WO2002006356A1

WO2002006356A1 - Method for the production of polyolefins with a narrow bimodal molecular weight distribution

Info

Publication number: WO2002006356A1
Application number: PCT/EP2001/008235
Authority: WO
Inventors: Marc Oliver Kristen; Dieter Lilge; Peter Jutzi; Christian Mueller
Original assignee: Basell Polyolefine Gmbh
Priority date: 2000-07-18
Filing date: 2001-07-17
Publication date: 2002-01-24
Also published as: DE10035308A1

Abstract

The invention relates to a method for the production of polyolefins at pressures of from 1 to 4,000 bar and temperatures of from 20 to 350 °C in the presence of a catalyst system, comprising an organometallic compound from the group of the metallocenes or the catalytically active iron, cobalt, nickel, or palladium complexes. The organometallic compound comprises a Lewis base functionality which is arranged such that said functionality can co-ordinate intramolecularly to the central metal atom of the organometallic compound. The reaction temperature is adjusted such that the resulting polyolefin has a bimodal molecular weight distribution MW/MN of ∫5.0, measured by gel permeation chromatography.

Description

Process for the preparation of polyolefins with a narrow, bimodal molecular weight distribution

description

The present invention relates to a process for the preparation of polyolefins at pressures from 5 to 4,000 bar and temperatures from 20 to 350 ° C. in the presence of a catalyst system which is an organometallic compound from the group of the metallocenes or the catalytically active iron or cobalt -, Nickel or palladium complexes, which organometallic compound has a Lewis base functionality which is arranged so that it can coordinate intramolecularly to the central metal atom of the organometallic compound.

Monomodal, based on the molecular weight distribution M _w / M _n , means in the present application that the molar mass distribution has a single maximum.

In the present application, bimodal, based on the molecular weight distribution M _w / M _n , means that the course of the molar mass distribution curve has two turning points on one flank.

Catalyst systems with a uniformly defined active center, so-called single-site catalysts, are becoming increasingly important in the polymerization of olefins. These catalyst systems lead to polymers with monomodal, narrow molecular weight distributions, which results in particularly favorable mechanical properties. However, the monomodal molecular weight distribution often makes it difficult to process polymers produced in this way.

In order to improve the processing of such polymers, attempts are increasingly being made to produce polymer blends. Such blends are generally easier to process and mostly still have the advantageous mechanical properties of the single-site-catalyzed polymers to a satisfactory extent.

Such a polymer mixture or, more generally, polymers with a broadened and often bimodal molecular weight distribution can be obtained in various ways. Thus, of course, two or more polymer granules or polymer granules can be homogeneously mixed with one another, for example in an extruder. _' The The disadvantage of this method is the additional processing costs due to the additional processing step.

Another possibility for the production of such polymers is the use of a reactor cascade, two reactors with different reaction conditions being coupled in series. The disadvantage of such cascade processes lies primarily in the additional outlay on equipment, but also in the difficulty in maintaining constant reaction conditions.

A third possibility for producing bimodal or multimodal polymers is to premix several catalysts with different polymerization properties. Such polymerization processes using several catalysts are e.g. known from EP-A 128 045, EP-A 0 619 325 or EP-A 0 516 018.

More and more chemical variations of the metallocene catalysts, the best-known group of single-site catalysts, are known. For example, also describes metallocene compounds with substituents that carry a Lewis base group. The Lewis base groups are primarily oxygen or nitrogen functionalities. Unbridged metallocene complexes or metallocene catalysts with Lewis base functionalities are e.g. in WO 97/27227, US-A 5 563 284 and DE-A 43 03 647. Bridged metallocene catalysts with Lewis base substituents are described in EP-A 0 608 054. However, all of these descriptions have in common that, as far as polymerizations with these metallocene complexes are described, the polymers obtained have narrow and monomodal molecular weight distributions, as are typical for single-site catalysts. In Angew. Chemie 2000, vol. 112, pages 800-803 describes polymers which have a broad, bimodal or monomodal molar mass distribution.

Therefore, the method according to the invention had the object, using only a catalyst complex and to get Polyolefinpolymerisate with fewer machines, which have good processing properties and a narrow bimodal molecular ^'''weight distribution.

Accordingly, a process for the preparation of polyolefins at pressures of 5 to 4,000 bar and temperatures of 20 to 350 ° C in the presence of a catalyst system which is an organometallic compound from the group of metallocenes or the catalytically active iron, cobalt, nickel or Palladium complexes, wherein this organometallic compound has a Lewis base function nality, which is arranged so that it can coordinate intramolecularly to the central metal atom of the organometallic compound, found which method is characterized in that the reaction temperature is adjusted so that the resulting polyolefin has a bimodal molecular weight distribution

MW / MN, measured by gel permeation chromatography, of <5.0.

Furthermore, the use of such an organometallic compound for the production of polyolefins with a bimodal molecular weight distribution M _W / M _M , measured by gel permeation chromatography, of <5.0 and the corresponding polyolefins were found.

The present invention is based on the observation that when using special single-site catalyst systems, namely those which have a Lewis base functionality which is able to coordinate to the central metal atom of the complex, a bimodal one at certain temperatures Molecular weight distribution occurs with a molecular weight distribution M _w / M _n of <5, so that a bimodal adjustment of the molecular weight distribution in the direction of the desired polymer properties is possible by suitable temperature control using only one catalyst complex.

The method according to the invention is suitable in principle for the production of very different polyolefins. According to the invention, e.g. Polymerize or copolymerize ethylene, propylene or higher olefins alone or as a mixture of these monomers. In particular in the case of catalyst systems which are based on organometallic compounds from the Villa group of the Periodic Table, it is also advantageously possible to copolymerize polar comonomers such as vinyl acetate, acrylic or methacrylic acid esters or these acids themselves with ethylene or olefins. The process is also suitable for the production of vinyl aromatic polymers.

Propylene is preferably homopolymerized or copolymerized with higher α-olefins and / or vinyl aromatic compounds. Highly suitable higher α-olefins are C - bis

Cιo-Alk-1-enes such as ethylene, 1-butene, 1-hexene, 1-octene; well-suited vinyl aromatic compounds are styrene and styrene derivatives.

' Preferred bimodal propylene copolymers with Mw / Mn <5 are those which contain at least 50 mol% of propylene. Copolymers of this type which have isotactic and / or hemisotactic propylene sequences are particularly preferred.

Preferred bimodal propylene homopolymers with M _w / M _n <5 are isotactic and hemiisotactic propylene homopolymers.

The process according to the invention can be carried out in a pressure range from 5 to 4,000 bar. The process can be carried out in the customary polymerization plants known to those skilled in the art and by the customary polymerization processes. Examples include polymerization processes in gas phase reactors, in particular in gas phase fluidized bed reactors, polymerizations in solution or suspension polymerization processes. The methods mentioned are usually operated at pressures between 1 and 50 bar, in particular between 5 and 40 bar. The process according to the invention is carried out at a reaction temperature which results in a molecular weight distribution of <5.0, preferably <4.0. Reaction temperatures which are very suitable are from 20 to 120 ° C., particularly preferably 60 to 100 ^oC - The process ^{according to the} invention can also be carried out in high-pressure ^{polymerization} processes, for example in a stirred autoclave or in tubular reactors, pressures of 500 to 4000 bar, preferably 1000 to 3000 bar and Temperatures of 160 ° C to 350 ° C, preferably 200 ° C to 240 ° C are used.

The reaction temperature of the process according to the invention depends on the one hand on the catalytically active organometallic compound used and on the other hand on the desired molecular weight distribution and the bimodal curve shape of the GPC chromatogram of the polymer. The suitable polymerization temperature can easily be determined by a few preliminary tests.

An important feature of the process according to the invention is that the organometallic compounds which are part of the catalyst system have a Lewis base functionality which is arranged in such a way that it can coordinate intramolecularly to the central metal atom of the organometallic compound. This feature can be achieved through a variety of possible chemical structures and arrangements, as well as through a variety of substitution patterns. The type of substitution or the chemical nature of the Lewis base ligands is therefore less critical than the possibility of the above-mentioned coordination ability. When selecting suitable organometallic compounds, it can be checked, for example, in a simple manner with the aid of molecular models whether a particular catalyst complex does Requirement that the Lewis base functionality can coordinate to the metal atom is met.

The catalyst systems used in the process according to the invention can contain various organometallic compounds as the catalytically active compound. A preferred embodiment of the process is characterized in that a metallocene complex of the general formula I is used as the organometallic compound

) o (X ²⁾ p ⁽ X ³ ) q (X ⁴ ) r

in which the substituents and indices have the following meaning:

M titanium, zirconium, hafnium or vanadium,

R ¹ to R ^{5 are} hydrogen, C] _- to Cio-alkyl, 5- to 7-membered cycloalkyl, which in turn can carry a Ci- to Cio-aryl as a substituent, C ₆ - to C ₅ -aryl or arylalkyl , where appropriate also two adjacent radicals together can stand for cyclic groups having 4 to 15 carbon atoms, Si (R ⁶ ), a group with Lewis base functionality or together with a radical X ^α to X ⁴ a bridge member to Metal atom M,

R ⁵ Ci to Cio-alkyl, C ₆ to C ₁₅ aryl or C ₃ to Cio-cycloalkyl,

X ¹ to X ⁴ fluorine, chlorine, bromine, iodine, hydrogen, C] _- to Cio-alkyl, Cβ- to Ci ₅ ~ aryl, alkylaryl with 1 to 10 C-atoms in the alkyl radical and 6 to 20 C- Aryl atoms, -OR ¹² , -NR ¹ R ¹³ or

With Rl2 and R ¹³ to Ci- Cι ₀ alkyl, C ₆ - to C ₁₅ -aryl, alkylaryl, arylene lalkyl, fluoroalkyl or fluoroaryl each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 C atoms in the aryl radical,

R ⁷ to R ^{11 are} hydrogen, C ~ to Cio-alkyl, 5 to 7-membered

Cycloalkyl, which in turn can carry a C 1 -C 8 -alkyl as a substituent, C 6 ~ to Cχ ₅ aryl or arylalkyl, where optionally two adjacent radicals together can also represent cyclic groups having 4 to 15 C atoms, Si (R ¹⁴ ) ₃ , a group with Lewis base functionality or, together with a radical R ¹ to R ^5, a bridge member between the cyclopentadienyl systems,

Rl ⁴ Ci to C ₁₀ alkyl, C ₆ to C ₅ aryl or C ₃ to

Cio-cycloalkyl,

and

o, p, q, r integers in the range 0 to 4, the sum o + p + q + r + 1 corresponding to the valency of M,

with the condition that either at least one of the radicals R ¹ to R ⁵ or R ⁷ to R ¹¹ denotes a group with Lewis base functionality, or the bridge between the cyclopentadienyl systems or between a cyclopentadienyl system and the metal atom M is such a group Group with Lewis base functionality.

Preferred metals M are titanium and zirconium, in particular zirconium.

In addition to hydrogen, in particular C 1 -C 6 -alkyl groups, very particularly suitable methyl R ¹ to R ⁵ are methyl, ethyl, propyl, n-butyl, isobutyl and tert-butyl. The cyclopentadienyl nucleus can be substituted one or more times, preferably once or twice, with such alkyl groups. In addition to these alkyl-substituted cyclopentadienyl radicals, cyclopentadienyl systems are particularly suitable in which two adjacent radicals R ¹ to R ⁵ are linked to form cyclic groups which in turn can carry substituents. Examples include substituted and unsubstituted indenyl, tetrahydroindenyl, benzindenyl and fluorenyl residues. In addition to the above A substituent with a Lewis base group can additionally be present.

As a rule, one of the ligands X ¹ to X ⁴ is also a cyclopentadienyl system, so that a biscyclopentadienyl complex is therefore present. Furthermore, one of the radicals X ¹ to X ⁴ can also represent a bridge member which is connected to the cyclopentadienyl nucleus depicted in formula I, so that a monocyclopentadienyl complex is present. The further radicals X ¹ to X ⁴ are preferably halogen, in particular chlorine, or C 1 -C ₄ -alkyl, chlorine being particularly advantageous as a ligand, in particular for precursors of the catalytically active complex.

For the radicals R ⁷ to R ¹¹ , the same radicals are preferred as were mentioned for the radicals R ¹ to R ⁵ .

Organometallic compounds which have a bridged metallocene complex have proven particularly advantageous for use in the process according to the invention. Bridged metallocene complexes are understood to mean those which either have a bridge between a cyclopentadienyl radical and the central metal atom, or those in which the bridge member connects two cyclopentadienyl radicals to one another.

A particularly advantageous embodiment of the process according to the invention is characterized in that the metallocene complex of the formula I has a bridge member between two cyclopentadienyl systems.

A further particularly advantageous embodiment consists in a process which is characterized in that the bridge member between two cyclopentadienyl systems has the structure of the general formula II

\ /

Si II

/ \

_R 16

in which

R ¹⁵ and R ^{16 are} a C ₁ -C ₂ -hydrocarbyl radical with at least one oxygen, sulfur, nitrogen or phos ιi- ^' phosphorus-containing substituent means.

R ¹⁵ and R ¹⁶ are chemically very different C 1 -C 8 -hydrocarbyl groups. Examples include alkoxyphenyl radicals which are connected to the silicon atom via an alkylene group. Alkylamino or alkoxy groups which are bonded to the silicon via alkylene radicals having a length of 1 to 10 carbon atoms are also suitable. Also to be mentioned are residues in which the Lewis base functionality is based in a thioether or ester group. Examples include C 1 -C ₄ -alkyl esters of carboxylic acid groups, the carboxylic acid in turn being able to be bonded to the silicon atom via an alkylene radical. In addition to the alkoxy functions, cyclic ethers such as tetrahydrofuranyl groups, which are likewise bonded to the silicon atom via a suitable alkylene radical, are also suitable. In addition to the silyl bridges of the general formula II, analog bridge members with germanium atoms or C ₁ -C ₃ -alkylene groups, which can be substituted in an analogous manner to the silicon atom, are also suitable.

A further preferred embodiment of the process is characterized in that at least one of the radicals R ¹ to R ⁵ or R ⁷ to R ¹¹ denotes a radical of the general formula lilac or Illb

(CR ¹⁷ R ¹⁸ ) _n YR ¹⁹ R ²⁰ purple (CR ¹⁷ R ¹⁸ ) _n ZR ¹⁹ Illb

in which the variables have the following meaning:

R ¹⁷ and R ^{18 are} hydrogen, C 1 to C ₁₀ alkyl, C ₅ to C ₅ aryl or C ₃ to C ₁₀ cycloalkyl,

R ¹⁹ and R ^{20 are} Ci to Cι ₀ alkyl, C ₆ - to Cι ₅ aryl or C ₃ - to Cio-cycloalkyl,

n is an integer in the range from 0 to 10

Y nitrogen or phosphorus and

Z oxygen or sulfur. The radicals R ¹⁷ and R ¹⁸ are preferably hydrogen or lower alkyl such as methyl or ethyl, the radicals R ¹⁹ and R ²⁰ are preferably short alkyl groups such as methyl, ethyl, propyl or butyl. n is preferably a number between 2 and 6, in particular 2 or 4. y is preferably nitrogen, z is preferably oxygen.

Metallocene complexes in which one of the cyclopentadienyl systems is a substituted or unsubstituted fluorenyl system have proven to be particularly advantageous for use in the process according to the invention.

In addition to the metallocene complexes, other organometallic compounds can also be used in the process according to the invention. In principle, all single-site catalysts known to the person skilled in the art, as are described, for example, in WO 96/23010, WO 98/27124 or WO 96/23004, are suitable, provided that they are suitably with a substituent with Lewis base functionality are equipped. A further embodiment of the process according to the invention is therefore characterized in that a compound of the general formula IV is used as the organometallic compound

where the variables have the following meaning:

R ²¹ to R ^{32 are} hydrogen, Ci- to Cio-alkyl, 5- to 7-membered cycloalkyl, which in turn is a Cι ~ to Cio-alkyl

Can carry substituent, Cς- to Cis-aryl or arylalkyl, where optionally two adjacent radicals together can also represent cyclic groups having 4 to 15 C atoms, Si (R ⁶ ) ₃ or a group with Lewis Base functionality, at least one radical R ²¹ to R ³² must be such a group with Lewis base functionality, R ³³ and R ³⁴ fluorine, chlorine, bromine, iodine, hydrogen, Cι ~ bis

Cio-alkyl, C ₆ - to C ₅ -aryl, alkylaryl with 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, -OR ¹² or -NR ¹² R ¹³ > and

M 'a metal from the Villa group of the Periodic Table.

In addition to hydrogen, radicals R ²¹ to R ³² are in particular lower alkyl groups such as methyl, ethyl, propyl or butyl, the aromatic ring systems preferably being substituted one to three times with such alkyl groups. For the structure of the group with Lewis base functionality, this already applies to the corresponding metallocene complexes. At least one of the radicals R ²¹ to R ³² preferably denotes a radical of the general formula lilac or Illb.

According to the invention, the use of an organometallic compound, as described above, for the production of polyolefins with a molecular weight distribution iy ^, / M _n , measured by gel permeation chromatography, of <5.0, preferably <4.

The catalyst complexes can be prepared by customary methods known to those skilled in the art. Information on the production of metallocene complexes can be obtained, for example, from WO 97/27227.

In order to develop catalytic polymerization activity, the above-mentioned organometallic complexes generally have to be activated by a cocatalyst. The methods for activating the catalyst complexes are generally known and do not constitute a special feature of this invention. For example, the metallocene complexes can be activated in a known manner with alumoxanes, in particular with methylalumoxane, or with ionizing compounds which are capable of complexing a metallocenium cation in a non-coordinating manner.

Examples

The following conditions were selected for the GPC examinations based on DIN 55672: solvent: 1, 2, 4-trichlorobenzene, flow: 1 mL / min, temperature: 140 ° C, calibration: PE standards, device: Waters 15OC.

Isopropylidene [3- (NN-diethalaminoethyl) cyclopentadienyl-fluoro- ^1- ren-9-yl] zirconocene dichloride (1) (1) was as in Eur. J. Inorg. Che 1998, 663-674.

Polymerization of propylene

General procedure for the polymerization of propylene:

A previously carefully heated 11-Büchi laboratory autoclave (2 h under high vacuum at 90 ° C), equipped with mass flow, pressure and temperature controllers, was m counter-argon with the

Solvent toluene and part of the MAO solution filled (see respective test instructions). The total volume during the polymerization was 200 ml. The contents were brought to the desired temperature and 5 bar of propylene were injected; The propylene pressure was kept constant over the entire polymerization period. The preactivated catalyst solution was introduced into the autoclave using a pressure burette. The polymerization was stopped by adding 20 ml of isopropanol.

General working procedure for working up the polymerization reaction:

The polymerization of propylene with (1) / MA0 resulted in a propylene polymer that is soluble in toluene. The polymer-containing solution was therefore concentrated after the polymerization process in a solution of 200 ml of methanol, 200 ml of water and 50 ml. HCl solution added and stirred for 18 h. The organic phase was then separated off and concentrated to about 5 ml. Acetone (approx. 20 ml) was then added, the polypropylene being obtained as a colorless, stretchable and elastic solid.

example 1

Catalyst system: (l) / MAO

Preactivation: (1) (16.0 mg, 3.0xl0 ^{~ 5} mol),

10.00 ml MAO (16.7 mmol AI)

Autoclave content: 182 ml toluene, 8.0 ml MAO (13.3 mmol)

Mole ratio Zr: Al: 1: 1000 polymerization temperature: T = 50 ° C

Propylene pressure: p = 5 bar

Polymerization time: t = 1.5 h

Yield of polymer: 1.9 g

Activity of the catalyst: 8.4 kg PP / (mol Zr-h-bar) GPC analysis of the polymer: M ^: 20466, M _n : 5300; Mw / M _n , - 3.94 Example 2

Preactivation: (1) (26.6 mg, 5th OxlO " ⁵ mol),

16.7 ml MAO (16.7 mmol AI) autoclave content: 170 ml toluene, 20 ml MAO (33.3 mmol)

Molar ratio Zr: Al: 1: 1000 polymerization temperature: T = 25 ° C propylene pressure: p = 5 bar polymerization time: t = 2.0 h polymer yield: 4.1 g

Activity of the catalyst: 10.9 kg PP / (mol Zr.h.bar) GPC analysis of the polymer: M _M 58265, M _n : 11784; M _w / M _n ; 4.94

Claims

claims

1. Process for the preparation of polyolefins at pressures from 1 to 4,000 bar and temperatures from 20 to 350 ° C in the presence of a catalyst system which is an organometallic compound from the group of metallocenes or the catalytically active iron, cobalt, nickel or palladium complexes which organometallic compound has a Lewis base functionality which is arranged so that it can coordinate intramolecularly to the central metal atom of the organometallic compound, which method is characterized in that the reaction temperature is adjusted so that the resulting Polyolefin has a bimodal molecular weight distribution Mw / M _N , measured by gel permeation chromatography, of <5.0.

2. The method according to claim 1, characterized in that a metallocene complex of the general formula I is used as the organometallic compound

in which the substituents and indices have the following meaning:

M titanium, zirconium, hafnium or vanadium,

R ¹ to R ^{5 are} hydrogen, Ci- to Cio-alkyl, 5- to 7-membered cycloalkyl, which in turn can carry a Ci- to C o-aryl as a substituent, Cg- bis

Cis-aryl or arylalkyl, where optionally two adjacent radicals together can represent cyclic groups having 4 to 15 carbon atoms, Si (R ⁵ ) ₃ , a group with Lewis base functionality or together with a radical X ¹ to X ⁴ a bridge member to the metal atom M,

R ⁶ C - to Cio-alkyl, C ₆ - to -C ₅ aryl or C ₃ - to

Cio-cycloalkyl, X ¹ to X ⁴ fluorine, chlorine, bromine, iodine, hydrogen, Cι ~ bis

Cio-alkyl, Cg to cis aryl, alkylaryl with 1 to 10 C atoms in the alkyl radical and 6 to 20 C atoms in the aryl radical, -OR ¹² , -NR ¹² R ¹³ or

With

R ¹ and R ¹³ Ci to Cio-alkyl, C ₆ - to Cis-aryl, alkylaryl, arylalkyl, fluoroalkyl or fluoroaryl with each

1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical,

R ⁷ to R ¹¹ are hydrogen, ~ to Cio-alkyl, 5 to 7-membered cycloalkyl which may in turn bear a Cι ~ to Cio-alkyl as a substituent, C _ß - to C ₅ -aryl or arylalkyl, where appropriate, two neighboring radicals together can represent cyclic groups having 4 to 15 carbon atoms, Si (R ¹⁴ ) ₃ , a group with Lewis base functionality or together with a radical R ¹ to R ⁵ a bridging member between the cyclopentadienyl systems,

With

R ¹⁴ Ci to Cio-alkyl, Cβ ~ to Cis-aryl or C ₃ - bis

Cio-cycloalkyl,

and

with the condition that either at least one of the radicals R ¹ to R ⁵ or R ⁷ to R ¹¹ denotes a group with Lewis base functionality or the bridge between the cyclopentadienyl systems or between a cyclopentadienyl system and the metal atom M is such a group with Lewis Base radio functionality bears'.

3. The method according to claim 2, characterized in that a bridged metallocene complex is used as the organometallic compound.

4. Process according to claims 1 to 3, characterized in that at least one of the radicals R ¹ to R ⁵ or R ⁷ to R ^{11 represents} a radical of the general formula purple or Illb

(CR ¹ R ¹⁸ ) _n YR ¹⁹ R ²⁰ purple (CR ¹⁷ R ¹⁸ ) _n ZR ¹⁹ Illb

in which the variables have the following meaning:

R ¹⁷ and R ^{18 are} hydrogen, Ci to Cι ₀ alkyl, C ₆ to Cι ₅ aryl or C ₃ to Cio cycloalkyl,

R ¹⁹ and R ⁰ Cι ~ to Cι ₀ alkyl, C ₆ - to Cι ₅ -aryl or C ₃ - bis

Cio-cycloalkyl,

n is an integer in the range from 0 to 10

Y nitrogen or phosphorus and

Z oxygen or sulfur.

5. The method according to claim 4, characterized in that one of the cyclopentadienyl syste e is a substituted or unsubstituted fluorenyl system.

6. The method according to claim 1, characterized in that a compound of the general formula IV is used as the organometallic compound

where the variables have the following meaning: R ²¹ to R ^{32 are} hydrogen, C 1 -C 1 -alkyl, 5- to 7-membered cycloalkyl, which in turn can carry a C 1 -C 1 -C 6 alkyl as a substituent, Cg- to cis-aryl or arylalkyl, optionally also two adjacent ones Leftovers together for 4 to

Cyclic groups containing 15 carbon atoms can be Si (R ⁶ ) ₃ or a group with Lewis base functionality, at least one radical R ²¹ to R ³² having to be such a group with Lewis base functionality,

R ³³ and R ³⁴ fluorine, chlorine, bromine, iodine, hydrogen, Cι ~ bis

Cio-alkyl, Cg to cis-aryl, alkylaryl with 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, -OR ¹² or -NR ¹² R ¹³ and

M 'a metal from the Villa group of the Periodic Table.

7. The method according to claim 6, characterized in that at least one of the radicals R ²¹ to R ^{32 is} a radical of the general

Formula is purple or illb.

8. The method according to claims 1 to 7, wherein the polyolefins are propylene homopolymers or propylene copolymers with higher α-olefins and / or vinyl aromatic compounds.

9. Polyolefins obtainable by the process according to claims 1 to 8.

10. Use of an organometallic compound according to claims 1 to 8 for the production of polyolefins with a molecular weight distribution Mw / M _n , measured by gel permeation chromatography, of <5.0.