Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
2001-02-13
2004-08-17
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
Reexamination Certificate
active
06777366
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to supported stereorigid metallocene catalyst systems useful in the polymerization of ethylenically unsaturated compounds and, more particularly, to processes for the preparation of supported metallocene catalysts incorporating large pore silica supports.
BACKGROUND OF THE INVENTION
Numerous catalyst systems for use in the polymerization of ethylenically unsaturated monomers are based upon metallocenes. Metallocenes can be characterized generally as coordination compounds incorporating one or more cyclopentadienyl (Cp) groups (which may be substituted or unsubstituted) coordinated with a transition metal through &pgr; bonding. When certain metallocene compounds are combined with an activator or cocatalyst such as methylaluminoxane (MAO) and optionally an alkylation/scavenging agent such as trialkylaluminum compound, highly active polymerization catalysts are formed. Various types of metallocenes are known in the art. As disclosed, for example, in U.S. Pat. No. 5,324,800 to Welborn et al, they include monocyclic (a single cyclopentadienyl group), bicyclic (two cyclopentadienyl groups, as shown in Formula 1), or tricyclic (three cyclopentadienyl groups) coordinated with a central transition metal. Homogeneous or non-supported metallocene catalysts are known for their high catalytic activity especially in olefin polymerizations. Under polymerization conditions where polymer is formed as solid particles, these homogeneous (soluble) catalysts form deposits of polymer on reactor walls and stirrers. These deposits should be removed frequently as they prevent an efficient heat-exchange, necessary for cooling the rector contents, and cause excessive wear of the moving parts. In addition, solid particles formed by such homogeneous catalysts possess undesirable particle morphologies with low bulk densities which make them difficult to circulate in the reactor, limiting throughput and they are difficult to convey outside of the reactor. In order to resolve these difficulties several supported metallocene compounds have been proposed. As disclosed in Welborn et al, typical supports include inorganic oxides such as silica, alumina or polymeric materials such as polyethylene.
Metallocene compounds, whether supported or unsupported, can further be characterized in terms of stereoregular catalysts which result in polymerization of alpha olefins, such as propylene, to produce crystalline stereoregular polymers, the most common of which are isotactic polypropylene and syndiotactic polypropylene. In general, stereospecific metallocene catalysts possess at least one chiral center and the ligand structure (usually cyclopentadienyl-based) are conformationally restricted. Due to the fluxional nature of Cp-type ligands, it is common for at least one of the Cp ligands to be suitably substituted to impart some measure of stereorigidity. Such stereospecific metallocenes can include un-bridged bicycle compounds of the general formula bicyclic coordination compounds of the general formula:
(Cp)
2
MeQn (1)
which are characterized by the isospecific metallocenes as described below and dicyclopentadienyl compounds of the general formula:
CpCp′MeQn (2)
characterized by the syndiospecific metallocenes described below. In the aforementioned formulas, Me denotes a transition metal element and Cp and Cp′ each denote a cyclopentadienyl group which can be either substituted or unsubstituted wit hCp′ being different from Cp, Q is an alkyl or other hydrocarbyl or a halogen group and n is a number within the range of 1-3. In such instances stereorigidity can be provided through substituent groups which result in steric hindrance between the two cyclopentadienyl moieties, as described, for example in U.S. Pat. No. 5,243,002 to Razavi. Alternatively, the cyclopentadienyl groups are in a conformationally restricted relationship provided by a bridged structure between the metallocene rings (not shown in Formulas (1) and (2) above). It is sometimes advantageous to utilize metallocene compounds in which the two cyclopentadienyl moieties (same or different) are covalently linked by a so-called bridging group such as a dimethylsilylene group. The bridging group restricts rotation of the two cyclopentadienyl moieties and in many instances improves catalyst performance. Metallocenes containing such a bridging group are often referred to as stereorigid. While bridged metallocenes normally incorporate two cyclopentadienyl groups (or substituted cyclopentadienyl groups), bridged metallocenes incorporating a single cyclopetadienyl group which is bridged to a heteroatom aromatic group (both being coordinated with a transition metal) are also known in the art. For example, U.S. Pat. No. 5,026,798 to Canich discloses dimethylsilyl-bridged cyclopentadienyl-anilino or other heteroatom ligand structures with coordination to the transition metal being provided through the nitrogen atom of the anilino group as well as the cyclopentadienyl-group. Other common bridging groups include CR
1
R
2
, CR
1
R
2
CR
2
R
3
, SiR
1
R
2
SiR
1
R
2
where the R
i
substituents can be independently selected from H or a C
1
-C
20
hydrocarbyl radical. Alternate bridging groups can also contain nitrogen, phosphorus, boron or aluminum.
As noted previously, isospecific and syndiospecific metallocene catalysts are useful in the polymerization of sterospecific propagation of monomers. Sterospecific structural relationships of syndiotacticity and isotacticity may be involved in the formation of stereoregular polymers from various monomers. Sterospecific propagation may be applied in the polymerization of ethylenically unsaturated monomers such as C
3
to C
20
alpha olefins which can be linear, branched or cyclic, 1-dienes such as 1,3-butadiene, substituted vinyl compounds such as vinyl aromatics, e.g., styrene, vinyl chloride, vinyl ethers such as alkyl vinyl ethers, e.g., isobutyl vinyl ether, or even aryl vinyl ethers. Stereospecific polymer propagation is probably of most significance in the production or polypropylene or isotactic or syndiotactic structure.
The structure of isotatic polypropylene can be described as one having the methyl groups attached to the tertiary carbon atoms of successive monomeric units falling on the same side of a hypothetical plane through the main chain of the polymer, e.g., the methyl groups are all above or below the plane. Using the Fischer projection formula, the stereochemical sequence of isotatic polypropylene can be described as follows:
In Formula 3 each vertical segment indicates a methyl group on the same side of the polymer backbone. In the case of isotatic polypropylene the majority of inserted propylene units possess the same relative configuration in relation to its neighboring propylene unit. Another way of describing the structure is through the use of NMR. Bovey's NMR nomenclature for an isotatic sequence as shown above is . . . mmmm . . . with each “m” representing a “meso” dyad in which there is a mirror plane of symmetry between two adjacent monomer units, or successive pairs of methyl groups on the same said of the plane of the polymer chain. As is known in the art, any deviation or inversion in the structure of the chain lowers the degree of isotacticity and subsequently the crystallinity of the polymer.
In contrast to the isotatic structure, syndiotactic propylene polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the chain lie on alternate sides of the plane of the polymer. In the case of syndiotactic polypropylene, the majority of inserted propylene units have opposite relative configuration relative to its neighboring monomer unit. Syndiotactic polypropylene using the Fisher projection formula can be indicated by racemic dyads with the syndiotactic rrr shown as follows:
Bovey's NMR nomenclature for a syndiotactic sequence as shown above is . . . rrr . . . with each “r” representing a “racemic” dyad in which successive pairs of methyl groups a
Campbell, Jr. Don Gordon
Gauthier William John
Kerr Margaret Elaine
Lopez Margarito
Rauscher David John
Bell Mark L.
Brown Jennine
Fina Technology, Inc.
Jackson William D.
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