Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1995-05-25
2001-09-25
Bell, Mark L. (Department: 1755)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S161000, C526S943000
Reexamination Certificate
active
06294625
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the use of Group 13 element compounds to improve the productivity of ionic transition metal catalyst systems. More specifically the invention relates to the use of a Group 13 element organometallic compound as an additive to an ionic mono(cyclopentadienyl)/heteroatom transition metal olefin polymerization catalyst system. These catalyst systems have enhanced productivity over similar catalysts, in the absence of Group 13 compounds, for the polymerization of unsaturated monomer, e.g., olefinically unsaturated monomers such as ethylene, other ethylenically unsaturated olefins or olefinic species, diolefins, cyclic olefins, ethylenically unsaturated non-cyclic non-conjugated polyenes, cyclic non-conjugated polyenes, and acetylenically unsaturated monomers or combinations thereof, to form polymers such as polyolefins having narrow molecular weight distributions.
2. Background
Ziegler-Natta type catalysts for the polymerization of olefins are well known. The traditional Ziegler-Natta type systems comprise a metal halide activated to a catalyst species by reaction with a metal alkyl cocatalyst, particularly an aluminum alkyl cocatalyst. The activation of these traditional heterogeneous Ziegler-Natta catalysts generates a variety of different active sites. As a consequence of this non-uniformity of the active sites, the catalysts produce polymer products of broad molecular weight distribution (MWD). In many application, this broad MWD is undesirable. Furthermore, the polymer products exhibit relatively poor composition distribution (CD), comonomer incorporation and sequence distribution.
Also known are catalyst systems comprising a bis(cyclopentadienyl) (“Cp”) transition metal and a compound cocatalyst. Such bis Cp transition metal compounds, in the presence of activators catalyze the polymerization of olefin monomers to polyolefins. Bis (Cp) transition metal compounds of the Group 4 metals, particularly of titanium and zirconium, have been used. When such transition metal components are cocatalyzed with an aluminum alkyl—the cocatalyst used with traditional Ziegler-Natta catalysts—the catalytic activity is generally to low for commercial applications.
From EP-A-129368 (Exxon) it is known that bis (Cp) transition metal components may be activated by alumoxanes. The bis(Cp) transition metal compound-alumoxane catalysts systems, whether homogeneous or supported, are versatile in that they may have a range of activities from low to high and may be used effectively to produce a variety of polymer products including, for example, low molecular weight copolymers high density linear polyethylene (HDPE), linear low density polyethylene (LLDPE), ethylene-propylene copolymer (EP), atactic polypropylene (a-PP), syndiotactic (s-PP) polypropylene and isotactic polypropylene (i-PP). The bis (Cp) transition metal compound-alumoxane catalyst systems also offer a significant advantage over the traditional Ziegler-Natta catalysts in that they are able to produce polymers with narrow MWD.
EP-A-0277003 (Exxon) and EP-A-0277004 (Exxon) teach a catalyst systems comprising a transition metal component and a non-coordinating anion. Such catalyst systems may be formed by activating the transition metal compound to a catalytic state by reaction with certain types of ionic exchange compositions.
U.S. Pat. No. 5055438 (Exxon), incorporated herein by reference, EP-A-420436 (Exxon), WO 91/04257 (Exxon) and EP-A-416815 (Dow) describe a further class of catalysts having a single cyclopentadienyl ring ligand and a heteroatom bonded to the metal atom, and their use in conjunction with alumoxanes. Similar catalyst systems are taught in U.S. Pat. No. 5,064,802 (Dow), incorporated herein by reference, EP-A-418044 (Dow) and WO 92/00333 (Exxon), but having a non-coordinating anion as activating cocatalyst. Here the catalyst system is prepared as a reaction product of a mono(cyclopentadienyl) heteroatom metal compound and an ionic activator compound. Such catalyst systems referred to as an “ionic mono (Cp)/heteroatom transition metal catalyst” or an “ionic mono(Cp) catalyst” permits the production of polyolefin products of narrow MWD at high rates of catalytic activity with good incorporation of comonomers and control of the chain end chemistry of the polymer products.
The active catalytic ion pair species of the ionic mono (Cp) catalyst may be irreversibly inactivated by Lewis base impurities contained in components of the polymerization medium such as the diluent or the monomer supply with which the ionic mono (Cp) catalyst is used. Despite the most elaborate control some, albeit minute, quantity of such Lewis base impurities will invariably be present in the polymerization medium, especially the commercial monomer supply. Therefore there is a need for an additive effective for use during polymerization to neutralize impurities contained in the polymerization medium without affecting the ability of these ionic mono (Cp) catalysts to produce polyolefin products.
SUMMARY OF THE INVENTION
This invention provides a catalyst system comprising an ionic mono (Cp) transition metal catalyst and an additive which neutralizes deactivators of the ionic catalyst active sites. More specifically, the invention provides a catalyst system comprising a mono(cyclopentadienyl)heteroatom Group 4 transition metal catalyst activated by an ion exchange reagent, and as a third or additive component, an organometallic compound preferably a Group 13 element organo compound. The presence of the specified additive neutralizes those impurities capable of deactivating the active catalytic sites of the ionic mono (Cp) catalyst, so providing a catalyst system which generally has greatly improved productivity without significantly affecting molecular weight or extent of comonomer incorporation.
The ionic mono (Cp) catalyst component of this invention comprises a complex having (i) a cationic portion derived from a Group 4 transition metal compound having a single delocalized substituted or substituted pi-bonded moiety bound in an n
5
bonding mode to the metal, and a heteroatom-containing moiety bonded to the metal through the heteroatom; and (ii) an anionic portion which is a non-coordinating compatible anion of a Bronsted acid salt. Such catalyst components are described in WO 92/00333. Thus the catalyst component may comprise derivatives of a Group 4 transition metal compound containing at least one ligand which will combine with an activator component or at least a portion thereof, such as a cation portion. The activator component of the catalyst, of which there may be more than one, is an ion-exchange compound comprising a cation which will irreversibly react with at least one ligand contained in said transition metal compound and an anion which is a single coordination complex comprising a plurality of lipophilic radicals or a plurality of boron atoms, covalently coordinated to and shielding a central formally charge-bearing metal or metalloid atom. The anion is bulky, labile and stable to any reaction involving the cation of the activator component. The charge-bearing metal or metalloid may be any metal or metalloid capable of forming a coordination complex which is not hydrolyzed by aqueous solutions. Upon combination of the mono (Cp) component and activator component, the cation of the activator component reacts with one of the ligands of the mono (Cp) component. That anion is compatible with, and noncoordinating toward, the metal cation formed from the mono (Cp) component. It is important that the anion of the activator compound be capable of stabilizing the transition metal cation complex without interfering with the ability of the transition metal cation or its decomposition product to function as a catalyst, and further that it be sufficiently labile to, permit displacement by an olefin, diolefin, acetylenically unsaturated monomer, or other polymerizable species, during polymerization. The selection of suitable mono (Cp) transition metal component(s)-
Canich Jo Ann Marie
Hlatky George G.
Turner Howard William
Bell Mark L.
ExxonMobil Chemical Patents Inc.
Muller William G.
Pasterczyk J.
Runyan Charles E.
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