Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
1998-09-14
2001-04-24
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S075000, C526S160000, C526S943000, C526S352000, C502S117000, C502S153000
Reexamination Certificate
active
06221981
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a new type of solid particulate metallocene catalyst system useful for the polymerization and/or copolymerization of olefins. The invention is also related to a process for conducting polymerization of olefins using the inventive solid metallocene catalyst system and to the polymers and films produced thereby.
BACKGROUND OF THE INVENTION
The term “Metallocene” as used herein refers to a derivative of cyclopentadienylidene which is a metal derivative containing at least one cyclopentadienyl component which is bonded to a transition metal. The transition metal is selected from Groups IVB, VB, and VIB, preferably IVB and VIB. Examples include titanium, zirconium, hafnium, chromium, and vanadium. A number of metallocenes have been found to be useful for the polymerization of olefins. Generally, the more preferred catalysts are metallocenes of Zr, Hf, or Ti.
Generally, in order to obtain the highest activity from metallocene catalysts, it has been necessary to use them with an organoaluminoxane cocatalyst, such as methylaluminoxane. This resulting catalyst system is generally referred to as a homogenous catalyst system since at least part of the metallocene or the organoaluminoxane is in solution in the polymerization media. These homogenous catalysts systems have the disadvantage that when they are used under slurry polymerization conditions, they produce polymer which sticks to reactor walls during the polymerization process and/or polymer having small particle size and low bulk density which limits the commercial utility.
Some attempts to overcome the disadvantages of the homogenous metallocene catalyst systems are disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804. Typically, these procedures have involved the prepolymerization of the metallocene aluminoxane catalyst system either in the presence of or in the absence of a support. An evaluation of these techniques has revealed that there is still room for improvement, particularly when the catalyst is one which is to be used in a slurry type polymerization where the object is to produce a slurry of insoluble particles of the end product polymer rather than a solution of polymer which could result in fouling of the reactor. In the operation of a slurry polymerization in a continuous loop reactor it is extremely important for efficient operations to limit polymer fouling of the internal surfaces of the reactor. The term “fouling” as used herein refers to polymer buildup on the surfaces inside the reactor.
U.S. Pat. No. 5,498,581 discloses a technique for producing insoluble polymerization catalysts by combining a metallocene having polymerizable groups with an aluminoxane and a particulate solid and then prepolymerizing. PCT /US96/13000, the disclosure of which is incorporated herein by reference, and a commonly owned copending application disclose that at least one such catalyst is capable of producing polyethylenes having ethyl branches which are uniformly distributed at the intra and intermolecular level without using any comonomer.
An object of the present invention is to provide a method for producing an insoluble polymerization catalyst that is capable of producing even more ethyl branches without the addition of comonomer. Another object of the present invention is to provide a process for producing polyethylene having unusually high levels of ethyl branches without the use of a comonomer. Still another object of the present invention is to provide polyethylenes that are particularly useful for making films of unusual clarity at a given density, said polyethylenes having a very narrow molecular weight distribution and no detectable amounts of long chain branching.
Another object of the present invention is to provide polyethylene having ethyl branches wherein the level of ethyl branches is substantially the same regardless of the molecular weight of the polymer molecules.
Another object of the present invention is to provide certain types of polyethylene having ethyl branches wherein the molar percent of ethyl branches is substantially the same for molecular fractions across the molecular weight distribution of the polymer. One type of such polyethylene is substantially free of any other type branches. In a preferred embodiment the polyethylene is substantially free of branches having 6 or more carbon atoms.
Another object of the present invention is to provide certain polyethylene having significant amounts of terminal vinyl groups, a very narrow molecular weight distribution, and a lower density than one would normally expect for the amount of branching due to comonomer insertions in the polymer chains.
Another object of this invention is to provide certain narrow molecular weight polyethylenes having an unusually low density for the amount of short chain branching at a given molecular weight. Still another object is to provide polyethylene films having a desirable combination of properties.
SUMMARY OF THE INVENTION
In accordance with the present invention, a solid particulate metallocene-containing catalyst system is produced by (a) combining an organoaluminoxane and at least one bridged metallocene having an indenyl radical bonded to a fluorenyl radical by a bridging group having at least one olefinic unsaturated substituent in a liquid to form a liquid catalyst system, (b) conducting prepolymerization of at least one olefin in the presence of said liquid catalyst system, to produce a prepolymerized solid catalyst, and (c) separating the resulting solid from the liquid and the components dissolved in the liquid, said solid being the solid particulate metallocene catalyst system. The phrase “liquid catalyst system” as used herein refers to the combination of the aluminoxane, the metallocene, and the liquid, irrespective of whether the aluminoxane and/or the metallocene are dissolved in the liquid.
In accordance with another aspect of the present invention, the resulting inventive solid particulate metallocene-containing catalyst system is employed in the polymerization of an olefin by contacting the olefin with the inventive solid particulate metallocene-containing catalyst system under suitable reaction conditions. In a particularly preferred embodiment the polymerization is conducted in the absence of any comonomer. In accordance with yet another aspect of the present invention there is provided a polymer of ethylene having uniformly distributed ethyl branches and no significant amounts of other branches. In accordance with another aspect there is provided unique films produced from polymers of ethylene having uniformly distributed ethyl branches and no significant amounts of other branches.
REFERENCES:
patent: 5498581 (1996-03-01), Welch et al.
patent: 5753785 (1998-05-01), Reddy et al.
patent: WO 97/06951 (1997-02-01), None
Alt Helmut G.
Dockter David W.
Hauger Bryan E.
Jung Michael
Jurkiewicz Antoni
Bowman Edward L.
Harlan R.
Phillips Petroleum Company
Wu David W.
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