Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-05-16
2003-02-18
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S127000, C526S160000, C526S352000, C526S943000, C502S108000, C502S103000
Reexamination Certificate
active
06521728
ABSTRACT:
TECHNICAL FIELD
This invention relates to novel, highly effective solid aluminoxane/metallocene olefin polymerization catalysts, their preparation, and their use.
BACKGROUND
Hydrocarbylaluminoxanes (also known as alumoxanes) complexed with transition metal compounds, such as metallocenes, have been found to be effective olefin polymerization catalysts. Methylaluminoxanes are especially effective catalyst components in forming homogeneous catalyst systems with various metallocenes. However, these catalyst systems have proven to be considerably less effective in productivity per unit weight of catalyst when used as supported heterogeneous catalysts, either in the form of dispersions in a liquid medium or as supported solid catalysts in gas-phase polymerizations. For example, in U.S. Pat. No. 5,126,301 issued Jun. 30, 1992 to Tsutsui et al. it is pointed out that when an olefin is polymerized or copolymerized in a dispersion or gas-phase polymerization system by utilizing carrier-supported metallocene-aluminoxane catalysts, polymerization activity is markedly reduced, that the properties inherent to the catalyst comprising the transition metal compound and the aluminoxane catalyst component are not fully exerted, and that powder properties such as bulk density of the thus prepared polymer were insufficient. The approach taken by Tsutsui et al. was to form a solid catalyst by contacting an &agr;-olefin with a mixture obtained by mixing an organoaluminum compound having a branched alkyl radical, an aluminoxane of specified aluminum content, a fine-particle carrier, and a transition metal metallocene compound.
Despite various improvements made during the course of extensive research activities by various laboratories, a need has existed for olefin polymerization catalysts having even better performance characteristics. For example, U.S. Pat. No. 5,498,581 issued Mar. 12, 1996 to Welch et al., points out that evaluation of attempts disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 to overcome the disadvantages of metallocene catalysts has revealed that there is still room for improvement, particularly when the catalyst is one which is to be used in a slurry-type polymerizations. The techniques disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 involve prepolymerization of the metallocene-aluminoxane catalyst system either in the presence or absence of a support.
The improved method of Welch et al. U.S. Pat. No. 5,498,581 for preparing a solid metallocene-containing catalyst system comprises (a) combining in a liquid an organoaluminoxane and at least one metallocene having at least one cyclopentadienyl, indenyl, tetrahydroindenyl, octahydrofluorenyl, or fluorenyl ligand having at least one olefinically unsaturated substituent to form a liquid catalyst system, (b) conducting prepolymerization of at least one olefin in the presence of said catalyst system to produce a prepolymerized solid catalyst containing no more than about 95 weight percent prepolymer, and (c) separating the resulting solid from the liquid and components dissolved in the liquid. The patent reports in Table I that by use of the Welch et al. method, catalysts having productivities as high as 9840 grams of polyethylene per gram of catalyst per hour were formed.
SUMMARY OF THE INVENTION
This invention provides solid olefin polymerization catalysts that are believed to have substantially higher productivities than any previously known heterogeneous olefin catalyst or catalyst system devoid of an inorganic support and any other kind of preformed support.
In addition, this invention makes possible the provision of catalysts that have excellent morphology and handling characteristics, and that are capable of producing olefin homopolymers and copolymers having a combination of very desirable physical attributes and properties. In fact, the morphology of the particulate catalysts formed in the preferred manner of this invention is comparable to (on a par with) the best particulate catalysts previously made in these laboratories or received heretofore from outside sources. It is worth observing that such prior catalysts were formed using a silica support.
In accordance with one embodiment of this invention there is provided a particulate &agr;-olefin prepolymer-Group 4 metallocene-aluminoxane catalyst composition having a productivity of at least 18,000 grams of polyethylene per gram of catalyst in one hour. Preferred catalysts are those in which this productivity characteristic is at least 25,000, and particularly preferred catalysts are those in which this productivity characteristic is at least 30,000.
It has been discovered that particulate olefin polymerization catalysts having such exceptionally high productivities can be prepared by prepolymerizing &agr;-olefin with a Group 4 metallocene-aluminoxane solution, provided the proportion of &agr;-olefin (most preferably, ethylene) is in the range of about 150 to about 1500, and preferably in the range of about 175 to about 1000, moles per mole of Group 4 metallocene used in forming the solution. It is also important in carrying out this process to use a solution in which the atom ratio of aluminum to Group 4 metal in the solution is in the range of about 150:1 to about 1500:1, and preferably in the range of about 175:1 to about 1000:1. In addition, the Group 4 metallocene ingredient used in forming these new, highly productive catalysts has in its molecular structure at least one polymerizable olefinic substituent.
Another feature of these catalysts is that they are self-supporting catalysts. By this is meant that the catalyst particles do not contain, and thus are not produced in the presence of, a preformed support such as an inorganic compound (silica or etc.) or a preformed particulate polymeric support. Instead, the prepolymer is formed in the presence of the combination of at least one Group 4 metallocene and at least one aluminoxane in an initially homogeneous liquid organic solvent phase from which the catalyst particles precipitate, wherein such combination is in whatever chemical composition or makeup it assumes or acquires when the metallocene and the aluminoxane are brought together in the solvent. According to the present state of knowledge in the art, when a metallocene and an aluminoxane are brought together in an inert organic solvent they are understood to undergo chemical reaction with each other to thereby form a reaction product. Accordingly, in accordance with the present state of knowledge in the art, the prepolymer of the catalyst compositions of this invention is believed to be formed in the presence of the reaction product of at least one Group 4 metallocene and at least one aluminoxane in an initially homogeneous organic liquid solvent phase from which the catalyst particles precipitate.
In preferred embodiments, the above catalysts of this invention have a specific surface area of no more than about 20 square meters per gram (m
2
/g), and preferably less than 10 m
2
/g.
A preferred method for producing the highly productive catalysts of this invention is a process which comprises:
a) mixing together in an organic solvent medium at least one metallocene, preferably a metallocene of a Group 4 metal, and at least one aluminoxane, preferably a methylaluminoxane to form a catalytic solution; and
b) contacting catalytic solution from a) with a controlled amount of &agr;-olefin monomer, preferably ethylene, under polymerization conditions such that particulate solids are formed having a specific surface area of no more than about 20 square meters per gram (m
2
/g).
When performed properly, the recovered and dried catalyst has a productivity of at least 18,000 grams of polyethylene per gram of catalyst in one hour.
It is interesting to compare the unsupported catalysts of this invention and the productivity thereof with the catalysts and productivity (“polymerization activity”) of the catalysts reported in U.S. Pat. No. 4,923,833 issued to Kioka et al. on May 8, 1990. Unlike the present invention, Kioka et al. produce solid unsu
Albemarle Corporation
Lu Caixia
Pippenger Philip M.
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