Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-02-12
2004-01-06
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S160000, C526S348000, C526S943000, C502S152000, C502S103000, C502S117000, C502S118000
Reexamination Certificate
active
06673882
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to an improved method for preparing supported “single-site” catalysts based on heterocyclic ligands such as carbazolyl and quinolinoxy ligands.
BACKGROUND OF THE INVENTION
While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of &agr;-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Metallocenes commonly include one or more cyclopentadienyl groups, but many other ligands have been used. Putting substituents on the cyclopentadienyl ring, for example, changes the geometry and electronic character of the active site. Thus, a catalyst structure can be fine-tuned to give polymers with desirable properties. “Constrained geometry” or “open architecture” catalysts have been described (see, e.g., U.S. Pat. No. 5,624,878). Bridging ligands in these catalysts lock in a single, well-defined active site for olefin complexation and chain growth.
Other known single-site catalysts replace cyclopentadienyl groups with one or more heteroatomic ring ligands that are pi-electron donors, such as boraaryl (see, e.g., U.S. Pat. No. 5,554,775 or azaborolinyl groups (U.S. Pat. No. 5,902,866).
U.S. Pat. No. 5,539,124 (hereinafter “the '124 patent”) and U.S. Pat. No. 5,637,660 teach the use of anionic, nitrogen-functional heterocyclic groups such as indolyl, carbazolyl, 2-pyridinoxy or 8-quinolinoxy as ligands for single-site catalysts. These ligands, which are produced by simple deprotonation of inexpensive and readily available precursors, are easily incorporated into a wide variety of transition metal complexes. When used with common activators such as alumoxanes, these catalysts polymerize olefins to give products with narrow molecular weight distributions that are characteristic of single-site catalysis.
One drawback of the catalysts described above is their relatively low activity. Normally, a large proportion of an alumoxane activator must be used to give even a low-activity catalyst system. For example, in the '124 patent, Example 16, a bis(carbazolyl)zirconium complex is used in combination with methylalumoxane at an aluminum:zirconium mole ratio [Al:Zr] of 8890 to 1 to give a catalyst having a marginally satisfactory activity of 134 kg polymer produced per gram Zr per hour. The activator is expensive, and when it is used at such high levels, it represents a large proportion of the cost of the catalyst system. Ideally, much less activator would be needed to give a catalyst system with better activity. Recently, I developed an improved way to make organometallic complexes based on heterocyclic ligands and useful for olefin polymerization (see copending application Ser. No. 09/716,954, filed Nov. 21, 2000).
An unresolved challenge relates to maintaining high activity, long catalyst lifetime, and favorable polyolefin properties when the complex is used with a support. Often, combining a complex with silica, alumina, or other common supports results in a dramatic loss of catalyst activity or lifetime. These issues are not addressed in the '124 patent, which talks only in generalities about catalyst supports and provides no actual example in which a supported catalyst is used. Moreover, while application Ser. No. 09/716,954 indicates that supports can be used, the application provides no examples of how to make supported catalysts that maintain a high level of performance.
In sum, there is a continuing need for single-site catalysts that can be prepared inexpensively and in short order from easy-to-handle starting materials and reagents. In particular, there is a need for ways to make supported catalysts that have high activities and good aging properties even at low activator levels. Ideally, the supported catalysts would produce polyolefins with desirable physical properties such as low density, narrow molecular weight distribution, favorable melt-flow characteristics, and high bulk density.
SUMMARY OF THE INVENTION
The invention is a five-step method for making supported single-site catalysts useful for olefin polymerization. First, a nitrogen-functional heterocycle is deprotonated to produce an anionic ligand precursor. The heterocycle is an indole, carbazole, 8-quinolinol, 2-pyridinol, or a mixture thereof. In the second step, the anionic ligand precursor reacts with about 0.5 equivalents of a Group 4 transition metal compound in a hydrocarbon solvent to give a mixture that contains the desired organometallic complex. Third, the mixture is reacted with an alumoxane activator, preferably using high-intensity mixing. Fourth, the product from step three is combined with a hydrocarbon slurry of an inorganic support. Finally, the solvents are removed to give a solid, supported catalyst.
The invention includes supported catalysts made by this method as well as olefin polymerization processes that use the catalysts. The supported catalysts actively polymerize olefins, even when used with an exceptionally low level of an activator.
I surprisingly found that introducing the alumoxane at the right time during preparation is crucial for making highly active, supported catalysts with good aging characteristics. Moreover, by judicious selection and chemical treatment of the inorganic support, one can further improve the catalysts. The supported catalysts give olefin polymers with a favorable balance of physical properties, including low density, narrow molecular weight distribution, good melt-flow properties, and high bulk density.
DETAILED DESCRIPTION OF THE INVENTION
Although they defy easy characterization by common analytical techniques, supported catalysts prepared by the method of the invention are considered to be “single site” in nature, i.e., they incorporate distinct chemical species rather than mixtures of different species. They qualify as single-site catalysts because they typically give polyolefins with characteristically narrow molecular weight distributions (Mw/Mn<3) and good, uniform comonomer incorporation.
The supported catalysts include a complex that contains a Group 4 transition metal, M, i.e., titanium, zirconium, or hafnium. Preferred complexes include titanium or zirconium. The catalysts often include some unreacted starting materials and by-products, e.g., alkali metal or alkaline earth metal salts derived from the deprotonating agent.
In one aspect, the invention is a five-step method for preparing a supported catalyst. In the first step, a nitrogen-functional heterocycle is deprotonated. Suitable nitrogen-functional heterocycles are indoles, carbazoles, 8-quinolinols, and 2-pyridinols. These compounds can have substituents that do not interfere with deprotonation or the subsequent reaction with the transition metal compound. Many of these compounds are commercially available or are easily synthesized. For example, indole, carbazole, 8-quinolinol, and 2-pyridinol are all inexpensive and commercially available, and many indoles are easily made from arylhydrazones of aldehydes or ketones and a Lewis acid using the well-known Fischer indole synthesis (see J. March,
Advanced Organic Chemistry,
2d ed. (1977), pp. 1054-1055, and references cited therein). Additional examples of suitable nitrogen-functional heterocycles are described in U.S. Pat. Nos. 5,637,660 and 5,539,124, the teachings of which are incorporated herein by reference.
Any suitable base can be used to deprotonate the nitrogen-functional heterocycle. Examples are alkyllithium compounds (e.g., methyllithium or n-butyllithium), alkali metals (e.g., sodium metal), alkali metal hydride
Choi Ling-Siu
Equistar Chemicals LP
Schuchardt Jonathan L.
LandOfFree
Supported single-site catalysts useful for olefin... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Supported single-site catalysts useful for olefin..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Supported single-site catalysts useful for olefin... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3187043