CA2152279A1

CA2152279A1 - Micropowders

Info

Publication number: CA2152279A1
Application number: CA002152279A
Authority: CA
Inventors: Michael Schoenherr; Juergen Ahlers; Hermann Buchert
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1993-01-08
Filing date: 1994-01-04
Publication date: 1994-07-21
Also published as: EP0678109A1; BR9405783A; ATE168393T1; AU5859394A; GR3027603T3; WO1994015999A1; DK0678109T3; JP3369181B2; CN1116428A; ES2118378T3; EP0678109B1; JPH08505180A

Abstract

The invention concerns a micropowder with spherical particles having an essentially smooth surface structure and containing as the essential component polyarylene ether sulphones or ketones and obtained by prilling melts of such compounds of by spray-drying solutions thereof.

Description

~ 0050/43792 21~227~

Micropowders The present invention relates to micropowders which have spheri-5 cal particles possessing an essentially smooth surface structure, contain polyarylene ether sulfones or polyarylene ether ketones as essential components and are obtainable by prilling melts or spray-drying their solutions. The present invention furthermore relates to a process for the preparation of these micropowders 10 and to the use thereof. The present invention also relates to aqueous dispersions which contain the micropowders and to coat-ings produced therefrom.

Micropowders based on polyarylene ether sulfones or polyarylene 15 ether ketones are known per se and are used, for example, as ad-hesion promoters between metallic surfaces and polytetrafluoroe-thylene, for example for producing coatings having a nonadhesive effect and good sliding behavior (cf. for example GB 1 426 342).
Such known micropowders are obtained by rendering the substrates 20 brittle by cooling and then m; 11; ng them (cf. for example EP-A2-377 170). W0 91/00876 discloses that micropowders of polyary-lene ether sulfones are also obtA;n~hle by processing the poly-arylene ether sulfones with a liquid to give a paste, emulsifying the latter in water with vigorous stirring and drying the emul-25 sion. The micropowders obtainable by milling all have irregularangular surfaces. For example, this has an adverse effect on the flow and the bulk density of the powders and on the behavior of the powders in the fluidized bed. Moreover, surfaces cannot be very uniformly coated, as is required for many intended uses. The 30 micropowders prepared from an emulsion with the action of a shear gradient contain oval to elongated particles which, like the milled particles, are not arranged satisfactorily on the surface to be coated. GB-A 2 151 202 disclosed that microcapsules which consist of an oily substance enclosed by walls of polysulfone can 35 be prepared by spraying corresponding solutions by means of a pressure nozzle. Since certain applications require particles having a very smooth surface structure, neither the particles ob-tained from the emulsion nor the microcapsules meet these re-quirements. Furthermore, EP-A2-441 047 states that small par-40 ticles having a porous surface are obtained if solutions of amor-phous thermoplastics, such as polyarylene ether sulfones, are spray-dried.

` ` 0050/43792 It is an object of the present invention to provide micropowders which are based on polyarylene ether sulfones or polyarylene ether ketones and which consist of spherical particles having a regular surface.

We have found that this object is achieved by the novel micro-powders.

The novel micropowders contain, as essential components, polyary-10 lene ether sulfones or polyarylene ether ketones. They may of course also contain mixtures of polyarylene ether sulfones and polyarylene ether ketones. Surprisingly, the novel micropowders are obtainable by melting or dissolving the polyarylene ether sulfones or polyarylene ether ketones or reducing their viscosity 15 by means of a suitable liquid and then prilling or spray-drying them.

According to the invention, the particles thus obtainable are regular and round and have a virtually poreless surface. The 20 volume average particle diameter is as a rule 1 ~m or more. It may also be less but it is in general not less than 0.5 ~m. In general, the average particle diameters may be up to 80 ~m. It is also possible for them to be slightly larger, for example 100 ~m.
Larger average particle diameters are generally of no interest 25 for most applications, in particular for the preparation of aqueous dispersions. The average particle diameter is preferably from 2 to 70 ~m, particularly preferably from 2 to 50 ~m, for example from 5 to 50 ~m, very particularly preferably from 1 to 20 ~m, in particular from 1 to 10 ~m. The particles are essen-30 tially solid, ie. they are not hollow and generally have the den-sity of the polyarylene ether sulfones or polyarylene ether ke-tones on which they are based. However, the density of the par-ticles may also be slightly below this, for example if small amounts of gas are enclosed.
The novel micropowders have a narrow particle size distribution.
The relative span factor ~ may be stated as a measure of the width of the particle size distribution (cf. A.H. Lefebvre:
Atomization and Sprays, Hemisphere Publishing Corporation, 1989, 40 page 100, equation 3.40). The relative span factor of the novel micropowders is in general from 1 to 2. However, it may be above this but in general is not more than 2.5. The span factors are preferably up to about 1.5, very particularly preferably less than 1.

` 0050/43792 215227g The novel micropowders contain, as essential components A, poly-arylene ether sulfones or polyarylene ether ketones. These con-tain repeating units I

N Art-T - Arl~-Zt-Ar2 _ Q-~Ar3 (I) t and q independently of one another may be identical or different and are each 0 or an integer from 1 to 3. N is either 10 -0- or -S-, preferably -0-. T and Q independently of one another may be identical or different. They may be a chemical bond or a group selected from -0-, -S-, C=0, SsO, -SO2-, -N=N-, -RaC=CRb-and -CRCRd. Among these, -0-, C=O, -S02- and -CRCRd- are particu-larly preferred. T and Q are preferably also a chemical bond. Ra 15 to Rd independently of one another may be identical or different and may each be either hydrogen or C1-C10-alkyl, such as methyl, ethyl, propyl or tert-butyl, preferably hydrogen or methyl. Fur-thermore, Rc and Rd may also be Cl-C10-alkoxy, Cl-C10-alkylaryl or C6-Cl8-aryl. The preferred groups include methoxy, ethoxy, pro-20 poxy, tert-butoxy, benzyl and phenyl. The abovementioned groups may each furthermore be substituted by fluorine and/or chlorine.
Examples are trifluoromethyl and p-chlorophenyl. According to the invention, Z is a group selected from C=0, S=0 and -S02-, C=0 and -S02- being particularly preferred. Ar to Ar3 independently of one 25 another may have the same meAn;ngs or may differ from one another. According to the invention, they are each C6-Cl8-aryl.
These include phenyl, biphenyl and naphthyl. The aryl groups are preferably unsubstituted but may have substituents selected from the group consisting of Cl-ClO-alkyl, C1-C10-alkylaryl, C6-C18-30 aryl, Cl-C10-alkoxy and halogen. Examples of suitable substituents are methyl, ethyl, propyl, isopropyl, n-butyl, isopentyl, n-hexyl, methoxy, ethoxy, propoxy, butoxy, benzyl, ethylphenyl, phenyl, fluorine and chlorine.
35 Some of the preferred repeating units I are listed below:

o ~ 21~2279 ~o~so2~L (Il) 0~ 1 ~0~ S02~ ( I2 ) ~ ~ ~so2~3 (I3) ~o~o~o~3so2~3 ( I4 ) ~3 ( I5 ) 20 ~ ~52~~~0~ (I6) ~ ~3 o~3 SO2 ~S02 g~3 ( I 7 ) ~o~S0z \~ o~S2~3 (I8) ~o~3 0~S02~ ( Ig ) ~~ O~SO2 = soZ~3 (Ilo) ~~ _~o~so~S~3 ( Ill ) ~0~ ~ (~ SO~ C~3 ( I 12 ) ` ' 0050/43792 21~2279 5~ ~ Z~C~C~3 (Il3) ~ 0~ SO~O~ So~S~3 ( I 14 ) ~ O ~ O ~ C ~ (I15) --~ ~3 C ~:~ C ~3 (I16) O O
~ O ~ O ~ C ~ C ~3 (I17) 25 ~ \~ ~ C ~L (Il8) O O
O ~ O ~ C ~ C ~3 (Ilg) ~ O ~ O ~ C ~ (I20) O O
~ O ~ O ~ C ~ C ~L ( I21 ) 400 o ~o ~3 o ~ c ~ c ~L (I22) 0050/43792 2 1 ~ 2 2 7 9 ` 6 O O
~o ~ c ~ o ~ c ~L (I23) O O

10~3/ ~ ~ C ~} (I2~,) o o 15c ~ o ~ C ~ C ~ (I25) O o O

~0 ~ C ~ O ~ C ~ C ~ (I26) O O

~ ~3~ ~ C ~ c ~ ( I27) Very particularly preferred micropowders are those which contain, as essential components A, polyarylene ether sulfones or polyary-lene ether ketones having structural units (Il), (I2), (I25) or 30 (I26). These include, for example, micropowders which contain, as essential components A, polyarylene ether sulfones having from 0 to 100, preferably from 5 to 95, mol% of structural units (Il) and from 0 to 100, preferably from 5 to 95, mol% of structural units (I2)-35The polyarylene ether sulfones or polyarylene ether ketones may furthermore be copolymers or block copolymers in which polyary-lene ether segments and segments of other thermoplastic polymers, such as polyamides, polyesters, aromatic polycarbonates, polyes-40 ter carbonates, polysiloxanes, polyimides or polyether imides,are present. The molecular weights of the blocks or of the grafts in the copolymers are as a rule from 1000 to 30,000 g/mol. The blocks having different structures may be arranged alternately or randomly. The amount by weight of the polyarylene ether sulfones 45 or polyarylene ether ketones in the copolymers or block copoly-mers is in general at least 3, preferably at least 10, % by weight and may be up to 97 % by weight. Preferred copolymers or ~ 0050/43792 2 1 ~ 2 2 7 ~
. .

block copolymers are those containing up to 90 % by weight of polyarylene ether sulfones or polyarylene ether ketones. Copolym-ers or block copolymers containing from 20 to 80 % by weight of polyarylene ethers are particularly preferred.

The polyarylene ether sulfones or polyarylene ether ketones may contain any terminal groups, for example halogen, methoxy, benzy-loxy, phenoxy or amino. Preferred terminal groups are halogen and methoxy.
In general, the polyarylene ether sulfones or polyarylene ether ketones have number average molecular weights Mn from 15,000 to 60,000 g/mol and relative viscosities of from 0.25 to 0.95 dl/g.
Depending on the solubility of the polyarylene ether sulfones or 15 polyarylene ether ketones, the relative viscosities are measured either in 1 % strength by weight N-methylpyrrolidone solution, in a mixture of phenol and dichloromethane or in 96 ~ strength sulfuric acid, in each case at 20 C and 25 C.

20 The polyarylene ether sulfones or polyarylene ether ketones which are suitable as component A are known per se and can be prepared by methods which are known per se. Polyarylene ether sulfones or polyarylene ether ketones are formed, for example, by condensa-tion of aromatic bishalogen compounds and the alkali metal double 25 salts of aromatic bisphenols. They can also be prepared, for example, by autocondensation of alkali metal salts of aromatic halophenols in the presence of a catalyst. DE-A-38 43 438 gives, for example, a detailed list of suitable monomers. Suitable pro-cesses are described, inter alia, in US-A-3 441 538 and 30 4 108 837, DE-A1-27 38 962 and EP-Al-361. Polyarylene ether ketones are also obtainable by electrophilic (Friedel-Crafts) polycondensation, as described, inter alia, in WO 84/03892. For the formation of carbonyl bridges in electrophilic polycon-densation, either dicarbonyl chlorides or phosgene are reacted 35 with aromatics which contain two hydrogen atoms replaceable by electrophilic substituents, or an aromatic carbonyl chloride which contains both an acyl chloride group and a substitutable hydrogen atom is subjected to autopolycondensation.
40 Preferred process conditions for the synthesis of polyarylene ether sulfones or polyarylene ether ketones are described, for example, in EP-A-113 112 and 135 130. The reaction of the mono-mers in aprotic solvents, in particular N-methylpyrrolidone, in the presence of an anhydrous alkali metal carbonate, in particu-45 lar potassium carbonate, is particularly suitable. Reacting themonomers in the melt has also proven advantageous in many cases.

0050/43792 21 ~ 2 2 7 According to the invention, the micropowders may contain, as es-sential components B, polyarylene ether sulfones or polyarylene ether ketones which are obtainable by reacting a polyarylene ether sulfone or polyarylene ether ketone A with a reactive com-5 pound. The reactive compounds contain, in addition to a C-C
double or triple bond, one or more carbonyl, carboxyl, carboxy-late, anhydride, amide, carboxylic ester, amino, hydroxyl, epoxy, oxazoline, urethane, urea, lactam or halobenzyl groups.

10 Typical suitable compounds are, for example, maleic acid, methyl-maleic acid, itaconic acid, tetrahydrophthalic acid, their anhy-drides and imides, fumaric acid, the mono- and diesters of these acids, for example of C1-C18-alkanols, and the mono- or diamides of these acids, such as N-phenylmaleimide or maleic hydrazide.
a,~-unsaturated dicarboxylic acids and their anhydrides, diesters and monoesters having the following general structures IV and V

oR30 ~ (IV) Rl R2 ~~
~ (V) Rl R2 where Rl, R2, R3 and R4 independently of one another may each be hydro-35 gen or C1-C18-alkyl, are preferably used.

Particularly suitable compounds are maleic anhydride, fumaric acid and itaconic acid.
The polymers and the reactive compound can be reacted with one another, for example, in an aromatic solvent. Solvents which have proven particularly suitable are chlorobenzene, o-dichlorobenzene and N-methylpyrrolidone. In general, a conventional theoretical 45 initiator is used. The reaction is carried out in general at 75 - 150 C. The reaction product is obtained by precipitation with a conventional precipitating agent, such as a low molecular 0050/43792 ~ 2152279 ~ ~ g weight alcohol or ketone, or by removing the solvent (for example in a devolatilization extruder or thin-film evaporator).

However, the reactants may also be reacted at, for example, 5 270 - 350 C in the melt in a continuous or batchwise mixing unit (for example a single-screw or twin-screw extruder or a kneader).

The reactive compound is preferably metered in liquid form into the melt of the polymer, in particular within the kneading zone 10 of a mixing unit.

Modified polyarylene ether sulfones or polyarylene ether ketones A which have been obtained by reacting from 80 to 99.9, in par-ticular from 90 to 99, % by weight of the unmodified polyarylene 15 ether sulfones or polyarylene ether ketones A with from 0.1 to 20, in particular from 1 to 10, % by weight of the reactive com-pound are preferably used as polyarylene ether sulfones or poly-arylene ether ketones B in the novel micropowders.

20 Polyarylene ether sulfones grafted with from 0.1 to 1.5 % by weight of maleic anhydride are particularly preferred as compo-nent B. Polyarylene ether sulfones containing from 5 to 95 mol~
of units I1 and from 5 to 95 mol% of units I2 are preferred.

25 Polyarylene ether sulfones having from 80 to 95, preferably from 85 to 95, mol% of units of the formulae I2 and I1 and accordingly from 5 to 20, preferably from 5 to 15, mol% of units of the for-mulae Il and I2, respectively, may be mentioned in particular here.
The compounds described in the technical literature (eg.
J.K. Kochi, Free Radicals, J. Wiley, New York, 1973) may as a rule be used as free radical initiators.
35 The free radical initiators are usually used in amounts of from about 0.01 to about 1 % by weight, based on the polyarylene ether sulfones or polyarylene ether ketones A employed. Mixtures of different free radical initiators may of course also be used.
40 According to the invention, the micropowders may also contain mixtures of the components A and B. In addition to the essential components, the micropowders may also contain, for example, up to 40 % by weight of further additives, such as flameproofing agents, colorants or stabilizers.

~ ` 0050/43792 21 ~2279 The spray-drying of the polyarylene ether sulfones or polyarylene ether ketones is carried out by atomizing the melts or solutions into a gas which is inert under the process conditions, such as air or nitrogen. The polyarylene ether sulfones or polyarylene 5 ether ketones are preferably dissolved in a solvent before being sprayed.

Suitable solvents are dipolar aprotic liquids. The suitable sol-vents include N-substituted amides, sulfoxides and sulfones.
10 Examples are N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfone, tetramethylene sulfone (sulfolane) and diphenyl sulfone. Among these, N-methylpyrroli-done, dimethyl sulfoxide and dimethylformamide are particularly preferred. Diphenyl sulfone, ditolyl sulfone and trifluoroacetic 15 acid are especially suitable solvents for particularly sparingly soluble polyarylene ether ketones.

Either the atomization temperature can be chosen so that the melt or the solution has the viscosity suitable for atomization or the 20 solids content of the solution can be chosen so that the solution has the suitable viscosity at a certain atomization temperature, the latter being preferred. The reduced viscosity of the solution at the atomization temperature is up to 8000 mPa.s. It may also be higher, for example 10,000 mPa.s. In general, solutions having 25 higher viscosities are difficult to atomize. The reduced viscosi-ties are preferably 1000, particularly preferably from 5 to 500, in particular from 10 to 100, mPa.s.

In general, solutions which are at room temperature are atomized.
30 In order to reduce their viscosity, it may be necessary to spray the solutions at elevated temperatures, for example at from 50 to 100 C. As a rule, however, the atomization temperatures are below the boiling point of the particular solvent.

35 Pneumatic atomizers, such as multimaterial nozzles, in particular two-material nozzles, may be used for atomization. Examples of these are double-flow or triple-flow two-material nozzles. In order to generate angular momentum or flow deflection, the two-material nozzles may contain baffles. These may be mounted both 40 on the gas side and on the liquid side. It is also possible to use ultrasonic atomizers.

The ratio of mass throughput of atomizing gas to mass throughput of liquid is in general greater than 2, particularly advanta-45 geously from 3 to 10. As a rule, gas pressures of 5 bar or more 11are required. A gas pressure of more than 100 bar is rarely necessary. In general, the gas pressures are from 10 to 70 bar.

After the atomization, the liquid droplets can be dried in a dry-5 ing chamber, for example in a spray tower of known design (cf.
for example K. Masters: Spray Drying Handbook, Leonhard Hill Books, London 1972). The solvent can be evaporated either at at-mospheric pressure or at reduced pressure. The heat required for evaporating the solvent is preferably supplied at the top of the 10 tower by means of an inert drying gas. A particularly suitable drying gas is nitrogen. However, other gases, such as carbon dioxide or air, may also be used. The gas temperature at the top of the drying tower is preferably greater than the evaporation temperature of the solvent and may be from room temperature to 15 500 C. In general, it is at 100 C or more, preferably from 200 to 300-C.

The drying gas preferably flows together with the liquid droplets through the drying tower and is sucked off at the outlet of the 20 tower together with the dry material. The gas temperature at the outlet of the tower depends on the desired residual solvent con-tent of the powder. It may be from room temperature to slightly less than the gas temperature at the top of the drying tower. As a rule, it is 50 C or more, for example from 120 to 170 C. In 25 general, temperatures greater than 200 C are not required.

The powder can in general be separated from the gas stream in a conventional manner by filters or cyclones. Filters for sepa-rating off solids are preferably used for the preparation of the 30 novel micropowders.

The residual solvent content of the novel micropowder without subsequent drying is in general not more than 5 %, in particular less than 2 %. In order further to reduce the residual solvent 35 content, the spray drying may be followed by a subsequent drying procedure, which can be combined with subsequent cooling. The ~ subsequent drying may be carried out, for example, in a fluidized bed.
40 In the spray drying, it is possible concomitantly to use spray systems. Examples of spray systems are fine-particled inorganic materials, such as silica, hydrophobic silica or alumina, and in particular polytetrafluoroethylene. The spray systems are used, as a rule, in amounts of from 0.1 to 20, in particular from 1 to 45 5, % by weight, based on polyarylene ether sulfone or polyarylene ether ketone, calculated as 100 % strength.

0050/43792 ~ 1 ~ 2 2 7 ~

The novel micropowders are particularly suitable for coating sur-faces. Said micropowders can preferably be used for coating me-tallic surfaces. The micropowders are very particularly suitable for producing surfaces having sliding properties or antiadhesion 5 coatings for articles of all types, such as sliding bearings, household appliances or electronic components. This may be effected, for example, by means of a fluidized-bed coating pro-cess or by applying a dispersion of the micropowder. It is also possible to coat surfaces by spraying the micropowder, for 10 example with the aid of an electrostatic field, onto the surface.

The novel micropowders may be dispersed in nonsolvents, prefer-ably in water. The aqueous dispersions usually contain from 5 to 50, preferably from 10 to 30, % by weight of micropowder. In 15 addition to the micropowder, the aqueous dispersions may also contain thermoplastics in dispersed form. Preferred plastics are fluorine-containing olefin polymers, in particular polytetra-fluoroethylene. It is also possible to add dispersants, such as polyvinyl alcohol or glycerol, to the dispersions. The disper-20 sions may furthermore contain flow assistants and pigments andmay, for example, be sprayed or brushed onto the surface.

Examples 25 Determination of the particle sizes The particle sizes were determined by means of a particle size analyzer (Helos model from Sympatec). For this purpose, 1 g of the micropowder in each case was dispersed in 100 ml of H2O with 30 the addition of a surfactant by means of ultrasonics, and 1 ml of the dispersion thus obtained was taken and was once again dis-persed in 100 ml of water. The particle sizes were measured by laser diffraction (laser diffraction particle size measuring instrument Cilas 715).
Example 1 A polyarylene ether sulfone cont~;n;ng essentially repeating units I

~O~S02~ (Il) 45 and having a viscosity number of 52 ml/g (measured in a 1 %
strength by weight solution in 1:1 phenol/1,2-dichlorobenzene at 25 C) and a volume flow index of 140 ml/10 min (measured at 360 C) . 0050/43792 _ 21 522 73 ~ .

was used. A 10 % strength by weight solution of this polyarylene ether sulfone in N-methylpyrrolidone was prepared. This solution, which had a reduced viscosity of 50 mPa.s, was atomized at 25 C in an ultrasonic atomizer (US 1, type 7/0.017.16.60 from Lechler).
5 The drying chamber used was a drying tower having a diameter of 20 cm and a length of 2 m. The nitrogen used as drying gas was at 205 C at the top of the tower. The temperature at the outlet of the tower was 150 C. The throughput of the drying gas was 20 kg/h and that of the solution was 300 g/h.
Spherical particles having a smooth surface structure and a num-ber average diameter of 20 ~m were obtained. The residual solvent content of the powder was 5 %. The particles are shown in Figures 1-3.
Example 2 A mixture of 16 % by weight of the polyarylene ether sulfone de-scribed in Example 1 and N-methylpyrrolidone was prepared. This 20 solution, which had a reduced viscosity of 200 mPa.s at room tem-perature, was atomized in a pneumatic two-material nozzle having a 0.5 mm liquid insert (model 970 from Schlick) at 2 bar. The liquid throughput was 300 g/h. Nitrogen at 220 C served as the nozzle gas. The drying chamber used was the drying tower de-25 scribed under Example 1. Nitrogen, which was at 180 C at the topof the drying tower, was used as the drying gas. The nitrogen temperature at the outlet of the tower was 155 C.
Spherical particles having a smooth surface and a number average 30 diameter of 6.5 ~m were obtained. 96 % by weight of the micro-powder comprised particles having a diameter of less than 24 ~m.
The relative span factor was 2.5. The particle density was 1.37 g/ml and the bulk density of the powder was 200 g/l.

35 Figures 4 and 5 show particle size distributions as typically ob-tained in the case of the novel spray drying of the polyarylene ether sulfone stated under Example 1, dissolved in N-methylpyrro-lidone, in further experiments.
40 Figures 6 and 7 show scanning electronmicrographs of the novel micropowders typically obtained in further experiments and com-prising the polyarylene ether sulfone stated under Example 1 and obtained by spray drying from N-methylpyrrolidone solutions.

Claims

We claim:

1. A micropowder having spherical particles possessing an essen-tially smooth surface structure, containing, as an essential component, a polyarylene ether sulfone or polyarylene ether ketone, and having a density which essentially corresponds to that of the polyarylene ether sulfone or polyarylene ether ketone, obtainable by prilling the melt thereof or spray-drying a solution thereof.

2. A micropowder as claimed in claim 1, containing, as essential components, A) a polyarylene ether sulfone or polyarylene ether ketone containing repeating units I

?N?Ar?T?Ar1t?Z?-Ar2?Q?qAr3? (I) where t and q may each be 0 or an integer from 1 to 3, N
may be -O- or -S-, T and Q may be a chemical bond or a group selected from -O-, -S-, C=O, S=O, -SO2-, -N=N-, -RaC=CRb- or -CRcRd-, Ra and Rb may each be hydrogen, C1-C10-alkyl, Rc and Rd may each be hydrogen, C1-C10-alkyl, C1-C10-alkoxy, C1-C10-alkylaryl or C6-C18-aryl, where each of the abovementioned groups may furthermore be substituted by fluorine or chlorine, Z may be a group selected from C=O, S=O and -SO2- and Ar, Ar1, Ar2 and Ar3 are each C6-C18- aryl, each of which may have substituents selected from C1-C10-alkyl, C1-C10-alkylaryl, C6-C18-aryl, C1-C10- alkoxy and halogen, or a random copolymer or block copolymer thereof or B) polyarylene ether sulfone or polyarylene ether ketone ob-tainable by reacting A with a reactive compound which, in addition to a C-C double or triple bond, contains one or more carbonyl, carboxyl, carboxylate, anhydride, amide, imide, carboxylic ester, amino, hydroxyl, epoxy, oxazo-line, urethane, urea, lactam or halobenzyl groups, or a random copolymer or block copolymer thereof.

3. A micropowder as claimed in claim 1 or 2, containing, as an essential component, a polyarylene ether sulfone containing from 5 to 95 mol% of repeating units II

II (I2) and from 5 to 95 mol% of repeating units III

(I2) .

4. A micropowder as claimed in any of claims 1 to 3, wherein the average particle diameter is from 1 to 100 µm.

5. A micropowder as claimed in any of claims 1 to 4, obtainable by spray drying a polyarylene ether sulfone solution, the solvent used being N-methylpyrrolidone, dimethyl sulfoxide or dimethylformamide.

6. A process for the preparation of a micropowder possessing an essentially smooth surface structure, containing, as an es-sential component, a polyarylene ether sulfone or polyarylene ether ketone, and having a density which essentially corre-sponds to that of the polyarylene ether sulfone or polyary-lene ether ketone, wherein a solution of the polyarylene ether sulfone or of the polyarylene ether ketone is spray-dried.

7. Use of a micropowder as claimed in any of claims 1 to 6 for the preparation of aqueous dispersions.

8. An aqueous dispersion containing a micropowder as claimed in any of claims 1 to 7.

9. A coating produced using an aqueous dispersion as claimed in

claim 8.