NL8700158A - Heat resistant adhesive - comprising polymer obtd. by reacting tetra:carboxylic di:anhydride with e.g. 1,3-bis-(4-(3-amino:phenoxy)-benzoyl) benzene - Google Patents

Abstract

Adhesive comprises a polymer having a repeating unit of formula (I). In (I), X = gp. (II) and/or (III) and R is a tetravalent gp. selected from aliphatic, alicyclic, monocyclic aromatic, condensed polycyclic aromatic gp. and non-condensed polycyclic aromatic gp. where aromatic gps. are mutually connected directly or by way of a crosslinking member. The polymer includes polyamic acids or polyimides. The polyamic acid can be prepd. by reacting a diamine i.e., 1,4-bis(4-(3-aminophenoxy) benzoyl) benzene and/or 1,3-bis(4-(3-aminophenoxy) benzoyl) benzene and one or more tetracarboxylic dianhydrides. The polyamic acid is dehydration cyclised to give a polyimide.

Description

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-1-26173 / Vk / mvL

Short designation: Polyimide, process for the preparation of polyimide, high temperature adhesive based on polyimide and process for the adhesion.

5

The present invention relates to a new polyimide and to a process for its preparation. The invention further relates to adhesives based on the polyimide and to a method for the application thereof.

This invention particularly relates to adhesives with excellent adhesive strength and high temperature stability.

Different types of adhesives based on organic synthetic high polymers are known. Polybenzimidazole and polyimide-15 type adhesives have already been developed as adhesives with excellent high temperature stability. Furthermore, other adhesives have been developed based on fluorine-containing polymers, polyamideimide, silicone, epoxy novolac, epoxy acrylic, nitrile rubber phenol resins and polyesters.

However, the properties of these adhesives are not satisfactory because good high temperature stability causes low adhesive strength while high adhesive strength results in poor high temperature stability.

Therefore, one of the objects of this invention is to obtain a new polyimide to be used as an adhesive having excellent bond strength and durability at high temperatures for a long period of time.

Another object of this invention is to provide a method of preparing the adhesives and a method of performing an adhesive operation therewith.

The present study investigated how to improve the bonding strength of the adhesives at high temperatures and found a new polyimide derived from new ether diamines.

The present invention is characterized in that it has polyimide repeating units corresponding to formula 1, stated on the formula sheet, where the positions of two carbonyl radicals are placed in a benzene ring meta or para and R is a tetravalent radish τ nf * -κ ï vi V »· .. ·, rv» <-2- 26173 / Vk / mvl bald is selected from the group consisting of an aliphatic radical of not less than two carbon atoms, cycloaliphatic radical, mono-aromatic radical, condensed polyaromatic radical and non-condensed polyaromatic radical, wherein the aromatic radicals are joined together by a bond or a cross-linking function.

A process for the preparation of the polyimide with repeating units of formula 1, wherein the positions of the two carbonyl radicals and R are the same as stated above, consists in that a diamine of formula 2, stated on the formula sheet, wherein the positions 10 of two carbonyl radicals are the same as previously mentioned, are reacted with a tetracarboxylic dianhydride of formula 3, stated on the formula sheet, where R has the same meaning as previously indicated, in an organic solvent and thermally or chemically imidizing the resultant polyamic acid with repeating units of formula 4, stated on the formula sheet.

Thus, a high temperature active adhesive based on a polyimide with repeating units of formula 1 is obtained, wherein the positions of two carbonyl radicals and R are the same as previously stated.

A method of performing the adhesion consists in that a polyimide with repeating units of formula 1, mentioned on the formula sheet, where the positions of two carbonyl radicals and R are the same as mentioned above, is applied to a substrate, the coated surface of the substrate is covered with an untreated or treated surface of another substrate and is heated under pressure to above the glass transition point of the polyimide.

A further method of carrying out the bonding consists in that polyamic acid with repeating units of formula 4, wherein the positions of two carbonyl radicals and R are the same as indicated above, which is a precursor of the polyimide, is applied to a substrate, imidization is performed to obtain the polyimide with repeating units of formula 1, and the covered surface of the substrate is covered with an untreated or treated surface of another substrate, followed by heating under pressure above the glass transition temperature of the polyimide.

Preferably R has the meaning of a radical of formula 6 or 7, stated on the formula sheet.

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The invention is further elucidated with reference to the following description, reference being made to the accompanying drawing, in which: Figures 1 and 2 are IR absorption spectra of the polyimide prepared according to two examples of the present invention.

A novel polyimide of this invention with repeating units of formula 1, stated on the formula sheet, wherein the positions of two carbonyl radicals in a benzene ring are meta or para and R is a tetravalent radical selected from the group consisting of an aliphatic radical of not less than two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical and non-condensed polyaromatic radical, the aromatic radicals being joined together by a bond or a cross-linking function, can be prepared by reacting the following diamine with tetracarboxylic dianhydride in organic solvents and further cyclization of the obtained polyamic acid by dehydration.

The diamine that can be used according to this invention is 1,3-bis [4-13-aminofendxy) benzoyl] benzene of formula 8, stated on the formula sheet, or 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene of formula 5, 20 listed on the formula sheet.

These ether diamines can be used individually or in mixtures.

Tetracarboxylic dianhydride used in the process of the invention has formula 3, stated on the formula sheet, wherein R is a tetravalent radical selected from the group consisting of an aliphatic radical of not less than two carbon atoms, cycloaliphatic radical, monoaromatic radical condensed polyaromatic radical and non-condensed polyaromatic radical, wherein the aromatic radicals are joined together by a bond or a cross-linking function.

Tetracarboxylic dianhydride used according to this method includes, for example, ethylene tetracarboxylic dianhydride, cyclopentaantetracarboxylic dianhydride, pyromellitic dianhydride, 3.3 ', 4.4, benzophenone tetracarboxylic dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic dianhydride, 3,3,3,4,4 ' -bi phenyitet racarboxylic dianhydride, 2,21,3,31-bi phenyitetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propanedianhydride, 2,2-bis- (2,3-dicarboxyphenyl) propanedianhydride, bis (3 , 4-dicarboxyphenyl) etherdian-; 7 on * § * v * * 3 t 1 -4- 26173 / Vk / mvl hydride, bis (3,4-dicarboxyphenyDsulfondianhydride, 1,1-bis (2,3-dicarboxy- phenyL) ethanedianhydride, bis (2,3-dicarboxyphenyl) methanedianhydride, bis (3,4-dicarboxyphenyl) methanedianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1,2, 5,6-5 Naphthalene tetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylene tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dia. nhydride and 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride.

Of these dianhydrides, pyro-10-mellitic acid dianhydride and 3,3,4,4-benzophenone-tetracarboxylic dianhydride are particularly preferably used.

Tetracarboxylic dianhydride can be used singly or mixed with two or more other anhydrides.

1 The polymer can normally be prepared by reacting the diamine with tetracarboxylic dianhydride in organic solvents. The organic solvents used in this reaction include, for example, Ν, Ν-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, Ν, Ν-dimethylmethoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl -2-imidazolidinone, N-methylcaprolactam, 1,2-di-20-methoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis [2- (2-methoxyethoxy) ethyl] ether , tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, pyridine, picoline, dimethyl sulfoxide, dimethyl sulfone, tetramethyl urea and hexamethylphosphoramide. These solvents can be used singly or as a mixture of two or more of these solvents.

The reaction temperature is usually 60 ° C or less, preferably 50 ° C or less. The reaction pressure is not particularly limited and atmospheric pressure is sufficient to conduct the reaction. The reaction time depends on the type of solvent, the reaction temperature and the starting materials such as diamines and tetracarboxylic dianhydrides and is normally sufficient to stop the formation of polyamic acid represented by the formula below. The reaction for 4 to 24 hours is usually sufficient.

Such a reaction gives polyamic acid with repeating units of formula 4, stated on the formula sheet.

In the next step, the thermal dehydration of polyamic acid in solution takes place at 100 to 300 ° C or the chemical dehydration by 6'0 C 158 'V * -5-26173 / Vk / mvl by treatment with an imidizing agent such as acetic anhydride to the corresponding polyimide is obtained with repeating units of formula 1.

The method of applying the poly-5 thus obtained as an adhesive is roughly divided into two operations.

1) The polymer is used as an adhesive solution containing polyamic acid precursor as main component and imidized before the adhesion takes place.

2) The polymer is used in the form of the polyimide 10 as such.

In method 1), the adhesive solution is a solution of the polyamic acid in an organic solvent. The resulting polyamic acid reaction mixture may be obtained by reacting ether diamine with tetracarboxylic dianhydride in organic solvents. It is also possible that the solution contains polyamic acid as the main component and polyimide, which is a cyclized product of polyamic acid. Thus, the adhesive solution containing polyamic acid can be the solution or suspension containing polyimide as an auxiliary.

When the adhesive containing the polyamic acid is applied, a thin layer of polyamic acid is formed on the surfaces to be bonded together, followed by preheating the coated surfaces to air for a period of time at a temperature of 180-350 ° C , preferably at 200-300 ° G. The excess of solvents are removed and polyamic acid is converted into a more stable polyimide. The surfaces are then strongly bonded together by compression at a pressure of 1-1000 kg / cm at a temperature of 50-400 ° C, followed by curing at a temperature of 100-400 ° C.

In method 2) using the polyimide as an adhesive, it is roughly divided into three possibilities.

a) The polyimide is used as such in powder form.

b) The polyimide is dissolved in the solvents or used in the form of an obtained solution at the end of the imidation.

C) The polyimide is first formed into a film before it is used.

In these cases, some of the polyamic acid may be present in the polyimide.

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In possibility a) the adhesives can be strongly bonded by applying powder between the surfaces / compression under a pressure of 1-1000 kg / cm at a temperature of 50-400 ° C and curing at a temperature of 100-400 ° C .

In possibility b), the thin layer of polyimide / containing the dissolved adhesive is formed on the surfaces to be coated to be bonded together, followed by preheating the adhesives to air for a period of time at about 30-200 ° C to remove the solvents. The coated surfaces are then combined with other surfaces, compressed under a pressure of 1-1000 kg / cm @ 2 at a temperature of 50-400 ° C and cured at a temperature of 100-400 ° C to obtain highly bonded articles.

The invention is further illustrated by the following syntheses and examples.

Synthesis_1 1,3-Sis [4- (3-aminophenoxy) benzoylbenzene to be used according to the invention was prepared as follows.

In a 1 L reaction vessel, 70 g (0.22 mol) of 1,3-bis (4-fluorobenzoybenzene, 50.1 g (0.46 mol) of m-aminophenol, 63.5 g of anhydrous potassium carbonate and 550 ml of 1 , 3-dimethyl-2-imidazolidinone was added and reacted for 5 hours at 150-160 ° C. After the completion of the reaction, the reaction mixture was cooled to room temperature and filtered to remove inorganic salt. The solvent was distilled off under reduced pressure from the filtrate To the residue was added 60 g of 35% hydrochloric acid, 850 g of water and 150 g of isopropyl alcohol and dissolved under heating The resulting solution was supplemented with 50 g of sodium chloride and cooled to 20-25 ° C. The precipitated crystals of hydrochloride were filtered, dissolved by heating in 600 ml of 50% aqueous isopropyl alcohol, stirred after addition of 5 g of activated carbon, filtered hot and cooled, the separated crystals were filtered and the hydrochloride crystals thus obtained were dissolved by heating in a mixture of 750 g of water and 350 g of isopropyl alcohol, again treated with activated carbon and neutralized with aqueous ammonia. The separated crystals were filtered, washed with water and dried to obtain 90.2 g (82% yield) of 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene in the form of white crystals with a melting point of 147-149 ° C and a purity of 99.7%, liquid 8700158

Vi -7- 26173 / Vk / mvl determined by chromatography, at a high speed.

The elemental analysis data for the compound of formula cj2H24 ^ 2 Z1in: C (%) HC%) N (%) 5 Calcd: 76.8 4.8 5.6 Found: 76.7 4.7 5, 54.

-1 IR (KBr, cm): 3450 and 3390 (amino group), 1630 and 1595 (carbonyl group), 1250 (ether bond).

Synthesis 2 1,4-Bis [4-C3-aminophenoxy) benzoyl] benzene used according to the invention was prepared as follows.

50 g (0.16 mol) 1,4-bis (4-fluorobenzoyl) benzene, 42 g (0.39 mol) m-aminophenol, 54 g anhydrous potassium carbonate and 400 ml sulfuran were placed in a 1 l reaction vessel and Reacted at 150-160 ° C for 6 hours. After the completion of the reaction, the reaction mixture was poured into water to obtain a total of 2 l. The separated crystals were then filtered, washed with water and dissolved in 400 ml of 2-methoxyethanol with heating. To the obtained solution, 8 g of activated carbon was added, stirred, filtered hot and cooled. The separated crystals were filtered and recrystallized from 2-methoxyethanol and activated carbon to obtain 60 g (75% yield) 1,4-bis [5- (3-aminophenoxy) benzoyl] -benzene as light brown crystals of melting point 161-163 ° C and 99.3% purity by high speed liquid chromatography.

The data from the elemental analysis for the compound of formula C32H24N2 are: C (%) H (%) N (%) calculated: 76.8 4.8 5.6 30 found: 76.4 4.72 5 , 5.

-1 IR (KBr, cm): 3420 (amino group), 1640 and 1595 (carbonyl group), 1245 (ether bond).

Example I

A reaction vessel equipped with a stirrer, reflux condenser 35 and nitrogen supply tube was charged with 5Q g (0.1 mol) 1,3-bis [4- (3-amino-phenoxy) benzoyl] benzene and 215.4 g N, N- dimethylacetamide, cooled to about 0 ° C, to which was added 17.44 g (0.08 mol) of pyromellitic dianhyde-6700158 * -8-26173 / Vk / mvl dride in four portions under nitrogen atmosphere, carefully taking place to keep the temperature of the not to increase the solution. After stirring at about 0 ° C for about 2 hours, the temperature of the reaction solution was raised to room temperature. Pyromellitic acid-5 dianhydride was added in an amount of 4/36 g (0.02 mol) under a nitrogen atmosphere and then stirred for 20 hours under a nitrogen atmosphere.

The polyamic acid thus obtained had an inherent viscosity of 1.82 dl / g at 35 ° C in 0.5% Ν, Ν-dimethylacetamide solution.

In the next step, a vessel equipped with a stirrer, reflux condenser and nitrogen supply tube was charged with 200 g of the above polyamic acid solution and 300 g of Ν, dim-dimethylacetamide. The mixture was added dropwise with 28.4 g (0.28 mole) acetic anhydride and 10.5 g (0.104 mole) triethylamine with stirring under nitrogen atmosphere at room temperature and further stirred for 20 hours. After the completion of the reaction, the precipitate was filtered off, washed with methanol and dried under a reduced pressure at 150 ° C for 8 hours to obtain 45.8 g (96.5% yield) of polyimide as a light yellow powder. The powder had a glass transition temperature of 228 ° C in accordance with the DSC method and a temperature of 522 ° C with a weight reduction of 5% in accordance with DTA-TG.

The IR absorption spectrum of the polyimide powder thus obtained is shown in Fig. 1. In this spectrum, remarkable -1 -1 absorption bands were found at about 1780 cm and 1720 cm, which are -1 25 absorbances of imide and at about 1240 cm, which is the characteristic absorption of the ether bond.

The powdered polyimide was applied to a cold-rolled steel plate (JIS G3141, spcc / SD, 25 x 100 x 1.6 mm), which was washed with trichlorethylene and preheated at 130 ° C. The coated plate 30 was covered with another cold-rolled steel plate and compressed at 320 ° C for 5 minutes under a pressure of 20 kg / cm 2.

The overlapping shear strength of the interconnected objects was 330 kg / cm at room temperature and was 200 kg / cm at 240 ° C in accordance with JIS K6848 and 6850.

Furthermore, the above-mentioned polyamic acid solution was applied to a cold-rolled steel plate which was first washed with trichlorethylene and dried for 1 hour at both 100 ° C and 220 ° C.

8700158 t.% -9- 26173 / Vk / mvl

The coated plate was covered with another cold-rolled steel plate and pressed at 320 ° C for 5 minutes under 2 pressure of 20 kg / cm. The thickness of; the layered adhesive was 36 µm. The overlapping shear strength of the interconnected objects was 330 kg / cm at room temperature and 200 kg / cm at 240 ° C.

Furthermore, the above-mentioned polyamic acid solution was poured onto a bag plate and heated at 100 ° C, 200 ° C and 300 ° C for 1 hour.

The polyimide film thus obtained had a glass transition temperature of 230 ° C, in accordance with the TMA penetration method, and a weight reduction of 5% at a temperature of 520 ° C.

The polyimide film was placed between cold-rolled steel plates preheated at 130 ° C and compressed at 320 ° C

2 for 5 minutes under a pressure of 20 kg / cm.

The shear strength of the overlap of the bonded articles was 320 kg / cm at room temperature and 200 kg / cm at 240 ° C.

Example II

The reaction vessel as used in Example I was charged with 50 g (0.1 mol) of 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene and 246.6 g of Ν-dim-dimethylacetamide cooled to about 0 ° C and to this was added 25.76 g (0.08 mol) of 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride in four portions, which was carefully done so as not to raise the temperature of the reaction solution. After stirring at about 0 ° C for about 2 hours, the temperature of the solution of the reaction mixture was raised to room temperature. Then 6.44 g (0.02 mol) of 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride were added under nitrogen atmosphere and further stirred for 20 hours under nitrogen atmosphere.

The polyamic acid thus obtained had an inherent viscosity of 1.20 dl / g.

The polyamic acid solution was poured onto a glass plate and heated at 100 ° C, 200 ° C and 300 ° C for 1 hour.

The polyimide film thus obtained had a glass transition temperature of 215 ° C and a 5% drop occurred at 532 ° C. The film also had a tensile strength of 1600 kg / cm and an elongation to break of 68% at 23 ° C.

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The compression-bonded sample of cold-rolled steel sheets, obtained using the film and the same procedure as in Example 1, had an overlap shear strength of 330 kg / cm @ room temperature and 210 kg / cm @ 240 ° C.

Example III

The procedure of Example I was repeated, except that 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene was used instead of 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene. The polyamic acid thus obtained had an inherent viscosity of 1.25 dl / g.

The above polyamic acid solution was applied as an adhesive to two plates of cold-rolled steel previously washed with trichlorethylene and dried for 1 hour at 100 ° C and 220 ° C.

The coated surfaces of these steel plates were assembled and pressed at 320 ° C for 5 minutes 2 under a pressure of 20 kg / cm.

The composite sample had a shear strength at the 2 2 overlap of 290 kg / cm at room temperature and of 180 kg / cm at 240 ° C.

Furthermore, the polyamic acid was treated in the same manner as in Example 1. The obtained polyimide film had a glass transition temperature of 238 ° C and a weight reduction of 5% at 520 ° C.

The compression-bonded sample of the cold-rolled steel plates, using the film and under the same conditions as in Example 1, had a shear strength at the overlap of 285 kg / cm 2 at room temperature and 180 kg / cm 2 at 240 ° C. Example IV

The procedure of Example II was repeated, except that 1,4-bis [4-C3-aminophenoxy) benzoyl] benzene was used instead of 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene. The polyamic acid thus obtained had an inherent viscosity of 1.05 dl / g.

In the next step, a vessel equipped with a stirrer, reflux condenser and nitrogen supply tube was charged with 200 g of a solution of polyamic acid obtained as mentioned above and 300 g of N, N-dimethylacetamide. The mixture was added dropwise with 24.48 g (0.24 mol) acetic anhydride and 9.09 g (0.09 mol) triethylamine with stirring under nitrogen atmosphere at room temperature and further stirred for 20 hours.

870 0 1 5 8 * $ -11- 26173 / Vk / mvl

After the completion of the reaction, the reaction mixture was poured into 500 g of methanol. The precipitate was filtered, washed with methanol and dried under reduced pressure at 150 ° C for 8 hours to obtain 45.0 g (95.5% yield) of polyimide in the form of a pale yellow powder. The powder had a glass transition temperature of 212 ° C and a 5% weight drop at 520 ° C.

The IR absorption spectrum of the polyimide powder thus obtained is shown in Fig. 2. In the spectrum, remarkable absorption bands are found at about 1780 cm and 1720 cm, which indicate the characterization. -1 is physical absorption of the imide and at about 1240 cm, which is the characteristic absorption of the ether bond.

The powdered polyimide was placed between cold-rolled steel plates preheated at 130 ° C and compressed at 320 ° C for 5 minutes under a pressure of 20 kg / cm 2.

The shear strength of the overlapping of the joined objects was 300 kg / cm at room temperature and 180 kg / cm at 240 ° C.

Furthermore, the polyamic acid solution thus obtained was poured onto a glass plate and heated for 1 hour at both 100 ° C, 200 ° C and 300 ° C.

The polyimide film thus obtained had a glass transition temperature of 215 ° C and a 5% weight reduction occurred at 519 ° C.

The compression-bonded sample of the cold-rolled steel plates, produced using the film and under the same conditions as in Example 1, had a shear strength at 2 2 overlapping of 290 kg / cm at room temperature and of 180 kg / cm cm at 240 ° C.

Thus, the present invention relates to the repeating unit polyimide of formula 1, wherein the positions of two carbonyl radicals are placed in a benzene ring meta or para and R is a tetravalent radical selected from the group consisting of an aliphatic radical of no less then two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical, and non-condensed polyaromatic radical, the aromatic radicals being joined together by a bond or cross-linking function.

£ ”00158

-12- 26173 / Vk / mvL

*

The polyimide can be prepared by reacting diamine with tetracarboxylic dianhydride in organic solvents and imidizing the resulting polyamic acid.

The diamine used is ether diamine and includes 1,3-bis [4-5 (3-aminophenoxy) benzoyl] benzene and 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene.

Various tetracarboxylic dianhydrides can be used, and pyromellitic dianhydride and 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride are particularly preferred.

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Claims (9)

Polyimide with repeating units, characterized in that these units correspond to formula 1 stated on the formula sheet, 5 where the positions of the two carbonyl radicals in one benzene ring are meta or para and R is a tetravalent radical selected from the group consisting of from an aliphatic radical of not less than two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical and non-condensed polyaromatic radical, the aromatic radicals being joined together by a bond or a cross-linking function. Polyimide according to claim 1, characterized in that R is a tetravalent radical of formula 6 or 7 stated on the formula sheet. A process for the preparation of a polyimide with repeating units of formula 1, wherein the positions of two carbonyl radicals in a benzene ring are meta or para and R is a tetravalent radical selected from the group consisting of an aliphatic radical with no less then two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical and non-condensed polyaromatic radical, the aromatic radicals bonded together via a bond or a cross-linking function, by a diamine of formula 2, mentioned on the formula sheet, wherein the positions of two carbonyl radicals are the same as indicated above, to react with a tetracarboxylic dianhydride of formula 3, stated on the formula sheet, where R has the same meaning as indicated above, in an organic solvent and thermal or chemical imidization, whereby polyamic acid is obtained with repeating units of formula 4, listed on the formula sheet, where the positions of the two carbonyl radicals and R are the same as indicated above. A process for preparing a polyimide according to claim 3, wherein R is a tetravalent radical of formula 6 or 7. 5. «High temperature foodstuff based on a polyimide with repeating units of formula 1, stated on the formula sheet, wherein the positions of the two carbonyl radicals in a benzene ring are meta or para and R is a tetravalent radical selected from the group consisting of an aliphatic radical having not less than two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical and non-condensed polyaromatic radical. 7 G 0 15 8 -14- 26173 / Vk / mvl W * / wherein the aromatic radicals are bonded together with a bond or a cross-linking function. High temperature adhesive according to claim 5 / characterized in that R is a tetravalent radical of formula 6 or 7. 7. A method of rendering by applying a polyimide, characterized in that it is a polyimide with repeating units of formula 1, stated on the formula sheet, wherein the positions of the two carbonyl radicals in a benzene ring are meta or para and R is a tetravalent radical selected from the group consisting of aliphatic radical of not less than two carbon atoms, cycloaliphatic radical, monoaromatic radical, condensed polyaromatic radical, and non-condensed polyaromatic radical, the aromatic radicals bonded together with a bond or a cross-linking function, on a substrate, overlapping the surface coated with the substrate, with an untreated or treated surface of another substrate and heating under pressure above the glass transition temperature of the polyimide. 8. A method of bonding according to claim 7, characterized in that the polyimide is prepared by applying polyamic acid to repeating units of formula 4 stated on the formula sheet, which is a precursor of the polyimide, on a substrate and then imidizing the polyamic acid. Process according to claim 7 or 8, characterized in that R is a tetravalent radical of formula 6 or 7, stated on the formula sheet. 30 Eindhoven, January 1987 8700158