WO2025168379A1 - Solvent soluble polyimide powders and a method for making them - Google Patents

Abstract

The invention relates to novel solvent soluble polyimide powders having high molecular weight and improved properties, which can be prepared in a simple way by cutting fibres, which have been prepared from a polyimide or polyamic acid solution in a dipolar aprotic solvent, by reacting one or more aromatic tetracarboxylic acid dianhydrides with one or more aromatic diisocyanates respectively aromatic diamines. Cutting such fibres to an average length (x_{50, LF}) of from 30 to 250 μm can be done with a guillotine cutting machine, provides low dust forming powders with a narrow particle size distribution.

Description

Solvent soluble polyimide powders and a method for making them

The invention is directed at solvent soluble polyimide powders with improved properties, in particular good solubility, good processability and transportability with lower safety efforts, good mechanical properties and high molecular weight, and an efficient method for making these powders.

US 3,708,458 discloses the preparation of a solvent soluble polyimide by reacting 3,3’,4,4’-benzophenonetetracarboxylic acid dianhydride and a mixture of 4,4’-methylenebis(phenyl diisocyanate) and 2,4- and 2,6-toluene diisocyanate in dimethylformamide, and precipitation of the polymer by introducing the polyimide solution into a polar solvent and drying of the precipitated polymer.

US 4,016,227 teaches that sticking of precipitated polyimide polymer can be prevented by introducing droplets or thin strands of a polyimide solution in a dipolar aprotic solvent into water. The precipitated polyimide obtained can then be milled to a polyimide powder.

Polyimide powders prepared by precipitation in water as described before are commercially available from Ensinger Sintimid GmbH under the trade name P84®. These powders are used for coating components of electrical and electronic devices by processes, where the powder is redissolved in a dipolar aprotic solvent and the component is coated with the resulting polymer solution. The powders are also used for making polyimide shaped bodies by a hot compression molding process with compression and sintering of the powder. The precipitation and grinding process is simple but leads to a significant loss of molecular weight of the polyimide. In addition the polymers require high safety efforts during transport and processing.

EP 0279 807 A2 discloses a method for preparing powders of P84® polyimide where precipitation is carried out in the swirl cone of a dual fluid nozzle to produce a worm-shaped precipitate, which is collected as a fleece, washed, dried in a high frequency induction drier, followed by several milling steps. This complex process provides polyimide powders with higher molecular weight.

The prior art precipitation and milling processes provide polyimide powders which have a broad particle size distribution, often low molecular weight and poor processability. Due to high dust formation these polyimide powders require cost intense safety measures when being transported and processed. Sieving out the small particles fraction to reduce dust formation is not economic since the product loss is high and re-dissolution, re-precipitation and re-milling of the sieved-out fraction would cause further loss of molecular weight and generate additional production costs, while again a high amount of small particles would be obtained.

EP 3 375 609 A1 discloses resin powders with pillar-like shape for additive manufacturing by a powder bed fusion process and a method for preparing these powders by melt spinning of a thermoplastic resin and cutting of the spun fibres. The obtained particles after cutting are subjected to a spheroidizing treatment, including a melting process of the thermoplastic polymer, to round edges of the powder. The document mentions polyimide as an example of a suitable thermoplastic resin. However, aromatic polyimides, such as the P84® polyimide, have high glass transition temperatures and cannot be processed by melt spinning. The process of EP 3 375 609 A1 is complex and cost intensive.

US 3,985,934 and US 4,801 ,502 disclose the preparation of aromatic polyimide fibres by wet spinning or dry spinning of a solution of the polyimide in a dipolar aprotic solvent. The resulting fibres are used for hot gas filtration and producing heat protective clothing. Bag filters comprising needle felts of P84® fibres prepared by dry spinning are commonly used for hot gas filtration in cement production and in power plants.

Accordingly, a high demand exists for polyimide powders having good solubility, good processability and transportability with lower safety efforts, good mechanical properties and high molecular weight.

Object of the invention was to provide new, solvent soluble polyimide powders not having the disadvantage of the polyimide powders of the prior art respectively having these disadvantages to a reduced degree. Another object of the invention was to provide an improved process for production of the new solvent soluble polyimide powders.

A specific object of the invention was to provide solvent soluble polyimide powder having a higher molecular mass and/or a higher bulk density and/or better solubility compared to commercially available polyimide powders made from the same polyimide respectively to polyimide powders made from the same polyimide but being precipitated in a water bath, followed by washing, drying and grinding.

Another specific object of the present invention was to provide new solvent soluble polyimide powders showing improved processability and transport property requiring less safety efforts, in particular less safety measures to avoid dust explosions, than commercially available polyimide powders made from the same polyimide respectively to polyimide powders made from the same polyimide but being precipitated in a water bath, followed by washing, drying and grinding.

Preferably the particles should have a homogeneous and narrow particle size distribution as well as improved mechanical properties compared to commercially available polyimide powders made from the same polyimide respectively to polyimide powders made from the same polyimide but being precipitated in a water bath, followed by washing, drying and grinding.

Also, an object of the invention was to provide solvent soluble polyimide powder being suitable for a broad range of applications. The polyimide powders of the invention should preferably be soluble in a broad range of solvents.

An object of the present invention was to provide a new process for manufacture of solvent soluble polyimide powders being technically and/or economically beneficial compared to precipitation processes used in the prior art. With the process of the invention it should be possible to produce soluble polyimide particles with a homogeneous and narrow particle size distribution without the need for sieve fractioning which usually causes high waste material outside the desired particle size. Further benefits not explicitly mentioned here become evident from the contact of the subsequent description, examples, claims and figures.

The inventors of the present invention surprisingly found out that solvent soluble polyimide powders having the desired advantages and solving above identified problems can be obtained in a very efficient manner by a process as defined in claim 1. The process of the invention comprises the steps: a) providing a solution of a solvent soluble aromatic polyimide or aromatic polyamic acid, in an aprotic dipolar solvent or solvent mixture b) spinning of a polymer fibre from the solution of the aromatic polyimide or the aromatic polyamic acid provided in step a) and d1) cutting the polymer fibre obtained in step b) or the optional step c) described below, or d2) cutting the fibre(s) of the aromatic polyamic acid obtained in step b) to obtain particles, and subsequent imidation of the particles, to obtain particles having an average length xso, LF of from 30 to 250 pm after step d1 ) or d2).

If an aromatic polyamic acid solution is provided in step a) and used for spinning in step b), imidation of the aromatic polyamic acid to obtain the corresponding aromatic polyimide is necessary as additional step. Said imidation can be done either in an additional step c) before step d1 ) or after step d2).

Thus, in case an aromatic polyamic acid solution is provided in step a) and used for spinning in step b), the process of the invention preferably comprises a step c), obtaining fibre(s) of the aromatic polyimide by imidation of the aromatic polyamic acid fibre(s) obtained in step b) or a step e) obtaining powder particles of the aromatic polyimide by imidation of the aromatic polyamic acid powder particles obtained in step d2).

The use of cutting machines instead of mills in the process of the invention results in much more homogeneous particles with a very narrow size distribution with regard to particle length and particle diameter. The average particle diameter xso, Fmin as well as the average particle length xso LF, can be controlled very good via the spinning and cutting conditions. No sieve fractionation is necessary. In contrast to processes including sieving, nearly no waste powder is obtained.

The precisely predeterminable particle size and particle size distribution leads to powders with excellent processability and transportability properties since powders with very low dust formation can be obtained. Simultaneously and surprisingly the inventive powders show comparably high solubility compared to powders made of the same polymer by use of precipitation and milling processes of the prior art. The solubility performance was surprising, since it was expected that prior art powders with much higher contents of small particles should dissolve faster. It was also found that the bulk density of the polyimide powders obtained by the process of the invention was high.

The particles of the invention show a very homogeneous and good to control shape. The shape of the cross-section of the fibres as well as the diameter of the fibres, and thus, of the final particles, can be controlled by the spinning conditions. The length of the final particles can be controlled via the cutting process. This is a big advantage compared to unspecific precipitation and/or milling steps, where the fibres break randomly and also the integrity of the fibre structure may be affected because of squashing and spalling. The homogeneous and good controllable shape contributes to the processability and transportability, i.e. low dust formation, and solubility as well as of the bulk density of the inventive powder.

The inventors further found out that precipitation and milling, as used in the prior art processes, lead to a loss of molecular mass of the polyimide powder compared to the molecular mass the polyimide polymer had after polymerization. Post treatment of the polyimide powder to re-increase the molecular mass is therefore necessary in the prior art. With the process of the invention it is possible to widely maintain the molecular mass of the initial polyimide polymer during the powder production process. Thus, high molecular weight polyimide powders can be obtained without post treatment by a much more economic process.

Further advantages not explicitly mentioned here et obvious and can be derived from the description, examples, claims and figures.

Before describing the invention in more details some important terms are defined as follows:

The verb “to comprise” as is used in the description, examples and the claims and its conjugation is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. “Comprising” includes “consisting of’ meaning that items following the word “comprising”, are included without any additional, not specifically mentioned items, as preferred embodiment.

Reference to an element be the indefinite article “a” or “an” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there is one and only one of the elements. The indefinite article “a” or “an” thus usually means “one or more”.

“Obtainable by” as is used in the description and the claims is used in its non-limiting sense. A product obtainable by can but does not need to be obtained by the described process. If an identical product can be obtained by a different process it is also covered. “Obtainable” includes “obtained by” as preferred embodiment.

“Molecular mass” and “molecular weight” are used synonymously. “Soluble aromatic polyimide” means that the aromatic polyimide is soluble in an aprotic dipolar solvent, preferably selected from the group consisting of Dimethylformamide (= DMF), N-Methylpyrrolidone (= NMP), gamma-Butyrolactone (= GBL), N-Ethylpyrrolidone (= NEP), Dimethylsulfoxide (= DMSO), Dimethylacetamide (= DMAc), Dimethylpropionamid (= DMPr), 3-methoxy-N,N-dimethylpropionamide and mixtures thereof respectively mixtures comprising said solvents under the condition described in detail in the analysis section below.

“Minimum Feret diameter XFmin” as used in the present invention is defined in accordance with DIN ISO 9276-7 (see Figure 1 below). ’’Average Minimum Feret diameter xso, Fmin" is the XFmin value of the XFmin distribution curve (length distribution q1 ) where half of the population resides above this point, and half resides below this point, xso Fmin correlates to the average particle diameter.

“Particle length XLF” as used in the present invention means the Feret diameter perpendicular to the minimum Feret diameter XFmin, as defined in DIN ISO 9276-7 (see Figure 1 below). ’’Average particle length xso, LF” is the XLF value of the XLF distribution curve (length distribution q1) where half of the population resides above this point, and half resides below this point.

The terms “rectangular fibre shape “ preferably “sharp rectangular fibre shape” of the particles as used herein have a meaning analogue to AST F 1877 - 16, in particular Fig. X2.21. “Rectangular” includes approximately rectangular-shaped (examples are marked in Figure 2b with arrows), approximately square-shaped (example are marked in Figure 2c with arrows) and approximately trapezoidal-shaped (example are marked in Figure 2d with arrows), i.e. a shape wherein one or two pair(s) of sides of the particles being approximately parallel to each other. “Sharp” means that two or more sides of the particles, preferably two or more sides being approximately parallel to each other, are approximately smooth and that the majority of the edges of the particles, wherein “edge” refers to the connections of the sides of the rectangles, squares or trapezoids, are not rounded. Figures 2a) to d) show examples of particles having a “sharp” shape. In contrast thereto, Figures 4a) and 4b) show examples of rectangular particles having widely rounded edges, i.e. having a none “sharp” shape. Particles with rather spheroidal shape are shown in Figures 4a) to 4b), too.

“Fibre” includes fibres with and without hollow core. The terms fibres and filaments are used synonymously for the present invention.

“Polyimide(s)” as well as “polyamic acid(s)” means, unless stated otherwise, aromatic polyimides respectively aromatic polyamic acids.

The present invention relates to a method for making a solvent soluble polyimide powder, comprising the steps a) Providing a solution of a solvent soluble aromatic polyimide or aromatic polyamic acid, in an aprotic dipolar solvent, preferably selected from the group consisting of DMF, NMP, GBL, NEP, DMSO, DMAc, DMPr, 3-methoxy-N,N-dimethylpropionamide and mixtures thereof respectively solvent mixtures comprising one or more of said solvents, b) Spinning of a polymer fibre from the solution of the aromatic polyimide or the aromatic polyamic acid provided in step a) c) Optionally, in case an aromatic polyamic acid solution is provided in step a) and used for spinning in step b), obtaining fibre(s) of the aromatic polyimide by imidation of the aromatic polyamic acid fibre(s) obtained in step b), and is characterized in that it comprises a step d) Preparation of a polyimide powder by d1) cutting the fibre(s) of the aromatic polyimide obtained in step b) or c) to obtain particles or d2) cutting the fibre(s) of the aromatic polyamic acid obtained in step b) to obtain particles, and subsequent imidation of the particles, wherein the fibre(s) of the aromatic polyimide or of the aromatic polyamic acid is/are cut in step d1 ) respectively d2) to particles having an average length xso, LF of from 30 to 250 pm, preferably 40 to 200 pm, even more preferred 50 to 180 pm, especially preferred 50 to 150 pm and most preferred 60 to 100 pm, and wherein in case step d2) is carried out, the process comprises step e), obtaining powder particles of the aromatic polyimide by imidation of the aromatic polyamic acid powder particles obtained in step d2).

In addition, the process of the invention preferably comprises one or more washing steps f), one or more solvent exchange steps g) and one or more drying steps h), wherein the one or more washing steps f) are selected from the group consisting of f1 ) washing the polymer fibre f2) washing the polyimide particles f3) washing the polyamic acid particles, and the one or more solvent exchange steps g) are selected from the group consisting of g 1 ) solvent exchange of the polymer fibre g2) solvent exchange of the polyimide particles g3) solvent exchange of the polyamic acid particles and the one or more drying steps h) are selected from the group consisting of hi) drying the polymer fibre h2) drying the polyimide particles h3) drying the polyamic acid particles and wherein step f1 ), if comprised, is carried out after step b) or c) or g) or g) + h) , step f2) , if comprised, is carried out after step d1) or e) or g) or g) + h) and step f3), if comprised, is carried out after step d2) or g) or g) + h), and wherein step g1), if comprised, is carried out after step b) or c) or f) or f) + h), step g2), if comprised, is carried out after step d1) or e) or f) or f) + h) and step g3), if comprised, is carried out after step d2) or f) or f) + h), and wherein step hi ), if comprised, is carried out after step b) or c) or f) or g) , step h2), if comprised, is carried out after step d1 ) or e) or f) or g) and step h3), if comprised, is carried out after step d2), or f) or g).

The inventors have found out that it is beneficial to avoid loss of molecular weight of the polymers during powder production if the content of the aprotic dipolar solvent is reduced before conducting any drying step h) and/or any thermal imidation of polyamic acid fibres in step c) or polyamic acid particles in step e). In addition, it was found that crosslinking, which might occur during such drying or thermal imidation if the content of the aprotic dipolar solvent is too high during these steps, can be avoided. Crosslinking might negatively impact the solubility of the polyimides. Preferably the residual content of the aprotic dipolar solvent of the fibres and/or particles is reduced to below 5% by weight, preferably below 3% by weight, even more preferred below 1 % by weight and most preferred of not more than 0.5% by weight, in each case based on the overall weight of the fibres respectively particles before any drying step h) and/or any thermal imidation of polyamic acid fibres in step c) or polyamic acid particles in step e) is carried out. Various techniques can be used for this, preferably washing f) and/or solvent exchange g), most preferably washing f).

Washing in step f) can be done with polymer fibre(s) obtained from steps b) and/or c) and/or with the solvent exchanged fibres after step g). It can also be done with polyimide particle(s) and/or polyamic acid particle(s) obtained in step d1 ) or d2) or e) or with solvent exchanged particles after step g) or both can be done. Preferably washing is done of the polyimide particles after cutting in step d1).

If the fibres are washed, it is preferred to wash at a point downstream of the precipitation bath, if wet spinning is used, or downstream of the spin tube, if dry spinning I used. It is preferable to use a continuous process whereby the fibres pass through one or more successive water baths.

It is also possible for the fibres obtained from the precipitation bath or spin tube to be wound up and be washed in water off-line. The same can be applied for particles.

The wash can take place at any temperature. Preferably, however, comparatively high temperatures are used for the wash. It is particularly preferable to heat the water to 40 to 100°C, preferably 50 to 95°C, to achieve a more effective wash.

Solvent exchange in step g) can be done with polymer fibre(s) obtained from steps b) and/or c) and/or f) and/or f) + h). It can also be done with polyimide particle(s) and/or of the polyamic acid particle(s) obtained in step d1 ) and/or d2) and/or e) and/or f) and/or f) + h). Combinations of these measures are also possible. Solvent exchange f), more preferably in isopropanol and/or hexane, can be used to remove water and the dipolar aprotic solvent. The solvent exchange can be carried out as a continuous operation (on-line) or off-line, like the wash. For an on-line solvent exchange, the fibres are led through one or more solvent baths, preferably downstream of the wash bath(s).

The following sequence of steps are particular preferred:

I) washing f) of the polyimide fibre, optionally followed by solvent exchange g),

II) washing f) of the polyimide particles after cutting of the polyimide fibre in step d1), optionally followed by solvent exchange g),

III) washing f) of the polyamic acid particles after cutting of the polyamic acid fibre in step d2), optionally followed by solvent exchange g)

IV) washing f) of the polyamic acid fibre, optionally followed by solvent exchange g).

It is further preferred that the processes according to alternatives I) to IV) include a drying step h) and that that steps f) and/or g) are executed before step h) and/or any thermal imidation of the polyamic acid in case such step is conducted.

In a preferred embodiment the fibres and/or particles are dried in step h), preferably at a temperature in the range from room temperature to 100°C, more preferably between 50 and 90°C in recirculating gas, preferably air, or vacuum, to remove residual water and/or the exchanges solvent, preferably isopropanol and hexane. The overall water and/or residual solvent content after drying is preferably in the range from 0% to 5% by weight, more preferred <3% by weight and even more preferred in the range from 0.1% to 3% by weight in each case of the dried fibres or powder, and preferably consists of the water and/or the solvents used for solvent exchange, preferably isopropanol and hexane.

Solvent soluble aromatic polyimides and aromatic polyamic acids, preferably made from dianhydrides and diisocyanates respectively diamines, as well as methods for their manufacture are known to a man skilled in the art. Homo-, random-, or copolymer or a mixture or blend of different polymers may be used. All kinds of solvent soluble aromatic polyimides and aromatic polyamic acids can be used in the present invention.

Preferably the aromatic polyimide(s) used in step a) comprise(s) identical or different recurring units of Formula (1a) or the polyamic acid(s) used in step a) comprise(s) identical or different recurring units of Formula (1b) Formula (1a) Formula (1 b) wherein the functional group R^A represents one or more, identical or different moieties selected from the group consisting of the moieties R^A1, R^A2 and R^A3 the functional group R^B represents one or more, identical or different moieties selected from the group consisting of the moieties R^B1, R^B2 and R^B3 wherein Yi , Y2, Y3 and Y4 are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Y = -CH2-, - (CH₃)₂C-, SO2. -(CF₃)C-. -CO-, -COO-, -CONH-, -O-.

More preferred the polyimide(s) or polyamic acid(s) provided in step a) is/are prepared by reacting a dianhydride, selected from the group consisting of 3,4,3’,4’-benzophenonetetracarboxylic acid dianhydride (BTDA), 1 ,2,4,5-benzenetetracarboxylic acid dianhydride (PMDA), 3, 4, 3’, 4’- biphenyltetracarboxylic acid dianhydride (BPDA),1 ,1 ,1 ,3,3,3-hexafluoro-2,2-propylidenediphthalic acid dianhydride (6-FDA), 4,4'-Oxydiphthalic acid dianhydride (ODPA), 3,3',4,4'-Diphenylsulphone tetracarboxylic acid dianhydride (DSDA), and mixtures thereof with a diisocyanate, selected from the group consisting of toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6- diisocyanate (2,4-TDI), 4,4’-methylenediphenyl-diisocyanate (MDI), 2,4,6-trimethyl-

1 ,3-phenylenediisocyanate (MesDI), 2,3,5,6-tetramethyl-1 ,4-phenylenediisocyanate, diethylmethylbenzenediisocyanate and mixtures thereof in a dipolar aprotic solvent to obtain the polyimide, or a diamine, selected from the group consisting of toluene-2,4-diamine (2,4-TDA), toluene-2,6-diamine (2,6-TDI), 4,4’-methylenediphenyl-diamine (MDA), 2,4,6-trimethyl-1 ,3-phenylenediamine (MesDA), 2,3,5,6-tetramethyl-1 ,4-phenylenediamine, diethylmethylbenzenediamine and mixtures thereof, in a dipolar aprotic solvent to obtain the polyamic acid.

Even more preferred at least 90 mol-% of building blocks R^A are 3,3’,4,4’-benzophenonetetrayl and at least 90 mol-% of building blocks R^B are 2,4-toluenediyl, 2,6-toluenediyl or 4,4’-methylenediphenyldiyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1 and a molar ratio of the combined amount of

2,4-toluenediyl and 2,6-toluenediyl to the amount of 4,4’-methylenediphenyldiyl of from 70 : 30 to 100 : 0 or at least 90 mol-% of building blocks R^A are 3,3’,4,4’-benzophenonetetrayl or

1 ,2,4,5-phenylenetetrayl, with a molar ratio of 3,3’,4,4’-benzophenonetetrayl to 1 ,2,4,5-phenylenetetrayl of from 50 : 50 to 95 : 5, preferably of from 55 : 45 to 65 : 35, and at least 90 mol-% of building blocks R^B are

2,4-toluenediyl or 2,6-toluenediyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1

In a first particular preferred embodiment of the invention polyimides provided in step a) having the following structure according to Formula (2): where 0 < x < 0.5 and 1 > y > 0.5, the sum of x and y = 1 and R represents one or more, identical or different moieties selected from the group consisting of the moieties L1 , L2, L3 and L4.

The polyimide is very particularly preferably a polymer according to Formula (2) where x = 0, y = 1 and R consists of 64 mol% L2, 16 mol% L3 and 20 mol% L4. Such solvent soluble polyimides are known as P84® or P84® type 70 and have the following CAS number: 9046-51-9.

Also, very particular preferred the polyimide of Formula (2) is a polymer having the composition x = 0.4, y = 0.6 and R consists of 80 mol% L2 and 20 mol% L3. This solvent soluble polyimide is known as P84® HT or P84® HT 325 and has the following CAS number: 134119-41-8.

Polyamic acids corresponding to Formula (2) and to the preferred embodiments described before are also preferably used.

Details regarding the production of these and further similar polyimides according to Formula (2) can be extracted from WO 2011/009919 A1 , the whole content of the documents is hereby explicitly incorporated in the description of the present invention by reference. All polymers described in the examples of WO 2011/009919 A1 are particularly preferably used in the process of the present invention. The whole content of WO 2011/009919 A1 is incorporated by reference.

DE 21 43 080 describes the manufacture of solvent soluble polyimides made from BTDA and mixtures of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate and 4,4’-methylenediphenyl-diisocyanate. It also describes the manufacture of solvent soluble polyamic acid from BTDA and mixtures of toluene-2,4- diamine, toluene-2,6-diamine, 4,4’-methylenediphenyl-diamine as well as the subsequent imidation to the corresponding polyimide. Details regarding the production of these and further similar polyimides and polyamic acids can be extracted from DE 21 43 080, the whole content of bot documents is hereby explicitly incorporated in the description of the present invention by reference. All polymers described in the examples of DE 21 43 080 are particularly preferred used in the process of the present invention. The whole content of DE 21 43 080 is incorporated by reference.

In a second particular preferred embodiment of the present invention the aromatic polyimide or aromatic polyamic acid provided in step a) is a solvent soluble a block-copolyimide or block-copolyamic acid, i.e. copolymer comprising, preferably consisting of, the blocks (A) as per the ensuing formulae (3a), or (3b) and (B) as per the ensuing formulae (4a) or (4b):

Said blocks A and B have a differing composition, i.e. the pairs Ri and R3 on the one hand and R2 and R4 on the other cannot each be identical at one and the same time.

The block copolyimide comprises a continuous phase of block A. The functional group Ri therein comprises either or both of the following functional groups:

R2 comprises at least one or 2 or 3 of the following functional groups

R2a

Block A has the following compositions in embodiments that are most preferable:

AF1 : 100 mol% Rib and 64 mol% R2a, 16 mol% R2b and 20 mol% R2C.

AF2: 40 mol% Ria, 60 mol% Rib and 80 mol% R2a, 20 mol% R2b. The recited mole percentages relate to the functional groups Ri and R2 such that the amounts of the various units are each selected such that the sum is 100 mol% for each of these groups.

Block B is elected to be a polymer that is distinctly more permeable than block A. R3 in block B comprises at least one or more of the following functional groups:

R4 comprises at least one or more of the following functional groups where Y1 , Y2, Y3 and Y4 are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Z = -CH2-, - (CH3)2C-, SO2. -(CF3)C-. -CO-, -COO-, -CONH-, -O-, with the proviso that at least one of the radicals Y1 to Y4, preferably at least two of the radicals Y1 to Y4, more preferably at least three of the radicals Y1 to Y4 and most preferably all the radicals Y1 to Y4 are equal to CH3 or a C2 to C4 alkyl radicals. is preferably -CH2-, - (CH3)2C- -(CFs^C- or -O-, more preferably Z = -CH2- or -(CHs^C- It is very particularly preferable for R4C to have the following composition: Y1, Y2 and Y3 = H, Y4= CH3 or a C2 to C4 alkyl radical and Z = -CH2- or -(CHs^C- or, respectively, Y1 and Y3 = CH3 or a C2 to C4 alkyl radical, Y2 and Y4 = H or CH3 and Z = -CH2- or -(CH3)2C- It is most preferable for R4C to have the following composition: Yi, Y2, Y3 and Y4 = CH3 or a C2 to C4 alkyl radical and Z = -CH2- or -(CHs^C- preferably -CH2-. It is most preferable for the radicals Y1 to Y4 in the abovementioned preferred embodiments to be CH3 if they are not H.

In one particularly preferred embodiment, block (B) has the following composition:

AF3: 40 to 60 mol% Rsa, 0 to 10 mol% Rsb, 60 to 30 mol% R3C and 90 to 100 mol% R4a, 0 to 10 mol% R4b and 0 to 10 mol% R4C.

AF4: 50 mol% Rsa, 50 mol% R3C and 100 mol% R4a.

The mole percentages stated for AF3 and AF4 relate to the functional groups R3 and R4, respectively, in total, so the amounts of the various units are each selected such that they sum to 100 mol% for each of these groups.

Very particular preference is given to the combinations of the abovementioned AF1 and/or AF2 with AF3 and/or AF4. Combinations of AF1 or AF2 with AF4 are most preferable.

The block lengths n and m of blocks A and B are preferably in the range from 1 to 1000, more preferably in the range from 1 to 500, yet more preferably in the range from 1 to 200, yet still more preferably in the range from 5 to 150, yet still more preferably in the range from 10 to 100, yet still even more preferably in the range from 10 to 50 and most preferably in the range from 10 to 40.

The block lengths of blocks A and B may be the same or different. The block-copolyimide or block- copolyamic acid may further exhibit some distribution with respect to the particular block lengths of blocks A and B; that is, not all bocks A or all blocks B need to have the same length. The ratio between blocks A and B may thus be varied across a wide range. Proportions in the block copolyimide or block-copolyamic acid of this second preferred embodiment of the present invention may be from 5 to 90% for block B and from 10 to 95% for block A. Particular preference is given to the ratio of A: B - 80:20 or 70:30 or 60:40 or most preferably 50:50.

Details regarding the production of the block-copolyimides and block-copolyamic acids of the second preferred embodiment can be extracted from WO 2015/091122, the whole content of which is hereby explicitly incorporated in the description of the present invention by reference. All polymers described in the examples of WO 2015/091122 are particularly preferably used as polymer in the process of the present invention.

In a third preferred embodiment the solvent soluble polyimide(s) or polyamic acid(s) used in the process of the invention is/are selected from the group consisting of Matrimid 5128 (CAS No 104983-64-4, based on BTDA DAPI [Diaminophenylindane]).

Preferably polyimide(s) or polyamic acid(s) comprising at least 90 % by weight, more preferred 90 to 100% by weight, even more preferred 95 to 100% by weight, particular preferred 98 to 100% by weight and most preferred 99 to 100% by weight of a polyimide or polyamic acid of recurring units according to formula (1a) or formula (1 b) or of any other of the preferred polyimide(s) or polyamic acid(s) defined above are used in step a).

Spinning of polyimide fibres respectively polyamic acid fibres in step b) is process known in the art. The fibres of the invention can be produced by any method suitable to spin soluble polyimide or polyamic acid polymers, like for example wet spinning, dry spinning and dry-wet spinning. Preferred are dry and wet spinning, most preferred dry-spinning.

As mentioned before, the use of cutting machines instead of mills in the process of the invention results in much more homogeneous particles with a very narrow size distribution with regard to particle length and particle diameter. The average particle diameter xso, Fmin as well as the average particle length X50, LF, can be controlled very good via the spinning and cutting conditions. It is, thus, preferred that the fibres being cut in step d) having a rectangular shape, more preferred having a sharp rectangular shape, wherein for the terms “rectangular fibre shape “ and “sharp rectangular fibre shape” the definitions provided above for the inventive particles, referring to AST F 1877 - 16, in particular Fig. X2.21 , shall be apply analogously for the fibres.

It is even more preferred that the fibres being cut in step d), having, at the points of the fibre where they are cut, a minimum Feret diameter XFmin of from 1 to 100 pm, preferably 10 to 90 pm, more preferred 10 to 85 pm, even more preferred 10 to 80 pm, particular preferred 10 to 75 pm, very particular preferred 15 to 62.5 pm and most preferred 20 to 60 pm.

The shape of the front and back cross-section of the fibres can be controlled with the spinning process, too.

In a dry spinning process the polymer solution obtained in step a) is spun by use of a spinneret having one or more orifices, preferably 20 to 800 orifices. The spun fibres pass through a spin tube where a spin gas, which is passed through the spin tube in the opposite direction, flows around the fibres. In the spin tube the fibre solidifies and most of the aprotic dipolar solvent is removed. As consequence the initially rather regular shape of the fibre cross-section, which correlates to the geometry of the orifice, becomes irregular, preferably lobed or serrated. In addition, the diameter of the fibre shrinks to preferably 10 to 25 % of the original orifice diameter. Preferably orifices are used with a diameter of 100 to 300 pm, preferably 150 to 250 pm, more preferred 180 to 220 pm. The extrusion speed may be 20 to 100 m/min,. The amount of spin gas preferably is in the range of 40 to 100 m³/h, more preferred 50 to 90 m³/h and most preferred 60 to 80 m³/h and its temperature is preferably in the range of from 200 to 350°C, more preferred 250 to 300°C and most preferred 260 to 280°C. Other parameters like the wheel up speed of the fibres and the concentration of the spin solution, which preferably has a polymer content of from 20 to 40 wt.%, more preferred 22 to 35 wt.% and most preferred 25 to 30.%, based on the overall weight of the solution, can be adjusted based on the desired properties of the fibre. A particular preferred dry spinning method for the fibres of the invention is described in US 4,801 ,502 B1, the whole content of this document is hereby explicitly incorporated in the description of the present invention by reference.

In a wet spinning process the orifices of the spinneret are usually positioned beneath the surface of the liquid in a spinning bath. Thus, in contrast to dry spinning, where the fibres pass a spin tube with a spin gas, in the wet spinning process the fibres pass through a coagulation bath comprising a coagulant fluid, wherein the coagulant fluid is chosen from a variety of non-solvent or mixtures of solvents and nonsolvents, as long as they act in a non-solvent capacity for the poly imides or polyamic acids. In the coagulation bath the aprotic dipolar solvent from the spinning solution is removed. Due to the different method to remove the content of the dipolar aprotic solvent from the spun fibres, the fibre cross-section obtained in a wet spinning process differs from that obtained in a dry spinning process.

The concentration of aprotic dipolar and other solvents such as, for example, but not limited to dimethylformamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, sulpholane, dimethyl sulphoxide, tetrahydrofuran, dioxane, isopropanol, ethanol or glycerol in the coagulation bath in the wet spinning method is preferably between 0.01% by weight and 20% by weight, more preferably between 0.1% by weight and 10% by weight and most preferably between 0.2% by weight and 1% by weight, the remainder being water. It is likewise preferable to use pure water in the water bath.

A particular preferred wet spinning method for the fibres of the invention is described in US 3,985,934 and DE 2442 203, the whole content of these documents is hereby explicitly incorporated in the description of the present invention by reference.

In another preferred embodiment the fibres produced in the process of the invention might be hollow fibres as for example described in the above cited and incorporated by reference documents WO 2015/091122 and WO 2011/009919.

The most preferred spinning methods of the present invention is dry spinning. It is cost efficient since large amounts of coagulation solution can be avoided and very beneficial cross-sections of the fibres can be obtained.

If a polyamic acid is used in the process of the invention, either the polyamic acid fibre must be imidized (dehydrated) to the polyimide in step c) or the polyamic acid particles must be imidized (dehydrated) in step e). Various methods are known for dehydration/imidation of polyamic acid. In principle all known methods of imidation from the literature may be employed here, for example a thermal imidation or a chemical imidation. Because of the better process control, chemical imidation is preferred.

Chemical imidation is preferably done with water-withdrawing agent, more preferably acetic anhydride or propionic anhydride or benzoic anhydride or acetyl chloride or thionyl chloride in the presence of a base, more preferably with a tertiary nitrogen base, especially pyridine or triethylamine. Especially if a polymer block (B) consisting of BTDA/PMDA and MesDA is used the polymer can be imidized without adding a stoichiometric amount of base. Adding a catalytic amount of a tertiary base, preferably from 0.1 to 1 mol%, of preferably DABCO (diazabicyclooctane) or DBU (diazabicycloundecane), and of a slightly superstoichiometric amount, especially 5 to 30 mol% above stoichiometric, of a water-withdrawing agent, preferably acetic anhydride or acetyl chloride or thionyl chloride, most preferably acetic anhydride, led to full imidation. Details regarding the imidation of block- copolyamic acids can be extracted from WO 2015/091122, the whole content of which is hereby explicitly incorporated in the description of the present invention by reference.

The addition of the water-withdrawing agent is preferably first followed by continued stirring - first at -10 to 40°C, preferably at 20 to 30°C for 0.1 to 20 h, preferably 5 to 12 h, then preferably for 0.1 to 20 h, preferably for 5 to 12 h, at elevated temperature, preferably at 40 to 120°C, more preferably at 50 to 90°C, to complete the reaction.

Thermal imidation is carried out preferably at temperatures above 200°C, more preferred 200 to 350°C. It might be beneficial to apply specific temperature profiles during thermal imidation as described in CN 109734909 A, the whole content of the documents is hereby explicitly incorporated in the description of the present invention by reference.

To minimize loss of molecular weight and crosslinking it is particular preferred to reduce the residual content of the aprotic dipolar solvent of the fibres and/or particles to below 5% by weight, preferably below 3% by weight, even more preferred below 1% by weight and most preferred of not more than 0.5% by weight, in each case based on the overall weight of the fibres respectively particles, before thermal imidation is carried out.

In step d) the polyimide or polyamic acid fibre(s) is/are cut to obtain particles having an average length X5O,LF of from 30 to 250 pm, preferably 40 to 200 pm, even more preferred 50 to 180 pm, especially preferred 50 to 150 pm and most preferred 60 to 100 pm. The inventors found out that if too many particles are too long or too short, they do not show the desired performance properties. Polyimide particles having a length above 350 pm entangle to each other and behave like flocks. Too small particles are dusty and thus, show worse handling and transport properties.

The inventors further found out that an average particle length XSO.LF in the above defined ranges is beneficial for good solubility of the particles. They found out that polyimide particles having a length XLF above 350 pm may clump during dissolution and are thus more difficult to dissolve. In some cases, they cannot be dissolved. It is thus, preferred that less than 5% by weight, more preferred less than 3% by weight, even more preferred less than 2% by weight and most preferred 0 to 1 % by weight of the sum of all particles having a length XLF above 350 pm.

Cutting of the fibres can in principle be done by any suitable machine or device. For example, cutting can be done with one or more blades. Preferably the blades act as a guillotine, where the fibres are cut generally perpendicular to their length. Other useful methods may be for example include cutting by laser, waterjet, air jet, or any combination thereof. Most preferred the polymer fibre(s) is/are cut with a blade or with a guillotine cutting machine.

The distance the fibre(s) move(s) respectively is/are moved in between cuts may be referred to herein as cutting intervals and may define the length of the particles. Cutting of the fibres may be carried out at particular cutting intervals corresponding to a desired length of the plurality of polyimide particles. Preferably, to achieve a low dust formation of the inventive polyimide powder and to obtain a narrow particle size distribution, the polyimide particles are moved by a constant cutting interval between cuts.

In specific cases, however, the cutting intervals can vary. For example, the intervals can be generally the same for a desired number of cuts, and then can be changed to a different interval or the intervals can vary throughout a cutting operation.

The polymer fibre(s) can be moved by, for example, a movable clamp. The clamp may compress the polymer fibres and then move them a predetermined length between cuts. In certain embodiments, the polymer fibres can be compressed before and or during cutting. Compression of the fibres can reduce the space in between fibres and improve the cutting efficiency. It is also preferred to fix the fibre(s) after each moving and before each cut. This can be beneficial to obtain a good and homogeneous particle size distribution.

To enhance efficiency of the cutting process it is also preferred to aggregate multiple polymer fibres, more preferred with an approximately parallel orientation of the fibres to each other, before cutting. Even more preferred, multiple polymer fibres are being aggregated to a yarn or tow before cutting. For example, a plurality of polymer fibres may be aggregated to form a polymer yarn.

Aggregating a plurality of polymer fibres may include any process of placing, collecting or combining the plurality of polymer fibres into a single group or cluster of polymer fibres to form the polymer yarn. Aggregating the polymer fibres into a polymer yarn may be done with or without twisting the plurality of polymer fibres together.

A polymer tow may be formed from a plurality of polymer yarns. The process may include aggregating the plurality of polymer yarns to form the polymer tow. Aggregating a plurality of polymer yarns may include any process of placing, collecting or combining the plurality of polymer yarns into a single group or cluster of polymeric based yarns to form the polymeric based tow.

Aggregating the plurality of polymer yarns into a polymer tow may be done with or without twisting the plurality of polymer yarns.

It is further possible to form and aggregated polymer tow by aggregating a plurality of polymer tows. Aggregating a plurality of polymer tows may include any process of placing, collecting or combining the plurality of polymer tows into a single group or cluster of polymer tows to form the aggregated polymer tow. Aggregating the plurality of polymer tows into an aggregated polymer tow may be done with or without twisting the plurality of polymer tows. The polyimide particles of the invention may be obtained by either cutting individual fibres or a plurality of fibres or a yarn or a plurality of yarns or a tow or of a plurality of tows or of an aggregated tow. It will be appreciated that if the aggregated polymer tow is cut, it is the plurality of polymer fibres, which have been aggregated together to form polymer yams, polymer tows and ultimately that aggregated polymer tow, that separate after being cut to create the plurality of polymeric based particles.

Use of the cutting technology, in particular of the preferred methods described before, allows to obtain fibres with a sharp rectangular shape (see Figures 2a to 2d). Most of the particles have a rectangular shape with some particles having a square or trapezoidal shape. The very homogeneous particle shapes and particle size distribution of the fibres of the invention contribute to a higher tamped density, excellent dissolution and lower dust formation compared to polyimide powders obtained by milling or precipitation. Figures 4a and 4b show a non-inventive powder obtained by milling polyimide fibres. The particle size distribution is very broad with a significant amount of small and rather spheroidal particles. Figure 6 shows a commercially available polyimide powder obtained by precipitation and milling technology. The particles are none rectangular and the particle size distribution is broad.

The cutting process used in the present invention allows to precisely control the particle length and particle length distribution. Preferable many fibres are cut simultaneously as described above. This causes that only a small amount, preferably 0 to 10 wt. %, more preferred 0.001 to 5 wt. %, even more preferred 0.01 to 2%, most preferred 0.1 to 1 wt.% of the overall powder weight, of particles might be obtained having a length above 350 pm. These particles can be separated by sieving. Such sieving, however, is not a sieve fractionation. It is only a separation of a low amount of too long off-spec particles.

Too short particles having a particle size below the range specified above are usually not or only in a minor amount, preferably 0 to 10 wt. %, more preferred 0.001 to 5 wt. %, even more preferred 0.01 to 2%, most preferred 0.1 to 1 wt.% of the overall powder weight, obtained. As consequence the cutting process is very efficient and the amount of waste, that has to be disposed or re-processed, for example by redissolution, re-precipitation and re-cutting, is very low compared to milling methods where the particle size cannot be controlled exactly, and large amounts of very small particles are obtained (see Figures 4a and 4b).

The inventive powder comprises particles of solvent soluble aromatic polyimides. Preferably the particles comprise at least 90 % by weight preferably 90 to 100% by weight, more preferred 95 to 100% by weight and most preferred 98 to 100% by weight of a solvent soluble aromatic polyimide, more preferred of a polyimide comprising recurring units of formula (1a), even more preferred of one or more polyimides described as preferred embodiments above. The polyimides may comprise identical or different recurring units according to formula (1a).

Preferably the majority of the polyimide particles of the invention, i.e. more than 50%, preferably more than 60%, even more preferred more than 70 %, especially preferred more than 80%, particular preferred more than 85% and most preferred more than 90% based on the number of the counted particles, have a rectangular shape, preferably a sharp rectangular shape, even more preferred having approximately the shape of a rectangle or of a square or of a trapezoid. For this evaluation a representative number of particles is evaluated.

The particles of the invention having an average length XSO.LF of from 30 to 250 pm, preferably 40 to 200 pm, even more preferred 50 to 180 pm, especially preferred 50 to 150 pm and most preferred 60 to 100 pm. The particle length span (X9O_;LF - XW;LF) / XSO;LF, i.e. the particle length distribution, is preferably in the range of from 0.1 to 2.5, more preferred 0.3 to .2 even more preferred 0.5 to 1.8, particular preferred 0.5 to 1.5 and most preferred 0.5 to 1.2 to ensure a narrow particle size distribution.

Handling and transport properties, e.g. low dust formation, as well as fast and homogeneous solubility as well as mechanical properties of the polyimide particles of the invention are particular good if the particle length distribution is narrow. It can be further improved, if particle diameter distribution is narrow, too, and/or if the particle diameter is not too small. It is thus, preferred if the polyimide particles have an average minimum Feret diameter xso, Fmin of from 10 to 100 pm, preferably 10 to 80 pm, more preferred 20 to 70 pm, even preferred 30 to 70 pm and most preferred 30 to 60 pm and/or a particle diameter distribution, i.e. span (x90; Fmin - xio; Fmin) I xso; Fmin, of from 0.1 to 2.5, more preferred 0.2 to 2 even more preferred 0.3 to 1.5, particular preferred 0.4 to 1.2 and most preferred 0.5 to 1.0

The particles of the invention preferably having a monomodal particle length distribution for particles with XLF > 30 pm and/or a monomodal particle diameter distribution for particles with XFmin > 20 pm.

The process of the invention has the advantage that the fibres are cut while the geometry of the fibre is maintained. It is therefore possible and preferred to obtain polyimide particles having a cross-section having an irregular shape.

The inventive polyimide particles are preferably obtained by cutting of a fibre having an irregular, preferably lobed or serrated, cross-section. As consequence the cross-section of the particles preferably has an irregular shape, more preferred a lobed or serrated shape, most preferred is a multiloba! form. The irregular shape can be verified by image analysis of the cross-section of the powders but can also be seen in a side view of the particles, perpendicular to the cross-section. In the side view of a two- dimensional black and white image of the particles, stripes can be seen in black, grey and wide colors (see Figures 2a to 2d).

The polyimide particles of the invention can be used in all known applications for solvent soluble polyimides. Since the process of the invention allows to obtain solvent soluble polyimide powders with high molecular mass, the powders of the invention show superior performance compared to commercially available polyimide powders made from the same polymer but via precipitation and milling.

The polyimide powder of the present invention can preferably be used for hot compression molding, to produce polyimide coatings of substrates and as fillers for finished or semi-finished polymeric products, for example made of PTFE. They can also be used as raw material to produce fibres or hollow fibres or flat sheet and the respective membranes, which can be used in hot gas filtration (fibres) or gas or liquid separation (hollow fibre and flat sheet membranes). Because of the high bulk density and low dust formation as well as of the good solubility the polyimide powder of the invention is superior to the prior art if it is used to store and transport the polyimide from the production site to the site where it is used and further processed.

Analysis methods

Microscopy and imaging of particles

A two-dimensional picture of the particles was obtained by Sympatec QicPic/L02 with the measurement setting M6.

Particle shape

The particle shape was evaluated by use of a two-dimensional image obtained via image analysis in accordance with ASTM F 1877 - 16.

Minimum Feret diameter XFmin

The minimum Feret diameter XFmin is defined in accordance with DIN ISO 9276 - 6 : 2012-01 as the minimum distance between pairs of parallel tangents to a projected outline of the particle to be evaluated. It is determined via image analysis of a two-dimensional image (see Figure 1).

The average minimum Feret diameter xso.Fmin

The average minimum Feret diameter xso.Fmin is the median value of the minimum Feret diameter XFmin distribution curve (length distribution q1 ) of a powder. A QicPic analyzing software, Version L02 was used to measure xso.Fmin. The average value of two measurements was used as xso.Fmin

The span (breadth) of the minimum Feret diameter distribution curve

The span (breadth) of the minimum Feret diameter distribution curve calculates as:

Span ⁼ (X90; Fmin — X10; Fmin) / X50; Fmin

It was measured based on the minimum Feret diameter XFmin distribution curve (length distribution q1 ), using QicPic analyzing software, Version L02. The average value of two measurements were used.

Length of the particles XLF

The length of the particles XLF is defined in accordance with DIN ISO 9276 - 6 : 2012-01 to be the Ferret diameter perpendicular to the minimum Feret diameter xpmin of the particle to be evaluated. It is determined via image analysis of a two-dimensional image (see Figure 1).

The average particle length XSO.LF

The average particle length XSO.LF represents to the median value of the XLF distribution curve (length distribution) of a powder. QicPic analyzing software, Version L02was used to measure XSO.LF The average value of two measurements was used as XSO.LF The span (length) of the particle length distribution curve

The span (length) of the XLF distribution curve calculates as: span = (X90;LF - X10;I_F) / X50;LF

It was measured based on the XLF distribution curve (length distribution q1), using QicPic analyzing software, Version L02. The average value of two measurements were used

Bulk density

Bulk density is measured according to ISO 60 with a SMG 53466 from Powtec.

Determination of dust formation

The dust development was determined according to DIN55992-1 on the Heubach Dustmeter Type 1. A sample of the product (approx. 75g) to be tested is placed in the dust generation vessel of the testing device. Through rotation is used to move the sample during the measurement, with the mechanical stress being applied at the same time practical processes are simulated. Existing dust and dust generated by mechanical stress are removed from captured by an axially entering air stream and deposited on a filter of defined porosity. The amount of the separated dust is determined gravimetrically.

The index SR for dust development using the rotation process, in mg per 100 g, is calculated using the following equation: mo Mass of the sample, in g rm Mass of the filter housing with the filter inserted before the measurement, in g m2 Mass of the filter housing with the filter inserted after the measurement, in g

A duplicate determination was carried out from all samples.

Determination of the solubility

To measure solubility, a 20 g quantity of the polyimide or polyamic acid polymer, fibre or powder is introduced at room temperature into 80 g of the solvent or solvent mixture in a Schott-flask and was rolled on a rolling stand for 3 hours. After the time had elapsed, the quality of the solution was visually assessed.

Determination of residual solvent content

The residual solvent (DMF) content after solvent exchange is determined via gas chromatography by headspace injection of the polymer, fibre or particles dissolved/dispersed in dimethylsulfoxide (DMSO) as follows: A 250-300 mg quantity of the sample is weighed out accurately to 0.1 mg (= initial weight) into a fared vial. Then, 5.00 ml of DMSO are added using a full pipette or a Dispensette and the vial is sealed with the septum using the cap crimper. The sample is thermostated to 155°C in the headspace sampler for 90 min, which is followed by headspace injection onto the GC column.

GC: Perkin Elmer Clarus 580

Column: Perkin Elmer WAX ETR, 30 m x 0.53 mm, df = 2.00 pm, #N931- 6570

Headspace autosampler: Perkin Elmer TurboMatrix 40

Carrier gas: 5 ml helium 4.6 (or better)

FID detector gases: 40 ml/minute hydrogen, 400 ml/min synthetic air

Temperature programme of GC:

Init.temp.: 175°C for 3 minutes,

Rampl : 207min to 220°C for 4 minutes

Run time: 9.25 minutes

Cycle time: 15 minutes

After effected analysis, the residual solvent content is automatically computed according to the formula area

- 100= residiiakolvent(%) cal. curve initialweighifmg] and printed out under "Concentration [%]“.

For residual solvent of NEP or NMP, 1 ,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (DMPU) is used as dispersing agent/solvent.

Determination of residual solvent (DMF) content of moist polymer fibre or powder

Residual dipolar aprotic solvent of the moist polymer, fibre or powder sample is determined by Soxhlet extraction in ethanol. Subsequent quantification is by direct injection of the extract onto GC.

Determination of residual water content

Residual water content is determined by heating the moist polymers, fibres, or powder with solvent in an oven sampler and subsequent analysis by Karl Fischer titration.

0.25 g to 0.5 g of the polymer sample is weighed accurately to 0.001 g into a fared vial. Then, 500 pl of over molecular sieve dried DMF are added by microlitre syringe. The vial is sealed with a septum cap using the cap crimper. The sample is placed into the oven sample processor where it is heated up to 160°C. A double hollow needle pierces the septum and a dry carrier gas stream transports the released moisture into the titration cell, where the Karl Fischer titration takes place.

Total Moisture of polymer powders

The material moisture is determined using the thermogravimetric method, i.e., a sample is dried to constant mass by halogen or IR drying. The difference between the initial weight and the weight after drying corresponds to the moisture contained in the sample.

Molecular weight

Determination of molecular weights Mn was conducted by using gel permeation chromatography, which is calibrated versus polystyrene standards. Therefore, the reported molecular weights are relative molecular weights.

The following parameters and equipment were used:

HPLC WATERS 2690/5 (pump), 2489 UV-Detector precolumn PSS SDV precolumn column PSS SDV 10pm 1000, 10⁵ und 10⁶ A eluent 0.01 M LiBr + 0.03M H3PO4 in DMF (filtered with 0.45 pm) flow 1.0 ml/min running time 43 min pressure -1100 psi detection wavelength 270 nm injection volumes 50 pl or 20 pl (for solutions c >1 g/l) standards PS(Polystyrol)-Standards (narrow distributed, 600-3x10®, PSS)

Examples

The examples below are intended to illustrate and describe the present invention in more detail but shall not be construed in any way to limit the scope of the claims.

Example 1

A filament yarn of polyimide P84®-Type 70 (1060 dtex, 480 single threads with 80 twists per meter) obtained from Evonik s GmbH Austria, was collected to build a larger tow. Twelve tows were fed into a Pierret P26 Guillotine cutting machine. The tows were cut with a cutting size of 0.1 mm with 400 cuts/min. The powder was collected and screened with a 0.5 mm screen to remove small fibres.

The polyimide particles obtained are shown in Figures 1 and 2a to 2d. The particles have a sharp shape. Most of the particles have a rectangular shape (Figure 2b) and only a minor number of particles having a square (Figure 2c) or trapezoidal (Figure 2d) shape. Stripes at the side view confirm the irregular shape of the cross-section of the particles that was maintained during cutting. Analytic data of the particles are given in Table 1 . Particle length distribution xso, LF and particle diameter distribution xso, Fmin, are shown in Figures 3a and 3b.

Comparative Example 1

Fibre filaments of polyimide P84® Type 70 (same polymer solution as in Example 1 ) having a length of 5 mm, were prepared via dry spinning according to US4,801502 B2. The filaments were washed in in 4 washing cycles at room temperature in demineralized water in a mass ratio 1 :40 (filaments : water) to remove DMF and then dried in a hurdle dryer at 80°C with circulating air. The dried fibre bulk was then milled by using a Retsch ZM200 laboratory mill: Two times milling at 18000 mim¹ with 0.25 mm mill insert. The fibre powder was then sieved with 250 pm sieve insert in a Retsch AS200 laboratory sieve tower.

A two-dimensional image of the obtained particles is shown in Figures 4a and 4b. It can be seen that a large amount of very small particles was formed and that the particle size distribution is wide. This is confirmed by the particle size analysis shown in Figures 5a and 5b, which also show that the particle size distributions are multimodal. Figures 4a and 4b further show that most of the small particles had a rather spherical shape. The larger particles had a rectangular but not sharp shape, i.e. most of the edges of the particles were rounded during milling. The shape of the particles clearly differs from the structure of the inventive powders according to Figures 1 and 2a to 2d. Analytic data of the particles are given in Table 1.

Comparative Example 2

Commercially available P84® Type 70 polyimide powder, made by Ensinger Sintimid GmbH by use of a precipitation and milling process, was sieved. The 200-mesh sieve fraction was used for image analysis. As shown in Figure 6, the polyimide powder has a granular, irregular, rough shape according to the classification of ASTM F 1877 - F. The shape of the particles clearly differs from the structure of the inventive powders according to Figures 1 and 2a to 2d. The particle size analysis shown in Figures 7a and 7b shows that the particle size distributions are multimodal. Analytic data of the particles are given in Table 1.

Table 1 :

Table 1 shows that the SPAN of the particles of invention according to Example 1 is low, i.e. the particles have very homogeneous particle length and diameter distribution. This is confirmed in Figures 3a and 3b.

In contrast thereto the milled fibres of Comparative Example 1 as well as the precipitated powder of Comparative Example 2 have much higher SPAN. In particular the amount of very small, as indicated by the Xw values, and larger particles is much higher. The particle size distribution curves of Comparative Example 1 (as shown in Figure 5a and 5b) as well as of Comparative Example 2 (as shown in Figure 7a and 7b) clearly show inhomogeneous, multimodal particle size distributions.

The bulk densities of all three powders are comparable.

Example 2:

The molecular mass Mn of the polyimide polymer used as raw material in Example 1 and Comparative Example 1 was compared with the molecular mass distribution of the final polyimide powder obtained in Example 1 respectively Comparative Example 1 as well as to the molecular mass distribution of the powder of Comparative Example 2. The results are given in Table 2.

Table 2

Table 2 shows that polyimide powders obtained via the filament routes in Example 1 and Comparative Examplel exhibit much higher molecular weight Mn compared to the powder obtained from the same polymer via the precipitation process as used by Ensinger Sintimid GmbH in Comparative Example 2. The molecular mass loss is obviously caused by the precipitation step, which can be avoided in the process of the invention.

Example 3

The polyimide powders obtained in Example 1, Comparative Example 1 and Comparative Example 2 show similar dissolution performance if dissolved in DMF to obtain 20% solutions. All three samples were completely dissolved after 3 hours of rolling on the rolling stand. Thus, the powder obtained via the process of the invention, even though having the desired higher molecular mass Mn (as shown in Example 3), do not have any disadvantages concerning their dissolution performance compared to commercially available products.

Example 4

The dust formation of the polyimide powders according to Example 1 , Comparative Example 1 and Comparative Example 2 was tested as described above! As shown in Figure 8, the inventive powder of Example 1 shows by far the lowest dust number SR compared to milled filaments according to Comparative Example 1 and the commercially available polyimide powder of Comparative Example 2. This confirms significant benefits achieved with the polyimide powders and process of the invention. Handling and transport of the inventive polyimide powder as well as execution of the inventive process can be done with significantly lower safety efforts to avoid dust explosions for example.

Example 5

Comparison of mechanical properties of semi-finished HCM parts made out of polyimide powders of

Example 1 and Comparative Example 2 is shown in Table 3

Table 3

Table 3 shown that semi-finished HCM parts made out of polyimide powders have higher mechanical strength compared to part made from commercially available polyimide powders, even though both powders were made from the same polyimide.

Claims

Claims:

1. A method for making a solvent soluble polyimide powder, comprising the steps a) Providing a solution of a solvent soluble aromatic polyimide or aromatic polyamic acid in an aprotic dipolar solvent, preferably selected from the group consisting of DMF, NMP, GBL, NEP, DMSO, DMAc, DMPr, 3-methoxy-N,N-dimethylpropionamide, mixtures thereof and solvent mixtures comprising one or more of said aprotic dipolar solvents, b) Spinning of a polymer fibre from the solution of the aromatic polyimide or the aromatic polyamic acid provided in step a) c) Optionally, in case an aromatic polyamic acid solution is provided in step a) and used for spinning in step b), obtaining fibre(s) of the aromatic polyimide by imidation of the aromatic polyamic acid fibre(s) obtained in step b), characterized in that the method comprises a step d) Preparation of a polyimide powder by d1) cutting the fibre(s) of the aromatic polyimide obtained in step b) or c) to obtain particles or d2) cutting the fibre(s) of the aromatic polyamic acid obtained in step b) to obtain particles, and subsequent imidation of the particles, wherein the fibre(s) of the aromatic polyimide or of the aromatic polyamic acid is/are cut in step d1) respectively d2) to particles having an average length xso, LF of from 30 to 250 pm, preferably 40 to 200 pm, even more preferred 50 to 180 pm, especially preferred 50 to 150 pm and most preferred 60 to 100 pm, and wherein in case step d2) is carried out, the process comprises step e), obtaining powder particles of the aromatic polyimide by imidation of the aromatic polyamic acid powder particles obtained in step d2).

2. The method of claim 1 further comprising one or more washing steps f), one or more solvent exchange steps g) and one or more drying steps h), wherein : the one or more washing steps f) are selected from the group consisting of f1 ) washing the polymer fibre f2) washing the polyimide particles f3) washing the polyamic acid particles, and the one or more solvent exchange steps g) are selected from the group consisting of g 1 ) solvent exchange of the polymer fibre g2) solvent exchange of the polyimide particles g3) solvent exchange of the polyamic acid particles and the one or more drying steps h) are selected from the group consisting of hi) drying the polymer fibre h2) drying the polyimide particles h3) drying the polyamic acid particles and wherein step f1), if comprised, is carried out after step b) or c) or g) or g) + h), step f2) , if comprised, is carried out after step d1) or e) or g) or g) + h) and step f3), if comprised, is carried out after step d2) or g) or g) + h), and wherein step g1), if comprised, is carried out after step b) or c) or f) or f) + h), step g2), if comprised, is carried out after step d1) or e) or f) or f) + h) and step g3), if comprised, is carried out after step d2) or f) or f) + h), and wherein step hl), if comprised, is carried out after step b) or c) or f) or g), step h2), if comprised, is carried out after step d1 ) or e) or f) or g) and step h3), if comprised, is carried out after step d2), or f) or g).

3. The method according to claim 2, characterized in that the residual content of the aprotic dipolar solvent in the polyimide fibre or polyimide particles or polyamic acid fibre or polyamic acid particles is reduced in step f) and/or g) to below 5% by weight, preferably below 3% by weight, even more preferred below 1% by weight and most preferred of not more than 0.5% by weight, in each case based on the overall weight of the fibres respectively particles, before any drying step h) and/or any thermal imidation of polyamic acid fibres in step c) or polyamic acid particles in step e) is carried out.

4. The method according to any one of the preceding claims, characterized in that the polymer fibre is cut with a blade or with a guillotine cutting machine, preferably by moving the polymer fibre by a constant cutting interval between cuts.

5. The method according to any one of the preceding claims, characterized in that multiple polymer fibres are aggregated with an approximately parallel orientation of the fibres to each other, before cutting, preferably multiple polymer fibres are being aggregated to a yarn and/or tow before cutting.

6. The method according to any one of the preceding claims, characterized in that the aromatic polyimide provided in step a) comprises, identical or different, recurring units of Formula (1a) or that the aromatic polyamic acid provided in step a) comprises, identical or different, recurring units of Formula (1b) Formula (la) Formula (lb) wherein the functional group R^A represents one or more, identical or different, moieties selected from the group consisting of the moieties R^A1, R^A2 and R^A3 and the functional group R^B represents one or more, identical or different moieties selected from the group consisting of the moieties R^B1, R^B2 and R^B3 wherein Yi , Y2, Y3 and Y4 are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Y - - CH2-, -(CH₃)₂C-, SO₂. -(CF₃)C-. -CO-, -COO-, -CONH-, -O-.

7. The method according to claim 6, wherein at least 90 mol-% of building blocks R^A are 3, 3’, 4,4’- benzophenonetetrayl and at least 90 mol-% of building blocks R^B are 2,4-toluenediyl, 2,6-toluenediyl or 4,4’-methylenediphenyldiyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1 and a molar ratio of the combined amount of 2,4-toluenediyl and 2,6-toluenediyl to the amount of 4,4’-methylenediphenyldiyl of from 70 : 30 to 100 : 0.

8. The method according to claim 6, wherein at least 90 mol-% of building blocks R^A are 3, 3’, 4,4’- benzophenonetetrayl or 1 ,2,4,5-phenylenetetrayl, with a molar ratio of 3, 3’, 4,4’- benzophenonetetrayl to 1 ,2,4,5-phenylenetetrayl of from 50 : 50 to 95 : 5, preferably of from 55 : 45 to 65 : 35, and at least 90 mol-% of building blocks R^B are 2,4-toluenediyl or 2,6-toluenediyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1.

9. The method according to claim 6, wherein the solvent soluble aromatic polyimide or aromatic polyamic acid is a solvent soluble a block-copolyimide or block co-polyamic acid comprising, preferably consisting of, the blocks (A) as per the ensuing formulae (3a), or (3b) and (B) as per the ensuing formulae (4a) or (4b): wherein the functional group Ri therein comprises either or both of the following functional groups: and R2 comprises at least one or 2 or 3 of the following functional groups and wherein

R3 comprises one or more of the following functional groups: and R4 comprises one or more of the following functional groups

^4a R_4b R₄C where Yi, Y2, Y3 and Y4 are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Z = - CH2-, -(CH3)2C-, SO2. -(CF3)C-. -CO-, -COO-, -CONH-, -O-, with the proviso that at least one of the radicals Y1 to Y₄, preferably at least two of the radicals Y1 to Y₄, more preferably at least three of the radicals Y1 to Y₄ and most preferably all the radicals Y1 to Y₄ are equal to CH3 or a C2 to C₄ alkyl radical.

10. The method according to any one of the preceding claims, characterized in that the fibres being cut in step d) having a rectangular shape, more preferred having a sharp rectangular shape and/or, at the points of the fibre where they are cut, a minimum Feret diameter XFmin of from 1 to 100 pm, preferably 10 to 90 pm, more preferred 10 to 85 pm, even more preferred 10 to 80 pm, particular preferred 10 to 75 pm, very particular preferred 15 to 62.5 pm and most preferred 20 to 60 pm.

11. A solvent soluble polyimide powder, comprising polyimide particles comprising at least 90 % by weight of a solvent soluble aromatic polyimide, wherein more than 50% of the polyimide particles, preferably more than 60%, particular preferred more than 70 %, especially preferred more than 80%, even more preferred more than 85% and most preferred more than 90%, based on the number of the counted particles, having a rectangular fibre shape, preferably a sharp rectangular shape, the particles having an average length xso, LF of from 30 to 250 pm, preferably 40 to 200 pm, even more preferred 50 to 180 pm, especially preferred 50 to 150 pm and most preferred 60 to 100 pm, and the particles having a fibre length span (X90, LF - xw, LF)/ XSO, LF in the range of from 0.1 to 2.5, more preferred 0.3 to 2 even more preferred 0.5 to 1.8, particular preferred 0.5 to 1.5 and most preferred 0.5 to 1.2.

12. A polyimide powder according to claim 11 , characterized in that the cross-section of the particles having an irregular shape.

13. A polyimide powder according to claim 11 or 12, characterized in that the particles having an average minimum Feret diameter xso, Fmin of from 10 to 100 pm, preferably 10 to 80 pm, more preferred 20 to 70 pm, even preferred 30 to 70 pm and most preferred 30 to 60 pm and/or a particle diameter distribution span (xgo_; Fmin - xw_; Fmin) / xso; Fmin, of from 0. 1 to 2.5, more preferred 0.2 to 2 even more preferred 0.3 to 1.5, particular preferred 0.4 to 1.2 and most preferred 0.5 to 1.0.

14. A polyimide powder according to any one of claims 11 to 13, characterized in that the particles having a monomodal particle length distribution for particles with X F > 30 pm and/or a monomodal particle diameter distribution for particles with XFmin > 20 .

15. A solvent soluble polyimide powder, according to any one of claims 11 to 14, comprising at least 90 % by weight of an aromatic polyimide of having identical or different recurring units of formula (1a) Formula (la) wherein the functional group R^A represents one or more, identical or different moieties selected from the group consisting of the moieties R^A1, R^A2 and R^A3 and the functional group R^B represents one or more, identical or different moieties selected from the group consisting of the moieties R^B1, R^B2 and R^B3 and where Yi, Y2, Y3 and Y4 are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Y = -CH2-, -(CH₃)₂C-, SO₂. -(CF₃)C-. -CO-, -COO-, -CONH-, -O-.

16. The solvent soluble polyimide powder according to claim 15, characterized in that at least 90 mol-% of building blocks R^A are 3,3’,4,4’-benzophenonetetrayl and at least 90 mol-% of building blocks R^B are 2,4-toluenediyl, 2,6-toluenediyl or 4,4’-methylenediphenyldiyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1 and a molar ratio of the combined amount of 2,4-toluenediyl and 2,6-toluenediyl to the amount of 4,4’-methylenediphenyldiyl of from 70 : 30 to 100 : 0 or at least 90 mol-% of building blocks R^A are 3,3’,4,4’-benzophenonetetrayl or

1.2.4.5-phenylenetetrayl, with a molar ratio of 3,3’,4,4’-benzophenonetetrayl to

1.2.4.5-phenylenetetrayl of from 50 : 50 to 95 : 5, preferably of from 55 : 45 to 65 : 35, and at least 90 mol-% of building blocks R^B are 2,4-toluenediyl or 2,6-toluenediyl, with a molar ratio of 2,4-toluenediyl to 2,6-toluenediyl of from 1 : 9 to 9 : 1.

17. The solvent soluble polyimide powder according to claim 15, characterized in that the solvent soluble polyimide is a block-copolyimide comprising, preferably consisting of, the blocks (A) as per the ensuing Formula (3a) and (B) as per the ensuing Formula (4a): Formula (4a) wherein the functional group Ri therein comprises either or both of the following functional groups: and R2 comprises at least one or 2 or 3 of the following functional groups and wherein R3 comprises one or more of the following functional groups: and R4 comprises one or more of the following functional groups

Ria R_4b R₄C where Yi, Y2, Y3 and Y₄ are either H or CH3 or alkyl radicals with 2 to 4 carbon atoms and Z = -

CH2-, -(CH3)2C-, SO2. -(CF3)C-. -CO-, -COO-, -CONH-, -O-, with the proviso that at least one of the radicals Y1 to Y₄, preferably at least two of the radicals Y1 to Y₄, more preferably at least three of the radicals Y1 to Y₄ and most preferably all the radicals Y1 to Y₄ are equal to CH3 or a C2 to C₄ alkyl radical.

18. Use of a polyimide powder according to any one of claims 11 to 17 for hot compression molding or to produce polyimide coatings of substrates or as fillers for finished or semi-finishes polymeric products or as raw material to produce fibres or hollow fibres or flat sheets or the corresponding membranes, or to store and transport of the polyimide from its production site to the site where it is used and further processed.