U.S. patent application number 10/772005 was filed with the patent office on 2004-08-26 for block copolymer based on conjugated diolefins and polar monomers.
Invention is credited to Friebe, Lars, Nuyken, Oskar, Obrecht, Werner, Scholl, Christine, Scholl, Johannes, Scholl, Philipp, Scholl, Thomas, Scholl, Ulrike, Stere, Cristina, Vierle, Mario, Windisch, Heike.
Application Number | 20040167276 10/772005 |
Document ID | / |
Family ID | 7679267 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040167276 |
Kind Code |
A1 |
Windisch, Heike ; et
al. |
August 26, 2004 |
Block copolymer based on conjugated diolefins and polar
monomers
Abstract
The block copolymers according to the invention which are based
on conjugated diolefins and polar monomers and are prepared in the
presence of catalysts based on the rare earth metals have a high
cis-1,4 content in the polydiene block and, because of their polar
polymer part and their non-polar diene polymer part, can be used as
agents which impart compatibility in the preparation of
vulcanizates with a filler content for the production of tires and
tire components, as a filler in the preparation of such
vulcanizates, and as a blend component in the preparation of
thermoplastic elastomers or in the modification of
thermoplastics.
Inventors: |
Windisch, Heike;
(Leverkusen, DE) ; Obrecht, Werner; (Moers,
DE) ; Stere, Cristina; (Leverkusen, DE) ;
Scholl, Thomas; (Bergisch Gladbach, DE) ; Scholl,
Ulrike; (Bergisch Gladbach, DE) ; Scholl,
Philipp; (Bergisch Gladbach, DE) ; Scholl,
Christine; (Bergisch Gladbach, DE) ; Scholl,
Johannes; (Bergisch Gladbach, DE) ; Nuyken,
Oskar; (Munchen, DE) ; Friebe, Lars; (Munchen,
DE) ; Vierle, Mario; (Munchen, DE) |
Correspondence
Address: |
BAYER POLYMERS LLC
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7679267 |
Appl. No.: |
10/772005 |
Filed: |
February 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10772005 |
Feb 3, 2004 |
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10102761 |
Mar 21, 2002 |
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6734257 |
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Current U.S.
Class: |
525/55 ;
525/178 |
Current CPC
Class: |
C08F 297/06
20130101 |
Class at
Publication: |
525/055 ;
525/178 |
International
Class: |
C08F 255/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2001 |
DE |
10115106.3 |
Claims
What is claimed is:
1. Block copolymers based on conjugated dienes and polar monomers,
wherein the block copolymers comprise the polymerized conjugated
dienes in amounts of 5 to 95 wt. % and the polymerized polar
monomers in amounts of 95 to 5 wt. %, the polymerized dienes having
a cis-1,4 content of .gtoreq.60 wt. %.
2. Block copolymers according to claim 1, wherein said conjugated
dienes are selected from the group consisting of 1,3-butadiene,
1,3-isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene
and/or 2-methyl-1,3-pentadiene.
3. Block copolymers according to claim 1, wherein said polar
monomers are selected from the group consisting of lactones,
lactams, thiolactams, epoxides, cyclic sulfides and cyclic
carbonates.
4. Block copolymers according to claim 3, wherein said polar
monomers are selected from the group consisting of
.epsilon.-caprolactone, .gamma.-valerolactone,
.delta.-valerolactone, .gamma.-butyrolactone and/or
.beta.-butyrolactone.
5. A process for the preparation of block copolymers based on
conjugated dienes- and polar monomers, wherein the block copolymers
comprise the polymerized conjugated dienes in amounts of 5 to 95
wt. % and the polymerized polar monomers in amounts of 95 to 5 wt.
%, the polymerized dienes having a cis-1,4 content of .gtoreq.60
wt. %. comprising the steps of (i) polymerizing the conjugated
dienes in the presence of catalysts comprising (A) at least one
compound of the rare earth metals, (B) at least one organoaluminum
compound and (C) at least one Lewis acid and in the presence of
inert organic solvents up to a conversion of .gtoreq.50 wt. %; (ii)
adding the polar monomers to the polymerization mixture and
polymerization is carried out up to a conversion of .gtoreq.30 wt.
% and (iii) isolating the resulting block copolymer, and (iv)
employing the conjugated dienes in the reaction mixture in amounts
of 5 to 30 wt. % and the polar monomers in amounts of 1 to 30 wt.
%.
6. The process according to claim 5, wherein said conjugated dienes
are selected from the group consisting of 1,3-butadiene,
1,3-isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene
and 2-methyl-1,3-pentadiene.
7. The process according to claim 5, wherein said polar monomers
are selected from the group consisting of lactones, lactams,
thiolactams, epoxides, cyclic sulfides and cyclic carbonates.
8. The process according to claim 7, wherein polar monomers are
selected from the group consisting of .epsilon.-caprolactone,
.gamma.-valerolactone, .delta.-valerolactone, .gamma.-butyrolactone
and/or .beta.-butyrolactone.
9. The process according to claim 5, wherein the compounds of the
rare earth metals which are employed are their alcoholates,
phosphonates, phosphinates, phosphates and carboxylates and the
complex compounds of the rare earth metals with diketones, the
addition compounds of the halides of the rare earth metals with an
oxygen or nitrogen donor compound and allyl compounds of the rare
earth metals.
10. The process according to claim 9, wherein said compounds of the
rare earth metals are selected from the group consisting of
neodymium versatate, neodymium octanoate and neodymium
naphthenate.
11. The process according to claim 5, wherein said organoaluminum
compound is selected from the group consisting of aluminumtrialkyl,
dialkylaluminum hydride and alumoxanes.
12. The process according to claim 5, wherein said Lewis acid is
organometallic halides of group IIIA and IVA and/or halides of
elements of group IIIA, IVA and VA of the periodic table.
13. The process according to claim 5, wherein said inert solvents
are aliphatic or aromatic solvents.
14. The process according to Claim 13 wherein said aliphatic
solvents are selected from the group consisting of butane, pentane,
hexane or heptane or said aromatic solvents are selected from the
group consisting of benzene, toluene, ethylbenzene or
dimethylbenzene or mixtures.
15. Vulcanizates with a filler content for the production of tires
and tire components comprising block copolymers based on conjugated
dienes and polar monomers, wherein the block copolymers comprise
the polymerized conjugated dienes in amounts of 5 to 95 wt. % and
the polymerized polar monomers in amounts of 95 to 5 wt. %, the
polymerized dienes having a cis-1,4 content of .gtoreq.60 wt.
%.
16. A thermoplastic elastomer containing block copolymers based on
conjugated dienes and polar monomers which comprise the polymerized
conjugated dienes in amounts of 5 to 95 wt. % and the polymerized
polar monomers in amounts of 95 to 5 wt. %, the polymerized dienes
having a cis-1,4 content of .gtoreq.60 wt. %.
17. A blend material for the modification of thermoplastics
comprising block copolymers based on conjugated dienes and polar
monomers which comprise the polymerized conjugated dienes in
amounts of 5 to 95 wt. % and the polymerized polar monomers in
amounts of 95 to 5 wt. %, the polymerized dienes having a cis-1,4
content of .gtoreq.60 wt. %.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a block copolymer based on
conjugated diolefins and polar monomers, and to a process for the
preparation of the block copolymer in the presence of catalysts of
the rare earths.
BACKGROUND OF THE INVENTION
[0002] The polymerization of conjugated diolefins has been known
for a long time and is described, for example, by W. Hoffman,
Rubber Technology Handbook, Hanser Publishers (Carl Hanser Verlag)
Munich, Vienna, New York, 1989. Thus, for example, polybutadiene is
now predominantly prepared by solution polymerization with the aid
of coordination catalysts of the Ziegler-Natta type, for example
based on compounds of titanium, cobalt, nickel and neodymium, or in
the presence of alkyllithium compounds. The nature of the solvent
used in each case depends greatly on the type of catalyst employed.
Benzene or toluene and aliphatic or cycloaliphatic hydrocarbons are
preferably employed.
[0003] The polymerization of unsaturated organic compounds, in
particular conjugated dienes, in the presence of catalysts based on
rare earth metals has been known for a long time (see e.g. DE-A 28
33 721, U.S. Pat. No. 4,429,089, EP-A 76 535, EP-A 92 270, EP-A 92
271, EP-A 207 558, WO-A 93/05083, U.S. Pat. No. 5,627,119, EP-A 667
357, U.S. Pat. No. 3,478,901, EP-A 637 589). Thus, for example,
EP-A 11 184 and EP-A 7027 disclose a catalyst system which is based
on rare earth metals, in particular based on neodymium compounds,
and is particularly suitable for the polymerization of conjugated
dienes, in particular butadiene. In the polymerization of, for
example, butadiene, these catalysts give a polybutadiene in very
good yields and with a high selectivity, which is distinguished, in
particular, by a high content of cis-1,4 units.
[0004] It is, furthermore, known to employ anionic initiators, such
as butyllithium, for the polymerization of butadiene in hexane.
Anionic catalysts are also suitable for a block copolymerization of
butadiene with further non-polar monomers, such as styrene and
isoprene, or polar monomers, such as ethylene oxide, propylene
oxide and acrylates [H. L. Hsieh, R. P. Quirk, Marcel Dekker Inc.,
New York Basel, 1996; R. K. Sadhir, R. M. Luck, Expanding Monomers,
CRC Press Boca Raton, 1992]. In this case, the butadiene is first
polymerized in an inert solvent and, after addition of a further
monomer to the live system, a second block is then formed from the
further monomer. The preparation of three-block copolymers is also
possible with these anionic initiators.
[0005] The disadvantage is that it is not possible, with anionic
initiators, to prepare a copolymer with a high cis content, in
which the cis-1,4 content of the butadiene block is above 50%,
under conditions which are relevant in use.
[0006] It is known that compounds for tire mixtures, in particular
for treads, are made of several rubbers and fillers in order to
achieve an optimum in their properties, such as e.g. the rolling
resistance and the abrasion and wet skidding resistance. Polydienes
with a high cis content, such as the two synthetic rubbers,
polybutadiene and polyisoprene or natural rubber, are preferably
employed in these rubbers.
[0007] To reduce the rolling resistance, some of the filler carbon
black in the "green tires" is replaced by silica. One of the main
problems of using silica as a filler in rubber is the great
difference in polarity between the two components. This results in
a poor miscibility. Binding of polar silica to the non-polar rubber
matrix has hereto been achieved only by means of coupling reagents,
such as e.g. Si-69.RTM.(Degussa AG).
[0008] However, for use of the block copolymer as an agent which
imparts compatibility of, for example, high cis-BR and silica in
vulcanizate mixtures, a low cis-1,4 content in the polydiene part
of the block copolymer has an adverse effect on the compatibility
of the block copolymer with the high cis-BR rubber matrix and
therefore, an adverse effect on the product properties.
[0009] In the case of catalysts based on the rare earths, those
catalyst systems which allow homopolymerization of polar monomers
are also described. Examples of these are the samarium catalyst
[(C.sub.5Me.sub.5)SmH].sub.2 for the polymerization of acrylates
[H. Yasuda et al., Macromolecules, 1993, 22, 7134; J. Am. Chem.
Soc., 1992, 1:14, 4908; E. Ihara et al., Macromolecules, 1995, 28,
7886] and lactones [M. Yamashita et al., Macromolecules, 1996, 29,
1798] and for the block copolymerization of ethylene with meth
acrylate or .epsilon.-caprolactone [H. Yasuda et al.,
Macromolecules, 1992, 25, 5115], the samarium catalyst
[(C.sub.5Me.sub.5).sub.2SmMe] for the formation of tri-block
copolymers from variously substituted acrylates [E. Ihara et al.,
Macromolecules, 1995, 28, 7886] and for the polymerization of
cyclic carbonates [H. Yasuda, Prog. Polym. Sci., 2000, 25, 573],
the ytterbium catalyst Yb[C(SiMe.sub.3).sub.3].sub.2 for the
polymerization of methacrylate [H. Yasuda et al., Prog. Polym.
Sci., 1993, 18, 1097; E. Ihara et al., J. Organomet. Chem., 1999,
574, 40] and neodymium catalysts based on
Nd(acac).sub.3(H.sub.2O).sub.3/AIR.sub.3 and
Nd(naphthenate).sub.3/AIR.su- b.3 for the polymerization of
lactones [Z. Shen et al., J: Polym. Sci., Polym. Chem. Ed., 1994,
32, 597] and based on Nd(ethyl acetoacetate).sub.2(OPr) for the
block copolymerization of cyclic carbonate with lactones [H.
Yasuda, Prog. Poly. Sci., 2000, 25, 573].
[0010] The preparation of block copolymers with a high
cis-1,4-polydiene part and therefore, a low glass transition
temperature has not so far been possible.
SUMMARY OF THE INVENTION
[0011] The object of the present invention was to provide a process
for the block copolymerization of conjugated diolefins and polar
monomers with which copolymers in which the polymer composition can
be varied with respect to the content of conjugated dienes and of
polar monomers, at an unchanged high cis-1,4 content in the
polydiene content of .gtoreq.60%, are obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows TEM photograph of a PB/PCL mixture (weight
content of PCL=62%) after dissolving in CHCl.sub.3 and
precipitation. Contrasted by OsO.sub.4, ultra-thin section. Dark
regions: PB, grey regions: PCL, white regions: holes. Bar length:
10 .mu.m.
[0013] FIG. 2 shows a TEM photograph of the polymer at the phase
boundary isolated by FEEF (weight content of PCL=70%, contains
PB-block-PCL). Contrasted by OsO.sub.4, ultra-thin section. Dark
regions: PB, light regions: PCL.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention relates to a process for the block
copolymerization of conjugated diolefins and polar monomers with
which copolymers in which the polymer composition can be varied
with respect to the content of conjugated dienes and of polar
monomers, at an unchanged high cis-1,4 content in the polydiene
content of .gtoreq.60%, preferably .gtoreq.80%, more preferably
.gtoreq.90%, are obtained.
[0015] With the catalyst systems according to the present invention
described in more detail below, there is the possibility of
preparing a block copolymer in which the content of polymerized
dienes and polar monomers can be adjusted within a wide range at an
unchanged high cis-1,4 content of the polydiene. These block
copolymers with a high cis content are not possible with the known
catalyst systems used in the art which are based on
lithium-alkyls.
[0016] With the catalyst systems employed according to the present
invention, it is, therefore, possible to establish a high cis-1,4
content in the polydiene content, in order to achieve in this
manner, an optimum compatibility with the rubbers of high cis
content employed, while also, via establishing of a suitable ratio
of polymerized dienes and of polymerized polar monomers, to ensure
optimum binding of the rubber mixture to polar components, which
manifests itself in low abrasion and a long life in the industrial
use of the mixtures.
[0017] The present invention, therefore, provides a block copolymer
based on conjugated dienes and polar monomers, which is
characterized in that it comprises the polymerized conjugated
dienes in amounts of 5 to 95 wt. % and the polymerized polar
monomers in amounts of 95 to 5 wt. %, the polydienes having a
cis-1,4 content of .gtoreq.60%.
[0018] Preferably, the amount of dienes is 20 to 90 wt. % and the
amount of polar monomers is 10 to 80 wt. %, the polydienes having a
cis-1,4 content of .gtoreq.80%, preferably .gtoreq.90%.
[0019] The present invention also provides a process for the
preparation of block copolymers based on conjugated dienes and
polar monomers, which is characterized in that conjugated dienes
are polymerized in the presence of catalysts comprising
[0020] A) at least one compound of the rare earth metals,
[0021] B) at least one organoaluminum compound and
[0022] C) at least one Lewis acid
[0023] and in the presence of inert organic solvents up to a
conversion of .gtoreq.50%, preferably .gtoreq.70%, polar monomers
are then added to the polymerization mixture and polymerization is
carried out up to a conversion of .gtoreq.30%, preferably
.gtoreq.50%, and the resulting block copolymer is then isolated,
the conjugated dienes being employed in the reaction mixture in
amounts of 5 to 30 wt. %, preferably 10-20 wt. %, and the polar
monomers in amounts of 1 to 30 wt. %, preferably 5-20 wt. %.
[0024] The molar ratio in which catalyst components (A) to (C) are
employed can be varied within wide limits. The molar ratio of
component (A) to component (B) is 1:1 to 1:1,000, preferably 1:3 to
1:200, more preferably 1:3 to 1:100. The molar ratio of component
(A) to component (C) is 1:0.2 to 1:15, preferably 1:0.4 to 1:5,
more preferably 1:0.5 to 1:3. If alumoxanes are used as component
(B), all or some of component (C) can be dispensed with.
[0025] Possible compounds of the rare earth metals (component (A))
are, in particular, those which are chosen from:
[0026] an alcoholate of the rare earth metals,
[0027] a phosphonate, phosphinates and/or phosphates of the rare
earth metals,
[0028] a carboxylate of the rare earth metals,
[0029] a complex compound of the rare earth metals with
diketones
[0030] an addition compound of the halides of the rare earth meals
with an oxygen or nitrogen donor compound and/or
[0031] an allyl compound of the rare earth metals.
[0032] The above-mentioned compounds of the rare earth metals are
described in more detail, for example, in EP-B-011184 and WO
96/31544.
[0033] The compounds of the rare earth metals are based, in
particular, on the elements with the atomic numbers 21, 39 and 57
to 71. Rare earth metals which are preferably employed are
lanthanum, praseodymium or neodymium or a mixture of elements of
the rare earth metals which comprises at least one of the elements
lanthanum, praseodymium or neodymium to the extent of at least 10
wt. %. Lanthanum or neodymium are preferably employed as rare earth
metals, and these, in turn, can be mixed with other rare earth
metals. The content of lanthanum and/or neodymium in such a mixture
is preferably at least 30 wt. %.
[0034] Possible alcoholates, phosphonates, phosphinates, phosphates
and carboxylates of the rare earth metals or possible complex
compounds of the rare earth metals with diketones are, in
particular, those in which the organic group contained in the
compound contains, in particular, straight-chain or branched alkyl
radicals having 1 to 20 carbon atoms, preferably 1 to 15 carbon
atoms, such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,
isopropyl, isobutyl, tert-butyl, 2-ethylhexyl, neo-pentyl,
neo-octyl, neo-decyl or neo-dodecyl.
[0035] Alcoholates of the rare earths which are mentioned are
e.g.:
[0036] neodymium(III) n-propanolate, neodymium(III) n-butanolate,
neodymium(III) n-decanolate, neodymium(III) iso-propanolate,
neodymium(III) 2-ethyl-hexanolate, praseodymium(III) n-propanolate,
praseodymium(III) n-butanolate, praseodymium(III) n-decanolate,
praseodymium(III) isopropanolate, praseodymium(III)
2-ethyl-hexanolate, lanthanum(III) n-propanolate, lanthanum(III)
n-butanolate, lanthanum(III) n-decanolate, lanthanum(III)
iso-propanolate and lanthanum(III) 2-ethyl-hexanolate, preferably
neodymium(III) n-butanolate, neodymium(III) n-decanolate and
neodymium(III) 2-ethyl-hexanolate.
[0037] Phosphonates, phosphinate and phosphates of the rare earths
which are mentioned are e.g.:
[0038] neodymium(III) dibutylphosphonate, neodymium(III)
dipentylphosphonate, neodymium(III) dihexylphosphonate,
neodymium(III) diheptylphosphonate, neodymium(III)
dioctylphosphonate, neodymium(III) dinonylphosphonate,
neodymium(III) didodecylphosphonate, neodymium(III)
dibutylphosphinate, neodymium(III) dipentylphosphinate,
neodymium(III) dihexylphosphinate, neodymium(III)
diheptylphosphinate, neodymium(III) dioctylphosphinate,
neodymium(III) dinonylphosphinate and neodymium(III)
didodecylphosphinate, preferably neodymium(III) dioctylphosphonate
and neodymium(III) dioctylphosphinate.
[0039] Carboxylates of the rare earth metals which are suitable
are:
[0040] lanthanum(III) propionate, lanthanum(III) diethylacetate,
lanthanum(III) 2-ethylhexanoate, lanthanum(III) stearate,
lanthanum(III) benzoate, lanthanum(III) cyclohexanecarboxylate,
lanthanum(III) oleate, lanthanum(III) versatate, lanthanum(III)
naphthenate, praseodymium(III) propionate, praseodymium(III)
diethylacetate, praseodymium(III) 2-ethylhexanoate,
praseodymium(III) stearate, praseodymium(III) benzoate,
praseodymium(III) cyclohexanecarboxylate, praseodymium(III) oleate,
praseodymium(III) versatate, praseodymium(III) naphthenate,
neodymium(III) propionate, neodymium(III) diethylacetate,
neodymium(III) 2-ethylhexanoate, neodymium(III) stearate,
neodymium(III) benzoate, neodymium(III) cyclohexanecarboxylate,
neodymium(III) oleate, neodymium(III) versatate and neodymium(III)
naphthenate, preferably neodymium(III) 2-ethylhexanoate,
neodymium(III) versatate and neodymium(III) naphthenate. Neodymium
versatate is preferred.
[0041] Complex compounds of the rare earth metals with diketones
which may be mentioned are:
[0042] lanthanum(III) acetylacetonate, praseodymium(III)
acetylacetonate and neodymium(III) acetylacetonate, preferably
neodymium(III) acetylacetonate.
[0043] Addition compounds of the halides of the rare earth metals
with an oxygen or nitrogen donor compound which are mentioned are,
for example:
[0044] lanthanum(III) chloride with tributyl phosphate,
lanthanum(III) chloride with tetrahydrofuran, lanthanum(III)
chloride with iso-propanol, lanthanum(III) chloride with pyridine,
lanthanum(III) chloride with 2-ethylhexanol, lanthanum(III)
chloride with ethanol, praseodymium(III) chloride with tributyl
phosphate, praseodymium(III) chloride with tetrahydrofuran,
praseodymium(III) chloride with iso-propanol, praseodymium(III)
chloride with pyridine, praseodymium(III) chloride with
2-ethylhexanol, praseodymium(III) chloride with ethanol,
neodymium(III) chloride with tributyl phosphate, neodymium(III)
chloride with tetrahydrofuran, neodymium(III) chloride with
iso-propanol, neodymium(III) chloride with pyridine, neodymium(III)
chloride with 2-ethylhexanol, neodymium(III) chloride with ethanol,
lanthanum(III) bromide with tributyl phosphate, lanthanum(III)
bromide with tetrahydrofuran, lanthanum(III) bromide with
isopropanol, lanthanum(III) bromide with pyridine, lanthanum(III)
bromide with 2-ethylhexanol, lanthanum(III) bromide with ethanol,
praseodymium(III) bromide with tributyl phosphate,
praseodymium(III) bromide with tetrahydrofuran, praseodymium(III)
bromide with isopropanol, praseodymium(III) bromide with pyridine,
praseodymium(III) bromide with 2-ethylhexanol, praseodymium(III)
bromide with ethanol, neodymium(III) bromide with tributyl
phosphate, neodymium(III) bromide with tetrahydrofuran,
neodymium(III) bromide with isopropanol, neodymium(III) bromide
with pyridine, neodymium(III) bromide with 2-ethylhexanol and
neodymium(III) bromide with ethanol, preferably lanthanum(III)
chloride with tributyl phosphate, lanthanum(III) chloride with
pyridine, lanthanum(III) chloride with 2-ethylhexanol,
praseodymium(III) chloride with tributyl phosphate,
praseodymium(III) chloride with 2-ethylhexanol, neodymium(III)
chloride with tributyl phosphate, neodymium(III) chloride with
tetrahydrofuran, neodymium(III) chloride with 2-ethylhexanol,
neodymium(III) chloride with pyridine, neodymium(III) chloride with
2-ethylhexanol and neodymium(III) chloride with ethanol.
[0045] Possible allyl compounds of the rare earth metals (component
(A)) are, in particular, those which are chosen from the
[0046] tetra(allyl) complexes of the rare earths of the formula
(I)
[M(D).sub.n].sup.+[Ln(C.sub.3R.sub.5).sub.4].sup.-,
[0047] tris(allyl) complexes of the rare earths of the formula
(II)
LN(C.sub.3R.sub.5).sub.3(D).sub.n,
[0048] bis(allyl) complexes of the rare earths of the formula
(III)
Ln(C.sub.3R.sub.5).sub.2(X)(D).sub.n and
[0049] mono(allyl) complexes of the rare earths of the formula
(IV)
Ln(C.sub.3R.sub.5)(X).sub.2(D).sub.n,
[0050] wherein
[0051] Ln denotes a trivalent element of the rare earths with the
atomic numbers 21, 39 and 57 to 71,
[0052] X is identical or different and denotes an anion,
[0053] D is identical or different and denotes a neutral
ligand,
[0054] M represents an element of group Ia of the periodic table of
the elements (PTE) [F. A. Cotton, G. Wilkinson, Anorganische Chemie
[Inorganic Chemistry], 4th edition, VCH Verlagsgesellschaft mbH,
Weinheim, 1985],
[0055] R is identical or different and represents hydrogen,
represents a linear or branched; saturated or mono- or
polyunsaturated C.sub.1-C.sub.30-alkyl radical or
C.sub.5-C.sub.30-cycloalkyl radical, which can optionally contain
one or more heteroatoms, such as N, P, O or S, represents a
C.sub.6-C.sub.30-aryl radical which optionally contains one or more
heteroatoms and is optionally mono- or polysubstituted by alkyl,
alkinyl or alkenyl radicals having 1 to 30 C atoms or phenyl groups
having 6 to 30 carbon atoms and can be fused with other aromatic
radicals containing 6 to 30 carbon atoms, or represents a silyl
group substituted by alkyl, alkenyl or alkinyl groups having 1 to
30 C atoms or phenyl groups having 6 to 30 C atoms,
[0056] n represents any desired number from 0 to 10, preferably 0
to 5.
[0057] Examples of compounds of the formula (I) to (IV) are
.pi.-allyl complexes of a trivalent element of the rare earths,
such as e.g. the allyl compounds already described in WO
96/31544.
[0058] The following allyl compounds are particularly suitable:
[0059] Nd(C.sub.3H.sub.5).sub.3(O.sub.2C.sub.4H.sub.8),
Nd(C.sub.3H.sub.5).sub.3, La(C.sub.3H.sub.5).sub.3,
C.sub.5Me.sub.5*La(C.sub.3H.sub.5).sub.2,
C.sub.5H.sub.5La(C.sub.3H.sub.5- ).sub.2,
C.sub.5Me.sub.5Nd(C.sub.3H.sub.5).sub.2, C.sub.5H.sub.5Nd(C.sub.3-
H.sub.5).sub.2, La(C.sub.3H.sub.5).sub.2Cl(THF).sub.2,
Nd(C.sub.3H.sub.5).sub.2Cl(THF).sub.2,
La(C.sub.3H.sub.5).sub.2Br(THF).su- b.2,
La(C.sub.3H.sub.5).sub.2I(THF).sub.2, La(C.sub.3H
.sub.5)Cl.sub.2(THF).sub.2, Nd(C.sub.3H.sub.5)Cl.sub.2(THF).sub.2,
La(C.sub.3H.sub.5)Br.sub.2(THF).sub.3 and
Nd(C.sub.3H.sub.5)Br.sub.2(THF)- .sub.2.
[0060] Neodymium versatate, neodymium octanoate and/or neodymium
naphthenate are preferably employed as compounds of the rare earth
metals.
[0061] The above-mentioned compounds of the rare earth metals can
be employed both individually and as a mixture with one
another.
[0062] Organoaluminum components (B) which are employed are
compounds chosen from an aluminum-trialkyl, a dialkylaluminum
hydride and/or an alumoxane of the formulae (I)-(IV): 1
[0063] In the formulae (I) to (IV) of component (B), R can be
identical or different and can denote straight-chain and branched
alkyl radicals having 1 to 10 C atoms, preferably 1 to 4 C atoms,
cycloalkyl radicals having 3 to 20 C atoms and aryl radicals having
6 to 20 C atoms and n can denote 1 to 50.
[0064] Examples of suitable aluminum-alkyls of the formulae (I) and
(II) are:
[0065] trimethylaluminum, triethylaluminum, tri-n-propylaluminum,
triisopropylaluminum tri-n-butylaluminum, triisobutylaluminum,
tripentylaluminum, trihexylaluminum, tricyclohexylaluminum,
trioctylaluminum, diethylaluminum hydride, di-n-butylaluminum
hydride and di-iso-butylaluminum hydride. Triethylaluminum,
triisobutylaluminum and di-iso-butylaluminum hydride are
preferred.
[0066] Examples of alumoxanes (III) and (IV), which are mentioned
are:
[0067] methylalumoxane, ethylalumoxane and iso-butylalumoxane,
preferably methylalumoxane and iso-butylalumoxane.
[0068] The aluminum-alkyls can be employed individually or as a
mixture with one another.
[0069] So-called Lewis acids are employed as component (C).
Examples which may be mentioned are the organometallic halides in
which the metal atom belongs to group 3a) or 4a), and halides of
elements of group 3a), 4a) and 5a) of the periodic table as
described in "Handbook of Chemistry and Physics", 45th Edition
1964-65.
[0070] Compounds, which are mentioned in particular are:
[0071] methylaluminum dibromide, methylaluminum dichloride,
ethylaluminum dibromide, ethylaluminum dichloride, butylaluminum
dibromide, butylaluminum dichloride, dimethylaluminum bromide,
dimethylaluminum chloride, diethylaluminum bromide, diethylaluminum
chloride, dibutylaluminum bromide, dibutylaluminum chloride,
methylaluminum sesquibromide, methylaluminum sesquichloride,
ethylaluminum sesquibromide, ethylaluminum sesquichloride, aluminum
tribromide, antimony trichloride, antimony pentachloride, silicon
tetrachloride, methyltrichlorosilane, dimethyldichlorosilane,
trimethylchlorosilane, ethyltrichlorosilane, diethyldichlorosilane,
triethylchlorosilane, vinyltrichlorosilane, divinyldichlorosilane,
trivinylchlorosilane, phosphorus trichloride, phosphorus
pentachloride and tin tetrachloride.
[0072] Diethylaluminum chloride, ethylaluminum sesquichloride,
ethylaluminum dichloride, diethylaluminum bromide, ethylaluminum
sesquibromide and/or ethylaluminum dibromide are preferably
employed.
[0073] The reaction products of aluminum compounds such as are
described as component (B) with halogens or halogen compounds, e.g.
triethylaluminum with bromine or triethylaluminum with butyl
chloride, can also be employed as component (C). In this case, the
reaction can be carried out separately, or the amount of
alkylaluminum compound required for the reaction is added to the
amount required as component (B).
[0074] Ethylaluminum sesquichloride, butyl chloride and butyl
bromide are preferred.
[0075] If the alumoxanes (III) and (IV) are used as component (B),
all or some of component (C) can be dispensed with, as already
mentioned above.
[0076] It is also possible, additionally, to add a further
component (D) to the proven catalyst components (A) to (C). This
component (D) can be a conjugated diene, which can be the same
diene as is to be polymerized later with the catalyst. Butadiene
and/or isoprene are preferably used.
[0077] If component (D) is added to the catalyst, the amount of (D)
is preferably 1 to 1,000 mol per 1 mol of component (A), more
preferably 1 to 100 mol. 1 to 50 mol, per 1 mol of component (A),
of (D) are preferably employed.
[0078] In the preparation of the rubber solutions, the catalysts
are employed in amounts of 1 .mu.mol to 10 mmol, preferably 10
.mu.mol to 5 mmol, of the compound of the rare earth metals per 100
g of the monomers.
[0079] It is, of course, also possible to employ the catalysts as
any desired mixture with one another.
[0080] Conjugated dienes (diolefins) which can be employed in the
process according to the invention are e.g. 1,3-butadiene,
1,3-isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene
and/or 2-methyl-1,3-pentadiene, preferably 1,3-butadiene and/or
1,3-isoprene.
[0081] Polar monomers which can be employed in the process
according to the invention are e.g. compounds of the formula (V) to
(XI) 2
[0082] In the formulae (V) to (XI), R can be identical or different
and can denote hydrogen, straight-chain and branched alkyl radicals
having 1 to 10 C atoms, preferably 1 to 4 C atoms, cycloalkyl
radicals having 3 to 20 C atoms and aryl radicals having 6 to 20 C
atoms, where alkyl radicals, cycloalkyl radicals and aryl radicals
can also contain heteroatoms, such as halogen, oxygen, sulfur or
nitrogen, and n can denote 1 to 10.
[0083] Compounds of the formula (V) to (XI) are, for example,
lactones, such as caprolactone, valerolactone and butyrolactone,
lactams, such as caprolactam, valerolactam and butyrolactam,
thiolactams, such as thiocaprolactam, thiovalerolactam and
thiobutyrolactam, epoxides, such as ethylene oxide, propylene
oxide, butene oxide, cyclohexene oxide, styrene oxide and
epichlorohydrin, cyclic sulfides, such as ethylene sulfide,
propylene sulfide and styrene sulfide, and/or cyclic carbonates,
such as ethylene carbonate, propylene carbonate and neo-pentyl
carbonate. The lactones are preferably employed, and
.epsilon.-caprolactone, .gamma.-valerolactone,
.delta.-valerolactone, .gamma.-butyrolactone and
.beta.-butyrolactone are to be mentioned as preferred.
[0084] Solvents which are employed for the process according to the
present invention are inert, aromatic, aliphatic or cycloaliphatic
solvents. Suitable solvents are, for example, benzene, toluene,
pentane, n-hexane, iso-hexane, heptane and cyclohexane, or
halogenated hydrocarbons, such as e.g. methylene chloride and
chlorobenzene. The solvents can also be employed as a mixture with
one another.
[0085] The process according to the present invention is preferably
carried out at temperatures from -20 to 200.degree. C., preferably
at 0 to 180.degree. C., more preferably at 20 to 160.degree. C.
[0086] The process according to the present invention can be
carried out under normal pressure or under increased pressure (0.1
to 12 bar).
[0087] The process according to the present invention can be
carried out discontinuously, semi-continuously and continuously. In
the continuous embodiment, it is to be ensured that the
polymerization zone of the conjugated dienes is separate from the
polymerization zone of the polar monomers and back-mixing of the
polar monomers into the polymerization zone of the conjugated
dienes is avoided.
[0088] In an advantageous embodiment of the block copolymerization,
the conjugated dienes are polymerized up to a conversion of
.gtoreq.50% in a mixture with inert solvent by addition of the
catalyst of the rare earth metals while mixing in one or more
continuously operated stirred tanks in cascade or in a grafting
flow reactor which effects mixing and/or a combination of the two
reactor types. The active, non-terminated polymer solution is led
to a further polymerization reactor. The block copolymerization is
carried out in at least one further stage after addition of the
polar monomer to the polydiene solution, with mixing in one or more
further continuously operated stirred tanks in cascade or in a
grafting flow reactor which effects mixing and/or a combination of
the two reactor types. When the desired conversion of polar
monomers of .gtoreq.30% has been reached, the catalyst can be
deactivated by addition of small amounts of, for example, water,
carboxylic acids and/or alcohols and the block polymer can be
isolated by evaporation of the polymer solution, by precipitation
with a non-solvent, such as e.g. methanol, ethanol and acetone, or
by steam distillation of the solvent. Additives, such as
stabilizers, anti-ageing agents and/or fillers, can be added during
the polymerization and during the isolation of the polymer.
[0089] It is of course possible for the block copolymer formed to
be separated off from homopolymers of the dienes and/or
homopolymers of the polar monomers which may have been formed. A
suitable process for this separation is e.g. the method of demixing
liquids [R. Kuhn, Macromol. Chem., 1976, 177, 1525; 1980, 181,
725].
[0090] The block copolymers obtained have an average molecular
weight of 5,000 to 10.sup.6 g/mol. The T.sub.g values are
<-90.degree. C., preferably <-100.degree. C.
[0091] The particular feature of the block copolymers is that
polymers or polymer blocks which are not miscible are coupled to
one another by the block copolymer formation. However, the block
copolymers obtained here still have the properties of the
corresponding individual polymers, for example the same or similar
melting and/or glass transition temperatures as occur in the
corresponding individual polymers. Due to the use of a non-polar
diene and a polar monomer, the block copolymers have an amphiphilic
character which can be utilized for dispersing, imparting phases or
for coating applications. As a result of the possibility of
choosing the ratio between the various monomers in the block
copolymer as desired, the polar or non-polar character of the block
copolymer can be accurately adjusted as desired.
[0092] There are diverse possibilities for the use of the block
copolymers. One field of use lies e.g. in the preparation of
vulcanizate mixtures with silica for tires and tire components. The
block copolymers can be employed as a substitute for the
conventional coupling reagents (e.g. Si-69.RTM. from Degussa AG)
for binding silica fillers to the rubber matrix, where the
polydiene part is bound to the rubber matrix and the polymer part
of the polar polymer is bound to the silica filler. However, a pure
mixture homogenization effect of the block copolymer without
vulcanization is also conceivable. The polar polymer part of the
block copolymer can, furthermore, itself serve as a filler in a
vulcanizate mixture and can be bound to the rubber matrix via the
polydiene part, or can merely be admixed.
[0093] It is, furthermore, possible to employ the block copolymers
as thermoplastic elastomers, the elastomer part being formed by the
polymerized polydienes and the thermoplastic part being formed by
the polymerized polar monomers.
[0094] The block copolymers can moreover be used as a blending
material for modification of thermoplastics, for example for
improving the impact strength. All thermoplastic materials are in
principle possible here, such as, for example, polycarbonates,
polyvinyl halides (e.g. PVC), polyamides, polyesters (e.g. PET,
PBT), polyethers (e.g. polypropylene oxide, polyethylene oxide),
polyacrylates and derivatives thereof (e.g PMMA), polyvinyl acetate
or polyoxymethylene.
EXAMPLES
[0095] All the polymerization reactions were carried out with
exclusion of air and moisture in an inert gas atmosphere using the
Schlenk technique. Argon was used as the inert gas.
[0096] The solvents n-hexane and cyclohexane are predried over
aluminum oxide/silica gel. .epsilon.-Caprolactone was obtained from
Aldrich, distilled before the polymerization and stored over a
molecular sieve 4 .ANG.. Neodymium(III) versatate was employed as a
0.1 M solution in n-hexane. DIBAH was purchased from Aldrich as a
0.1 M solution in a hexane fraction and employed in this form. EASC
was obtained as a pure substance from Witco. A 1.0 M EASC solution
in n-hexane was prepared from this. The technical-grade methanol
used for precipitation of the polymer originated from Kraemer &
Martin GmbH. Bayer AG provided the stabilizer
2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) (Vulkanox.RTM.
BKF).
[0097] The IR measurements were carried out on an IR spectrometer:
BOMEM-Arid Zone.TM.. The polymers were swollen in carbon disulfide
and then applied as thin films between two potassium bromide plates
and measured. The microstructure of the polybutadiene samples was
determined as described in the literature [M. Kraft in Struktur und
Absorptionsspektroskopie der Kunststoffe [Structure and Absorption
Spectroscopy of Plastics], VCH, Weinheim, 1973, p. 93, E. O.
Schmalz, W. Kimmer, Z. Anal. Chem. 1961, 181, 229.].
[0098] The polymer samples for the GPC were employed for the
measurement as tetrahydrofuran solutions with a concentration of 1
mg.multidot.ml.sup.-1. Before the measurement, the THF solutions
were filtered through a 0.2 .mu.m syringe filter. Calibration of
the GPC was carried out with 1,4-polybutadiene standards from
Fluka. The 1,4-polybutadiene standards of weights 2,000, 5,000,
20,000, 30,000, 66,000, 160,000, 200,000, 300,000 and 800,000 g
.multidot.mol.sup.-1 were used for the calibration. GPC unit:
Thermo Separation.RTM. Products. Column set: 3.times.PL gel 10 .mu.
Mixed-B. RI detector: Shodex RI 74. Eluent: THF; flow rate: 1.0
ml/min.
[0099] The conversions were determined gravimetrically; for this,
the polymer solutions were weighed after sampling (still with
solvent and monomer) and after drying (at 65.degree. C. in a vacuum
drying cabinet).
[0100] The polymers were separated in accordance with the principle
of demixing liquids [R. Kuhn, Macromol. Chem., 1976, 177, 1525;
1980, 181, 725]. In a 500 ml three-necked flask with a precision
glass stirrer and reflux condenser, 1.0 to 1.2 g of polymer were
heated under reflux for two hours with the addition of approx. 1 mg
of stabilizer (2,2'-methylene-bis(4-methyl-6-cyclohexylphenol)) in
a solvent mixture of 120 ml DMF and 180 ml MCH. The solution was
transferred to centrifuge glasses and centrifuged at a speed of
3,000 min.sup.-1 for 18 hours. The centrifugation was carried out
at 60.degree. C. for the first hour and then at 25.degree. C. The
upper phase was then sucked off with a pipette and the lower phase
was separated off from the middle phase via the bottom opening of
the centrifuge glass. All the phases were transferred to separate
glass flasks and the solvent was distilled off in vacuo. The
polymers which remained were dried in flasks overnight in a vacuum
drying cabinet at 125.degree. C. The individual percentage contents
by weight in the phases could be determined by weighing.
[0101] The NMR measurements were carried out on a nuclear magnetic
resonance spectrometer from Bruker, carrier frequency
(.sup.1H-NMR): 400.13 MHz, solvent CDCl.sub.3, standard:
tetramethylsilane (.delta.0.00 ppm), measurement temperature: 298
K.
[0102] Polymerization Experiments:
[0103] Autoclave bottles: In-house production of Bayer AG, 200 ml
thick-walled glass bottle with metal attachment, Teflon seal and
safety spring. 2 l glass autoclave: Buchi laboratory autoclave BEP
280 with U-shaped stirrer.
Examples 1 to 4
[0104] Polymerization Procedure (Autoclave):
[0105] Before the experiment, the autoclave (2 litre glass
autoclave, Buchi laboratory autoclave BEP 280) was heated
thoroughly in vacuo at 90.degree. C. and secured. By applying a
reduced pressure, 1 l of solvent was sucked into the autoclave
under argon via a cannula. The autoclave was temperature-controlled
at 60.degree. C. The addition of 1,3-butadiene was then carried out
via a septum. The catalyst reagents neodymium(III) versatate (0.1
molar solution in hexane), diisobutylaluminium hydride (0.1 molar
solution in hexane) and ethylaluminium sesquichloride (1 molar
solution in hexane) were then added. For the conversion/time
measurement series, samples of the reaction mixture were taken via
a globe stop-cock at certain intervals of time. The reaction of
these samples was stopped with MeOH (+Vulkanox.RTM.BKF). The
butadiene polymerization ran up to high conversions; the polar
comonomer (.epsilon.-caprolactone, methyl acrylate or vinyl propyl
ether) was then added. Further samples were then taken for the
conversion/time determination. At the end of the experiment, the
residual of the reaction mixture remaining in the autoclave was
poured into methanol/Vulkanox.RTM. BKF and the polymerization was
stopped in this manner. The polymer samples taken were dried
overnight at 65.degree. C. in a vacuum drying cabinet.
1TABLE 1 Examples 1 to 4 Example 1 2 3 4 Solvent cyclohexane
n-hexane n-hexane n-hexane Solvent 1000 ml 419 ml 436 ml 428 ml
Butadiene 190 g 47.7 g 44.4 g 46.6 g Nd (versatate).sub.3 0.4 mmol
0.17 mmol 0.17 mmol 0.17 mmol DIBAH 8 mmol 8.5 mmol 5.1 mmol 1.7
mmol EASC 0.27 mmol 0.17 mmol 0.17 mmol 0.17 mmol Butadiene
polymerization Temperature 60.degree. C. 60.degree. C. 60.degree.
C. 60.degree. C. Time 67 min 90 min 115 min 123 min Butadiene 95%
100% 100% 100% conversion Block copolymerization Active BR solution
1190 g 280.1 g 267.7 g 270.6 g Comonomer .epsilon.-caprolactone
.epsilon.-caprolactone .epsilon.-caprolactone
.epsilon.-caprolactone Comonomer 182 g 51.5 g 51.5 g 51.5 g
Temperature 60.degree. C. 60.degree. C. 60.degree. C. 60.degree. C.
Time 118 min 80 min 128 min 110 min Comonomer 59.9% 100% 100% 100%
conversion Polymer (total) 289 g 92.9 g 87.6 g 90.3 g
Example 1
Separation of the Copolymer + Analysis
[0106] The copolymer was separated by the method of demixing
liquids, it being possible for the block copolymer to be isolated
at the phase boundary with a total weight content of 10 wt. % of
the total polymer in the case of the experiment with the polar
monomer .epsilon.-caprolactone.
[0107] In the IR and in the .sup.1H-NMR, the block copolymer
isolated showed the signals of the two polymerized monomers:
[0108] Poly(.epsilon.-caprolactone) Content in the Block
Copolymer
[0109] IR: {tilde over (.upsilon.)}=713 (w), 732 (w), 754 (w), 842
(w), 934 (w), 962 (w), 1048 (m), 1067 (w), 1108 (m), 1191 (s), 1244
(s), 1295 (m), 1367 (m), 1397 (w), 1420 (w), 1437 (w), 1471 (w),
1634 (w), 1726 (s), 2866 (m), 2944 (s).
[0110] .sup.1H-NMR (CDCl.sub.3): .delta.=1.37 (m, 2H, 4-CH.sub.2),
1.65 (m, 4H, 3.5-CH.sub.2), 2.31 (t, .sup.3J.sub.HH=7.5 Hz, 2H,
O-COCH.sub.2), 4.06 (t, .sup.3J.sub.HH=6.7 Hz, 2H,
COOCH.sub.2).
[0111] cis-1,4-Poly(butadiene) Content in the Block Copolymer
[0112] IR: {tilde over (.upsilon.)}=737 (s), 778 (w), 911 (w), 965
(w), 993 (m), 1019 (w), 1093 (w), 1161 (w), 1238 (w), 1260 (w),
1308 (m), 1402 (m), 1432 (s), 1451 (s), 1656 (s), 1738 (w), 2852
(s), 2938 (S), 3006 (s).
[0113] .sup.1H-NMR (CDCl.sub.3):.delta.=2.08 (m, 4H,
CH.sub.2).delta.5.38 (m, 2H, CH).
[0114] To rule out the possibility that only two homopolymers
(polybutadiene and poly-.epsilon.-caprolactone) are formed in the
polymerization, after the separation with demixing liquids a GPC
analysis of the fractions obtained was carried out, this showing
that the GPC signal of the block copolymer is in the highest
molecular weight range.
[0115] The average molecular weight was approx. 300,000 g/mol, the
T.sub.g value was -103.degree. C. The diene content was 30 wt. %,
the content of polar monomers was 70 wt. %. The cis-1,4 content in
the diene block was 96%.
[0116] Further evidence of the formation of block copolymers was
obtained from the morphology of the polymer. For this, the block
copolymer was analysed by transmission electron microscopy (TEM)
(FIG. 2) and the morphology thereof was compared with a
cis-1,4-polybutadiene/poly-.epsilo- n.-caprolactone blend which was
prepared (FIG. 1). For this, 0.90 g poly-.epsilon.-caprolactone and
0.55 g cis-1,4-polybutadiene were dissolved in 1 l CHCl.sub.3 by
stirring in a 2 l round-bottomed flask. The polymer mixture was
precipitated in 500 ml MeOH (+0.1 g Vulkanox.RTM. BKF) and then
dried in a vacuum drying cabinet at 50.degree. C.
Comparative Examples 5 to 7
[0117] Polymerization Procedure (Autoclave):
[0118] The polymerization was carried out analogously to Examples 1
to 4. The reaction quantities and the results are summarized in
Table 2.
2TABLE 2 Comparative examples 5 to 7 Example 5 6 7 Solvent n-hexane
cyclohexane cyclohexane Solvent 434 ml 1000 ml 1000 ml Butadiene
46.5 g 120 g 120 g Nd (versatate).sub.3 0.17 mmol 0.2 mmol 0.2 mmol
DIBAH 8.5 mmol 4 mmol 4 mmol EASC 0.17 mmol 0.13 0.13 Butadiene
polymerization Temperature 60.degree. C. 60.degree. C. 60.degree.
C. Time 120 min 83 min 260 min Butadiene 100% 93% 99% conversion
Block copolymerization Active BR solution 275.0 g 1200 g 1200 g
Comonomer octamethyl methyl acrylate vinyl propyl
cyclotetrasiloxane ether Comonomer 72.1 g 190 g 200 g Temperature
60.degree. C. 60.degree. C. 60.degree. C. Time 168 min 252 min 200
min Comonomer not detectable not detectable not detectable
conversion Polymer (total) 37.5 g 112 g 119 g
* * * * *