Note: Descriptions are shown in the official language in which they were submitted.
CA 02399158 2002-08-16
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Process for decolorizing diene polymers
Field of the invention
This invention relates to a process for decolorizing polymers comprising
s repeating units derived from at least one conjugated diene monomer and
optionally repeating units derived from at least one vinyl aromatic monomer.
In
a more specific aspect, the present invention relates to a process for
decolorizing polymers comprising repeating units derived from at least one
conjugated diene monomer and optionally repeating units derived from at least
io one vinyl aromatic monomer by treating them with at least one water soluble
mineral acid and/or organic acid in the presence of at least one
compatibilizer
that enhances the interaction of the polymer chain with the acid compound.
Backclround of the invention
is Most of the commercially available elastomeric diene polymers or diene-
vinyl aromatic copolymers are prepared by the polymerization of conjugated
diene monomers and optionally vinyl aromatic monomers in the presence of an
alkali metal catalyst system. This results in elastomers with good mechanical
properties. However, the catalyst system leads to unwanted coloration of the
2o product and results in yellow-brownish rubbers. It is very important, not
only for
appearance but also for the uses of the polymers with e.g. foodstuffs, to make
this yellowish color disappear and to obtain transparent and colorless
(co)polymers.
Many methods have been established to effect the desired decoloration.
2s US-4,877,863 teaches a process for decolorizing polymers of the vinyl
aromatic-conjugated diene block copolymer type by using various
thiocarboxylic acids, such as octylthiopropionic acid and 3,3'-thiodipropionic
acid. However, this document is silent about using a compatibilizer.
US-2,893,982 discloses a process for decolorizing hydrogenated
3o butadiene polymers with a saturated carboxylic acid. However, this document
does not disclose the advantage of using a compatibilizer.
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EP-A1-0 084 793 is relating to a treatment of copolymers with
dicarboxylic acids. This document also does not mention the use of a
compatibilizer.
Summary of the invention
s It is an object of the present invention to provide a process for
decolorizing polymers comprising repeating units derived from at least one
conjugated diene monomer and optionally repeating units derived from at least
one vinyl aromatic monomer. A further object of the present invention is to
provide a process for decolorizing polymers comprising repeating units derived
to from at least one conjugated diene monomer and optionally repeating units
derived from at least one vinyl aromatic monomer by treating them with at
least
one water-soluble mineral acid and/or organic acid in the presence of at least
one compatibilizer that enhances the interaction of the polymer chain with the
acid compound. Another object of the present invention is to provide a process
Is for decolorizing polymers comprising repeating units derived from at least
one
conjugated diene monomer and optionally repeating units derived from at least
one vinyl aromatic monomer by treating them with at least one water soluble
mineral acid and/or organic acid in the presence of at (east one
compatibilizer
selected from the group consisting of a surfactant, a phase-transfer-catalyst
or
ao a mixture therof.
Detailed description of the invention
The process of the present invention is applicable to homo- and
copolymers of the thermoplasic and the elastomeric kind which are prepared by
2s the polymerization in solution, suspension or emulsion of at least one
diene
monomer and optionally at least one vinyl aromatic monomer and optionally
further anionically copolymerizable monomers in the presence of
catalysts/initiators, such as alkali metals and alkali metal compounds.
Suitable diene monomers are all conjugated diene monomers known to
3o the skilled in the art. Preferred conjugated diene monomers are C4-C14
conjugated dienes, such as butadiene, isoprene, dimethylbutadienediene,
piperylene, and 3-butyl-1,3-octadiene.
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Suitable vinyl aromatic monomers are all vinyl aromatic monomers
known to the skilled in the art. Preferred vinyl aromatic monomers are C8-C4o
vinyl aromatic monomers, such as styrene, alpha-methylstyrene,
vinylnaphthalene, and alkyl substituted styrenes.
s Preferred polymers to be treated by the process of the invention
comprise butadiene rubber, and random or block- styrene-butadiene
copolymers.
The polymerization is typically performed in the presence of an inert
diluent and/or solvent, such as a hydrocarbon or substituted hydrocarbon.
lo Suitable diluents/solvents will be apparent to the skilled in the art.
Usually the
polymerization is performed at a temperature in the range of from -100
°C to
150 °C. It might be advantageous to polymerize in the presence of a
modifier
to control the molecular weight and/or the microstructure of the copolymer.
Suitable modifiers are well known to the skilled in the art and comprise
is compounds such as alcohols or ethers. Typical of the polymerization
processes that lead to polymers of the type suitable for treatment are
published
US-3,862,100, US-5,595,951, US-5,393,843, WO-00/22004, and WO-
02/008300 which are hereby incorporated herein by reference with regard to
jurisdictions allowing for this method.
2o Suitable water soluble organic acids are well known to the skilled in the
art. Preferred are organic acids having in the range of from 2 - 12 carbon
atoms and in the range of from 1-3 carboxylic groups, such as acetic acid,
propionic acid, butyric acid, pentanoic acid, tartatric acid, citric acid,
heteroatom
containing organic acids, such as thiocarboxylic acids, and thiodicarboxylic
2s acids. Suitable water soluble mineral acids are apparent to the skilled in
the
art. Preferred water soluble mineral acids are boric acid, phosphoric acid,
and
sulphuric acid.
In some cases it might be advantageous to use a mixture of several
mineral and/or organic acids.
3o It is advantageous to treat the polymers immediately after the
polymerization is completed. As the polymerization usually takes place in an
unpolar solvent, said water soluble organic and/or mineral acids loose
effectivity due to an inherent inmiscibility with the organic phase in which
the
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polymer is residing. Without wishing to be bound to this theory, it is
believed
that the color is a result of remainders of the initiator/catalyst that
renders the
polymer/polymer cement basic and by the invention the reaction between the
acidic short-stop water and the basic cement is improved. The usage of said
s compatibilizer will enhance the interaction between polymer and acid.
It might be advantageous to conduct the inventive process in the
presence of a pH buffer such as monosodium citrate.
It is preferred to use at least one surfactant and/or at least on phase
transfer catalyst as compatibilizer. Suitable surfactants are all surfactants
that
io will not be affected by the conditions present during decoloration.
Preferred are
non-ionic soaps such as Tween~ 60 available from ICI Americas Inc., TamoIC~
731A available from Rohm and Haas Company. Suitable phase transfer
catalysts are all phase-transfer catalysts (PTC) that will not be affected by
the
conditions present during decoloration. A preferred PTC is neodecanoic acid,
is e.g. available from Sun Chemical.
The inventive process provides transparent and colorless polymers
which are well suited for the production of shaped articles, such as
telephones,
television and computer, typewriter casings, bowling balls, and linings for
refrigerators.
2o The invention is further illustrated by the following examples:
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EXAMPLES
Chemicals
Hexane - Phillips 66 Company - conditioned with 3A, 4A and 13X sieves
s before use
1,3 butadiene - Bayer Rubber Inc. - conditioned with 3A sieves before
use
1,2 butadiene - Bayer Rubber inc. - conditioned with 3A sieves before
use
io n-butyl lithium - Aldrich Chemical Company Inc. - diluted to appropriate
concentration
Octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (Irganox~ 1076) -
Ciba Specialty Chemicals Canada Inc. - diluted to appropriate concentration
Trisnonylpheny! phosphite (TNPP) (Doverphos~ HiPure 4HR) - Dover
is Chemical Corporation - diluted to appropriate concentration
Citric acid - Aldrich Chemical Company Inc. - diluted to appropriate
concentration
Monosodium citrate - Aldrich Chemical Company Inc. - diluted to
appropriate concentration
2o Boric Acid - Aldrich Chemical Company Inc. - diluted to appropriate
concentration
Carbonic acid - made in house - bubbled water with C02 for 10 min until
pH reached 4
3,3 Thiodipropionic acid - Aldrich Chemical Company Inc. - diluted to
2s appropriate concentration
Acetic acid - Aldrich Chemical Company Inc. - diluted to appropriate
concentration
Phosphoric acid - Aldrich Chemical Company Inc. - diluted to
appropriate concentration
3o Neodecanoic Acid - Sun Chemical - diluted to appropriate concentration
Polyoxyethylene (20) sorbitan monosterate (Tween 60) - ICI America -
diluted to appropriate concentration
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Sodium salt of isobutylene/methacrylate copolymer (Tamol 731 A)-
Rohm and Haas Company - diluted to appropriate concentration
Styrene - Aldrich Ghemical Company Inc. - conditioned with alumina
before use
s 1-tent butoxy-2-ethoxyethane - Aldrich Chemical Company Inc. -
conditioned with 3A and 4A sieves before use
Exam-Ales 1-23
A bottle polymerization was carried out by adding hexane (195 g) and
Io 1,3 butadiene (40g) to a clean dry bottle, using a top loading balance and
schlenck techniques. 1,2 butadiene (0.89mMoles) was added via gas-tight
syringe. The sample was shaken for 1 min in a shaker tray. N-butyl lithium
(0.25-0.28 mMoles) was added via syringe to the caged bottle. Immediately
after injection of the catalyst, the caged bottles were placed in a
polymerization
Is bath equilibrated to 70°C. The bottles were tumble rotated in the
constant
temperature bath for 3 hours. The polymerization were short stopped using
various solutions (see Table 1 - the amount of acid and compatibilizer was
added as aqueous solution in distilled water) and tumbled for an additional 10
min. Antioxidant Irganox~ 1076 (0.25phr) and TNPP (0.70phr) was added and
2o the bottles were tumbled for additional 15 minutes. The content of the
bottle
was poured into a glass jar and the cement-water mixture was agitated
vigorously using an air-powered stirrer for 45 min. Then, the water was
changed and the cement was steam coagulated using a steam rod placed into
cement and water. The solid was milled at 100°-105°C with mill
gap of
2s 0.25mm+/-0.05mm until transparent and then dried in a vacuum oven @
70°C.
Table 1
Exp. Acid compatibilizer Average
Yellowness
Index
1 * none none 9.5
2* 0.15 mmol of citric none 6.0
acid
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Exp. Acid compatibilizer Average
Yellowness
Index
3 0.15 mmol of citric 0.03 phr of Tamol~ 4.8
acid 731 A
4 0.15 mmol of citric 0.03 phr of Tween~ 1.8
acid 60
0.15 mmol of citric 300 ppm of 4.0
acid
Neodecanoid acid
6 0.15 mmol of citric 0.03 phr of Tamol~ 0.91
acid 731 A
300 ppm of
Neodecanoid acid
7 0.15 mmol of citric 0.03 phr of Tween~ 0.95
acid 60
300 ppm of
Neodecanoid acid
8* 25 ml of carbonic none 6.75
acid
9 25 ml of carbonic 300 ppm of Neodecanoid3.6
acid
Acid
25 ml of carbonic 0.03 phr of Tamol~ 2.16
acid 731 A
300 ppm of
Neodecanoid acid
11 25 ml of carbonic 0.03 phr of Tamol~ 5.2
acid 731 A
12 25 ml of carbonic 0.03 phr of Tween~ 1.8
acid 60
300 ppm of
Neodecanoid acid
13 25 ml of carbonic 0.03 phr of Tween~ 3.25
acid 60
14* 0.25 mmol of boric none 8.19
acid
0.25 mmol of boric 0.03 phr of Tamol~ 4.63
acid 731 A
16 0.25 mmol of boric 0.03 phr of Tween~ 4.77
acid 60
17* 0.25 mmol of 3,3- none 2.4
thiodipropionic acid
18 0.25 mmol of 3,3- 0.03 phr of Tamol~ 0.76
731 A
thiodipropionic acid
19 0.25 mmol of 3,3- 0.03 phr of Tween~ 0.62
60
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Exp. Acid compatibilizer Average
Yellowness
Index
thiodipropionic acid
20* 0.3 mmol of acetic none 6.1
acid
21 0.3 mmol of acetic 300 ppm of 3.1
acid
Neodecanoid acid
22* 0.33 mmol of phosphoricnone 0.62
acid
23 0.33 mmol of phosphoric300 ppm of 0.41
acid Neodecanoid acid
* denotes a comparative example
Examples 24-34
s A bottle polymerization was carried out by adding hexane (200 g),
styrene (10g) and 1,3 butadiene (30g) to a clean dry bottle, using a top
loading
balance and schlenck techniques. 1-tent-butoxy-2-ethoxyethane
(2.67mMoles) was added via syringe. The bottle was shaken for 1 min in a
shaker tray. N-butyl lithium (0.79mMoles) was added via syringe to the caged
to bottle. Immediately after injection of the catalyst, the caged bottles were
placed
in the polymerization bath equilibrated to 70°C. The bottles were
tumble
rotated in a constant temperature bath for 3 hours. The polymerizations were
short stopped using various solutions (see table 2 - the amount of acid and
compatibilizer was added as aqueous solution in distilled water) and tumbled
is for an additional 10 min. Antioxidant Irganox~ 1076 (0.25phr) and TNPP
(0.70phr) was added and the bottles were tumbled for additional 15 minutes.
The content of the bottle was poured into a glass jar and the cement-water
mixture was agitated vigorously using an air-powered stirrer for 45 min. Then,
the water was changed and the cement was steam coagulated using a steam
2o rod placed into cement and H20. The solid was milled at 100°-
105°C with mill
gap of 0.25mm+/-0.05mm until transparent and then dried in a vacuum oven @
70°C
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The analytical method is the Yellowness Index (Y1), measured by the
Hunter Yellowness Index Meter (HunterLab MiniscanT"" XE Plus). This method
determines the degree of yellowness (or change of degree of Yellowness)
under day light illumination of homogeneous, non-fluorescent, nearly
colourless
s transparent or opaque plastic or rubber.
The rubber samples from Experiments 1-35 were cut in a 1 inch thick
slice, and the instrument lens opening was placed in contact with the surface
of
the sample directly. Yellowness Index (Y1) was determined using ASTM
method E-313-98.
to
Table 2
Exp. Acid compatibilizer Average
Yellowness
Index
24* none none 10.2
25* 0.2 mmol of citric none 7.86
acid
26 0.2 mmol of citric 0.03 phr of Tamol~ 6.11
acid 731 A
27 0.2 mmol of citric 0.03 phr of Tween~ 5.63
acid 60
28* 0.25 mmol of 3,3- none 7.18
thiodipropionic
acid
29 0.25 mmol of 3,3- 0.03 phr of Tamol~ 5.66
731 A
thiodipropionic
acid
30 0.25 mmol of 3,3- 0.03 phr of Tween~ 2.85
60
thiodipropionic
acid
31 0.28 mmol of citricnone 8.33
* acid
32 0.28 mmol of citric300 ppm of 3.33
acid
Neodecanoid acid
33* 0.79 mmol of none 7.86
phosphoric acid
34 0.79 mmol of 300 ppm of 2.18
phosphoric acid Neodecanoid acid
* denotes a comparative example
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Example 35
Example 21 was repeated but additionally 0.3 mmoles of monosodium
citrate as a pH-buffer were added. The average yellowness index was 0.62
s compared to 3.1 in Example 21.
The examples show that the use of acids in combination with
compatibilizers result in an improved neutralization step and an elimination
of
color formation in the final product. As demonstrated in Example 35 further
to addition of a buffer can further reduce the color formation.
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