Note: Descriptions are shown in the official language in which they were submitted.
- 213~2~
STYRENE-ISOPRENE RUBBER FOR TIRE TREAD COMPOUNDS
Background of the Invention
It is highly desirable for tires to have good wet
skid resistance, low rolling resistance, and good wear
characteristics. It has traditionally been very
difficult to improve a tire's rolling resistance
without sacrificing its wet skid resistance and
traction characteristics. These properties depend to
a great extent on the dynamic viscoelastic properties
of the rubbers utilized in making the tire.
In order to reduce the rolling resistance of a
tire, rubbers having a high rebound have traditionally
been utilized in making the tire's tread. On the
other hand, in order to increase the wet skid
resistance of a tire, rubbers which undergo a large
energy loss have generally been utilized in the tire's
tread. In order to balance these two viscoelastically
inconsistent properties, mixtures of various types of
synthetic and natural rubber are normally utilized in
tire treads. For example, various mixtures of
styrene-butadiene rubber and polybutadiene rubber are
commonly used as a rubbery material for automobile
tire treads. However, such blends are not totally
satisfactory for all purposes.
United States Patent 4,843,120 discloses that
tires having improved performance characteristics can
be prepared by utilizing rubbery polymers having
multiple glass transition temperatures as the tread
rubber. These rubbery polymers having multiple glass
transition temperatures exhibit a first glass
transition temperature which is within the range of
2135023
- 2
about -110C to -20C and exhibit a second glass
transition temperature which is within the range of
about -50C to 0C. According to United States Patent
4,843,120 these polymers are made by polymerizing at
lease one conjugated diolefin in a first reaction zone
at a temperature and under conditions sufficient to
produce a first polymeric segment having a glass
transition temperature which is between -110C and -
20C and subsequently continuing said polymerization
in a second reaction zone at a temperature and under
conditions sufficient to produce a second polymeric
segment having a glass transition temperature which is
between -20C and 20C. Such polymerizations are
normally initiated with an organolithium initiator and
are generally carried out in an inert organic solvent.
United States Patent 5,137,998 discloses that
terpolymers of styrene, isoprene, and butadiene which
exhibit multiple viscoelastic responses result from
terpolymerizations of styrene, isoprene, and 1,3-
butadiene in the presence of an alkali metal alkoxideand an organolithium initiator. By utilizing this
technique, such terpolymers which exhibit multiple
glass transition temperatures can be prepared in a
single reaction zone. The SIBR (styrene-isoprene-
butadiene rubber) made by the technique of UnitedStates Patent 5,137,998 offers an outstanding
combination of properties for utilization in making
tire tread rubber compounds. For example, utilizing
such SIBR in tire tread compounds results in improved
wet skid resistance without sacrificing rolling
resistance or tread wear characteristics.
It is known in the art that 3,4-polyisoprene can
be used in tire tread compounds to improve tire
performance characteristics, such as traction. Polar
modifiers are commonly used in the preparation of
synthetic polydiene rubbers which are prepared
213~0~3
_ - 3
utilizing lithium catalyst systems in order to
increase their vinyl content. Ethers and tertiary
amines which act as Lewis bases are commonly used as
modifiers. For instance, United States patent
4,022,959 indicates that diethyl ether, di-n-propyl
ether, diisopropyl ether, di-n-butyl ether,
tetrahydrofuran, dioxane, ethylene glycol dimethyl
ether, ethylene glycol diethyl ether, diethylene
glycol dimethyl ether, diethylene glycol diethyl
ether, triethylene glycol dimethyl ether,
trimethylamine, triethylamine,
N,N,N',N'-tetramethylethylenediamine, N-methyl
morpholine, N-ethyl morpholine, and N-phenyl
morpholine can be used as modifiers.
United States Patent 4,696,986 describes the use of
1,2,3-trialkoxybenzenes and 1,2,4-trialkoxybenzenes as
modifiers. The vinyl group content of polydienes
prepared utilizing Lewis bases as modifiers depends
upon the type and amount of Lewis base employed as
well as the polymerization temperature utilized. For
example, if a higher polymerization temperature is
employed, a polymer with a lower vinyl group content
is obtained (see A.W. Langer; A. Chem. Soc. Div.
Polymer Chem. Reprints; Vol. 7 (1), 132 [1966]). For
this reason it is difficult to synthesize polymers
having high vinyl contents at high polymerization
temperatures utilizing typical Lewis base modifiers.
Higher temperatures generally promote a faster
rate of polymerization. Accordingly, it is desirable
to utilize moderately high temperatures in commercial
polymerizations in order to maximize throughputs.
However, it has traditionally been difficult to
prepare polymers having high vinyl contents at
temperatures which are high enough to attain maximum
polymerization rates while utilizing conventional
Lewis bases as modifiers.
i
213~02~
_ - 4
United States Patent 5,231,153 reports that
compounds having the following structural formulae can
be used as modifiers in the synthesis of polydienes:
~
(i) (CH2)n ~CH-CH2-0-R
~ / R
( i i ) ( CH2 ) n CH - CH2 - N
(iii) (CH2) n CH-CH2-O-R
Rl
~ /R
( iv) ( CH2 ) n CH - CH2 - N
--N/ \ Rl
~ ~
(v) ( CH2 ) n CH - CH2 - O - CH2 - CH ( CH2 ) n
~ 0/ ~ O~
3 0 (vi ) ( CH2 ) n CH - CH2 - O - CH2 - CH ( CH2 ) n
~ N/ ~OJ
213~025
-- 5
~ R ~ ~
(vi i ) ( CH2 ) n CH - CH2 - N- CH2 - CH ( CH2 ) n
` O~ ~ O~
\ R ~
(vi i i ) ( CH2 ) n CH - CH2 - N - CH2 - CH ( CH2 ) n
N/ ~N/
Rl R2
~ R ~
( ix) ( CH2 ) n CH - CH2 - N- CH2 - CH ( CH2 ) n
N~ ~ 0/
Rl
(x) ( CH2 ) n CH - CH2 - O - CH2 - CH ( CH2 ) n
~ N/ ~N~
2 0 Rl R2
( xi ) ( CH2 ) n CH - CH2 - O - CH2 - CH2 - O - R
O
wherein n represents an integer within the range of 3
to 6, and wherein R, R1, and R2 can be the same or
different and represent alkyl groups containing from 1
30 to 10 carbon atoms, aryl groups containing from 6 to
10 carbon atoms, or hydrogen atoms.
United States Patent 5, 231,153 reports that these
modifiers remain stable at conventional polymerization
temperatures and lead to the formation of polymers
3 5 having high vinyl contents at such temperatures.
Accordingly, they can be used to promote the formation
~13~029
_ - 6
of high vinyl polymers at temperatures which are high
enough to promote very fast polymerization rates.
Japenese Patent 5255540 to Noriyuki which is
assigned to Toyo Tire & Rubber discloses a rubber
composition for pneumatic tire treads which is
reported to provide improved wear and skid resistance.
This tire tread compound is comprised of a styrene-
isoprene copolymer, a styrene-butadiene copolymer, and
carbon black. These compositions contain 50 to 150
parts by weight of carbon black per 100 parts by
weight of the rubbers in the compound.
Summary of the Invention
It has been unexpectedly found that rubbery
copolymers of styrene and isoprene which exhibit
essentially a single glass transition temperature can
be synthesized utilizing lithium initiators and an
alkyl tetrahydrofurfuryl ether modifier when the molar
ratio of modifier to the lithium initiator is within
the range of 2:1 to 40:1. It has further been
unexpectedly found that 2,2-ditetrahydrofurylpropane
can be used as the modifier to produce such styrene-
isoprene rubbers having essentially a single glass
transition temperature at molar ratios of the modifier
to the lithium initiator of greater than 1:1. In such
techniques it is important for the ratio of styrene to
isoprene to be less than about 15:85. The styrene-
isoprene rubbers made utilizing the techniques of this
invention typically contain from about 2 weight
percent to about 15 weight percent styrene and from
about 85 weight percent to about 98 weight percent
isoprene.
By utilizing this technique, such copolymers
which exhibit essentially a single glass transition
temperature can be prepared in a single reaction zone.
The styrene-isoprene rubber made by the technique of
'213~02~
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this invention offers an outst~n~lng combination of
properties for utilization in making tire tread rubber
compounds. For example, utilizing such styrene-
isoprene rubbers in tire tread compounds results in
improved wet skid resistance without sacrificing
rolling resistance or tread wear characteristics.
Improved wet and dry handling as well as improved
treadwear characteristics can also be realized by
utilizing the styrene-isoprene rubbers of this
invention in tire tread compounds.
The subject invention more specifically discloses
a process for the synthesis of styrene-isoprene
rubbers which exhibit essentially a single glass
transition temperature and which are particularly
useful in tire tread rubber compounds, said process
comprising copolymerizing a monomer mixture containing
from about 2 weight percent to about 15 weight percent
styrene monomer and from about 85 weight percent to
about 98 weight percent isoprene monomer in an organic
solvent in the presence of a catalyst system which is
comprised of (a) a lithium initiator and (b) a
modifier having the structural formula:
(CH2) n CH-CH2-0-R
~ 0 J
wherein n represents an integer within the range of 3
to 6, wherein R represents an alkyl group containing
from 1 to about 10 carbon atoms, and wherein the molar
ratio of the modifier to the lithium initiator i~
within the range of 2:1 to 40:1.
The subject invention also reveals a process for
the synthesis of styrene-isoprene rubbers which
exhibit essentially a single glass transition
temperature and which are particularly useful in tire
tread rubber compounds, said process comprising
copolymerizing a monomer mixture containing from about
213S02~
- 8
2 weight percent to about 15 weight percent styrene
monomer and from about 85 weight percent to about 98
weight percent isoprene monomer in an organic solvent
in the presence of a catalyst system which is
comprised of (a) a lithium initiator and (b) 2,2-
ditetrahydrofurylpropane as a modifier, wherein the
molar ratio of the modifier to the lithium initiator
is within the range of 1:1 to 40:1.
There are valuable benefits associated with
utilizing the styrene-isoprene rubbers of this
invention in making tire tread compounds. The present
invention also discloses that a particularly preferred
tire tread compound is comprised of, based on 100
parts by weight of rubber, (a) from about 5 parts to
about 55 parts of the styrene-isoprene rubber, (b)
from about 10 parts to about 40 parts of natural
rubber, (c) from about 15 parts to about 40 parts of
styrene-butadiene rubber, and (d) from about 20 parts
to about 35 parts of high cis-1,4-polybutadiene
rubber.
The subject invention further reveals a pneumatic
tire having an outer circumferential tread where said
tread is a sulfur cured rubber composition comprised
of, based on 100 parts by weight of rubber, (a) from
about 5 parts to about 55 parts of the styrene-
isoprene rubber made by the process of this invention,
(b) from about 10 parts to about 40 parts of natural
rubber, (c) from about 10 parts to about 60 parts of
styrene-butadiene rubber and (d) from about O part~
to about 50 parts of high cis-1,4-polybutadiene
rubber.
Detailed Description of the Invention
The relative amount of isoprene and styrene
employed in synthesizing the rubbers of this invention
will typically be within a very specific range. In
- 2~3S02~
g
practicing this invention, the weight ratio of styrene
to isoprene in the monomer charge will typically be
within the range of about 2:98 to 15:85. In most
cases the monomer charge composition will contain from
about 3 weight percent to about 10 weight percent
styrene and from about 90 weight percent to 97 weight
percent isoprene. It is normally preferred for the
monomer charge composition to contain from about 4
weight percent to about 7 weight percent styrene and
from about 93 weight percent to about 96 weight
percent isoprene.
The polymerizations of the present invention
which are carried out in a hydrocarbon solvent which
can be one or more aromatic, paraffinic, or
cycloparaffinic compounds. These solvents will
normally contain from 4 to 10 carbon atoms per
molecule and will be liquids under the conditions of
the polymerization. Some representative examples of
suitable organic solvents include pentane, isooctane,
cyclohexane, normal hexane, benzene, toluene, xylene,
ethylbenzene, and the like, alone or in admixture.
The modifiers of this invention are also useful in
bulk polymerizations which are initiated with lithium
catalyst systems.
In solution polymerizations which utilize the
modifiers of this invention, there will normally be
from 5 to 35 weight percent monomers in the
polymerization medium. Such polymerization mediums
are, of course, comprised of an organic solvent,
monomers, an organolithium initiator, and the
modifier. In most cases it will be preferred for the
polymerization medium to contain from 10 to 30 weight
percent monomers. It is generally more preferred for
the polymerization medium to contain 20 to 25 weight
percent monomers.
213502~i
- 10 -
The organolithium initiators employed in the
process of this invention include the monofunctional
and multifunctional types known for polymerizing the
monomers described herein. The multifunctional
organolithium initiators can be either specific
organolithium compounds or can be multifunctional
types which are not necessarily specific compounds but
rather represent reproducible compositions of
regulable functionality.
The amount of organolithium initiator utilized
will vary with the monomers being polymerized and with
the molecular weight that is desired for the polymer
being synthesized. However, as a general rule from
0.01 to 1 phm (parts per 100 parts by weight of
monomer) of an organolithium initiator will be
utilized. In most cases, from 0.01 to 0.1 phm of an
organolithium initiator will be utilized with it being
preferred to utilize 0.025 to 0.07 phm of the
organolithium initiator.
The choice of initiator can be governed by the
degree of branching and the degree of elasticity
desired for the polymer, the nature of the feedstock,
and the like. With regard to the feedstock employed
as the source of conjugated diene, for example, the
multifunctional initiator types generally are
preferred when a low concentration diene stream is at
least a portion of the feedstock, since some
components present in the unpurified low concentration
diene stream may tend to react with carbon lithium
bonds to deactivate initiator activity, thus
. necessitating the presence of sufficient lithium
functionality in the initiator so as to override such
effects.
The multifunctional initiators which can be used
include those prepared by reacting an
organomonolithium compounded with a
2~35023
- 11
multivinylphosphine or with a multivinylsilane, such a
reaction preferably being conducted in an inert
diluent such as a hydrocarbon or a mixture of a
hydrocarbon and a polar organic compound. The
reaction between the multivinylsilane or
multivinylphosphine and the organomonolithium compound
can result in a precipitate which can be solubilized
if desired, by adding a solubilizing monomer such as a
conjugated diene or monovinyl aromatic compound, after
reaction of the primary components. Alternatively,
the reaction can be conducted in the presence of a
minor amount of the solubilizing monomer. The
relative amounts of the organomonolithium compound and
the multivinylsilane or the multivinylphosphine
preferably should be in the range of about 0.33 to 4
moles of organomonolithium compound per mole of vinyl
groups present in the multivinylsilane or
multivinylphosphine employed. It should be noted that
such multifunctional initiators are commonly used as
mixtures of compounds rather than as specific
individual compounds.
Exemplary organomonolithium compounds include
ethyllithium, isopropyllithium, n-butyllithium,
sec-butyllithium, tert-octyllithium, n-eicosyllithium,
phenyllithium, 2-naphthyllithium,
4-butylphenyllithium, 4-tolyllithium,
4-phenylbutyllithium, cyclohexyllithium, and the like.
Exemplary multivinylsilane compounds include
tetravinylsilane, methyltrivinylsilane,
diethyldivinylsilane, di-n-dodecyldivinylsilane,
cyclohexyltrivinylsilane, phenyltrivinylsilane,
benzyltrivinylsilane, (3-ethylcyclohexyl)
(3-n-butylphenyl)divinylsilane, and the like.
Exemplary multivinylphosphine compounds include
trivinylphosphine, methyldivinylphosphine,
- '213~02~
- 12 -
dodecyldivinylphosphine, phenyldivinylphosphine,
cyclooctyldivinylphosphine, and the like.
Other multifunctional polymerization initiators
can be prepared by utilizing an organomonolithium
compound, further together with a multivinylaromatic
compound and either a conjugated diene or
monovinylaromatic compound or both. These ingredients
can be charged initially, usually in the presence of a
hydrocarbon or a mixture of a hydrocarbon and a polar
organic compound as diluent. Alternatively, a
multifunctional polymerization initiator can be
prepared in a two-step process by reacting the
organomonolithium compounded with a conjugated diene
or monovinyl aromatic compound additive and then
adding the multivinyl aromatic compound. Any of the
conjugated dienes or monovinyl aromatic compounds
described can be employed. The ratio of conjugated
diene or monovinyl aromatic compound additive employed
preferably should be in the range of about 2 to 15
moles of polymerizable compound per mole of
organolithium compound. The amount of
multivinylaromatic compound employed preferably should
be in the range of about 0.05 to 2 moles per mole of
organomonolithium compound.
Exemplary multivinyl aromatic compounds include
1,2-divinylbenzene, 1,3-divinylbenzene,
1,4-divinylbenzene, 1,2,4-trivinylbenzene,
1,3-divinylnaphthalene, 1,8-divinylnaphthalene,
1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl,
3,5,4'-trivinylbiphenyl, m-diisopropenyl benzene,
p-diisopropenyl benzene,
1,3-divinyl-4,5,8-tributylnaphthalene, and the like.
Divinyl aromatic hydrocarbons containing up to 18
carbon atoms per molecule are preferred, particularly
divinylbenzene as either the ortho, meta, or para
isomer, and commercial divinylbenzene, which is a
213502~1
- 13 -
mixture of the three isomers, and other compounds such
as the ethylstyrenes, also is quite satisfactory.
Other types of multifunctional initiators can be
employed such as those prepared by contacting a sec-
or tert-organomonolithium compounded with
1,3-butadiene, on a ratio of such as about 2 to 4
moles of organomonolithium compound per mole of
1,3-butadiene, in the absence of added polar material
in this instance, with the contacting preferably being
conducted in an inert hydrocarbon diluent, though
contacting without the diluent can be employed if
desired.
Alternatively, specific organolithium compounds
can be employed as initiators, if desired, in the
preparation of polymers in accordance with the present
invention. These can be represented by R (Li)X
wherein R represents a hydrocarbyl radical of such as
1 to 20 carbon atoms per R group, and x is an integer
of 1 to 4. Exemplary organolithium compounds are
methyllithium, isopropyllithium, n-butyllithium,
sec-butyllithium, tert-octyllithium, n-decyllithium,
phenyllithium, 1-naphthyllithium,
4-butylphenyllithium, p-tolyllithium,
4-phenylbutyllithium, cyclohexyllithium,
4-butylcyclohexyllithium, 4-cyclohexylbutyllithium,
dilithiomethane, 1,4-dilithiobutane,
1,10-dilithiodecane, 1,20-dilithioeicosane,
1,4-dilithiocyclohexane, 1,4-dilithio-2-butane,
1,8-dilithio-3-decene,
1,2-dilithio-1,8-diphenyloctane, 1,4-dilithiobenzene,
1,4-dilithionaphthalene, 9,10-dilithioanthracene,
1,2-dilithio-1,2-diphenylethane,
1,3,5-trilithiopentane, 1,5,15-trilithioeicosane,
1,3,5-trilithiocyclohexane, 1,3,5,8-tetralithiodecane,
1,5,10,20-tetralithioeicosane,
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- 14 -
1,2,4,6-tetralithiocyclohexane, 4,4'-dilithiobiphenyl,
and the like.
The modifiers which can be employed in the
synthesis of the styrene-isoprene rubbers of this
invention include 2,2-ditetrahydrofurylpropane (DTP)
and compounds which have the structural formula:
~.
(CH2) n CH-CH2-0-R
~O~
wherein n represents an integer within the range of 3
to 6, and wherein R represents alkyl groups containing
from 1 to 10 carbon atoms.
As a general rule, n will represent the integer
3 or 4. More commonly n will represent the integer 3.
The preferred types of modifiers are alkyl
tetrahydrofurfuryl ethers, such as methyl
tetrahydrofurfuryl ether, ethyl tetrahydrofurfuryl
ether, propyl tetrahydrofurfuryl ether, butyl
tetrahydrofurfuryl ether, pentyl tetrahydrofurfuryl
ether, and hexyl tetrahydrofurfuryl ether. The most
preferred modifier is hexyl tetrahydrofurfuryl ether.
The modifier being utilized can be introduced
into the polymerization zone being utilized in any
manner. In one embodiment, it can be reacted with the
organometallic compound with the reaction mixture
therefrom being introduced into the polymerization
zone as the initiator. In another embodiment, the
modifier can be introduced into the polymerization
zone directly without first being reacted with the
organometallic compound being utilized as the
initiator. In other words, the modifiers can be
introduced into the polymerization zone in the form of
a reaction mixture with the organometallic initiator
213~029
- 15 -
or they can be introduced into the polymerization zone
separately.
The amount of modifier needed will vary with the
vinyl content which is desired for the styrene-
isoprene rubber being synthesized. However, in caseswhere an alkyl tetrahydrofurfuryl ether is utilized as
the modifier at least 2 moles of the modifier per mole
of lithium in the initiator will be utilized. If
polymers having very high vinyl contents are desired,
then large quantities of the modifier can be used.
However, normally there will be no reason to employ
more than about 40 moles of the modifier per mole of
lithium in the organometallic initiator system
employed. In most cases from about 2 to about 15
moles of the alkyl tetrahydrofurfuryl ether modifier
will be employed per mole of lithium metal in the
organometallic initiator system utilized. Preferably
from about 2 to 10 moles of the alkyl
tetrahydrofurfuryl ether modifier will be utilized per
mole of lithium with from about 2 to 5 moles of the
alkyl tetrahydrofurfuryl ether modifier per mole of
lithium being most preferred.
In cases where DTP is utilized as the modifier a
molar ratio of DTP to the lithium in the initiator of
at least 1:1 will be utilized. In most cases from
about 2 to about 15 moles of the DTP modifier will be
employed per mole of lithium metal in the
organometallic initiator system utilized. Preferably
from about 2 to 10 moles of the DTP modifier will be
utilized per mole of lithium with from about 2 to 5
moles of the DTP modifier per mole of lithium being
most preferred.
The polymerization temperature utilized can vary
over a broad range of from about -20C to about 150C.
In most cases a temperature within the range of about
30C to about 125C will be utilized. Temperatures
~13~23
- 16 -
within the range of about 50C to about 90C are
generally the most preferred polymerization
temperatures. The pressure used will normally be
sufficient to maintain a substantially liquid phase
under the conditions of the polymerization reaction.
The polymerization is conducted for a length of
time sufficient to permit substantially complete
polymerization of monomers. In other words, the
polymerization is normally carried out until high
conversions are attained. The polymerization can then
be terminated using a standard technique. The
polymerization can be terminated with a conventional
noncoupling type of terminator, such as water, an
acid, a lower alcohol, and the like or with a coupling
agent.
Coupling agents can be used in order to improve
the cold flow characteristics of the rubber and
rolling resistance of tires made therefrom. It also
leads to better processability and other beneficial
properties. A wide variety of compounds suitable for
such purposes can be employed. Some representative
examples of suitable coupling agents include:
multivinylaromatic compounds, multiepoxides,
multiisocyanates, multiimines, multialdehydes,
multiketones, multihalides, multianhydrides,
multiesters which are the esters of polyalcohols with
monocarboxylic acids, and the diesters which are
esters of monohydric alcohols with dicarboxylic acids,
and the like.
Examples of suitable multivinylaromatic compounds
include divinylbenzene, 1,2,4-trivinylbenzene,
1,3-divinylnaphthalene, 1,8-divinylnaphthalene,
1,3,5-trivinylnaphthalene, 2,4-divinylbiphenyl, and
the like. The divinylaromatic hydrocarbons are
preferred, particularly divinylbenzene in either its
ortho, meta, or para isomer. Commercial
2l3sa23
- 17 -
divinylbenzene which is a mixture of the three isomers
and other compounds is quite satisfactory.
While any multiepoxide can be used, those which
are preferred are liquid since they are more readily
handled and form a relatively small nucleus for the
radial polymer. Especially preferred among the
multiepoxides are the epoxidized hydrocarbon polymers
such as epoxidized liquid polybutadienes and the
epoxidized vegetable oils such as epoxidized soybean
oil and epoxidized linseed oil. Other epoxy compounds
such as 1,2,5,6,9,10-triepoxydecane, and the like,
also can be used.
Examples of suitable multiisocyanates include
benzene-1,2,4-triisocyanate,
naphthalene-1,2,5,7-tetraisocyanate, and the like.
Bspecially suitable is a commercially available
product known as PAPI-l, a polyarylpolyisocyanate
having an average of 3 isocyanate groups per molecule
and an average molecular weight of about 380. Such a
compound can be visualized as a series of
isocyanate-substituted benzene rings joined through
methylene linkages.
The multiimines, which are also known as
multiaziridinyl compounds, preferably are those
containing 3 or more aziridine rings per molecule.
Examples of such compounds include the triaziridinyl
phosphine oxides or sulfides such as
tri(l-ariridinyl)phosphine oxide,
tri(2-methyl-1-ariridinyl)phosphine oxide,
tri(2-ethyl-3-decyl-1-ariridinyl)phosphine sulfide,
and the like.
The multialdehydes are represented by compounds
such as 1,4,7-naphthalene tricarboxyaldehyde,
1,7,9-anthracene tricarboxyaldehyde, 1,1,5-pentane
tricarboxyaldehyde, and similar multialdehyde
containing aliphatic and aromatic compounds. The
'~13~02~
- 18 -
multiketones can be represented by compounds such as
1,4,9,10-anthraceneterone,
2,3-diacetonylcyclohexanone, and the like. Examples
of the multianhydrides include pyromellitic
dianhydride, styrene-maleic anhydride copolymers, and
the like. Examples of the multiesters include
diethyladipate, triethylcitrate,
1,3,5-tricarbethoxybenzene, and the like.
The preferred multihalides are silicon
tetrahalides, such as silicon tetrachloride, silicon
tetrabromide, and silicon tetraiodide, and the
trihalosilanes such as trifluorosilane,
trichlorosilane, trichloroethylsilane,
tribromobenzylsilane, and the like. Also preferred
are the multihalogen-substituted hydrocarbons, such as
1,3,5-tri(bromomethyl)benzene,
2,4,6,9-tetrachloro-3,7-decadiene, and the like, in
which the halogen is attached to a carbon atom which
is alpha to an activating group such as an ether
linkage, a carbonyl group, or a carbon-to-carbon
double bond. Substituents inert with respect to
lithium atoms in the terminally reactive polymer can
also be present in the active halogen-containing
compounds. Alternatively, other suitable reactive
groups different from the halogen as described above
can be present.
Examples of compounds containing more than one
type of functional group include
1,3-dichloro-2-propanone, 2,2-dibromo-3-decanone,
3,5,5-trifluoro-4-octanone, 2,4-dibromo-3-pentanone,
1,2,4,5-diepoxy-3-pentanone,
1,2,4,5-diepoxy-3-hexanone,
1,2,11,12-diepoxy-8-pentadecanone,
1,3,18,19-diepoxy-7,14-eicosanedione, and the like.
In addition to the silicon multihalides as
described hereinabove, other metal multihalides,
213S02~
- 19
particularly those of tin, lead, or germanium, also
can be readily employed as coupling and branching
agents. Difunctional counterparts of these agents also
can be employed, whereby a linear polymer rather than
a branched polymer results.
Broadly, and exemplarily, a range of about 0.01
to 4.5 milliequivalents of coupling agent are employed
per 100 grams of monomer, presently preferred about
0.01 to 1.5 to obtain the desired Mooney viscosity.
The larger quantities tend to result in production of
polymers containing term; n~ 1 ly reactive groups or
insufficient coupling. One equivalent of coupling
agent per equivalent of lithium is considered an
optimum amount for maximum branching, if this result
is desired in the production line. The coupling agent
can be added in hydrocarbon solution, e.g., in
cyclohexane, to the polymerization admixture in the
final reactor with suitable mixing for distribution
and reaction.
Styrene-isoprene rubbers which are made by
utilizing the techniques of this invention in solution
polymerizations can be recovered utilizing
conventional techniques. In many cases it will be
desirable to destroy residual carbon-lithium bonds
which may be present in the polymer solution and to
recover the synthetic styrene-isoprene rubber
produced. It may also be desirable to add additional
antioxidants to the polymer solution in order to
further protect the polydiene produced from
potentially deleterious effects of contact with
oxygen. The styrene-isoprene rubber made can be
precipitated from the polymer solution and any
remaining lithium moieties can be inactivated by the
addition of lower alcohols, such as isopropyl alcohol,
to the polymer solution. The styrene-isoprene rubber
can be recovered from the solvent and residue by means
213~023
- 20 -
such as decantation, filtration, centrification, and
the like. Steam stripping can also be utilized in
order to remove volatile organic compounds from the
rubber.
There are valuable benefits associated with
utilizing the styrene-isoprene rubbers of this
invention in making tire tread compounds. Such tire
tread compounds are blends of the styrene-isoprene
rubber with one or more additional sulfur curable
elastomers. For instance, the styrene-isoprene rubber
can be blended with natural rubbers and, optionally,
high cis 1,4-polybutadiene and/or styrene-butadiene
rubbers in making tire tread compounds.
One particularly preferred tire tread compound is
comprised of, based on 100 parts by weight of rubber,
(a) from about 5 parts to about 55 parts of the
styrene-isoprene rubber, (b) from about 10 parts to
about 40 parts of natural rubber, (c) from about 10
parts to about 60 parts of styrene-butadiene rubber,
and (d) from about 0 parts to about 50 parts of high
cis-1,4-polybutadiene rubber.
It is preferred for such tire tread compounds to
further contain a silica filler. A combination of
carbon black and silica can be employed. For
instance, a combination of about 30 parts to about 80
parts of carbon black with about 10 parts to about 40
parts of silica can be usefully employed in such
blends. The weight ratio of silica to carbon black
will normally be at least 1:1. It is generally
preferred for the weight ratio of silica to carbon
black to be at least 4:1.
It is generally preferred to utilize blends which
contain from about 60 parts to 100 parts of silica and
essentially no carbon black. It is more preferred for
the blends to contain from 60 parts to 80 parts of
silica. Even though these blends contain essentially
213~02~
-
- 21 -
no carbon black as filler, it is contemplated that a
small amount of carbon black will be incorporated into
the blends as a black color imparting agent or used as
a carrier for chemical additives, such as coupling
agents. Generally, the amount of carbon black needed
for color imparting purposes will be less than 10
parts per 100 parts of rubber in the blend and will
typically be less than 5 part per 100 parts of rubber
in the blend.
It is important to utilize a coupling agent in
cases where silica is employed as a reinforcing
filler. This is because at least as compared to
carbon black, there tends to be a lack of, or at least
an insufficient degree of, physical and/or chemical
bonding between the silica perticles and the rubber to
enable the silica to become a sufficient reinforcing
filler for the rubber for most purposes, including
tire treads, if the silica is used without a coupler.
While various treatments and procedures have been
devised to overcome such deficiencies, coupling agents
capable of reacting with both the silica surface and
the rubber molecule are generally employed with great
success. Such coupling agents may be premixed, or
pre-reacted, with the silica particles or may be added
to the rubber mix during the rubber/silica processing
or mixing stage. If the coupling agent and silica are
added separately to the rubber compound during the
rubber/silica mixing, or processing stage, it is
believed that the coupling agent then combines ~in
situ" with the silica.
Such coupling agents are generally composed of a
silane which has a constituent component or moiety
which is capable of reacting with the silica surface
(the silane portion) and a constituent component or
moiety which is capable of reacting with the rubbers
in the blend. In this manner the coupling agent acts
- 22 - 21~023
as a connecting bridge between the silica and the
rubbers in the blend and thereby enhances the rubber
reinforcement aspect of the silica.
In one type of coupling agent the silane
apparently forms a bond to the silica surface,
possibly through hydrolysis, and the rubber reactive
component of the coupling agent chemically reacts with
the rubber itself. Usually the rubber reactive
component of the coupling agent is temperature
sensitive and tends to chemically react with the
rubber during the final and higher temperature sulfur
vulcanization stage and, thus, subsequent to the
rubber/silica/coupler mixing stage and, therefore,
after the silane group of the coupler has combined
with the silica. However, partly because of typical
temperature sensitivity of the coupler, some degree of
combination, or bonding, may occur between the rubber-
reactive component of the coupler and the rubber
during an initial rubber/silica/coupler mixing stage
and, thus, proir to a subsequent vulcanization stage.
The rubber-reactive group component of the
coupling agent may be, for example, one or more
- mercapto groups, amino groups, vinyl groups, epoxy
groups, and/or sulfur groups, preferably a sulfur or
mercapto group. It is most preferred for the rubber-
reactive group to be a sulfur group. Numerous
coupling agents are known for use in combining silica
and rubber. Representative examples of coupling
agents which can be employed include silane coupling
agents containing a polysulfide component, or
structure, such as bis-(3-
triethoxysilylpropyl)tetrasulfide.
U.S. Patent 3,451,458, U.S. Patent 3,664,403,
U.S. Patent 3,768,537, U.S. Patent 3,884,285, U.S.
Patent 3,938,574, U.S. Patent 4,482,663, U.S. Patent
4,590,052, U.S. Patent 5,089,554, and British Patent
213~23
- 23 -
1,424,503 all relate to silicas and silica reinforced
tire treads and the teaching of these patents are
hereby incorporated herein by reference.
The high cis 1,4-polybutadiene utilized in such
blends typically has a microstructure wherein at least
80~ of the butadiene repeat units are cis 1,4-isomeric
units. In most cases, the high cis 1,4-polybutadiene
will contain at least about 90~ cis 1,4-isomeric
polybutadiene units. The high cis 1,4-polybutadiene
can be prepared by solution polymerization utilizing a
catalyst consisting of (1) an organoaluminum compound,
(2) an organonickel compound and (3) a hydrogen
fluoride complex as described in United States Patent
3,856,764.
These styrene-isoprene rubber containing blends
can be compounded utilizing conventional ingredients
and standard techniques. For instance, the styr~ne-
isoprene rubber containing blends will typically be
blended with carbon black and/or silica fillers,
sulfur, accelerators, oils, waxes, scorch inhibiting
agents and processing aids. In most cases, the
styrene-isoprene containing rubber blends will be
compounded with sulfur and/or a sulfur containing
compound, at least one filler, at least one
accelerator, at least one antidegradant, at least one
processing oil, zinc oxide, optionally a tackifier
resin, optionally a reinforcing resin, optionally one
or more fatty acids, optionally a peptizer and
optionally one or more scorch inhibiting agents. Such
blends will normally contain from about 0.5 to 5 phr
(parts per hundred parts of rubber by weight) of
sulfur and/or a sulfur containing compound with 1 phr
to 2.5 phr being preferred. It may be desirable to
2135029
- 24 -
utilize insoluble sulfur in cases where bloom is a
problem.
Normally from 10 to 150 phr of at least one
filler will be utilized in the blend with 30 to 95 phr
being preferred. In most cases, at least some carbon
black will be utilized in the filler. The filler can,
of course, be comprised totally of carbon black.
Silica can be included in the filler to improve tear
resistance and heat build-up. Clays and/or talc can
be included in the filler to reduce cost.
The commonly employed siliceous pigments used in
rubber compounding applications can be used as the
silica in this invention, including pyrogenic and
precipitated siliceous pigments (silica), although
precipitate silicas are preferred. The siliceous
pigments preferably employed in this invention are
precipitated silicas such as, for example, those
obtained by the acidification of a soluble silicate,
e.g., sodium silicate.
Such silicas might be characterized, for example,
by having a BET surface area, as measured using
nitrogen gas, preferably in the range of about 40 to
about 600, and more usually in a range of about 50 to
about 300 square meters per gram. The BET method of
measuring surface area is described in the Journal of
the American Chemical Society, Volume 60, page 304
(1930).
The silica may also be typically characterized by
havinq a dibutylphthalate (DBP) absorption value in a
range of about 100 to about 400, and more usually
about 150 to about 300.
The silica might be expected to have an average
ultimate particle size, for example, in the range of
0.01 to 0.05 micron as determined by the electron
microscope, although the silica particles may be even
smaller, or possibly larger, in size.
213~02~
-
- 25 -
Various commercially available silicas may be
considered for use in this invention such as, only for
example herein, and without limitation, silicas
commercially available from PPG Industries under the
Hi-Sil trademark with designations 210, 243, etc;
silicas available from Rhone-Poulenc, with, for
example, designations of Z1165MP and Z165GR and
silicas available from Degussa AG with, for example,
designations VN2 and VN3, etc. The PPG Hi-Sil silicas
are currently preferred.
The blend will also normally include from 0.1 to
2.5 phr of at least one accelerator with 0.2 to 1.5
phr being preferred. Antidegradants, such as
antioxidants and antiozonants, will generally be
included in the blend in amounts ranging from 0.25 to
10 phr with amounts in the range of 1 to 5 phr being
preferred. Processing oils will generally be included
in the blend in amounts ranging from 2 to 100 phr with
amounts ranging from 5 to 50 phr being preferred. The
SIR containing blends of this invention will also
normally contain from 0.5 to 10 phr of zinc oxide with
1 to 5 phr being preferred. These blends can
optionally contain from 0 to 10 phr of tackifier
resins, 0 to 10 phr of reinforcing resins, 1 to 10 phr
25 of fatty acids, 0 to 2.5 phr of peptizers, and 0 to 1
phr of scorch inhibiting agents.
The styrene-isoprene rubber containing rubber
blends of this invention can be used in tire treads in
conjunction with ordinary tire manufacturing
techniques. Tires are built utilizing standard
procedures with the styrene-isoprene rubber blend
simply being substituted for the rubber compounds
typically used as the tread rubber. After the tire
has been built with the styrene-isoprene rubber
containing blend, it can be vulcanized using a normal
tire cure cycle. Tires made in accordance with this
213~ 02~
- 26 -
invention can be cured over a wide temperature range.
However, it is generally preferred for the tires of
this invention to be cured at a temperature ranging
from about 132C (270F) to about 166C (330F). It
is more typical for the tires of this invention to be
cured at a temperature ranging from about 143C
(290F) to about 154C (310F). It is generally
preferred for the cure cycle used to vulcanize the
tires of this invention to have a duration of about 10
to about 14 minutes with a cure cycle of about 12
minutes being most preferred.
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, parts and percentages are given by weight.
Example 1
In this experiment, 2,300 grams of a
silica/alumina/molecular sieve/NaOH dried premix
containing 19.5 weight percent styrene/isoprene
mixture in hexane was charged into a 1-gallon (3.8
liter) reactor. The ratio of styrene to isoprene was
10:90. After the impurity level of 2 ppm being
determined, 4.56 ml of MTE (methyl tetrahydrofurfuryl
ether, 1.0 M in hexane) and 1.8 ml of a 1.0 M solution
of n-butyl lithium (in hexane, 1.54 ml for initiation
and 0.26 ml for scavenging the premix) were added to
the reactor. The molar ratio of modifier to n-butyl
lithium ( n-BuLi) was 3:1.
The polymerization was allowed to proceed at 70C
for 2 hours. The GC analysis of the residual monomers
contained in the polymerization mixture indicated that
the polymerization was complete at this time. Three
ml of 1 M ethanol solution (in hexane) was added to
- 27 - 213502~
the reactor to shortstop the polymerization and
polymer was removed from the reactor and stabilized
with 1 phm of antioxidant. After evaporating hexane,
the resulting polymer was dried in a vacuum oven at
50C
The styrene-isoprene copolymer rubber (SIR)
produced was determined to have a glass transition
temperature (Tg) at -13C. It was then determined to
have a microstructure which contained 46 percent 3,4-
polyisoprene units, 39 percent 1,4-polyisoprene units,
5 percent 1,2-polyisoprene units and 10 percent random
polystyrene units. The Mooney viscosity (ML-4) was 83
for this SIR.
Example 2
The procedure described in Example 1 was utilized
in these examples except that the MTE/n-BuLi ratio was
changed from 3:1 to 2.5:1. The glass transition
temperatures, Mooney ML-4 viscosities, and
microstructures of the resulting SIR are listed in
Table I.
TABLE I
Example Styrene/ MTE/ Tg ML-4 Microstructure (~)
Number I~oprene n-BuLi (C) (lOOC) 3,4-¦1,4-¦1,2-¦ Sty
Ratio Ratio PI ¦ PI ¦ PI ¦
1 1o:so 3:1 -13 83 46 39 5 10
2 10:90 2.5:1 -18 82 43 43 4 10
Examples 3-4
The procedure described in Example 1 was utilized
in these examples except that the ETE (ethyl
tetrahydrofurfuryl ether) was used as the modifier and
the modifier/n-BuLi ratio was changed from 3:1 to 5:1
- 21~502~
- 28 -
and 10:1. The Tg's and microstructures of these SIRs
are listed in TABLE II.
. TABLE II
Example Styrene/ ETE/ Tg ML-4 Microstructure (~)
NumberI60prene n-BuLi (C) (lOOC) 3,4-¦1,4-¦1,2-¦ Sty
Ratio Ratio PI ¦ PI ¦ PI ¦
3 10:90 5:1 -5 74 54 30 6 10
410:90 10:1 +2 75 58 23 8 11
Example 5
The procedure described in Example 3 was utilized
in this example except that the HTE (hexyl
tetrahydrofurfuryl ether) was used as the modifier.
The Tg and Mooney ML-4 viscosity of this SIR are -8C
and 84, respectively.
Examples 6-8
The procedure described in Examples 2-3 was
utilized in these examples except that the ETE/n-BuLi
ratio was changed to 2. 5:1, 4:1 and 5:1 and the ratio
of styrene to isoprene in the premix was from 10:90 to
5: 95. Their Tg's and microstructures are listed in
TABLE III.
TABLE III
Example Styrene/ ETE/ Tg ML-4 Microstructure (~)
NumberI60prene n-BuLi(C) (lOOC) 3,4-¦1,4-¦1,2-¦ Sty
Ratio Ratio PI ¦ PI ¦ PI ¦
65:95 2.5:1 -16 80 50 40 5 5
7 5:95 4:1 -10 75 57 32 6 5
8 5:95 5:1 -5 76 60 28 7 5
213i~02~
-
- 29 -
Examples 9-10
The procedure described in Examples 2-3 was
utilized in these examples except that the styrene to
isoprene ratio was changed from 10:90 to 15:85 and the
ETE/n-BuLi ratios used were 2:1 and 5:1. The Tg's and
microstructures of these SIRs are listed in TABLE IV.
TABLE IV
Example Styrene/ ETE/ Tg ML-4 Microstructure (~)
NumberIsoprene n-BuLi (C) (lOOC) 3,4-¦1,4-¦1,2-¦ Sty
Ratio Ratio PI ¦ PI ¦ PI ¦
915:85 2:1 -14 67 43 37 4 16
1015:85 5:1 -3 76 53 26 6 15
Example 11
The procedure described in Example 10 was
utilized in this example except that the
polymerization temperature was changed from 70C to
50C. The Tg and microstructure of this SIR are
listed in TABLE V.
TABLE V
Example Styrene/ ETE/ Tg ML-4 Microstructure (~)
Number I~oprene n-BuLi (C) (lOOC) 3,4-¦1,4-¦1,2-¦ Sty
Ratio Ratio PI ¦ PI ¦ PI ¦
11 15:85 5:1 +6 74 60 1 17 1 8 1 15
Example 12-15
This invention relates to a pneumatic tire with a
tread composed of a blend of at least three rubbers,
including high Tg styrene/isoprene copolymer and at
least two additional diene-based rubbers; such as, cis
1,4-polybutadiene, styrene/butadiene copolymers
213~02~
- 30 -
(prepared by solution or emulsion polymerization
methods), cis 1,4-polyisoprene, high and medium vinyl
(1,2-) polybutadiene, styrene/isoprene/butadiene
rubber, epoxidized natural rubber, carboxylated
nitrile rubber, isoprene/butadiene copolymers and
acrylonitrile/styrene/butadiene rubber.
The high Tg SIR added benefits, including
handling, traction and treadwear, without
significantly affecting rolling resistance. When
compared to high Tg 3,4-polyisoprene in a typical
tread recipe, the SIR copolymer improved the carbon
black incorporation into the high Tg polymer phase,
thus resulting in improved tire handling and
treadwear. These treads contained 30 to 80 parts of
carbon black and 10 to 20 parts of silica and bis-(3-
triethoxysilylpropyl)tetrasulfide as a silane coupling
agent. Examples 12 and 14 were conducted as controls
- and did not contain any of the SIR of this invention
in the blends make.
- 213S~29
- 31 -
TIRE TEST RESULTS
Example Number 12 13 14 15
Cis 1,4-Polybutadiene 35.0 35.0 -- --
Natural Rubber 40.0 40.0 30.0 30.0
S-SBR 15.0 15.0 50.0 50.0
3,4-Polyisoprene 10.0 -- 20.0 --
Styrene/Isoprene -- 10.0 -- 20.0
(SIR)
~ Carbon Black in 1.2 23.1 6.1 9.0
3,4-PI or SIR
Tire Treadwear 100 105 100 107
Rolling Resistance 100 98 100 99
Traction lO0 100 -- --
Compound Processing -- Better -- --
Tire Handling -- Better -- Better
In this series of tire tests tire treadwear,
rolling resistance, and traction characteristics of
the control tires (Examples 12 and 14) were normalized
to a value of 100 for comparative purposes. As can be
seen from the table above, the tire tread compounds
made with the SIR of this invention showed better tire
treadwear and handling characteristics that the
control tires. Example 13 showed better compound
processing over the blend made for utilization in
Example 12. The tires made with the tire tread
compounds made with the SIR of this invention also
showed similar rolling resistance and traction
characteristics as compared to the control tires.
This series of examples shows that the SIR of this
invention can be included in tire tread compounds to
0 2 ~
- 32 -
improve tire treadwear and handling characteristics
without sacrificing rolling resistance or traction
characteristics.
Example 16-21
In this set of experiments the SIR of this
invention was evaluated in tire tread compounds in
place of styrene-butadiene rubber made by solution
polymerization (S-SBR). When the SIR of this
invention was evaluated in place of solution SBR in
compounds containing micropearl silica, 50/50 carbon
black/silica and all carbon black, significant
increases in tan delta at 0C and dynamic stiffness
(E*) were observed, suggesting improved tire traction
and handling. Furthermore, Example 17 (which
contained SIR) had a significantly higher tan delta at
0C and lower tan delta at 60C compared to Example
18, 20 and 21 suggesting much improved traction and
rolling resistance with a tread which contains silica
as the major reinforcing agent.
2135029
~ 33 ~
LABORATORY COMPOUND RESULTS
E~mplc Nurnber 16 17 18 19 20 21
S-SBR 70.0 50.0 70.0 50.0 70.0 50.0
CiJ 1,4-P~ . ' 30.0 30.0 30.0 30.0 30.0 30-0
Styrene/Isoprer~c -- 20.0 -- 20.0 -- 20.0
Zeosil 1165MP Silica 70.0 70.0 35 0 35 0
N299 CarbonBlack -- -- 35.0 35.0 70.0 70.0
Degussa X50S Coupling Agent 11.0 11.0 5.5 5.5
Modulus, MPa
0 100% 1.9 1.9 1.6 1.6 1.6 1.6
300% 8.7 8.6 7.3 7.1 5.9 5.9
Brealc Strength, MPa 18.9 17.5 17.2 17.0 14.6 14.7
Elongation e~\ Break, % 561 549 604 623 672 682
Rebourld, %
Room Temperature 48 40 43 36 34 27
100'C 65 63 57 55 48 48
Hardness, Shore A
Room TemperAture 58 57 57 56 59 60
100C 56 56 51 51 52 52
DIN Abrasion, cc ¦79 ¦85 ¦65 ¦90 ¦ 88 ¦ 97
(Volume LOJJ) l l l l l l
tan dclta, 0C 0.196 0.337 0.181 0.348 0.114 0.237
25 tan delta, 60C 0.086 0.088 0.119 0.147 0.128 0.136
E~ ~10-8, 0C 1.47 1.99 1.96 2.51 4.36 5.19
El ~10-7, 60C 7.06 7.40 7.49 8.68 17.7 17.6
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.
