Supported olefin polymerization catalyst composition

Details Supported olefin polymerization catalyst composition Supported olefin polymerization catalyst composition

2001-01-22

2004-04-13

Rabago, Roberto (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S124300, C526S129000, C526S153000, C526S160000, C526S161000, C526S172000, C526S943000, C502S104000, C502S107000, C502S117000, C502S132000, C502S152000, C502S155000

Reexamination Certificate

active

06720394

ABSTRACT:

The present invention relates to a process for the preparation of a supported olefin polymerization catalyst composition, comprising a support optionally treated with an organometallic compound, a metallocene, and an alumoxane. The invention also relates to a supported olefin polymerization catalyst composition which has been prepared according to said process and to the use of such a supported olefin polymerization catalyst composition for the polymerization of at least one olefin.
In many olefin polymerization processes using a single site catalyst, it is desirable to support the catalyst on a carrier or support. Usually such supported catalyst compositions include a metallocene and an alumoxane supported on an inorganic oxide carrier such as silica and/or alumina.
For example, WO 96/00243 describes a method for producing a supported catalyst composition by mixing a bridged bis-indenyl metallocene and an alumoxane in a solvent to form a solution, and then combining the solution and a porous support, whereby the total volume of the solution is less than that at which a slurry is formed. A typical support used was previously heated silica MS 948 (Grace) and a typical alumoxane used was gel-free methyl alumoxane (MAO), both of which were used in all of the examples.
According to S. Srinvasa Reddy, Polymer Bulletin, 36 (1996) 317-323, the ethylene polymerization activity of tetraisobutyldialumoxane cocatalyst was clearly lower than the activity of methylalumoxane cocatalyst. This reflects the previous general opinion, that only methyl alumoxane as a cocatalyst gave satisfactory ethylene polymerization catalyst activities.
In the present application a catalyst system has been described where the catalyst composition comprises a support optionally treated with an organometallic compound, a metallocene, and an alumoxane. Now it has been realized that when an aluminium oxide support and a metallocene with at least one silyl substituent in the cyclopentadienyl ring are used in polymerization with an alumoxane as an external cocatalyst, the polymer morphology does not meet the requirements when using the known polymerization methods. When alumoxane with large molecular size, like hexaisobutylalumoxane, is used as an external cocatalyst, it has difficulties to diffuse evenly into a very porous catalyst particle, which causes the polymerization to start from the surface of the catalyst particle where the alumoxane is capable to activate the metallocene. Because polymerization starts only at the surface of the catalyst particle, an uncontrolled break down of the catalyst takes place and causes high risk for reactor fouling and inhomogenous polymer. Also when a high molecular weight alumoxane is used as an external coactivator in a gas phase process, there is a tendency of the solvent of the alumoxane to evaporate forming a solid alumoxane. When the coactivator becomes solid, it has no possibilities to enter into the metallocene catalyst pores and it is not anymore able to activate metallocene compounds.
The purpose of the present invention is to improve the quality of the product when metallocenes with at least one silyl substituent in the cyclopentadienyl ring are used with a non-methyl alumoxane in olefin polymerization. More specifically, the present invention aims at providing an olefin polymerization catalyst composition including a metallocene with at least one silyl substituent in the cyclopentadienyl ring and a C
2
-C
12
alkyl alumoxane, which has commercially satisfactory activity when producing olefin homopolymers and copolymers. A further goal of the present invention is a supported olefin polymerization catalyst composition for use in gas phase, slurry phase or liquid/solution phase polymerizations.
The above mentioned purposes of the invention have now been realized by a novel process for the preparation of a supported olefin polymerization catalyst composition, comprising a porous carrier optionally treated with an organometallic compound, a metallocene, and an alumoxane. If an alkylated metallocene is used, the carrier need not to be treated with an organometallic compound. The porous carrier is preferably an inorganic oxide, most preferably a silicon dioxide. The claimed process comprises mainly impregnating a support comprising a solid compound being a porous carrier, previous to or immediately before the beginning of the olefin polymerization, in any order, optionally with
a) an organometallic compound of the general formula (1):
R
1
MX
v−1
  (1)
 wherein each R is the same or different and is a C
1
-C
10
alkyl group; M is a metal of Group 1, 2, 12 or 13 of the Periodic Table (IUPAC 1990); each X is the same or different and one of a halogen atom, a hydrogen atom, a hydroxyl radical or a C
1
-C
8
hydrocarbyloxy group; 1 is 1, 2 or 3; v is the oxidation number of the metal M,
and with a complex solution of at least
b) a metallocene of the general formula (2):
(CpY)
m
M′X′
n
Z
o
  (2)
 wherein each CpY is the same or different and is one of a mono- or polysubstituted, fused or non-fused, homo- or heterocyclic cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, or octahydrofluorenyl ligand, the ligand being covalently substituted at its cyclopentadienyl ring with at least one substituent Y which is one of a —OR′, —SR′, —NR′
2
, —CR′═, or —PR′
2
radical, each R′ being the same or different and being one of a tri-C
1
-C
8
hydrocarbyl silyl group or a tri-C
1
-C
8
hydrocarbyloxy silyl group; M′ is a transition metal of Group 4 of the Periodic Table and bound to the ligand CpY at least in an &eegr;
5
bonding mode; each X′ is the same or different and is one of a hydrogen atom, a halogen atom, a C
1
-C
8
hydrocarbyl group, a C
1
-C
8
hydrocarbylheteroatom group or a tri-C
1
-C
8
hydrocarbylsilyl group or two X′ form a ring with each other; Z is a bridge atom or group between two CpY ligands or one CpY ligand and the transition metal M′; m is 1 or 2; o is 0 or 1; and n is 4-m if there is no bridge Z or Z is a bridge between two CpY ligands or n is 4-m-o if Z is a bridge between one CpY ligand and the transition metal M′, and
c) an alumoxane of the following general formulas (3):
 wherein each R″ and each R′″ is the same or different and is a C
2
-C
12
alkyl group; and p is an integer between 1 and 40,
and recovering said supported olefin polymerization catalyst composition.
At step (a) the support can be treated for example with an aluminiumalkyl to alkylate the support. However, when an alkylated metallocene compound is used, the alkylation of the support is not needed. When an alkylated metallocene is used it is advantageous to treat the support by heat for removing some hydroxyl groups from the surface of the carrier particle.
By mono- or polysubstituted is meant that, in addition to said substituent Y, there may optionally be other substituents at the rings at said ligands CpY.
By fused or non-fused is meant that any ring at said ligands may be fused or non-fused, i.e. have at least two atoms in common, with at least one further ring.
By homo- and heterocyclic is meant that any ring of said ligands may have only carbon ring atoms (homo- or isocyclic) or may have other ring atoms than carbon (heterocyclic).
It has thus been realized that a C
2
-C
12
alkyl alumoxane (i.e. a non-methyl alumoxane) can successfully be used as an internal coactivator, if a support comprising a porous carrier is treated with a solution of metallocene having at least one silyl substituent at the cyclopentadienyl ring and with a non-methylalumoxane based alumoxane. It is advantageous first to treat the porous carrier particle with an organometallic compound to alkylate the surface of the particle. However, this is not needed if a alkylated metallocene is used.
According to a non-limiting model, said electron pair of double bond substituents at the cyclopentadienyl ring delocalize it's negative charge and help to ionize the metallocene, w

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