Mixed phosphinimine catalyst

Details Mixed phosphinimine catalyst Mixed phosphinimine catalyst

2000-07-14

2001-05-22

Wu, David W. (Department: 1713)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Organic compound containing

C502S103000, C502S117000, C526S127000, C526S161000, C526S172000, C526S901000, C526S943000

Reexamination Certificate

active

06235672

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to catalysts for the preparation of polyethylene having a broad molecular weight distribution.
BACKGROUND OF THE INVENTION
It is well known that linear polyethylene may be prepared by the polymerization of ethylene (optionally with one or more olefins or diolefins such as butene, hexene, octene or hexadiene) using a “Ziegler” catalyst system which comprises a transition metal compound (such as a titanium halide or avanadium halide and an aluminum alkyl). Polyethylene produced in this manner, particularly “linear low density polyethylene”, is in widespread commercial use. However, the conventional linear low density polyethylene (“lldpe”) made with Ziegler catalysts suffers from a number of deficiencies. Most notably, conventional lldpe is a heterogeneous product which contains a small fraction of low molecular weight wax and a comparatively large amount of very high molecular weight homopolymer. The heterogeneous nature of these polymers generally detracts from the physical properties made from them.
Accordingly, a great deal of effort has been directed towards the preparation of “homogeneous” lldpe resins which mitigate this problem. In particular, it is now well known to those skilled in the art that so-called “metallocene” catalysts may be used to produce homogeneous lldpe resin. These homogeneous resins are, however, not without problems. Most notably, these homogeneous resins typically have a narrow molecular weight distribution and are difficult to “process” or convert into finished polyethylene products. Thus, efforts to improve the processability of homogeneous polyethylene resin by broadening the molecular weight distribution have been made and are disclosed, for example in U.S. Pat. No. 4,530,914; 4,701,432; 4,935,474; 4,937,299; 5,124,418 and 5,183,867.
In copending and commonly assigned patent applications there are disclosed certain phosphinimine catalysts which may be used to produce homogeneous polyethylene.
SUMMARY OF THE INVENTION
The present invention provides a catalyst system for the (co)polymerization of ethylene to polyethylene having a broad molecular weight distribution, said catalyst system comprising:
a) at least two different mono or di-phosphinimine catalysts;
b) at least one cocatalyst; and
c) a particulate support.
It will be understood by those skilled in the art that said two different mono or di-phosphinimine catalysts must have different propagation and/or termination constants in order to produce a polymer having a broad molecular weight distribution.
As used herein, the term “mono-phosphinimine catalyst” refers to a catalyst having a single phosphinimine ligand and “di-phosphinimine catalyst” refers to a catalyst having two phosphinimine ligands.
It is required that at least two different catalysts be employed. The differences may be achieved, for example, by the use of different transition metals, different cyclopentadienyl ligands, different phosphinimine ligands or combinations thereof.
DETAILED DESCRIPTION
It is preferred that each of at least two phosphinimine catalysts used in this invention is defined by the formula:
(Cp)
m
M(PI)
n
(L)
q
wherein Pl is a phosphinimine ligand (see section 1.1 below); Cp is a cyclopentadienyl-type ligand (section 1.2 below); L is a monoanionic activatable ligand (section 1.3 below); m is a metal selected from Ti, Hf and Zr; and
wherein m is 0 or 1; n is 1 or 2; and m+n+q=the valence of the metal m.
The two phosphinimine catalysts must be different as further described in the Examples.
The most preferred catalysts are those in which the metal is 4 valent. For example, a catalyst may be a cyclopentadienyl (phosphinimine) complex of titanium, zirconium, or hafnium having two additional, monoanionic ligands. It is particularly preferred that each catalyst contains one phosphinimine ligand, one cyclopentadienyl ligand and two chloride or alkyl ligands.
1.1 Phosphinimine Ligand
Each catalyst must contain at least one phosphinimine ligand which is covalently bonded to the metal. Phosphinimine ligands are defined by the formula:
wherein each R
1
is independently selected from the group consisting of a hydrogen atom, a halogen atom, C
1-20
hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C
1-8
alkoxy radical, a C
6-10
aryl or aryloxy radical, an amido radical, a silyl radical of the formula:
—Si—(R
2
)
3
wherein each R
2
is independently selected from the group consisting of hydrogen, a C
1-8
alkyl or alkoxy radical, C
6-10
aryl or aryloxy radicals, and a germanyl radical of the formula:
Ge—(R
2
)
3
wherein R
2
is as defined above.
The preferred phosphinimines are those in which each R
1
is a hydrocarbyl radical. A particularly preferred phosphinimine is tri-(tertiary butyl) phosphinimine (i.e. where each R
1
is a tertiary butyl group).
1.2 Cyclopentadienyl Ligands
As used herein, the term cyclopentadienyl-type ligand is meant to convey its conventional meaning, namely a ligand having a five carbon ring which is bonded to the metal via eta-5 bonding. Thus, the term “cyclopentadienyl-type” includes unsubstituted cyclopentadienyl, substituted cyclopentadienyl, unsubstituted indenyl, substituted indenyl, unsubstituted fluorenyl and substituted fluorenyl. An exemplary list of substituents for a cyclopentadienyl ligand includes the group consisting of C
1-10
hydrocarbyl radical (which hydrocarbyl substituents are unsubstituted or further substituted); a halogen atom, C
1-8
alkoxy radical, a C
6-10
aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two C
1-8
alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C
1-8
alkyl radicals; silyl radicals of the formula —Si—(R)
3
wherein each R is independently selected from the group consisting of hydrogen, a C
1-8
alkyl or alkoxy radical C
6-10
aryl or aryloxy radicals; germanyl radicals of the formula Ge—(R)
3
wherein R is as defined directly above.
1.3 Activatable Ligand
The term “activatable ligand” refers to a ligand which may be activated by a cocatalyst, (or “activator”, to facilitate olefin polymerization. Exemplary activatable ligands are independently selected from the group consisting of a hydrogen atom, a halogen atom, a C
1-10
hydrocarbyl radical, a C
1-10
alkoxy radical, a C
5-10
aryl oxide radical; each of which said hydrocarbyl, alkoxy, and aryl oxide radicals may be unsubstituted by or further substituted by a halogen atom, a C
1-8
alkyl radical, a C
1-8
alkoxy radical, a C
6-10
aryl or aryloxy radical, an amido radical which is unsubstituted or substituted by up to two C
1-8
alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C
1-8
alkyl radicals.
The number of activatable ligands depends upon the valency of the metal and the valency of the activatable ligand. The preferred first catalyst metals are group 4 metals in their highest oxidation state (i.e. 4
+
) and the preferred activatable ligands are monoanionic (such as a halide—especially chloride or an alkyl—especially methyl). Thus, the preferred first catalyst contains a phosphinimine ligand, a cyclopentadienyl ligand and two chloride (or methyl) ligands bonded to the group 4 metal. In some instances, the metal of the first catalyst component may not be in the highest oxidation state. For example, a titanium (III) component would contain only one activatable ligand. Also, it is permitted to use a dianionic activatable ligand although this is not preferred.
2. Description of Cocatalyst
The catalyst components described in part 1 above are used in combination with at least one cocatalyst (or “activator”) to form an active catalyst system for olefin polymerization as described in more detail in sections 2.1 and 2.2 below.
2.1 Alumoxanes
The alumoxane may be of the formula:
(R
4
)
2
AlO(R
4
AlO)
m
Al(R
4
)
2
wherein each R
4
is independently selected from the group consisting of C
1-20
hydrocarbyl radicals and m is from 0 to 50, preferably R
4
is a C
1-4
alkyl ra

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