EP1354242A1

EP1354242A1 - Crosslinkable oligoimides

Info

Publication number: EP1354242A1
Application number: EP02708404A
Authority: EP
Inventors: Eric Toussaere; Bernard Boutevin; Laurence Bes; Alain Rousseau; Régis Mercier; Bernard Sillion
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2001-01-22
Filing date: 2002-01-21
Publication date: 2003-10-22
Also published as: JP2004524557A; WO2002057845A9; US20040082732A1; WO2002057845A1; FR2819892B1; FR2819892A1

Abstract

The invention concerns a method for obtaining an electrooptic material characterised in that it consists in depositing on a substrate a solution of oligoimides whereon are grafted colouring agents capable of being oriented and in performing a treatment designed to cross-link the oligoimides and to provide orientation to the colouring agents.

Description

CROSSLINKABLE OLIGOIMIDES

The present invention relates to the manufacture of electrooptical materials and in particular the manufacture of electrooptical components. These components can be used in optical signal processing applications, in particular the modulation, switching and coding of one or more optical carriers.

In particular, this invention applies to components using polymers having second order nonlinearity optical properties.

Electrooptical polymers have great potential in the telecommunications field. These are materials likely to allow the manufacture of components at low cost and to be implemented in distribution networks by otic fiber directly to the user (Y.Shi et al. "Fabrication and characterization of High-Speed Polyurethane-Disperse Red 19 Integrated Electrooptic Modulators for Analog System Applications ", IEEE J. of Selected Topics in Quantum Electronics, Vol 2 (2), 1996, 289-298) (fiber to the home, FTTH), or over the air (SA Hamilton, DR Yankelevich, A.Knoesen, RTWeverka, RAHiïl, GCBjorklund, "Polymer in-line fiber modulators for broadband radio-frequency optical links", J. Opt. Soc. Am., B, 15 (2) 1998, 740-750). Furthermore, thanks to their rapid response time of electronic origin (D. Chen et al., "Demonstration of 110GHz electro-optic polymer modulators", App. Phys. Lett, 70 (25), 1997), and to the low dispersion of their dielectric constant, they can be used in more complex circuits for the processing of the microwave signal (T.Nagatsuma, M.Yaita, M. Shinagawa, "External electrooptic sampling using poled polymers", Jpn. Appl. Phys. 31, 1992, 1373- 1375) or optical delay lines (RLQIi. H. Tand, G. Cao, TTChen, "Optically heterodyned 25 GHz true-time delay Unes on thick LD-3 polymer - based planar waveguides", Appl. Opt., 36 (18), 1997, 4269). Their shaping is simple and implements proven technologies in the field of semiconductors (US-5291574, Levenson Régine, Liang Julienne, Carenco Alain, Zyss Joseph, "Method for manufacturing strip optical waveguides" (1994)). They thus make it possible to simply produce waveguides and more generally optical circuits on various substrates. Their formatting in other formats also allows them to be used for the storage of information by linear holography (Z. Sekkat, J. Wood, W. Knoll, W. Volken, R. Miller, A. Knoesen, " Light induced orientation in azo-polyimide polymers 325 ° C below the glass transition temperature ", J. Opt. Soc. Am. B, 14 (4) (1997), 829-833) or non-linear (J. Si, T. Mitsuyu, P.ye, Y.shen, K.Hirao, "Optical poling and its application in optical storage of a polyimide film with high glass transition temperature", Appl. Phys. Lett., 72 (7), 1998, 762- 764).

To obtain quadratic nonlinear optical properties, these polymers must be oriented in a non-centro-symmetrical manner. For example, to obtain an orientation under an electric field at high temperature (close to the glass transition temperature), the polymer to be oriented is placed between electrodes. A large electric field (of the order of 100 V / μm or more) is applied between these electrodes. This field directs the molecules by dipolar interaction; this orientation is then fixed by cooling the polymer while maintaining the applied field. To test the electrooptical effects of the substrate thus obtained, an electric modulation field is applied between the electrodes and makes it possible to modulate the refractive index of the polymer via the Pockels effect. This results in a phase shift of the optical wave propagating in the oriented polymer; this phase shift can be used to process the optical signal (modulation or switching).

Stability of components is important for practical applications. An issue that has been the subject of many studies is the orientation stability of "chromophores" (also called "dyes") in polymer films. Indeed, this induced molecular order, at the origin of non-linearity, is likely to relax over time. These studies led to the development of materials in which the orientation of the dyes could be permanently fixed. From the first doped polymers, we quickly moved to grafted polymers in which the active molecules are covalently linked to the matrix. This bond limits the relaxation of the orientation, but it can be further reinforced by a subsequent chemical reaction which attaches the dye by other covalent bonds (J. Liang, R. Levenson, C. Rossier, E. Toussaere, J .Zyss, A.Rousseau, B.Boutevin, F.Foll, D.Bosc, "Thermally stable cross-linked polymers for electro-optic applications", J.Phys. III France, 4, (1994, 2441-2450)) . This approach was supplemented by the sol-gel technique, the use of which allowed the synthesis of materials which can be crosslinked at low temperature (US 5449733, Zyss Joseph, Ledoux Isabelle, Pucetti Germain, Griesmar Pascal, Sanchez Clément, Livage Jacques, " Inorganic sol-gel material which has a susceptibility of the second order ", 1995).

Another solution consists in finding polymeric matrices with a high glass transition temperature and in modifying them in order to introduce a large quantity of dyes (T. Verbiest, DM Burland, MC Jurich, VY Lee, RD Miller , W. Volksen, "Exceptionnaly Thermally stable Polyimides for Second Order Nonlinear Optical Applications", Science, Vol 268, 1995, 1604-1606). Finally, a last approach consists in making interpenetrating networks combining polymers such as polyimides and a sol-gel matrix onto which the dyes are grafted (RJJen, YM Chen, AK Jain, J. Kumar, SK Tripathy, "Stable Second- Order Nonlinear Optical Polyimide / lnorganic Composite ", Chem. Mater. 1992, 4, 1141-1144).

These different approaches combine either polymers or sol-gel matrices. The first class of materials (not crosslinked) can cause problems of solubility (a good solvent must be found for the deposition of polymers) and insolubility (to allow the successive deposition of multilayers necessary for the production of waveguides) . Sol-gel materials are relatively difficult to control because the repeatability of their implementation, and therefore the stability of the orientation of the dyes, depends on the reproducibility of the temperature and hygrometry conditions. Furthermore, the stability of the orientation of molecules in the sol-gel matrix depends on the density of the crosslinking. Significant rigidity of the network therefore implies a lower concentration of dyes, which limits the effectiveness of the final component.

The object of the invention is to overcome these drawbacks by proposing a process for obtaining a matrix of polymers which can be dissolved by conventional solvents and which has better rigidity. The invention proposes for this purpose a process for obtaining an electrooptical material characterized in that a solution of oligoimides is deposited on a substrate on which are orientable dyes, in that the crosslinking of the oligoimides is carried out by annealing and the dyes are oriented. By the term "polymers" is meant a molecule in which a motif, the monomer is repeated a large number of times (up to several thousand). By "oligomer" is meant a molecule in which the motif is repeated less than 20 times.

The use of oligoimides in place of the polyimides conventionally used allows better solubility of the matrix obtained, which facilitates its shaping. This increased solubility is due both to the presence of terminal groups and to the fact that the chains are shorter than that of polyimides. Thanks to this new structure, films of micron thickness can easily be obtained, which makes them compatible for the manufacture of waveguides. This solubility also makes it possible to dissolve them in conventional solvents which are not very toxic.

In particular, the invention proposes to use fluorinated oligoimides. The use of fluorinated oligomers introduced during the polymerization makes it possible to reduce the sensitivity of the material obtained to humidity. The oligoimide solution used in the process is obtained by the following steps: - the synthesis of oligoimides terminated by reactive double bonds, the addition of dyes which can be oriented on the lateral OH functions of the oligoimides,

- the grafting of crosslinking groups on the double bonds at the chain end. The use of crosslinking groups of the alkoxysilane, nadic or allylic type for example allows crosslinking and densification of the films after deposition. This crosslinking makes them insoluble while giving them optical transparency.

In addition to the alkoxysilane groups, it is also possible to envisage the preparation of oligoimides terminated by maleimide, acetylenic, benzocyclobutenes or cyanate groups which crosslink by thermal autocondensation.

The oligoimides can be self-crosslinkable (via the alkoxysilane, nadic or allylic functions) or crosslinkable via an additional crosslinking agent (for example 1, 1, 1-tris (4-hydroxyphenyl) ethane or oxalic acid). The crosslinkable oligoimides can therefore be in the form of a monocomponent material, that is to say having the two functions crosslinkable on the oligoimide chain, or bicomponent, that is to say resulting from a reaction between two components. In the case of a bicomponent material, crosslinking can be done by reaction of alkoxysilane with hydroxylated crosslinking agents, but it can be envisaged in the form of a reaction of a compound carrying at least three functions capable of react with the double bonds located at the end of the chain. For example, to obtain oligoimides with non-linear optical properties terminated by nadic double bonds, crosslinking can be envisaged by radical addition to the nadic double bonds of a multifunctional compound of the tri or tetrathiol type such as pentaerythitol tetrakis (3-mercaptopropionate). To obtain oligoimides terminated by allylic double bonds, crosslinking can be carried out by hydrosilylation reaction with functional tetra or penta compounds such as tetramethylcyclotetrasiloxane.

Cross-linking reactions can be elementary: a simple annealing is enough. This annealing also makes it possible to evaporate the residual solvents. Crosslinking makes the material insoluble, which allows it to be easily used in multilayer deposits since the lower layers are not altered during the deposition of additional layers. Furthermore, this insolubility does not prevent a subsequent orientation of the dyes, which allows it to be effectively used as a technological step without prejudice to the non-linear efficiency of the material if the latter is oriented after crosslinking.

In addition to the crosslinking of the oligoimides, it is possible to crosslink reaction sites placed on the dyes, which makes it possible to further strengthen the stability of the material obtained. This type of crosslinking has already been used in the past, for example in the case of methacrylic polymers.

This family of materials implements synthesis reactions of soluble polyimides which are well controlled and which are carried out with good yields. Their synthesis and implementation can take place at relatively low temperatures (below 300 ° C). Thanks to their high glass transition temperature due to the imide groups in the main chain, the matrices obtained remain stable at temperatures above the temperatures envisaged for their uses (below 85 ° C.). These polyimides can easily lend themselves to mixing operations because their chemical structures are close. One can thus finely adjust, at the time of use and shaping, by mixing different synthesis batches, specific properties such as the refractive index, the resistivity or the dielectric constant of the material. We can therefore obtain products suitable for a specific use. For example, the refractive indices of the various layers making up a waveguide can be adjusted to optimize their thicknesses. We can also adjust the different resistivities in a multilayer to optimize the transfer of electric field to the active layer. Finally, the dielectric constant of the material can be adapted to adapt phase speeds in very high frequency electrooptical modulation. These mixing facilities also make it possible to envisage simply making new multifunctional materials in which a new function can be simply introduced or reinforced. For example, it is possible to combine electro-optical properties with photoluminescence, electroluminescence or photovoltaic effects in the same material. It is also possible to reinforce its hydrophobic character.

The non-linear optical properties of the materials made up of a matrix of oligoimides are comparable or superior to that obtained using the corresponding model polyimides. As regards the quadratic nonlinear optical components, the dyes used must be hyperpolarizable to ensure their orientation, that is to say that they must preferably have a tensor of quadratic optical hyperpolarisability of which at least one coefficient is greater than 10 ^{~ 30} esu The orientational stability of organic dyes can be characterized by the measurement of the non-linear optical coefficient as a function of the temperature by measurement during its heating of the variation of the intensity of second harmonic generated by a film of the compound .

Other characteristics and advantages will also emerge from the description which follows, which is purely illustrative and nonlimiting and must be read with reference to the appended drawings in which: - Figures 1 to 4 represent the successive steps allowing obtaining a electrooptical material according to the invention. FIGS. 5 to 7 are reaction diagrams illustrating the different stages of the process for manufacturing an electrooptical material, in which the oligoimide is oligohydroxyimide, the grafted dye is Disperse Red One, and the crosslinking agent is a derivative mercaptosilane. FIGS. 8a and 8b represent two chemical structures of crosslinkable oligoimides on which stability measurements have been made, FIG. 9 represents the relaxation curves of the signals obtained for the two types of electrooptical material of FIGS. 8a and 8b, FIG. 10 combines the resistivity measurement curves of different electrooptical materials as a function of the applied electric field.

In Figures 1 to 4, we can see the different stages of manufacturing an electrooptical material. The first step represented in FIG. 1 consists in synthesizing an oligohydroxyimide 1 having reactive double bonds 2 at its ends and lateral OH functions.

In a second step represented in FIG. 2, chromophores 3 are added to the lateral OH functions via the Mitsunobu reaction. In a third step, crosslinking groups 4 of trialcoxysilane type are added to the double bonds 2 at the chain end. Finally, in a fourth step, the oligohydroxyimides are crosslinked by thermal voice, which leads to the formation of bonds 5 between the crosslinking groups 4. The following example is a detailed example of a process for manufacturing a conforming electrooptical material to the invention. In this example, the starting materials prepared or identified as follows are used.

The oligohydroxyimides are synthesized with 4,4'-hexafluoroisopropylidene biphtalic anhydride (6FDA). Three families of oligoimides which differ in the hydroxydiamine used were prepared. The three types of hydroxydiamine are:

- 4- (4-amino, 2-hydroxy) phenoxyaniline (HODA),

- 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP),

- 3,3'-dihydroxy-4,4'-diaminobiphenyl (DHB). 4,4'-hexafluoroisopropylidene biphtalic anhydride (6FDA)

(sublimed at 200 ° C under 0.1 mm Hg), nadic anhydride (recrystallized from acetic acid) and the chromophore Dispersed Red One (DR1), purified by chromatography on a silica column (eluent chloroform), are supplied by Aldrich (France).

The synthesis of diamine 4-phenoxy- (4-amino-2-hydroxy) -aniline (HODA) and its isomer 4-phenoxy- (3-amino-2-hydroxy) -aniline is described in the literature. Diamine 2, -2bis- (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) (Interchim) is purified by sublimation at 170 ° C at 5 Pa and diamine 3,3'-dihydroxy-4,4'- diaminobiphenyl (DHB) (Interchim) is used as is.

Example of a process for producing an electrooptical material:

Step 1: Synthesis of oligohydroxyimides (OIA) terminated by nadic and allylic double bonds.

The reaction scheme for the synthesis of oligoimide based on

HODA and 6FDA terminated with nadic double bonds is given in Figure 5.

A general procedure is described below applicable for the synthesis of active oligomers (OIA). The amounts of the various monomers are collated in Table 1.

In a 100 ml three-necked flask fitted with mechanical stirring and a nitrogen inlet, the diamine (HODA, 6-FAP or DHB) and the dianhydride 6FDA are dissolved in a solution of 1-methyl-2-pyrrolidinone ( NMP) with a mass concentration of 20%. The solution is stirred at room temperature for 18 hours under a stream of nitrogen, then it is gradually heated to 160 ° C. and is left for 3 hours at this temperature. The solution is cooled to room temperature and the terminating agent (either allylamine AA or nadic anhydride AN) is added. The solution undergoes the same temperature cycle as above, then it is cooled and precipitated in a liter of a 1: 1 mixture of methanol-water. The white product is filtered then washed several times with methanol and dried. The physicochemical characteristics of each oligomer are given in table 2.

Step 2: Addition of the chromophore DR1 on the oligohydroxyimides (OIA).

The reaction scheme for grafting DR1 onto HODA and 6FDA-based oligoimides terminated by nadic double bonds is given in FIG. 6. A general procedure is described below applicable for the synthesis of the OIA-DR1 oligomers. The amounts of the various reagents are collated in Table 3.

In a three-necked flask fitted with a nitrogen inlet and a dropping funnel, one equivalent of DR1 oligohydroxyimide and 1.5 equivalents of triphenylphosphine (PPh ₃ ) are dissolved in the NMP. The solution is stirred until all of the compounds are dissolved. The solution is heated to 80 ° C. and 2.5 equivalents of diethylazodicarboxylate (DEAD) are added to the solution. The reaction mixture is stirred at 80 ° C for 24 hours. Monitoring by thin layer chromatography (TLC) makes it possible to report on the progress of the reaction. The solution is then precipitated in methanol. The red precipitate is filtered and washed with methanol. The polymer is purified by Soxhlet extraction with methanol until elimination of the residual chromophore (TLC monitoring) and is finally dried under vacuum at 100 ° C. An assay in UV-visible spectrometry makes it possible to determine the grafting rates. The characteristics of the UV-visible assay are given in Table 4.

Step 3: Synthesis of α, ω-alkoxysilane oligoimides grafted with DR1. The reaction scheme for the synthesis of oligoimide α, ω-trialcoxysilanes based on HODA and 6FDA is given in FIG. 7. An example of synthesis and characterization is described below for the radical addition of mercaptosilane derivative on nadic double bonds. It is applicable to all other α, ω- trialcoxysilane oligoimides. In a 100 ml bicol with magnetic stirring and a nitrogen outlet, one equivalent of oligoimide terminated by nadic double bonds, two equivalents plus 10% excess (2, 1) of (3- mercaptopropyl) trialcoxysilane and 10 mol% of azobisisobutyronitrile (AIBN) are dissolved in tetrahydrofuran (THF). The solution is heated at 70 ° C for 12 hours under a stream of nitrogen. The solution is precipitated in one liter of ethyl ether then the product is filtered and dried under vacuum. The physicochemical characteristics of the trialkoxysilane-terminated oligomers are collated in Table 5. Tg is the glass transition temperature of the matrix.

Step 4: Crosslinking thermally.

The DR1 grafted trialkoxysilane-terminated oligoimide is dissolved in a deposition solvent such as 1,1,2-trichloroethane. The deposits are prepared from solutions consisting of 20 parts by weight in 100 parts by volume of solvent (200 mg of product in 1 ml of 1, 1, 2-trichloroethane). After complete dissolution of the monomer and filtration (0.2 μm filter); the solution is deposited on a glass support by spinning (v = 1500 rpm ^"1 , t = 15 s, a = 2000 rpm ^{" 1} .s ^"1 ), which causes the evaporation of the The thickness of the film is of the order of a few microns. The film obtained is heated for between one hour and two hours in a humid atmosphere, at temperatures between 190 and 200 ° C. to make it insoluble. observed by immersing the film in the deposition solvent. Step 5: Orientation and measurement of the stability of the electrooptical properties

Studies have been carried out on the nonlinear optical properties and the stability of two oligoimides: OIA-6FAP3-DR1-TMS and OIA-

6FAP3-DR1-TES, the chemical structures of which are shown in FIGS. 8a and 8b and the physicochemical characteristics are collated in Table 6.

For each sample, the polymer film previously oriented under a 5kV electric field for 2 hours at 150 ° C, is heated with a temperature ramp of 3 ° C / min. The relaxation curves of the signal l _2ω (intensity of the second harmonic generated by the film when it is irradiated by a pulsed laser of wavelength 1.34 μm and detected by a photomultiplier at 670 nm) of the oligoimides OIA-6FAP3- DR1-TMS and OIA-6FAP3-DR1 -TES are given in Figure 5.

FIG. 9 is the superposition of the relaxation curves of the l _2ω signals of OIA-6FAP3-DR1-TES, of OIA-6FAP3-DR1-TMS crosslinked for 2 h at 150 ° C. The measured relaxation temperatures (l _2ω / 2) are 147 ° C for cross-linked OIA-6FAP3-DR1-TMS and 155 ° C for cross-linked OIA-6FAP3-DR1-TES.

Characterization of the resistivity of the material obtained:

The resistivity of the materials studied decreases with temperature. The resistivities of the reference materials are measured at lower temperature (120 ° C) and have lower resistivities. The resistivity is calculated from the isochronous value (measured 10 minutes after the application of the voltage across the terminals of the sample) of the current passing through a cell with a thickness close to 1 micrometer of polymer comprised between two gold electrodes and thermostatically controlled at 120 ° C or 150 ° C. NOA65 and NOA61 are crosslinkable optical adhesives from commercial sources (Norland Optical Adhesives). AVO01 is a crosslinkable fluoropolymer based on methacrylic base (Liang, J., Toussaere E., Hierle R., Levenson R., Zyss

J., Ochs AN., Rousseau A., Boutevin B., "Low loss, low refractive index fluorinated self-crosslinking polymers waveguides for optical applications", Optical Materials, 9, 1998, 230-235). OIP11 and OIP14 are crosslinked passive oligoimides described in this memo. PIA4-95 is a model polyimide substituted with DR1 (grafting rate 95%).

The results obtained are reproduced in FIG. 10 in which the resistivity measurements are grouped for each material along a curve:

OIP11 (150 ° C): curve (1)

PIA4-95 (150 ° C): curve (a)

OIP14b (150 ° C): curve (2)

ΝOA65 (120 ° C): curve (b) AVO01 (120 ° C): curve (c)

NOA61 (120 °): curve (d).

OIP11 and OIP14 are crosslinkable passive oligoimides (without crosslinking site for grafting a dye). They are obtained by copolymerization of 6FDA and of fluorinated diamine 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (BTDB). The crosslinking groups are of the nadic type.

The main difference between these two oligoimides is their molecular mass: M = 6220 for OIP11 and M = 5900 for OIP14.

TABLE 1

Quantities of product in g (mmol) necessary for the synthesis of oligohydroxyimides terminated by nadic or allylic double bonds:

TABLE 2

Physico-chemical characterizations of oligohydroxyimides:

TABLE 3

Quantities of products in g (mmol) used for the addition of DR1 to the OIA oligohydroxyimides via the Mitsunobu reaction:

TABLE 4

UV-visible characterizations of the DR1 grafted oligoimides, measured in the DMF at Imax = 490 nm with an extinction coefficient of 32102 I. mol ^"1. cm ^{" 1} :

TABLE 5

Characteristics of the oligohydroxyimides α, ω-trialcoxysilanes grafted DR1:

a) Tg of the starting oligoimides α, ω-dienes, b) TES: triethoxysiiane, TMS: trimethoxysilane and DMS: dimethoxysilane, c) Tg of the oligoimides α, ω-trialcoxysilanes measured during the second temperature rise from 50 to 240 ° C to 20 ° C. min ^"1 , d) 1, 1, 2-trichloroethane. TABLE 6

Characteristics of crosslinkable oligoimides:

Claims

1. A process for obtaining an electrooptical material characterized in that a solution of oligoimides is deposited on a substrate onto which orientable dyes are grafted and in that a treatment is applied which is capable of crosslinking the oligoimide and to orient the dyes.

2. Method for obtaining an electrooptical material according to claim 1, characterized in that the dyes are oriented under an electric field.

3. Method for obtaining an electrooptical material according to claim 1, characterized in that the dyes are oriented under the optical field.

4. Method for obtaining an electrooptical material according to one of the preceding claims, characterized in that the oligoimide solution is obtained by the steps consisting of:

- the synthesis of oligoimides terminated by reactive double bonds,

the addition of dyes which can be oriented on the lateral OH functions of the oligoimides,

- the grafting of crosslinking groups on the double bonds at the chain end.

5. Method for obtaining electrooptical material according to claim 1, characterized in that the crosslinking of the oligoimides is obtained by adding a crosslinking agent.

6. Method for obtaining electrooptical material according to claim 5, characterized in that the crosslinking agent used is chosen from the following compounds: 1,1,1-tris (4-hydroxyphenyl) ethane or oxalic acid or pentaerythritiol tetrakis (3-mercaptopropionate) or tetramethylcyclotetrasiloxane.

7. A method of obtaining electrooptical material according to claim 5, characterized in that the crosslinking groups are of alkoxysilane or nadic or allylic type.

8. A method of obtaining electrooptical material according to claim 1, characterized in that the crosslinking is obtained without adding crosslinking agent, via a reaction between the crosslinking groups located at the end of the chain of oligoimides.

9. A process for obtaining electrooptical materials according to claim 8, characterized in that the crosslinking groups are of alkoxysilane or nadic or allylic or maleimides or acetylenic or benzocyclobutene or cyanate type.

10. Polyimide solution, characterized in that for the implementation of the method according to claim 1, it comprises crosslinkable oligoimides on which are orientable dyes.

11. Solution for implementing the method according to claim 10, characterized in that the dye used is a hyperpolarizable compound.

12. Solution for implementing the method according to claim

10, characterized in that the oligoimides are fluorinated.

13. Solution for implementing the method according to claims 10 and 12, characterized in that said oligoimides are oligohydroxyimides.

14. Solution for implementing the method according to claim

13, characterized in that the oligohydroxyimides are obtained from 4,4'-hexafluoroisopropylidene (6FDA) and from one of the following compounds: 4- (4-amino, 2-hydroxy) phenoxyaniline (HODA) or 2.2 -bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) or 3,3'-dihydroxy-4,4'-diaminobiphenyl (DHB).

15. Solution for implementing the method according to claim 10, characterized in that the crosslinking groups are of the alkoxysilane or nadic or allylic or maleimides or acetylene or benzocyclobutene or cyanate type.

16. Solution for implementing the method according to claim

15, characterized in that the crosslinking groups are α, ω- trialcoxysilanes or triethoxysilanes (TES) or trimethoxysilanes (TMS).