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
2002-06-04
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S135000, C526S169100, C526S335000
Reexamination Certificate
active
06399732
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed toward a process for producing conjugated diene polymers by polymerizing conjugated diene monomers in the presence of an iron-based catalyst composition that is formed by combining an iron-containing compound, a hydrogen phosphite, and an organoaluminum compound. The preferred embodiments are directed toward the synthesis of polybutadiene polymers.
BACKGROUND OF THE INVENTION
Polybutadiene is the most common conjugated diene polymer. One type of polybutadiene is syndiotactic 1,2-polybutadiene, which 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.
Syndiotactic 1,2-polybutadiene can be made by solution, emulsion, or suspension polymerization. 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.
The following two cobalt-based catalyst systems are well known for the preparation of syndiotactic 1,2-polybutadiene on a commercial scale: (1) a catalyst system containing cobalt bis(acetylacetonate), triethylaluminum, water, and triphenylphosphine (U.S. Pat. Nos. 3,498,963 and 4,182,813), and (2) a catalyst system containing cobalt tris(acetylacetonate), triethylaluminum, and carbon disulfide (U.S. Pat. No. 3,778,424). These cobalt-based catalyst systems also have serious 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.
Another useful polybutadiene is amorphous high-vinyl polybutadiene, which is a rubbery elastomer that has a stereoirregular or atactic structure in which the vinyl groups as side chains are located randomly on the opposite sides in relation to the polymeric main chain. Amorphous high-vinyl polybutadiene rubber is utilized in a variety of applications. For example, amorphous high-vinyl polybutadiene rubber is useful in tire tread compositions because it provides both good traction and low rolling resistance.
Amorphous high-vinyl polybutadiene is commonly produced by anionic polymerization utilizing alkyllithium initiators which are modified with Lewis bases such as chelating diamines, ethers, tertiary amines, acetals, ketals, and compounds of similar structures. The vinyl content of polybutadiene prepared utilizing such Lewis base modifiers decreases drastically as the polymerization temperature is increased. For this reason, it is difficult to prepare high-vinyl polybutadiene at high polymerization temperatures utilizing Lewis base modifiers. Because high polymerization temperatures generally promote a higher polymerization rate, it is often desirable to utilize moderately high temperatures in commercial polymerizations in order to maximize productivity as well as to reduce the production cost.
Japanese patent JP-A-7306939 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 contains a portion of gel.
U.S. Pat. No. 4,912,182 discloses a process for synthesizing amorphous high-vinyl polybutadiene by polymerizing 1,3-butadiene in the presence of a catalyst system comprising a molybdenum-containing compound prepared by modifying molybdenum pentachloride, molybdenum trichloride, or molybdenum tetrachloride with an alkyl carboxylic acid or an aryl carboxylic acid; and an aluminum-containing compound prepared by modifying a trialkylaluminum compound with 2-allylphenol. This molybdenum-based catalyst system has only moderate activity, and the polymer yields are about 75%.
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 conjugated dienes. 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 conjugated diene polymers are useful, and since the catalysts known heretofore in the art for polymerizing conjugated dienes 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 conjugated diene monomers, especially 1,3-butadiene, into conjugated diene polymers such as syndiotactic 1,2-polybutadiene and amorphous high-vinyl polybutadiene.
SUMMARY OF THE INVENTION
In general, the present invention provides a process for preparing conjugated diene polymers comprising the step of polymerizing conjugated diene monomers in the presence of a catalytically effective amount of a catalyst composition that is formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) an organoaluminum compound.
The present invention also provides a process for preparing amorphous high-vinyl polybutadiene rubber comprising the step of polymerizing 1,3-butadiene in the presence of a catalytically effective amount of a catalyst composition that is formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) an organoaluminum compound, where the molar ratio of the organoaluminum compound to the iron-containing compound is relatively low.
The present invention further provides a process for preparing syndiotactic 1,2-polybutadiene comprising the step of polymerizing 1,3-butadiene in the presence of a catalytically effective amount of a catalyst composition that is formed by combining (a) an iron-containing compound, (b) a hydrogen phosphite, and (c) an organoaluminum compound, where the molar ratio of the organoaluminum compound to the ir
Bridgestone Corporation
Burleson David G.
Reginelli Arthur M.
Teskin Fred
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