Note: Descriptions are shown in the official language in which they were submitted.
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This invention is directed to a method of preparing ~:
A-B-A type block copolymers and especiall~ to the prepara- .
- tion of A-B-A bloc.k copolymers wherein the A bloc.k is poly-
a-methylstyrene and the B block is the copolymer of a con-
;:. 5 jugated diene.
Conventional A-B-A type thermoelastic block copoly- .
mers of polystyrene and the polymer of a conjugated diene,
such as polystyrene-polybutadiene-polystyrene or polystyrene-
polyisoprene-polystyrene have excellent tensile strengths .
.. 10 at ambient temperatures but soften and have practically no
strength at temperatures approaching 100C~ It is thought
-: that at temperatures near 100C. the plastic bloc.ks of poly- ~.;~ styrene become soft, thus loslng its strength. ~ .
~ However, poly (a-methylstyrene) has.a higher so~ten~
:~: 15 ing temperature and should be useful in rubberized goods
l which have to withstand a certain amount of heating. Thus~
:. by replacing polystyrene with poly (a-methylstyrene) it is
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possible to make a polymer with a higher softening point~
~ Using poly-a-methylstyrene as the plastic block is -
.~ ~ 20 not without its problems; however, the monomer a-methyl- ~:
styrene has a ceiling temperature of about 61C. and hlgh
yields of poly-a-methylstyrene polymer can be obtained from
.~Y, it at temperatures in the region of OoC. or below. Ceiling
.~ temperature is the temperature, for any monomer, at which ..
25 the rate of propagation equals the rate of depropagation. .
.j A monomer-polymer equilibrium exists, and polymer yield
.~ falls steadily as temperature increases, reaching zero at ... ~`
the ceiling temperature. Thus, preparation of A-B-A bloc.k
copolymers~ using poly-a-methylstyrene as the plastic bloc.k
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and using conventional methods is costly and difficult -to
attain.
In prior art methods~ the use of a-methylstyrene for
polymerization purposes required the use of low reaction
temperatures to obtain high yields of the poly-a-methylsty-
rene. The low reaction temperature also results in low
rates of reaction and usually the poly-a-methylstyrene had
to be polymerized in a separate reactor, then other monomers `
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sequentially added to it thus making several laboratory
~ lO manipulations necessary. Also a polar compound was neces~
`~ sary to speed the polymerization since it polymerizes so ~
;~ slowly at low temperatures. ~ ~.
;l The present invention has several advantages over the
prior art. As already mentioned~ all of the conjugated `
diene and a-methylstyrene are charged to the polymerization
mixture at the start of the reaction. This aids in making
these polymerizations possible to be run at temperatures
.. . .
higher than in the prior art. Another advantage iS that
~` there is no need for a powerful accelerator for the a-methyl-
styrene polymerization because tetrahydrofuran or dimethox~- ;
ethane is eliminated as in the prior art. The need for low
température in preparation of the poly-a-methylstyrene poly- ~ `
~; mer is eliminated by utilizing the process taught in this
invention. In the prior art~ at temperatures about 450C.,
the poly-a-methylstyrene block (A) cannot at-tain sufficient-
ly high molecular weight for the development of good physi~
cal properties in the block polymers. Below 20C. the poly-
merization rate becomes too slow~ thus making it too costly
for commercial purposes. In the present invention~ within
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the temperature range of about 20G. to about 450C., good
polymerization rates and good physical properties can be at-
~-` tained, thus eliminating the need to conduct the a-methylsty-
rene polymerizations at low temperatures.
~- 5 This invention relates to a single-step reaction
. method for preparing A-B-A type block polymers by contacting
~.
~ a-methylstyrene and a conjugated diene (B) with an organodi-
.. lithium compound~ at temperatures from about 20C. to about - :
-~ 450C.~ the improvement being using a large excess of a-methyl- :~ 10 styrene in the polymerization mixture. This excess of ~me- -~
~: thylstyrene is at least about 2 moles/liter of the polymeri-
zation mixture when the polymerization temperature is about :
20C. and at least about three moles of a-methylstyrene per
liter of the total polymerization mixture when the polymeri-
15 zation temperature is at least ~50C. ..
By the term "organodilithium compound" is meant any ~ .
~j organodilithium compound responding to the formula Li-R-Li .
.. in which R is selected from the group consisting of alkyl, ~ .
., cycloal.kyl~ aryl~ alkaryl and arylal.kyl. Representative of
the compounds responding to the formula set forth are dili- -: :
thiomethane, l,~-dilithiobutane, l~10-dilithiodecane~
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dilithiodiphenylene~ dilithionaphthalene, dilithioisoprene,
dita-lithio-3-methylpentyl) benzene~ a-(dilithio diisoprenyl)~
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:~ 3-methylpentyl toluene and the li.ke. : .
~ 25 It should be understood that the catalyst used for
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:~, the pol~merization of this solution mixture.is not the thrust
for which this particular.invention is directed. There~re
any type of organodilithium compound which will promote poly- ~ :~
merization would be suitable as a catalyst in this invention. .
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The organodilithium initiator is the type of initia-
tor that propagates polymerization from both sites of ths
lithium. In other words~ the polymer grows from both ends
of the initiator.
The amount of catalyst used in the practice of this
invention cannot be specifically set down since the amount
of catalyst used depends on the molecular weight of polymer
desired. What can be said is that a catalytic amount is
necessary for polymerization. As a general rule, the mole-
cular weight of the polymer is equal to the grams of polymer
formed,divided by the moles of catalyst initiator employed. - -
Thus, one skilled in the art can adjust the catalyst level `~
~i to get any desired molecular weight polymer.
Representative examples of conjugated dienes are
butadiene, isoprene, dimethyl butadiene, 1~3-pentadiene~ ;
1,3-hexadiene and the like. Other conjugated diene monomers -
which are capable of copolymerizing with a-methylstyrene are
also suitable within the scope of this invention.
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The polymerizations may be conducted in any of the
inert hydrocarbon solvents. By "inert" is meant that the
solvent does not enter into or adversely affect the polymeri-
zation rate~ Representative of such hydrocarbon solvents
are benzene, toluene, naphthalene~ hexane, heptane, cyclo~
hexane and~the like. -
~- ~ 25 The amount of desired poly-a-methylstyrene (A) in
.~ the block~polymer determines the characteristics for which
the polymer will best be suited. For instance~ block poly-
;~ mers containing no poly-a-methylstyrene to about forty-five
percent (~5%) poly-a-methylstyrene can be useful as a ther-
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moplastic elastomer. A block polymer may be prepared con-
taining more than forty-five percent (45~) poly-a-methylsty-
~- rene up to about elghty percent (80%) or more of poly-a-
methylstyrene with such block polymer having more or less
plastic-like characteristics.
In the practice of this invention it will be found
that after the initiator is introduced to the polymerization
mixture the conjugated diene will polymerize first to form a
polymer block and then the a-methyl styrene will polymerize
on the ends of the conjugated diene polymer block. The
amount of a-methylstyrene one desires to form as a block~has ;~
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to be in excess of the level at which the depropagation reac-
tion starts to take place. In other words~ enough excess
a-methylstyrene should be added at the start of the reaction --~
~:~ 15 to include the minimum of 3 moles per liter of polymeriza-
~ tion mi~ture plus the amount to be polymerized as part of
'~ ; the block polymer.
The practice of this inventlon is further illustra-
ted by reference to the following examples which are inten-
ded to be representative rather than restrictive o~ itsscope.
EXPERIMENTAL
In the examples shown, a small amount of styrene
was added to the polymerization mixture to aid in the cross-
over reaction from the conjugated diene block to the a-methyl
`~ styrene block. The conjugated diene polymerizes preferen~ " ' ~
;, tially and when it is nearly exhausted the a-methyl styrene ` ;
~ polymerization takes place predominately. However, the ini~
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~ tiation of a-methyl styrene by the conjugated diene anion
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is very slow. Initiatlon of the a-methylstyrene by the sty- ~
ryl anion is fast compared to the conjugated diene anion. ;
Thus~ the initiation of the a-methylstyrene is enhanced by
the small addition of the styrene.
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DSV means dilute solution viscosity. ~ ;
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~ EXAMPLE I
3 A solution was prepared containing 12 grams of bu
:~ tadiene~ 0.25 grams of styrene 9 and 35 grams of a-methylsty-
. ~ .
rene in a total of 80 milliliters o~ solution using benzene
as the solvent. ~he solution was dried by passing it through
silica gel column, and was placed in a 4-ounce bottle. The
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3, solution was then sparged 10 seconds with nitrogen and 1.3 ~-
,. 1 . , .
~j milliliters of a 0.20 molar solution of dilithiodiisoprene ~
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`~ were added. The bottle was capped and tumbled in a water ;~ ;
bath at 250C. for 30 hours. The viscous cement was coagula-
ted in methanol containing a phenolic antioxidant, and dried
in vacuo at 50oC. Yield was 24 grams of a polymer contain- ;~
ing about 42 percent by weight of poly-a-methylstyrene. It
had 3600 pounds per square inch tensile strength at 580 per- ;
cent elongation at 750F. and 875 pounds per square inch ten~
sile strength with 620 percent elongation at 212F.
EXAMPLE II
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'`',5 . A solution was prepared to contain 12 grams o~ bu-
~s tadiene and approximately 0.3 gram of styrene in 55 grams of
a-methylstyrene. The solution was dried by passage through
a silica gel column and was placed in a 4-ounce bottle. It
was sparged 10 seconds with nitrogen and 1.5 mls. of an
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0.20 M solution of a di(a-lithio-3-methylpentyl) benzene
were added. The bottle was capped and tumbled in a water
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bath for elght hours at 400C. The cement was coagulated in
methanol containing a phenolic antioxidant and dried in
vacuo at 750C. Yield was 21 grams of a polymer containing
about ~7 percent by weight of poly-a-methylstyrene. It had
4025 pounds per square inch tensile strength at 6~o percent
.
elongation at 750F., and 875 pounds per square inch tensile
strength at 730 percent elongation at 212F. Polymer had
DSV in toluene at 30C. of o.96.
EXAMPLE III
A solution prepared as in ExampleII was initiated
with 1.5 mls. of an 0.20 M solution of a-~dilithio diiso~
prenyl)-3-methylpentyl toluene. The 4-ounce bottle contain- ~
~ ing the solution was capped and tumbled in a water bath for ~ ;
;i eight hours at 400C. The cement was coagulated in methanol ;
, 15 containing a phenolic antioxidant and dried in vacuo at 750C.
; Yield was 19.4 grams of a polymer containing about 38 per-
cent poly-~-methylstyrene by weight. It had 2890 pounds
per square inch tensile strength wlth 880 percent elongation
i at 750F.-and 520 pounds per square inch tensile strength
with 775 percent elongation at 212F. The polymer had a DS~ ~ -
;~ of 0.97 in toluene at 30C.
EXAMPLE IV , ;~
A solution prepared as in Example IIwas initiated
with 1.5 mls. of 0.20 M solution of dilithio diisoprene.
25 The 4-ounce bottle containing the solution was capped and ~ ;
tumbled in a water bath for four and one-half hours at 400C.
The coment was coagulated in methanol containing a phenolic
antioxidant and dried in vacuo at 750C. Yield was
;~ grams of a polymer containing about ~5 percent poly-a-methyl~
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styrene by weight. It had 3610 pounds per square inch ten- -
sile strength with 740 percent elongation at 750F. and 465
pounds per square inch tensile strength with 600 percent ~ -~
i elongation at 212F. The polymer had a DSV of 0.66 in to-
. j
,~ 5 luene at 30C.
~! EXAMPLE V
-~ A solution prepared as in ExampleII was initiated
with 1.5 mls.of 0.20 ~ solution of dilithio diisoprene. The
~-ounce bottle containing the solution was capped and tumbled
in a water bath for six hours at ~0C. The cement was coagu-
lated in methanol containing a phenolic antioxidant~ and the
j polymer was dried in vacuo at 750C. Yield was 18 grams of
a polymer containing about 33 percent poly-a-methylstyrene
by weight. It had 3070 pounds per square inch tensile
j 15 strength with 965 percent elongation at 750F.1 and 3~0
~ pounds per square inch tensile strength at 660 percent elon-
;~i, gation at 212F. The polymer had a DSV of 0.92 in toluene
at 30C. ;~
While certain representative embodiments and de-
20 tails have been shown for the purpose of illustrating the ;~
i~vention~ it will be apparent to those skilled in this art
.~ ~
that various changes and modifications may be made therein
without departing from the spirit or scope of the invention.
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