POLYIMIDE AND HIGH-TEMPERATURE ADHESIVE THEREOF

Abstract: This invention relates to a novel polyimide which is high-temperature resistant and capable of being molded in a fused state. This invention also relates to a high-temperature adhesive using the polyimide. The polyimide consists essentially of recurring units of the formula: where R is a tetra-valent radical selected from the group consisting of an aliphatic radical having 2 or more carbon atoms, alicyclic radical, monoaromatic radical, condensed polyaromatic radical, and non-condensed polyaromatic radical wherein aromatic radicals are linked to one another directly or via a bridge member. The polyimide can be prepared by reacting bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone with a tetracarboxylic dianhydride in an organic solvent and imidizing the resultant polyamic acid. Various tetracarboxylic dianhydrides can be used and preferred dianhydride are pyromellitic dianhydride, 3,3′,4,4′-benzophenone­ tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) ether dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 4,4′-(p-phenylenedioxy)diphthalic dianhydride.

Description: This invention relates to a novel polyimide which is high-temperature resistant and capable of being molded in the fused state, and also to a high-temperature resistant adhesive using the polyimide. Polyimides obtain by the reaction of tetracarboxylic dianhydrides with diamines have so far been excellent in regard to various properties and are outstanding in high-temperature resistance. Therefore, these polyimides are expected to be widely used in the future in various fields where high-temperature resistance is required. Many polyimides which have been developed to date exhibit outstanding properties. Various polyimides, however, have a disadvantage in processing ability in that the polyimides have no glass transition temperature, even though they have excellent high-temperature resistance, and must be processed by such methods as sinter molding when they are used as molding materials. Various polyimides have the drawback of high water absorption which gives adverse effects on dimensional stability, insulative properties and the solder heat resistance of the molded products when they are used as materials for electrical and electronic parts. On the other hand, polyimide resins having excellent processing ability has also been developed. These resins, however, have low glass transition temperatures and are also soluble in halogenated hydrocarbons such as methylene chloride, and are thereby unsatisfactory in many cases from a high-temperature resistance and solvent resistance point of view. The object of this invention is to provide a polyimide which has an excellent processing ability in addition to outstanding high-temperature stability and solvent resistance, a low water absorption, a good transparency, and notable high-temperature resistance adhesion and which is thus capable of being used for many purposes. The present inventors have investigated extensively to achieve the above objective. As a consequence, a novel polyimide, and a high-temperature resistant adhesive using this polyimide, have been found. Accordingly, the present invention provides a polyimide consisting essentially of recurring units of the formula: where R is a tetra-valent radical selected from aliphatic radicals having 2 or more carbon atoms, alicyclic radicals, monocyclic aromatic radicals, fused polycyclic aromatic radicals, and polycyclic aromatic radicals wherein the aromatic radicals are linked to one another either by a direct bond or via a bridging group. According to another aspect of the invention, a high-temperature resistant adhesive comprises a polyimide which consists essentially of recurring units of the formula: where R is a tetra-valent radical selected from aliphatic radicals having 2 or more carbon atoms, alicyclic radicals, monocyclic aromatic radicals, fused polycyclic aromatic radicals, and polycyclic aromatic radicals wherein the aromatic radicals are linked to one another either by a direct bond or via a bridging group. The polyimide of this invention may be prepared by the use of a novel etherdiamine, bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone, represented by the following formula: The etherdiamine is polymerized with at least one tetracarboxylic dianhydride and the resultant polyamic acid is subjected to a dehydration and ring closing reaction to obtain the polyimide. The resulting polyimide is a thermoplastic polyimide having crystallinity in addition to high-temperature stability and solvent resistance, as well as having an excellent processing ability and the property of high-temperature resistant adhesion. An etherdiamine having a rather similar structure, bis[4-(4-aminophenoxy)phenyl] sulfone, which is represented by the following formula, has been described [Georgel, Brode et al., J. Polym. Sci., Polym. Chem. Edition, 12 , 575-587 (1974)]. However, polyimides prepared from this etherdiamine have no distinct glass transition temperature, exhibit almost no adhesion and are poor in processing ability. On the other hand, the polyimide of this invention is outstanding in high-temperature resistance and can be processed by fusion molding. That is, as already stated, the polyimide of this invention is thermoplastic in addition to having excellent high-temperature stability and solvent resistance. Thus the polyimide of this invention can be processed by fusion molding techniques such as extrusion molding and injection molding and is expected to be used as a basic material for aerospace components as well as for electrical and electronic parts. Furthermore, because the polyimide has excellent high-temperature resistance due to its crystallinity it can be used for many other purposes, such as in the preparation of high-temperature resistant fibers of high strength. Therefore, the new polyimide of this invention is expected to be a very valuable addition to the range of plastics materials available. The polyimide of this invention can, as stated, be prepared by using the above new etherdiamine as a raw material. Other diamines can also be used in combination with this etherdiamine within the range which has no adverse effect on the advantageous properties of the polyimide. Example of diamines which may be used in admixture with the new etherdiamine include, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, bis(3-aminophenyl) ether, (3-aminophenyl) (4-aminophenyl) ether, bis(4-aminophenyl) ether, bis(3-aminophenyl) sulfide, (3-aminophenyl) (4-aminophenyl) sulfide, bis(4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, (3-aminophenyl) (4-aminophenyl) sulfoxide, bis(4-aminophenyl) sulfoxide, bis(3-aminophenyl) sulfone, (3-aminophenyl) (4-aminophenyl) sulfone, bis(4-aminophenyl) sulfone, 3,3′-diaminobenzophenone, 3,4′-diaminobenzophenone, 4,4′-diaminobenzophenone, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy) benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy) benzene, 4,4′-bis(3-aminophenoxy)biphenyl, 4,4′-bis(4-aminophenoxy) biphenyl, bis[4-(3-aminophenoxy)phenyl] ketone, bis[4-(4-aminophenoxy)phenyl] ketone, bis[4-(3-aminophenoxy)phenyl] sulfide, bis[4-(4-aminophenoxy)phenyl] sulfide, bis[4-(4-aminophenoxy)phenyl] sulfoxide, bis(4-(4-aminophenoxy)phenyl] sulfoxide, bis[4-(3-aminophenoxy)phenyl] sulfone, bis[4-(4-aminophenoxy)phenyl] sulfone, bis[4-(3-aminophenoxy)phenyl] ether, bis[4-(4-aminophenoxy)phenyl] ether, 1,4-bis[4-(3-aminophenoxy)benzoyl] benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl] benzene, 4,4′-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone and bis[4-(4-(4-amino-α,α-dimethylbenzyl)phenoxy)phenyl] sulfone. The polyimide of this invention can be prepared by the following process. In the first step, [4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone is polymerized with a tetracarboxylic dianhydride in an organic solvent to obtain polyamic acid. The tetracarboxylic dianhydride used in the process is represented by the formula: where R is a tetra-valent radical selected from aliphatic radicals having 2 or more carbon atoms, alicyclic radicals, monocyclic aromatic radicals, fused polycyclic aromatic radicals, and polycyclic aromatic radicals wherein the aromatic radicals are linked to one another either by a direct bond or via a bridging group. The tetracarboxylic dianhydrides that may be used in the method include, for example, ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 2,2′,3,3′-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, bis(3,4-dicarboxyphenyl) ether dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, bis(3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,3,6,7-napthalenetetracarboxylic dianhydride, 1,4,5,8-napthalenetetracarboxylic dianhydride, 1,2,5,6-napthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, bis[4-(3,4-dicarboxyphenoxy)phenyl] sulfide dianhydride, 3,3′-(p-phenylenedioxy)diphthalic dianhydride, 4,4′-(p-phenylenedioxy)diphthalic dianhydride, 3,3′-(m-phenylenedioxy)diphthalic dianhydride and 4,4′-(m-phenylenedioxy)diphthalic dianhydride. Examples of preferred tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic diahydride, bis(3,4-dicarboxyphenyl) ether dianhydride, 3,3′,4,4′-tetracarboxybiphenyl dianhydride and 4,4′-(p-phenylenedioxy)diphthalic dianhydride. These tetracarboxylic dianhydrides may be used singly or in mixtures of two or more. Examples of organic solvents which may be used in the method include, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, 1,2-dimethoxyethane, 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, tetramethylurea, hexamethylphosphoramide, phenol, m-cresol, p-cresol, p-chlorophenol and anisole. These organic solvents may be used singly or in mixtures thereof. The reaction temperature is normally 250°C or less and is preferably 50°C or less. Any reaction pressure may be used and the reaction can be conducted at atmospheric pressure. The reaction time depends upon the kinds of tetracarboxylic dianhydrides and solvents used as well as the reaction temperature. The reaction is usually conducted for a sufficient time to complete the formation of the polyamic acid, and the time is normally 4-24 hours. A polyamic acid consisting of recurring units represented by the following formula is formed by this reaction: where R is the same as before. The resultant polyamic acid is dehydrated by heating at 100-400°C or subjected to a chemical imidization to obtain the corresponding polyimide consisting of recurring units represented by the following formula: where R is the same as before. The polyamic acid is generally formed as above at relatively low temperatures, this being followed by imidizing thermally or chemically. The polyimide can, however, also be prepared by simultaneously conducting the formation of the polyamic acid and its thermal imidization reaction. That is, the polyimide having recurring units of the above formula can also be prepared by suspending or dissolving bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and the tetracarboxylic dianhydride in the organic solvent, and then carrying out the reaction by heating sufficiently to obtain the formation of the polyamic acid and its dehydrating imidization at the same time. A polyimide prepared as above can be used as an adhesive by the following procedure. The polyamic acid mentioned above is dehydrated thermally or chemically to obtain the polyimide in the form of, for example, a film or powder. The film or powder is inserted between substrates, pressed with a pressure of 1-1000 kg/cm² at a temperature of 50-450°C and then cured at a temperature of 100-450°C to obtain a strong bond between the substrates. No adverse effects are found even if a proportion of the polyamic acid groups remains in the polyimide. As an alternative process, a solution obtained by dissolving the aforementioned polyamic acid or the complete reaction mixture obtained on forming the polyamic acid in the organic solvent is used. Such solution is applied as a thin layer on the substrate to be bonded and preheated for the time required at 150-450°C, preferably at 220-300°C, to remove the excess solvent. The polyamic acid is converted to the polyimide by this procedure on the surface of the substrate. The treated surface of the substrate is then contacted with another substrate and pressed with a pressure of 1-1000 kg/cm² at a temperature of 50-400°C and cured at a temperature of 100-450°C. This process is also very suitable for obtaining strongly bonded substrates. When the polyimide of this invention is processed by fusion molding, other thermoplastic resins may be incorporated in suitable amount depending upon the application so long as no adverse effects are found on the objects to be achieved. Examples of thermoplastic resins which may be used include polyethylene, polypropylene, polycarbonate, polyarylate, polyamide, polysulfone, polyethersulfone, polyetherketone, polyphenylene sulfide, polyamideimide, polyetherimide and modified polyphenylene oxide. Fillers such as are commonly used in resin compositions may be employed, in an amount which has no adverse effects on the objects to be achieved. The fillers which may be used include, for example, wear resistance improvers such as graphite, carborundum, quartz powder, molybdenum disulfide and fluororesins; reinforcing materials such as glass fiber, carbon fiber, boron fiber, silicon carbide fiber, carbon whisker, asbestos, metal fiber and ceramic fiber; flame retardants such as antimony trioxide, magnesium carbonate and calcium carbonate; electrical property improvers such as clay and mica; tracking resistance improvers such as asbestos, silica and graphite; acid resistance improvers such as barium sulfate, silica and calcium metasilicate; thermal conductivity improvers such as iron powder, zinc powder, aluminum powder and copper powder; and other miscellaneous additives such as glass beads, glass spheres, talc, diatomaceous earth, alumina, silas balloon, hydrated alumina, metal oxides and coloring agents. EXAMPLES Figures 1 and 2 of the accompanying drawings are examples of infrared absorption spectra obtained from polyimides according to the invention. The invention will hereinafter be illustrated by an example of synthesis of the novel etherdiamine, examples of the production and use of polyimides according to the invention, and a comparative test using an etherdiamine outside the scope of the invention. Synthesis Example Bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone, for use in the production of polyimides according to the present invention, was prepared by the following procedures. A reaction vessel equipped with a stirrer, thermometer and reflux condenser was charged with 150.9 g (0.75 mole) of (4-aminophenyl) (4-hydroxyphenyl) ether, 42.8 g (0.73 mole) of 96% potassium hydroxide, 450 g of 1,3-dimethyl-2-imidazolidinone and 45 g of toluene. The mixture was heated with stirring in a nitrogen atmosphere and water generated in the reaction system was removed by a water separator upon refluxing toluene. The temperature of the reaction mixture was lowered to less than 100°C and a solution of 102.6 g (0.357 mole) of bis(4-chlorophenyl) sulfone in 205.2 g of 1,3-dimethyl-2-imidazolidinone was added dropwise. After the addition, the temperature was raised to 180-190°C and the reaction was carried out for 4 hours. After completing the reaction, the resultant mixture was cooled and poured into 500 g of methanol. The separated light brown crystals were filtered, washed and recrystallized from 2-methoxyethanol to obtain 183 g (83.0% yield) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone as white crystals having a melting point of 212-214°C. Example 1 A reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube was charged with 6.167 g (0.01 mole) of bis [4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 47.3 g of N,N-dimethylacetamide. To the mixture was added 2.18 g (0.01 mole) of pyromellitic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for 20 hours at room temperature. Polyamic acid thus obtained had an inherent viscosity of 1.52 dl/g. The inherent viscosity was measured at 35°C in a concentration of 0.5 g per 100 ml of N,N-dimethylacetamide solvent. A part of the polyamic acid solution was cast on a glass plate and heated to 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The polyimide film had a tensile strength of 14.2 kg/mm² and an elongation of 19.6% in accordance with ASTM D-882. The polyimide film also had a glass transition temperature of 290°C in accordance with the DSC method and a 5% weight loss temperature in air of 540°C in accordance with DTA-TG. The polyimide film was inserted between cold rolled steel panels (JIS G3141, SPCC/SD, 25 × 100 × 1.6 mm) which had been preheated at 130°C and pressed for 5 minutes at 350°C with a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 230 kg/mm² at room temperature and 200 kg/mm² at 250°C in accordance with JIS K-6848 and K-6850. The film had an excellently low water absorption of 1.03% after immersion in water at 23.5°C for 24 hours in accordance with ASTM D-570-63. The film was quite insoluble in halogenated hydrocarbons such as methylene chloride, chloroform, trichloroethylene and 1,1,2,2-tetrachloroethane. Comparative Test The same reaction vessel as in Example 1 was charged with 4.32 g (0.01 mole) of bis[4-(4-aminophenoxy)phenyl] sulfone and 36.8 g of N,N-dimethylacetamide. To the mixture was added 2.18 g (0.01 mole) of pyromellitic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution and the mixture stirred for about 20 hours. Polyamic acid thus obtained had an inherent viscosity of 1.60 d/g. A part of the polyamic acid solution was cast on a glass plate and heated at 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The film had a glass transition temperature of 326°C and a 5% weight loss temperature in air of 525°C. The polyimide film was inserted between cold rolled steel panels which had been preheated at 130°C and pressed for 5 minutes at 350°C with a pressure of 20 kg/cm². The bonded specimen had a poor lap shear strength of 80 kg/cm² at room temperature. The polyimide film had also a poor water absorption of 2.3%. Example 2 The same reaction vessel as in Example 1 was charged with 61.67 g (0.1 mole) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 466.8 g of N,N-dimethylacetamide. To the mixture was added 20.7 g (0.095 mole) of pyromellitic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for about 20 hours. Polyamic acid thus obtained had an inherent viscosity of 0.56 dl/g. To the polyamic acid solution was added 275 g of N,N-dimethylacetamide, and then 40.4 g (0.4 mole) of triethylamine and 61.2 g (0.6 mole) of acetic anhydride were added dropwise with stirring in a nitrogen atmosphere. After 2 hours from the completion of dropwise addition, polyimide started to precipitate as a yellow powder. The mixture was further stirred for 20 hours and filtered to obtain the polyimide powder. The powder was washed with methanol and dried at 180°C for 5 hours under reduced pressure to obtain 77.2 g (98% yield) of the polyimide powder. The polyimide powder had a glass transition temperature of 285°C, a melting point of 420°C in accordance with DSC method, and a 5% weight loss temperature of 542°C. Figure 1 illustrates the infrared absorption spectrum of the polyimide powder. In this spectrum, remarkable absorption is found in the neighbourhood of the following wave numbers. The characteristic absorption of imide is 1780 cm⁻¹ and 1720 cm⁻¹. That of an ether linkage is 1240 cm⁻¹, and that of a sulfone linkage is 1330 cm⁻¹ and 1150 cm⁻¹. The polyimide powder had a crystallinity of 34% based on X-ray analysis. The polyimide powder was quite insoluble in halogenated hydrocarbons such as methylene chloride, chlorofrom, trichloroethylene and 1,1,2,2-tetrachloroethane and acetone. The melt viscosity of the polyimide powder thus obtained was measured with a flow tester of the Japan Polymer Society (Model CFT-500, a product of Shimadzu Seisakusho). An orifice having a diameter of 0.1 cm and a length of 1 cm was used under 100 kg load. The melt viscosity measured at 440°C was 7.0 × 10² Pa · s. The strand obtained was light yellow, transparent and very flexible. The polyimide powder was compression molded at 440°C for 30 minutes with a pressure of 300 kg/cm². The molded specimen had a notched Izod strength of 19 kg.cm/cm in accordance with ASTM D-256 and a heat distortion temperature (18.6 kg load) of 265°C in accordance with ASTM D-648. Example 3 The same reaction vessel as in Example 1 was charged with 12.334 g (0.02 mole) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 105.7 g of N,N-dimethylacetamide. To the mixture was added 6.311 g (0.0196 mole) of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for 20 hours at room temperature. Polyamic acid thus obtained had an inherent viscosity of 1.10 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated to 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The polyimide film had a tensile strength of 12.7 kg/mm² and an elongation of 8.8%. The polyimide film also had a glass transition temperature of 242°C, a 5% weight loss temperature in air of 535°C and a water absorption of 0.98%. The polyimide film was inserted between cold rolled steel panels which had been preheated at 130°C and pressed for 5 minutes at 320°C with a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 260 kg/cm² at room temperature and 180 kg/cm² at 220°C. As an alternative, the above polyamic acid solution was applied on a cold rolled steel panel and dried by heating at 100°C and 220°C each for an hour. The panel thus treated, was contacted with another steel panel and pressed at 320°C for 5 minutes with a pressure of 20 kg/cm². The bonded specimen thus obtained had a lap shear strength of 265 kg/cm² at room temperature. A mixture of 50 g of the above polyamic acid solution and 25 g of N,N-dimethylamine had added to it 3.23 g (0.032 mole) of triethylamine and 4.89 g (0.048 mole) of acetic anhydride dropwise with stirring in a nitrogen atmosphere at room temperature. After 3 hours from the completion of the addition, polyimide started to separate as a yellow powder. Stirring was further continued for about 20 hours after this first separation. The yellow powder was then filtered, washed with methanol and dried at 180°C for 5 hours under reduced pressure. The polyimide powder thus obtained had a 7.03 g (97.5% yield). Figure 2 illustrates the infrared absorption spectrum of the polyimide powder. In this spectrum, remarkable absorption is found in the neighbourhood of the same wave numbers as in Figure 1. The polyimide powder was inserted between cold rolled steel panels and pressed at 320°C for 5 minutes at a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 260 kg/cm². Example 4 The same reaction vessel as in Example 1 was charged with 6.167 g (0.01 mole) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 52.5 g of N,N-dimethylacetamide. To the mixture was added 3.10 g (0.01 mole) of bis(3,4-dicarboxyphenyl) ether dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for 20 hours at room temperature. Polyamic acid thus obtained had an inherent viscosity of 1.45 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated to 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The polyimide film had a tensile strength of 13.5 kg/mm² and an elongation of 14.0%. The polyimide film had a glass transition temperature of 235°C, a 5% weight loss temperature in air of 525°C and a water absorption of 0.92%. The polyimide film had a light transmittance of 88% and a haze of 0.52% in accordance with ASTM D-1003. The polyimide film was inserted between cold rolled steel panels which had been preheated at 130°C and pressed for 5 minutes at 320°C with a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 275 kg/cm² at room temperature. Example 5 The same reaction vessel as in Example 1 was charged with 6.167 g (0.01 mole) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 51.4 g of N,N-dimethylacetamide. To the mixture was added 2.91 g (0.0099 mole) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for 20 hours at room temperature. Polyamic acid thus obtained had an inherent viscosity of 1.10 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated to 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The polyimide film had a tensile strength of 14.5 kg/mm² and an elongation of 16.0%. The polyimide film had a glass transition temperature of 261°C, a 5% weight loss temperature in air of 532°C and a water absorption of 0.90%. The polyimide film had a light transmittance of 87% and a haze of 0.36%. The polyimide film was inserted between cold rolled steel panels which had been preheated at 130°C and pressed for 5 minutes at 320°C with a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 245 kg/cm² at room temperature. Example 6 The same reaction vessel as in Example 1 was charged with 6.167 g (0.01 mole) of bis[4-(4-(4-aminophenoxy)phenoxy)phenyl] sulfone and 57.5 g of N,N-dimethylacetamide. To the mixture was added 3.98 g (0.0099 mole) of 4,4′-(p-phenylenedioxy)diphthalic dianhydride at room temperature in a nitrogen atmosphere in portions so as to cause little temperature rise of the solution, and the mixture stirred for 20 hours at room temperature. Polyamic acid thus obtained had an inherent viscosity of 1.15 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated to 100°C, 200°C and 300°C each for an hour to obtain a polyimide film having a thickness of about 35 micrometres. The polyimide film had a tensile strength of 14.9 kg/mm² and an elongation of 18.5%. The polyimide film had a glass transition temperature of 219°C, a 5% weight loss temperature in air of 535°C and a water absorption of 0.83%. The polyimide film had a light transmittance of 89% and a haze of 0.32%. The polyimide film was inserted between cold rolled steel panels which had been preheated at 130°C and pressed for 5 minutes at 320°C with a pressure of 20 kg/cm². The bonded specimen had a lap shear strength of 295 kg/cm² at room temperature.

Claims: 1. A polyimide consisting essentially of recurring units of the formula: where R is a tetra-valent radical selected from aliphatic radicals having 2 or more carbon atoms, alicyclic radicals, monocyclic aromatic radicals, fused polycyclic aromatic radicals, and polycyclic aromatic radicals wherein the aromatic radicals are linked to one another either by a direct bond or via a bridging group. 2. A polyimide as claimed in claim 1, wherein R is a tetravalent radical selected from the following: 3. A high-temperature resistant adhesive comprising a polyimide which consists essentially of recurring units of the formula: where R is a tetra-valent radical selected from aliphatic radicals having 2 or more carbon atoms, alicyclic radicals, monocyclic aromatic radicals, fused polycyclic aromatic radicals, and polycyclic aromatic radicals wherein the aromatic radicals are linked to one another either by a direct bond or via a bridging group. 4. A high-temperature resistant adhesive as claimed in claim 3, wherein R is a tetravalent radical selected from the following:

Inventors: IIYAMA, KATSUAKI, KAWASHIMA, SABURO, OHTA, MASAHIRO, OIKAWA, HIDEAKI, TAMAI, SHOJI, YAMAGUCHI, AKIHIRO
Applicants: MITSUI TOATSU CHEMICALS INC.
Application year: 1988
Main classification: C08G73
IPC codes: C08G73