Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-06-11
2003-10-07
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, C526S943000, C526S161000, C502S155000, C502S152000
Reexamination Certificate
active
06630547
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for making polyolefins. In particular, the invention relates to a polymerization process with a catalyst precursor, an activator, and an organosilane modifier. The modifier increases polyolefin molecular weight without significantly reducing catalyst activity.
BACKGROUND OF THE INVENTION
Organosilane modifiers have been studied with Ziegler-Natta catalysts. Y. V. Kissin,
J. Polym. Sci. Part A: Polym. Chem
., 33 (1995) 227, reports a series of ethylene-hexene copolymerization experiments with varying amounts of diphenyldimethoxysilane. The silane increases the M
w
and decreases the catalyst activity. M. Harkonen, J. V. Seppala and T. Vaananen,
Makromol. Chem
. 192 (1991) 721, studied Ziegler-Natta catalyzed propylene polymerizations with fourteen alkoxysilanes. In each case, the activity of the catalyst decreased (18-66%) versus the control experiment without organosilane. In all but two instances, the viscosity-average molar mass increased.
Interest in single-site (metallocene and non-metallocene) catalysts continues to grow rapidly in the polyolefin industry. These catalysts are 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.
Traditional metallocenes commonly include one or more cyclopentadienyl groups or cyclopentadienyl-like groups such as indenyl, fluorenyl, and substituted varieties of these, but many other ligands have been used. Thus, a catalyst structure can be fine-tuned to give polymers with desirable properties. Other known polymerization-stable ligands are heteroatomic ligands such as boraaryl, pyrrolyl, indolyl, indenoindolyl, quinolinoxy, pyridinoxy, and azaborolinyl as described in U.S. Pat. Nos. 5,554,775, 5,539,124, 5,637,660, 5,902,866 and 6,232,260.
The incorporation of hydrosilanes in polymerizations using cyclopentadienyl metallocene catalysts is described in EP 0739910 A2
, J. Am. Chem. Soc
. 121 (1999) 8791, and in U.S. Pat. Nos. 5,578,690, 6,075,103 and 6,077,919. High levels of hydrosilane are used to lower the polymer molecular weight. For instance, in EP 0739910A2, 0.8 to 10.6 mmoles of silane are used per 0.029 mmoles cyclopentadienyl metallocene catalyst. At these levels, the polymer molecular weight decreases with increasing hydrosilane.
One attribute of many metallocene and single-site catalysts is their propensity to produce lower molecular weight polymers. Thus for certain commercial applications, increased molecular weight is desirable. For instance, polymer toughness and strength generally increase with increased molecular weight. Despite the importance of olefin polymerizations and the considerable research that has been done on various catalyst systems, there remains a need to modify the catalyst to be able to increase the molecular weight of the resultant polyolefin. Surprisingly, we have found that low levels of organosilanes can be used to increase polyolefin molecular weight without significantly reducing catalyst activity.
SUMMARY OF THE INVENTION
This invention is a process for the polymerization of an olefin. An olefin is polymerized with a catalyst precursor in the presence of an activator and an organosilane modifier. The organosilane allows the catalyst to maintain high activity while increasing polyolefin molecular weight. The process is robust, easy to practice and affords polyolefins with improved properties.
DETAILED DESCRIPTION OF THE INVENTION
The invention is a process for polymerizing olefins. Suitable olefins are C
2
-C
20
&agr;-olefins, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene and mixtures thereof. Preferred olefins are ethylene, propylene and mixtures thereof with &agr;-olefins such as 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.
The polymerization is performed with a catalyst precursor comprising a Group 3 to 10 transition or lanthanide metal, M, and at least one polymerization-stable, anionic ligand. Examples of suitable anionic ligands include substituted and unsubstituted cyclopentadienyl, fluorenyl, and indenyl, or the like, 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. A preferred group of polymerization-stable ligands are heteroatomic ligands such as boraaryl, pyrrolyl, indolyl, indenoindolyl, quinolinoxy, pyridinoxy, and azaborolinyl as described in U.S. Pat. Nos. 5,554,775, 5,539,124, 5,637,660, 5,902,866 and 6,232,260, the teachings of which are incorporated herein by reference. Complexes that incorporate indenoindolyl ligands are particularly preferred (see U.S. Pat. No. 6,232,260 and PCT Int. Appl. WO 99/24446).
The catalyst precursor also usually includes one or more labile ligands such as halides, alkyls, alkaryls, aryls, dialkylaminos, or the like. Particularly preferred are halides, alkyls, and alkaryls (e.g., chloride, methyl, benzyl).
The polymerization-stable ligands can be bridged. Groups that can be used to bridge the ligands include, for example, substituted or unsubstituted methylene, ethylene, 1,2-phenylene, and dialkyl silyls. Normally, only a single bridge is included. Bridging changes the geometry around the transition or lanthanide metal and can improve catalyst activity and other properties such as comonomer incorporation.
Exemplary catalyst precursors are bis(cyclopentadienyl)zirconium dimethyl, bis(cyclopentadienyl)zirconium dichloride, bis(indenyl)titanium dibenzyl, cyclopentadienyl(indenoindolyl)zirconium dichloride, bis(fluorenyl) zirconium dimethyl, 8-quinolinoxy(cyclopentadienyl)titanium dimethyl, bis(2-pyridinoxy)titanium diethyl, (1-dimethylaminoborabenzene)cyclopentadienyl-zirconium dichloride, bis(1-methylborabenzene)zirconium dimethyl, bis(indolyl)zirconium dimethyl, and the like.
Preferred transition metals are Group 4-6 transition metals and of these zirconium is especially preferred.
The process is performed in the presence of an activator. Suitable activators ionize the catalyst precursor to produce an active olefin polymerization catalyst. Suitable activators are well known in the art. Examples include alumoxanes (methyl alumoxane (MAO), PMAO, ethyl alumoxane, diisobutyl alumoxane), alkylaluminum compounds (triethylaluminum, diethyl aluminum chloride, trimethylaluminum, triisobutyl aluminum), and the like. Suitable activators include acid salts that contain non-nucleophilic anions. These compounds generally consist of bulky ligands attached to boron or aluminum. Examples include lithium tetrakis(pentafluorophenyl)borate, lithium tetrakis(pentafluorophenyl)-aluminate, anilinium tetrakis(pentafluorophenyl)borate, and the like. Suitable activators also include organoboranes, which include boron and one or more alkyl, aryl, or aralkyl groups. Suitable activators include substituted and unsubstituted trialkyl and triarylboranes such as tris(penta-fluorophenyl)borane, triphenylborane, tri-n-octylborane, and the like. These and other suitable boron-containing activators are described in U.S. Pat. Nos. 5,153,157, 5,198,401, and 5,241,025, the teachings of which are incorporated herein by reference.
Suitable activators also include aluminoboronates—reaction products of alkyl aluminum compounds and organoboronic acids—as described in U.S. Pat. Nos. 5,414,180 and 5,648,440, the teachings of which are incorporated herein by reference.
The amount of activator needed relative to the amount of catalyst precursor depends on many factors, including the nature of the catalyst precursor and activator, the desired reaction rate, the kind of polyolefin product, the reaction conditions, and other factors. Generally, however, when the activator is an alumoxane or an alkyl aluminum compound, the amount used will be within the range of about 0.01 to about 5000 moles, prefera
Lynch Michael W.
Sartain William J.
Wang Shaotian
Choi Ling-Siu
Equistar Chemicals LP
Schuchardt Jonathan L.
Tyrell John
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