Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2000-11-21
2003-12-09
Choi, Ling-Siu (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S103000, C502S117000, C502S118000, C526S160000, C526S943000, C526S161000
Reexamination Certificate
active
06660678
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 “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 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. In Example 22, a similar complex is used with less activator (i.e., [Al:Zr/h]=1956 to 1) to give a catalyst with an activity of only 10 kg/g Zr/h. 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.
Another drawback relates to polymer properties. While the '124 patent teaches that catalysts made by its method give polymers with “a narrow molecular weight distribution,” the actual molecular weight distributions of polymers made with the bis(carbazolyl)zirconium dichloride catalysts of Examples 16 and 22 of this reference are not reported. In fact, the molecular weight distributions of these polymers would preferably be narrower. I found that the MWDs of polymers made using the '124 catalysts are actually greater than 3 (see Comparative Examples 6-8 and 11-13, below).
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 catalysts that have good activities even at low activator levels. Ideally, the catalysts would produce, at low activator levels, polyolefins with desirable physical properties such as good comonomer incorporation, favorable melt-flow characteristics, and narrow molecular weight distributions.
SUMMARY OF THE INVENTION
The invention is a method for making single-site catalysts useful for olefin polymerization. The method comprises two steps. First, a nitrogen-functional heterocycle is deprotonated with an alkyllithium compound 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 tetrahalide (or with about 1 equivalent of an indenyl Group 4 transition metal trihalide) in a hydrocarbon solvent at a temperature greater than about 10° C. to give a mixture that contains the desired organometallic complex.
Catalyst systems comprising the organometallic complex-containing mixtures and an activator, as well as olefin polymerization processes that use the catalyst systems, are also included.
The complex-containing mixture actively polymerizes olefins, even when used with an exceptionally low level of an activator. Solvent dilution further enhances catalyst activity. In addition, the resulting polymers have a favorable balance of physical properties, including narrow MWD. The method provides a simple route to a variety of heterocycle-based, single-site catalysts and reduces the overall cost of these systems by reducing the amount of costly activator needed for high activity.
DETAILED DESCRIPTION OF THE INVENTION
Catalyst systems prepared by the method of the invention comprise an activator and an organometallic complex-containing mixture. The catalysts are “single site” in nature, i.e., they are distinct chemical species rather than mixtures of different species. They typically give polyolefins with characteristically narrow molecular weight distributions (Mw/Mn<3) and good, uniform comonomer incorporation.
The organometallic complex-containing mixture includes a complex that contains a Group 4 transition metal, M, i.e., titanium, zirconium, or hafnium. Preferred complexes include titanium or zirconium. The mixture also normally includes unreacted starting materials and lithium halides.
In one aspect, the invention is a method for preparing the organometallic complex-containing mixture. The method comprises two steps: deprotonation of the ligand, and reaction of the anionic ligand precursor with a Group 4 transition metal tetrahalide.
In the first step, a nitrogen-functional heterocycle is deprotonated with an alkyllithium compound. 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 halide. 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.
An alkyllithium compound is used to deprotonate the nitrogen-functional heterocycle. Suitable alkyllithium compounds can be made by reacting lithium with an alkyl halide. More often, they are purchased as solutions in a hydrocarbon (e.g., toluene or hexanes) or ether (e.g., diethyl ether or tetrahydrofuran) solvent. Preferred alkyllithium compounds are C
1
-C
8
alkyllithiums such as methyllithium, isopropyllithium, n-butyllithium, or t-butyllithium. n-Butyllithium is particularly preferred because it is readily available,
Equistar Chemicals LP
Schuchardt Jonathan L.
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