Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1992-03-02
2003-09-09
Nazario-Gonzalez, Porfirio (Department: 1204)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S012000, C556S021000, C556S053000, C502S103000, C502S117000, C526S160000, C526S943000
Reexamination Certificate
active
06617466
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to certain monocyclopentadienyl metal compounds of a Group IV B transition metal of the Periodic Table of Elements, to a catalyst system comprising a monbcyclopentadienyl Group IV B transition metal compound and an alumoxane, and to a process using such catalyst system for the production of polyolefins, particularly polyethylene, polypropylene and &agr;-olefin copolymers of ethylene and propylene having a high molecular weight. The catalyst system is highly active at low ratios of aluminum to the Group IV B transition metal, hence catalyzes the production of a polyolefin product containing low levels of catalyst metal residue. Titanium species of the catalyst are stable at high pressures in unsupported form, unlike their bis-cyclopentadienyl titanium compound counterparts, and exhibit the ability to catalyze the incorporation of higher &agr;-olein comonomer contents for production of higher molecular weight &agr;-olefin copolymers than analogous zirconium and hafnium species of a monocyclopentadienyl transition metal compound.
BACKGROUND OF THE INVENTION
As is well known, various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications it is of primary importance for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin or an ethylene-&agr;-olefin copolymer with high strength properties.
Traditional Ziegler-Natta catalysts system—a transition metal compound cocatalyzed by an aluminum alkyl—are capable of producing polyolefins having a high molecular weight but a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has two or more cyclopentadienyl ring ligands—such transition metal compound being referred to as a metallocene—which catalyzes the production of olefin monomers to polyolefins. Accordingly, metallocene compounds of a Group IV B metal, particularly, titanocenes and zirconocenes, have been utilized as the transition metal component in such “metallocene” containing catalyst system for the production of polyolefins and ethylene-&agr;-olefin copolymers. When such metallocenes are cocatalyzed with an aluminum alkyl—as is the case with a traditional type Ziegler-Natta catalyst system—the catalytic activity of such metallocene catalyst system is generally too low to be of any commercial interest.
It has since become known that such metallocenes may be cocatalyzed with an alumoxane—rather than an aluminum alkyl—to provide a metallocene catalyst system of high activity for the production of polyolefins.
The zirconium metallocene species, as cocatalyzed or activated with an alumoxane, are commonly more active than their hafnium or titanium analogous for the polymerization of ethylene alone or together with an &agr;-olefin comonomer. When employed in a non-supported form—i.e., as a homogeneous or soluble catalyst system—to obtain a satisfactory rate of productivity even with the most active zirconium species of metallocene typically requires the use of a quantity of alumoxane activator sufficient to provide an aluminum atom to transition metal atom ratio (Al:TM) of at least greater than 1000:1; often greater than 5000:1, and frequently on the order of 10,000:1. Such quantities of alumoxane impart to a polymer produced with such catalyst system an undesirable content of catalyst metal residue, i.e., an undesirable “ash” content (the nonvolatile metal content). In high pressure polymerization procedures using soluble catalyst systems wherein the reactor pressure exceeds about 500 bar only the zirconium or hafnium species of metallocenes may be used. Titanium species of metallocenes are generally unstable at such high pressures unless deposited upon a catalyst support.
A wide variety of Group IV B transition metal compounds have been named as possible candidates for an alumoxane cocatalyzed catalyst system. Although bis(cyclopentadienyl) Group IV B transition metal compounds have been the most preferred and heavily investigated for use in alumoxane activated catalyst systems for polyolefin production, suggestions have appeared that mono and tris(cyclopentadienyl) transition metal compounds may also be useful. See, for example U.S. Pat. Nos. 4,522,982; 4,530,914 and 4,701,431. Such mono(cyclopentadienyl) transition metal compounds as have heretofore been suggested as candidates for an alumoxane activated catalyst system are mono(cyclopentadienyl) transition metal trihalides and trialkyls.
More recently, International Publication No. WO 87/03887 describes the use of a composition comprising a transition metal coordinated to at least one cyclopentadienyl and at least one heteroatom ligand as a transition metal component for use in an alumoxane activated catalyst system for &agr;-olefin polymerization. The composition is broadly defined as a transition metal, preferably of Group IV B of the Periodic Table, which is coordinated with at least one cyclopentadienyl ligand and one to three heteroatom ligands, the balance of the transition metal coordination requirement being satisfied with cyclopentadienyl or hydrocarbyl ligands. Catalyst systems described by this reference are illustrated solely with reference to transition metal compounds which are metallocenes, i.e., bis(cyclopentadienyl) Group IV B transition metal compounds.
Even more recently, at the Third Chemical Congress of North American held in Toronto, Canada in June 1988, John Bercaw reported upon efforts to use a compound of a Group III B transition metal coordinated to a single cyclopentadienyl heteroatom bridged ligand as a catalyst system for the polymerization of olefins. Although some catalytic activity was observed under the conditions employed, the degree of activity and the properties observed in the resulting polymer product were discouraging of a belief that such monocyclopentadienyl transition metal compound could be usefully employed for commercial polymerization processes.
A need still exists for discovering catalyst systems that permit the production of higher molecular weight polyolefins and desirably with a narrow molecular weight distribution. It is further desirable that a catalyst be discovered which, within reasonable ranges of ethylene to &agr;-olefin monomer ratios, will catalyze the incorporation of higher contents of &agr;-olefin comonomers in the production of ethylene-&agr;-olefins copolymers.
SUMMARY OF THE INVENTION
The catalyst system of this invention comprises a transition metal component from Group IV B of the Periodic Table of the Elements (
CRC Handbook of Chemistry and Physics
, 68th ed. 1987-1988) and an alumoxane component which may be employed in solution, slurry or bulk phase polymerization procedure to produce a polyolefin of high weight average molecular weight and relatively narrow molecular weight distribution.
The “Group IV B transition metal component” of the catalyst system is represented by the formula:
wherein: M is Zr, Hf or Ti in its highest formal oxidation state (+4, d
0
complex);
(C
2
H
5−y−x
R
x
) is a cyclopentadienyl ring which is substituted with from zero to five substituent groups R, “x” is 0, 1, 2, 3, 4 or 5 denoting the degree of substitution, and each substituent group R is, independently, a radical selected from a group consisting of C
1
-C
20
hydrocarbyl radicals, substituted C
1
-C
20
hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amido radical, a phosphido radical, and alkoxy radical or any other radical containing a Lewis acidic or basic functionality; C
1
-C
20
hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the Group IV A of the Periodic Table of Elements; halogen radical, amido radicals, phosphido radicals, alkoxy radicals, alkylborido radicals or any other radical containing Lewis acidic or basic
ExxonMobil Chemical Patents Inc.
Nazario-Gonzalez Porfirio
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