EP3500617A1

EP3500617A1 - Method for producing polyimides

Info

Publication number: EP3500617A1
Application number: EP17777150.8A
Authority: EP
Inventors: Miriam Margarethe UNTERLASS; Sebastian ESPANA-OROZCO
Original assignee: Technische Universitaet Wien
Current assignee: Technische Universitaet Wien
Priority date: 2016-08-19
Filing date: 2017-08-21
Publication date: 2019-06-26
Also published as: AT519038B1; AT519038A1; US20190177483A1; WO2018032023A1

Abstract

The invention relates to a method for producing polyimides by the polycondensation of previously produced stoichiometric salts from polycarboxylic acids or their polyanhydrides and polyamines, by heating the salts for dehydration, the method being characterised in that: a) an aqueous solution of a water-soluble stoichiometric salt is produced from polycarboxylic acid and polyamine; b) the aqueous solution undergoes a processing step; and c) the salt contained in the solution is simultaneously or subsequently polycondensed, by means of heating, to form a polyimide.

Description

Process for the preparation of polytmides

The present invention relates to a novel production process for polyimides. STATE OF THE ART

Polyimides are valuable materials for various applications. Their synthesis is usually carried out by polycondensation of diamines with dianhydrides in solution, in the melt or even in a solid state. Surprisingly, it was found several years ago that - despite the elimination of water during the condensation reaction - even water can be used as a solvent for the polyimide synthesis, when so-called "hydrothermal conditions" prevail, to understand a reaction under pressure at temperatures above 100 ° C. (see Hodgkin et al., "Water as a Polymerization Solvent-cyclization of Polyimides: Le Chatelier Confounded", Polym. Prep. (American Chemical Society, Division of Polymer Chemistry) 41, 208 (2000), and WO 99 / 06470). When solvents other than water are used, the term "solvothermal conditions" is used at temperatures above their boiling points.

The mechanism of this condensation reaction proceeds in two stages through the formation of amic acids, which subsequently undergo cyclodehydration to the corresponding imides. Dao et al. In 1999, factors significantly influencing the imidization reaction were investigated (Dao, Hodgkin and Morton, "Important Factors Controlling Synthesis of Imides in Water", High Perform Polym. 1 1, 205-218 (1999), "Dao 1999") and found, among other things, that the higher the temperature of the imidization reaction, the more pure the products.

The reason why the reaction equilibrium of this dehydration-proceeding cyclization, even in water, as a solvent on the product side, is the changed properties of the solvent under solvothermal conditions. For example, water behaves like a pseudo-organic solvent under these conditions (Hodgkin et al., Supra). Furthermore, it is customary to form a stoichiometric salt of diamide and dianhydride before the polymerization, which usually takes place simply by mixing the monomers in water and filtering off the water-insoluble and therefore precipitated salts, as is currently the case in WO 2016/032299 A1 is described. The anhydrides undergo hydrolysis to form the free tetracarboxylic acids, of which two carboxyl groups each having one amino group form an ammonium salt (Unterlass et al., "Mechanistic study of hydrothermal synthesis of aromatic polyimides", Polym. Chem. 201 1, 2, 1744 ). In the monomer salts thus obtained, which are sometimes referred to as "AH salts" (in analogy to polyamide and especially nylon synthesis), the two monomers are thus present exactly in a molar ratio of 1: 1, which is why their subsequent polymerization leads to very pure polyimides , Below is an example of the reaction scheme of two typical aromatic monomers:

Another modern technology that has been used for several years to synthesize organic compounds and, more recently, polyimides is microwave radiation, which significantly reduces reaction times and increases the selectivity of reactions (Lindstrom et al., "Microwave Assisted Organic Synthesis: a Review ", Tetrahedron 57, 9225-9283 (2001); Perreux et al.," A Tentative Rationalization of Microwave Effects in Organic Synthesis According to the Reaction Medium and Mechanistic Considerations ", Tetrahedron 57, 9199-9223 (2001)). Microwaves have also been used in the synthesis of polyimides (Lewis et al., Accelerated Imidization Reactions using Microwave Radiation, J. Polym., Part A: Polym. Chem. 30, 1647-1653 (1992) and US 5,453. 161).

A combination of the hydrothermal process described above and heating by means of microwave radiation is also known. On the one hand, Dao et al. (Dao, Groth and Hodgkin, "Microwave-assisted aqueous polyimidization using high-throughput Techniques ", Macromol, Rapid Commun., 28, 604-607 (2007);" Dao 2007 ") by means of serial experiments with a ternary monomer mixture of a diamine (4,4-oxydi- aniline, ODA) and two dianhydrides (4,4 '). - (Hexafluorisopropyliden) diphthalic acid anhydride, 6-FDA, pyromellitic dianhydride, PMDA) at temperatures between 120 ° C and 200 ° C found that the best results at 180-200 ° C can be achieved if the goal is the highest possible molecular weight obtained random (block copolymers of the following formula:

And on the other hand, only a few years ago Brunei et al. (Brunei, Marestin, Martin and Mercier, "Waterborne Polyimides via Microwave-assisted Polymerization", High Perform Polym. 22, 82-94 (2010)) using a binary polyimide of ODA and 4,4'- (4, 4'-isopropylidenediphenoxy) bis (phthalic anhydride) (bisphenol A dianhydride, BPADA)

confirmed once again that the use of microwave can significantly reduce the reaction times, ie from 4 to 12 h to just 5 to 10 min. The sales generated in this short time, however, are extremely low at only about 20%. In both cases, however, no crystalline products could be obtained. US 2008/300360 A1 discloses an alternative process using water as a solvent to prepare waterborne coating solutions. However, it is not assumed that AH salts, but it is first from previously dehydrated polyamines and polyanhydrides in the presence of a defined proportion of, for example, 5 to 60 mol% of monoanhydrides as terminators prepolymers, ie low molecular weight oligomers, prepared from which in the sequence Suspensions or - after grinding them to obtain smaller particle sizes - colloidal solutions are formed in water, which are used for coating surfaces. In order to prepare stable suspensions and colloidal solutions, it is also preferable to add suspension stabilizers to the prepolymers obtained, which are characterized as being insoluble in water. These aqueous systems are made into coatings, particularly laminates, by application to a surface, evaporation of the water, and heating to initiate polycondensation of the prepolymers into macromolecules having molecular weights of at least 10,000.

With respect to solvothermal synthesis of polyimides, the present inventors have recently found that under hydrothermal conditions, crystalline polyimides may well be obtained when either the solvent is heated to solvothermal conditions and only then the monomers are added to initiate the reaction or the monomers are mixed with the solvent and the mixture is heated to solvothermal conditions within 5 minutes, during which the reaction temperature is kept solid under the polymerization temperature of the monomers (B. Baumgartner, MJ Bojdys, P. Skrinjar and MM Unterlass, "Design Strategies in Hydrothermal Polymerization of Polyimides", Macromol Chem. Phys., 217, 485-500 (2016)].

Despite these advantageous recent developments, the high expenditure on equipment and energy for generating hydrothermal conditions in order to be able to use water as solvent for the polycondensation reaction continues to represent a considerable disadvantage. Against this background, the object of the present invention was Invention to provide a method by which this disadvantage can be overcome.

DISCLOSURE OF THE INVENTION

The present invention solves this problem by providing a process for the preparation of polyimides by polycondensation of stoichiometric salts of polycarboxylic acids or their polyanhydrides and polyamines previously prepared by heating the salts for dehydration, which is characterized in that

a) an aqueous solution of a water-soluble stoichiometric salt of polycarboxylic acid and polyamine is prepared;

b) subjecting the aqueous solution to a processing step; and

c) simultaneously or subsequently the salt contained in the coating is polycondensed by heating to a polyimide.

This invention is based on the inventors' most surprising finding that some monomer salts of polycarboxylic acid and polyamide are water-soluble, and thus do not precipitate upon mixing of the monomers from an aqueous solution, in contrast to all other known such salts. Due to this unique property, it is possible to subject such an aqueous solution of the monomer salts directly to a processing step and simultaneously or sequentially by heating - preferably to a temperature Tp which is above the solid state polymerization temperature of the salt to complete conversion of the To ensure polycondensation reaction - to undergo a polycondensation.

In preferred embodiments, the aqueous solution is applied to a support or a substrate to obtain a coating and the resulting coating is polycondensed by heating. In this case, the coating is preferably dried before the polycondensation in step c), whereby a film or a solid film is formed on the substrate, which is easier to handle than the moist coating. In alternative preferred embodiments, the aqueous solution is foamed in processing step b), after which the resulting foam is cured by polycondensation in subsequent step c) to obtain a cured polyimide foam. In still other preferred embodiments, in the processing step b) the aqueous solution is fed to a nozzle heated to a temperature above Tp, where the stoichiometric salt in step c) is simultaneously cured by polycondensation and the resulting polyimide is forced through the nozzle opening (s), to obtain a molded polyimide product. The polyimide thus obtained can be wet-spun, press-molded or extruded into filaments, for example, depending on the particular nozzle used and the associated molding apparatus. Wet-spun filaments are then preferably wound on spools to obtain polyimide fibers.

The water-soluble stoichiometric salt is preferably prepared in step a) by mixing stoichiometric amounts of polycarboxylic acid or its polyanhydride and polyamine in water or in an aqueous solvent mixture. Furthermore, the water-soluble stoichiometric salt is preferably precipitated by adding at least one organic solvent for intermediate storage prior to the polycondensation. The organic solvent used therefor is not particularly limited so long as it sufficiently lowers the solubility of the stoichiometric salt in the formed aqueous solvent mixture to cause precipitation thereof, provided that it is itself a nonsolvent for the stoichiometric salt. Both water-miscible and water-immiscible solvents can be used for this purpose, for example alcohols, e.g. such as methanol or other lower alcohols, ethers, e.g. THF, acetone, etc.

In preferred embodiments of the present invention, as already mentioned above, in the processing step b), a film is drawn from the aqueous solution of the water-soluble stoichiometric salt on a substrate so as to optionally follow the subsequent polycondensation of the salt to the corresponding polyimide a composite material or, after peeling the cured polyimide film from the substrate, to obtain a polyimide film.

Preferably, according to the present invention, a water-soluble stoichiometric salt of a tetracarboxylic acid and a diamine is prepared and polycondensed, since these are the most common starting materials in polyimide production. However, of course, combinations of other polyhydric amines and / or polycarboxylic acids or their anhydrides are also possible, e.g. the preparation of stoichiometric salts of triamine and dianhydride, diamine and trianhydride, triamine and trianhydride, etc. as long as these monomers form water-soluble salts in the corresponding stoichiometric composition.

The tetracarboxylic acid is particularly preferably selected from benzophenone tetracarboxylic acid, tetrahydrofurantetracarboxylic acid, butanetetracarboxylic acid and their dianhydrides, since the inventors have already found water-soluble stoichiometric salts of these polycarboxylic acids. For the same reason, the diamine is preferably selected from benzenedimethanamine and ethylenediamine. In particular, the stoichiometric salts of 1,3-benzenedimethanammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (1), 1,3-benzenedimethanammonium dihydrogen-1,2,3,4-butanetetracarboxylate (2), 1,3-benzenedimethanammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (3), ethane-1,2-diammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (4), Ethane-1, 2-diammonium dihydrogen-tetrahydrofuran-2,3,4,5-tetracarboxylate (5) and their hydrates selected, with which excellent results have already been achieved in the inventive method, the hydrates easier to produce in crystalline form are as the anhydrous ammonium salts.

Since these salts are all new, ie synthesized and characterized for the first time by the inventors, which at the same time is the reason why their solubility in water has not yet been discovered, in a second aspect the present invention also provides these specific compounds, namely 1,3-Benzenedimethanammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (1):

1,3-Benzenediimethanammonium dihydrogen-1,2,3,4-butanetetracarboxylate (2):

1,3-benzenedimethanammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate Ethane-1,2-diammonium dihydrogen-3,3,4,4'-benzophenone tetracarboxylate (4):

Ethane-1,2-diammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (5):

Furthermore, the present invention also provides two novel polyimides synthesized and characterized for the first time by the inventors - from the corresponding water-soluble stoichiometric salts (3) and (5), namely:

Poly (N, N '- (benzene-1,3-dimethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic acid diimide) (6):

and

Poly (N, N '- (1,2-ethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic acid diimide) (7):

where: n≥ 2.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be further described, by way of non-limitative example, with reference to the accompanying drawings, in which: Figs. 1 to 5 are IR spectra of the water-soluble stoichiometric monomer salts obtained in Examples 1, 4, 6, 7 and 8 and Figs Figures 6 and 7 show IR spectra of the polyimides obtained in Examples 12 and 13.

EXAMPLES

All reagents used in the experiments below are commercially available and used without further purification. The IR spectra shown in the accompanying drawings were recorded by FT-IR ATR spectroscopy on a Bruker Tensor 27 and ¹ H NMR spectra on an Avance 250, also Bruker, at 250 MHz. By "Tp" below is meant the solid state polymerization temperature of the obtained stoichiometric salts. example 1

Preparation of 1,3-benzenedimethanammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (1)

150 mg (0.47 mmol) of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride were dissolved in 10 ml of dist. Water, and 61.4 μΙ (0.47 mmol) of 1,3-benzenedimethanamine were added to form a clear, yellowish solution. After stirring for 30 minutes, the water was removed on a rotary evaporator in a water bath (50 ° C) in a vacuum of about 60 mbar and the residue dried under high vacuum. The title compound was quantitatively obtained as a colorless amorphous solid whose IR spectrum is shown in FIG. The solid is highly hygroscopic and gradually deliquesces in the air to a yellow liquid phase of the tetrahydrate.

Tp .: 151 ° C (DSC) or 161 ° C (TGA) (heating rate: 10 K / min)

¹ H-NMR (250 MHz, DMSO-de) δ: 8.51 (d, 2H, ar), 8.32 (d, 2H, ar), 7.85 (q, 2H, ar), 7.45 (m, 4H, ar), 4.01 (s, 4H, aliph).

IR (cm ^-1 ): 2882, 2619, 1694, 1601, 1540, 1359. Example 2

Precipitation of the tetra hydrate of (1) by addition of solvent

The batch of Example 1 was repeated, to which 30 ml of THF were added to the resulting aqueous solution of (1) (here: in 5 ml of distilled water), a precipitate forming in the form of a white turbidity. The mixture was allowed to stand overnight, with the initial precipitate turning yellow formed second liquid phase, which was crystallized after a further 24 hours rest to colorless crystals.

The data correlated with those of Example 1, except for the presence of water.

Example 3

Preparation of (1) as an aqueous solution and coating of a surface

Example 1 was repeated, using instead of the isolation of the stoichiometric salt (1) by evaporation of the water, the aqueous solution for coating a glass plate. For this purpose, a few drops of the solution were dropped on a glass plate and allowed to air dry. Subsequently, the polycondensation to poly (N, N '- (benzene-1, 3-dimethylene) benzophenone-3,3', 4,4'-tetracarboxylic diimide) was carried out in a vacuum oven maintained at 200 ° C overnight. The IR spectrum of the polyimide thus obtained corresponded to that of the product known from the literature.

Example 4

Preparation of 1,3-benzenedimethanammonium dihydrogen-1,2,3,4-butanetetracarboxylate (2):

150 mg (0.64 mmol) of 1,2,3,4-butanetetracarboxylic acid were dissolved in 10 ml of dist. Water, and 84.5 μΙ (0.64 mmol) of 1,3-benzenedimethanamine were added at once, after which the reaction mixture was shaken until a clear solution had formed. Work-up and drying were carried out analogously to Example 1, the title compound being obtained in quantitative yield as a hygroscopic, colorless, amorphous solid whose IR spectrum is shown in FIG.

Tp .: 151 X (TGA)

¹ H NMR (250 MHz, D ₂ O) δ: 7.5 (m, 4H, ar), 4.2 (s, 4H, aliph), 2.9 (m, 2H, aliph), 2.6 (m, 2H, aliph), 2.4 (m, 2H, aliph).

IR (cm- ¹ ): 3386, 2918, 2626, 1701, 1620, 1542.

Example 5

Precipitation of the tetra hydrate of (2) by addition of solvent

The batch of Example 4 was repeated, to which 30 ml of THF were added to the resulting aqueous solution of (2) (here: in 5 ml of distilled water), a precipitate forming in the form of a white turbidity. The mixture was allowed to stand overnight, with the initial precipitate forming a yellow colored second liquid phase, which crystallized after a further 24 hours rest to colorless crystals.

The data correlated with those of Example 4, except for the presence of water.

Example 6

Preparation of 1,3-benzenedimethanammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (3):

(3)

150 mg (0.60 mmol) of tetrahydrofuran-2,3,4,5-tetracarboxylic acid were dissolved in 10 ml of dist. Dissolved water, and 79.8 μΙ (0.60 mmol) of 1, 3-benzenedimethanamine were added all at once, after which the reaction mixture was shaken until a clear solution had formed. Work-up and drying were carried out analogously to Example 1, giving a hygroscopic, colorless, amorphous solid in quantitative yield, the IR spectrum of which is shown in FIG.

Mp .: 62 ° C (DSC)

Tp .: 144 ° C (DSC) or 151 ° C (TGA) (heating rate: 10 K / min)

¹ H-NMR (250 MHz, DMSO-de) δ: 7.5 (s, 1H, ar), 7.4 (m, 3H, ar), 4.4 (m, 2H, aliph), 4, 0 (s, 4H, aliph), 3.0 (m, 2H, aliph).

IR (cm ¹ ): 3393, 3052, 2929, 1714, 1600, 1568.

Example 7

Preparation of ethane-1,2-diammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (4):

150 mg (0.47 mmol) of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride were dissolved in 10 ml of dist. Water was dissolved and 31.1 pl (0.47 mmol) of 1,2-ethylenediamine was added in one portion, after which the reaction mixture was shaken until a clear solution had formed. Work-up and drying were carried out analogously to Example 1, whereby a hygroscopic, colorless, amorphous solid was obtained in quantitative yield, whose IR spectrum is shown in Fig. 4. Tp .: 128 ° C (DSC) or 149 C (TGA) (heating rate: 10 K / min)

¹ H-NMR (250 MHz, D ₂ O) δ: 8.1 (d, 2H, ar), 7.9 (q, 2H, ar), 7.7 (d, 2H, ar), 3.4 (s, 4H, aliph).

IR (cm ¹ ): 3386, 3030, 2929, 1699, 1602, 1541.

Example 8

Preparation of ethane-1,2-diammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (5):

150 mg (0.60 mmol) of tetrahydrofuran-2,3,4,5-tetracarboxylic acid were dissolved in 10 ml of dist. Water was dissolved and 40.4 μΙ (0.60 mmol) of 1,2-ethylenediamine was added in one portion, after which the reaction mixture was shaken until a clear solution had formed. Work-up and drying were carried out analogously to Example 1, giving a hygroscopic, colorless, amorphous solid whose IR spectrum is shown in FIG. 5.

Tp .: 128 ° C (DSC) or 149 ° C (TGA) (heating rate: 10 K / min)

¹ H-NMR (250 MHz, D ₂ O) δ: 4.8 (m, 2H, aliph), 3.5 (m, 2H, aliph), 3.4 (s, 4H, aliph).

IR (cm- ¹ ): 3400, 3031, 2926, 1713, 1600, 1561.

Examples 9 to 13

Coating and polycondensation

The batches of Examples 1, 4, 6, 7 and 8 were repeated, using the aqueous solutions for coating glass plates, similar to Example 3, instead of isolating the stoichiometric salts. For this purpose, 5 to 10 ml of the respective aqueous solution were applied to a glass plate, which was then in an oven at a heating rate of 5 K / min was heated to 250 ° C and then maintained at this temperature for 30 min.

The polyimides thus obtained were three products known from the literature, namely in Example 9 (with the stoichiometric salt obtained analogously to Example 1):

Poly (N, N '- (benzene-1,3-dimethylene) benzophenone-3,3', 4,4'-tetracarboxylic diimide); in Example 10 (with the stoichiometric salt obtained analogously to Example 4): poly (N, N '- (benzene-1,3-dimethylene) butane-1,2,3,4-tetracarboxylic acid diimide) and in Example 1 ( with the stoichiometric salt obtained analogously to Example 7): poly (N, N '- (1, 2-ethylene) benzophenone-3,3', 4,4'-tetracarboxylic acid diimide);

and two previously unknown polyimides, namely:

in Example 12 (with the stoichiometric salt obtained analogously to Example 6): poly (N, N '- (benzene-1,3-dimethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic diimide) (6); and in Example 13 (with the stoichiometric salt obtained analogously to Example 8): poly (N, N '- (1,2-ethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic diimide) (7).

These polyimides were analyzed inter alia by means of IR spectroscopy. The IR spectra of the products of Examples 9 to 1 1 corresponded to those of the literature known polyimides.

Of the novel polyimides (6) and (7), the decomposition points were determined in addition to the IR spectra shown in FIGS. 6 and 7, and a ¹ H-NMR spectrum of polyimide (6) was also recorded (for polyimide (FIG. 7) impossible because it was insoluble in the tested solvents) to give the following data.

Poly (N, N '- (benzene-1,3-dimethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic diimide)

(6):

Mp .: 456 ° C (decomp.) (TGA, heating rate: 10 K / min)

¹ H-NMR (250 MHz, DMSO-de) δ: 7.3 (s, 1H, ar), 7, 1 (d, 3H, ar), 5.2 (t, 1H, aliph), 4 , 7 (s, 1H, aliph), 4,6 (s, 2H, aliph), 4,5 (s, 2H, aliph), 3,9 (s, 2H, aliph).

IR (cm- ¹ ): 1784, 1695, 1333.

Mp .: 438 ° C (decomp.) (TGA, heating rate: 10 K / min)

IR (cm ^1): 1785, 1690, 1339 hits.

The present invention thus provides a process by which polyimide coatings can be prepared from aqueous solutions of the stoichiometric monomer salts, which is a considerable advantage over the prior art, as it limits the use of expensive and only with enormous energy expense to be removed solvent or even avoided altogether.

Moreover, the invention should not be limited to the five monomer combinations disclosed herein, especially since the person skilled in the art - who now has the knowledge that such water-soluble monomer salts actually exist - is easily able to do so by simple routine experiments, including other combinations of polycarboxylic acid or Polyanhydride and polyamines, which give a water-soluble stoichiometric salt.

Claims

1 . Process for the preparation of polyimides by polycondensation of previously prepared stoichiometric salts of polycarboxylic acids or their polyanhydrides and polyamines by heating the salts for dehydration,

characterized in that

b) subjecting the aqueous solution to a processing step; and

2. The method according to claim 1, characterized in that in step c) is heated to a temperature Tp, which is above the solid state polymerization temperature of the salt.

3. The method according to claim 1 or 2, characterized in that in the processing step b) with the aqueous solution, a substrate is coated to obtain a coating which is cured in the subsequent step c) by polycondensation.

4. The method according to claim 3, characterized in that the coating obtained in the processing step b) before the polycondensation in step c) is dried.

5. The method according to claim 4, characterized in that in the processing step b) a film is drawn from the aqueous solution of the water-soluble stoichiometric salt on the substrate.

6. The method according to claim 1, characterized in that in the processing step b), the aqueous solution is foamed to obtain a foam, the in the subsequent step c) is cured by polycondensation to obtain a cured polyimide foam.

7. The method according to claim 1, characterized in that in the processing step b) the aqueous solution is fed to a heated temperature above Tp nozzle, where the stoichiometric salt in step c) simultaneously cured by polycondensation and the resulting polyimide through the nozzle opening (s) is pressed to obtain a molded polyimide product.

8. The method according to claim 7, characterized in that the resulting polyimide is wet-spun, press-molded or extruded.

9. The method according to any one of claims 1 to 8, characterized in that the water-soluble stoichiometric salt is prepared in step a) by mixing stoichiometric amounts of polycarboxylic acid or its polyanhydride and polyamine in water or in an aqueous solvent mixture.

10. The method according to claim 9, characterized in that the water-soluble stoichiometric salt is precipitated by the addition of an organic solvent for intermediate storage before the polycondensation.

1 1. Method according to one of claims 1 to 10, characterized in that a water-soluble stoichiometric salt of a tetracarboxylic acid and a diamine is prepared and polycondensed.

12. The method according to claim 1 1, characterized in that the tetracarboxylic acid from Benzophenontetracarbonsäure, Tetrahydrofurantetracarbonsäure and Butantetracarbonsäure is selected.

13. The method of claim 1 1 or 12, characterized in that the diamine is selected from benzenedimethanamine and ethylenediamine.

14. The method according to claim 13, characterized in that the stoichiometric salt of 1,3-benzenedimethanammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (1), 1, 3-benzenedimethanammonium dihydrogen 1, 2,3,4-butanetetracarboxylate (2), 1,3-benzenedimethanammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (3), ethane-1,2-diammonium dihydrogen 3,3 ', 4,4'-benzophenontetracarboxylat

(4) and ethane-1,2-diammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate

(5) is selected.

15. The method according to claim 14, characterized in that as stoichiometric salt 1, 3-benzenedimethyne-dihydrogen-tetrahydrofuran-2,3,4,5-tetracarboxylate (3) is used and in the polycondensation of the polyimide poly ( N, N'- (benzene-1,3-dimethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic acid diimide) (6). 16. Process according to claim 14, characterized in that the stoichiometric salt used is ethane-1,2-diammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (5) and in the polycondensation the polyimide Poly (N, N '- (1,2-ethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic acid diimide) (7).

18. 1, 3-benzenedimethanammonium dihydrogen-1,2,3,4-butanetetracarboxylate (2):

19. 1, 3-Benzoldimethanammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (3):

20. Ethane-1,2-diammonium dihydrogen-3,3 ', 4,4'-benzophenone tetracarboxylate (4):

21. Ethane-1,2-diammonium dihydrogen tetrahydrofuran-2,3,4,5-tetracarboxylate (5)

22. Poly (N, N'-benzene-1, S-dimethylene, etrahydrofuran-2,3,4,5-tetracarboxylic diimide) (6):

where n≥2.

23. Poly (N, N '- (1, 2-ethylene) tetrahydrofuran-2,3,4,5-tetracarboxylic acid diimide) (7):

where n≥2.