Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1996-04-26
2001-07-17
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...
C526S160000, C526S943000, C502S103000, C502S117000, C502S152000, C502S154000, C556S011000, C556S043000, C556S052000, C556S053000, C556S058000, C556S087000
Reexamination Certificate
active
06262197
ABSTRACT:
The present invention relates to a multinuclear metallocene compound which is suitable as a catalyst component in the preparation of polyolefins. The invention also relates to a process for preparing these metallocenes. In addition, the invention relates to a process for preparing polyolefins using the metallocene compound of the invention.
Known from the literature is the preparation of polyolefins using soluble metallocene compounds in combination with aluminoxanes or other cocatalysts which, owing to their Lewis acidity, can convert the neutral metallocene into a cation and stabilize it.
Soluble metallocene compounds based on bis(cyclopentadienyl)zirconium dialkyl or dihalide in combination with oligomeric aluminoxanes can polymerize ethylene with good activity and propylene with moderate activity. The polyethylene obtained has a narrow molecular weight distribution and an intermediate molecular weight. The polypropylene prepared in this way is generally atactic and has a relatively low molecular weight.
The preparation of isotactic polypropylene is achieved by means of ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride together with an aluminoxane in a suspension polymerization (EP 185 918). The polymer has a narrow molecular weight distribution. The disadvantage of this process is that at polymerization temperatures relevant in industry only polymers having a very low molecular weight can be prepared.
Also known are catalysts based on ethylenebisindenyl-hafnium dichloride and ethylenebis(4,5,6,7-tetrahydro-1-indenyl)hafnium dichloride and methylaluminoxane using which relatively high molecular weight polypropylenes can be prepared by suspension polymerization (J. Am. Chem. Soc. (1987), 109, 6544). However, under polymerization conditions relevant in industry, the particle morphology of the polymers produced in this way is unsatisfactory and the activity of the catalyst systems used is comparatively low. In addition, these systems have high catalyst costs, so that low-cost polymerization is not possible using these systems.
A significant increase in the molecular weight was able to be achieved by using metallocenes in which the indenyl ligands fixed by means of a bridge bear substituents in the 2 position (EP 485 822) or in the 2 and 4 positions (EP 530 647).
A further increase in the molecular weight has been achieved by the use of indenyl ligands having substituents in the 2, 4 and 6 positions (BP 545 303) or of aromatic &pgr; ligands of the 4,5-benzoindenyl type (EP 549 900).
A disadvantage in the case of the stereospecific polymerization of prochiral monomers, e.g. of propylene, using metallocene catalysts is the relatively low isotacticity which in the case of isotactic polypropylene results in low melting points. Metallocenes having substituents in the 2 and 4 positions in particular and specifically rac-dimethylsilylbis(2-methyl-4-isopropylindenyl)zirconium dichloride in combination with methylaluminoxane give, in the case of propylene, a polymer having high isotacticity and therefore a high melting point (EP 530 647). A further increase in the melting point has been achieved by the use of 4-aryl-substituted bisindenyl systems (EP 576 970).
However, there are industrial applications in which low melting points are desired.
A disadvantage with the use of soluble (homogeneous) metallocene-methylaluminoxane catalyst systems in processes in which the polymer formed is obtained as a solid is the formation of heavy deposits on reactor walls and stirrer. These deposits are formed by agglomeration of the polymer particles if the metallocene or aluminoxane or both are present in dissolved form in the suspension medium. Such deposits in the reactor systems have to be regularly removed since they rapidly reach considerable thicknesses, have a high strength and prevent heat exchange to the cooling medium.
To avoid reactor deposits, metallocenes can be supported. Processes for this purpose are known (EP 578 838). For technical reasons, it would be advantageous to omit the additional process step of application to a support. EP 528 041 discloses binuclear metallocenes which are suitable for preparing syndiotactic polymers having a low molecular weight.
In many publications concerning metallocenes it is stated that metallocene mixtures are also suitable for the polymerization of olefins. However, the use of supported metallocene mixtures results in the following difficulties:
a) If mixtures of supported metallocenes are used, i.e. there is only one type of metallocene on each support particle, nonuniform particle size distributions are obtained in the reactor, which adversely affects the polymerization and the subsequent work-up of the polymerization products in respect of the throughput and the susceptibility to faults (e.g. limitation of the solids content in the polymerization in a liquid medium; instability of the fluidized bed in gas-phase processes; deposit formation; nonuniform particle separation in cyclones). In addition, the polymerization product obtained is a mixture of particles which each consist of a uniform polymer, so that the mixture has to be homogenized in the melt in a further extrusion step. Such a homogenization is increasingly incomplete with increasing difference between the polymers of the individual particles (e.g. molecular weight, viscosity) and increasing granulation throughput. Inhomogeneities in the corresponding polyolefins are the result.
b) If metallocene mixtures are supported as such, i.e. there are at least two different types of metallocene on each support particle, there is the problem of setting a particular composition of the mixture, since the composition of the mixture of the metallocenes fixed on the support changes as a function of the method of application to the support and the conditions of application to the support.
It is therefore an object of the invention to find a catalyst system which overcomes the disadvantages of the prior art.
It has surprisingly been found that this object is achieved by multinuclear metallocene compounds containing at least two metallocene fragments which are different from one another.
The present invention accordingly provides a multinuclear metallocene compound containing at least two metallocene fragments L—MX
2
—L which are different from one another and having the formula I
where B is a bridging unit, m is an integer from 2 to 100,000, preferably from 2 to 10, M is a metal atom of group IVb, Vb or VIb of the Periodic Table of the Elements, X are identical or different in one metallocene fragment L—MX
2
—L and are each, independently of one another, hydrogen, a C
1
-C
40
-hydrocarbon-containing group, an OH group, a halogen atom or a pseudohalogen, L are identical or different in one metallocene fragment L—MX
2
—L and are each, independently of one another, a &pgr; ligand or another electron donor.
The m metallocene fragments L—MX
2
—L are different from one another or identical, with at least two of the m metallocene fragments L—MX
2
—L being different from one another. Two metallocene fragments L—MX
2
—L can be different from one another in one or more of the structural elements L, M and X.
Examples of M are titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten. Preference is given to metallocenes of group IVb of the Periodic Table of the Elements, for example zirconium, hafnium and titanium.
The radicals X are each a hydrogen atom, a C
1
-C
40
-hydrocarbon-containing group such as a C
1
-C
10
-, preferably C
1
-C
4
-alkyl group, a C
1
-C
10
-, preferably C
1
-C
3
-alkoxy group, a C
6
-C
10
-, preferably C
6
-C
8
-aryl group, a C
6
-C
10
-, preferably C
6
-C
8
-aryloxy group, a C
2
-C
10
-, preferably C
2
-C
4
-alkenyl group, a C
7
-C
40
-, preferably C
7
-C
12
-arylalkyl group, a C
7
-C
40
-, preferably C
7
-C
12
-alkylaryl group, a C
8
-C
40
-, preferably C
8
-C
12
-arylalkenyl group, an OH group, a halogen atom such as fluorine, chlorine, bromine or iodine, preferably chlorine, or a pseudohalogen such as nitrile.
The ligands L are preferably ea
Aulbach Michael
Brekner Michael-Joachim
Kuber Frank
Zenk Roland
Connolly Bove & Lodge & Hutz LLP
Rabago R.
Targor GmbH
Wu David W.
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