MXPA00007698A - Method for retarded anionic polymerization - Google Patents

Abstract

The invention relates to a method for homopolymerization of vinyl-aromatic monomers or copolymerization of vinyl-aromatic monomers or dienes in the presence of at least one alkali metal organyl, at least one magnesium organyl and at least one aluminum organyl. The invention also relates to an initiator composition for implementing the inventive method.

Description

DELAYED ANIONIC POLYMERIZATION The present invention relates to a process for the co-polymerization of vinyl aromatic monomers or the copolymerization of vinylaromatic monomers and dienes in the presence of at least one alkali metal organole, at least one magnesium organole and at least one aluminum organole and a composition initiator to perform the process. Anionic polymerizations usually proceed very fast so that it is difficult to control them on an industrial scale due to the considerable amount of heat generated. The reduction of the polymerization temperature gives rise to an excessive increase in viscosity, in particular with a concentrated solution. Reducing the concentration of the initiator increases the molecular weight of the polymer formed. The control of the reaction by suitable dilution of the monomers results in a higher solvent requirement and lower space-time yield. Therefore, it has been proposed to include in the initiators of the anionic polymerization different additives to influence the speed of the polymerization. The effect of Lewis acids and Lewis bases on the speed of anionic polymerization of styrene has been described in Welch, Journal of the American Chemical Society, vol. Q2_ (1960), pages 6000-6005. For example, it has been found that small amounts of Lewis bases such as ethers and amines accelerate the polymerization initiated by n-butyllithium of styrene at 30 ° C in benzene, while Lewis acids such as zinc and aluminum alkyls reduce the speed of the polymerization or, when used in super stoichiometric quantities, completely interrupt the polymerization. In Macromolecules, Vol. 19 (1966), pages 299 to 304, Hsieh and Wang investigated the dibutylmagnesium complex with the alkyllithium initiator and / or the latent polymer chain in the presence and absence of tetrahydrofuran and found that dibutylmagnesium reduces the polymerization rate of styrene and butadiene without affecting the stereochemistry. U.S. Patent No. 3 716 495 discloses initiator compositions for the polymerization of conjugated and vinylaromatic dienes, where a more efficient use of the alkyllithium as an initiator is achieved by the addition of a metal alkyl of a metal of group 2a, 2b or 3a of the Periodic Table of the Elements, such as diethyl zinc and polar compounds such as ethers or amines. Due to the large quantities required of the solvent, relatively low temperatures and long reaction times in the region of a few hours, the space-time yields are correspondingly poor. W097 / 33923 describes initiator compositions which are used for the anionic polymerization of vinyl monomers and contain alkali metals and magnesium compounds carrying hydrocarbon radicals and with a molar ratio [Mg] / [alkali metal] of at least 4. PCT / EP97 / 04497, which was published on the priority date of the present invention, describes continuous processes for the anionic polymerization or copolymerization of styrene or diene monomers using alkali metal alkyl as the polymerization initiator in the presence of at least one bivalent element as a retarder. Various mixtures of initiators which may contain alkali metals, alkaline earth metals, aluminum, zinc or rare earth metals are known, for example, from EP-A 0 234 512 for the polymerization of conjugated dienes with a high degree of 1,4-linkage. trans. German Patent 26 28 380 teaches, for example, the use of alkaline earth aluminates as co-catalysts together with an organolithium initiator for the preparation of polymers or copolymers of conjugated dienes having a high trans-1,4 link content and low content of 1.2 or 3.4 links. It is said that this gives rise to an increase in the speed of the polymerization.

The polydienes having a high proportion of bonds 1, 2 of the monomeric units of dienes have been prepared using cyclogenic glyoxal acetals (US 4,520,123, US 4,591,624) or trisubstituted phosphine oxides (US 4,530,984). It is also possible to use the anionic initiators based on lithium, magnesium and / or aluminum alkyls as co-initiators. The use of additives such as aluminum alkyls that have a strong retarding effect on the anionic polymerization requires accurate dosing and temperature control. A slight underdosing can cause an insufficient retardation of the reaction rate, while a slight overdose can completely interrupt the polymerization. To obtain a sufficient retardation of the reaction rate, weakly retarding additives such as magnesium dialkyls must be added in amounts that are significantly greater than the stoichiometric amount, based on the alkali organo initiator. Magnesium alkyls do not act as polymerization initiators by themselves, but can initiate additional polymer chains in the presence of lithium organyls. The molecular weight of the polymers is, therefore, not only dependent on the molar ratio of the alkali organo initiator to the monomer, but is also affected by the amount of magnesium organole, the temperature and the concentration. In addition to higher costs, larger amounts of the retarding additives may also cause altered product properties such as poor transparency, since the initiator components usually remain in the polymer. An object of the present invention is to provide a process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes that do not have the aforementioned disadvantages and, in particular, to provide an initiating composition for the process which makes it possible to adjust the speed of Polymerization within wide ranges of temperature and concentration. We have found that this objective is achieved by a process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes, which is to polymerize the monomers in the presence of at least one alkali metal organole, at least one magnesium organole and at least one aluminum organole. The invention also provides an initiator composition containing at least one alkali metal organole, at least one magnesium organole and at least one aluminum organole, wherein: a) the molar ratio of magnesium to alkali metal is in the range of 0.2 to 3.8, b) the molar ratio of aluminum to alkali metal is in the range from 0.2 to 4, and a process for the preparation of an initiator composition, in which the metal organils, dissolved in inert hydrocarbons, are mixed together and they cure at a temperature in the range from 0 to 120 ° C for at least 5 minutes. The alkali metal organyls that may be used are the alkyls, aryls or aralkyl mono- or multifunctional aralkyl commonly used as initiators of the anionic polymerization. It is advantageous to use organolithium compounds such as etillithium, propillithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium, diphenylhexylthio, hexamethylenedylithium, butadienillithium, isoprenyllithium, polystyrellithium or the multifunctional compounds 1,4-dilithiobutane, 1,4. -dilithium-2-butene or 1,4-dilithiobenzene. The amount of alkali metal organole needed depends on the desired molecular weight, the type and amount of the other metal organils used and the temperature of the polymerization, and is usually in the range of from 0.0001 to 5 mol%, based on the total amount of the monomers. The magnesium organyls that can be used are those of the formula RMg, wherein R are each, independent of each other, hydrogen, halogen, C 1 -C 0 alkyl or C 6 -C 2 aryl- Preference is given to the use of the ethyl, propyl or butyl compounds which are commercially available. Particular preference is given to the use of (n-butyl) (s-butyl) magnesium which is soluble in hydrocarbons. The aluminum organyls that can be used are those of the formula R3AI, wherein the radicals R are each, independent of each other, hydrogen, halogen, C1-C20 alkyl or C6-C20 aryl- Preferred aluminum organyls are aluminum trialkyls such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, triisopropylaluminum, tri-n-hexylaluminum. Particular preference is given to the use of triisobutylaluminum. It is also possible to use aluminum organyls which are formed by partial or complete hydrolysis, alcoholysis, aminolysis or oxidation of the alkyl- or arylaluminum compounds or those which carry alkoxide, thiolate, amide, imide or phosphide groups [sic]. Examples are diethylaluminum ethoxide, diisobutylaluminum ethoxide, diisobutyl- (2,6-di-tert-butyl-4-methyl-phenoxy) aluminum (CAS No. 56252-56-3), methylaluminoxane, isobutylated methylaluminoxane, isobutylaluminoxane, tetraisobutyldialuminoxane , bis (diisobutyl) aluminum or diethylaluminum oxide (N, N-dibutylamide).

The molar ratios between metal organils can vary within wide limits, depending mainly on the desired retardation effect, the temperature of the polymerization, the composition and concentration of the monomer and the desired molecular weight. The molar ratio of magnesium to alkali metal is advantageously in the range from 0.1 to 10, preferably in the range from 0.2 to 3.8, particularly preferably in the range from 1 to 3. The molar ratio of aluminum to alkali metal is the range from 0.1 to 10, preferably in the range from 0.2 to 4, particularly preferably in the range from 0.7 to 2. The molar ratio of magnesium to aluminum is preferably in the range from 0.05 to 8. In the process of the invention It is used mainly alkaline metal organils, magnesium organyls and aluminum organyls. The barium, calcium or strontium organyls are preferably only present in ineffective amounts without having a significant effect on the speed of polymerization or the parameters of the copolymerization. Transition metals or lanthanoids, especially titanium or zirconium, should not be present in significant amounts. The alkali metal, magnesium and aluminum organyls can be added to the monomer mixture together or separately and at different times or different places. The alkali metal, magnesium and aluminum alkyls are preferably used in the form of a premixed initiator composition. The initiator composition can be prepared by dissolving the alkali metal organyls, magnesium organyls and aluminum organyls in an inert hydrocarbon solvent, for example, n-hexane, n-heptane, cyclohexane, ethylbenzene or toluene, and combining the solutions. The metal organils dissolved in the hydrocarbons are preferably mixed together and cured at a temperature in the range from 0 to 120 ° C for at least 5 minutes. To avoid precipitation of one of the components of its initiator solution, if necessary, it is possible to add a solubilizer, for example diphenylethylene. The initiator solution is suitable for the polymerization of ammonically polymerizable monomers. The initiator composition is preferably used for the hompolymerization or copolymerization of vinylaromatic monomers and dienes. The preferred monomers are styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or 1,1-diphenylethylene, butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene or piperylene or mixtures thereof.

The polymerization can be carried out in the presence of a solvent. Suitable solvents are aliphatic, cycloaliphatic or aromatic hydrocarbons having from 4 to 12 carbon atoms which are generally used for anionic polymerization, such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, isooctane, decalin, benzene, alkylbenzenes such as toluene, xylene, ethylbenzene or eumeno or convenient mixtures. Of course, the solvent must have the high purity commonly required for the process. The solvent can be dried on aluminum oxide or molecular sieve and / or distilled before use to remove the protic substances. The solvent of the process of preference is reused after the aforementioned condensation and purification. It is possible to adjust the retarding effect within wide ranges of temperature through the composition and amount of metal organils. Therefore, it is possible to carry out the polymerization at the initial concentrations of the monomer in the range from 50 to 100% by volume, particularly from 70 to 100% by volume, which gives rise to highly viscous polymer solutions and require higher temperatures, when less to higher conversions. After the polymerization is complete, the latent polymer chains can be capped with a chain terminator. Suitable chain terminators are protic substances or Lewis acids, such as water, alcohols, aliphatic or aromatic carboxylic acids and inorganic acids such as carbonic acid or boric acid. The target products can be homopolymers or copolymers and mixtures thereof. Polystyrene and styrene / butadiene block copolymers are preferably obtained. The process of the invention can also be used to prepare high impact polystyrene (HIPS), in which case polybutadiene, styrene / butadiene block copolymers or mixtures thereof can be used as rubbers. The block copolymers can be coupled using multifunctional compounds such as aldehydes, ketones, esters, anhydrides or polyfunctional epoxides. The process of the invention can be carried out in any reactor resistant to pressure and temperature, it being possible in principle to use reverse mixing reactors or without backward mixing (i.e., reactors having the tank with stirring or tubular reactor characteristics). Depending on the choice of the concentration and composition of the initiator, the trajectory of the particular process applied and other parameters such as the temperature and the possible temperature profile, the process of the present invention gives rise to polymers having high or low molecular weights. It is possible to use, for example, stirred tanks, tower reactors, tube reactors and tubular reactors or reactors in bundles of tubes with or without internal elements. The internal elements can be static or mobile. The preference process is carried out continuously. It is preferred to carry out at least a part of the conversion, particularly conversions of between 50 and 100%, in a reactor without back-mixing or reactor sectioning. The initiator composition according to the invention makes it possible to significantly reduce the reaction rate or increase the temperature, respectively, without affecting the properties of the polymer as compared to the anionic polymerization using an alkali metal organyl; this makes it possible, on the one hand, to disperse the heat generation of the polymerization over a longer time and thus to control, in a continuous process, the temperature profile as a function of time or location, for example, in a tubular reactor. It is possible, for example, to ensure that a high temperature does not occur at the initially high concentration of the monomer, while, on the other hand, polymerization is possible without problems at the high temperature that is finally reached (ie at a higher conversion). ) achieving at the same time a high space-time performance. No incrustation occurs in this process.

Examples: Preparation of the initiator compositions: Suitable amounts of a 1.6 molar solution of s-butyllithium (sBuLi) in cyclohexane (from Chemmentall), a 1 molar solution of (n-butyl) (s-butyl) magnesium (DBM) in n-heptane (from Aldrich) and a 1.6 molar solution of triisobutylaluminum (TIBA) in toluene (from Witco) were combined at 25 ° C and stirred for at least 20 minutes before use.

Example 1 A stirred tank, of 2.35 liters, equipped with an anchor stirrer was charged with 320 g of styrene and 1280 g of toluene under nitrogen and heated to 80 ° C with stirring. Upon reaching this temperature, an initiator solution (molar ratio Li / Mg / Al = 1/3 / 0.9) composed of 1.07 ml of a 1.6 molar solution of s-butyllithium in cyclohexane, 5.1 ml of a 1 molar solution was added. of DBM in n-heptane and 0.97 ml of a 1.6 molar solution of triisobutylaluminum and the polymerization solution was maintained at 80 ° C. The conversion was 24% after 25 minutes, 51% after 60 minutes, 74% after two hours. After three hours at 80 ° C, the polymerization was terminated at an 86% conversion by adding 4 ml of ethanol. The polymer was obtained in the form of a viscous solution and had a number average molecular weight MN of 93.600 g / mol and a MW / MN polydispersity of 1.51.

Example 2 Example 1 was repeated, except that an initiator solution (molar ratio Li / Mg / Al = 1 / 1.5 / 0.9) composed of 1.55 ml of a 1.6 molar solution of s-butyllithium in cyclohexane, 3.71 ml of a solution was used. molar of DBM in h-heptane and 1.4 ml of a 1.6 molar solution of triisobutylaluminum in toluene. The conversion was 61% after 30 minutes, 82% after 60 minutes. After 2.5 h at 80 ° C, the polymerization was terminated at a conversion of 97% by adding 4 ml of ethanol. The polymer was obtained in the form of a viscous solution and had a number average molecular weight MN of 94.340 g / mol and a MW / M polydispersity of 1.35.

Comparative Experiment 1: Example 2 was repeated, except that an initiator solution (Li / Mg = 1 / 1.5 molar ratio) composed of 1.55 ml of a 1.6 molar solution of s-butyryl in cyclohexane, 3.71 ml of a 1 molar solution of DBM in n-heptane. The polymerization solution could not be maintained at 80 ° C.

Example 3 Example 1 was repeated, except that an initiator solution (molar ratio Li / Mg / Al = 1 / 2.25 / 0.9) composed of 3.0 ml of a 1.6 molar solution of s-butyllite in cyclohexane, 11 ml of a solution was used. molar of DBM in n-heptane and 2.8 ml of a 1.6 molar solution of triisobutylaluminum in toluene that was added to the monomer solution that had been heated to 100 ° C. The conversion was 29% after 10 minutes and 53% after 25 minutes. After 40 minutes at 100 ° C, the polymerization was terminated at a conversion of 61% by adding 4 ml of ethanol. The polymer was obtained in the form of a viscous solution with a number average molecular weight MN of 161,300 g / mol and a MW / MN polydispersity of 1.53.

Comparative experiment 2: Example 3 was repeated, except that 2.8 ml of a 1.6 molar solution of triisobutylaluminum in toluene, 11 ml of a 1 molar solution of DBM in n-heptane and 3.0 ml of a 1.6 molar solution of s-butylaluminum in cyclohexane were added to the solution of the monomer that had been heated to 100 ° C. After the addition of the s-butyllithium solution, a large increase in the temperature of the content of the rqactor was observed which could not be controlled.

Example 4 A glass ampoule was baked and then charged with 6 g of styrene and 24 g of toluene under inert gas and sealed to the gas with a septum or stopper. The initiator solution composed of the appropriate amounts of a 1.6 molar solution of s-butyllithium (sBuLi) in cyclohexane (from Aldrich), a 1 molar solution of (n-butyl) (s-butyl) agnesium (DBM) in n-heptane (from Chemmetall) and a 1.6 molar solution of triisobutylaluminum (TIBA) in toluene (from Witco) was added using a syringe. The ampule was then submerged in a heating bath to 100 ° C. After 12 or 24 hours, respectively, the polymerization was terminated by adding 1 ml of ethanol. The starter composition, the reaction conditions and the conversion are summarized in Table 1.

Table 1: Polymerization of styrene using an initiator composition composed of s-BuLi / DBM / TIBA * mhm = mmol per 100 g of styrene The polymerization of styrene using s-BuLi is almost inhibited by the addition of triisobutylaluminum at an Al / Li molar ratio of 3/1 (4d). Surprisingly, this inhibition is reversed by further addition of DBM (4a, b, c).

Example 5: Example 4 was repeated using the initiator components and the reaction conditions summarized in Tables 2a and 2b.

Table 2a: Polymerization of styrene (initiator composition containing different aluminum components) a) mhm = mmol per 100 g of styrene Table 2b: Polymerization of styrene (initiator composition containing different magnesium components) a) mhm = mmol per 100 g of styrene b) BOM = (n-butyl) 1.5 (n-octyl) o.sMg Continuous polymerization of styrene: Example ßa: The reactor used for the continuous polymerization was a stirred tank, 3 liters, with double jacket, equipped with a normal anchor agitator. The reactor was designed for a pressure of 60 bar and was maintained at a specified temperature through a heat transfer medium to allow isothermal polymerization. The temperature of the polymerization mixture was monitored by means of two temperature sensors directly immersed in the polymerization mixture. All operations were carried out under inert gas. The tank with stirring was stirred (100 rmp per minute) and fed with 200 g / h of toluene and 800 g / h of styrene. At the same time, a premixed starter solution (molar ratio Li / Mg / Al = 1 / 0.2 / 0.95) composed of 2.38 ml / h of a 1.6 molar solution of s-butyllithium in ciolohexane, 0.76 ml / h of a 1 molar solution of DBM in n-heptane, 2.26 ml / h of a 1.6 molar solution of triisobutylaluminum in toluene and 16.2 ml / h of toluene was premixed and metered through a common feed pipe equipped with mixing elements. Upon reaching a filling level of 3 liters, the reaction was exchanged to a continuous mode and the polymerization solution was maintained at a relative temperature of 85 ° C. A stable, steady operating state was reached after 12 hours. Being the solids content (SC) of 12%. The number average molecular weight MN was 46,000 g / mol and the MW / MN polydispersity was 2.61. Example 6a was repeated using the parameters and obtaining the results shown in Table 3 (Examples 6b, c and d): Table 3: Continuous polymerization of styrene in a tank with agitation: Comparative example 3: Example 6a was repeated, except that a solution composed of 2.66 ml / h of a 1.6 molar solution of s-butyryl in cyclohexane and 12.34 ml / h of toluene and a solution composed of 2.58 ml / h of a 1.6 molar solution of triisobutylaluminum in toluene and 10.4 ml / h of toluene (molar ratio Li / Al = 0.97) were added by separate feed lines. Over the course of a few days, the solids content in the agitated tank varied in the range of 3 to 25% by weight and the relative temperature could not be constant at 85 ° C.

Example 7 A tank with agitation similar to that used in Example 6 was charged continuously with 300 g / h of toluene, 1200 g / h of styrene and a starter solution composed of 0.98 ml / h of a 1.6 molar solution of s- butyllithium in cyclohexane, 5.78 ml / h of a 1 molar solution of DBM in n-heptane and 0.78 ml / h of a 1.6 molar solution of triisobutylaluminum in toluene (molar ratio Li / Mg / Al = 1 / 3.7 / 0.8), premixed through a common feed pipe, and the mixture was stirred (100 revolutions per minute) at a relative temperature of 97 ° C. The effluent from the stirred tank was transported to a 4 liter tower reactorwith agitation. Two heating zones of equal length that were arranged in series were used to establish an internal temperature of 120 ° C at the end of the first zone and 162 ° C at the end of the second zone. The polymerization mixture was mixed with 20 g / h of a 10% solution by weight concentration of methanol in toluene at the outlet of the tower reactor using a mixer, subsequently passed through a tubular section heated to 260 ° C and released to a vacuum vessel maintained at 20 mbar through a pressure control valve. The melt was discharged by means of a propeller and pellet conveyor. After a few hours a steady state of equilibrium was reached in all parts of the unit. The pressure drop across the entire unit was 1.8 bar. The solids content was 41% by weight at the outlet of the tank with agitation and 80% by weight at the outlet of the tower reactor, which corresponds to a monomer conversion of 100%. The polystyrene obtained had a molecular weight MN of 176,000 g / mol and a polydispersity M ^ / M of 2.52. The analysis showed a styrene content of less than 10 ppm, an ethylbenzene content of less than 10 ppm and a toluene content of 105 ppm.

Example 8 The reactor used for continuous polymerization was a tubular reactor with double jacket having an internal diameter of 29.7 mm and a length of 2100 mm. The tubular reactor was designed for a pressure of up to 100 bar and for a temperature of up to 350 ° C. The tubular reactor was maintained at a specified temperature through a flow of co-current heat transfer medium and the temperature of the polymerization mixture was monitored by means of three temperature detectors arranged at regular intervals throughout the section of the reaction. The tubular reactor was fed continuously with 1 1 / h of styrene, 0.15 1 / h of ethylbenzene and 60.37 ml / h of an initiator solution composed of 0.75 ml of a 1.6 molar solution of s-butyllithium in cyclohexane, 4.1 ml of a 1 molar solution of DBM in n-heptane, 0.52 ml of a 1.6 molar solution of triisobutylaluminium in toluene and 55 ml of ethylbenzene (molar ratio Li / Mg / Al = 1 / 3.42 / 0.69) through three separate pumps. The dosed fed materials were each cooled to 5 ° C. The temperature of the heat transfer medium was 90 ° C at the inlet of the tubular reactor. The polymerization solution reached its highest temperature of 208 ° C at the outlet of the tubular reactor. The polymerization mixture was discharged from the tubular reactor and a solution at 20% concentration by weight of methanol in ethylbenzene was dosed at a rate of 100 ml / h using a pump for HPLC and homogenized in a tubular section downstream by means of a static mixer The polymer melt is released to a devolatilization vessel maintained at 20 mbar through a flow restriction valve, is removed by means of a propeller pump, extruded and granulated. The resulting polystyrene had a molecular weight M of 102,000 and a polydispersity M / MN of 1.41. This contains less than 10 ppm residual monomeric styrene.

Example 9 The reactor used was a double-jacket tubular reactor similar to that used in Example 8, but had a length of 3900 mm and included five temperature detectors arranged at regular intervals throughout the reaction section. The tubular reactor was fed continuously with 1 1 / h of styrene, 0.15 1 / h of ethylbenzene and 57.94 ml / h of an initiator solution composed of 1.0 ml of a 1.6 molar solution of s-butyllithium in cyclohexane, 3.4 ml of a 1 molar solution of DBM in n-heptane, 1.54 ml of a 1.6 molar solution of triisobutylaluminium in toluene and 52 ml of ethylbenzene (molar ratio Li / Mg / Al = 1 / 2.13 / 1.54) through three separate pumps. The dosed feed materials were each cooled to 5 ° C. The temperature of the heat transfer medium was 110 ° C at the entrance of the tubular reactor. The polymerization solution reached its highest temperature of 191 ° C at the outlet of the tubular reactor.

The polymerization mixture was discharged from the tubular reactor and a solution at 20% concentration by weight of methanol in ethylbenzene was dosed at a rate of 100 ml / h using a pump for HPLC and homogenized in a tubular section downstream by means of a static mixer The polymer melt was released into a devolatilization vessel which was maintained at 20 mbar through a flow restrictor valve, was removed by means of a propeller pump, extruded and granulated. The resulting polystyrene had a molecular weight Mw of 142,000 and a polydispersity MW / MN of 1.86. It contained less than 10 ppm residual monomeric styrene.

Claims (1)

1. CLAIMS A process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes, which consists in polymerizing the monomers in the presence of at least one alkali metal organyl, at least one magnesium organyl and at least one aluminum organyl in the absence of any cyclic acetal of a glyoxal and any phosphine oxide that is substituted with three saturated heterocyclic rings, each hetero ring containing a nitrogen atom and of 4 to 6 carbon atoms. The process as claimed in claim 1, wherein the alkali metal organyl used is a lithium organyl. The process as claimed in claims 1 or 2, wherein the molar ratio of magnesium to alkali metal is in the range from 0.2 to 3.8. The process as claimed in any of claims 1 to 3, wherein the molar ratio of aluminum to alkali metal is in the range from 0.2 to 4. The process as claimed in any of claims 1 to 4, wherein the Molar ratio of magnesium to aluminum is in the range from 0.05 to 8. A process for the homopolymerization of styrene as claimed in any of claims 1 to 5. The process as claimed in any of claims 1 to 6, wherein the polymerization is carried out at an initial concentration of monomers in the range from 50 to 100% in volume. The process as claimed in any of claims 1 to 7, wherein the polymerization is carried out continuously. The process as claimed in any of claims 1 to 8, wherein at least a part of the conversion is carried out in a reactor or reactor section without backward mixing. An initiator composition containing at least one alkali metal organole, at least one magnesium organole and at least one aluminum organole, wherein: a) the molar ratio of magnesium to alkali metal is in the range 0.2 to 3.8, b) the molar ratio of aluminum to alkali metal is in the range from 0.2 to 4, and the initiator composition does not contain any cyclic acetal of a glyoxal or any phosphine oxide that is substituted with three saturated heterocyclic rings, each hetero ring containing one nitrogen and 4 to 6 carbon atoms. A process for the preparation of an initiator composition as claimed in claim 10, which consists of mixing together the metal organils, dissolved in inert hydrocarbons, and curing at a temperature in the range from 0 to 120 ° C for at least 5 minutes.