Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-12-30
2001-09-11
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S138000, C526S139000, C526S142000, C526S169100, C526S335000, C526S337000, C502S117000
Reexamination Certificate
active
06288183
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a process for polymerizing conjugated dienes. More particularly, the process of the present invention employs a catalyst composition that is formed by combining an iron-containing compound, a hydrogen phosphite, and a blend of two or more sterically distinct organoaluminum compounds. By utilizing this catalyst composition, the characteristics, such as the melting temperature, of the resulting conjugated diene polymers can be manipulated. The preferred embodiments of the present invention are directed toward a process for polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene whereby the melting temperature of the resulting polymer can be controlled.
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 rubber.
Syndiotactic 1,2-polybutadiene can be made by solution, emulsion or suspension polymerization. The physical properties of syndiotactic 1,2-polybutadiene are largely determined by its melting temperature and molecular weight. 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. Accordingly, there is a need for means to regulate the melting temperature and molecular weight of syndiotactic 1,2-polybutadiene.
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.
The following two cobalt-based catalyst systems are well known for the preparation of syndiotactic 1,2-polybutadiene on a commercial scale: (1) a system containing cobalt bis(acetylacetonate), triethylaluminum, water, and triphenylphosphine (U.S. Pat. Nos. 3,498,963 and 4,182,813), and (2) a system containing cobalt tris(acetylacetonate), triethylaluminum, and carbon disulfide (U.S. Pat. No. 3,778,424). These cobalt-based catalyst systems also have disadvantages.
The first cobalt catalyst system referenced above 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 cobalt catalyst system referenced above uses carbon disulfide as one of the catalyst components. Because of its low flash point, obnoxious smell, high volatility, and toxicity, carbon disulfide 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 very high melting temperature of about 200-210° C., which makes it difficult to process the polymer. Although the melting temperature of the syndiotactic 1,2-polybutadiene produced with this cobalt catalyst system can be reduced by employing a catalyst modifier as a fourth catalyst component, the presence of this catalyst modifier has adverse effects on the catalyst activity and polymer yields. Accordingly, many restrictions are required for the industrial utilization of these cobalt-based catalyst systems.
Coordination catalyst systems based on iron-containing compounds, such as the combination of iron(III) acetylacetonate and triethylaluminum, have been known for some time, but they have shown very low catalytic activity and poor stereoselectivity for the polymerization of 1,3-butadiene. The product mixture often contains oligomers, low molecular weight liquid polymers, and partially crosslinked polymers. Therefore, these iron-based catalyst systems have no industrial utility.
Because syndiotactic 1,2-polybutadiene is useful 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 activity and stereoselectivity for polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene. It would be additionally advantageous if that catalyst system was versatile enough to control the melting temperature and molecular weight of the polymerization product.
SUMMARY OF THE INVENTION
In general, the present invention provides a process for preparing conjugated diene polymers with desired characteristics comprising the step of polymerizing conjugated diene monomers in the presence of a catalytically effective amount of a catalyst composition formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) a blend of two or more sterically distinct organoaluminum compounds.
The present invention also provides a method for controlling the melting temperature of a crystalline conjugated diene polymer that is prepared by polymerizing conjugated diene monomers with a catalyst composition that is formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) a blend of two or more sterically distinct organoaluminum compounds, the method comprising the steps of selecting at least one sterically hindered organoaluminum compound; selecting at least one sterically non-hindered organoaluminum compound; combining the selected organoaluminum compounds to form ingredient (c) of the catalyst composition; and thereafter polymerizing the conjugated diene monomers with the catalyst composition.
The present invention also provides a catalyst composition formed by a process comprising the step of combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) a blend of two or more sterically distinct organoaluminum compounds.
Advantageously, the catalyst composition utilized in the present invention has very high catalytic activity and stereoselectivity for polymerizing conjugated diene monomers such as 1,3-butadiene. This activity and selectivity, among other advantages, allows conjugated diene polymers, such as syndiotactic 1,2-polybutadiene, to be produced in very high yields with low catalyst levels after relatively short polymerization times. Significantly, the catalyst composition of this invention is very versatile. By blending sterically distinct organoaluminum compounds, it is possible to produce crystalline conjugated diene polymers, such as syndiotactic 1,2-polybutadiene, with a wide range of melting temperatures and molecular weights, thus eliminating the need to add a melting temperature regulator or a molecular weight regulator that adversely affects the catalyst activity and the polymer yield. In addition, the catalyst composition utilized in this invention does not contain carbon disulfide. Therefore, the toxicity, objectionable smell, dangers, and expense associated with the use of carbon disulfide are eliminated. Further, the catalyst composition utilized in this invention is iron-based, and iron compounds are generally stable, inexpensive, relatively innocuous, and readily available. Furthermore, the catalyst composition utilized in this invention has a high catalytic activity in a wide variety of solvents including the environmentally-preferred nonhalogenated solvents such as aliphatic and cycloaliphatic hydrocarbons.
Other advantages and features of the present inventio
Bridgestone Corporation
Burleson David G.
Rabago R.
Reginelli Arthur M.
Wu David W.
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