Polyolefin production

Details Polyolefin production Polyolefin production

2003-12-04

2004-10-05

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...

C526S352000, C526S943000, C526S351000, C502S103000, C502S152000, C556S001000, C556S011000, C556S027000, C556S043000, C556S053000, C556S058000

Reexamination Certificate

active

06800707

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a metallocene catalyst component for use in preparing polyolefins, especially polypropylenes. The invention further relates to a catalyst system which incorporates the metallocene catalyst component and a process for preparing such polyolefins.
BACKGROUND TO THE INVENTION
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 . . . rrrr . . . 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.
EP-A-0426644 relates to syndiotactic copolymers of olefins such as propylene obtainable using as a catalyst component isopropyl (fluorenyl) (cyclopentadienyl) zirconium dichloride. Syndiotacticity, as measured by the amount of syndiotactic pentads, rrrr was found to be 73-80%.
EP-A-577581 discloses the production of syndiotactic polypropylenes using metallocene catalysts which have fluorenyl groups substituted in positions 2 and 7 and an unsubstituted cyclopentadienyl ring.
EP-A-0419677 describes the production of syndiotactic polypropylene with an object to produce resin compositions having high stiffness when moulded. Metallocene catalysts such as isopropyl(cyclopentadienyl-1-fluorenyl) zirconium dichloride were used in the production of the polypropylene. However the molecular weight, melting point and syndiotacticity of these products would generally be relatively low. Moreover, in certain applications where crystallinity and crystallisation rate of the desired resins are critical, these catalysts are not suitable.
Accordingly, there is a need to provide polyolefins, such as polypropylenes, with improved physical properties.
SUMMARY OF THE INVENTION
The present invention aims to overcome the disadvantages of the prior art.
In a first aspect, the present invention provides use of a metallocene catalyst component for the preparation of a syndiotactic polyolefin having a monomer length of up to C10, which component has the general formula:
R″(C
p
R
1
R
2
)(C
p
′R
1
′R
2
′)MQ
2
  (I)
wherein C
p
is a cyclopentadienyl ring; C
p
′ is a 3,6 di substituted fluorenyl ring; R
1
and R
2
are each independently H or a substituent on the cyclopentadienyl ring which is proximal to the bridge, which proximal substituent is linear hydrocarbyl of from 1 to 20 carbon atoms or a group of the formula XR*
3
containing up to 7 carbon atoms in which X is chosen from Group IVA, and each R* is the same or different and chosen from hydrogen or alkyl; R
1
′ and R
2
′ are each independently substituent groups on the fluorenyl ring, each of which is a group of the formula AR′″
3
, in which A is chosen from Group IVA, and each R′″ is independently hydrogen or a hydrocarbyl having 1 to 20 carbon atoms; M is a Group IVB transition metal or vanadium; each Q is hydrocarbyl having 1 to 20 carbon atoms or is a halogen; R″ is a structural bridge imparting stereorigidity to the component and comprises the moiety TR
a
R
b
, in which T is chosen from group IVA, and each of R
a
and R
b
is independently (i) substituted or unsubstituted aryl linked to T directly or by C
1
-C
4
alkylene; or (ii) H.
Polyolefins produced using the metallocene catalyst component of the present invention are surprisingly found to have both very good microtacticity, especially as determined by pentad distribution levels in 13C nmr, and high weight average molecular weight, typically in excess of 500,000.
Without wishing to be bound by theory, it is thought that the combination in the present invention of an aromatic or hydrogen substituent on the bridge of the metallocene catalyst, in combination with disubstitution in positions 3 and 6 of the fluorenyl ring may contribute to an increase in the molecular weight, tacticity and crystallinity of the polymers, leading to improved mechanical properties of the final product.
The applicants have unexpectedly found that if in the metallocene catalysts the above substituent groups are present on the bridge and the fluorenyl ring is substituted in position 3 and 6, there is a significant improvement in the qualities of the produced polymer. Increases in microtacticity, melting point and molecular weight are all obtainable with these catalysts.
According to the present invention, the fluorenyl ring may be substituted by radicals of general formula: AR′″3 where A is preferably carbon or silicon and is more preferably carbon. Where A is carbon, AR′″ may be a hydrocarbyl selected from alkyl, aryl, alkenyl, alkyl aryl or aryl alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl; hexyl, heptyl, octyl, nonyl, decyl, cetyl or phenyl. Where A is silicon, AR′″3 may be Si(CH3)3. Preferably at least one of R′
1
and R′
2
is t-butyl. It is preferred that R′
1
and R′
2
are as similar as possible. More preferably both R′
1
and R′
2
are the same.
The structural bridge R″ comprises the moiety TR
a
R
b
in which T is directly or indirectly linked to Cp and Cp′. T may be indirectly linked to each of Cp and Cp′ by C
1
to C
4
alkylene but it is preferred that T is C or Si linked directly to the two Cp rings. Where R
a
and/or R
b
is aryl, each aryl may be substituted or unsubstituted and may be heteroaryl. Preferred aryl groups include substituted or unsubstituted phenyl, naphthyl and anthracyl. R
a
and R
b
are preferably the same. Most preferably, R″ is diphenylmethylidene.
M is preferably from Group IVB and may be hafnium, titanium or, most preferably, zironium. Q 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. Q is preferably a halogen.
In the proximal substituent groups R1 and R2, X is preferably C or Si. R* is preferably H. It is preferred that R1 and R2 are the same.
R
1
and R
2
should each be sufficiently small as not to interfere with syndiotactic polyolefin production. Whilst linear hydrocarbyl substituents of up to 20 carbon atoms may be tolerated, it is preferred that R
1
and R
2
each have no more than 7 carbon atoms. With non-linear substituents each R*
3
is preferably no larger than methyl. X is preferably C or Si. It is particularly preferred that at least one and most preferably both of R
1
and R
2
are hydrogen. In this way, production of syndiotactic polyolefin is favoured.
Production of syndiotactic polyolefin is particularly favoured when th

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