EP1115763A1

EP1115763A1 - Method for polymerizing conjugated diolefins (dienes) with catalysts based on cobalt compounds in the presence of vinylaromatic solvents

Info

Publication number: EP1115763A1
Application number: EP99932843A
Authority: EP
Inventors: Heike Windisch; Werner Obrecht; Gisbert Michels; Norbert Steinhauser
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1998-07-18
Filing date: 1999-07-07
Publication date: 2001-07-18
Also published as: AU4908499A; JP2002520455A; HK1039953A1; CA2337768A1; KR20010070979A; TW486491B; RU2001104873A; DE19832455A1; WO2000004064A1; CN1309672A; US6310151B1

Abstract

Conjugated diolefins, optionally combined with other unsaturated compounds that may be copolymerized with diolefins, are polymerized by conducting polymerization of the diolefins in the presence of catalysts based on cobalt compounds, organoaluminum compounds and modifiers in the presence of aromatic vinyl compounds at temperatures ranging from -30 DEG C to +80 DEG C. The invention provides a simple method for producing polydiolefin solutions such as polybutadiene with contents of 1,2-units of 10 to 30 % in aromatic vinyl compounds which can be further processed to obtain ABS or HIPS.

Description

Process for the polymerization of conjugated diolefins (dienes) with catalysts based on cobalt compounds in the presence of vinyl aromatic solvents

The present invention relates to a process for the polymerization of conjugated diolefins with catalysts based on cobalt compounds in the presence of aromatic vinyl compounds.

The polymerization of conjugated diolefins in the presence of a solvent has been known for a long time and is described, for example, by W. Hoffmann, Rubber

Technology Handbook, Hanser Publishers (Carl Hanser Verlag) Munich, Vienna. New York, 1989. For example, polybutadiene is now predominantly produced by solution polymerization using coordination catalysts of the Ziegler-Natta type, for example based on titanium, cobalt, nickel and neodymium compounds, or in the presence of alkyl lithium Links. The solvent used depends heavily on the type of catalyst used. Benzene or toluene and aliphatic or cycloaliphatic hydrocarbons are preferably used.

A disadvantage of the polymerization processes carried out today for the production of polydiolefins, e.g. BR, IR or SBR is the time-consuming work-up of the polymer solution to isolate the polymers, for example by stripping with water vapor or direct evaporation. A further disadvantage, particularly if the polymerized diolefins are to be processed further as impact modifiers for plastic applications, is that the polymeric diolefins obtained first have to be dissolved again in a new solvent, for example styrene, in order then to e.g. to be processed into acrylonitrile-butadiene-styrene copolymer (ABS) or high-impact polystyrene (HIPS).

US Pat. No. 3,299,178 describes a catalyst system based on TiCL / iodine / Al (iso-Bu) ₃ for the polymerization of butadiene in styrene to form homogeneous polymer. butadiene claimed. With the same catalyst system, Harwart et al. in Plaste and Kautschuk, 24/8 (1977) 540 describes the copolymerization of butadiene and styrene and the suitability of the catalyst for the production of polystyrene.

From US 4,311,819 it is known to use anionic initiators for the polymerization of butadiene in styrene. The disadvantage of the anionic initiators is that butadiene-styrene copolymers (SBR) are formed which, based on the butadiene units, allow only a slight control of the microstructure. By adding modifiers, only the proportion of 1, 2 or 1, 4-trans units can be increased, which leads to an increase in the glass transition temperature of the polymer. It is not possible to produce a high-cis-containing SBR with anionic initiators. This fact is particularly disadvantageous because SBR is formed in this process, which results in a further increase in the glass transition temperature as the styrene content increases compared to homopolymeric polybutadiene (BR).

However, when the rubber is used for impact modification of, for example, HIPS or ABS, a high glass transition temperature of the rubber has a disadvantageous effect on the low-temperature properties of the material.

Kobayashi et al. was e.g. in J. Polym. Be., Part A, Polym. Chem., 33 (1995)

2175 and 36 (1998) 241 describe a catalyst system consisting of halogenated rare earth acetates, such as Nd (OCOCCl ₃ ) ₃ or Gd (OCOCF ₃ ) ₃ , with tri (isobutyl) aluminum and diethyl aluminum chloride, which contains hexane in the inert solvent Copolymerization of butadiene and styrene enables. A disadvantage of these catalysts, in addition to the presence of inert solvents, is that the

Catalyst activity drops even at a low styrene incorporation from about 5 mol% to below 10 g polymer / mmol catalyst / h and that the 1,4-cis content of the polymer decreases significantly with increasing styrene content.

US 5096970 and EP 304088 describe a process for the preparation of polybutadiene in styrene using catalysts based on neodymphosphonates, organic aluminum compounds, such as di (iso-butyl) aluminum hydride (DIBAH), and a halogen-containing Lewis acid, such as ethyl aluminum sesquichloride, in which butadiene in styrene is added to a 1,4-cis- without further addition of inert solvents. Polybutadiene is implemented.

A disadvantage of this catalyst is that the polymers obtained have a very low 1,2 unit content of less than 1%. It is disadvantageous because a higher 1,2-content in the polymer has a positive effect on the grafting behavior between the rubber and the polymer matrix, e.g. Homo- or copolymers of vinyl aromatic compounds.

The rubber solutions in styrene described in the listed patent publications were used for the production of HIPS by adding free-radical initiators to the rubber solutions in styrene after removal of the unreacted monomer.

It was an object of the present invention to provide a process for the polymerization of conjugated diolefins in vinylaromatic solvents, with which it is possible to obtain polydienes with a content of 1,2 units above 1%, the content of 1 , 2 units can be varied in a simple manner and a high conversion of conjugated diolefins of over 50% can be obtained. In addition, there should be practically no conversion of the vinyl aromatic solvent used, i.e. sales should be less than 1%.

The present invention therefore relates to a process for the polymerization of conjugated diolefins, which is characterized in that the polymerization of the diolefins used in the presence of catalysts consisting of: a) Cobalt compounds, b) organoaluminium compounds and c) modifiers

and in the presence of aromatic vinyl compounds at temperatures of

-30 ° C to + 80 ° C, the molar ratio of components a): b): c) being in the range from 1:10 to 1,000: 0.1 to 100, the amount of component (a) used of the catalyst 1 μmol to 10 mmol, based on 100 g of the monomers used, and the amount of aromatic vinyl compounds 10 g to 2,000 g, based on 100 g of the monomers used.

Components a): b): c) are preferably used in the process according to the invention in the range from 1:10 to 500: 0.5 to 50.

As conjugated diolefins, e.g. 1.3-

Butadiene, 1,3-isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene and / or 2-methyl-1,3-pentadiene can be used.

Particularly suitable cobalt compounds (component (a)) are those which are soluble in inert organic solvents and which are selected from the groups consisting of

I complexes of β-diketones with cobalt,

II β-keto acid complexes of cobalt, III cobalt salts of organic acids with 6 to 15 carbon atoms,

IV complexes of halogenated cobalt compounds of the formula CoX _a D _D , where X represents a halogen atom, a denotes the numbers 2 or 3, D is an organic compound selected from a group consisting of tertiary amines, alcohols, tertiary phosphines, ketones and Is N, N-dialkylamides, and b is a number from 0 to 6, and

V Organometallic complexes of cobalt with π-bonded anions. The following can be used as cobalt compounds (component (a)) which are soluble in inert organic solvents:

(I) β-diketone-cobalt complexes, with β-diketonates of the formula R ¹ "-CO-CR ² " CO-R ³ , where R ¹ to R ^{3 can be the} same or different and represent hydrogen or an alkyl group with 1 are to 10, preferably 1 to 4 carbon atoms, for example Co (Me-CO-CH-CO-Me) ₂ and

Co (Me-CO-CH-CO-Me) ₃ ;

(II) β-keto acid ester complexes of cobalt, with keto acid esters of the formula R ¹ -CO-CR ² -CO-OR ³ , where R ¹ to R ^{3 can be the} same or different and represent hydrogen or an alkyl group with 1 to 10, preferably 1 to 4 carbon atoms, for example Co (Me-CO-CH-CO-O-Me) ₂ , Co (Me-CO-CH-CO-O-Et) ₂ , Co (Me-CO-CH- CO-O-Me) ₃ and

Co (Me-CO-CH ₂ -CO-O-Et) ₃ ;

(III) cobalt salts of organic acids with 6 to 15, preferably 6 to 10 carbon atoms, for example Co (octanoate) ₂ , Co (versatate);

(IV) Complexes of halogenated cobalt compounds of the above formula CoX _a D _b , for example CoCl ₂ - (pyridine) ₂ , CoBr ₂ - (pyridine) ₂ , CoCl ₂ - (PPh ₃ ) ₂ , CoBr ₂ - (PPh ₃ ) ₂ , CoCl ₂ - (vinylimidazole) ₄ , CoCl ₂ - (EtOH);

(V) Organometallic complexes of cobalt with π-linked anions, e.g. Tris

(π-allyl) cobalt, bis (π-allyl) cobalt chloride, bis (π-allyl) cobalt bromide, bis (π-allyl) cobalt iodide, bisacrylonitrile (π-allyl) cobalt, (1 , 3-butadiene) [1- (2-methyl-3-butenyl) -π-allyl] cobalt, bis- (π-1,5-cyclooctadienyl) - (tert-butyl-isonitrile) - Cobalt, (π-cyclooctenyl) - (π-1,5-cyclooctadienyl) cobalt, (π-cycloheptadienyl) - (π-1,5-cyclooctadienyl) cobalt, (bicyclo [3, 3, 0] octadienyl) - (π- 1,5-cyclooctadienyl) cobalt. The above-mentioned catalysts based on cobalt compounds are known and described, for example, and explained in more detail in the following references:

B. A. Dolgoplosk et al, Polym. Be, Ser. A, 36/10 (1994) 1380, L. Porri et al., Comp.

Polym. Be. 4/2 (1989) 53, O.K. Sharajew et al, Vysokomol. Soyed. A 38: No.3 (1996) 447, M. Takeuchi et al., Polym. Int. 29 (1992) L. Porri et al., Macromol. Chem., Macromol. Symp. 48/49 (1991) 239, G. Ricci et al., Polym. Comun. 29 (1988) 305, N.D. Golubeva et al. J. Polym. Be .: Polym. Symp. 68 (1980) 33 and S. S. Potapov et al. Vysokomol. Seyed. A 16: No. 11 (1974) 2515.

Suitable organoaluminum compounds of component (b) are, in particular, alumoxanes and / or aluminum organyl compounds.

Aluminum-oxygen compounds which, as is known to the person skilled in the art, are obtained as alumoxanes and are obtained by contacting organoaluminum compounds with condensing components, such as water, and the noncyclic or cyclic compounds of the formula (-Al (R) O-) _n contain, where R may be the same or different and represents a linear or branched alkyl group having 1 to 10 carbon atoms, which may also contain heteroatoms, such as oxygen or halogens. In particular, R represents methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-octyl or iso-octyl, particularly preferably methyl, ethyl or iso-butyl. Examples of alumoxanes are: methylalumoxane, ethylalumoxane and isobutylumoxane, preferably methylalumoxane and isobutylalumoxane.

The alumoxanes mentioned are described, for example, and are explained in more detail in “Alumoxanes” Macromol. Symp. 97 (1995).

As aluminum organyl compounds, compounds are used which are formed by reacting compounds of the formula A1R _3.C JX ₍ J, where R can be the same or different and represents an alkyl group with 1 to 12

Carbon atoms, a cycloalkyl group with 5 to 12 carbon atoms or an aryl group with 6 to 12 carbon atoms,

X represents a hydrogen or a halogen, such as chlorine, bromine, and

d represents a number from 0 to 2.

with compounds of the formula HYR ' _e , where

Y represents an element from groups Vb and VIb of the Periodic Table of the Elements, preferably oxygen, sulfur and nitrogen

R ^{'can be the} same or different and represents a hydrogen, an alkyl,

Cycloalkyl or aryl group having 1 to 12 carbon atoms and

e is 1 or 2 according to the valency of Y.

As compounds of the formula AlR ^ X _j . can be used in particular:

Tri-methyl-aluminum, triethyl-aluminum, tri-n-propyl-aluminum, tri-iso-propyl-aluminum, tri-n-butyl-aluminum, tri-iso-butyl-aluminum, tripentyl-aluminum, trihexyl-aluminum, tricyclohexyl-aluminum, trioctyl-aluminum, di-aluminum-aluminum hydride iso-butyl aluminum hydride, diethyl aluminum chloride, ethyl aluminum sesquichloride, ethyl aluminum dichloride,

Ethyl aluminum dibromide, diethyl aluminum bromide, ethyl aluminum diiodide, diethyl aluminum iodide, di-iso-butyl aluminum chloride, octyl aluminum dichloride, dioctyl aluminum chloride. The following are preferably used: triethyl aluminum, triethyl aluminum, tri-iso-butyl aluminum, trioctyl aluminum, di-iso-butyl aluminum chloride, octyl aluminum dichloride. In particular, compounds of the formula HYR ' _e can be used: water, alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, hexanol, octanol and glycol, phenols, such as phenol, methylphenol, ethylphenol, butylphenol, octylphenol, dodecylphenol, tert-butylphenol, bis-2,6-tert-butylphenol and 4-methyl-bis-2,6-tert-butylphenol, aliphatic and aromatic Amines such as methylamine, ethylamine, butylamine, phenolamine, dimethylamine, diethylamine, dibutylamine, diphenylamine, pyrolidine and pyridine.

The aluminum organyl compounds are described, for example, in Abel, Stone, Wilkinson, Comprehensive Organometallic Chemistry, Pergamon Press Ltd., Oxford,

1995.

Suitable modifiers (component (c)) are, in particular, those compounds which are known to the person skilled in the art as Lewis bases. Lewis bases which have at least one element from group Vb and VIb as the donor atom are particularly preferred

Periodic table of the elements, such as nitrogen, phosphorus, oxygen and sulfur, particularly preferably nitrogen or phosphorus.

In particular, the following modifiers can be used: pyridine, tertiary aliphatic or aromatic amines or tertiary aliphatic or aromatic

Phosphines, e.g. Pyridine, vinylimidazole, triethylphosphine and triphenylphosphine.

In this context, it should be noted that the cobalt compounds of component (a), the organoaluminum compounds of component (b) and the

Modifiers of component (c) can be used both individually and in a mixture with one another. The most favorable mixture ratio can easily be determined by appropriate preliminary tests.

In the process according to the invention, the catalysts are used in amounts of preferably 10 μmol to 5 mmol, based on 100 g of the monomers. Of course, it is also possible to use the catalysts in any mixture with one another.

The process according to the invention is carried out in the presence of aromatic vinyl compounds, in particular in the presence of styrene, α-methylstyrene, α-methylstyrene dimer, p-methylstyrene, divinylbenzene and / or other alkylstyrenes having 2 to 6 carbon atoms in the alkyl radical, such as p-ethylstyrene and p-butylstyrene.

Is very particularly preferred in the polymerization according to the invention in

Worked in the presence of styrene, α-methylstyrene, α-methylstyrene dimer and / or p-methylstyrene.

The solvents can be used individually or in a mixture; the most favorable mixing ratio can also be easily determined by means of appropriate preliminary tests.

The amount of aromatic vinyl compounds used is preferably 30 to 1,000 g, very particularly preferably 50 to 500 g, based on 100 g of the monomers used.

The process according to the invention is preferably carried out at temperatures from 0 to 70.degree.

The process according to the invention can be depressurized or at elevated pressure (0.1 to

12 bar).

The process according to the invention can be carried out continuously or batchwise, preferably in a continuous manner. The solvent (aromatic vinyl compound) used in the process according to the invention does not need to be distilled off, but can remain in the reaction mixture. In this way it is possible, for example when using styrene as solvent, to connect a second polymerization for the styrene, an elastomeric polydiene being obtained in a polystyrene matrix. In an analogous manner, acrylonitrile can be added to the styrenic polydiene solution before the second polymerization is carried out. In this way you get ABS. Such products are of particular interest as impact-modified thermoplastics.

It is of course also possible to remove part of the solvent and / or the unreacted monomers after the polymerization, preferably by distillation, if appropriate under reduced pressure, in order to obtain the desired polymer concentration.

It is furthermore possible to add further components to the polymer solution before or during the subsequent polymerization of the solvent, which can be initiated in a known manner by free radicals or thermally, e.g. unsaturated organic compounds, such as acrylonitrile, methyl methacrylate, maleic anhydride, maleimides, which can be copolymerized with the vinyl aromatic solvent, and / or common aliphatic or aromatic solvents, such as benzene, toluene, ethylbenzene, dimethylbenzene, hexane, heptane or octane and / or polar solvents , such as ketones, ethers or esters, which are usually used as solvents and / or diluents for the polymerization of the vinylaromatic.

As already mentioned above, the method according to the invention is characterized by particular economy and good environmental compatibility, since the solvent used can be polymerized in a subsequent step, the polymer contained in the solvent for the modification of thermoplastics (e.g.

Increases impact strength). The composition and thus the properties of the polymers obtained can be varied very widely by the process according to the invention. It is possible, for example, by varying the catalyst composition, preferably by varying the modifiers, to contain 1, 2 units, that is to say pendant

Double bonds in the polymer chain can be set within wide limits without polymerization or copolymerization of the vinyl aromatic solvent taking place.

It is also possible to influence the molecular weights, the branching of the polymers and thus also the solution viscosity of the polymers very simply, such as by varying the catalyst concentration, the diene concentration, the reaction temperature or by adding suitable molecular weight regulators, such as hydrogen, 1, 2-butadiene or cycloocytadiene.

Another advantage of the process according to the invention is that, in the direct polymerization in styrene, it is also possible to prepare and process further such low-molecular-weight polymers which are difficult to process and store as solids with a high cold flow or high stickiness.

The advantage of low molecular weight polymers is that even with a high content of the polymers in vinyl aromatic solvents, the solution viscosity remains as desired low and the solutions can thus be easily transported and processed. Examples

The polymerizations were carried out in the absence of air and moisture under argon. The isolation of the polymers from the styrenic solution described in individual examples was carried out only for the purpose of characterizing the polymers obtained. The polymers can of course also be stored in the styrenic solution without insulation and processed further accordingly.

The styrene used as solvent for the diene polymerization was stirred under argon over CaH ₂ at 25 ° C. for 24 h and distilled off at 25 ° C. under reduced pressure. In order to show that the polymerization is also possible with styrene, certain amounts of the stabilizer (2,6-di-tert-butyl) (4-methyl) phenol (= lonol) were added in some examples and the polymerization of the butadiene in the presence of the stabilizer.

The styrene content in the polymer is determined by means of NMR-NMR spectroscopy, the selectivity of the polybutadiene (1,4-cis, 1,4-trans and 1, 2 content) is determined by means of IR spectroscopy.

Examples 1 to 7

In a 0.5-1 bottle, which was provided with a crown cap with an integrated septum, the stated amount of liquid butadiene was added under argon at 25 ° C. to the styrene initially charged, and then the stated amounts of the individual catalyst components in the order Methylalumoxane (MAO, 10

% solution in toluene) and CoCl ₂ (pyridine) ₂ (0.0235 molar solution in CH ₂ C) were added. During the polymerization, the temperature was adjusted by means of a water bath, the polymer after the reaction time was removed by precipitating the polymer solution in methanol / BKF (BKF = bis [(3-hydroxy) (2,4-di-tert-butyl) methyl) - phenyljmethan) isolated and one day in a vacuum drying cabinet at 60 ° C dries. The batch sizes, reaction conditions and the properties of the polymer are given in Table 1.

Table 1: Examples 1 to 7

Example 1 2 3 4 5 6 7

CoBr ₂ (pyridine) ₂ in mmol 0.05 0.05 0.05 0.05 0.1 0.1 0.1

MAO in mmol 5 5 5 5 10 10 10

Polymerization

Styrene in ml 75 75 75 75 75 75 75

1,3-butadiene in g 18.1 20.9 29.5 20.6 23.2 18.1 18.5

Temperature in ° C 25 40 40 60 25 25 40

Response time in h 3 3 21 21 2 21 3

polymer

Yield in g 2.69 6.0 17.1 8.0 8.5 10.8 7.7

BR with 1,4-cis in% 92 95 92 89 92 93 93

1, 4-trans in% 5 3 4 6 5 4 4

1.2 in% 2 2 4 5 3 3 o J

PS * in% 0.08 0 0.25 0.95 0.12 0.16 0

PS *: content of polymerized styrene, based on the amount used in% by weight

Examples 8 to 13

In a 0.5-1 bottle, which was provided with a crown cap with an integrated septum, the stated amount of liquid butadiene was added under argon at 25 ° C. to the styrene initially charged, and then the stated amounts of the individual catalyst components in the order (2,6-Di-tert-butyl) (4-methyl) phenol (lonol), methylalumoxane (MAO, 10% solution in toluene) and CoCl ₂ (PPh ₃ ) ₂ (0.0086 molar solution in CH ₂ C1 ₂ ) added. During the polymerization, the temperature was adjusted by means of a water bath, which isolated the polymer after the reaction time by precipitating the polymer solution in methanol / BKF and dried for one day in a vacuum drying cabinet at 60 ° C. The batch sizes, reaction conditions and the properties of the polymer are given in Table 2.

Table 2: Examples 8 to 13

Example 8 9 10 11 12 13

CoCl ₂ (PPh ₃ ) ₂ in mmol 0.011 0.011 0.0057 0.011 0.011 0.011

MAO in mmol 1 1 0.5 1 1 1 lonol in mmol 0.05 0.2 0.5

Polymerization

Styrene in ml 40 40 40 40 40 40

1,3-butadiene i g 7.2 10.0 8.3 8.5 8.8 7.1

Temperature in ° C 0 30 25 30 30 30

Response time in h 0.25 0.03 1 0.03 0.03 1.03

polymer

Yield in g 6.4 6.6 5.7 6.1 7.1 5.1

BR with l, 4-cis in% 12 10 11 19 12 14 l, 4-trans in% 2 2 1 2 1 1

1.2 in% 86 88 88 79 87 85

PS * in% 0.35 0.58 0.51 0.34 0.63 0.45

PS *: content of polymerized styrene, based on the amount used in% by weight

Examples 14 to 19

In a 0.5-1 bottle, which was provided with a crown cap with an integrated septum, the stated amount of liquid butadiene was added under argon at 25 ° C. to the styrene provided, and then the stated amounts of individual catalyst components in the order (2,6-di-tert-butyl) (4-methyl) phenol (lonol), methylalumoxane (MAO, 10% solution in toluene) and CoBr ₂ (PPh ₃ ) ₂ (0.0459 molar solution in CH ₂ C1 ₂ ) added. During the polymerization, the temperature was adjusted by means of a water bath, the polymer was isolated after the reaction time by precipitating the polymer solution in methanol / BKF and dried for one day at 60 ° C. in a vacuum drying cabinet. The batch sizes, reaction conditions and the properties of the polymer are given in Table 3.

Table 3: Examples 14 to 19

Example 14 15 16 17 18 19

CoBr ₂ (PPh ₂ ) ₂ in mmol 0.01 0.05 0.01 0.01 0.01 0.01

MAO in mmol 1 5 2.5 1 1 1 lonol in mmol 0.05 0.2 0.5

Polymerization

Styrene in ml 40 75 75 40 40 40

1,3-butadiene in g 7.1 21.1 20.8 9.6 9.1 7.8

Temperature in ° C 24 24 40 24 24 24

Response time in h 1.75 1.25 0.9 1.75 1.75 1.75

polymer

Yield in g 5.1 18.6 8.5 6.1 6.5 7.1

BR with l, 4-cis in% 12 15 16 16 12 9 l, 4-trans in% 2 4 2 1 1 1

1.2 in% 86 81 82 83 87 90

PS * in% 0.28 0.74 0.40 0.17 0.18 0.39

PS *: content of polymerized styrene, based on the amount used in% by weight

Claims

claims

1. A process for the polymerization of conjugated diolefins, characterized in that the polymerization of the diolefins in the presence of catalysts consisting of:

(a) cobalt compounds,

(b) organoaluminum compounds and

(c) modifiers and in the presence of aromatic vinyl compounds at temperatures from -30 to 80 ° C, the molar ratio of components (a) :( b) :( c) in the range from 1:10 to 1,000: 0, 1 to 100, the amount of component (a) of the catalyst used is 1 μmol to 10 mmol, based on 100 g of the monomers used, and the amount of aromatic vinyl compounds 10 g to 2,000 g, based on 100 g of the monomers used, be.

2. The method according to claim 1, characterized in that 1,3-butadiene, 1,3-isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1, 3-pentadiene and / or 2-methyl as conjugated diolefins - uses 1, 3-pentadiene.

3. Process according to Claims 1 and 2, characterized in that at least one compound selected from the group of the complexes of β-diketones with cobalt, the β-keto acid complexes of cobalt, the cobalt salts of organic acids with 6 as cobalt compounds to 15

Carbon atoms, the complexes of halogenated cobalt compounds and / or the organometallic complexes of cobalt with π-bonded anions.

4th Process according to Claims 1 to 3, characterized in that at least one compound selected from the group of the alumoxanes is used as organoaluminum compounds.

5. Process according to Claims 1 to 3, characterized in that as

Organoaluminum compounds uses at least one aluminum organanyl compound, which is obtained by reacting compounds of the formula AlR ₃ . _c jX, where

R can be the same or different and for an organic alkyl,

Cycloalkyl or aryl group having 1 to 12 carbon atoms,

X represents a hydrogen or a halogen and

d represents a number from 0 to 2,

with compounds of the formula HYR ' _e , where

Y represents an element from groups Vb and VIb of the Periodic Table of the Elements,

R 'can be the same or different and represents a hydrogen, an alkyl, cycloalkyl or aryl group having 1 to 12 carbon atoms and

e is 1 or 2 according to the valency of Y,

is formed.

6. The method according to claims 1 to 5, characterized in that as

Modifiers uses at least one Lewis base, which acts as a donor atom contains at least one element from groups Vb and VIb of the Periodic Table of the Elements.

7. Process according to Claims 1 to 6, characterized in that styrene, α-methylstyrene, α-methylstyrene dimer, p-methylstyrene, divinylbenzene and / or alkylstyrenes having 2 to 6 carbon atoms in the alkyl radical are used as aromatic vinyl compounds.