CA2399158A1 - Process for decolorizing diene polymers - Google Patents

Abstract

The 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 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.

Description

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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.

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.

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 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:

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 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 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 thiodipropionic acid 19 0.25 mmol of 3,3- 0.03 phr of Tween~ 0.62 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

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 thiodipropionic acid 30 0.25 mmol of 3,3- 0.03 phr of Tween~ 2.85 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 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.
P(~S 1119 CA 10

Claims (8)

1. A process for decolorizing a polymer comprising repeating units derived from at least one conjugated diene monomer and optionally repeating units derived from at least one vinyl aromatic monomer and optionally further copolymerizable monomers by treating them with at least one water-soluble mineral acid and/or organic acid in the presence of at least one compatibilizer.

2. A process according to claim 1, wherein the compatibilizer is a surfactant or a phase transfer catalyst.

3. A process according to claim 1 or 2, wherein the polymer is butadiene rubber, a random styrene-butadiene copolymer or a styrene-butadiene block-copolymer.

4. A process according to any of claims 1-3, wherein the process is conducted immediately after the polymerization has been completed.

5. A process according to any of claims 1-4, wherein the mineral acid is boric acid or phosphoric acid.

6. A process according to any of claims 1-4, wherein the organic acid is citric acid, carbonic acid, acetic acid, or thio dipropionic acid.

7. A process according to any of claims 1-6, wherein the compatibilizer is neodecanoic acid and/or a non-ionic soap.

8. A process according to any of claims 1-7, wherein the process is conducted in the presence of a pH-buffer.