FR2791060A1 - PROCESS FOR PREPARING A STABLE FREE RADICAL CARRIER RUBBER AND USE OF THE SAID CARRIER RUBBER FOR THE PREPARATION OF A VINYLAROMATIC SHOCK POLYMER - Google Patents

Abstract

The invention concerns a method for making a rubber bearing a group of stable free radicals. Said rubber can be used for making shock resistant vinyl-aromatic polymer compositions, that is compositions comprising a matrix containing a vinyl-aromatic polymer, said matrix enclosing rubber nodules (that can be called particles). Depending on the morphology of said nodules, it is possible to use advantageously the shock-resistant properties, the brightness and transparency of the shock resistant composition.

Description

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PROCESS FOR PREPARING A CARRIER RUBBER
STABLE FREE RADICAL AND USE THEREOF
CARRIER RUBBER FOR THE PREPARATION OF A
VINYLAROMATIC POLYMER SHOCK.

 The invention relates to a method of manufacturing a carrier rubber of a group generating stable free radicals, hereinafter called carrier rubber. This carrier rubber may be used for the manufacture of impact vinyl aromatic polymer compositions hereinafter called shock composition, that is to say compositions comprising a matrix comprising a vinylaromatic polymer, said matrix surrounding nodules (may be called particles) of rubber.

 Depending on the morphology of these nodules, it is possible to play on the properties of impact resistance, brightness and transparency of the impact composition.

 The following morphologies of rubber nodules can be obtained: - the salami-type morphology, which means that the rubber particle contains several occlusions, generally substantially spherical, but not concentric, of vinylaromatic polymer, - labyrinth type morphology, which means that the rubber particle contains several elongate, curved, generally non-spherical, generally dissymmetrical occlusions of vinylaromatic plymer, - the onion-like morphology, which means that the rubber particle is substantially spherical and contains, concentrically with respect to itself, several occlusions of vinylaromatic polymer contained in each other,

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 the capsule-type morphology, which means that the rubber particle, generally substantially spherical, contains a single vinylaromatic polymer occlusion, the dense particle morphology, which can appear in the form of a droplet or stick and which corresponds to a rubber nodule without inclusion of vinylaromatic polymer.

The carrier rubber is obtained by a thermal treatment of an elastomer in the presence of a stable free radical.

The process according to the invention proposes an advantageous method of manufacturing rubber bearing free radical generating groups since the heat treatment: - takes place after the manufacture of the elastomer, - can be carried out with any commercial elastomer, can be carried out with any stable free radical, takes place in the absence of solvent or in the presence of a small amount of solvent, can be carried out with very short cycle times.

Due to the presence of the carrier rubber during the polymerization step, the invention allows the manufacture of an impact vinylaromatic polymer that can even be transparent without having to anionically polymerize the vinylaromatic monomer. The method according to the invention therefore avoids the disadvantages of anionic polymerization related to the need to work under conditions of high purity, both at the level of the reagents used and the reaction medium.

The invention relates to an advantageous method for producing a stable free radical generating group bearing rubber

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 randomly attached to the rubber chain, here called carrier rubber.

The invention also relates to a method for preparing a transparent impact composition, that is, a composition comprising a vinylaromatic polymer matrix surrounding rubber particles having zero, one or more vinylaromatic polymer occlusions. The impact composition according to the invention has the advantage, according to one of its embodiments, of combining impact and transparency properties.

Transparent impact vinylaromatic compositions are highly sought after in many applications and particularly in the field of packaging. The shock and transparency properties are very delicate to combine because of the difference in refractive index between the rubber and the vinylaromatic polymer. For this kind of composition, it is necessary to graft the rubber to disperse the finest rubber in the vinylaromatic polymer. The radical grafting of rubber being limited during the radical polymerization of the vinylaromatic monomer, the route commonly used for the manufacture of PS transparent shock is the synthesis of styrene-butadiene copolymers by anionic route, generally containing between 20% and 30% of butadiene in weight. These copolymers can then be mixed with crystal PS until the desired shock / transparency compromise is achieved. The disadvantage of such a process lies in the important purity conditions required by the anionic polymerization.

EP 69792 teaches that a transparent impact PS can be obtained by radical polymerization of styrene in the presence of an initiator and a rubber. However, the final composition should contain between 15 and 30% by weight of polydiene and rubber

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 The initial styrene-butadiene type, which must contain at least 20% by weight of styrene, involves the use of the rubber in large quantities and therefore makes this process particularly expensive.

The patent application WO 98/32797 teaches that a transparent impact vinyl aromatic polymer can be obtained by radical polymerization of the vinylaromatic monomer in the presence of a homopolydiene type rubber bearing hydroperoxide group. This generates during the polymerization step a surrefrosting of the rubber and thus avoids the use of SB type block copolymers. However, the carrier rubber hydroperoxide group is obtained after treatment of the rubber with an ozonide phosphite, itself obtained after a step of ozonization of a phospite. This method of manufacturing the carrier rubber hydroperoxide group is not easy to achieve on an industrial scale.

Another alternative for improving the grafting of the rubber by the vinylaromatic polymer is to use controlled radical polymerization controlled by stable free radicals.

The patent application FR97.11693 teaches that it is possible to achieve a shock PS by radical polymerization of styrene in the presence of a polybutadiene bearing stable free radical generating group. Such a polybutadiene is obtained after thermal treatment of a polybutadiene dissolved in a solvent in the presence of a peroxide and a stable free radical. Such a process then involves either the presence of a large amount of solvent during the styrene polymerization step if polybutadiene is used as obtained after the heat treatment, or a tedious step of removing the solvent prior to initiate the polymerization step. This document gives no indication of an improvement in transparency.

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 US Pat. No. 5,627,248 teaches that it is possible to produce an SBS triblock copolymer by using a specific radical initiator already carrying a group generating a stable free radical. The manufacture of such a copolymer thus necessarily passes through a polymerization step of butadiene monomer.

WO 97/36944 teaches that the polymerization of styrene in the presence of rubber, each chain carrying at least one stable free radical has an influence on the morphology of the final shock PS, and that in particular a transparent impact PS can be obtained. However, the functionalization stage of the rubber takes place during the manufacture of the rubber anionically and therefore requires a modification of the process. It can not be obtained from any commercial rubber. Moreover, this invention requires the organic synthesis of species carrying a stable free radical which is then used for the functionalization of the rubber. The stable free radical is therefore not used as it is.

The method according to the invention proposes a simple economical and advantageous solution for manufacturing carrier rubber since it can be made from any commercial elastomer (therefore does not intervene during the elastomer manufacturing process and does not occur during the manufacturing process of the elastomer. therefore does not modify this process as a consequence) and any stable free radical used in the state, and since it is carried out in the absence of solvent, or in the presence of a little solvent.

The process according to the invention for producing a carrier rubber which generates a stable free radical which is randomly attached to the rubber chain comprises a step of thermal treatment of an elastomer conventionally used for the preparation of the impact vinyl aromatic polymers, in the presence of a stable free radical, a free radical initiator capable of tearing a proton from the elastomer, and, preferably, in the absence of monomer

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 vinylaromatic. The stable free radical and the radical initiator are present at from 10 ppm to 10% and preferably from 100 ppm to 5% by weight with respect to the elastomer. If: - (SFR) is the number of moles of stable free radical, - FSFR the functionality of the stable free radical, ie the number of sites on the same stable free radical molecule exhibiting the radical state, - (INIT) the number of moles of initiator of free radicals, - FINISH the functionality of the initiator of free radicals, ie the number of free radicals that each molecule of initiator is capable of to generate, the ingredients necessary for the manufacture of the carrier rubber are generally introduced so that the ratio [(SFR) FSFR] / [(INIT) FINIT] is between 0.01 and 100, preferably between 0.1 and 10, and still more preferably between 0.5 and 10.

For the manufacturing process of carrier rubber, the temperature of the heat treatment is between 20 and 200 ° C., preferably between 50 and 150 ° C.

The heat treatment is preferably carried out in such a way that the free radical initiator has maximum efficiency, that is to say so that each radical that it is likely to generate actually pulls a proton. It is substantially under these conditions if the temperature of the heat treatment is between (T1 / 2 - 50 C) and (T1 / 2 + 50 C), T1 / 2 representing the temperature for which the half-life time of the free radical initiator is 1 hour. The person skilled in the art will know how to find the optimal temperature so as to induce a rapid decomposition of the initiator of free radicals, thus a duration of the heat treatment

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 of the reduced elastomer, and so as not to degrade the elastomer by crosslinking.

The duration of the heat treatment is between 10 seconds and 1 hour, preferably between 1 minute and 30 minutes.

The operating conditions relating to the heat treatment, namely the nature and amounts of the ingredients used, temperature, duration, should preferably be such that a rubber is obtained carrying on average from 0.1 to 10 randomly stable stable free radical generating groups. by rubber chain.

Those skilled in the art are able to search for the operating conditions for the heat treatment of the rubber leading to the fixing of the sufficient number of stable free radical generator group for the rubber to lead to the desired morphology, and therefore to the properties targeted, when the polymerization stage of the vinylaromatic monomer in the presence of the carrier rubber, given the fact that the present application gives it the following information: to increase the amount of stable free radical generating group on the carrier rubber, it is possible, during the treatment thermal: - increase the concentration of stable free radical - increase the temperature and / or the reaction time - use a higher graft initiator.

The free radical initiator may be chosen from organic peroxides and hydroperoxides and azo compounds. Preferably, the initiator of free radicals the initiator may be selected from peresters, alkyl peroxides, acyl peroxides, percarbonates and peracetals.

The free radical initiator should be selected preferentially so that it can improve the grafting on the rubber. By way of example, the free radical initiator may be chosen from the following list:

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 tert-butyl-isopropylmonoperoxycarbonate tert-butyl (2-ethylhexyl) monoperoxycarbonate dicumyl peroxide 1,1-di (tert-butylperoxy) cyclohexane 1,1-di (tert-butylperoxy) -3,3,5-trimethylcyclohexane tert-butyl peroxyacetate peroxide Cylyl and tert-butyl-tert-butyl peroxybenzoate tert-butylperoxy-2-ethylhexanoate Dicumyl peroxide, di-tert-butyl peroxide and tert-butyl-isopropyl-monoperoxycarbonate are preferred as initiators of free radicals.

Do not confuse a stable free radical with free radicals whose life is ephemeral (a few milliseconds) such as free radicals from the usual initiators of polymerization such as peroxides, hydroperoxides and azo initiators. The free radicals initiating polymerization tend to accelerate the polymerization. On the contrary, stable free radicals generally tend to slow down the polymerization. It can generally be said that a free radical is stable within the meaning of the present invention if it is not a polymerization initiator and if, under the conditions of use of the present invention, the average lifetime of the radical is at least five minutes. During this average life time, the molecules of the stable free radical constantly alternate the radical state and the group state linked by a covalent bond to a polymer chain. Of course, it is preferable that the stable free radical has good stability for the duration of its use in the context of the present invention. Generally, a stable free radical can be isolated in the radical state at room temperature. A stable free radical is

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 stable enough that its free radical state can be characterized by spectroscopic methods.

It is recalled that the notion of stable free radical is known to those skilled in the art to designate a radical so persistent and non-reactive with respect to air and moisture in the ambient air, that the radical pure can be handled and stored without more precaution at room temperature than are the majority of commercial chemicals (see D. Griller and K. Ingold, Accounts of Chemical Research, 1976, 9, 13-19, or Organic Chemistry of Stable Free Radicals, A. Forrester et al., Academic Press, 1968).

The family of stable free radicals includes in particular the compounds acting as radical polymerization inhibitors for the storage of monomers, stable nitroxyl radicals, that is to say comprising the = N-O 'group. For example, radicals represented by the following formulas can be used as stable free radicals:

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dans lesquelles n représente un nombre entier non nul et R 1, R2, R3, R4, R'1 et R'2 pouvant être identiques ou différents représentent un atome d'halogène tel que le chlore, le brome ou l'iode, un groupement hydrocarboné linéaire, ramifié ou cyclique, saturé ou insaturé tels qu'un radical alkyle ou phényle, ou un groupement ester-COOR ou un groupement alcoxyle -OR, ou un groupement phosphonate -PO(OR)2, ou une chaîne de polymère pouvant par exemple être une chaîne de polyméthacrylate de méthyle, de polybutadiène, de polyoléfine comme de polyéthylène ou de polypropylène, mais étant de préférence une chaîne de polystyrène, et dans lesquelles R5, R6, R7, R8, R9 et R10, pouvant être identiques ou différent, peuvent être choisis dans la même famille de groupement que celle qui vient d'être envisagée pour R1, R2, R3, R4, R'1 et R'2, et de plus peuvent représenter un atome d'hydrogène, un groupement hydroxyde-OH, un groupement acide tel que-COOH ou -PO (OH)2 ou -S03H.

in which n represents a non-zero integer and R 1, R 2, R 3, R 4, R '1 and R' 2 which may be identical or different represent a halogen atom such as chlorine, bromine or iodine, a linear, branched or cyclic hydrocarbon group, saturated or unsaturated, such as an alkyl or phenyl radical, or an ester-COOR group or an alkoxyl -OR group, or a phosphonate -PO (OR) 2 group, or a polymer chain that may be for example, be a chain of polymethyl methacrylate, polybutadiene, polyolefin such as polyethylene or polypropylene, but preferably being a polystyrene chain, and in which R5, R6, R7, R8, R9 and R10 may be identical or different, may be chosen in the same grouping family as that which has just been considered for R1, R2, R3, R4, R'1 and R'2, and further may represent a hydrogen atom, a hydroxide group OH, an acidic group such as -COOH or -PO (OH) 2 or -S03H.

In particular, the stable free radical may be 2,2,5,5-tetramethyl-1-pyrrolidinyloxy sold under the trade name PROXYL, 2,2,6,6-tetramethyl-1-piperidinyloxy, generally sold under the name TEMPO , 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy sold under the name 4hydroxy TEMPO, or bis (1-oxyl-2,2,6,6-tetramethylpiperidine-4-

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 yl) sebacate sold under the trademark CXA 5415 by the company Ciba Specialty Chemical.

The stable free radical may also be chosen from the following list - N-tert-butyl-1-phenyl-2-methylpropyl nitroxide, N-tert-butyl-1- (2-naphthyl) -2-methylpropyl nitroxide,
N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide,
N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide, N-phenyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, N-phenyl-1-diethylphosphono-1-methylethyl nitroxide, N- (1-phenyl-2-methylpropyl) -1-diethylphosphono-1-methylethyl nitroxide, -4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy, -2,4,6-tri tert-butylphenoxy.

As a stable free radical, the Tempo derivatives (including the Tempo itself), that is to say those comprising at least one six-atom ring (five of carbon and one of nitrogen), of which the nitrogen atom is that of the nitroxyl group = NO #, the ring being optionally substituted, for example by at least one hydroxyl group -OH (case of 4-hydroxy-Tempo) or at least one alkyl radical, are preferred.

Bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate sold under CXA 5415 by CIBA SPECIALTY CHEMICAL is part of this preferred family.

The heat treatment process according to the invention preferably involves the use of homopolybutadiene as the starting elastomer and therefore proposes an advantageous solution since it allows obtaining, after radical polymerization of the

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 vinylaromatic monomer in the presence of the carrier rubber, morphologies usually obtained using styrene-butadiene copolymers. However, it is not excluded to use as a rubber-bearing elastomer a styrene-butadiene copolymer, when it is desired to combine the advantage of the use of such a copolymer, and the advantage of the fact that that it carries a stable free radical generating group. Such a combination makes it possible to use a rubber bearing fewer groups than if the rubber was derived from a polybutadiene without a styrene unit as a comonomer.

The elastomer used during the heat treatment has a solution viscosity at 5% by weight in styrene (at 25 ° C.) of between 20 and 350 cP. The elastomer has a weight average molecular weight of between 50000 and 500000 g / mol.

The elastomer may be a mixture of several elastomers having the above properties. The elastomer may have a bimodal molar mass distribution, that is to say showing 2 populations of separate elastomer chains in mass. These properties are found at the level of the carrier rubber.

In addition to the elastomer and the stable free radical, the treatment medium may comprise a small amount of solvent and / or oil, the mass of the sum of the oil and the solvent being preferably less than 20%, so that still more preferably less than 10%, more preferably less than 5% by weight of the sum of all the ingredients used for this heat treatment. Preferably, in order to simplify the heat treatment process, no solvent and no oil are introduced.

The solvent may for example be selected from aromatic solvents such as toluene, benzene, ethylbenzene, or alicylic solvents such as cyclohexane.

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 The solvent can be removed at least partially during the kneading of the ingredients during the heat treatment, by evaporation under vacuum, especially through the extruder degassing wells, if an extruder is used.

The oil may be an oil commonly used by rubber processors, and may especially be an aromatic or aliphatic oil. The oil and / or the solvent serve to reduce the viscosity of the reaction mixture during the heat treatment.

If an oil is used, it should preferably be removed before using the carrier rubber for the manufacture of the impact composition.

The oil can be removed by a purification step described later.

The heat treatment process according to the invention is particularly advantageous because it can be carried out at a very high concentration of rubber, or even directly on the rubber in the pure state, without the use of oil or solvent. Thus, for this heat treatment, the rubber is generally present at least 80%, preferably at least 90%, and even at least 98% by weight.

The carrier rubber manufacturing process involves conventional rubber processing tools well known to those skilled in the art such as internal mixers or extruders.

In order to knead the ingredients during the heat treatment, conventional elastomer processing equipment, such as internal mixers or extruders, is used, these apparatus generally having shear rates greater than 5 s -1 and preferably greater than 10 s -1. 1 for a speed of 50 revolutions per minute.

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 An extruder is preferably used because it allows continuous manufacture and provides higher shear rates, generally greater than 100 s -1 for a speed of 50 revolutions per minute.

During heat treatment, the recommended equipment is to be used because of the high viscosities of the medium used for the heat treatment, ie greater than 100 Pa.s, generally greater than 1000 Pa .s.

Once prepared, the carrier rubber can be recovered as is and stored as for conventional rubbers. However, it can be subjected to a purification step, either by washing for example with acetone or by solubilization and precipitation, filtration and drying, before being stored, in order to eliminate the residual species or formed from the stable free radical and the free radical initiator used during the stable free radical generating group binding step on the rubber.

The invention also relates to a method for preparing a composition comprising a vinylaromatic polymer matrix and rubber particles exhibiting no, one or more vinylaromatic polymer occlusions, said method comprising a step of polymerizing at least one vinylaromatic monomer into presence of the carrier rubber.

The polymerization process according to the invention makes it possible in particular to obtain a transparent impact vinylaromatic composition.

During the polymerization step of the process according to the invention, the rubber releases the stable free radical, so that vinylaromatic monomer units can be inserted between the rubber and the stable free radical and thus lead to grafting of the rubber.

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The method according to the invention thus leads to very high grafting, much higher than when a non-carrier rubber is used. Very high grafting makes it possible to obtain particles (dispersed in the vinylaromatic polymer matrix) of very small size, which can even confer the transparency properties on the final composition.

Thus, for a very high grafting leading to a transparent impact composition, said impact composition mainly comprises particles whose diameter is less than 0.1 m, not containing an occlusion of vinylaromatic polymer. These dense particles are called droplets or rods according to the circular or rectangular shape that they present on electron microscope slides. Other particles with capsule morphology and / or onions and / or labyrinth and / or salami, larger and in small amounts relative to the dense particles may optionally also be present. The capsule, onion, labyrinth and salami morphologies are described in the patent application FR 98.06940.

The dense particles correspond to the finest possible dispersion in the vinylaromatic polymer matrix. This is obtained because of the very high grafting of the carrier rubber, itself obtained thanks to the presence of stable free radical generating group on the rubber. The number of generating groups can be adjusted to access lower grafting and therefore to compositions whose majority particles will be different from the droplet or the stick. Thus, the decrease in the number of groups carried by the rubber will gradually and successively generate the appearance of particles of cape, onion, labyrinth and finally salami type. The method according to the invention can therefore also lead to obtaining capsule and / or onion morphology and / or labyrinth and / or salami.

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 If it is desired that capsules and / or dense particles be present in the final impact composition, it is preferable for the rubber to have an average of 0.5 to 2, if necessary 0.5 to 0.9 generator groups. stable free radical by rubber chain.

In this case, one skilled in the art, taking into account the information provided by the present application, is able to search for the operating conditions for the heat treatment of the elastomer, leading to a rubber carrying on average from 0.5 to 0, 9 stable free radical generating groups per rubber chain.

In order to economize on the stable free radical, a relatively expensive product, it is possible to use a rubber bearing relatively little stable free radical, for example 0.5 to 0.9 average stable free radical generating groups per rubber chain. and to introduce a grafting initiator at the beginning of polymerization, in order to compensate for the loss of grafting due to the low content of stable free radical, on the rubber.

The process according to the invention is particularly well suited for controlling, from the same type of rubber preferably of the homopolybutadiene type, the morphology of the particles contained in the final composition and thus simply to obtain the desired properties for said composition. For example, in the case where the gloss is particularly desired, a final impact composition comprising exclusively capsule-type particles will be targeted. In the case where gloss and impact are particularly sought after, a final impact composition comprising capsule-type particles and onion-type particles and / or labyrinths and / or salami will be targeted. In the case where the impact is particularly sought after, a final impact composition comprising substantially

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 only salami-type particles will be targeted. In addition, the conditions during the polymerization step will be adjusted if possible so as to obtain a bimodal particle size distribution, that is to say having 2 distinct populations in size, in order to further improve the impact properties.

The method according to the invention is therefore a particularly advantageous solution and adapted to obtain impact compositions with impact properties and / or gloss and / or transparency controlled via a control of the morphology of the particles.

During the polymerization step, in addition to the carrier rubber, another non-carrier rubber, that is to say not having undergone the stable free radical binding step according to the method described above, may be present. If this is the case, the weight ratio of carrier rubber relative to the total weight of rubber present in the medium to be polymerized is between 10 and 90%.

The addition of a non-carrier rubber makes it possible, for example, to reduce overall the average number of groups carried by rubber chain.

For the purposes of the present invention, the term "vinylaromatic monomer" means an aromatic monomer with ethylenic unsaturation such as styrene, vinyltoluene, alphamethylstyrene, alphaethylstyrene, methyl-4-styrene, methyl-3-styrene or methoxy. Styrene, hydroxymethyl-2-styrene, ethyl-4-styrene, ethoxy-4-styrene, dimethyl-3,4-styrene, chloro-2-styrene, chloro-3- styrene, chloro-4-methyl-3-styrene, tert-butyl-3-styrene, 2,4-dichloro-styrene, 2,6-dichloro-styrene, vinyl-1-naphthalene, vinylanthracene.

Styrene is a preferred vinylaromatic monomer.

The polymerization medium may initially comprise:

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 per 100 parts by weight of vinylaromatic monomer, # 2 to 35 parts by weight of rubber and # 0 to 50 parts by weight of solvent.

The solvent may be organic and selected so that it does not boil under the polymerization conditions and so that it is miscible with the vinylaromatic monomer and vinylaromatic polymer derived therefrom. Alicyclic hydrocarbons such as cyclohexane or, preferably, aromatics such as toluene, benzene, ethylbenzene or xylene can be used.

The polymerization medium may further contain at least one copolymerizable monomer with the vinylaromatic monomer (s), such as for example at least one acrylic or methacrylic monomer or acrylonitrile. The term polymerization thus covers those of homopolymerization, copolymerization and interpolymerization and the term polymer covers those of homopolymer, copolymer and interpolymer.

It is possible to add to the polymerization medium, before or during the polymerization, at least one adjuvant customary for this kind of preparation. These adjuvants may be plasticizers such as mineral oils, butyl stearate or dioctyl phthalate, stabilizers such as antioxidants may be phenol substituted by an alkyl group such as ditertiobutylparacresol or phosphites such as trinonylphenylphosphite.

If a plasticizer is introduced, it may be in an amount such that it is present in the composition finally synthesized at 0 to 6% by weight.

If a stabilizer is introduced, it may be present in the polymerization medium at a rate of 0 to 3000 ppm.

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 During the polymerization occurs the well-known phenomenon of phase inversion leading to the formation of rubber nodules dispersed in a vinylaromatic polymer matrix. During this polymerization, stirring must be sufficient for the dispersion of the rubber nodules to be uniform.

Preferably, the polymerization is carried out, at least at the time of the phase inversion in a plug flow reactor (Plug Flowreactor).

After polymerization, the volatile species such as the unreacted monomers and any organic solvent should be removed. This can be achieved by conventional techniques such as the use of a devolatilizer operating hot and under vacuum.

The final content of the composition according to the invention of rubber and vinylaromatic polymer depends on the degree of progress of the polymerization carried out before removal of the volatile species. Indeed, if the degree of progress of the polymerization is low, the removal of the volatile species will produce the removal of a large amount of vinyl aromatic monomer and the final content of the rubber composition will be higher.

The progress of the polymerization can be monitored by taking samples taken during the polymerization step and by determining the level of solid on the samples taken. By solid rate is meant the percentage by weight of solid obtained after evaporation under a vacuum of 25 millibars for about 20 minutes at 200 ° C of the samples taken from the initial weight of the sample taken. We can push the polymerization, by

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 example until a solids level of between 60 and 80% by weight is obtained.

It is preferable to adjust the amounts of ingredients introduced and the polymerization conditions so that the final impact composition contains between 1 and 30% and more preferably between 2 and 15% of rubber.

The polymerization reaction may be initiated thermally, without a polymerization initiator or catalyst, or initiated by a polymerization initiator. If the polymerization is thermally initiated, it can be carried out between 100 and 200 ° C. and preferably between 110 and 160 ° C.

If the polymerization is initiated by a polymerization initiator, it can be irradiated between 50 and 200 ° C. and preferably between 90 and 160 ° C.

A polymerization initiator may be present during the polymerization step in order to further increase the grafting of the vinylaromatic monomer on the rubber, which will make it possible to use a rubber carrying a smaller quantity of stable free radical generating groups, and / or to increase the rate of polymerization.

The initiator may be chosen from the list of free radical initiators proposed for producing the carrier rubber.

The initiator may correspond to a portion of the unreacted initiator during the step of manufacturing the carrier rubber. The initiator may be added before or during polymerization. If this is the case, its content by weight relative to the vinylaromatic monomer initially present at the beginning of the polymerization is between 10 and 2000 ppm, and preferably between 50 and 1000 ppm.

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 A stable free radical, which can be chosen from the list of those proposed for the step of manufacturing the carrier rubber, can also be added during, and preferably before, the polymerization of the vinylaromatic monomer in order, for example, to increase the content of initiator, preferably of the grafting type, also added before said polymerization. If this is the case, the content by weight of the stable free radical relative to the vinylaromatic monomer initially present at the beginning of the polymerization is between 25 and 1000 ppm, and preferably between 50 and 500 ppm.

A coupling agent, preferably divinylbenzene, may also be added before or during the polymerization step in order, for example, to increase the molar mass of the vinylaromatic polymer. If this is the case, the content by weight of the coupling agent with respect to the vinylaromatic monomer initially present at the beginning of the polymerization is between 10 and 1000 ppm, and preferably between 50 and 500 ppm.

The impact compositions are characterized by a weight average molecular weight of the vinylaromatic polymer matrix of between 50,000 and 300,000 g / mol, and preferably between 100,000 and 250,000 g / mol. The polymolecularity index (ratio of the weight average molecular weight to the number-average molecular weight) is generally between 2 and 4, and preferably between 2 and 3.5.

The final impact compositions may be mixed with vinylaromatic homopolymer to provide the desired level of property, for example to improve transparency.

In the following examples, the following techniques were used:

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-Izod impact resistance on notched bar: ISO standard
180/1 A - Vicat temperature (1kg, temperature rise = 50 C / h): ISO 306A50 standard.

 - Flexural modulus of elasticity: ISO 178 - Flowability index (at 200 C under 5 kg): nomeISO 11 33H Morphology of nodules: nodules are observed by scanning electron microscopy on sample sections treated with tetroxide 'osmium. In Table 1, the morphologies observed are indicated. If one of them is underlined, it means that, in the cut of the material, more than 90% in number of the particles present the underlined morphology.

Haze: It is measured on a film of thickness about 300 microns obtained by hot compression of an injected gun of 60 mm in diameter and 2 mm thick. It is measured using the BYK GARDNER Spectrocolorimeter, according to ASTM D 1003.

Molar mass: it is determined by Steric Exclusion Chromatography. The chromatograph used is a WATERS 150 CV operating at 40 C. The set of columns used consists of 2 columns (Polymer Laboratories) filled with styrenedivinylbenzene gel whose pore size distribution is wide (PL-gel "Mixed B" 10 m 30 cm X 7.5 mm). The eluent is tetrahydrofuran (THF "Purex for analysis" of SDS). The flow rate used is 1 cm3 / min. The solutions are prepared at a concentration of 1 g / l and 100 l of solution are injected. The calibration curve is constructed from a set of 14 narrow-distribution polystyrene standards supplied by Tosoh Corporation (Tokyo) and Polymer Laboratories. The weight average mass of the standards ranges from 500 to 4480000. The molar mass distribution is calculated using the results of the refractometric detection.

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 and PS calibration. Various average magnitudes such as the number average mass (Mn) and the weight average mass (Mw) are calculated. The dispersity index (lp) is calculated by the ratio Mw / Mn.

In the text of the present application, and in particular in the examples, the following abbreviations are used: PS: polystyrene -PB: polybutadiene
The polybutadiene used in the examples was BUNA CB HX
527 SIC marketed by the company Bayer, this elastomer having a weight average molecular weight of 245,000 g / mol, a polymolecularity index of 2.35, a solution viscosity at 5% by weight in styrene at 25.degree. cP.

EPDM (ethylene-propylene-diene monomer): terpolymer of ethylene, propylene and a diene-P1: ditertiobutyl peroxide -P2: tert-butyl peroxy-2-ethylhexanoate -CR1: hydroxy tempo, c that is 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy -CR2: bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate marketed under the brand CXA 5415 by the company CIBA
SPECIALTY CHEMICAL -MW: weight average molecular weight -Mn: number average molecular weight

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 - Ip = Mw / Mn: polymolecularity Examples 1 to 10: Preparation of rubbers carrying groups generating stable free radicals.

The Meili internal mixer consists of a 300 cm3 tank (which can be preheated), and 2 blades with variable speed and rotation which make it possible to mix the reaction medium perfectly. The temperature control is done gradually without changing the setpoint temperature of the mixer but simply by playing on the speeds of the blades: self-heating effect.

For this study the initial operating conditions are to start at a temperature of the tank of 80 C. After stabilization of this temperature of the internal mixer, all the products (initiator, stable free radical and rubber) are introduced together into the tank: the quantity of rubber introduced is still 270 g, the amount of the other components is determined by the initial formulation. Then, the tank is no longer open during the reaction.

Depending on the products selected for rubber processing, the temperature and time are determined by the speed of rotation of the blades of the internal mixer. In the examples described in the following table, different temperatures were studied as well as different mixing times (see table below).

After this heat treatment of the finished rubber, the final product is recovered by rotating the blades in the opposite direction after opening the reactor. The hot-collected product can then undergo either a cooling step or a preliminary reconditioning step (rubber ball) followed by cooling.

Thus, the modified rubber may be identical from a packaging point of view to commercial rubber.

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<Tb>
<tb> radical <SEP> free
<tb> elastomer <SEP> radical <SEP> free <SEP> INIT <SEP> x <SEP> FINITE <SEP> Peroxide <SEP> Peroxide <SEP> Time <SEP> in
<tb> Example <SEP> stable <SEP> T <SEP> in <SEP> C
<tb> used <SEP> stable <SEP> SFR <SEP> x <SEP> FS <SEP> used <SEP> (% <SEP> mass) <SEP> min
<tb> (% <SEP> mass)
<tb> 1 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.5 <SEP> 1 <SEP> P1 <SEP> 0.2200 <SEP> 150-170 <SEP> 10
<tb> 2 <SEP> Polybutadiene <SEP> CR1 <SEP> 1 <SEP> 0.5 <SEP> P1 <SEP> 0.2200 <SEP> 150-170 <SEP> 10 <SEP>]
<tb> 3 <SEP> EPDM <SEP> CR1 <SEP> 0.5 <SEP> 1.86 <SEP> P1 <SEP> 0.3953 <SEP> 150-170 <SEP> 10
<tb> 4 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.5 <SEQ> 0.472 <SEP> P1 <SEP> 0.1000 <SEP> 150-170 <SEP> 10
<tb> 5 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.25 <SEP> 0.472 <SEP> P1 <SEP> 0.0500 <SEP> 150-170 <SEP> 10
<tb> 6 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.1 <SEQ> 0.472 <SEP> P1 <SEP> 0.0200 <SEP> 150-170 <SEP> 10
<tb> 7 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.25 <SEP> 0.944 <SEP> P1 <SEP> 0.1000 <SEP> 150-170 <SEP> 10
<tb> 8 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.0593 <SEP> 2 <SEP> P2 <SEP> 0.0500 <SEP> 110-130 <SEP> 10 <SEP> @
<tb> 9 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.1185 <SEP> 6 <SEP> P2 <SEP> 0.1000 <SEP> 110-130 <SEP> 10
<tb> 10 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.5926 <SEP> 2 <SEP> P2 <SEP> 1.5000 <SEP> 110-130 <SEP> 8
<Tb>

Example 11 Purification of the carrier PB of Example 2
10 g of PB carrier of Example 2 are introduced into 100 ml of acetone (PB immiscible in acetone but the nitroxyl radicals yes) and vigorously stirred vigorously at room temperature. After stirring for 3 hours, the PB is separated from the acetone solution by simple filtration: The PB is no longer colored. On the other hand, the acetone solution is orange red in color characteristic of nitroxyl radicals. The ratio of nitroxyl radical thus recovered relative to the initial PB is 0.3%.

Example 12 (comparative)
In a 16 liter stainless steel reactor equipped with a stirring system and a temperature control, 9450 g of styrene, 660 g of ethylbenzene and 165 g of plasticizing mineral oil are introduced at ambient temperature. brand Primol 352 marketed by the company
Esso, 11 g of an Irganox 1076 brand antioxidant marketed by Ciba and 660 g of a BUNA CB brand homopolybutadiene
HX 527 SIC marketed by Bayer, this rubber having a weight average molecular weight of 245000 g / mol, a polydispersity index of 2.35, a solution viscosity at 5% by weight in styrene at 25.degree. cP. The stirring is carried at 80 revolutions / min. After total solubilization of the polybutadiene, 2.85 g of tert-butyl isopropylmonoperoxycarbonate diluted to 75% in a hydrocarbon and marketed by Luperox under the trade name Luperox TBIC-M75 are introduced.
The solution is brought to 130 ° C. in 30 minutes. This temperature is

<Desc / Clms Page number 26>

<tb> Example <SEP> elastomer <SEP> radical <SEP> free <SEP> radical <SEP> free <SEP> stable <SEP> INIT <SEP> x <SEP> FINITE <SEP> Peroxide <SEP> Peroxide <SEP > in <SEP> C
<tb> Exempt <SEP> used <SEP> stable <SEP> (% <SEP> mass) <SEP> SFR <SEP> x <SEP> FSFR <SEP> used <SEP> (% <SEP> mass) <SEP > in
<tb> 1 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.5 <SEP> 1 <SEP> P1 <SEP> 0.2200 <SEP> 150-170
<tb> 2 <SEP> Polybutadiene <SEP> CR1 <SEP> 1 <SEP> 0.5 <SEP> P1 <SEP> 0.2200 <SEP> 150-170
<tb> 3 <SEP> EPDM <SEP> CR1 <SEP> 0.5 <SEP> 1.86 <SEP> P1 <SEP> 0.3953 <SEP> 150-170
<tb> 4 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.5 <SEP> 0.472 <SEP> P1 <SEP> 0.1000 <SEP> 150-170
<tb> 5 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.25 <SEP> 0.472 <SEP> P1 <SEP> 0.0500 <SEP> 150-170
<tb> 6 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.1 <SEP> 0.472 <SEP> P1 <SEP> 0.0200 <SEP> 150-170
<tb> 7 <SEP> Polybutadiene <SEP> CR1 <SEP> 0.25 <SEP> 0.944 <SEP> P1 <SEP> 0.1000 <SEP> 150-170
<tb> 8 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.0593 <SEP> 2 <SEP> P2 <SEP> 0.0500 <SEP> 110-130
<tb> 9 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.1185 <SEP> 6 <SEP> P2 <SEP> 0.1000 <SEQ> 110-130
<tb> 10 <SEP> Polybutadiene <SEP> CR2 <SEP> 0.5926 <SEP> 2 <SEP> P2 <SEP> 1.5000 <SEP> 110-130
<Tb>

<Desc / Clms Page number 27>

 maintained 1 h 30 and then increased to 145 C. The progress of the polymerization is monitored by regular sampling made during the polymerization step and by determining the level of solid on said samples.

By solid level is meant the percentage by weight of solid obtained after evaporation under a vacuum of 25 mbar for about 20 minutes at 200 C of the samples taken from the initial weight of the sample taken.

After about 60% solids content, the contents of the reactor are transferred to a superheater whose set temperature is set at 230 ° C. in order to crosslink the elastomer (passage time: about 5 minutes) and then in a devolatilizer whose temperature set point is 230 C under a vacuum of the order of 40 mbar to remove residual ethylbenzene and styrene. The molten polymer is then passed through a die whose set temperature is set at 222 ° C. and then cooled in a water tank. The polymer rod is then passed through a granulator in order to recover it in the form of granules which can then be injected in order to characterize the final composition.

The properties of the composition thus obtained are indicated in Table 1. The composition is mixed with 75% by weight of Lacqrène 1240 crystal PS granules (melt index = 2.5 g / l Omin, Vicat temperature (50N) = 91 C and modulus in flexion = 2900 MPa) marketed by the company Elf Atochem. The properties of the composition thus diluted are shown in Table 1.

EXAMPLE 13 The procedure is as in Example 12 except that 660 g of carrier polybutadiene, as obtained in Example N 2, are introduced. In addition, the stirring is 100 rpm during the polymerization at

<Desc / Clms Page number 28>

 80 rpm. The properties of the composition thus obtained are shown in Table 1.

EXAMPLE 14 The procedure is as in Example 13 except that 660 g of carrier polybutadiene as obtained in Example N 11 are introduced. The properties of the composition thus obtained are indicated in Table 1.

<Desc / Clms Page number 29>

<Tb>
<Tb>

UNITE <SEP> EXAMPLE <SEP>? <September>
<tb> 12 <SEP> (comparative) <SEP> 13 <SEP> 14
<tb> Type <SEP> of <SEP> polybutadiene <SEP> no <SEP> carrier <SEP> carrier <SEP> carrier <SEP>"purified"
<tb> Properties <SEP> composition <SEP> final <SEP>###########
<tb> Rate <SEP> of <SEP> PB <SEP>% <SEP> 8.5 <SEP> 8.7 <SEP> 7.8
<tb> Index <SEP> of <SEP> fluidity <SEP> g / 10 '<SEP> 2.9 <SEP> 13 <SEP> 2.8
<tb> Mw <SEP>(SEP> PS matrix) <SEP> g / mol <SEP> 195000 <SEQ> 124000 <SEP> 205300
<tb> Ip <SEP> (Mw / Mn) <SEP> 2.8 <SEP> 2.5 <SEP> 3.3
<tb> Temperature <SEP> Vicat <SEP> (1 <SEP> kg) <SEP> C <SEP> 96.3 <SEP> 95.2 <SEP> 96.7
<tb> shock <SEP> Izod <SEP> kJ / m2 <SEP> 11.6 <SEP> 2.0 <SEP> 4
<tb> Module <SEP> Bending <SEP> 1880 <SEP> 2410 <SEP> 2625
<tb> morphology <SEP> of <SEP> nodules <SEP>: <SEP> m <SEP> capsules <SEP> and <SEP> salamis <SEP> dense <SEP> particles <SEP> of <SEP> particles <SEP > dense <SEP> of
<tb> of <SEP> diameter <SEP> inclusive <SEP> diameter <SEP><<SEP> 0.1 m <SEP> diameter <SEP><<SEP> 0.1 m
<tb> m <SEP> between <SEP> 0.2 <SEP> and <SEP> 3 <SEP> m
<tb> + <SEP> +
<tb> particles <SEP> of <SEP> type <SEP> particles <SEP> of <SEP> type
<tb> capsules, <SEP> onions, <SEP> capsules, <SEP> onions,
<tb> labyrinths <SEP> and <SEP> salamis <SEP> of <SEP> labyrinths <SEP> and <SEP> salamis <SEP> from
<tb> diameter <SEP>><SEP> 0.2 <SEP> m <SEP> diameter <SEP>><SEP> 0.2 <SEP> m
<tb> Haze <SEP>% <SEP> 85 <SEP> 23 <SEP> 30
<tb> Properties <SEP> composition <SEP> diluted
<tb> in <SEP> of <SEP> PS <SEP> Crystal <SEP>: <SEP>
<tb> rate <SEP> of <SEP> PB <SEP>% <SEP> 2.1
<tb> shock <SEP> Izod <SEP> kJ / m2 <SEP> 4
<tb> Module <SEP> Bending <SEP> MPa <SEP> 2560
<tb> Haze <SEP>% <SEP> 53
<Tb>
Table 1: Properties of the shock compositions obtained

Claims (37)

 1. A process for preparing a carrier rubber of a stable free radical generating group comprising a step of heat treatment of an elastomer in the presence of a stable free radical and a free radical initiator capable of tearing a proton of the elastomer, when kneaded by apparatus having a shear rate greater than 5 s-1 for a speed of 50 revolutions per minute. 2. Method according to claim 1 characterized in that the apparatus has a shear rate greater than 10 s-1 for a speed of 50 revolutions per minute. 3. Method according to one of the preceding claims characterized in that the apparatus is an internal mixer. 4. Method according to one of claims 1 or 2 characterized in that the apparatus is an extruder. 5. Method according to the preceding claim characterized in that the extruder provides shear rates greater than 100 s-1 for a speed of 50 revolutions per minute. 6. Method according to one of the preceding claims characterized in that the medium used for the heat treatment has a viscosity greater than 100 Pa. S. 7. Method according to the preceding claim characterized in that the viscosity of the medium is greater than 1000 Pa. S. 8. Method according to one of the preceding claims characterized in that the elastomer has a solution viscosity at 5% by weight in styrene at 25 C between 20 and 350 cP. 9. Method according to one of the preceding claims characterized in that the elastomer has a weight average molecular weight of between 50 000 and 500 000 g / mol. <Desc / Clms Page number 31> 10. Method according to one of the preceding claims characterized in that the heat treatment medium comprises solvent and / or oil, the sum of the mass of the oil and the solvent being less than 20% by weight relative to all the ingredients used for the heat treatment. 11. Method according to the preceding claim characterized in that the sum of the mass of solvent and oil is less than 10% by weight relative to all the ingredients used for the heat treatment. 12. Method according to the preceding claim characterized in that the sum of the mass of solvent and oil is less than 5% by weight relative to all the ingredients used for the heat treatment. 13. Method according to the preceding claim characterized in that the medium contains no solvent and no oil. 14. Method according to one of the preceding claims characterized in that the rubber concentration is at least 80% by weight. 15. Process according to the preceding claim, characterized in that the concentration of rubber is at least 90% by weight. 16. Method according to the preceding claim characterized in that the rubber concentration is at least 98% by weight. 17. Method according to one of the preceding claims characterized in that the heat treatment is carried out in the absence of vinylaromatic monomer. 18. Method according to one of the preceding claims characterized in that the stable free radical is present in a proportion of 100 ppm to 5% by weight relative to the elastomer. 19. Method according to one of the preceding claims characterized in that the free radical initiator is present at a rate of 100 ppm to 5% by weight relative to the elastomer. <Desc / Clms Page number 32> 20. Method according to one of the preceding claims characterized in that [(SFR) FSFR] / / [(INIT) FINIT] is between 0.01 and 100, - (SFR) representing the number of moles of stable free radical. - FSFR representing the functionality of the stable free radical, - (INIT) representing the number of moles of free radical initiator, - FINIT representing the functionality of the free radical initiator. 21. Method according to one of the preceding claims, characterized in that [(SFR) FSFR] / / [(INIT) FINIT] is between 0.1 and 10. 22. Method according to the preceding claim characterized in that [(SFR) FSFR] / / [(INIT) FINIT] is between 0.5 and 10. 23. Method according to one of the preceding claims characterized in that the temperature of the heat treatment is between 20 and 200 C. 24. Method according to one of the preceding claims characterized in that the temperature of the heat treatment is between 50 and 150 C. 25. Method according to one of the preceding claims characterized in that the temperature of the heat treatment is between (T-50 C) and (T + 50 C), T representing the temperature for which the half-life time of Free radical initiator is 1 hour. 26. Method according to one of the preceding claims characterized in that the duration of the heat treatment is between 10 seconds and 1 hour. 27. Method according to one of the preceding claims characterized in that the operating conditions relating to the heat treatment are such that the rubber obtained carries an average of 0.1 to 10 stable free radical generating groups randomly fixed by rubber chain. <Desc / Clms Page number 33>  28. Process according to one of the preceding claims, characterized in that the operating conditions relating to the heat treatment are such that the rubber obtained carries on average 0.5 to 2 stable radical generating groups per rubber chain. 29. Method according to the preceding claim characterized in that the operating conditions relating to the heat treatment are such that the rubber obtained carries on average 0.5 to 0.9 stable free radical generating groups per rubber chain. 30. Method according to one of the preceding claims characterized in that the elastomer is a styrene-butadiene copolymer. 31. Method according to one of claims 1 to 29 characterized in that the elastomer is a homopolybutadiene. 32. A carrier rubber obtainable by the method of one of the preceding claims. A process for preparing a composition comprising a vinylaromatic polymer matrix and rubber particles, comprising a step of polymerizing at least one vinylaromatic monomer in the presence of the rubber of claim 32. 34. Process according to the preceding claim, characterized in that the polymerization is carried out, at least at the moment of the phase inversion, in a piston reactor. 35. Method according to one of claims 33 to 34 characterized in that a polymerization initiator is present during the polymerization to increase the grafting of the vinylaromatic monomer on the rubber. 36. Method according to one of claims 33 to 35 characterized in that a stable free radical is added during or before the polymerization. <Desc / Clms Page number 34>  37. Method according to one of claims 33 to 36 characterized in that the number of generator groups is adjusted so that the grafting of the vinyl aromatic monomer on the rubber is sufficient for the rubber particles are dense.