Note: Descriptions are shown in the official language in which they were submitted.
1067643
The invention relates to a process for the preparation
of a non-linear, elastomeric copolymer, to the copolymer
thus prepared and to articles manufactured from such
a copolymer.
One of the major deficiencies of commerclally
available, solution-polymerized, anionically~initiated
synthetic rubbers such as butadiene polymers and styrene/
butadiene copolymers, is the poor properties of the
uncured black stocks. In particular,the tack and green
; 10 strength are seriously deficient compared with, e.g.,
. emulsion styrene/butadiene copolymers, which leads
to difficulties in factory processing. By green strength
is meant the strength of the rubber or compound thereof
which has not been vulcanized.
It is an object of the present invention to provide
conjugated diene elastomers exhibiting improved green
strength while still having an adequate processability
and satisfactory properties of the vulcanized compound.
According to the present invention a process is
provided for the preparation of a non-linear, elastomeric
copolymer, which process comprises:
(a) polymerizing a conjugated diene in the presence
, ~
~i of a monolithium-terminated polymer of a monoalkenyl
, ;,. ~
or monoalkenylidene aromatic hydrocarbon, A-Li,
in which A indicates a polymer block of a monoalkenyl
or monoalkenylidene aromatic hydrocarbon, having
;1 an average molecular weight between 5000 and 35000,
. .
,: ,
,.
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~067643
so as to fo~m a block co-polymer A-B-Li, in which block B substantially
comprises polymerized, con~ugated diene molecules and in which block A-B
has an LVN (limiting viscosity number) between 0.1 and 10 d Vg;
(b) polymerizing a con~ugated diene in the presence of an
alkyllithium initiator, R-Li; R being an alkyl group, so as to form a
polymer block B'-Li substantially comprising polymerized, con~ugated diene
molecules, polymer block B' having an LVN between 0.1 and 10 dl/g, and the
molar ratio X between the initiator R-Li and the compound A-Li being
between 2.5:1 and 10:1;
(c) coupling the polymer blocks A-B-Li and B'-Li obtained by
the polymerizations mentioned sub (a) and (b) with a coupling agent C which
is at least trifunctional lnsofar as its coupling activity is concerned,
the molar ratio of the sum of A-B-Li and BILi polymer blocks to coupling
agent being from 3:1 to 5~
The products of the present invention are designed within
specific limits in their constitution and proportion so as to obtain the ;
desired results, i.e. improved green strength, building tack, elongation
as well as processability.
The con~ugated diene for ~he formation of the polymer blocks
. ,.:,
; 20 B' and A-B may be isoprene or piperylene, but is preferably butadiene.
The aromatic hydrocarbon for the formation of the polymer block A is
j preferably
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.
1067643
-
styrene. The molecular weight of poly~er block ~ is
suitably between 15,000 and 25,000 if the copolymer
is to be used in non-oil-extended compounds, and between
- 20,000 and 30,000 if the copolymer is to be used in
oil-extended compounds. The blocks B' and B may - and
preferably do - also contain a copolymerized monoalkenyl
or monoalkenylidene aromatic hydrocarbon, in particular
styrene in a minor amount. The amount o~ the aromatic
hydrocarbon thus copolymerized in blocks B' and B,
is suitably in the range of 10-30~ based on the weight
of said blocks. Blocks B' and B may be of the same
or different constitution, within the general limits
specified above. The LVN of blocks A-B and B' is preferably
; between 0.2 and 3 dl/g.
i::: , .
The molecular weight of the A block and the LVN
of the A-B and B' blocks are determined - after killing
the A-Li, A-B-Li and B'-Li blocks, e.g. with methanol
and dissolving them in a suitable solvent - by methods
, -. , ~
known in the art. Thus the molecular weight of the
A block may be determined by gel permeation chromatography
: .'
~ after calibration with polystyrene of known molecular
.,
~` weight. The LVN is determined in toluene at 30C. The
total styrene of the copolymer is determined by infrared
~`l analysis.
The polymer blocks A-B-Li and B~-Li are prepared
::
by solution polymerization utilizing the compounds
A-Li and R-Li, respectively, as initiators. The alkyl
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~67643
group R pre~erably contains from 3 to 9 carbon atoms,
in particular from 3 to 6 carbon atoms. Isopropyllithium
and secondary butyllithium are especially preferred.
The compound A-Li, used as the other initiator, may
be prepared by polymerization of a monoalkenyl or
monoalkenylidene aromatic hydrocarbon in solution in
the presence of an alkyl lithium, R Li, as described.
If the desired (number average) molecular weight of
the block A is denoted: Ms; the grammolar amount of
initiator: (R-Li); and the weight in grams of the
monoalkenyl or monoalkeny]ider.earomatic hydrocarbon:
, .
~ (Ar), then the following function exists:
~``.` 1 :
, Ms = (Ar~/(R-Li). This will serve to calculate the
amounts of aromatic hydrocarbon and alkyllithium required
, 15 to obtain a block A-Li of the desired molecular weight.
Monomers to be polymerized, the conjugated diene,
and, if desired the monovinylarene, are dissolved in
' a substantially inert solvent such as alkenes, alkanes
: and cycloalkanes. Suitable species of these include
pentane, cyclopentane, hexane, cyclohexane, and mixtures
~ of the same. The polymerization reactions (a) and (b)
s as well as the coupling reaction (c) may be carried
:,: ~
l out at 20C-150C, preferably at 45Oc-gooc, for 15
, , .
;^ minutes to 8 hours, in an inert atmosphere such as
under nitrogen. The concentration of the monomers in
the reactor is not critical, and is mainly chosen on
.
~ the basis of the ultimate, practically feasible viscosity
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' .
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- 6 -
o~ the elastomer solution, solutions of 20% solids
content being still stirrable.
The polymerizations may be carried out in the
presence of polar compounds such as ethers, amines
and other Lewis bases so as to obtain diene blocks
ha~ing an increased (e.g. 30-~0%) vinyl content.
Although the polymerizations according to the
invention may be carried out continuously, it is usually
more advantageous to effect these batchwise. A preferred
method for the copolymerization of a conjugated diene
with a minor amount of a monoalkenyl or monoalkenylidene
aromatic hydrocarbon so as to prepare the polymer blocks
. B and B', has been set out in British patent specification
1,283,327. According to this method, first a starting
mixture is prepared from the diluent and a part - preferably
less than 50 %w - of the totally needed quantity of
each of the monomers; subsequently initiating the mixture
by addition of the initiator R-Li or A-Li~ and keeping
the monomer ratio in the reaction mixture during copolymerization
substantially constant by addition of the remaining
part of each of the monomers. By "substantially constant"
is meant that the monomer weight ratio during the copolymerization
.: ~
should increase or decrease by not more than 20%.
The two types of polymerizations, (a) and (b)
,: ~
j 25 may be carried out separately or in the same reactor.
:. '
In this connection the following options exist, among
- others:
.. .
.
.
'
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1067643
-- 7 --
(1) the cQnjugated diene, lf desired in the presence
of the monoalkenyl or monoalkenylidene aromatic
hydrocarbon, is polymerized in separate reactors
in the presence of compounds A~Li and R-Li, so
as to form the polymer blocks A-B-Li and B'-Li,
; respectively. The blocks B and B' may be of the
- same or a different composition, within the limits
specified above;
(2) the compound A-Li is first prepared in the diluent
by polymerizing the monoalkenyl or monoalkenylidene
aromatic hydrocarbon in the presence of an amount,
p, of initiator R-Li. After completion of this
j .
i polymerization the conjugated diene, if desired
the aromatic hydrocarbon as comonomer, and a further
amount, q, of the same or a different initiator
i
R-Li are added to compound A-Li, formed in the
, diluent. The amounts of initiator R-Li employed
are such that the molar ratio of q/p is at least
2.5. In general, this molar ratio q/p will equal
., .~
~ 20 the ratio X. This second method is the preferred
.. ~
~;~ method~
Suitably the molar ratio X between R-Li and A-Li
is between 2.5 and 10. For use in oil-extended compounds,
i.e. in compounds containing 10-100 phr (parts by weight
1~ 25 per 100 parts of the non-linear, elastomeric copolymer)
of an extender oil, the preferred ratio X or q/p is
`l between 2.6 and 4.5. For use of the copolymer in non-oil-
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, :
~067643
-- 8 --
extended compounds - containing less than 10 phr of
oil - the preferred ratio X or q/p is between 3 and
6.
If they have been prepared separately, the solutions
of the active polymer blocks A-B-Li and B'~Li are mixed.
If prepared according to the above preferred second
method, these blocks are already available as a mixture,
of course. The mixture is coupled by contactin~ it
with the coupling agent C.
The preferred type of coupling agent is a tetrafunctional
- ester derived from a dicarboxylic acid and a monohydric
alcohol. Dimethyl adipate and diethyl adipate are especially
suitable for this purpose. Usually these diesters will
be used in an about equivalent ratio, i.e. in a molar
ratio of (A-B-Li + B'-Li) blocks to diester between
3:1 and 5:1, the equivalent ratio being 4:1.
A number of other polyfunctional coupling agents
~- may be employed in addition to or in place of the preferred
diesters. ~hese include polyepoxides, polyisocyanates,
polyamines, polyaldehydes, polyanhydrides, polyesters
and polyhalides, such as tribromobutane, tin tetrachloride
and silicon tetrachloride. Other useful types of coupling
agents are alpha-beta-olefinically unsaturated nitriles,
in particular acrylonitrile, and certain unsaturated
halides such as vinyl chloride, 1-chloro-1,3-butadiene,
p-halostyrene and 2-chloro-1-propene. The unsaturated
nitriles and halides are generally used in an amount
.
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iO67643
g
of 0.1-1.5% based on the sum of the weight of the A-B-Li
and B'/Li blocks, so as to provide a molar ratio of
nitrile or halide to the sum of A-B-Li plus B'/Li of
- approximately 3-15. It is assumed that under the conditions
of the coupling reaction the unsaturated nitrile or
halide forms small, polyfunctional end blocks on a part
of the A-B- or B'-blocks. Via the pendent nitrile groups
or halide atoms the remaining A-B-Li and B'-Li blocks
,
add to form the non-linear, elastomeric copolymers.
10Subsequent to the coupling operation, the product
may be hydrogenated though, of course, in applications
involving vulcanisation with sulphur, such hydrogenation
~' is undesirable.
EXAMPLES
' l 15The polymerizations were carried out at 750C
in a 10 litre autoclave charged with 8 1 of a 50/50
w/w mixture of cyclohexane and n-hexane. Next an amount
', i
of styrene, indicated in the Table, was added and the
mixture titrated at room temperature with a 12 %w
solution of secondary butyllithium (BuLi) in cyclohexane
to incipient polymerization, indicated by a temperature
i rise of 0.1C. Thereby any impurities present in the
;i,~ `.
solvent mixtures were scavenged. Thereafter, the temperature
was raised to and maintained at 75C, and a further
:: j
amount of the solution, containing the amount of butyllithium
~ indicated in the Table, was added. After 15 minutes
..... .
the block A-Li had been formed. Subsequently an initial
3l~
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, . .
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;;,. - . :
~067643
~ -- 10 --
~ mixture of styrene/butadiene was added, as indicated
i in the Table, together with the amount of butyllithium
indicated. After these additions, a feed mixture of
styrene and butadiene - as indicated in the Table -
., .
was added at a constant rate over a period of 3 hours.
, At the end of the polymerization the amount of DEAP
(diethyl adipate) indicated was added at 75C. After
about 2 hours 10 grams of 2,6-ditert.butyl-4-methylphenol
' was added after which the solvent was removed by steam
stripping. The polymer obtained was dried in an oven
at 90C. The results appear from the following Table.
In the calculation of molar ratio X between the initiator
~-~ Bu-Li, added after the A-Li formation, and the Bu-Li,
used in the A-Li formation - disregarding the Bu-Li
~ , 15 used for scavenging the solvent mixture -, it is assumed
,;~ that the total amount of Bu-Li used in the A-Li formation
, , .
, will be available as living A-Li blocks.
Black stocks were prepared according to the following
recipe:
Copolymer . . . . . . . . . . . . . 100 parts by weight
~;~ ZnO .............................. 5 " " "
Stearic acid. . . . . . . . . . . . 3 " " "
N-(1,3-dimethylbutyl)-N'-phenyl-p-
;- phenylenediamine . . . . . . . . 1.5 parts-by weight
,.. . .
'~, N,N'-bis(1,4-dimethylpentyl)-p-
~ ~ 25 phenylenediamine . . . . . . . 1 5 " " "
~:;
~` Paraffin wax. . . . . . . . . . . . 1 " " "
~ ' .
:
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.
~067643
Aromatic extender oil,"DUTREX"729/HP 5 parts by weig~t
ISAF carbon black . . . . . . ~ . . 50 " " "
Sulphur . . . . . . . . . . . . . . 2 " " "
N-cyclohexyl-2-benzothiazolsulphen-
amide. . . . . . . . . . . . . 1 " " "
The same recipe was used for the "oil-extended"
composition, containing 37.5 parts by weight of aromatic
extender oil, "DUTREX"729HP, except for the following
modifications:
Sulphur . . . . . . . . . . . . . . 1.85 parts by weight
-
N-cyclohexyl-2-benzothiazolsulphen-
amide. . . . . . . . . . . . . o.8
,':
. .
'.....
.,:
:
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.,.
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- 12 -
Image
1067643
- 13 -
From the data in the Table it follows that only
copolymers having a ratio X o~ at least 2.5 possess
a 100C-Mooney value wit~.in commercially acceptable
limits of 40 to 100 in addition to improved green strength.
At very high ratios of X the green strength values,
i.e. the tensile strength and elongation of the black
stock, are undesirably low.
