MXPA99009214A - Method for producing homopolymerizates and copolymerizates - Google Patents

Abstract

The method used to polymerize a microsuspension enables continuous production of particular homopolymerizates and copolymerizates from at least one polymerizable monomer. The polymerization of the microsuspension, to which addition agents can be added depending on the desired application, is carried out in a tubular reactor at a temperature of at least 0°C C in the presence of a hydrophobic radical polymerization initiator, resulting in particular homopolymerizates and copolymerizates of an average diameter d50 of at least 50&mgr;m. The polymerizates obtained by this method find applications as addition agents for thermoplastic moulding compounds, as copier toner components, as auxiliary agents for paper and leather, as coating agents for magnetic tapes and foils and as colour and paint components.

Description

PREPARATION OF PARTICULATED HOMOPOLIMEROS AND COPOLYMERS FROM MICROSPENSIONS IN A TUBULAR REACTOR The present invention relates to a process for the continuous preparation of particulate homopolymers and copolymers by the microsuspension polymerization technique. In these processes the monomers, including the derivatives of styrene and (meth) acrylic acid and together with an auxiliary suspension, are exposed to very high shear forces in a liquid immiscible in the monomers, usually water, and the microsuspension thus, it is polymerized with the use of a hydrophobic free radical polymerization initiator, ie, soluble in oil. Polymerization in a dispersed system such as an emulsion or suspension is an established industrial process for the preparation of particulate polymers.

The important products of these processes are polyvinyl acetate, polyvinyl chloride and polytetrafluoroethylene. To prepare certain products, industrial preparation processes focus on the particular use of finely dispersed monomers. This is the reason why the methods such as the mini-emulsion or microsuspension processes, which allow the intermediate production and the polymerization of these finely dispersed particular monomers, are becoming increasingly important. In the last process, the mixture of one or more monomers of an auxiliary stabilizing suspension, protective colloids or emulsifiers similar to surfactants are commonly used, first it is subjected in water to very high shear forces, giving rise to the formation of a Very fine emulsion of droplets with a diameter of approximately 0.1-2 μm. This emulsion, later known as microsuspension, is then mixed, in a second step, with a hydrophobic free radical polymerization initiator and, after heating at the necessary reaction temperature, is polymerized into particles with a diameter of about 0.1-50. μm (see for example "Handbuch der Tec nischen Polymerchemie", VCH Verlagsgesellschaft mbH, Weinheim, 1993, p 450). With regard to the additional polymerization reactions, the literature sometimes varies in the way it uses the terms emulsion, suspension and concepts derived from them, such as miniemulsion, microsuspension, emulsification, suspension and others. In some cases this gives rise to unclear descriptions. With regard to the definition of the terms emulsion polymerization, suspension and microsuspension used herein, refer to "Handbuch der Technischen Polymerchemie", VCH Verlagsgesellschaft mbH, Weinheim, 1993, p. 316 and p. 450. The process that is relevant in this case is a microsuspension polymerization. According to the definitions of the aforementioned literature reference, therefore, the terms are used as follows: microsuspension means the finished, finely divided mixture of the substances that are going to be pollinised. Emulsification means converting the mixture of substances that is going to be polymerized into a microsuspension.

Tubular reactors, as one of a plurality of reactor variants, are considered to have the disadvantages including: less flexibility in the case of a product change the risk of plugging the reactor and, in the case of poor radial mixing, a growing distribution of residence times and, associated with this, a wider distribution of particle sizes .

In particular, due to the last two points, only some addition polymerization reactions in tubular reactors have been described to date. For example, US-A 4,713,434 describes the continuous polymerization of emulsions of different monomers in a reaction that is carried out in tubular reactors coated on the inside with polyethylene or polypropylene. Two articles by D. Paquet, Jr. et al. in J. American Inst. Chem. Eng., vol. 40, No. 1, pp. 73 to 88 and 88 to 97, 1994 give an overview of some emulsion polymerizations operated in continuous form in which various methods are tried to solve the aforementioned disadvantages. For example, the configuration of a circulating reactor is described, where the ratio of the newly-fed monomer emulsion to the total amount of the emulsion in circulation is very small. Other possibilities are the pulsed operation of the reactor and the use of internal accessories of the reactor, for example chicanes, which guarantee increased turbulence and mixing. A similar method is described in J. Meuldijk et al. in Chem. Eng. Sci., vol. 47, No. 9-11, pp. 2603-2608, 1992. In this case, the emulsion polymerization of vinyl acetate is carried out using a tubular reactor packed with Raschig rings and also provided with a push button. EP-B 0 443 609 describes a microsuspension process in which different monomers are emulsified in water using a high-speed stirrer that generates very high shear forces. The entire microsuspension is subsequently reacted in a stirred vessel in a batch manufacturing process to obtain a polymer with a particle size of 5-50 μm in diameter. In DE-A 196 33 626, first in priority but not published before, the polymerization is proposed by a microsuspension of monomers that includes derivatives of (meth) acrylic acid and, as optional comonomers, of other (meth) acrylic acid derivatives and styrene derivatives. In the semi-continuous process specified in this application only part of the microsuspension containing monomers is charged to the container reactor with stirring and the remainder is dosed continuously as the reaction progresses. An article by G. W. Poehlein et al. in Trends in Polymer Science, vol. 1, No. 10, pp. 298-302, 1993 and an updated article from the same journal in vol. 4, No 6, pp. 173-176, 1996 report continuous polymerizations in emulsions and in mini-emulsions. The continuous polymerization in miniemulsions in this case refers to a container reactor with continuous stirring which is fed continuously with an injector produced in an upstream tubular reactor.

On the other hand, processes operated continuously in tubular reactors have not been described either in the field of mini-emulsion polymerization or in the field of microsuspension polymerization. An object of the present invention is to provide a process that can be performed on an industrial scale to polymerize microsuspensions of different monomers in a tubular reactor operated in a continuous manner while avoiding the disadvantage of the prior art. We have found that this objective is achieved starting from the known processes for preparing particulate homopolymers or copolymers of at least one polymerizable monomer by the microsuspension polymerization technique at not less than 0 ° C in the presence of at least one polymerization initiator. by hydrophobic free radicals. The novel process then consists in preparing the microsuspension in a continuous or discontinuous manner and includes the polymerization process with conversion of at least 50% in a tubular reactor, the products having an average particle diameter of less than 50 μm, and the reactor tubular consisting of a tube or hose with a length-to-diameter ratio (L / D) of at least 20. Examples of monomers suitable for this purpose are (meth) acrylic acid, (meth) acrylamide, (meth) acrylonitrile, ( met) acrylates of alkyl, butadiene, isoprene, alkylene oxides, styrene, substituted styrenes, vinyl acetate and vinyl chloride. Alkyl (meth) acrylates means esters of (meth) acrylic acid with branched C1-C32 or C3-C32 alkyl radicals, especially methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl or 2-ethylhexyl. These alkyls can be unsubstituted or can be substituted by functional groups, for example by hydroxyl, amino, ether, epoxide or sulfonic acid groups, or by chlorine. Preferred monomers having these functional groups in the alkyl are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, ethyldiglyc acrylate, and methyl methacrylate. butylaminoethyl, diethylaminoethyl acrylate, n-butoxymethylamino methacrylate, glycidyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid and 3-chloro-2-hydroxypropyl acrylate.

By using monomers that have polar, acid or basic groups, the polymers can obtain specific service properties. For example, the use of Alkyl (meth) acrylates functionalized with acid or base make the polymers suitable as opacifying agents for thermoplastic molding compounds. If the microsuspension of only one monomer is used in the polymerization step, then the homopolymers are formed. In order to prepare copolymers, the polymerization of the first monomer, which gives rise to the formation of the core of the polymer and which is conveniently allowed to proceed to a degree of at least 50%, can be followed by feeding the microsuspension of another monomer or monomer mixture in the reactor tube, so that this monomer or these monomers, respectively, is or are partly polymerized in the form of a shell on the initially formed polymer particles. This process can also be repeated several times with other monomers or mixtures of different composition in order to obtain particles having a plurality of covers. The metered addition of other monomers can be carried out even without preparing the microsuspension in advance, by direct dosing of the monomer or monomer mixture, water, the suspension aid and, if desired, other additives. In the same way it is possible to first transfer the initially formed polymer to another tubular reactor and then begin the dosed addition of at least one other monomer. Suitable comonomers are bifunctional and polyfunctional monomers, the examples being butadiene, isoprene, divinyl esters of carboxylic acids such as succinic and adipic acid, diallyl ethers and divinyl ether, and also bisacrylates and bismetacrylates of bifunctional alcohols such as ethylene glycol and 1,4-butanediol, 1,4-divinylbenzene and triallyl cyanurate. Alkyl alcohol acrylates and methacrylates and tricyclodecenyl alcohol acrylate (dihydrodicyclopentadienyl acrylate) are particularly suitable. The tubular reactor can also be operated in the form of a circulating reactor, the microsuspension being circulated and polymerized in the tubular reactor. In this case, a fraction of the polymerized microsuspension is withdrawn from the circulation continuously, and an equivalent fraction of the new microsuspension is dosed. The ratio between the amount of the microsuspension passing through a cross section of the tube at a certain time and the amount of microsuspension that is dosed into the circulating reactor at the same time is generally greater than 5, preferably greater than 10. and, with particular preference, greater than 20. In the context of the novel process, unless otherwise specified, the term "tubular reactor" refers to a reactor with circulation and a reactor not operated in circulation. The tubular reactor can, if desired, be packed with elements that guarantee the best radial mixing. The examples of the elements are Raschig rings, chicanes or other internal and static mixers. The best radial mixing can in the same way be obtained by pressing the operation of the reactor. This relates, in general, to a pulsed feed of the microsuspension in the tubular reactor. Preference is given to a pulse procedure with a feed rate of once every 30 seconds to ten times per second, in particular from once every 2 seconds to five times per second. The average residence time of the microsuspension in the tubular reactor depends, among others, on the monomers to be polymerized and is usually 10 minutes to 10 hours, preferably 10 minutes to 4 hours. The dimensions of the tubular reactor depend on the desired properties of the particulate polymers to be prepared. Preference is given to an L / D ratio greater than 5,000, in particular greater than 10,000. The choice of the appropriate reactor dimension depends, among others, on the polymerization rate of the monomers, the shape of the tube and the operation mode of the reactor. For the operation in circulation, the L / D ratio is, in general, from 50 to 1,000 and, in this way, smaller is chosen than in the case of a non-circulation mode of operation. The choice of reactor material will depend on the nature of the monomers to be polymerized. Preference is given to non-metallic materials, for example polytetrafluoroethylene, to metallic materials, for example steels of DIN 17440, which may be internally coated, for example with enamel or with polymers, especially polymers containing fluorine. The tubular reactor can be thermally conditioned by immersing it in a heat transfer medium, preferably, it has for the same purpose a jacket filled with a heat transfer medium. Suitable as a medium are, for example, water, brine, oils and other liquids. The temperature chosen for the polymerization in the reactor tube depends essentially on the nature of the monomers and polymerization initiators that are employed and is generally from 0 to 140 ° C, preferably from 20 to 130 ° C. The tubular reactor can also, of course, be operated with a temperature program. For example, polymerization can start at 70 ° C and finish at 100 ° C. In the preferred embodiments, the polymerization proceeds to a degree of at least 60%, particularly at least 80% in the tubular reactor. The fraction of the monomer that still does not react can, of course, after leaving the tubular reactor, to be subjected to another partial or complete polymerization, as long as the suspension is at a temperature that is still sufficient for the polymerization. In the case of incomplete conversion, the polymers can, if desired, be separated without problems from the unreacted monomers, and if appropriate, from other constituents of the suspension, for example by spray drying or by coagulation and drying. The polymers prepared according to the novel process have an average particle diameter d50 which is preferably from 0.03 to 50 μm, in particular from 0.1 to 30 μm. The average particle diameter can be determined by preparing optical micrographs or electron micrographs and then measuring and counting the particles. Another method is the Fraunhofer laser diffraction. Suitable suspension aids are those water-soluble compounds which are capable of wrapping the fine droplets of the monomer and the polymer particles formed from these droplets and thus protecting them against unwanted coagulation. Examples include cellulose derivatives such as carboxy and hydroxymethylcellulose, poly-N-vinylpyrrolidone, polyvinyl alcohol and polyethylene oxide, anionic polymers such as polyacrylic acid and copolymers thereof, and cationic polymers such as poly-N-vinylimidazole, in concentrations preferably from 0.02 to 5% by weight, based on the total mass of the microsuspension. Other suitable suspension aids are emulsifiers such as alkali metal salts of aryl and alkyl sulfonic acids and of aryl and alkyl carboxylic acids, examples being sodium stearate, potassium stearate, sodium oleate and potassium oleate, and also alcohols and phenols. ethoxylates and propoxylates. These emulsifiers in the same way are used in concentrations preferably from 0.02 to 5% by weight, based on the total mass of the microsuspension. Particular preference is given to the use of one or more polyvinyl alcohols having a degree of hydrolysis of less than 96 mol%, preferably from 60 to 94 mol% and, in particular, from 65 to 92 mol%. Preferred polyvinyl alcohols have a viscosity from 1 to 100 mPa / s, in particular from 2 to 69 mPa / s, measured as a solution in water at 4% concentration by weight, at 20 ° C, in accordance with DIN 53015. In many cases it has been found advantageous to add colloidal silicic acid in concentrations from 0.2 to 5% by weight, based on the total amount of the microsuspension. If it is desired to prepare particles having a cover structure, then the polymerization of a first monomer, which is suitably allowed to continue to a degree of at least 50%, preferably up to at least 75% and, in particular, at least %, is followed by the addition of the microsuspension of at least one other monomer or, respectively, the addition of at least one other monomer. This step can be repeated several times in order to obtain polymers with a multilayer structure. As already mentioned above, the copolymers can also be prepared so that, after the polymerization of a monomer or mixture of monomers, the polymer thus prepared is transferred to a second tubular reactor, and then at least one other monomer is dosed. Of course, it is also possible - the use of a stirred vessel reactor instead of a second tubular reactor, as is the inverse procedure, that is, first a polymer is prepared in a stirred reactor vessel and then dosed at least one other monomer in a tubular reactor. The transition from the core to the shell, and the transition from one shell to the next, is more severe when more fully one monomer has been polymerized before starting the metered addition of at least one other monomer, as such or in the form of a microsuspension. . In addition, in the same way it is possible to influence the morphology of the particle by an appropriate choice of monomers and reactor conditions. For example, the newly fed monomers can be polymerized not only in the form of a cover on the already fully polymerized particles of a previous monomer, of a different type, but can also be polymerized in these particles to a considerable degree, so that the core structure is less pronounced -cover. If reticulum monomers are polymerized to form a core or a shell, then it is possible that the C-C double bonds that are still reactive, i.e., polymerizable, remain, upon which another monomer can be grafted in the subsequent polymerization step. Graft-forming reactions of this kind are known to skilled workers. Suitable free radical polymerization initiators are compounds that form free radicals and are soluble in oil. These include peroxides, azo compounds and compounds that have unstable C-C bonds. If the monomers to be polymerized tend to undergo spontaneous polymerization at elevated temperature, then the addition of a free radical polymerization initiator is unnecessary. This group of monomers includes, in particular, styrene and its derivatives. Among the peroxides, preference is given to those having a carbon: oxygen ratio greater than 3: 1, examples being dílauryl peroxide, dibenzoyl peroxide, diacetyl peroxodicarbonate, dimyristyl peroxodicarbonate and bis peroxide (3, 5, 5). -trimethylhexanoyl), especially dilauryl peroxide. Among the azo compounds, 2, '-azobis (isobutyronitrile) and 2,2'-azobis (2-methylbutyronitrile) are preferred. From the group having labile C-C bonds, preference is given to the use of 3,4-dimethyl-3,4-diphenylhexane and 2,3-dimethyl-2,3-diphenylbutane. These polymerization initiators are used in an amount from 0.05 to 4% by weight, based on the amount of the monomer, preferably from 0.1 to 2% by weight and, in particular, from 0.3 to 1.0% by weight. These percentages, of course, do not apply when the monomer itself is used as the initiator. In the same way, it is possible to use the abovementioned polymerization initiator mixtures. Depending on the aggregate state of the polymerization initiator and its solubility properties it can be dosed as such or preferably as a solution, emulsion or suspension in the mixture to be emulsified to form a microsuspension, in the prepared microsuspension or in the microsuspension that is going to be polymerized and is already in the tubular reactor. The solvent or liquid phase for the polymerization initiator is, for convenience, an organic solvent such as benzene, toluene, xylene, ethylbenzene, cyclohexane and the monomers themselves. Depending on the proposed use of the polymers it is possible to add more than 0.1% by weight, preferably more than 1% by weight and, in particular, more than 5% by weight of at least one solid in the dissolved, swollen or suspended form. the mixture that is going to be emulsified or the microsuspension already prepared. These solids can be polymers, pigments that impart color and ferromagnetic and other substances, for example minerals. If carbon black is used, the result is black particulate polymers that find particular application as a copier toner. The use of ferromagnetic pigments gives rise to the formation of particulate polymers that have ferromagnetic properties. These polymers are particularly suitable for producing magnetic tapes and magnetic films. As is common with polymerizations, it is possible to add other additives that have an influence on the properties of the product, depending on the desired properties of the polymers, in the case of the novel process as well. These additives include: molecular weight regulators, for example ter-dodecyl mercaptan or 2-ethylhexyl thioglycolate, buffers for regulating pH, for example citrate buffer, sodium acid phosphate and sodium diacid phosphate, inhibitors that suppress the reaction process of undesirable competition of the emulsion polymerization, which occurs simultaneously in the polymerization in microsuspension and which gives rise to the formation of relatively small, practically unwanted polymers, the examples of inhibitors being salts of chromium VI, especially potassium dichromate and of sodium.

These other additives can be dosed continuously or discontinuously at the start and / or during the preparation of the microsuspension and / or during the course of the polymerization. The microsuspension used in the novel process is prepared from monomers, suspension aids, water, the aforementioned solids and other additives, if used, and also, if desired, a polymerization initiator, subjecting the mixture of these substances at very high shear forces. The methods for exerting very high shear forces are known to skilled workers and include: intense agitation with rotor-stator system homogenization with ultrasound using a pressure homogenizer, in which the mixture of substances to be emulsified is compressed under high pressure through a narrow slot or through narrow nozzles.

Examples of suitable agitators and homogenizers are: - Dispermat laboratory solvent, from VMA-Getzmann, Reichshof, DE - Ultra-Turrax, from Janke und Kunkel, Staufen, DE - Cavitron homogenizer from Hagen & Funke, Sprockhóvel, DE - homogenizers from Kotthoff, Essen, DE - pressure homogenizer from Gaulin, Lübeck, DE The microsuspension is usually prepared at room temperature, but it can also be prepared at a higher or lower temperature depending on the nature of the monomers and other substances. Ordinarily the agitators are operated at rotational speeds from 1000 to 25,000 revolutions per minute (rpm), preferably from 2000 to 15,000 rpm, for a period which may be from 0.1 seconds to several hours. The amount of water in which the monomers and auxiliaries of the suspension are dispersed is usually from 15 to 95% by weight, preferably from 35 to 85% by weight and, with particular preference, from 40 to 75% by weight. % by weight, based in each case on the sum of the monomers, water and auxiliary suspension. The microsuspension is prepared continuously or discontinuously. In the first case, the mixture of substances to be emulsified is processed to a microsuspension in a container with one of the aforementioned agitators or homogenizers. The homogenizer can also be arranged in parallel to the container, and the mixture is then circulated through the homogenizer. In the case of the second method, the substances to be emulsified are continuously supplied to the homogenizer and the resulting microsuspension is then in the same way supplied continuously to the tubular reactor. The continuous preparation mode of the microsuspension can also be carried out so that only part of the microsuspension is supplied to the tubular reactor and the rest passes through the homogenizer again. This circulation procedure is particularly advisable if the absolute size or droplet size distribution is unsatisfactory after only one step through the homogenizer. A combination of the two aforementioned preparation methods is also advantageous in the case of industrial application: in such a combination the substances to be emulsified are emulsified in a batchwise manner in a first step and then, in a second step, they are run in the form Continuous through a homogenizer and are fed to the tubular reactor. This combination offers the advantages of: the preparation of microsuspensions of high and uniform quality, the spatial separation of the discontinuous preparation that occupies space of the microsuspension of the actual polymerization, and the supply of the microsuspension to the tubular reactor according to the demand.

After the termination of the polymerization the particulate polymers are present in the dispersion in water and can, if required, be directly spray-dried or, after separation of the aqueous phase by, for example sieving, filtration, decanting or centrifugation, they can also be dried in the customary manner, for example by means of hot air or with the aid of a pneumatic conveying dryer. Depending on the proposed use, this dispersion containing the polymer, which in general has a viscosity of 100-500 mPa / s, can also be processed as such. Compared to the prior art, the novel process allows stable operation, that is, operation that proceeds without obstruction in the reactor. This is the case even with very long operating times in the tubular reactor that are a multiple of the average dwell time of the microsuspension in the tubular reactor. Under the chosen reaction conditions, the microsuspension used does not show a tendency towards the coagulation phenomenon. The homopolymers and copolymers prepared according to the invention have good operating properties. These are used, for example, as additives for thermoplastic molding compounds, as constituents of toner for copiers, auxiliary paper and auxiliary for leather, as a coating for magnetic tapes and magnetic films, and as components for paints and coatings. The following examples illustrate the invention.

Examples Experiments were performed using the following substances: Deionized water was used. Acrylonitrile, butyl acrylate, dihydrodicyclopentadienyl acrylate and styrene are products of BASF AG, Ludwigshafen, DE and were used without purification. The polyvinyl alcohols of the Mowiol® type are products of Hoechst AG, Frankfurt am Main, DE. The first number after the trademark indicates the viscosity of a solution at 4% concentration by weight of polyvinyl alcohol in water at 20 ° C in mPa / s, measured in accordance with DIN 53015. The second number characterizes the degree of hydrolysis of poly alcohol in molar percent. The polymerization initiators are customary commercial products.

Example 1 To prepare a homopolymer, a container was loaded with a mixture containing: 784. 0 g of butyl acrylate 16.0 g of dihydrodicyclopentadienyl acrylate 1500.0 g of water 160.0 g of a 10% solution by weight of polyvinyl alcohol Mowiol® 8/88 in water and 6.4 g of dilauryl peroxide and the mixture was emulsified for 20 minutes using Getzmann's Díspermat CV homogenizer at a rotation speed of 7000 rpm to form a microsuspension. This microsuspension was then metered with the help of a KP 2000 piston pump from Desaga, Heidelberg, DE to a tubular polytetrafluoroethylene reactor with an L / D ratio of 8300 and an internal diameter of 3 -mu. The speed of the dosage was 500 ml / h. The temperature of the contents of the reactor was maintained at 75 ° C using a water bath. After an average dwell time within the 20 minute tubular reactor, the polymerized suspension was collected. The tubular reactor was operated under these conditions for a total of 5 hours and 45 minutes. It was found that the suspension did not contain a coagulum and the tubular reactor showed no signs of obstruction. The solids content was 33% by weight and the average particle diameter d50 was 2.5 μm.

Example 2 To prepare a copolymer, the experiment of Example 1 was repeated and the resulting suspension, which contained the butyl acrylate polymer, was metered into a second tubular reactor with the same dimensions and composition of the material as that of Example 1. At 75 ° C the two mixtures A and B indicated below were dosed separately in a continuous manner. The dosage rate was chosen so that the weight ratio of mixture B to polybutyl acrylate was 20:80.

A: 600.0 g of water 264.2 g of a 10% solution by weight of polyvinyl alcohol Mowiol® 8/88 in water B: 495.5 g of styrene 165.1 g of acrylonitrile After an average stay of 20 min, the polymerized suspension was collected. The tubular reactor was operated under these conditions for a total of 5 hours. It was found that the suspension did not contain a coagulum and the tubular reactor showed no signs of obstruction. The average particle diameter d5o was 2 μm.

Claims (1)

1. CLAIMS A process for the preparation of particulate homopolymers and copolymers of at least one monomer polymerizable by the microsuspension polymerization technique at not less than 0 ° C in the presence of at least one hydrophobic free radical polymerization initiator, wherein the homopolymers or particulate copolymers resulting from the icrosuspension prepared in continuous or discontinuous form of one or more monomers with a conversion degree of at least 50% in a tubular reactor have an average particle diameter dso of less than 50 μm and the tubular reactor used in this case consists of a tube or hose with a length / diameter ratio of at least 20. The process as recited in claim 1, wherein the particulate homopolymers and copolymers have an average particle diameter of from 0.03 to 50 μm. The process as recited in claim 1 or 2, wherein the polymerization temperature is from 20 to 130 ° C. The process as recited in any of claims 1 to 3, wherein the monomer is at least selected from the group consisting of alkyl (meth) acrylate, (meth) acrylonitrile and styrene. The process as mentioned in any of claims 1 to 4, wherein the polymerization is carried out in a tubular reactor configured as a circulation reactor. The process as mentioned in any of claims 1 to 5, wherein the length / diameter ratio of the tubular reactor is from 50 to 1000 in the case of the operation in circulation and is greater than 5000 in the case of an operation mode. without circulation. The process as mentioned in any of claims 1 to 6, wherein the polymerization is carried out to a degree of conversion of at least 50%, based on the monomers used, and then another monomer or mixture of monomers is dosed and polymerized. . The process as mentioned in claim 7, wherein particulate copolymers are formed with a core-shell structure. The process as mentioned in any of claims 1 to 8, wherein more than 0.1% by weight of the polymer, color imparting or ferromagnetic pigments or other substances are added as additives in dissolved, swollen or suspended form before or after the preparation of the microsuspension.