MXPA00006876A - Method for producing impact-resistant modified thermoplastic moulding materials - Google Patents

Abstract

The present invention relates to a method for producing impact-resistant modified thermoplastic moulding materials, wherein said materials include a rubber-based soft phase which is dispersively distributed in a hard matrix of vinylaromatic monomers. The hard matrix is submitted to anionic polymerisation in the presence of the metallic alkyl or aryl of an element selected from the second or third main group or from the second secondary group of the periodic system.

Description

ICAS THERMOPLAS PREPARATIONS FOR MOLDING IMPACT RESISTANT The invention relates to a process for preparing thermoplastic compositions for impact-resistant molding consisting of a soft phase made of a rubber dispersed in a hard matrix composed of vinylaromatic monomers. There are different continuous processes and in known batches, in solution or suspension, to prepare impact resistant polystyrene. In these processes a rubber, usually polybutadiene, is dissolved in monomeric styrene, which is polymerized in a preliminary reaction until a conversion of approximately 30%. The formation of polystyrene and the associated depletion of monomeric styrene gives rise to a change in phase coherence. During this process, known as phase inversion, grafting reactions also occur in polybutadiene and these, together with the agitation intensity and viscosity, affect the formulation of the dispersed soft phase. The styrene matrix is constituted in the following main polymerization. Processes of this type carried out in different kinds of reactors are described, for example, in A. Echte, Handbuch der technischen Polymerchemie, VCH Verlagsgesellschaft Weinheim, Germany, 1993, page 484-489 and US Patent 2 727 884 and 3 903 202 These processes require complicated trituration and dissolution and rubber prepared separately, and the resulting polybutadiene rubber solution in styrene has to be filtered prior to polymerization to remove gel particles. The required rubber solution in styrene can also be prepared by anionic polymerization of butadiene or butadiene / styrene in non-polar solvents, such as cyclohexane or ethylbenzene, followed by addition of styrene (GB 1 013 205 and EP-A-0 334 715) or by incomplete conversion of butadiene to styrene (EP-A 0 059 231 and EP-A 0 304 088) followed by removal of non-converted butadiene. The rubber solution is then subjected to a free radical polymerization. Processes for the preparation of thermoplastic compositions for molding by anionic polymerization of styrene in the presence of a rubber are known, for example, from DE-A 42 35 978 and US 4 153 647. The resulting impact resistant products have lower contents of residual monomers and oligomers, compared to the products obtained by free radical polymerization. - The anionic styrene polymerization proceeds very quickly and produces very high conversions. The high polymerization rate and the heat generation associated with this means that on an industrial scale these processes are. limited to very diluted solutions, low conversions and low temperatures. The alkaline earth metal, zinc and aluminum alkyl compounds have therefore been described as retarding additives for anionic polymerization of styrene (WO 97/33923 and WO 98/07765) or butadiene in styrene (WO 98/07766). The controlled anionic polymerization of styrene and butadiene to obtain styrene-butadiene homopolymers or copolymers is possible with these additives. In addition, WO 98/07766 describes the continuous preparation of impact modified molding compositions using styrene-butadiene rubbers which can be obtained by means of retarding additives in styrene solution. However, the rubbers that can be obtained by this process always contain small amounts of copolymerized styrene in the butadiene blocks. An object of the invention is to avoid the aforementioned disadvantages and to develop a process that allows the preparation of impact resistant molding compositions having low content of residual monomers and oligomers. The process must also guarantee simple and reliable control of the reaction. It must be suitable to use a large number of types of rubbers, to allow a wide range of properties in impact resistant molding compositions. Another objective was a continuous process for the anionic polymerization of impact resistant molding compositions with simple and reliable reaction control. We have found that this objective is achieved by means of a process to prepare impact resistant thermoplastic mold compositions comprising an elaborate soft phase of a caliche dispersed in a hard matrix composed of vinylaromatic monomers, wherein the hard matrix is prepared by anionic polymerization in the presence of a metal organyl compound of an element of the second or third major group, or of the second subgroup, of the Periodic Table. The organometallic compounds of an element of the second third major group, or of the second subgroup, of the Periodic Table that can be used are the organyl compounds of the elements Be, Mg, Ca, Sr, Ba, B, Al, Ga, In , TI, Zn, Cd, Hg. These organyl metal compounds are also retardant denominators, due to their effect during the anionic polymerization. Preference is given to magnesium and aluminum organo compounds. For the purposes of the invention, the organo compounds are the organometallic compounds of the aforementioned elements with at least one metal-carbon bond, in particular the alkyl or aryl compounds. The organometallic compounds can also contain, in the metal hydrogen, halogen, or organic radicals linked by heteroatoms, giving compounds, such as alcoholates or phenolates. The latter is obtained, for example, by hydrolysis, alcoholysis or complete or partial aminolysis. It is also possible to use mixtures of different organo-metal compounds. Suitable organo magnesium compounds have the formula R 2 Mg, where R, independently of another, are hydrogen, halogen, C 1 -C 2 alkyl, or C 6 -C 2 aryl. Preference is given to dialkylmagnesium compounds, in particular the ethyl, propyl, butyl or octyl compounds which are products that are available commercially. Particular preference is given to (n-butyl) (sec-butyl) magnesium, which is soluble in hydrocarbons. The organoaluminum compounds of the formula R3AI can be used, where R, independently of another, are hydrogen, halogen, C2-C2o alkyl or Cg-C2o aryl. The preferred organoaluminum compounds are the trialkylaluminum compounds, as can be triethylaluminum, triisobutyl aluminum, tri-n-butylaluminum, triisopropyl aluminum and tri-n-hexylaluminum. Particular preference is given to triisobutylaluminum. It is also possible to use organoluminum compounds produced by hydrolysis, alcoholysis, aminolysis or partial or complete oxidation of alkylaluminum compounds or arylaluminum compounds. Examples of these are diethylaluminium ethoxide, diisobutylaluminum ethoxide, diisobutyl (2,6-di-tert-butyl-4-methylphenoxy) aluminum (CAS No. 56252-56-3), methylaluminoxane, isubitylated methylaluminoxane, isobutylaluminoxane, tetraisobutyldialuminoxane and bis (diisobutyl) aluminum oxide. The retarders generally described do not act as initiators of the polymerization. The initiators of the anionic polymerization used are usually alkali metal alkyl compounds, alkali metal aryl compounds or mono-, di or polyfunctional alkali metal aralkyl compounds. It is useful to use organolithium compounds, such as ethyl-, propyl- / isopropyl-, n-butyl-, sec-butyl-, tert-butyl-, phenyl-, diphenylhexyl-, hexamethylene-, butadienyl-, isoprenyl- or polystyirillithium, or the polyfunctional compounds 1,4-dilithiobutane, 1,4-dilithio-2-butene or 1,4-dilithiobenzene, the amount of the alkali metal organo compound required depends on the desired molecular weight and the type and amount of the other organo compounds used, and also the temperature of the polymerization. This is generally in the range from 0.002 to 5 mol%, based on the total amount of the monomers. Preferred vinylaromatic monomers for the hard matrix are styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene and 1,1-diphenylethylene, or mixtures. Particularly preferred is styrene. - The rubber used for the soft phase can be any desired diene rubber or acrylate rubber, or mixtures that have a certain compatibility with the hard vinylaromatic matrix. Therefore, it is advantageous if the rubber consists of a certain proportion of styrene blocks, since the anionic polymerization of the hard matrix does not produce any compatibility of the rubber by the formation of the graft of the monomers that form the hard matrix. The rubber used is preferably a styrene-butadiene block copolymer or a mixture of styrene-butadiene block copolymers with a homopolybutadiene, where the styrene content, based on the strength of the rubber, is in the range from 5 to 50% by weight, preferably 10 to 45% by weight, particularly preferably 20 to 40% by weight. The residual butadiene content in the rubber should be less than 200 ppm, preferably less than 100 ppm, in particular less than 50 ppm. In a preferred version of the process, the rubber solution is prepared in a first step by the normal methods of anionic polymerization and styrene is used for dissolution. In a second step without further addition of solvents the hard matrix is polymerized with phase inversion until a conversion of at le90%, based on the hard matrix. It is useful to polymerize the rubber in an aliphatic, isocyclic or aromatic hydrocarbon or hydrocarbon mixture, preferably in benzene, toluene, ethylbenzene, xylene, cumene or cyclohexane. Toluene and ethylbenzene are particularly preferred. The polymerization of the rubber can also be carried out in the presence of liquid additives. These usually are not added until during or after polymerization of the hard matrix. The rubber can, for example, be prepared in mineral oil or in a mixture of mineral oil and the aforementioned hydrocarbons. This makes it possible to reduce the viscosity or the amount of the solvent. A very high solids content is selected for the resulting solution. Its upper limit is determined mainly by the viscosity of the solution. When a styrene-butadiene rubber is used, the viscosity, and hence the possible solids content, depends inter alia on the structure of the blocks and the styrene content. It is useful to select a solids content in the range of 15 to 50% by weight, preferably 20 to 40% by weight. The rubber polymerization can be carried out continuously or in batches with a buffer tank. The continuous preparation can be carried out in reactors tanks with continuous agitation (CSTR), such as tank reactors with agitation (or cascades of reactors with agitation) or in circulating reactors or piston-type flow reactors (PFR) such as tubular reactors. with or without internal elements, or in combinations of different reactors. The batch preparation is preferably carried out in a tank reactor with stirring. The rubbers can be polymerized in the presence of a polyfunctional alkali metal organo compound, or they can be bonded to obtain a star shape during or after the polymerization using a polyfunctional coupling agent, such as aldehydes, ketones, esters, anhydrides or polyfunctional epoxides. The symmetric or asymmetric star block copolymers can be obtained in this case by coupling identical or different blocks. After finishing the polymerization, the latent polymer chains can be closed with a chain terminator instead of a coupling process. Suitable chain terminators are protonating substances or Lewis acids, such as water, alcohols, aliphatic or aromatic carboxylic acids or also inorganic acids, such as carbonic or boric acid. The amount of chain terminator added is in proportion to the amount of the latent chains. It is useful to dilute the solution directly after the end of the reaction with the vinylaromatic monomer, to facilitate subsequent handling. The resulting rubber solution is polymerized as described above in a second step, if desired with the addition of more vinylaromatic monomer. The conversion, based on the vinylaromatic monomer of the hard matrix, it is generally greater than 90%. The process in principle can also obtain the complete conversion. The rubber content, based on the entire molding composition, is useful from 5 to 25% by weight. It depends mainly on the type of rubber used and the desired properties of the impact resistant molding composition. The solids content obtained at the end of the reaction in the second step is generally in the range from 70 to 90%, in particular from 75 to 85% for the aforementioned ranges of the solids content of the rubber solution and the content of normal cancho in the composition for molding. Surprisingly, it has been found that polymerization of the hard matrix can be carried out without further addition of anionic polymerization initiator if use is made of a rubber solution which, as already described, has been prepared by anionic and finished polymerization. by chain termination or copulation. In this case, the alkyl metal compounds, which otherwise only have a retarding effect, can initiate the polymerization of the hard matrix. This gives rise to a simpler dosing and control than when an initiator / retarder mixture is used. The anionic polymerization of the hard matrix in the second reaction zone is preferably initiated exclusively by the addition of a dialkylmagnesium compound. Preference is given to a dialkylmagnesium compound containing at least one secondary or tertiary alkyl group. Very particularly preferred is (N-butyl) (s-butyl) magnesium. The polymerization of the rubber and the hard matrix can be carried out in batches or continuously in stirred tank reactors, circulation reactors, tubular reactors, tower reactors or rotating disk reactors, as described in WO 97/07766.

The resulting molding compositions can be freed from the solvents and residual monomers in a traditional manner, using devolatilizers or extruders vented at atmospheric pressure or reduced pressure and at temperatures from 190 to 320 ° C. The removed solvent can be reintroduced to the synthesis of the rubber if desired after a purification step. To avoid the accumulation of contaminants, a relatively small amount of the solvent can be removed from the process and used at another time. The resulting product has a content of less than 200 -ppm of residual monomers, preferably less than 100 ppm, in particular less than 50 ppm. It may be useful to crosslink the rubber particles by controlling the temperature appropriately and / or adding peroxides in particular those with a high decomposition temperature, such as dicumyl peroxide.

Examples Synthesis of rubber solutions Molecular weights and molecular weight distributions were determined by gel permeation chromatography (GPC) in tetrahydrofuran and the resulting chromatograms were evaluated using polystyrene or polybutadiene calibration. The styrene content and the 1,2-vinyl content of the butadiene fraction in the rubber was determined by evaluating the nuclear resonance spectroscopy data H.

Example 1 14 kg of anhydrous toluene were charged to a tank reactor with stirring of 50 liters capacity and mixed with agitation with 1610 g of butadiene. The mixture was heated to 40 ° C and mixed at this temperature with 19.4 g of a 1.5 molar solution of sec-butyllithium in cyclohexane. Once the polymerization had begun, the internal temperature was raised to a maximum of 72 ° C. After 17 minutes, another 2168 g of butadiene was added over a period of 15 minutes at an internal temperature of 66 to 11 °, and the mixture was stirred for another 30 minutes at 65 ° C. 2222 g of styrene were then added. The temperature had now risen to 71 ° C. After 60 minutes, 1.6 g of isopropanol were used for the termination. The solution had a solids content of 30% by weight. The addition of 20 kg of styrene produced a rubber solution with a solids content of 17.5% by weight. The resulting butadiene-styrene block copolymer had an average molecular weight of Mw = 308,000 g / mol and a polydispersity Mw / Mn of 1.09 (determined by gel permeation chromatography, GPC, with calibration with polystyrene). The residual butadiene content was less than 10 ppm. The styrene content was 37%; 9% of the butadiene fraction of the rubber was of the 1,2-vinyl type (determined by H nuclear resonance spectroscopy). The solution viscosity of a 5.43% solution of toluene rubber was 42 mPas.

Example 2 14 kg of anhydrous toluene were charged to a tank reactor with stirring of 50 liters capacity and mixed with stirring, with 1612 g of butadiene. The mixture was heated to 32 ° C and mixed at this temperature with 17.4 g of a 1.33 molar solution of sec-butyllithium in cyclohexane. The solution was heated to 62 ° C within a period of 20 minutes. Another 2813 g of butadiene were added at an internal temperature from 62 to 79 ° C within a period of 25 minutes. The mixture was stirred for another 30 minutes at 65 ° C. Some of the produced butadiene blocks were then coupled using 52 ml of a 2% by weight solution of ethyl acetate, and 1575 g of styrene were then added. The temperature now rose to 69 ° C. After 60 minutes, 1.4 ml of isopropanol were used for the termination. The solution had a solids content of 30% by weight. The addition of 20 kg of styrene produced a rubber solution with a solids content of 17.5% by weight. The resulting polymer mixture had a bimodal distribution with a main peak of the molar mass at Mp = 329, 000 g / mol and another peak at Mp = 166,000 g / mol (GPC, calibration with polybutadiene). The residual butadiene content was less than 10 ppm. The styrene content of the isolated rubber was 26%. 12% of the butadiene fraction of the rubber was of the 1/2-vinyl type (H NMR) The solution viscosity of a 5.43% solution of rubber in toluene was 97 mPas Examples 3 to 5 were made in one form similarly using, respectively, phenylacetylene, ethyl acetate and diethyl adipate as coupling agents The parameters and results of the rubber solutions are given in Table 1: dosed as a 2 wt% solution in toluene.

Example 6 13. 8 kg of anhydrous toluene in a 50 liter stirred tank reactor were mixed, with stirring, with 228 g of styrene and 14.2 ml of a 1.33 molar solution of sec-butyllithium in cyclohexane. The solution was heated to 50 ° C within a period of 15 minutes. 3570 g of butadiene were then added within a period of 25 minutes, whereby the internal temperature rose to 74 ° C. The mixture was stirred for another 30 minutes at 65 ° C. Then 2100 g of styrene were added. The temperature had now risen to 70 ° C. After 60 minutes, 1.4 ml of isopropanol were added to the reaction mixture.

In this joint the solution had a solids content of 30% by weight. The solids content was adjusted to 15% by weight by adding styrene to the mixture. The GPC analysis of the resulting polymer mixture showed a distribution with a main peak of the molar mass at Mp = 296,000 g / mol and a shoulder at Mp = 225,000 g / mol, using calibration with polybutadiene. The residual butadiene content was less than 10 ppm. The H NMR gave the styrene content of the isolated rubber as 39%. 11% of the butadiene fraction of the rubber was of the 1,2-vinyl type. The viscosity of the solution of a 5.43% solution of the rubber in toluene was 54 mPas.

Synthesis of HIPS The limit of stress and elongation at break was determined at 23 ° C in accordance with DIN 53455. The test samples used were produced in accordance with ISO 3167. Impact resistance with notch was determined in accordance with DIN 53753 at 23 ° C in a test sample of dimensions 50 mm x 6 mm x 4 mm (with a hole diameter of 3 mm).

Example 7 A 3-liter, double-walled stirred tank reactor with a normal anchor stirrer was used for continuous polymerization. The reactor was designed for a pressure of 60 bar and was controlled at the temperature with a heat transfer medium for the isothermal polymerization. 394 g / h of styrene, 686 g / h of the rubber solution of Example 1 and 17 g / h of a 1.16 molar solution of (n-butyl) (s-butyl) agnesium in heptane / toluene (1 : 4 parts by weight) were metered in continuously, ~ with stirring at 100 rpm, in the tank reactor with stirring, and stirred at a constant temperature of the mixture of 79 ° C. The material discharged from the tank reactor with agitation was transported forward to two 4-liter tower reactors, with agitation arranged in series. The first tower reactor was operated at an internal temperature of 92 ° C. In the second tower reactor at temperature was adjusted by means of two heating zones of equal length arranged in series in such a way that the internal temperature at the end of the first zone was 124 ° C and at the end of the second zone was 158 ° C. At the exit of the tower reactor the polymerization mixture was mixed in a mixer with 5 g / h of methanol and then passed through a tubular section heated to 260 ° C and step, with pressure reduction, by a valve of pressure control towards a low pressure vessel maintained at 25 mbar. The melt was discharged using a propeller and pellet. After a few hours a stable equilibrium condition was established in all system parts. The pressure drop across the entire system was 2.9 bar. The solids content was 26% by weight at the outlet of the tank reactor with agitation, 58% by weight at the outlet of the first tower reactor and 73% by weight at the outlet of the second tower reactor, corresponding to 100% monomer conversion. The polystyrene matrix had a molecular weight Mw of 164,500 g / mol and a polydispersity Mw / Mn of 2.95. The distribution was onomodal. The determinations in the impact resistant polystyrene (or in the matrix) gave a content of less than 5 ppm of styrene, less than 5 ppm of ethylbenzene and 83 ppm of toluene. Impact resistant polystyrene had an effort limit of 27 N / mm, elongation at break of 25% and impact resistance with hole notch of 12 kJ / m. The vapors collected in the devolatilization unit were used, after distillation, for another rubber synthesis of Example 1.

Example 8 511 g / h of styrene, 488 g / h of the rubber solution of Example 2 and 17.4 g / h of a 0.16 molar solution of infant) (s-butyl) magnesium in heptane / toluene (1: 4 parts in weight) were dosed continuously, with agitation at 100 rpm, in the tank reactor with stirring of Example 8 and stirred at a constant temperature of the mixture of 86 ° C. The material discharged from the tank reactor with agitation was transported forward to a double-walled tubular reactor with 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 had temperature control by means of a concurrently conducted heat transfer medium, and the temperature of the polymerization mixture was determined by three temperature detectors evenly distributed over the entire path of the reaction. The temperature of the heat transfer medium at the entrance to the tubular reactor was 105 ° C. The highest temperature of the polymerization solution was obtained at the end of the tubular reactor, at 184 ° C. After the polymerization mixture had left the tubular reactor, a solution at 20% concentration by weight of methanol in toluene was added at 10 ml / h using an HPLC pump and a tubular section downstream with a static mixer was used to homogenize the mixture. The passage, with reduction of pressure, by a throat valve to a devolatilization vessel that was maintained at 20 mbar, was extracted using a screw pump, extruded and granulated. After a short time a stable equilibrium condition was established in all system parts. The pressure drop in the whole system was 2.2 bar. The solids content was 41% by weight at the outlet of the tank reactor with stirring, and 79% by weight at the outlet of the tubular reactor, corresponding to a conversion of 100% of monomers. The polystyrene matrix had a molecular weight Mw of 169,000 g of / mol and a polydispersity Mw / Mn of 2.62. The determination gave a content of less than 5 ppm of styrene, less than 5 ppm of ethylbenzene and 102 ppm of toluene. Impact-resistant polystyrene had a stress limit of 29 N / mm, elongation at break of 20% and impact resistance with hole notch of 11 kJ / m2. The vapors collected in the devolatilization unit were used in Example 2, after distillation, for another rubber synthesis.

Example 9 The reactor used was a double walled tubular reactor with an internal diameter of 29.7 mm and a length of 4200 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 divided into two zones of equal length, each controlled at the temperature by a concurrently conducted heat transfer medium, the temperatures of, respectively, the polymerization mixture and the heat transfer medium were determined by three temperature detectors distributed evenly throughout the reaction path. 387 g / h of styrene, 588 g / h of the rubber solution of Example 3 and 17.5 g / h of an initiator solution were metered in continuously to the tubular reactor. 100 g of the initiator solution were composed of 24 g of a 0.8 molar solution of (n-butyl) (s-butyl) magnesium in heptane, 1 g of a 1.6 M solution of sec-butyllithium in cyclohexane and 75 g of toluene. The temperature of the heat transfer medium at this point of entry in the first section of the reactor was 100 ° C. The temperatures of the polymerization solution at the end of the first section of the reactor was 134 ° C. The temperature of the heat transfer medium at the inlet to the second reactor section was 80 ° C. The temperature of the polymerization solution at the end of the second section of the tubular reactor was on average 183 ° C. After the polymerization mixture had left the tubular reactor, a solution at 20% by weight concentration of methanol in toluene was added at 10 ml / h using an HPLC pump, and a downstream tubular section with a static mixture [sic] was used to homogenize the mixture. The polymer melt passed, with pressure reduction, through a throat valve to a devolatilization vessel which was maintained at 17 mbar, extracted using a screw pump, extruded and granulated. - After a short time stable conditions were established in all parts of the system. The pressure drop across the entire system was 2.1 bar. The solids content was 31% by weight at the end of the first section of the tubular reactor and 80% by weight at the "outlet of the tubular reactor." The polystyrene matrix had a molecular weight Mw of 185,000 g / mol and a polydispersity Mw / Mn of 2.12 The determination gave a content of 12 ppm of styrene, less than 5 ppm of ethylbenzene and 87 ppm of toluene The impact resistant polystyrene had an effort limit of 26 N / mm, elongation at break of 23% and Impact resistance with hole notch of 11 kJ / m2.

The vapors collected in the devolatilization unit were used as in Example 3, after distillation, for another rubber synthesis.

Example 10 538 g / h of rubber solution of Example 4 and 682 g / h of styrene were metered in continuously, with stirring at 100 rpm, to a stirred tank reactor of 3 liters operated under pressure and equipped with an anchor stirrer.

Separately, a mixture of 25 g / h of a solution of a 0.32 molar solution of sec-butyllithium in cyclohexane / toluene (weight ratio 1: 4) and 24 g / h of a 4% by weight solution of triisobutylamine in toluene were metered into the reactor. To prepare this mixture, the components were mixed continuously in a tubular section of 12.5 ml capacity and passed to the reactor. The tank reactor with stirring was controlled by a thermostat at an internal temperature of 109 ° C. The solution was transported forward to a stirred-tower reactor, of 4 liters, operated at an internal temperature of 110 ° C. The material discharged from the reactor was introduced into a second 4-liter tower reactor provided with two heating zones of identical size. The first zone was controlled at an internal temperature of 121 ° C and the second at 158 ° C. The material discharged from the reactor was mixed with 20 g / h of a 10% by weight solution of methanol in toluene, passed through a mixer and then into a tubular section heated to 260 ° and, with pressure reduction, through a Pressure control valve to a low pressure vessel operated at 25 mbar. The melt was discharged using a propeller and pellet. After a few hours constant operating conditions were established. The solids content was 29% by weight at the outlet of the first reactor and 56% by weight after the first tower. Quantitative conversion was found in the output of the continuous system. The pressure drop across the entire system was 2.3 bar. The polystyrene matrix had a molecular weight Mw of 162,400 g / mol and polydispersity M / n of 2.68. The distribution was monomodal. The determination gave a content of less than 5 ppm of styrene, less than 5 ppm of ethylbenzene and 112 ppm of toluene. Impact-resistant polystyrene had an effort limit of 17 N / mm, elongation at break of 35% and impact resistance with hole notch of 14 kJ / m. The vapors collected in the devolatilization unit were used, after distillation, for another rubber synthesis as in Example 4.

Example 11 1252 g / h of the rubber solution of Example 5 and 603 g / h of styrene were metered in continuously, with stirring at 100 rpm, to a stirred tank reactor, of 3 liters operated under pressure and equipped with an agitator of anchor Separately, a mixture of 37 g / h of a solution of a 0.32 molar solution of sec-butyllithium in cyclohexane / toluene (weight ratio 1: 4) and 18 g / h of an 8% by weight solution of triisobutylaminium in toluene were dosed to the reactor. For this, the components were mixed continuously in a tubular section of 12.5 ml capacity and passed to the reactor. The tank reactor with stirring was controlled by a thermocouple at an initial temperature of 112 ° C. The solution was transported forward to a stirred turbine reactor, 4 liters, provided with two heating zones of identical size. The first zone was controlled at an internal temperature of 125 ° C and the second at 172 ° C. The material discharged from the reactor was mixed with 20 g / h of a 10% by weight solution of methanol in toluene, passed through a mixer and then to a tubular section heated to 260 ° and, with pressure reduction, by a Pressure control valve to a low pressure vessel operated at 25 mbar. The melt was discharged using a screw and granulate. After a short time, constant operating conditions were established. The solids content was 36% by weight at the outlet of the first reactor, Quantitative conversion was found in the output of the continuous system. The polystyrene matrix had a molecular weight Mw of 171,000 g / mol and polydispersity Mw / Mn of 2.83. The distribution was monomodal. The determination gave a content of less than 5 ppm of styrene, less than 5 ppm of ethylbenzene and 96 ppm of toluene. The impact-resistant polystyrene had a stress limit of 20 N / mm, elongation at break of 36% and impact resistance with hole notch of 15 kJ / m. The vapors collected in the devolatilization unit were used, after distillation, for another rubber synthesis as in Example 5.

Example 12 A 1.9-liter double-walled tank reactor with a standard anchor stirrer was used for continuous polymerization. The reactor was designed for a pressure of 60 bar and was controlled at the temperature with a heat transfer medium for isothermal polymerization. 280 g / h of styrene, 796 g / h of rubber solution of Example 6 and 19 g / h of a 0.16 molar solution of (n-butyl) (s-butyl) magnesium in heptane / toluene (weight ratio 1: 4) were dosed continuously, with stirring at 100 rpm, to a tank reactor with stirring, and stirred at a constant temperature of the mixture of 94 ° C. The material discharged from the tank reactor with agitation was transported forward to two 4-liter tower reactors, with agitation arranged in series. The first tower reactor was operated at an internal temperature of 102 ° C. In the second tower reactor the temperature was adjusted by means of two heating zones of equal length arranged in series in such a way that the internal temperature at the end of the first zone was 122 ° C and at the end of the second zone it was 160 ° C. At the exit of the tower reactor the polymerization mixture was mixed in a mixer with 5 g / h of a 1: 1 methanol / water mixture and then passed through a tubular section heated to 260 ° C and step, with reduction of pressure, by a pressure control valve to a low pressure vessel that was maintained at 25 mbar. The melt was discharged using a propeller and pellet. After a few hours, stable equilibrium conditions were established in all the system parts. The pressure drop across the entire system was 2.8 bar. The solids content was 37% by weight at the outlet of the tank reactor with stirring, 58% by weight at the outlet of the tank reactor with 58% by weight stirring at the outlet of the first tower reactor. A quantitative conversion was found in the output of the second tower reactor. The polystyrene matrix had a molecular weight Mw of 152,000 g / mol and a polydispersity Mw / Mn of 2.62. The distribution was monomodal. The determinations gave a content of less than 5 ppm of styrene, less than 5 ppm of ethylbenzene and 52 ppm of toluene. The material had an effort limit of 28 N / mm, impact resistance in hole notch of 13 kJ / m, thermal deformation temperature (Vicat B / 50) of 94 ° C and MVR melt rate of 200/5 (ISO 1133) of 3.9 cm / 10 min. An electron micrograph showed cell morphology of the particles. The average particle diameter was 3.2 mm.

Claims (1)

1. CLAIMS A process for preparing impact-resistant thermoplastic molding compositions comprising an elaborate soft phase of a rubber dispersed in a hard matrix composed of vinylaromatic monomers, which involves performing the anionic polymerization of the vinylaromatic monomers in the presence of a metal organometallic compound of an element of the second or third main group, or of the second subgroup, of the Periodic Table, and of rubber, which consists of using a rubber whose residual butadiene content is less than 200 ppm. The process as claimed in claim 1, wherein the metal organyl compound used is a trialkylaluminum compound or a dialkylaluminum compound. The process as recited in claim 1 or 2, wherein the rubber used is a styrene-butadiene block copolymer or a mixture of a styrene-butadiene block copolymer with a homopolybutadiene, wherein the styrene content, based on in all rubber, it is in the range from 5 to 50% by weight. The process as claimed in any of claims 1 to 3, wherein, in the first step, a rubber solution with a solids content in the range of 15 to 50% by weight is prepared by anionic polymerization of butadiene and styrene. in an aliphatic, isocrylic or aromatic hydrocarbon or mixture of hydrocarbons, it is reacted with a terminating and / or coupling agent and then diluted with vinylaromatic monomers and, in a second step, without further addition of solvents, the hard matrix is polymerized with phase inversion to a conversion of at least 90%, based on the hard matrix. The process as claimed in claim 4, wherein the hydrocarbon used is a mineral oil. The process as claimed in claim 4 or 5, wherein the polymerization of the hard matrix is carried out without further addition of an anionic polymerization initiator. The process as claimed in any of claims 4 or 6, wherein the polymerization of the rubber and the hard matrix is carried out continuously.