Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-05-25
2001-04-03
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...
C526S128000, C526S129000, C526S160000, C526S170000, C526S172000, C526S348000, C502S152000, C502S155000, C502S158000
Reexamination Certificate
active
06211311
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a supported catalyst for polymerizing olefins and its method of producton. The catalyst comprises a support treated with an effective amount of a chemical modifier, a single-site catalyst containing at least one anionic, polymerization-stable, heteroatomic ligand, and an activator. The modifier is an organoaluminum, organosilicon, organomag nesium, or organoboron compound.
BACKGROUND OF THE INVENTION
Many olefin polymerization catalysts are known, including conventional Ziegler-Natta catalysts. While these catalysts are inexpensive, they exhibit low activity, produce polymers having narrow to medium molecular weight distributions (M
w
/M
n
>4), and are generally poor at incorporating a-olefin comonomers. To improve polymer properties, highly active single-site catalysts, in particular metallocenes, are beginning to replace Ziegler-Natta catalysts. Although more expensive, the new catalysts give polymers with narrow molecular weight distributions, and good comonomer incorporation, which allows easier production of low-density polymers. One disadvantage of metallocene catalysts is that they tend to produce lower molecular weight polymers at higher temperatures.
Recent attention has focused on developing improved single-site catalysts in which a cyclopentadienyl ring ligand is replaced by a heteroatomic ring ligand. These catalysts may be referred to generally as “heterometallocenes.”
In particular, U.S. Pat. No. 5,554,775 discloses single-site catalysts containing a boraaryl moiety such as boranaphthalene or boraphenanthrene. U.S. Pat. No. 5,539,124 discloses catalysts containing a pyrrolyl ring, i.e., an “azametallocene.” Further, U.S. Pat. No. 5,637,660 discloses catalysts in which a cyclopentadienyl moiety of a metallocene is replaced by a readily available quinolinyl or pyridinyl ligand. In addition, PCT Int. Appl. WO 96/34021 discloses azaborolinyl heterometallocenes wherein at least one aromatic ring includes both a boron atom and a nitrogen atom.
Single-site catalysts are typically soluble in the polymerization reaction medium and are therefore valuable for solution processes. However, for gas-phase, slurry, and bulk monomer processes, it is useful to immobilize the catalyst on a carrier or support in order to control polymer morphology. Much effort has focussed on supporting metallocene and Ziegler-Natta catalysts. Various supports are taught, particularly inorganic oxides. Support modification techniques, which can improve activity, are also known. For example, supports for Ziegler-Natta catalysts modified with organomagnesiums, organosilanes, and organoboranes are disclosed in U.S. Pat. Nos. 4,508,843, 4,530,913, and 4,565,795. Metallocene catalyst support modification with organosilanes and aluminum, zinc, or silicon compounds is taught in U.S. Pat. Nos. 4,808,561 and 5,801,113.
In contrast, relatively little is known about supporting heterometallocenes. U.S. Pat. No. 5,744,417 discloses a silylamine polymer support, but the examples use only a metallocene catalyst. U.S. Pat. Nos. 5,554,775, 5,539,124, and 5,637,660 and PCT Int. Appl. WO 96/34021 teach that heterometallocenes can be supported on inorganic oxides, but these references give no examples.
Many heterometallocenes are inherently unstable. U.S. Pat. Nos. 5,554,775 and 5,539,124 teach that the catalyst should be used shortly after preparation because activity is lost on storage. Moreover, our own initial efforts to make supported heterometallocenes using untreated supports were largely unsuccessful (see Comparative Example 8 and Table 6 below). New supports for heterometallocenes would ideally provide for increased storage stability.
In sum, new supported heterometallocene catalysts and methods of making them are needed. Particularly valuable supported catalysts would have improved shelf-life and would give polymers with enhanced properties. Ideally, the new supports would have a negligible negative effect on catalyst activity.
SUMMARY OF THE INVENTION
The invention is a supported catalyst system and a method of making it. The catalyst system comprises a chemically treated support, a single-site catalyst that contains at least one anionic, polymerization-stable, heteroatomic ligand, and an activator. The support is modified by treating it with an effective amount of an organoaluminum, organosilicon, organomagnesium, or organoboron compound.
We surprisingly found that chemical modification is a key to making superior supported heterometallocenes for olefin polymerization. In particular, catalysts of the invention have higher activities and longer shelf-lives than comparable catalysts for which the support is not modified. In addition, the new catalysts more effectively incorporate comonomers, which is important for controlling polymer density.
DETAILED DESCRIPTION OF THE INVENTION
Supported catalyst systems of the invention include a single-site catalyst, an activator, and a chemically treated support.
“Single-site” catalysts include both metallocenes and nonmetallocenes. They are transition metal catalysts that are distinct chemical species rather than mixtures of different species. Single-site catalysts typically give polyolefins with characteristically narrow molecular-weight distributions (M
w
/M
n
<3) and good, uniform comonomer incorporation. In addition, the catalysts produce polyolefins with a wide range of melt indices compared with those of polyolefins that are readily accessible with Ziegler-Natta catalysts.
Single-site catalysts useful in the invention contain at least one anionic, polymerization-stable, heteroatomic ligand Suitable heteroatomic ligands include substituted or unsubstituted boraaryl, pyrrolyl, quinolinyl, and pyridinyl groups as described in U.S. Pat. Nos. 5,554,775, 5,539,124, and 5,637,660, the teachings of which are also incorporated herein by reference. Substituted or unsubstituted azaborolinyl ligands, such as those described in PCT Int. Appl. WO 96/34021 can also be used. The polymerization-stable ligands may also include cyclopentadienyl (substituted or unsubstituted) anions such as those described in U.S. Pat. Nos. 4,791,180 and 4,752,597, the teachings of which are incorporated herein by reference.
The polymerization-stable anionic ligands can be bridged. Groups that can be used to bridge the polymerization-stable anionic ligands include, for example, methylene, ethylene, 1,2-phenylene, and dialkyl silyls. Normally, only a single bridge is used in the single-site catalyst. Bridging the ligand changes the geometry around the transition metal and can improve catalyst activity and other properties, such as comonomer incorporation and thermal stability.
The single-site catalyst includes a transition or lanthanide metal. Preferably, the metal is from Groups 3 to 10 of the Periodic Table. More preferred catalysts include a Group 4 to 6 transition metal; most preferably, the catalyst contains a Group 4 metal such as titanium or zirconium.
The single-site catalyst usually includes at least one other ligand. Preferably, the other ligand is hydride, halide, C
1
-C
20
alkoxy, siloxy, hydrocarbyl, or dialkylamido. More preferably, the ligand is hydride, chloride, bromide, C
1
-C
8
alkoxy, C
3
-C
18
trialkylsiloxy, methyl, phenyl, benzyl, neopentyl, or C
2
-C
6
dialkylamido. Particularly preferred are hydrocarbyl groups that do not undergo &bgr;-hydrogen elimination reactions (e.g., olefin formation with loss of M-H); examples of preferred hydrocarbyl groups are methyl, phenyl, benzyl, neopentyl, and the like.
Suitable activators include alumoxanes. Preferred alumoxanes are polymeric aluminum compounds represented by the cyclic formula (R
1
—Al—O)
s
or the linear formula R
1
(R
1
—Al—O)
s
AlR
1
wherein R
1
is a C
1
-C
5
alkyl group and s is an integer from 1 to about 20. Preferably, R
1
is methyl and s is from about 4 to about 10. Exemplary alumoxane activators are (poly)methylalumoxane (MAO), ethylalumoxane, and diisobutylalumoxane. Optionally, the activator is a trialkyl or triaryl aluminum compound, which preferably has
Cribbs Leonard V.
Etherton Bradley P.
Liu Jia-Chu X.
Lynch Michael W.
Meyer Karen E.
Carroll Kevin M.
Choi Ling-Siu
Equistar Chemicals L.P.
Schuchardt Jonathan L.
Wu David W.
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