Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2000-02-15
2003-05-06
Wu, David W. (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S103000, C526S160000, C526S351000, C526S169200, C526S158000, C526S159000, C526S943000, C556S011000, C556S043000, C556S053000
Reexamination Certificate
active
06559089
ABSTRACT:
The present invention relates to a metallocene catalyst component for use in preparing isotactic polyolefins, especially polypropylenes. The invention further relates to a catalyst system which incorporates the metallocene catalyst component and a process for preparing such isotactic polyolefins.
Olefins having 3 or more carbon atoms can be polymerised to produce a polymer with an isotactic stereochemical configuration. For example, in the polymerisation of propylene to form polypropylene, the isotactic structure is typically described as having methyl groups attached to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the main chain of the polymer. This can be described using the Fischer projection formula as follows:
Another way of describing the structure is through the use of NMR spectroscopy. Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm with each “m” representing a “meso” diad or successive methyl groups on the same side in the plane.
In contrast to the isotactic structure, syndiotactic 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. Using the Fischer projection formula, the structure of a syndiotactic polymer is described as follows:
In NMR nomenclature, a syndiotactic pentad is described as . . . rrr . . . in which “r” represents a “racemic” diad with successive methyl groups on alternate sides of the plane.
In contrast to isotactic and syndiotactic polymers, an atactic polymer exhibits no regular order of repeating unit. Unlike syndiotactic or isotactic polymers, an atactic polymer is not crystalline and forms essentially a waxy product.
While it is possible for a catalyst to produce all three types of polymer, it is desirable for a catalyst to produce predominantly an isotactic or syndiotactic polymer with very little atactic polymer. C
2
-symmetric metallocene catalysts are known in the production of the polyolefins. For example, C2 symmetric bis indenyl type zirconocenes which can produce high molecular weight high melting isotactic polypropylene. The preparation of this metallocene catalyst is costly and time-consuming, however. Most importantly, the final catalyst consists of a mixture of racemic and meso isomers in an often unfavourable ratio. The meso stereoisomer has to be separated to avoid the formation of atactic polypropylene during the polymerisation reaction.
EP-A-0537130 discloses the use of a C1 symmetric metallocene catalysts for the production of isotactic polypropylene. A preferred catalyst is isopropylidene (3-t-butyl-cyclopentadienyl fluorenyl)ZrCl
2
. This catalyst has a bulky t-butyl group positioned on the cyclopentadienyl ring distal to the isopropylidene bridge. This catalyst has the advantage that it consists of only one stereoisomer and so no isomeric metallocene separation is required at the final stage of its synthesis. Whilst polypropylene preparation using this catalyst produces isotactic polypropylene, the polymer product has poor mechanical properties because of the presence of regiodefects and relatively low molecular weight.
Regiodefects occur in the polymer chain when, instead of producing a perfect isotactic polyolefin in which each monomeric unit is positioned head-to-tail in relation to the next, mis-insertions of the monomers occur so as to give either a head-to-head or tail-to-tail mis-match. In the polymerisation process according to EP-A-0619325, there is a typical mis-insertion frequency of around 0.4%. These so called (2-1) regiodefects are partially transferred to the so called (1-3) insertion through an isomerisation process leaving units of four CH
2
groups in the backbone of the polypropylene chain. This has a deleterious effect on the physical and mechanical properties of the polymer and results in low molecular weight isotactic polypropylene with a low melting point.
The present invention aims to overcome the disadvantages of the prior art.
In a first aspect, the present invention provides a metallocene catalyst component for use in preparing isotactic polyolefins, which component has the general formula:
R″(C
p
R
1
R
2
R
3
)(C
p
′R′
n
)MQ
2
(I)
wherein C
p
is a substituted cyclopentadienyl ring; C′
p
is a substituted or unsubstituted fluorenyl ring; R″ is a structural bridge imparting stereorigidity to the component; R
1
is a substituent on the cyclopentadienyl ring which is distal to the bridge, which distal substituent comprises a bulky group of the formula XR*
3
in which X is chosen from Group IVA, and each R* is the same or different and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon atoms, R
2
is a substituent on the cyclopentadienyl ring which is proximal to the bridge and positioned non-vicinal to the distal substituent, and is of the formula YR#
3
, in which Y is chosen from group IVA, and each R@ is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, R
3
is a substituent on the cyclopentadienyl ring which is proximal to the bridge and is a hydrogen atom or is of the formula ZR$
3
, in which Z is chosen from group IVA, preferably carbon, and each R$ is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, each R′
n
is the same or different and is hydrocarbyl having 1 to 20 carbon atoms in which 0≦n≦8; M is a Group IVB transition metal or vanadium; and each Q is hydrocarbyl having 1 to 20 carbon atoms or is a halogen. In one embodiment, the metallocene catalyst component of the present invention has the general formula:
R″(C
p
R
1
R
2
R
3
)(C
p
′R′
n
)MQ
2
(II)
wherein C
p
is a substituted cyclopentadienyl ring; C
p
′ is a substituted or unsubstituted fluorenyl ring; R″ is a structural bridge imparting stereorigidity to the component; R
1
is a substituent on the cyclopentadienyl ring which is distal to the bridge, which distal substituent comprises a group of the formula XR*
3
; in which X is chosen from Group IVA, preferably carbon or silicon, and each R* is the same or different and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon atoms, R
2
is a substituent on the cyclopentadienyl ring which is proximal to the bridge and positioned non-vicinal to the distal substituent and is of the formula YR#
3
in which Y is chosen from group IVA, preferably carbon, and each R# is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon each R′
n
, is the same or different and is hydrocarbyl having 1 to 20 carbon atoms in which hydrocarbyl having 1 to 20 carbon atoms in which 0≦n≦8; is a Group IVB transition metal or vanadium; and each Q is hydrocarbyl having 1 to 20 carbon atoms or is a halogen.
Polyolefins produced using metallocene catalyst component of the present invention are not only found to be isotactic but are also found to be substantially free of regiodefects. Accordingly, the polyolefins produced thereby have improved mechanical properties including a high weight average molecular weight typically of the order of 150,000-600,000 and elevated melting point. Without wishing to be bound by any theory, it is postulated that the bulky group on the cyclopentadienyl ring contributes to the stereospecificity of the polymerisation reaction whereas the proximal substituent(s) on the cyclopentadienyl ring contribute to the regiospecificity of monomer insertion and the increase of molecular weight.
In the bulky distal substituent group R
1
, X is preferably C or Si. R* may be a hydrocarbyl such as alkyl, aryl, alkenyl, alkylaryl or aryl alkyl, preferably methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, octyl, nonyl, decyl, cetyl or phenyl. RI may comprise a hydrocarbyl which is attached to a single carbon atom in the cyclopentadienyl ring or may be bonded to two carbon atoms in that ring. Preferably, R
1
is C(CH
3
)
3
, C(CH
3
)
2
Ph,
Bellia Vincenzo
Razavi Abbas
Alexander David J.
Choi Ling-Siu
Fina Technology, Inc.
Gilbreth J M. (Mark)
Gilbreth Mary A.
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