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
1999-03-22
2002-08-13
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...
C502S109000, C502S117000, C502S120000, C502S527160
Reexamination Certificate
active
06432860
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to supported stereorigid metallocene catalysts useful in the production of stereospecific polymers from ethylenically unsaturated compounds and, more particularly, to such catalysts incorporating amorphous silica supports and their use.
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 groups (which may be substituted or unsubstituted) coordinated with a transition metal. Various types of metallocenes are known in the art. They include bicyclic coordination compounds of the general formula:
(Cp)
2
MQn (1)
characterized by the isospecific metallocenes as described below and dicyclopentadienyl compounds of the general formula:
Cp Cp′MQ
n
(2)
characterized by the syndiospecific metallocenes described below. In the aforementioned formulas the M denotes a transition metal and Cp and Cp′ each denote a cyclopentadienyl group which can be either substituted or unsubstituted with Cp′ being different from Cp, Q is an alkyl or other hydrocarbyl or a halo group and n is a number within the range of 1-3. The cyclopentadienyl groups are in a stereorigid relationship normally provided by a bridged structure between the metallocene rings (not shown in Formulas (1) and (2) above) although stereorigidity can be provided through substituent groups which result in steric hindrance, as described, for example, in U.S. Pat. No. 5,243,002 to Razavi. Also, while bridged metallocenes normally incorporate two cyclopentadienyl groups (or substituted cyclopentadienyl groups), bridged metallocenes incorporating a single cyclopentadienyl 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 noted previously, isospecific and syndiospecific metallocene catalysts are useful in the polymerization of stereospecific propagation of monomers. Stereospecific structural relationships of syndiotacticity and isotacticity may be involved in the formation of stereoregular polymers from various monomers. Stereospecific propagation may be applied in the polymerization of ethylenically unsaturated monomers such as C
3
+ alpha olefins, 1-dienes such as 1,3-butadiene, substituted vinyl compounds such as vinyl aromatics, e.g. styrene or vinyl chloride, 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 of polypropylene of isotactic or syndiotactic structure.
The structure of isotactic 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 isotactic polypropylene is described as follows:
In Formula (3) each vertical segment indicates a methyl group on the same side of the polymer backbone. Another way of describing the structure is through the use of NMR. Bovey's NMR nomenclature for an isotactic pentad as shown above is . . . mmmm . . . with each “m” representing a “meso” dyad, 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 crystallinity of the polymer.
In contrast to the isotactic 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. Syndiotactic polypropylene in using the Fisher projection formula can be indicated by racemic dyads with the syndiotactic pentad rrrr shown as follows:
Here, the vertical segments again indicate methyl groups in the case of syndiotactic polypropylene, or other terminal groups, e.g. chloride, in the case of syndiotactic polyvinyl chloride, or phenyl groups in the case of syndiotactic polystyrene.
Syndiotactic polymers are semi-crystalline and, like the isotactic polymers, are insoluble in xylene. This crystallinity distinguishes both syndiotactic and isotactic polymers from an atactic polymer, which is non-crystalline and highly soluble in xylene. An atactic polymer exhibits no regular order of repeating unit configurations in the polymer chain and forms essentially a waxy product.
Yet another polymer configuration which has both isotactic and atactic features is exemplified by hemi-isotactic polypropylene. Hemi-isotactic polypropylene is characterized by every other methyl group being on the same side of the polymer with the remaining methyl groups randomly being on the same side or on the opposite side of the polymer backbone. Hemi-isotactic polypropylene can be characterized by the following Fisher projection formula in which, as indicated by the broken lines, alternate methyl groups have random stearic configurations.
Thus, as shown in Structure 5, the methyl groups indicated by the solid lines are in a mesa relationship with one another, with the alternating methyl groups indicated by the broken lines being randomly configured. Hemi-isotactic polypropylene, while having a semi-ordered structure, is primarily non-crystalline because of the disorder of the alternate methene units.
In most cases, the preferred polymer configuration will be a dominantly isotactic or syndiotactic polymer with very little atactic polymer. Catalysts that produce isotactic polyolefins are disclosed in U.S. Pat. Nos. 4,794,096 and 4,975,403. These patents disclose chiral, stereorigid metallocene catalysts that polymerize olefins to form isotactic polymers and are especially useful in the polymerization of highly isotactic polypropylene. As disclosed, for example, in the aforementioned U.S. Pat. No. 4,794,096, stereorigidity in a metallocene ligand is imparted by means of a structural bridge extending between cyclopentadienyl groups. Specifically disclosed in this patent are stereoregular hafnium metallocenes which may be characterized by the following formula:
R″(C
5
(R′)
4
)
2
HfQ
p
(6)
In formula (7), (C
5
(R′)
4
) is a cyclopentadienyl or substituted cyclopentadienyl group, R′ is independently hydrogen or a hydrocarbyl radical having 1-20 carbon atoms, and R″ is a structural bridge extending between the cyclopentadienyl rings. Q is a halogen or a hydrocarbon radical, such as an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl, having 1-20 carbon atoms and p is 2.
Catalysts that produce syndiotactic polypropylene or other syndiotactic polyolefins and methods for the preparation of such catalysts are disclosed in the aforementioned U.S. Pat. No. 4,892, 851. These catalysts are also bridged stereorigid metallocene catalysts, but, in this case, the catalysts have a structural bridge extending between dissimilar cyclopentadienyl groups and may be characterized by the formula:
R″(CpR
n
) (CpR′
m
)MQ
k
(7)
In formula (7), Cp represents a cyclopentadienyl or substituted cyclopentadienyl ring, and R and R′ represent hydrocarbyl radicals having 1-20 carbon atoms. R″ is a structural bridge between the rings imparting stereorigidity to the catalyst. M represents a transition metal, and Q a hydrocarbyl radical or halogen. R′
m
is selected so that (CpR′
m
) is a sterically different substituted cyclopentadienyl ring that (CpR
n
). In formula (8) n varies from 0-4 (0 des
Lopez Margarito
Shamshoum Edwar S.
Bell Mark L.
Fina Technology, Inc.
Jackson William D.
Pasterczyk J.
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