Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-02-19
2002-10-15
Wood, Elizabeth D. (Department: 1755)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S126000, C526S127000, C526S135000, C526S136000, C526S145000, C526S160000, C526S169000, C526S170000, C526S193000, C526S335000, C502S152000, C502S153000, C502S154000, C502S155000, C502S158000, C502S162000, C502S171000
Reexamination Certificate
active
06465585
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a chromium-based catalyst composition for polymerizing conjugated dienes such as 1,3-butadiene into polymers such as syndiotactic 1,2-polybutadiene.
BACKGROUND OF THE INVENTION
Syndiotactic 1,2-polybutadiene is a crystalline thermoplastic resin that has a stereoregular structure in which the side-chain vinyl groups are located alternately on the opposite sides in relation to the polymeric main chain. Syndiotactic 1,2-polybutadiene is a unique material that exhibits the properties of both plastics and rubber, and therefore it has many uses. For example, films, fibers, and various molded articles can be made from syndiotactic 1,2-polybutadiene. It can also be blended into and co-cured with natural or synthetic rubbers in order to improve the properties thereof. Generally, syndiotactic 1,2-polybutadiene has a melting temperature within the range of about 195° C. to about 215° C., but due to processability considerations, it is generally desirable for syndiotactic 1,2-polybutadiene to have a melting temperature of less than about 195° C.
Various transition metal catalyst systems based on cobalt, titanium, vanadium, chromium, and molybdenum for the preparation of syndiotactic 1,2-polybutadiene have been reported. The majority of these catalyst systems, however, have no practical utility because they have low catalytic activity or poor stereoselectivity, and in some cases they produce low molecular weight polymers or partially crosslinked polymers unsuitable for commercial use.
Two cobalt-based catalyst systems are known for preparing syndiotactic 1,2-polybutadiene. The first comprises a cobalt compound, a phosphine compound, an organoaluminum compound, and water. This catalyst system yields syndiotactic 1,2-polybutadiene having very low crystallinity. Also, this catalyst system develops sufficient catalytic activity only when halogenated hydrocarbon solvents are used as the polymerization medium, and halogenated solvents present toxicity problems.
The second catalyst system comprises a cobalt compound, an organoaluminum compound, and carbon disulfide. Because carbon disulfide has a low flash point, obnoxious smell, high volatility, and toxicity, it is difficult and dangerous to use and requires expensive safety measures to prevent even minimal amounts escaping into the atmosphere. Furthermore, the syndiotactic 1,2-polybutadiene produced with this cobalt catalyst system has a melting temperature of about 200-210° C., which makes it difficult to process. Although the melting temperature of the syndiotactic 1,2-polybutadiene produced with this cobalt catalyst system can be reduced by employing a catalyst modifier, the use of this catalyst modifier has adverse effects on the catalyst activity and polymer yields.
Coordination catalyst systems based on chromium-containing compounds, such as the combination of chromium(III) acetylacetonate and triethylaluminum are known. But, they have very low catalytic activity and poor stereoselectivity for polymerizing conjugated dienes. The product mixture often contains oligomers, low molecular weight liquid polymers or partially crosslinked polymers. Therefore, these catalyst systems have no industrial utility.
For example, the prior art discloses a process for polymerizing 1,3-butadiene into amorphous 1,2-polybutadiene by using a catalyst system comprising a soluble chromium(III) compound, a trialkylaluminum compound, and a dialkyl hydrogen phosphite. The resulting polymer product has an extremely high molecular weight and is partially a gel.
The prior art also discloses a method for preparing elastomers by polymerizing trans-1,3-pentadiene and isoprene in the presence of a catalyst system comprising a soluble chromium compound, a trialkylaluminum compound, and a dihydrocarbyl hydrogen phosphite.
Because syndiotactic 1,2-polybutadiene is a useful product and the catalysts known heretofore in the art have many shortcomings, it would be advantageous to develop a new and significantly improved catalyst composition that has high catalytic activity and stereoselectivity for polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene.
SUMMARY OF THE INVENTION
The present invention provides a catalyst composition that is the combination of or the reaction product of ingredients comprising (a) a chromium-containing compound, (b) an organomagnesium compound, and (c) a silyl phosphonate.
The present invention also includes a catalyst composition formed by a process comprising the steps of combining (a) a chromium-containing compound, (b) an organomagnesium compound, and (c) a silyl phosphonate.
The present invention further includes a process for forming conjugated diene polymers comprising the step of polymerizing conjugated diene monomers in the presence of a catalytically effective amount of a catalyst composition formed by combining (a) a chromium-containing compound, (b) an organomagnesium compound, and (c) a silyl phosphonate.
Advantageously, the catalyst composition of the present invention does not contain carbon disulfide. Therefore, the toxicity, objectionable smell, dangers, and expense associated with the use of carbon disulfide are eliminated. In addition, the chromium-containing compounds are generally stable, inexpensive, and readily available. Further, the catalyst composition has high catalytic activity in a wide variety of solvents including the environmentally-preferred nonhalogenated solvents such as aliphatic and cycloaliphatic hydrocarbons. Furthermore, the syndiotactic 1,2-polybutadiene produced with the catalyst composition has a higher melting temperature and higher syndiotacticity than the syndiotactic 1,2-polybutadiene produced with the chromium-based catalyst systems of the prior art.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The catalyst composition is formed by combining (a) a chromium-containing compound, (b) an organomagnesium compound, and (c) a silyl phosphonate. In addition to the three catalyst ingredients (a), (b), and (c), other organometallic compounds or Lewis bases can also be added, if desired.
Various chromium-containing compounds or mixtures thereof can be employed as ingredient (a) of the catalyst composition. Preferably, these chromium-containing compounds are soluble in a hydrocarbon solvent such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons. Hydrocarbon-insoluble chromium-containing compounds, however, can be suspended in the polymerization medium to form the catalytically active species and are therefore also useful.
The chromium atom in the chromium-containing compounds can be in various oxidation states including, but not limited to, the 0, +2, +3, +4, and +6 oxidation states. Divalent chromium compounds (also called chromous compounds), wherein the chromium atom is in the +2 oxidation state, and trivalent chromium compounds (also called chromic compounds), wherein the chromium atom is in the +3 oxidation state, are preferred. Suitable chromium-containing compounds include, but are not limited to, chromium carboxylates, chromium organophosphates, chromium organophosphonates, chromium organophosphinates, chromium carbamates, chromium dithiocarbamates, chromium xanthates, chromium &bgr;-diketonates, chromium alkoxides or aryloxides, chromium halides, chromium pseudo-halides, chromium oxyhalides, and organochromium compounds.
Suitable chromium carboxylates include chromium(II) formate, chromium(III) formate, chromium(II) acetate, chromium(III) acetate, chromium(Il) acrylate, chromium(III) acrylate, chromium(Il) methacrylate, chromium(III) methacrylate, chromium(II) valerate, chromium(III) valerate, chromium(II) gluconate, chromium(III) gluconate, chromium(II) citrate, chromium(III) citrate, chromium(II) fumarate, chromium(III) fumarate, chromium(II) lactate, chromium(III) lactate, chromium(II) maleate, chromium(III) maleate, chromium(II) oxalate, chromium(III) oxalate, chromium(II) 2-ethylhexanoate, chromium(III) 2-ethylhexanoate, chromium(II) neodecanoate, chromium(III) neodecano
Bridgestone Corporation
Wood Elizabeth D.
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