. In most cases, it will be most preferred to use 
an amount of the soap system which is within the range of about 2.7 phm to 
2.9 phm. The precise amount of the soap system required in order to attain 
optimal results will, of course, vary with the specific soap system being 
used. However, persons skilled in the art will be able to easily ascertain 
the specific amount of soap system required in order to attain optimal 
results. 
The free radical emulsion polymerization will typically be conducted at a 
temperature which is within the range of about 35.degree. F. (2.degree. 
C.) to about 65.degree. F. (18.degree. C.). It is generally preferred for 
the polymerization to be carried out at a temperature which is within the 
range of 40.degree. F. (4.degree. C.) to about 60.degree. F. (16.degree. 
C.). It is typically more preferred to utilize a polymerization 
temperature which is within the range of about 45.degree. F. (7.degree. 
C.) to about 55.degree. F. (13.degree. C.). To increase conversion levels, 
it can be advantageous to increase the temperature as the polymerization 
proceeds. 
After the desired monomer conversion is reached in the second 
polymerization zone, the SBR latex made is removed from the second 
polymerization zone and a short stop is added to terminate the 
copolymerization. This is a convenient point to blend the emulsion of the 
high molecular weight SBR with the emulsion of the low molecular weight 
SBR. The weight ratio of the high molecular weight SBR to the low 
molecular weight SBR in the blend will typically be within the range of 
about 80:20 to about 25:75. In most cases, the weight ratio of the high 
molecular weight SBR to the low molecular weight SBR in the blend will be 
within the range of about 70:30 to about 30:70. It is typically preferred 
for the weight ratio of the high molecular weight SBR to the low molecular 
weight SBR in the blend to be within the range of about 60:40 to about 
40:60. 
The styrene-butadiene rubber composition of this invention made by blending 
the two latices will have an M.sub.n3F which is within the range of 50,000 
to 150,000. The styrene-butadiene rubber composition will typically have 
an M.sub.n3F which is within the range of 60,000 to 145,000 and will more 
typically have an M.sub.n3F which is within the range of 75,000 to 
140,000. The styrene-butadiene rubber composition will preferably have an 
M.sub.n3F which is within the range of 90,000 to 135,000. The 
styrene-butadiene rubber composition will also have a light scattering to 
refractive index ratio (LS/RI) which is within the range of 1.8 to 3.9. 
The styrene-butadiene rubber composition will typically have a light 
scattering to refractive index ratio which is within the range of 2.0 to 
3.8 and will more typically have a light scattering to refractive index 
ratio of 2.1 to 3.7. It is preferred for the styrene-butadiene rubber 
composition to have a light scattering to refractive index ratio which is 
within the range of 2.2 to 3.0. 
In the styrene-butadiene rubber compositions of this invention, if the 
dynamic oscillation frequency sweep of frequency versus elastic modulus 
(G') and frequency versus loss modulus (G") are plotted, there is a 
crossover at a frequency within the range of 0.001 radians per second to 
100 radians per second when conducted at 90.degree. C. to 120.degree. C. 
using a parallel plate geometry. In other words, at low frequencies, at 
120.degree. C., such as 0.1 radians per second, G' is lower than G". 
However, G' increasing with increasing frequency until it equals G" and is 
ultimately greater than G" at a high frequency, such as 10 radians per 
second. The crossover point will typically be within the frequency range 
of 0.001 radians per second to 10 radians per second and will more 
typically be within the frequency range of 0.01 radians per second to 5 
radians per second. In most cases, the crossover point will be within the 
frequency range of 0.05 radians per second to 1 radians per second at 
120.degree.. In the test procedure used, the rubber sample is preformed 
into a sample 20 mm in diameter having a thickness of 2 mm. The sample is 
then placed in a control stress or control strain rheometer between 
parallel plates at a given gap distance. The sample is then run through a 
frequency sweep (such as 0.01 Hz to 100 Hz) at some applied stress (such 
as 20,000 Pa). This procedure is performed at different temperatures 
between 90.degree. C. and 120.degree. C. at some defined temperature 
interval. G' is the storage modulus and represents the elastic portion of 
the polymer and is very sensitive to changes in gel and molecular weight. 
G" is the loss modulus and is representative of the viscous portion of the 
sample. 
Asphalt cement can be modified with the SBR latex composition by simply 
mixing the latex into hot asphalt. The latex of the SBR composition may be 
added to the asphalt in an amount of from about 1 to about 10 parts by dry 
weight of the latex. Preferably, from about 1 to about 6 parts by dry 
weight is used with a range of from about 2 to about 4 parts being 
particularly preferred. 
The SBR latex is slowly added to heated asphalt with agitation. The asphalt 
is generally heated to a temperature ranging from about 150.degree. C. to 
about 170.degree. C. At the elevated temperatures used, the water in the 
latex quickly evaporates leaving only the rubbery polymer which was in the 
latex. After the rubber latex has been thoroughly mixed with the asphalt 
cement, one should store the modified asphalt cement at elevated 
temperatures to avoid solidification prior to use. 
Asphalt is defined by ASTM as a dark brown to black cementitious material 
in which the predominant constituents are bitumens that occur in nature or 
are obtained in petroleum processing. Asphalts characteristically contain 
very high molecular weight hydrocarbons called asphaltenes. These are 
essentially soluble in carbon disulfide, and aromatic and chlorinated 
hydrocarbons. Bitumen is a generic term defined by ASTM as a class of 
black or dark colored (solid, semi-solid or viscous) cementitious 
substances, natural or manufactured, composed principally of high 
molecular weight hydrocarbons, of which asphalts, tars, pitches and 
asphaltites are typical. ASTM further classifies asphalts or bituminous 
materials as solids, semi-solids or liquids using a penetration test for 
consistency or viscosity. In this classification, solid materials are 
those having a penetration at 25.degree. C. under a load of 100 grams 
applied for 5 seconds, of not more than 10 decimillimeters (1 millimeter). 
Semi-solids are those having a penetration at 25.degree. C. under a load 
of 100 grams applied for 5 seconds of more than 10 decimillimeters (1 
millimeter) and a penetration at 25.degree. C. under a load of 50 grams 
applied for 1 second of not more than 35 millimeters. Semi-solid and 
liquid asphalts predominate in commercial practice today. 
Asphalts are usually specified in several grades for the same industry, 
differing in hardness and viscosity. Specifications of paving asphalt 
cements generally include five grades differing in either viscosity level 
at 60.degree. C. or penetration level. Susceptibility of viscosity to 
temperatures is usually controlled in asphalt cement by its viscosity 
limits at a higher temperature such as 135.degree. C. and a penetration or 
viscosity limit at a lower temperature such as 25.degree. C. For asphalt 
cements, the newer viscosity grade designation is the mid-point of the 
viscosity range. 
The asphalt materials which may be used in the present invention are those 
typically used for road paving, repair and maintenance purposes. Petroleum 
asphalts are the most common source of asphalt cements. Petroleum asphalts 
are produced from the refining of petroleum and used predominantly in 
paving and roofing applications. Petroleum asphalts, compared to native 
asphalts, are organic with only trace amounts of inorganic materials. Some 
representative examples of asphalt cements that may be used in the present 
invention have an ASTM grade of AC-2.5, AC-5, AC-10, AC-20 and AC-40. The 
preferred asphalt cements include AC-5, AC-10 and AC-20. 
In addition to the rubbery polymer and the asphalt cement, the modified 
asphalt cement of the present invention may contain other conventional 
additives. Examples of conventional additives include antistripping 
compounds, fibers, release agents and fillers. Some specific examples of 
additives which can be employed include sulfur, kaolin clay, calcium 
carbonate, bentonite clay, sanders dust and cellulose fibers. 
After the asphalt cement has been modified, it can be mixed with aggregate 
to make asphalt concrete using standard equipment and procedures utilized 
in making asphalt concrete. As a general rule, from about 1 weight percent 
to about 10 weight percent of the modified asphalt cement and from about 
90 weight percent to about 99 weight percent aggregate will be included in 
the asphalt concrete. It is more typical for the asphalt concrete to 
contain from about 3 weight percent to about 8 weight percent of the 
modified asphalt cement and from about 92 weight percent to about 97 
weight percent of the aggregate. It is normally preferred for the asphalt 
concrete to contain from about 4 weight percent to about 7 weight percent 
of the modified asphalt cement and from about 93 weight percent to about 
96 weight percent of the aggregate. 
The aggregate is mixed with the asphalt to attain an essentially 
homogeneous asphalt concrete. The coated aggregate is mixed with the 
asphalt cement utilizing conventional techniques and standard equipment. 
For instance, the aggregate can be dried and mixed with asphalt to produce 
asphalt concrete on a continuous basis in a standard mixer. 
Standard aggregate can be utilized in the practice of this invention. The 
aggregate is essentially a mixture containing rocks, stones, crushed 
stone, gravel and/or sand. The aggregate will typically have a wide 
distribution of particle sizes ranging from dust to golf ball size. The 
best particle size distribution varies from application to application. In 
many cases, it will be advantageous to coat the aggregate with latex in 
accordance with the teachings of U.S. Pat. No. 5,262,240 to improve 
resistance to stripping by water. 
The asphalt concrete made using the modified asphalt cement of this 
invention can then be used to pave roads, highways, exit ramps, streets, 
driveways, parking lots, airport runways or airport taxiways utilizing 
conventional procedures. However, pavements made utilizing the asphalt 
concretes of this invention offer resistance to rutting, shoving and low 
temperature cracking. Additionally, they can be applied without 
encountering processing difficulties due to the latex used for the 
modification being incompatible with the asphalt.

This invention is illustrated by the following examples which are merely 
for the purpose of illustration and are not to be regarded as limiting the 
scope of the invention or the manner in which it can be practiced. Unless 
specifically indicated otherwise, all parts and percentages are given by 
weight. 
EXAMPLE 1 
In this experiment, an SBR latex was synthesized by copolymerizing 
1,3-butadiene monomer and styrene monomer by the FIM process. This 
procedure was conducted in a pilot plant which consisted of a series of 
five polymerization reactors. All of the reactors used in this procedure 
were 30-gallon stirred reactors which were connected to operate in series 
(the reactor chain had a total chain volume of 150 gallons). The reactor 
chain was continuously operated at an actual running rate of 18.53 gallons 
per hour which provided an actual reaction time of 8.1 hours. 
The monomer charge was split between the first reactor and the third 
reactor. The monomers were continuously fed into the first reactor at a 
rate of 29.6 pounds per hour and into the second reactor at a rate of 19.1 
pounds per hour. The monomer charge employed contained 69 weight percent 
1,3-butadiene and 31 weight percent styrene. An activator solution, a soap 
solution, a scavenger solution, a modifier, a secondary surfactant and an 
initiator were also continuously changed into the first reactor. 
The activator solution was an aqueous solution containing 0.67 percent 
sodium ferric ethylenediaminetetraacetate. It was charged into the first 
reactor at a rate which was sufficient to maintain a 0.026 phm level of 
sodium ferric ethylenediaminetetraacetate. The secondard surfactant 
charged into the first reactor was an aqueous solution containing 0.503 
phm of Witconate.RTM. 1223L, the sodium salt of a linear alkylbenzene 
sulfonic acid (from Witco Chemicals). 
The soap solution charged into the first reactor contained 98.0 percent 
water, 0.25 percent potassium hydroxide, 0.13 percent potassium chloride, 
0 percent of the potassium soap of disproportionated wood rosin, 1.18 
percent hydrogenated mixed tallow fatty acids, 0.28 percent of the 
potassium soap of disproportionated tall oil rosin, 0.12 percent of the 
sodium salt of a condensed naphthalene sulfonic acid, 0.02 percent 
tetrapotassium pyrophosphate, 0.02 percent sodium formaldehyde sulfoxylate 
and 0.01 percent sodium hydrosulfite. The soap system solution was charged 
into the first reactor at a rate which was sufficient to maintain a 0.435 
phm level of potassium hydroxide, a 0.230 phm level of potassium chloride, 
a 0 phm level of the potassium soap of disproportionated wood rosin, a 
2.076 phm level of hydrogenated mixed tallow fatty acids, a 0.492 phm 
level of the potassium soap of disproportionated tall oil rosin, a 0.206 
phm level of the sodium salt of a condensed naphthalene sulfonic acid, a 
0.035 phm level of tetrapotassium pyrophosphate, a 0.035 phm level of 
sodium formaldehyde sulfoxylate and a 0.019 phm level of sodium 
hydrosulfite. 
The scavenger solution contained 99.31 percent water, 0.096 percent sodium 
hydroxide and 0.60 percent sodium hydrosulfite. The scavenger solution was 
charged into the first reactor at a rate which was sufficient to maintain 
a 0.004 phm level of sodium hydroxide and a 0.026 phm level of sodium 
hydrosulfite (the total level of sodium hydrosulfite was 0.045 phm). 
The modifier charged into the first reactor was t-dodecyl mercaptan. It was 
charged into the reactor at a rate of 0.137 phm. The initiator charged 
into the first reactor was pinane hydroperoxide and it was charged at a 
rate of 0.11 phm. 
In this procedure, the polymerization was terminated by adding a mixture of 
diethylhydroxylamine and sodium dimethyldithiocarbamate to the latex as a 
shortstop after it exited the fifth reactor. The latex made by procedure 
was stable. The utilization of this technique results in the production of 
an emulsion SBR having a number average molecular weight of about 130,000 
and a weight average molecular weight of about 490,000. 
EXAMPLE 2 
A low molecular weight emulsion SBR latex can be made by utilizing the 
technique described in Example 1 by simply increasing the level of 
t-dodecyl mercaptan to 0.39 phm. In this case, the number average 
molecular weight of the emulsion SBR produced will be about 60,000 and its 
weight average molecular weight will be about 185,000. Low molecular 
weight SBR latex having a low level of bound styrene can be made by 
adjusting the amount to styrene charged to a lower level. Using such a 
technique, a low molecular weight SBR containing 5 percent bound styrene 
can be synthesized. 
EXAMPLE 3 
A low molecular weight emulsion SBR latex having a high level of bound 
styrene can be made by utilizing the technique described in Example 1 by 
simply increasing the level of t-dodecyl mercaptan and styrene charged. 
Using such a technique, a low molecular weight SBR containing about 48 
percent bound styrene was synthesized. A low molecular weight SBR 
synthesized using such a technique had a number average molecular weight 
of 56,000, a weight average molecular weight of 137,000 and a Mooney ML 
1+4 viscosity of 11.4. 
EXAMPLE 4 
In this experiment, two styrene-butadiene (SBR) latices were synthesized by 
emulsion copolymerization of 1,3-butadiene monomer and styrene monomer in 
a continuous process. After polymerization, the latices were blended in a 
specific ratio. 
A latex having a high Mooney ML 1+4 viscosity and medium bound styrene 
content was synthesized in a series of 13 continuous stirred-tank reactors 
(CSTRs). A styrene stream, a 1,3-butadiene stream and a modifier stream 
were mixed and fed into a Ligtnin static mixer having a diameter of about 
3 inches (7.6 cm) and a length of about 30 inches (76 cm) prior to being 
split and fed into polymerization reactors. About 60 percent of this 
monomer/modifier stream was mixed with soft water and cooled in a heat 
exchanger to a temperature of about 52.degree. F. (11.degree. C.). An 
activator solution, soap solution, oxygen scavenger solution and initiator 
were added to the stream after it had exited the heat exchanger but before 
it entered into a second Ligtnin static mixer having a length of about 36 
inches (91 cm) and a diameter of about 4 inches (10.2 cm). After this 
static mixer, the combined stream had a residence time of about 40 seconds 
in the tubular reactor before entering the first CSTR. The remaining 40 
percent of the monomer/modifier stream was fed continuously into the fifth 
reactor in the chain. The reactor chain configuration is described in the 
following table: 
______________________________________ 
Agitation 
Vol Pzm Temp 
Impeller 
Speed 
RV Type (gal) (deg F.) Type (rpm) 
______________________________________ 
0 Tubular 100 63 
1 CSTR 5700 50 Brumagin 71 
2 CSTR 5700 50 Brumagin 71 
3 CSTR 5700 50 Brumagin 71 
4 CSTR 5700 50 Brumagin 71 
5 CSTR 5700 50 Brumagin 71 
6 CSTR 5700 50 Brumagin 71 
7 CSTR 5700 50 Brumagin 71 
8 CSTR 5700 50 Brumagin 71 
9 CSTR 5700 50 Axial 71 
Flow 
Turbine 
10 CSTR 5700 50 Axial 71 
Flow 
Turbine 
11 CSTR 5700 50 Axial 71 
Flow 
Turbine 
12 CSTR 5700 50 Axial 71 
Flow 
Turbine 
13 CSTR 5700 50 Axial 71 
Flow 
Turbine 
______________________________________ 
The following streams were charged to this reactor configuration 
continuously: 
______________________________________ 
Mass Flow 
Stream 
Rate Composition 
(lbs/min) (%) 
______________________________________ 
First Stage: Streams added to tubular reactor 
Butadiene Monomer: 
209.65 
1,3-butadiene 90.00 
impurities 10.00 
(mixed butenes, 
isobutylene, 
4-vinylcyclohexene, 
et al) 
Styrene Monomer: 85.93 
Styrene 91.00 
Impurities 9.00 
(4-vinylcyclohexene, 
ethylbenzene, 
mixed xylenes, et al) 
Soap Solution: 124.25 
soft water 79.33 
45% aqueous solution 2.04 
of potassium hydroxide 
40% aqueous solution 2.06 
of tripotassium phosphate 
20% aqueous solution 1.71 
of sodium hydroxide 
mixed hydrogenated 8.21 
tallow fatty acid 
47% aqueous solution 1.70 
of sodium napthelene 
sulfonate 
potassium soap of 1.95 
disproportionated tall 
oil rosin (80% active) 
23% aqueous solution 3.00 
of sodium dodecylbenzene 
sulfonate 
Soft Water 702.64 100.00 
Initiator: 0.68 
pinane hydroperoxide 100.00 
(44% active) 
Activator Solution: 65.59 
soft water 98.69 
20% aqueous solution 0.41 
of ferrous sulfate 
40% aqueous solution 0.56 
of tetrasodium ethylene- 
diaminetetraacetate 
sodium formaldehyde 0.34 
sulfoxylate 
Modifier (Chain Transfer 0.29 
Agent): 
tertiary dodecylmercaptan 100.00 
Oxygen Scavenger Solution: 2.46 
soft water 97.00 
sodium hydrosulfite 3.00 
Second Stage: Streams added to fifth CSTR 
Butadiene Monomer: 
139.76 
1,3-butadiene 90.00 
impurities 10.00 
(mixed butenes, 
isobutylene, 
4-vinylcyclohexene, 
et al) 
Styrene Monomer: 57.28 
styrene 91.00 
impurities 9.00 
(4-vinylcyclohexene, 
ethylbenzene, 
mixed xylenes, et al) 
Modifier (Chain Transfer 0.20 
Agent): 
tertiary dodecylmercaptan 100.00 
Shortstop: Added after 42.56 
13th CSTR at 62% conversion 
(or 22.6% solids) 
soft water 97.08 
85% aqueous solution 0.38 
of diethylhydroxylamine 
40% aqueous solution 0.80 
of sodium 
dimethyldithiocarbamate 
47% aqueous solution 0.89 
of sodium napthelene 
sulfonate 
45% aqueous solution 0.85 
of potassium hydroxide 
Defoamer: Added to latex 0.30 
during monomer recovery 
operations 
soft water 50.00 
Nalco-Exxon EC9060A 50.00 
defoamer 
______________________________________ 
The latex made was continuously removed from the thirteenth reactor and 
passed through a filter to remove coagulum. The filter consisted of a 
basket strainer having holes with a diameter of about 3/8 inch (9.5 mm). 
The latex was then passed through blow-down tanks for recovery of residual 
1,3-butadiene monomer. The defoamer identified in the table above was 
added to the stream after it exited the blow-down tanks. The latex stream 
was then passed through a first flash tank with a vacuum of about 3-5 psig 
(1.2.times.10.sup.5 Pa to 1.4.times.10.sup.5 Pa) being applied. It was 
subsequently passed through a second flash tank with a vacuum of about 22 
inches of mercury (7.4.times.10.sup.4 Pa) being applied. The latex then 
went through a 12-tray steam-stripping column with about 15 psig of steam 
being injected into the bottom of the column and a vacuum of about 22 
inches of mercury (7.4.times.10.sup.4 Pa) being applied to the top of the 
column. After unreacted monomers were removed from this stable latex by 
steam-stripping, it was found to have a solids content of 20.8 percent, a 
23.4 percent bound styrene content and a Mooney ML 1+4 viscosity of 105. 
The latex was stored in a storage tank having a capacity of about 45,000 
gallons after it had passed through the steam-stripping column. 
A second latex having a low Mooney ML 1+4 viscosity and a high bound 
styrene content was also synthesized in a reactor system similar to the 
one used in making the high viscosity latex. The reactor chain 
configuration used in synthesizing the low viscosity latex is described in 
the following table: 
______________________________________ 
Agitation 
Vol Pzm Temp 
Impeller 
Speed 
RV Type (gal) (deg F.) Type (rpm) 
______________________________________ 
0 Tubular 150 63 
1 CSTR 3750 50 Axial 107 
Flow 
Turbine 
2 CSTR 3750 50 Axial 107 
Flow 
Turbine 
3 CSTR 3750 50 Brumagin 71 
4 CSTR 7500 50 Brumagin 71 
5 CSTR 7500 50 Brumagin 71 
6 CSTR 3750 50 Axial 107 
Flow 
Turbine 
7 CSTR 3750 50 Axial 107 
Flow 
Turbine 
8 CSTR 3750 50 Axial 107 
Flow 
Turbine 
9 CSTR 3750 50 Axial 107 
Flow 
Turbine 
______________________________________ 
The following streams were charged to this reactor configuration 
continuously: 
______________________________________ 
Mass Flow 
Stream 
Rate Composition 
(lbs/min) (%) 
______________________________________ 
First Stage: Streams added to tubular reactor 
Butadiene Monomer: 
38.02 
1,3-butadiene 90.00 
impurities 10.00 
(mixed butenes, 
isobutylene, 
4-vinylcyclohexene, 
et al) 
Styrene Monomer: 54.10 
Styrene 91.00 
Impurities 9.00 
(4-vinylcyclohexene, 
ethylbenzene, 
mixed xylenes, et al) 
Soap Solution: 40.62 
soft water 79.33 
45% aqueous solution 2.04 
of potassium hydroxide 
40% aqueous solution 2.06 
of tripotassium phosphate 
20% aqueous solution 1.71 
of sodium hydroxide 
mixed hydrogenated 8.21 
tallow fatty acid 
47% aqueous solution 1.70 
of sodium napthelene 
sulfonate 
potassium soap of 1.95 
disproportionated tall 
oil rosin (80% active) 
23% aqueous solution 3.00 
of sodium dodecylbenzene 
sulfonate 
Soft Water 217.15 100.00 
Initiator: 0.20 
pinane hydroperoxide 100.00 
(44% active) 
Activator Solution: 17.68 
soft water 98.69 
20% aqueous solution 0.41 
of ferrous sulfate 
40% aqueous solution 0.56 
of tetrasodium ethylene- 
diaminetetraacetate 
sodium formaldehyde 0.34 
sulfoxylate 
Modifier (Chain Transfer 0.19 
Agent): 
tertiary dodecylmercaptan 100.00 
Oxygen Scavenger Solution: 0.65 
soft water 97.00 
sodium hydrosulfite 3.00 
Second Stage: Streams added to third CSTR 
Butadiene Monomer: 
25.34 
1,3-butadiene 90.00 
impurities 10.00 
(mixed butenes, 
isabutylene, 
4-vinylcyclohexene, 
et al) 
Styrene Monomer: 36.07 
styrene 91.00 
impurities 9.00 
(4-vinylcyclohexene, 
ethylbenzene, 
mixed xylenes, et al) 
Modifier (Chain Transfer 0.12 
Agent): 
tertiary dodecylmercaptan 100.00 
Shortstop: Added after 9th 13.31 
CSTR at 62% conversion (or 
21.6% solids) 
soft water 97.08 
85% aqueous solution 0.38 
of diethylhydroxylamine 
40% aqueous solution 0.80 
of sodium 
dimethyldithiocarbamate 
47% aqueous solution 0.89 
of sodium napthelene 
sulfonate 
45% aqueous solution 0.85 
of potassium hydroxide 
Defoamer: Added to latex 0.05 
during monomer recovery 
operations 
Nalco-Exxon EC9060A 100.00 
defoamer 
______________________________________ 
After unreacted monomers were removed from this stable latex by 
steam-stripping, it was found to have a solids content of 20.5 percent, a 
50.6 percent bound styrene content and a Mooney ML 1+4 viscosity of 13. 
A blend of 222,646 lbs (100992 kg) of the high viscosity latex and 184,828 
lbs (83,838 kg) of the low viscosity latex (55 percent:45 percent dry 
weight blend) was made in an agitated tank. Added to the latex blend was 
2105 lbs (955 kg) of a 50 percent active Goodyear Wingstay.RTM. C 
antioxidant emulsion. 
EXAMPLES 5-9 
In this series of experiments, various latices were evaluated as modifiers 
for Koch AC-10 asphalt. Example 5 was carried out as a control and was not 
modified with latex. Example 6 was also carried out as a control wherein 
the asphalt cement was modified with Pliolite.RTM. 7576 SBR latex. 
Pliolite.RTM. 7576 latex has a solids content of about 69 percent. The SBR 
in Pliolite.RTM. 7576 latex has a bound styrene content of 23.5 percent 
and a Mooney ML/4 viscosity of within the range of 45 to 65. 
The asphalt cement of Example 7 was modified with an SBR latex made by 
blending 50 parts of an SBR latex having a bound styrene content of 23.5 
percent, a number average molecular weight of about 130,000 and a weight 
average molecular weight of about 490,000, and 50 parts of a low molecular 
weight SBR latex having a bound styrene content of about 48 percent, a 
number average molecular weight of 56,000, a weight average molecular 
weight of 137,000 and a Mooney ML 1+4 viscosity of 11.4. In Example 8, the 
SBR latex blend evaluated in Example 7 was further evaluated except that 2 
phr (parts per hundred parts of rubber) of sulfur was additionally added 
to the asphalt. 
In the procedure used, the latices being evaluated were slowly added to hot 
asphalt cement at 340.degree. F.-350.degree. F. (171.degree. 
C.-177.degree. C.) under propeller agitation at moderate speeds. The 
latices were added in amounts sufficient to attain a dry weight of rubbery 
polymer in the asphalt cements of 3 percent. The modified asphalt cements 
were then stirred for about 2 hours at a temperature of about 163.degree. 
C. (325.degree. F.). 
The physical properties of the modified asphalt cements made were then 
determined using standard test procedures. The strength and flexibility of 
the asphalt binder cement at moderate or low temperatures are measured by 
force ductility, toughness and tenacity. These properties measure the 
resistance to deformation. Increasing strength and toughness gives greater 
resistance to surface abrasion and wear and provides better retention of 
aggregate. Force ductility was determined by a procedure based upon ASTM 
D113 whereby a force measuring apparatus was used to measure the force 
exerted on the specimen as it was being stretched at a temperature of 
4.degree. C. and a pulling rate of 5 cm per minute. In particular, the 
force ductility value in pounds force was recorded at 800 percent and 1000 
percent elongation. 
Compatibility was determined by utilizing a separation test wherein the 
modified asphalt sample was placed in a tube having a diameter of 1 inch 
(2.54 cm) and a length of 5.5 inches (14 cm) and heated in an oven at 
325.degree. F. (163.degree. C.) for 48 hours. The tube was maintained in a 
vertical position throughout the heating step. The tube containing the 
asphalt sample was then placed in a freezer at about 20.degree. F. 
(-7.degree. C.) for a minimum time period of 4 hours. Then, the sample was 
removed from the freezer and cut into three portions of equal length. The 
ring and ball softening point of the top and bottom portions of the sample 
was then determined by ASTM Method D36. Compatibility is reported as the 
temperature difference between the softening points of the top and bottom 
samples. Compatibility is considered to be excellent in cases where the 
difference in temperatures between the softening points between the top 
and bottom samples is no greater than 2.degree. C. The absolute 
viscosities of the modified asphalts shown in Table I were carried out at 
a temperature of 60.degree. C. The ductility, toughness, tenacity and 
compatibility of the modified asphalt cements are reported in Table I. 
Forced ductility was determined at a temperature of 4.degree. C. with 
toughness and tenacity being determined at a temperature of 25.degree. C. 
TABLE I 
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Example 5 6 7 8 
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Absolute Viscosity, poise 
1182 1968 2122 1905 
Force Ductility @ 800%, lbs 0.45 1.73 3.47 5.21 
Force Ductility @ 1000%, lbs broke 1.68 3.61 5.53 
Toughness, lb-in 51.6 76.2 153.1 144.7 
Tenacity, lb-in 17.2 46.0 116.3 112.7 
Compatibility, .DELTA..degree. C. -- 0.1 0.2 0.5 
______________________________________ 
Table I shows that asphalt cements can be modified with the SBR 
compositions described herein to improve compatibility, force ductility, 
toughness and tenacity (see Examples 7 and 8). This is in contrast to the 
utilization of standard high Mooney polymers which are capable of 
improving force ductility, toughness and tenacity but which are not very 
compatible with asphalt. It is also in contrast to the employment of 
standard latices of low Mooney viscosity polymers which are compatible 
with asphalt but which do not provide significant improvements in force 
ductility, toughness and tenacity. 
In asphalt pavements, improved force ductility, toughness and tenacity 
translate into improved resistance to rutting and shoving. Increasing 
strength and toughness gives greater resistance to surface abrasion and 
wear and provides better retention of aggregate. It is accordingly 
important for the latex utilized in modifying asphalt cements to be 
compatible with the asphalt and for it to improve force ductility, 
toughness and tenacity. This highly desirable combination of properties is 
attained in Examples 7 and 8 which utilize the techniques of this 
invention. 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the subject invention, it will be apparent to 
those skilled in this art that various changes and modifications can be 
made therein without departing from the scope of the subject invention.