Catalyst for the polymerization of olefins

Details Catalyst for the polymerization of olefins Catalyst for the polymerization of olefins

2001-03-26

2003-09-02

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S169000, C526S161000, C526S172000, C526S126000, C526S348000, C526S943000, C502S117000, C502S103000, C502S155000, C502S167000

Reexamination Certificate

active

06613851

ABSTRACT:

This invention relates to novel catalysts and their use in polyolefin production, in particular to cyclic-carbene-&eegr;-ligand catalysts useful in the preparation of polyolefins, in particular polymers of C
2-8
olefins, more especially polypropylenes and most especially polyethenes.
Polyolefins of superior mechanical and processing properties may be obtained if the molecular-weight distribution is tailored to the end use of the polymer. Traditional olefin polymerization catalysts, such as chromium on silica, produce polyethylenes with a wide molecular weight distribution. Such materials are well suited for making moulded products. However, these moulded products would be significantly improved if it were possible to produce a polymer containing a tailored molecular weight distribution combined with controlled insertion of comonomer into the desired part of the molecular weight distribution.
One solution to this problem is to produce the olefin polymer using two or more metallocene complex catalysts simultaneously. Typically, combinations of zirconocene complexes have been disclosed. However, while zirconocene dichloride is useful to produce the low molecular weight fraction of a polymer, no satisfactory comonomer control is achieved, ie. branched polyolefin chains are produced in the presence of a mixed olefin feedstock (for example ethylene-hexene) This is generally true for the overwhelming majority of the known metallocene complexes.
It is therefore desirable to identify an olefin polymerization catalyst exhibiting comonomer control, ie. which will not build certain comonomers into the growing polymer chain even though such comonomers are present in the polymerisation feedstock.
It is an object of the invention to provide such a catalyst system.
Thus viewed from one aspect the invention provides a process for the catalysed polymerization of a an olefin, especially a C
2-8
&agr;-olefin, preferably a C
2
or C
3
&agr;-olefin, more preferably ethene, characterised in that as a catalyst or catalyst precursor is used a cyclic carbene-&eegr;-ligand complex comprising a catalytically effective coordinated metal, preferably a group 6 metal, and more especially chromium.
Viewed from a further aspect the invention provides an olefin polymerization catalyst or catalyst precursor comprising a cyclic carbene-&eegr;-ligand complex comprising a catalytically effective coordinated metal, preferably a group 6 metal, and more especially chromium.
In the cyclic carbene-&eegr;-ligand complex, the cyclic carbene ligand may be any cyclic carbene capable of coordinating to the metal. Typically the carbene is heterocyclic with the C: providing one ring atom, and especially preferably with the ring unsaturated. In general, the atoms adjacent the C: will be substituted, preferably with bulky substituents containing up to 30 non-hydrogen atoms, preferably at least 4 non-hydrogens e.g. containing 4 to 12 carbon atoms. Moreover the substituent itself may comprise a further carbene structure. More preferably, the carbene comprises a 5 membered, preferably mono-unsaturated, heterocyclic ring which contains 2, 3 or 4 ring nitrogens, two of which are optionally substituted and 1, 2 or 3 ring carbons one of which (the C: atom) is adjacent at least one ring nitrogen and is unsubstituted with any remaining ring carbon optionally being substituted. Thus for example the carbene may be of formula Ia or Ib
where each X may independently represent N or an optionally substituted CH group; and each R
1
is hydrogen, or an optionally substituted organic group.
Carbenes of formula Ia, especially where the R
1
groups are bulky substituents and more especially where the ring atoms of each X are carbon, are particularly preferred.
The carbenes of formula Ia or Ib are sometimes referred to as Arduengo carbenes (as opposed to the Fischer and Schrock carbenes which are more commonly encountered in publications relating to organometallic complexes). The Arduengo carbenes tend to be more stable—if they dissociate from a metal complex they usually have sufficiently large half lives to re-enter the metal's coordination sphere. Such stability facilitates the synthesis of substituted derivatives allowing greater freedom to modify the electronic and steric properties of the carbene. The Arduengo carbenes moreover tend to bind efficiently to metals whether in low or high oxidation states as opposed to Fischer and Schrock carbenes which favour low and high oxidation states respectively; this is advantageous in polymerization catalysis where oxidation state changes may occur. The Arduengo carbenes are efficient 2-electron donor ligands (comparable to P(CH
3
)
3
or P(C
6
H
11
)
3
) with no tendency to act as Π acceptors—again in contrast to Fischer and Schrock carbenes—and may be used in place of phosphine ligands.
The strong metal:Arduengo carbene bond strengths (comparable to or greater than metal:phosphine bond strengths) mean that the complexes are thermally robust. Accordingly such carbenes have good catalyst lifetimes and thermal stabilities.
Many such carbenes of formulae Ia or Ib are already known as ligands, e.g. compounds having the following skeletal structures (ie. omitting ring substituents):
(where n is from 1 to 6).
The range of substituents the carbene ring nitrogens and ring carbons may carry is very large, with different substitution patterns resulting in variations in the properties of the resulting catalyst.
Thus for example substituents may be selected from halogen atoms, non-carbon oxyacid groups and derivatives thereof, and optionally substituted alkyl, aralkyl and aryl groups, e.g. such groups substituted by groups selected from alkyl, aryl, amino, hydroxy, alkoxy, oxo, oxa, carboxy, thia, sulphur oxyacid and halo groups and combinations thereof. Examples of particular ring substituents include for example methyl, ethyl, i-propyl, t-butyl, n-butyl, n-hexyl, cyclohexyl, phenyl, hydroxyphenyl, optionally substituted ferrocenyl (e.g. (C
5
H
4
)Fe(C
5
H
5
)), benzyl, methylbenzyl, l-phenyl-ethyl, mesityl, methylnaphthyl, ethoxyethyl, diphenylmethyl, ethylaminoethyl, diethylamino-methyl, 2-(diethylamino)-ethyl, 2-carboxy-ethyl, 2-sulphoxy-ethyl, 4-sulphoxy-butyl, 2-ethoxycarbonyl-ethyl, chlorophenyl, adamantyl, dihydroimidazol-ylidinylmethyl, dihydropyrazolylidinylmethyl, 2,6-diisopropylphenyl, or dihydrotriazolylidinylmethyl groups.
Particular examples of suitable carbenes include compounds of formulae IIa to IIj
wherein n is from 1 to 6 and each R
1
, which is the same or different, preferably the same, represents a C
1-6
alkyl group, a C
4-10
mono or polycyclic cycloalkyl group, a C
4-10
cycloalkyl-C
1-4
alkyl group, an aryl group, an aryl-C
1-4
alkyl group, a C
1-6
alkyl-aryl-C
1-4
alkyl group, a carboxy group or derivative thereof (e.g. an ester group), or a ferrocenyl group, in which any alkyl, alkylene, aryl or arylene moiety is optionally substituted, e.g. with amino, hydroxy, alkoxy, halo, nitro, cyano, oxyacid (e.g. carbon oxyacid or sulphur oxyacid) or oxyacid derivative (thus by way of example R
1
might represent 2-hydroxy-phenyl); and R
2
which may be the same or different is hydrogen, halogen, C
1-6
alkyl or an aryl group or two R
2
groups on adjacent carbons can together form an optionally substituted carbocyclic group, e.g. a 5 to 7 membered ring.
Unless otherwise specified, alkyl groups or alkylene moieties referred to herein may conveniently contain 1 to 10, more preferably 1 to 6 carbons and are linear or branched. Likewise unless otherwise specified aryl groups are preferably homo or heterocyclic containing 5 to 7 ring atoms per ring and with such rings containing 0, 1, 2, 3 or 4 ring heteroatoms selected from 0, N and S, preferably 0, 1, 2 or 3 N atoms, and with the groups containing a total of 5 to 16 ring atoms. The ring atoms may be substituted, e.g. by alkyl groups and other groups listed above or by fused saturated or unsaturated rings. Examples of typical aryl groups include phenyl, naphthyl, mesityl, 2,6-diisopropyl-phenyl, 2,6-ditertbutyl-phenyl, and 2,6-dite

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