Catalyst system and its use for the polymerization of propylene

Details Catalyst system and its use for the polymerization of propylene Catalyst system and its use for the polymerization of propylene

2000-11-15

2003-06-10

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...

C526S148000, C526S160000, C526S161000, C526S169000, C526S141000, C526S139000, C526S151000, C526S152000, C526S153000, C526S126000, C526S904000, C526S351000, C526S905000, C526S943000

Reexamination Certificate

active

06576723

ABSTRACT:

The present invention relates to catalyst systems and their use in the polymerization of propylene.
Processes for preparing polyolefins with the aid of soluble, homogeneous catalyst systems comprising a transition metal component of the metallocene type and a cocatalyst component such as an aluminoxane, a Lewis acid or an ionic compound are known. These catalysts have a high activity and give polymers and copolymers having a narrow molar mass distribution.
In polymerization processes using soluble, homogeneous catalyst systems, thick deposits are formed on reactor walls and stirrers if the polymer is obtained as a solid. These deposits are formed by agglomeration of polymer particles whenever metallocene and/or cocatalysts are present in dissolved form in the suspension. Such deposits in the reactor systems have to be removed regularly since they quickly attain considerable thicknesses, have a high strength and prevent heat transfer to the cooling medium. Such homogeneous catalyst systems cannot be used in modern industrial polymerization processes in the liquid monomer or in the gas phase.
To avoid deposit formation in the reactor, it has been proposed that supported catalyst systems in which the metallocene and/or the aluminum compounds serving as cocatalyst are immobilized on an inorganic support material be used.
EP-A-0,576,970 discloses metallocenes and corresponding supported catalyst systems.
Highly active supported catalyst systems for preparing industrially important polyolefins having high tacticity and a high melting point, in particular polypropylenes, comprise ansa-metallocenes in racemic or pseudoracemic form and are known, for example, from EP-A-0,530,647; EP-A-0,576,970 and EP-A-0,653,433.
Ansa-Metallocenes are obtained in the synthesis as isomer mixtures (rac form and meso form or pseudo rac/pseudo meso form), so that an additional and complicated process step for separating rac and meso forms (or the pseudo forms) is necessary. A definition of the terms rac form and meso form may be found in Brinzinger et al., Journal of Organometallic Chemistry, 232 (1982) page 233 and Schlögl, Top. Stereochem., 1 (1967) page 39 ff.
In addition, methylaluminoxane (MAO) as hitherto the most effective cocatalyst has the disadvantage of having to be used in a large excess. Such aluminoxanes are described, for example, in JACS 117 (1995), 6465-74, Organometallics 13 (1994), 2957-2969.
The preparation of cationic alkyl complexes opens a route to MAO-free catalysts having comparable activity in which the cocatalyst can be used in a virtually stochiometric amount.
Industrial utilization of metallocene catalysts necessitates, as described above, their conversion into a heterogeneous catalyst system in order to ensure an appropriate morphology of the resulting polymer. The application of cationic metallocene catalysts based on borate anions to supports is described in WO-91/09882. Here, the catalyst system is formed by application of a dialkyl-metallocene compound and a Brönsted-acid, quaternary ammonium compound having a noncoordinating anion such as tetrakispentafluorophenylborate to an inorganic support. The support material is modified beforehand using a trialkylaluminum compound. A disadvantage of this process for application to a support is that only a small part of the metallocene used is immobilized by physisorbtion on the support material. When the catalyst system is introduced into the reactor, the metallocene can easily be leached from the support surface. This leads to a polymerization which occurs partly homogeneously, resulting in an unsatisfactory morphology of the polymer.
It is an object of the present invention to find an inexpensive, highly active catalyst system for the preparation of polypropylene having high tacticity and a high melting point and also to provide a simple and economical process for preparing such a catalyst system, which process requires no additional separation of rac and meso forms of the metallocene components present and does not use aluminoxanes such as methylaluminoxane (MAO) as cocatalyst.
We have found that this object is achieved by a catalyst system comprising at least one metallocene as rac/meso isomer mixture, at least one organoboroaluminum compound, at least one passivated support, at least one Lewis base and, if desired, at least one further organometallic compound.
The present invention accordingly provides a catalyst system comprising
a) at least one substituted metallocene of the formula A
 where
R
1
and R
2
are identical or different and are each a hydrogen atom, a C
1
-C
20
-hydrocarbon group such as a C
1
-C
20
-alkyl group, preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl or hexyl, a C
6
-C
14
-aryl group or a C
2
-C
20
-alkenyl group, with the proviso that R
1
is not methyl when R
2
is hydrogen,
M
1
is a transition metal of group 4, 5 or 6 of the Periodic Table of the Elements, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten, preferably titanium, zirconium or hafnium, particularly preferably zirconium,
A is a bridge of the formula
 or ═BR
3
, AIR
3
, —S—, —SO—, —SO
2
—, ═NR
3
, ═PR
3
, ═P(O)R
3
, o-phenylene, 2,2′-biphenylene, where
M
2
is carbon, silicon, germanium, tin, nitrogen or phosphorus, preferably carbon, silicon or germanium, in particular carbon or silicon,
o is 1, 2, 3 or 4, preferably 1 or 2,
R
3
and R
4
are identical or different and are each, independently of one another, a hydrogen atom, halogen, a C
1
-C
20
group such as C
1
-C
20
-alkyl, in particular a methyl group, C
6
-C
14
-aryl, in particular a phenyl or naphthyl group, C
1
-C
10
-alkoxy, C
2
-C
10
-alkenyl, C
7
-C
20
-arylalkyl, C
7
-C
20
-alkylaryl, C
6
-C
10
-aryloxy, C
1
-C
10
-fluoroalkyl, C
6
-C
10
-haloaryl, C
2
-C
10
-alkynyl, C
3
-C
20
-alkylsilyl, for example trimethylsilyl, triethylsilyl or tert-butyldimethylsilyl, C
3
-C
20
-arylsilyl, for example triphenylsilyl, or C
3
-C
20
-alkylarylsilyl, for example dimethylphenylsilyl, diphenylsilyl or diphenyl-tert-butylsilyl, or R
3
and R
4
may together form a monocyclic or polycyclic ring system, and
A is preferably dimethylsilanediyl, dimethylgermanediyl, ethylidene, methylethylidene, 1,1-dimethylethylidene, 1,2-dimethylethylidene, tetramethylethylidene, isopropylidene, phenylmethylmethylidene, diphenylmethylidene, particularly preferably dimethylsilanediyl, dimethylgermanediyl or ethylidene,
X are identical or different and are each a hydrogen atom, a halogen atom such as fluorine, chlorine, bromine or iodine, a hydroxyl group, a C
1
-C
10
-alkyl group such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hexyl or cyclohexyl, a C
6
-C
15
-aryl group such as phenyl or naphthyl, a C
1
-C
10
-alkoxy group such as methoxy, ethoxy or tert-butoxy, a C
6
-C
15
-aryloxy group, a benzyl group, an NR
5
2
group, where R
5
are identical or different and are each a C
1
-C
10
-alkyl group, in particular methyl and/or ethyl, a C
6
-C
15
-aryl group, a (CH
3
)
3
Si group, preferably a chlorine atom, a fluorine atom, a methyl group, a benzyl group or an NMe
2
group, particularly preferably a chlorine atom or a methyl group,
where the ratio of rac isomer to meso isomer of the metallocene of the formula (A) in the novel catalyst system is from 1:10 to 2:1, preferably from 1:2 to 3:2,
b) at least one Lewis base of the formula I,
M
3
R
6
R
7
R
8
  (I)
 where
R
6
, R
7
and R
8
are identical or different and are each a hydrogen atom, a C
1
-C
20
-alkyl group, a C
1
-C
20
-haloalkyl group, a C
6
-C
40
-aryl group, a C
6
-C
40
-haloaryl group, a C
7
-C
40
-alkylaryl group or a C
7
-C
40
-arylalkyl group, where two radicals or all three radicals R
6
, R
7
and R
8
may be joined to one another via C
2
-C
20
units and M
3
is an element of main group V of the Periodic Table of the Elements,
c) a support,
d) at least one organoboroaluminum compound which is made up of units of the formula II
R
i
9
M
4
—O—M
4
R
j
10
 &

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