AU2014256431A1 - Process for preparing polymer powder - Google Patents

Abstract

201300210 Foreign Countries Abstract The subject of the present invention is a process for preparing polymers in powder form.

Description

zuliuuziu foreign countries Process for preparing polymer powder The subject of the present invention is a process for preparing polymers in 5 powder form. Polymers, particularly polyimides, are required for many applications in powder form. Thus, for example, polyimides are used for a multitude of applications, particularly for the production of phase inversion membranes, 10 fibres for hot gas filters, coatings in the electronics sector, and other applications where a part is played by high thermal stability. For many applications components are produced from polyimide powder. 15 As well as polyimide components filled with PTFE or with graphite, polyimide powder is also used as a filler in PTFE compounds, where it is state of the art for reducing the creep behaviour of the PTFE at high temperatures. 20 The economic production of polyimide in powder form poses a particular challenge. Consequently there has been no lack of attempts to date to develop corresponding processes. WO 2012096374, JP 2001-163973, JP 2006-124530 and JP 2011 162570 disclose 25 methods for recycling polyimide wastes by dissolving the polyimide with an aqueous alkali and then reprecipitating it by addition of an acid, and isolating the powder. The process of dissolution is accompanied by partial hydrolysis of the polyimide, and this - owing to the attendant reduction in molar mass - may have adverse consequences for the physical properties. 30 US 4464489 describes a process in which a tetracarboxylic acid and a polyisocyanate are reacted in the presence of a catalyst, with direct precipitation of a powder. This process has not become industrially established. 35 US 20120245239 discloses a process in which a non-solvent, in other words a liquid in which the polymer does not dissolve, is added to a polyimide solution, with strong shearing, until an emulsion - that is, a liquid/liquid mixture - is formed. The solvent and the non-solvent are 40 stripped off from this emulsion to give a fine powder. The procedure 1 2UiJUU21U Foreign Countries carried out is therefore not a precipitation to give a suspension - that is, a solid-in-liquid mixture - but rather the drying of an emulsion. To allow this to happen, the emulsion in US'239 has to be stabilized by addition of a wetting agent, this entailing increased cost and complexity 5 and introducing impurities into the product. Moreover, the procedure from US '239 is very limited in respect of the size of the particles which can be produced accordingly (minimum 75 pm). Small, dust-free particles cannot be obtained. 10 EP 2345687 - see Example 1, for instance - describes a procedure for preparing polymer powder by dissolving a polymer and subsequently mixing this polymer solution continuously with a non-solvent until an emulsion is formed. This emulsion is then pumped through a special tube in which the solvent is stripped from the emulsion droplets, a process accompanied by 15 formation of polymer particles. The process therefore resembles that of US '239 - that is, an emulsion is formed and the solvent is stripped from it. The process described here is even more specific and more expensive, however, because of the apparatus, and is therefore not commercially utilizable. 20 In EP 2623542, a polymer B is added to a solution of another polymer A which is intended for precipitation, in order thereby to form an emulsion of the two polymers. The emulsion therefore consists of a mixture of droplets of two different polymers. This emulsion is then admixed with a 25 non-solvent in order to precipitate polymer A. This process is very costly and inconvenient and is environmentally unsound because of the need for a second polymer B as an assistant. The same applies to the process disclosed in EP 2287236. 30 US 4089843 describes a process in which a) a polymer solution is prepared, b) an emulsion is prepared from the polymer solution and a mineral oil, and c) a non-solvent is added to this emulsion, and the polymer is obtained 35 as a result. Like the above-discussed EP 2623542, this process has the disadvantage of the need to use a second polymer as assistant, with the mineral oil, in order to prepare the emulsion. 2 zuiJuuzlu Woreign countries EP 2502952 - see Claim 1 and Examples 14 to 16 - discloses a process for preparing polymer powders by dissolving the polymer in a solvent and subsequently adding the polymer solution to a non-solvent with stirring. The process has the disadvantage that the concentration of the polymer in 5 the solvent cannot be more than 5 wt %, since otherwise bulky particles or bulky materials are obtained. In order to be able to realize higher solids contents of up to max. 10 wt %, it is necessary in EP'952 to carry out a flash crystallization in an autoclave at high pressure and high temperatures. Both processes are uneconomic. 10 J.Y. Xiong et al, "Surfactant free fabrication of polyimide nanoparticles", Apple. Phys. Lett., Vol. 85, No. 23, 5733 - 5735, disclose a process in which polyimides are dissolved in NMP and in which storage-stable nanoparticle suspensions are prepared by addition of a non-solvent. The aim 15 is to prepare stable suspensions, and is achieved by surrounding the particles with a solvate shell which stabilizes the suspension and thus prevents the nanoparticles precipitating. There is no indication of whether and, if so, how powders can be isolated from the suspensions without any instances of aggregation or agglomeration. Since the very purpose of the 20 solvate shell is to prevent caking, it is likely that such agglomeration will occur on removal of the solvate shell. The particles, moreover, have sizes only in the nanometer range. Accordingly, this does not provide a solution to the problem addressed by the invention. 25 US 2002/0022673 - see examples and Figures 2a to 2f - discloses a process in which first of all a polymer powder A is mixed with a "soluble" 2nd powder. Added subsequently to this mixture is a solvent for polymer A, in order to cause partial dissolution of the surface of the polymer particles - i.e. not to dissolve the whole particles. When reduced pressure is 30 applied, the polymer particles "melt together" with their partially dissolved surface. After that, the soluble 2nd powder is washed out with water, and at the same time the partially dissolved surface of the polymer particles is reprecipitated. This produces a porous polymer block (see US '673, Fig. 2f). The process is therefore not one of producing a polymer 35 powder. EP 0336 995, JP 2007-112926, JP 2006-233023, US 20060039984 and JP 04 272934 disclose processes for preparing insoluble polyimide powders. In each of these processes, a polyamic acid solution is prepared to start 40 with. By addition of a non-solvent, the polyamic acid is precipitated and 3 2013UU210 Foreign Countries is subsequently freed from the solvent and non-solvent. The polyamic acid obtained in this way must thereafter be subjected to a separate imidizing step, generally a heat treatment at high temperatures, in order for a polyimide to be obtained. During the imidizing, the polyamic acid particles 5 undergo caking, meaning that the polyimide at the end must be ground again in order to give a polyimide powder. These processes are therefore likewise very laborious and are not suitable for solving the problem addressed by the present invention. 10 As evident from the above compilation of the prior art, there has been no lack of attempts within the last 30 years to prepare polyimide powders by a very wide variety of ways. None of the stated processes has acquired any commercial relevance at all. 15 Within the art, therefore, particularly for polyimides from the P84® family, a process according to EP 0279807 has instead become established, comprising in a first step a spinning with water from a P84 polycondensation solution via a specific 2-fluid nozzle. This produces what are called fibrids, with a size of 10 to 15 mm. The fibrids are isolated, 20 at cost and with complexity, in a plurality of washing steps, in order to remove the DMF from the fibrids. Removal by washing is possible because the fibrids have a porous, membrane-like structure, which is produced during spinning process, which means that the DMF can be removed by washing. After the removal of the DMF by washing, drying takes place. Lastly, the dried 25 fibrids are additionally ground, in order to be able to provide the particle sizes required for various applications. The resulting P84 powder is decidedly hard and cannot be readily ground using conventional impact mills. The finer the target powder, the greater the cost and complexity. As a result, even commercially, the end point is reached at a particle size of 30 around 1200 mesh (10 to 15 p). Finer powders have to date not been commercially preparable. After being ground, moreover, the powders must still be classified and sieved - at cost and with complexity - in order to give the appropriate fractions. Fines arising from the grinding procedure either are not separated off, and remain in the powder, or else a fine 35 fraction is produced, which must be disposed of as waste and which diminishes the yield. Fine fractions in the product are often disruptive to the application, since they cause dust during handling, may bring about unwanted properties in the product, and are the cause of poor free-flow properties in the powder. 40 4 2UIJUU2IU Foreign Countries As a consequence of the grinding procedure, the particle size distributions of the ground powders are often very wide and inhomogeneous. The particle morphology as well is non-uniform. Furthermore, owing to the hardness of the material, metal abrasion occurs to a not inconsiderable extent: this 5 problem is also addressed in the above-stated Japanese property rights on polyimide recycling. There continues, then, to be a high demand for an economic process for preparing polyimide powders. This process ought ideally to be applicable to 10 other polymers too. A problem addressed with the present invention was therefore that of providing a process which diminishes or does away with the disadvantages of the prior art processes. 15 One specific problem was to provide a simplified process which operates without grinding procedures. Another specific problem was to provide a process which allows the 20 reproducible preparation of polymer powders, but in particular not just polyimide powders, having a specified particle size distribution and/or uniform particle morphology, without costly and inconvenient sieving, classifying and fractionating. 25 Likewise a particular problem was to develop a process with which the particle size of the powder is freely adjustable and reproducible. In particular, it ought also to be possible in this way to prepare relatively small particles, economically, than with the commercially employed process described above. The resulting powders ought ideally to be free from fine 30 fractions, to have good free-flow behaviour, and to have very high bulk densities. Likewise a problem addressed by the present invention was the provision of a process which can be integrated into as many as possible commercially 35 employed processes for the preparation of polymers, particularly of polyimides and polyamideimides, especially into - the preparation of polyimides and polyamideimides by the reaction of aromatic tetracarboxylic dianhydrides or trimellitic anhydride with aromatic diisocyanates, 5 zuiuuziu Iforeign countries - the preparation of polyimides which have been prepared by a thermal or chemical process of imidization of a polyamic acid, prepared preferably from an aromatic tetracarboxylic acid and an aromatic diamine, 5 - the preparation of polyimides which generally in the course of preparation remain in solution and do not precipitate, and - the preparation of soluble polyimides which can be redissolved by a special production procedure. 10 Further problems, not explicitly stated, will become apparent from the overall context of the description, examples and claims hereinafter. Before the invention is described in detail, a number of important terms will first be defined. 15 The terms "particle" and "grain" are used synonymously in the context of the present invention. "Non-solvent" denotes a liquid or a mixture of liquids in which the polymer 20 to be processed to powder, at 23'C and atmospheric pressure, is insoluble or is soluble only to a very small extent, i.e. < 5 wt %, preferably < 3 wt %, more preferably < 2 wt % and very preferably < 1 wt %. Preference is given to using at least one non-solvent which is completely miscible with the solvent at 23 0 C and atmospheric pressure over a wide range of mixing 25 ratios, and very preferably is completely miscible at all mixing ratios. The fraction of non-solvents or non-solvent mixtures which are miscible with the solvent as described above, as a proportion of the total amount of the non-solvents or non-solvent mixtures used in the process of the invention, is preferably 50 to 100 wt %, more preferably 70 to 100 wt %, 30 very preferably 80 to 100 wt %, especially preferably 90 to 100 wt %, very especially preferably 95 to 100 wt %. In the most-preferred embodiment, use is made exclusively, as described above, of non-solvent mixtures or non solvents which are miscible with the solvent. 35 "Solvent" denotes a liquid in which the polymer to be processed to powder can be dissolved completely at 23 0 C. A "polymer solution" is the solution of at least one polymer that is prepared in step a) of the process of the invention, and to which the non 6 zuiiuuziu foreign countries solvent or the mixture of a solvent and a non-solvent is added in step b) of the process of the invention. The polymer solution may correspond to the solution which is obtained 5 during the procedure of preparing a polymer, preferably at the end of a polycondensation, more preferably at the end of a polycondensation by one of the processes described earlier on above, very preferably by a reaction of a tetracarboxylic dianhydride and a diisocyanate. Alternatively it may be a solution which is obtained by dissolution of a soluble polymer 10 obtained preferably by polycondensation. The polymer solution may be processed in other process steps before step b) is carried out. Preferred examples of such process steps are dilution, filtration, concentration, solvent exchange, addition of additives, etc. 15 Details of this, and also of other possibilities for the preparation of the polymer solution, are elucidated later on below. The inventors have surprisingly discovered that it is possible to obtain a suspension from a polymer solution by addition of a non-solvent or of a 20 mixture of at least one non-solvent and at least one solvent, in which preferably at least one non-solvent is miscible completely, as described above, with the solvent or with the solvent mixture of the polymer solution, with exposure to stabilizing energy, preferably shearing energy, and to obtain from said suspension, ultimately, a polymer having a defined 25 and, if desired, narrow particle size distribution and also with an adjustable average particle size. A feature of the process of the invention is that addition of the non solvent is accompanied first by formation of an emulsion, which is formed 30 from the homogeneous phase by a phase separation. A miscibility gap develops, and causes two phases to develop. One phase is characterized by a high solids content of polymer with solvent and a little non-solvent; the second phase is the dilute phase, with low solids content, relatively low solvent fraction and relatively high non-solvent fraction. Without exposure 35 to stabilizing energy, preferably shearing energy, the emulsion would collapse and would form a material like chewing gum, which would not produce a well-defined powder. In contrast to the process of the invention, US 20120245239 uses only 40 precipitants (immiscible non-solvents), which cannot be mixed with the 7 2Ul3UU2iU Foreign Countries solvents of the polymer solution, to obtain a two-phase region. The process according to US 20120245239 is therefore feasible only with specific solvents, and is very costly and inconvenient and very unenvironmental. 5 In the process of the invention, after the emulsion has been formed, and in contrast to US 20120245239, addition of non-solvent or a mixture of non solvent and solvent is continued, until a suspension is formed. The polymer powder may be isolated from this suspension by simple means. In comparison to US 20120245239, a greater number of non-solvents can be used. The 10 process of the invention is therefore more variable, less costly and inconvenient, and more environmental. In the process of the invention, the particle size distribution and the average particle size can be adjusted by various parameters, preferably by 15 the solids content and/or by the pH of the polymer solution. The process of the invention is therefore very variable and there is no need either for grinding or for the costly and inconvenient classifying. The process of the invention comprises the following steps: 20 a) preparing a polymer solution comprising a polymer or mixture of two or more polymers, selected from the group consisting of polyimides, polyetherimides, polyamideimides and polyamides, and at least one solvent for said polymer or polymer mixture, b) adding at least one non-solvent or a mixture of at least one non 25 solvent and at least one solvent, the terms non-solvent and solvent refer to the polymers listed in step a), with accompanying exposure to stabilizing energy, preferably shearing energy, to the solution from step a) until a suspension is formed, c) optionally reducing the solvent and/or non-solvent content in the 30 liquid phase of the suspension, d) removing the powder from the liquid phase of the suspension obtained by step b) or c), e) optionally drying the powder. 35 Stabilizing energy in the context of the present invention means the input of energy, during the precipitation in step b) and/or possibly even before, as for example during preparation of the solution in step a), into the reaction mixture, with the stabilizing energy, which is preferably shearing energy, being of a magnitude such that coagulation of the emulsion formed 40 intermediately in step b) is prevented, this emulsion being stabilized 8 ZUIJUU2iU Foreign Countries accordingly. This allows the formation of a suspension of fine particles from the stabilized emulsion by further addition of non-solvent, i.e. by precipitation. 5 The polymer solution in step a) is on the one hand a solution which is obtained by redissolving a polymer, obtained preferably by polycondensation, or which is obtained directly from the preparation process of a polymer, obtained preferably by polycondensation, 10 or the polymer solution is alternatively the above-defined polymer solution after having been modified in at least one further process step. In this case, the process of the invention comprises at least one process step al) 15 of "modifying the polymer solution", which with particular preference comprises at least one of the following steps: al.1) diluting the polymer solution with the solvent used in the polymer preparation, preferably in the polycondensation, or with 20 another completely miscible solvent, al.2) diluting the polymer solution with a completely miscible non solvent, in which case preferably up to 20% of non-solvent is admixed, and so as yet there is no precipitation of the polymer, al.3) filtering to remove solids from the polymer solution, 25 al.4) concentrating the polymer solution, al.5) adding a polymer or additive which dissolves in the polymer solution, al.6) adding additives in powder form which do not dissolve in the polymer solution and can be dispersed or suspended therein, 30 al.7) replacing some or all of the solvent by a solvent which is miscible with the solvent and/or non-solvent or mixture of solvent and non-solvent, so that as yet there is no precipitation of the polymer. 35 The measures of step al) influence the precipitation behaviour and the resulting particle size, the particle shape and the particle size distribution. In one particularly preferred embodiment, step a) of the process of the 40 invention comprises at least one of the following sub-steps: 9 2Ui3UU2iU Foreign Countries a2) homogenizing the polymer solution, preferably by input of shearing energy, a3) adjusting the polymer solution temperature, 5 a4) adjusting the polymer solution pH, a5) adjusting the polymer solution solids content. Suitable polymers for the purposes of the invention are all polymers which are soluble in organic solvents and which in principle form a solid phase 10 on addition of a non-solvent. Preference is given to soluble representatives of the polymer classes selected from the group consisting of polyimides, polyetherimides, polyamideimides, polyamides, or mixtures thereof, being converted into powders with the process of the invention. Particular preference is given to using polyimides, polyetherimides and 15 polyamideimides, and very preferably polyimides or polyamideimides. Particularly preferred polyimides and polyamideimides can be obtained respectively by polycondensation of 20 at least one aromatic tetracarboxylic (di)anhydride and/or of an aromatic tricarboxylic acid, preferably selected from the group consisting of 3,4,3',4'-benzophenonetetracarboxylic dianhydride, 1,2,4,5 benzenetetracarboxylic dianhydride, 3,4,3'4'-biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, sulphonyldiphthalic dianhydride, 25 1,1,1,3,3,3-hexafluoro-2,2-propylidenediphthalic dianhydride and 1,3,4 benzenetricarboxylic acid, and 30 at least one aromatic diisocyanate, preferably selected from the group consisting of toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, 4,4' methylenediphenyl diisocyanate, 2,4,6-trimethyl-1,3-phenylene diisocyanate and 2,3,4,5-tetramethyl-1,4-phenylene diisocyanate 35 or by reaction of at least one tetracarboxylic (di)anhydride, preferably selected from the group consisting of 3,4,3',4'-benzophenonetetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,4,3'4' 40 biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, 10 2U3UU21U Foreign Countries sulphonyldiphthalic dianhydride, 1,1,1, 3,3,3-hexafluoro-2,2 propylidenediphthalic dianhydride and 4,4'-(4,4' isopropylidenediphenoxy)bis(phthalic anhydride); 5 and at least one diamine, preferably selected from the group consisting of 2,4-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminodiphenylmethane, 2,4,6-trimethyl-1,3-phenylenediamine, 2,3,4,5-tetramethyl-1,4 10 phenylenediamine, bis(4-amino-3,5-dimethylphenyl)methane, bis(4-amino-3 methylphenyl)methane, 1, 3-phenylenediamine, 1, 4-phenylenediamine, 4,4' diaminodiphenyl ether, 5(6)-amino-i-(4' aminophenyl)-1,3,4-trimethylindane, and subsequent imidization of the polyamic acid. Especially preferred polyimides comprise 00 N -R(A) 0 0 N-R---(B 00 15 ([JO CH3 11 zui-uu2iu foreign countries (L2)

CH

3 \ CCH20\/ where 0 x 0.5 and 1 ! y 0.5 and R corresponds to one or more identical or different radicals selected from the group consisting of L1, 5 L2, L3 and L4. With particular preference x = 0, y = 1 and R is 64 mol% L2, 16 moi% L3 and 20 mol% L4. This polymer is available commercially under the name P84 or P84 type 70 from Evonik Fibres and is registered under CAS number: 9046-51 10 9. In the case of a further particularly preferred polymer, x = 0.4, y = 0.6 and R is 80 mol% L2 and 20 mol% L3. This polymer is available commercially as P84HT from Evonik Fibres and is registered under the CAS number: 134119-41-8. 15 Especially preferred polyimides may be prepared in accordance with WO 2011/009919. In order to avoid pure repetition, the content of that application is adopted in full into the description of the present specification. 20 Another preferred polyimide is Matrimid 5218, available commercially from Huntsman Advanced Materials and with the following chemical structure: 00 CH 12 zulluuzlu toreign countries One particularly preferred polyetherimide has the chemical structure below and is available commercially under the name ULTEM 1000 from Sabic. 0 o HC N0 N --N j H 3 0 (I 00 5 Particularly preferred polyamideimides are the polymers with brand names Torlon and Kermel, with the composition given below 0 H N- R-- 0 0

CH

3 (L2) CH2 where the radical R corresponds to one or more identical or different 10 radicals selected from the group consisting of L2, L3 and L4. Suitable solvents for preparing the polymer solution are all solvents which completely dissolve the polymers of the process of the invention and which preferably are completely miscible with at least one of the non-solvents 15 used, more preferably with all non-solvents used. In the process of the invention, preference is given to using the solvent which was also used when preparing the polymer. 13 ZUIjUUZIU foreign countries Solvents used are preferably aprotic dipolar solvents, more preferably dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylpropionamide (DMPr), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), dimethylsulphoxide (DMSO), sulpholane, tetramethylurea, tetrahydrofuran 5 (THF), 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane or mixtures thereof. Particularly preferred in the process of the invention is the use of DMF, DMSO, DMAc, NMP and NEP as solvents. As already mentioned, the aforementioned solvents can be used in order to 10 dissolve polymer granules or polymer powders in order thereby to prepare polymer solutions for the process of the invention. The solvents are also used, however, in order to prepare the polymers directly therein, preferably via a polycondensation reaction. 15 Thus, for example, the reaction of one or more aromatic tetracarboxylic dianhydrides with one or more aromatic diisocyanates, with elimination of carbon dioxide, leads to a polycondensation solution which comprises the soluble polyimide, preferably in solvents such as DMF, DMAc, NMP and/or NEP. 20 By a similar reaction mechanism, polycondensation solutions of soluble polyamideimides as well (Torlon, Kermel) are obtained, by reaction of trimellitic anhydride with aromatic diisocyanates, preferably in DMF, DMAc or NMP. 25 Polycondensation solutions in the solvents described are also obtainable by nucleophilic substitution reactions on the aromatic nucleus, and are suitable as polymer solutions for preparing powders by the process of the invention. Thus, for example, ULTEM 1000 (for composition see above) can be 30 prepared by reaction of N-phenyl-4-nitrophthalimide and the disodium salt of bisphenol A in a solvent such as NMP. Energy is input into the polymer solution in step b) and optionally beginning even before, as for example in step a), more particularly in step 35 a2), preferably by means of a mixing device. Suitability for stabilizing in step b) and optionally also for use in step a) is possessed here by all internal and external assemblies, preferably mixers and stirrers, that are available on the market and that are able to input sufficient stabilizing energy, preferably shearing energy, into the system in order to prevent 40 coagulation of the emulsion formed intermediately in step b), allowing the 14 zu1iuuZiu toreign countries preparation of fine powders. The following stirrers can be used for example, but not exclusively, for the mixing and homogenizing, i.e. for preparing the solution in step a), and/or for stabilizing in step b) and optionally beginning as early as in step a) as well: 5 * propeller stirrers a inclined blade stirrers a disc stirrers e tumble disc stirrers a hollow blade stirrers 10 - impeller stirrers * cross arm stirrers * anchor stirrers * paddle stirrers * gate stirrers 15 * gas introduction stirrers e helical stirrers e toothed disc stirrers centrically with or without planetary drive and close-clearance scraper * magnetic stirrers 20 Particularly preferred are high-speed toothed disc stirrers, which introduce a high shearing energy into the polymer solution and hence ensure thorough mixing and dispersing. An ultrasound probe can also be used for homogenizing. 25 The process of the invention can be operated discontinuously or continuously. If the procedure is carried out continuously, the solution in step b) and optionally also step a2) is preferably passed through an assembly, preferably an in-line disperser or in-line emulsification pumps, 30 which introduces shearing energy into the solution. With particular preference in this case, at least one non-solvent or at least one mixture of solvent and non-solvent is metered in upstream and/or at the location of shearing to the solution. 35 In the discontinuous regime, stabilizing energy is introduced into the system in step b) and optionally also in step a), more particularly step a2), in the course of mixing and/or dispersing. High rotary speeds or large diameters of the stirring mechanisms can be used to introduce a particularly large amount of shearing energy into the system. Numerous 40 stirrer geometries can be utilized in principle for preparing powders by 15 zuiiuuziu foreign countries the process of the invention. Preferably, however, stirring systems with a high shearing input are used, such as a toothed disc stirrer, for example. The toothed disc in this case may have a diameter of a few centimetres (in the case of small vessels) up to a metre or more (in the case of large 5 tanks). Since the shearing rate of the stirring mechanism and the quality of dispersing affect the morphology and the particle size of the powder, the process of the invention preferably uses toothed disc stirrers having 10 rotational toothed disc speeds of between 100 and 15 000 revolutions per minute. Used with particular preference, depending on the rotary speed and circumference of the disc used, are shearing speeds (i.e. revolution rate of the toothed disc) of 0.01 to 100 m/s, preferably 0.1 to 30 m/s, more preferably 1 to 30 m/s and very preferably 2 to 20 m/s. If the process is 15 operated continuously or if stirrers other than toothed disc stirrers are used, then corresponding continuous or discontinuous shearing assemblies are used which generate a shearing field whose magnitude is the same as or higher than that described above for the toothed disc stirrer. 20 One specific example of a suitable assembly on the laboratory scale is a toothed disc stirrer from Mischtechnik Hoffmann of Austria. This stirrer is equipped with a stirring motor with up to 4000 rpm, a heatable and coolable jacketed tank with a volume of 10 1, a planetary drive which moves the dissolver disc eccentrically within the cylindrical tank, and a close 25 clearance scraper made from PTFE. A glass electrode is mounted on the tank base for the purpose of pH measurement. Step a2) can begin or be carried out at different points in time in the process of the invention. It may commence or be carried out even before 30 steps al) and a3) to a5), or else not until immediately before or with step b). It is likewise possible to commence the introduction of stabilizing energy, preferably shearing energy, at any point in time between or during one of steps al) and a3) to a5). This introduction may also begin even during the preparation of the polymer solution, such as during dissolution, 35 for example. The polymer solution is preferably exposed to a shearing field before the addition of the non-solvent in step b). With particular preference, step a2) takes place after step al) and, if steps a3) to a5) are carried out, before these steps. 16 zuliuuziu foreign countries It has emerged that the particle size of the powder and the particle size distribution can also be influenced by the temperature of the polymer solution in step a) and step b). Ideally this is regulated by indirect heating or cooling through a jacket of the stirring tank. However, other 5 heating and cooling facilities for stirred tanks, in accordance with the prior art, may also be used. The temperature of the process in step b) is preferably between -20 and 200'C, more preferably 0 and 150 0 C, very preferably between 20 and 100 0 C, 10 especially preferably between 20 and 80 0 C and very especially preferably between 30 and 60'C, differing also according to the nature and boiling point of the solvent and/or non-solvent used. If adaptation of the temperature is necessary, it takes place in step a3) and/or during step b). Step a3) can be carried out at different points in time. Step a3) may take 15 place even before steps al), a2) and a4) to a5), or else immediately prior to or with step b). It is also possible to begin temperature regulation and/or to carry it out at any point in time between or during one of steps al), a2) and a4) to a5). Step a3) may also begin or be carried out even during the preparation of the polymer solution, such as during the 20 dissolution of the polymer, for example. The temperature of the polymer solution is preferably adjusted to the target temperature prior to the addition of the non-solvent in step b), and left at this temperature in step b). With very particular preference, steps a3) and a4) are both carried out, with step a3) being carried out before, especially preferably 25 directly before, step a4). In the process of the invention it is preferable for the emulsion formed intermediately during the subsequent precipitating procedure to be stabilized further, in addition to the introduction of the stabilizing 30 energy, and to not undergo immediate separation. This is accomplished preferably via the adjustment of the pH. There are, however, other methods too which can be employed, such as the modification of the ionic strength by addition of salts, for example. In the process of the invention, the zeta potential of the polymers in the precipitation solution is preferably 35 adjusted in such a way that charge carrier layers on the particle surface formed, depending on the nature of the polymer and on the pH, produce a repellency effect with respect to other particles, and hence coagulation is prevented. 17 zuliuuziu toreign countries It has surprisingly been found that as well as the stabilizing effect on the emulsion formed intermediately, the particle size of the powder as well can be modified if the pH is changed by addition of acids or bases. By setting the optimum pH (which differs according to polymer and desired 5 particle size) it is possible to achieve optimum stabilization of the intermediately formed emulsion. If this stabilization operates well, it is possible in general to prepare powders with a very small particle size (< 10 pm or even < 1 pm). If the emulsion is stabilized less strongly or not at all, coarse particles are obtained with sizes of more than 500 pm, 10 or even coarse lumps with a size of a few mm or cm. The desired pH of the polymer solution in the process of the invention may be pH 0 to 14, preferably pH 2 to 11, more preferably pH 4 to 11, very preferably pH 4 to 10 or 6 to 11. 15 If it is not already within the correct range during the preparation of the polymer solution, the pH can be adjusted by addition of acids or bases in step a4). Acids employed are preferably aqueous mineral acids, more preferably hydrochloric acid, phosphoric acid or sulphuric acid, or organic 20 acids, more preferably formic acid, acetic acid or methanesulphonic acid. Bases employed are preferably mineral aqueous bases, more preferably aqueous ammonia, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate, potassium carbonate, or organic nitrogen bases, more preferably triethylamine, pyridine, diazabicyclooctane or alkoxides in 25 alcoholic solution, more preferably sodium methoxide, potassium methoxide or potassium tert-butoxide in ethanol. The acids and/or bases are added to the polymer solution and so set the desired pH which is measured with a pH measurement electrode. 30 As already mentioned, the pH is adjusted - if necessary - even before step b) of the process of the invention. The inventors have discovered that a further parameter with which the particle size and the particle size distribution of the powder to be 35 prepared can be controlled is the solids content of the polymer solution. It is preferably between 1 and 50 wt %, more preferably between 1 and 40 wt %, very preferably between 2 and 30 wt %, especially preferably between 5 and 25 wt % and very especially preferably between 7 and 20 wt %. The solids content may be set as early as during preparation of the polymer 40 solution. It is, however, also possible to reduce the solids content at a 18 zuiiuuziu foreign countries later point in time, but before the beginning of step b), in step a5) and/or in step al), by addition of at least one solvent and/or at least one non-solvent and/or of mixtures thereof, or to increase it by adding solid soluble polymer or by removal of the solvent by evaporation or other means, 5 such as by means of membranes, for example. The setting of the solids content is followed with particular preference by homogenization of the solution. After the preparation, adjustment and stabilizing of the polymer solution 10 in step a), the precipitating operation takes place in step b), accompanied by exposure to stabilizing energy, preferably shearing energy, as described above. In this operation, a non-solvent or a mixture of two or more non solvents or a mixture of at least one solvent and at least one non-solvent is supplied, preferably continuously, more preferably above the surface 15 level, to the polymer solution during energy input, preferably during shearing. A precipitate of the polymer may form even at this stage, at the location of dropwise introduction, but dissolves again rapidly in general. At least one non-solvent or non-solvent mixture, preferably miscible with 20 the solvent system of the polymer solution, is used as non-solvent for precipitating the polymer solution in step b) and/or in step al.2) and/or in step a5). Employed preferably here are water, alcohols, preferably Cl to C4 alcohols, such as methanol, ethanol and isopropanol, or ketones such as acetone or methyl ethyl ketone, or Cl to C8 alkyls, or mixtures thereof. 25 Particularly preferred are water and Cl to C4 alcohols. A miscible solvent may also be added to the non-solvent in step b), in a range preferably between 10 and 90 wt %. As a miscible solvent which is added to the non-solvent, suitable solvents are in particular those in 30 which the polymer for precipitation is in solution in the polymer solution. Solvents employed as an addition to the non-solvents in the process of the invention are preferably aprotic dipolar solvents, such as dimethylformamide, dimethylacetamide, dimethylpropionamide, N methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulphoxide, sulpholane or 35 tetramethylurea, or mixtures thereof. The purpose of adding the solvent to the non-solvent is to attenuate or fine-tune the non-solvency effect of the non-solvent. In many cases, accordingly, the use of the pure non-solvent is disadvantageous, since the non-solvency effect is too strong and the polymer precipitates right at the location of dropwise introduction 40 accordingly, there is uncontrolled formation of a precipitate of undefined 19 2UijUU2IU Foreign Countries particle size and morphology, which no longer dissolves. Accordingly it is advantageous, for example, to dilute strong non-solvents such as water or alcohols with solvents such as DMF, DMAc or NMP. In this context it is possible to add up to 90 wt % of the solvent to the non-solvent, but 5 preferably 20 to 80 wt % of solvent is added to the non-solvent, more preferably between 50 and 75 wt %. Particularly preferred mixtures of non solvent and solvent are, for example, mixtures of water and DMF, water and DMAc or water and NMP, with a ratio of water to non-solvent of 30:70 wt %. 10 In the case of the adding of the non-solvent to the polymer solution, the non-solvent is added preferably at a uniform rate and continuously. The metering rate may also be varied, i.e. may also be discontinuous, but should be monitored, since the metering rate as well may alter the particle size. Preferred metering rates are in the range between 0.1% and 100% of 15 the required amount of non-solvent per minute, more preferably between 0.5% and 20% per minute and very preferably between 1% and 10% per minute. The required amount of non-solvent is dependent on the composition of the non-solvent and on its non-solvency quality. The amount of non-solvent 20 required may be 1 to 500 wt % of the amount of precipitating solution originally introduced, but preferably 5 to 200 wt % and more preferably 10 to 100 wt %. During the addition of non-solvent, it is possible to observe how, up to a 25 defined amount of non-solvent, any precipitate of polymer that occurs at the location of dropwise introduction is dissolved again without residue. Above a defined amount of addition of non-solvent, there is a sudden switch from a homogeneous solution to a two-phase emulsion. Here, two immiscible liquid phases are obtained. If dispersing is stopped at this point, i.e. 30 the supply of stabilizing energy is halted, then the two phases separate, producing a relatively high-viscosity, polymer-rich liquid phase with a low non-solvent content, and a non-solvent-rich liquid phase of low polymer content. It is therefore important to ensure effective dispersing. With the effectiveness of dispersing, expressed in the stabilizing energy supplied, 35 as for example the shearing rate of the toothed disc of the dis.solver, it is possible to control the particle size and the breadth of the particle size distribution of the powder. The introduction of the stabilizing energy, preferably the shearing, takes place as described above with the apparatus discussed there. 40 20 20130021U Foreign Countries If further non-solvent is added, there is a further phase transition from an emulsion to a suspension. Now, solid particles of the polymers are obtained as a suspension in a mixture of solvent and non-solvent. When the polymer has been transferred entirely into the solid state, it is possible 5 with preference to add a defined amount of pure non-solvent as well, without addition of solvent, in order to ensure that all of the polymer fractions have actually precipitated. The amount of non-solvent in this case is 0.1 to 100 wt % of the original amount of polymer solution, preferably 1 to 50 wt % and more preferably 5 to 30 wt %. 10 At the end of step b) in the process of the invention a suspension is obtained which comprises a polymer powder in a mixture of solvents and non solvents. The solids concentration of the polymer in the suspension is preferably between 0.1 and 70 wt %, but preferably between 1 and 40 wt %, 15 more preferably between 2 and 30 wt % and very preferably between 5 and 25 wt %. The particle size of the resulting powders (d90) in the suspension after the process of the invention extends preferably over a range from 0.01 to 1200 pm, more preferably from 0.01 to 1000 pm, very preferably from 0.05 to 1000 pm, especially preferably from 0.3 to 1000 pm, more 20 particularly preferably from 0.4 to 1000 pm, with a special preference from 0.5 to 800 pm and most preferably 0.6 to 500 pm. After the precipitation procedure it is advantageous to wash the suspension free of solvents, before isolating and drying the powder. This makes it 25 possible to prevent redissolution or redilution of the polymer by residual solvent in the course of a drying operation at elevated temperature. Steps c) to e) of the process of the invention, from the end of precipitation up to the dried powder, can be carried out in different ways. 30 In one preferred process alternative, the solvent in step c) is removed very largely from the liquid phase of the suspension. This can be done by means, for example, of repeated isolation by filtration and resuspension of the powder with water or other non-solvents, until the residual solvent is 35 beneath a certain amount. This amount of solvent in the liquid phase is preferably less than 5 wt %, more preferably less than 1 wt % and very preferably less than 0.1 wt %. With very fine powders (< 20 pm) in particular, it is disadvantageous to 40 use a filter for the washing of the powder in step c), since the fine 21 2UIJUU2iU Foreign countries powder easily clogs the filter and the washing liquid is able only with difficulty to pass through the filter. In another preferred process alternative, the removal of the solvent from the liquid phase in step c) takes place using cross-flow filtration via a membrane. At a high flow rate 5 over the membrane, of several meters per second, no filtercake is formed on the preferably microporous or nanoporous membrane; the membrane hence remains permeable even with very fine particle sizes of the powder of the invention. In this case, therefore, dilution scrubbing is preferably carried out with the aid of a cross-flow filtration, until the desired 10 residual solvent concentration is within the ranges stated above. The suspension freed or largely freed from solvent, as described above in step c), can then be filtered in step d), and the resulting filtercake can be subsequently dried in step e) in a suitable drying assembly, preferably 15 a drying oven or moving dryer. All drying technologies available on the market may be employed for this purpose. The drying temperatures may vary, according to the polymer used, between 50 and 400'C. In an alternative, preferred embodiment there is a solid/liquid separation, 20 preferably by filtration and/or centrifugation, and then drying, preferably directly in a contact dryer. This process is suitable especially for coarse particles. Alternatively and with particular preference, the suspension in step d) is 25 dried by means of a spray dryer and deposition of the powder in a cyclone and/or filter house. This saves on the filtration step. A further advantage is that agglomerates are not formed during drying, and so the powder is free from agglomerates and no longer requires subsequent sieving or deagglomeration. Employed here are standard spray-drying systems with 30 centrifugal or two-fluid atomization, which are run in co- or countercurrent and are fed with air or with an inert gas. In this case, step e) is usually omitted, since drying has already taken place in step d). 35 In principle the process of the invention also encompasses embodiments in which step c) is omitted, i.e. in which the suspension obtained after step b) is filtered directly and both solvent and non-solvent are stripped off, in the course of drying, for example, or in which the suspension is spray dried directly after step b). The variants with step c), described earlier 40 above, are preferred for the reasons stated above. 22 2Ui3UU21U Foreign Countries The process of the invention produces a dry, solvent-free powder with various particle sizes (d90) of preferably 0.01 to 1200 pm, more preferably 0.01 to 1000 pm, very preferably 0.05 to 1000 pm, especially preferably 0.1 5 to 1000 pm, with a special preference from 0.3 to 1000 pm, with especial preference from 0.4 to 900 pm, very specially preferably 0.5 to 800 pm and most preferably 0.6 to 500 pm. The bulk density of the powders of the invention is preferably between 0.05 10 and 0.8 kg/l, more preferably, however, between 0.2 and 0.7 kg/l. The free flow behaviour of the powders is good; the dusting behaviour of the powders can be reduced by avoiding the formation of fines (< 30 p) during the production of the powders. 15 The powder from the process of the invention, in contrast to alternative production processes, typically comprises particles with an approximately spherical structure. This particle morphology can be shown clearly by means of scanning electron microscopy. This spherical morphology is brought about by the precipitating operation of the invention, and cannot be found with 20 powders that have been ground. This morphology may result in an improvement in the impact modifier effect in composites, and also in better filling properties in the context of Hot Compression Moulding (HCM). After the precipitation suspension has been worked up, the powders have a 25 very small BET specific surface area. Nitrogen sorption measurements on the powders of the invention show a specific surface area of significantly less than 1 m2/g. These specific surface areas are much smaller than powders from the alternative process that is currently employed commercially, from EP 0279807. In a hot compression moulding application, the smaller surface 30 areas produce mouldings having greater densities, and improved sintering is also likely. Measurement methods: 35 pH measurement: The pH was measured continuously during precipitation, using a Metrohm pH meter. The electrode used here was a Unitrode with built-in Pt1O00 temperature sensor. The Unitrode is equipped with the Idrolyt external electrolyte. This is a glycerol-based electrolyte with a chloride ion 40 activity corresponding to that of a KCl solution with c(KCl) = 3 mol/l. The 23 2UI3UU2IU Foreign countries Unitrode is suitable specifically for difficult systems such as suspensions, resins or polymers. With this system, as well, it is possible to measure the pH at relatively high temperatures of between 80 and 100'C. 5 Measurement of the solids content of the polymer solution in step a) The solids content of polymer solutions is determined gravimetrically by evaporation of the solvent present and subsequent determination of residual solvent. 10 Measurement of the solids content of the suspension in step b) The solids content of the suspension is determined gravimetrically by means of a Kern MRS 120-3 IR dryer. About 5 g of the suspension are weighed out onto an aluminium dish and placed in the dryer. The instrument dries the sample at 130 0 C. It automatically recognizes the end point of drying and 15 gives an analogue output of the dry matter content on paper strips. The dry content of the suspension varies according to the solids content at the precipitation stage. Measurement of the viscosity of the polymer solution 20 The viscosity of the polymer solution is measured using a HAAKE RS 600 instrument. The dynamic viscosity q is ascertained by shearing the polymer solution (17.0 ± 1.0 g) in a cylindrical gap at a constant 25 0 C temperature, once by mandating different rotation rates 0 (or shear gradients y) and subsequently by mandating different shear stresses T. The 25 shear gradient range traversed here is 1.25 to 40 s-, the shear stress range 2250 to 100 Pa. The dynamic viscosity is evaluated automatically via the Rheo Win software. Particle size measurement (dry, wet) 30 The measurement of the powder particle size is conducted by means of a Malvern Mastersizer 2000, and is determined both directly from the precipitated suspension and from the dried powder. For the determination of the particle size distribution in the suspension the HydroS wet dispersing unit is used, and for the determination of the powder the Scirocco dry 35 dispersing unit. The principle of the measurement is based on laser diffraction, with measurement of the intensity of the scattered light of a laser beam that penetrates a dispersed sample. According to the Fraunhofer theory, smaller 40 particles generate a greater scattering angle. From the diffraction pattern 24 zu1-uuz1u toreign countries obtained, the size of the particles and a statistical distribution are calculated. For the measurement by means of a wet dispersing unit a few drops are required, and for the measurement by means of a dry dispersing unit 2-3 g (according to bulk density) of the sample. 5 Bulk density of the powder The bulk density is determined gravimetrically in a duplicate determination using a Powtec SMG 53466. This determines the mass of 100 ml of powder. The bulk density of the powder can be calculated from the weighings obtained. 10 The examples which follow serve to provide more particular elucidation and better understanding of the present invention, but do not limit it in any way. Modifications to the examples and/or transposition to other polymers are an easy task for any person skilled in the art. 15 Examples: Example 1: Precipitation of P84 type 70 20 A polycondensation solution of P84 type 70 (Evonik Fibres GmbH, Austria) in DMF with a solids content of 27 wt %, obtained without isolation of the polyimide and re-dissolution, was diluted with DMF to a solids content of 17.5 wt %. 200 g of this solution were introduced into a high 1000 ml glass 25 beaker with a 10 cm diameter. The stirrer employed was an IKA T50 Ultraturrax with an R1402 toothed disc dissolver having a toothed disc diameter of 5 cm. The solution was stirred on setting 1 (stirrer speed 4400 rpm). The pH of the solution was brought to 9 by dropwise addition of aqueous 25% strength ammonia solution and was maintained at pH 9 throughout 30 the precipitating operation. The temperature of the polymer solution was 37 0 C. Metered into this polymer solution at a rate of 5 ml/min were 80 ml of a mixture of DMF and water (70/30). In the course of this addition, a twofold phase transition was observed, from a homogeneous phase into an emulsion and then from an emulsion, finally, into a suspension. This was 35 followed by further metered addition of 86 ml of pure water. The precipitation was thereby concluded. This gave a suspension of P84 type 70 polymer particles in water and DMF. The particle size was determined in the suspension and was as follows: 25 zuiuuzIu foreign countries Particle size d10: 2.8 pm Particle size d50: 16.6 pm Particle size d90: 118.6 pm 5 Example 2: Effect of polymer solution pH on particle size Example 1 was repeated with the same settings, but the pH of the polymer solution was changed from pH 9 to pH 7, 8, 8.5 and 10. Apparent from 10 Table 1 below is the clear effect of the pH on the particle size. Table 1: pH d(10) [pm] d(50) [pm d (90) [pm] 7 42.682 159.953 511.542 8 13.128 65.774 235.991 8.5 5.552 27.335 124.737 9 2.771 16.557 118.570 10 1.244 3.604 26.590 In the case of P84 type 70, the increase in pH brings about a marked 15 reduction in the particle size of the resultant polyimide powder. Example 3: Effect of polymer solution solids content on particle size Example 1 was repeated at pH levels of 7 and 10, but with the solids content of the solution changed by dilution, starting from a 27 wt % 20 strength solution, using DMF as solvent, to 7.5, 10, 12.5, 15, 17.5, 20 and 22.5 wt %. The results are shown in Table 2 below. Table 2: pH 7 pH10 Concentration d(10) d(50) d(90) d(10) d(50) d(90) [%] [pm] [pm] [Pm] [Pm] [pm] [pm] 7.5 3.386 6.134 10.72 0.090 0.155 0.290 10 7.479 12.145 21.519 0.077 0.160 0.379 12.5 17.186 32.042 76.507 0.404 1.008 3.321 15 32.645 101.019 321.957 0.891 1.856 11.207 17.5 42.682 159.953 511.542 1.244 3.604 26.590 20 - - - 2.996 23.583 121.568 22.5 - - - 2.751 12.696 50.605 26 zuiuuziu -oreign Uountries It is clearly apparent that at constant pH, the particle size increases markedly as the solids concentration goes up. 5 Example 4: Effect of polymer solution solvent on particle size Example 1 was repeated at a solids content of 10 wt % of P84 type 70 in a variety of different solvents (DMAc, NMP, DMSO) at a pH of 7. Used as non 10 solvent in each case was a mixture of the respective solvent with water in a ratio of 70 to 30 wt %. The results are summarized in Table 3: Table 3: Solvent d(10) [pm] d(50) [pm] d(90) [pm] DMAc 1.724 3.245 5.861 NMP 1.341 2.147 3.430 DMSO 5.644 9.788 75.671 DMF 7.479 12.145 21.519 15 Table 3 shows that the preparation of powders works from different aprotic dipolar solvents. The resulting particle size, however, is different in different solvents. 20 Example 5: Effect of base used on particle size Example 4 was repeated. Instead of the use of ammonia as base, however, triethylamine was used in order to bring the solution to the desired pH. Powders of pH P84 type 70 are obtained having the particle sizes indicated 25 in Table 4 below. Table 4: Solvent d(10) [pm] d(50) [pm] d(90) [im] NEP 0.833 1.336 2.205 DMAc 1.491 2.674 4.705 NMP 1.323 2.095 3.309 DMSO 2.923 5.275 11.835 Table 4 demonstrates that using triethylamine as well produces powders 30 according to the process of the invention. 27 zu1iuuzIu foreign Jountries Example 6: Effect of dissolver speed on particle size 5 For experiments on the 6 1 scale, a pilot-scale dissolver from Mischtechnik is employed, with a planetary drive, on which the dissolver disc, a scraper and a temperature sensor are present in a triangular arrangement. The speed of the dissolver disc can be adjusted steplessly, and a thermal conditioning assembly allows precipitation at constant temperature. The 10 tank diameter is 250 mm, the dissolver diameter 90 mm. The ratio of tank diameter to dissolver disc diameter, D/d, is therefore about 1/3. The maximum speed of the dissolver disc is limited at 4000 min-', that of the planetary drive at 132 min-'. 15 The precipitations for determining the effect of the speed of the dissolver were all carried out at 45 0 C and pH 7.0 with 10% strength polymer solution of P84 type 70 in DMF. In addition, the rotation of the planetary drive, at 50 min- 1 , and the metering rate of the precipitant, at 110 g/min, were kept constant. Precipitations of 2500 g of polymer solution in each case were 20 carried out at 1000, 2000 and 3000 min-. This requires in each case 720 g of DMF/H 2 0 in a 70/30 ratio and 1440 g of H 2 0 as precipitants. Table 5 below shows the results from the precipitations. The peripheral speed of the dissolver disc is calculated from the following formula: v=d-n-n 25 u........peripheral speed in m/s d........dissolver disc diameter in m n........speed of dissolver disc in s-1 Table 5: Peripheral Precipitation Speed Particle size distribution speed [min-' u [m/s] d(10) d(50) d(90) [Ipm] [pm] [pm] 1 1000 4.7 7.013 22.190 68.072 2 2000 9.4 8.960 22.128 54.793 3 3000 14.1 9.181 20.583 42.046 30 As is evident in Table 5, the particle size (d90) decreases as the speed of the dissolver disc goes up, but there is an increase in the fine fraction 28 ZUidUU21U Foreign Countries (dlO) at high speeds. Furthermore, there is a narrowing of the particle size distribution as the selected peripheral speed goes up. 5 Example 7: Effect of precipitant metering rate on particle size In order to determine the effect of the metering rate of the precipitant, precipitations were carried out at metering rates of 70, 110 and 300 g/min. As described in Example 6, the precipitations were carried out under 10 constant conditions (at pH 7.0, with 2500 g of 10 wt % polymer mass, at 45'C, with a dissolver speed of 2000 min', 50 min- in the case of the planetary drive, and the same amount of precipitant). The precipitants are metered using a toothed wheel pump and control device 15 Reglo-Z from ISMATEC. The maximum conveying rate of the metering pump is limited at 300 g/min. Table 6 below shows the results of the particle size determination from the precipitated suspensions. 20 Table 6: Precipitation Metering rate Particle size distribution d(10) d(50) d(90) [gimin] [PM] [,PM] [pm] 1 70 1.831 90.426 229.866 2 110 1.943 160.411 469.697 3 300 2.510 157.143 506.797 As shown by Table 6, the particle size goes up as the metering rate increases, with the difference between 70 and 110 g/min being much greater than between 110 and 300 g/min. This means that above a certain point, the 25 effect of the precipitant metering rate becomes fairly insignificant. It is nevertheless clearly apparent that the particle size distribution comes out as much narrower at low metering rates than at high rates. 30 Example 8: Effect of polymer solution temperature on particle size In order to examine the effect of temperature on the particle size, the above experiments were carried out with P84 type 70 in DMF at a pH of 7, with 7.5% and 12.5% solutions, in each case at 60'C and at 80 0 C. The 29 ZUliUUZiU toreign countries results were subsequently compared with those from existing results at 38 0 C. A change is seen in the particle size distribution with temperature at all solids contents in Table 7 below. 5 Table 7: Solids content [%] Temperature [*C] d(90) [pm] 38 10.720 7.5 60 16.632 80 27.847 38 76.507 12.5 60 32.828 80 45.707 Example 9: Precipitation by addition of different non-solvents 10 Example 1 was repeated at a solids content of 10% P84 type 70 in DMF. Bases used to bring the solution to the desired pH were NaOH (pH 11.0) and triethylamine (pH 8.0). Instead of a DMF/water mixture (70/30), mixtures of DMF/ethanol (70/30) and DMF/isopropyl alcohol (70/30) were used as precipitants. 15 Table 8 shows the results of the particle size distribution from the precipitated suspensions. Table 8: Solids content Precipitant Base pH d(90) [pm] [%] Triethylamine 8.0 41.222 Ethanol NaOH 11.0 50.010 10 Isopropyl Triethylamine 8.0 82.579 alcohol NaOH 11.0 15.388 20 Example 10: Use of ultrasound as dispersing means In order to investigate the use of ultrasound as dispersing means, precipitations of 10% and 15% P84 type 70 solutions in DMF were carried out 25 using a Hielscher UP200S ultrasound processor. The solution was in this 30 201300210 Foreign Countries case additionally stirred at 500 rpm with a magnetic stirrer. Throughout the precipitation, the ultrasound processor was operated with an amplitude of 50%. Additionally, NaOH and triethylamine bases were used, as in Example 9. 5 Table 9 below shows the results from the particle size determination on the precipitated suspensions. Table 9: Solids Magnetic Ultrasound d(90) content Base pH stirrer speed amplitude [%] [pm] [%] [rpm] 15 TEA 8.0 384.675 50 500 10 NaOH 11.0 15.212 10 Example 11: Application of the precipitation process to different polymers Example 1 was repeated with different polymers. Matrimid@ 5218 polyimide 15 and Torlon® 4000T-MV polyamideimide were employed. Both polymers were dissolved at 5% (m/m) in DMF and then precipitated. Triethylamine was the base used to set the pH to 8.5. Table 10 shows the results from the particle size determinations on the 20 suspensions. Table 10: Solids Polymer class Polymer content [%] pH d(90) [pm] Mat rimid@ Polyimide 5218 509.176 5 8.5 Tor lon@ Polyamide-imide 0.834 4000T-MV 31

Claims (15)

1. Process for preparing polymers in powder form from polymer solutions, 5 characterized in that it comprises the following steps: a) preparing a polymer solution comprising a polymer or mixture of two or more polymers, selected from the group consisting of polyimides, polyetherimides, polyamideimides and polyamides, and at least one 10 solvent for said polymer or polymer mixture, b) adding at least one non-solvent or a mixture of at least one non solvent and at least one solvent, the terms non-solvent and solvent refer to the polymers listed in step a), with accompanying exposure to stabilizing energy, preferably shearing energy, to the solution 15 from step a) until a suspension is formed, c) optionally reducing the solvent and/or non-solvent content in the liquid phase of the suspension, d) removing the powder from the liquid phase of the suspension obtained by step b) or c), 20 e) optionally drying the powder.

2. Process according to Claim 1, characterized in that the polymer solution is modified during step a), in step al), wherein 25 step al) preferably comprising at least one of the following steps: al.1) diluting the polymer solution with the solvent used in the polymer preparation, or with another completely miscible solvent, al.2) diluting the polymer solution with a completely miscible non 30 solvent, in which case preferably up to 20% of non-solvent is admixed, and so as yet there is no precipitation of the polymer, al.3) filtering to remove solids from the polymer solution, al.4) concentrating the polymer solution, al.5) adding a polymer or additive which dissolves in the polymer 35 solution, al.6) adding additives in powder form which do not dissolve in the polymer solution and can be dispersed or suspended therein, al.7) replacing some or all of the solvent by a miscible solvent or mixture of solvent and non-solvent, so that as yet there is no 40 precipitation of the polymer. 32 2UIJUU21U Foreign Countries

3. Process according to Claim 1 or 2, characterized in that step a) comprises at least one of the following process steps: 5 a2) homogenizing the polymer solution, preferably by input of shearing energy, a3) adjusting the polymer solution temperature, a4) adjusting the polymer solution pH, a5) adjusting the polymer solution solids content. 10

4. Process according to Claim 3, characterized in that the pH of the polymer solution in step a4) is adjusted by addition of an acid or a base, preferably in that it is adjusted to a range from 2 to 15 10 or 6 to 11.

5. Process according to Claim 3 or 4, characterized in that the solids content of the polymer solution in step al) and/or step a5) 20 is adjusted to 1 to 50 wt %, preferably in the range from 1 to 40 wt %, more preferably 2 to 30 wt %, especially preferably from 5 to 25 wt % and very especially preferably 7 to 20 wt %.

6. Process according to any of Claims 3 to 5, 25 characterized in that the temperature of the polymer solution in step a3), i.e. before or at the beginning of step b), and/or the temperature of the suspension obtained during step b) is adjusted to and/or maintained at a range between -20 and 200 0 C, preferably 0 and 150'C, more preferably between 30 20 and 100 0 C, especially preferably between 20 and 80'C and very especially preferably between 30 and 60'C.

7. Process according to any of Claims 1 to 5, characterized in that 35 the procedure is carried out as a non-continuous procedure and in that in step a2) and/or b) a shearing assembly, preferably a propeller stirrer, inclined blade stirrer, disc stirrer, tumble disc stirrer, hollow blade stirrer, impeller stirrer, cross arm stirrer, anchor stirrer, paddle stirrer, gate stirrer, gas introduction stirrer, helical 33 ZUI0uuzIU rureign countries stirrer or toothed disc stirrer centrically, with or without planetary drive and close-clearance scraper, or an ultrasound assembly, is used or in that the procedure is carried out continuously, the solution 5 according to step a) being passed in step a2) and/or b) through an assembly, preferably an in-line disperser or in-line emulsification pumps, which introduces shearing energy into the solution, and at least one non-solvent or at least one mixture of solvent and non-solvent being metered in upstream and/or at the location of shearing to the solution. 10

8. Process according to Claim 7, characterized in that energy is input in step a2) and/or b) with a toothed disc stirrer which has a dispersing-unit shearing speed of 0.01 to 100 m/s, preferably 0.1 15 to 30 m/s, more preferably 1 to 30 m/s and very preferably 2 to 20 m/s, or in that energy is input in step a2) and/or b) with other, discontinuous or continuous, assemblies which develop a shearing field of the same magnitude as or greater magnitude than the above-defined toothed disc 20 stirrer.

9. Process according to any of Claims 1 to 8, characterized in that the polyimide or the polyamideimide is obtained by polycondensation of 25 at least one aromatic tetracarboxylic (di)anhydride and/or of an aromatic tricarboxylic acid, preferably selected from the group consisting of 3,4,3'4'-benzophenonetetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,4,3'4' biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, 30 sulphonyldiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2 propylidenediphthalic dianhydride and 1,3,4-benzenetricarboxylic acid, and at least one aromatic diisocyanate, preferably selected from the group consisting of toluene 2,4-diisocyanate, toluene 2,6 35 diisocyanate, 4,4'-methylenediphenyl diisocyanate, 2,4,6-trimethyl 1,3-phenylene diisocyanate and 2,3,4,5-tetramethyl-1,4-phenylene diisocyanate, or in that the polyimide is obtained by reaction of at least one 40 tetracarboxylic (di)anhydride, preferably selected from the group 34 zu1iuuzIu toreign uounrries consisting of 3,4,3'4'-benzophenonetetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,4,3'4' biphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, sulphonyldiphthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2 5 propylidenediphthalic dianhydride and 4,4 ' - (4,4 ' isopropylidenediphenoxy)bis(phthalic anhydride); and at least one diamine, preferably selected from the group consisting of 2,4-diaminotoluene, 2,6-diaminotoluene, 4,4' 10 diaminodiphenylmethane, 2,4,6-trimethyl-1,3-phenylenediamine, 2,3,4,5 tetramethyl-1,4-phenylenediamine, bis(4-amino-3,5 dimethylphenyl)methane, bis(4-amino-3-methylphenyl)methane, 1,3 phenylenediamine, 1,4-phenylenediamine, 4,4'-diaminodiphenyl ether, 5(6)-amino-i-(4' aminophenyl)-1,3,4-trimethylindane, and subsequent 15 imidization of the polyamic acid.

10. Process according to Claim 9, characterized in that use is made as polymer of 20 a polyimide, comprising 0 0 -- N (A) 0 0 0 0 N-N CH, 35 2UIAUU21U Foreign countries CH 3 (L2) (L3) CH 3 H2(A) where 0 x 0.5 and 1 y 0.5 and R corresponds to one or more identical or different radicals selected from the group consisting of 5 L1, L2, L3 and L4; more preferably a polyimide with x = 0, y = 1 and R = 64 mol% L2, 16 mol% L3 and 20 mol% L4 or a polyimide with x = 0.4, y = 0.6 and R = 80 mol% L2 and 20 mol% L3, and/or a polymer having the following structure CH- C 100 10 fHo Cs o and/or a polyamideimide, with the composition indicated below 0 H N-R- --- x 0 0 15 36 zuijuuziu foreign countries CH, (L2) (LD) OH 3 ACH2) where the radical R corresponds to one or more identical or different radicals selected from the group consisting of L2, L3 and L4. 5

11. Process according to any of Claims 1 to 10, characterized in that use is made of non-solvents or non-solvent mixtures which are completely miscible with the solvent, in the temperature range used for the process according to claim 1. 10

12. Process according to Claim 11, characterized in that a solvent selected from the group consisting of dimethylformamide, dimethylacetamide, dimethylpropionamide, N-methylpyrrolidone, N 15 ethylpyrrolidone, dimethyl sulphoxide, sulpholane, tetramethylurea, tetrahydrofuran, 1,4-dioxane, 1,3-dioxane and 1,3-dioxolane, preferably dimethylformamide, dimethylacetamide and N methylpyrrolidone, or mixtures thereof, is used and 20 in that use is made as non-solvent of a liquid selected from the group consisting of water, alcohols such as methanol, ethanol and isopropanol or ketones such as acetone or methyl ethyl ketone, preferably water and C1 - C3 alcohols, or mixtures thereof, 25

13. Process according to either of Claims 11 and 12, characterized in that 37 2UIIUU21U Foreign countries in step b) a mixture of 10 to 90 wt % of solvent and 90 to 10 wt % of non-solvent, preferably of 20 to 80 wt % of solvent and 80 to 20 wt % of non-solvent and more preferably of 50 to 75 wt % of solvent and 35 to 50 wt % of non-solvent is used. 5

14. Polymer particles characterized in that the polymer comprises a polymer or mixtures of two or more polymers, selected from the group consisting of polyimides, polyetherimides, 10 polyamideimides and polyamides, and in that the particles have an approximately spherical structure.

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