POLYIMIDES AND HEAT-RESISTANT ADHESIVES COMPRISING THE SAME

Abstract: Polyimides having repeating units represented by the following general formula (I) and polyamic acids (precur­ sors of the polyimides) having repeating units represented by the following general formula (II). In the above formulae, Y represents a direct bond, a divalent hydrocarbyl group containing 1 to 10 carbon atoms, a hexafluorinated iso­ propylidene group, a carbonyl, a sulfonyl group or an oxide group, and R represents a tetravalent group selected from the group consisting of an aliphatic group having two or more carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a fused ring polycyclic aromatic group, and a non-fused ring polycyclic aromatic group wherein aromat­ ic groups are linked to each other directly or through a linking member. Typical examples thereof are those wherein Y is a thio group and R is formula (III) or formula (IV), Y is a direct bond and R is (III) or (IV), or Y is an isopropylidene group and R is (IV). These compounds can be obtained from corresponding diamines and tetracar­ boxylic acid dianhydrides. The polymides or polyamic acids are excellent as heat-resistant adhesives.

Description: The present invention relates to a polyimide and its use as a high-temperature adhesive. More particularly, the polyimide of this invention is excellent in high-temperature stability and bonding strength and capable of being applied with good processability. Polyimides obtained by reacting tetracarboxylic acid dianhydride with diamine are hereafter expected to be widely used in areas where high-temperature stability is required, because of their various excellent properties and good thermal stability. In addition to excellent high-temperature stability, polyimides have also good mechanical strength, dimensional stability, flame retardance and electrical insulation and are broadly applicable for use as a material in electrical and electronic appliances, aeronautics and space instruments and transport machinery; and also can be used as a high-temperature adhesive for various high performance materials in these fields. Conventional polyimides, however, normally have excellent thermal stability but poor processability due to their high softening point. On the other hand, the resin developed for improving the processability is inferior in high-temperature stability and solvent resistance. Thus the performance of polyimide has both merits and drawbacks. Generally on the use of conventional polyimides, for example, in film manufacture, wire coating, cover seat or adhesive, solvent removal and imidizing are performed by previously dissolving the polyamic acid precursor into organic solvents and applying on adherends, followed by treating at high temperatures. Insufficient thermal treatment, however, causes property reduction through the residual polyamic acid in the fílm. Thus the above stated heating period necessarily becomes longer and the polyimide forming process becomes very difficult, because slow rise of temperature by step-wise heating and reduction of film thickness are required for avoiding the generation of pinholes in the film. Besides cyclizing reaction by dehydration accompanied with heating has problems, for example, causing uneven thickness or voids in the film or coated layer. Furthermore, polyamic acid requires cold-storage because it is unstable and its solution gradually gels at or hydrolyses even at room temperature. The polyimide adhesive developed by D. J. Progar et al. for high-temperature bonding (US-A 4,065,345) is known to be excellent in both high-temperature stability and adhesive strength. Processing steps, however, are necessary on its use, where the polyamic acid solution in bis(2-methoxyethyl) ether is applied on the substrate surface and heated to cause solvent removal and cyclizing by dehydration. In addition, high-boiling solvents require selection of processing conditions on the rate and pattern of temperature rise up in order to avoid generation of pinholes and voids. A polyimide is therefore required for eliminating problems resulting from the processing method which applies the organic solvent solution of polyamic acid and heats the coated substrates to cause solvent removal and dehydrating imidization. Moreover, a thermoplastic polyimide which can be used for adhesives is desired as it is. According to the invention there is provided a polymer having repeating units of the formula: in which Z is: and R is a tetra-valent radical selected from an aliphatic radical having 2 or more carbons, a cyclo-aliphatic radical, a monoaromatic radical, a condensed polyaromatic radical, or a noncondensed polyaromatic radical wherein the aromatic radicals are mutually connected with a bond or a linking function. The polyimide and its polyamic acid precursor according to the invention are thermoplastic and have excellent processability, in addition to the essentially superior high-temperature stability inherent to polyimides and have outstanding high-temperature adhesion being capable of use in multipurpose applications. The polyamic acid polymer of this invention can be obtained by reacting a diamine having the formula (II): with a tetracarboxylic acid dianhydride having the formula (III) : where R is defined as above, the polyamine acid which is thus obtained can then be further cyclized to give the corresponding polyimide by dehydration or treatment with an imidizing agent. Suitable tetracarboxylic acid dianhydrides (III) to be used in the method include, for example, ethylene tetracarboxylic dianhydride, cyclopentane carboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-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-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,2,3,4-benzene tetracarboxylic dianhydride, 3,4,9,10-perylene tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride and 1,2,7,8-phenanthrene tetracarboxylic dianhydride. The tetracarboxylic acid dianhydride can be used alone or in mixtures of two or more. The polymer can be normally prepared by reacting the ether-diamine with the tetracarboxylic acid dianhydride in an organic solvent. Organic solvents which can be used in the reaction include, for example, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethyl-methoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methyl caprolactam, 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, m-cresol, p-chlorophenol and anisole. These solvents can be used alone or in mixtures of two or more. The reaction temperature is normally 60°C or less, preferably 50°C or less. The reaction pressure is not restricted in particular and atmospheric pressure is sufficient for carrying out the reaction. The reaction time depends upon the type of solvents and reaction temperature. Reaction for 4 to 24 hours is normally sufficient to complete the formation of polyamic acid represented by the formula (I). Such reaction affords the polyamic acid having repeating units of the formula; where Z is and R is as defined above. In the next step, the polyamic acid solution is thermally dehydrated at, for exmaple, 100 to 400 °C, preferably at 100 to 300 °C, or is chemically dehydrated by treatment with an imidising agent such as acetic anhydride to give the corresponding polyimide having repeating units of the formula: where Z is and R is as defined above. According to the invention there is provided a polymer having repeated units of the formula: in which Z is: and R is a tetra-valent radical selected from an aliphatic radical having 2 or more carbons, a cyclo-aliphatic radical, a monoaromatic radical, a condensed polyaromatic radical, or a noncondensed polyaromatic radical wherein the aromatic radicals are mutually connected with a bond or a linking function. The polyimide thus obtained is separated from the solution, it is filtered, washed and dried. When the polyimide is only partially separated or completely dissolved, the solution is poured into a poor solvent for polyimides such as water or methanol as it is. The separated product is, when needed, washed, purified and dried to give polyimide powder. When the resultant polyimide is dissolved in the polymerization solvent, the polyimide solution can also be used as it is. The method of applying the polymer thus obtained for adhesive is roughly divided into two procedures: (1) the polymer is used as an adhesive solution containing the polyamic acid as a main component; or (2) the polymer is mainly used in the form of the polyimide. In the procedure 1 , the adhesive solution is an organic polar solvent solution of polyamic acid. It may be the resultant reaction mixture of polyamic acid obtained by reacting ether diamine (II) with tetracarboxylic acid dianhydride (III) in the organic polar solvent. It also may be a solution containing polyamic acid as the main component and polyimide which is the cyclized product of said polyamic acid. Thus the adhesive solution containing polyamic acid may be a solution or suspension containing polyimide as a further ingredient. When applying the adhesive containing such polyamic acid, a thin layer of polyamic acid adhesive is applied to the adherends to be bonded, followed by preheating the coated adherends in air for a desired period of time at about 220°C. Excess solvents are removed and the polyamic acid adhesive is converted to the more stable polyimide. The adherends are then strongly bonded by pressing under a pressure of 1 - 1,000 kg/cm 2 at a temperature of 50 - 400°C, followed by curing at a temperature of 100 - 400°C. In the procedure 2 wherein said polyimide is used for the adhesive, it is roughly divided into three cases: (a) the polyimide is used as a powder as it is; (b) the polyimide is dissolved in a solvent or used in the form of the resultant solution at the end of imidization; or (c) the polyimide is previously formed to films before use. In these cases, some of polyamic acid may be contained in the polyimide. In the case a , the adherends can be strongly bonded by inserting the powder between the adherends, pressing under a pressure of 1 - 1,000 kg/cm 2 at a temperature of 50 - 400°C and curing at a temperature of 100 - 400°C. In the case b , a thin layer of polyimide containing adhesive solution is applied to the adherends to be bonded, followed by preheating the adherends in air for the desired period at about 30 - 200°C to remove the solvent. The coated adherends are assembled with other adherends, pressed under a pressure of 1 - 1,000 kg/cm 2 at a temperature of 50 - 400°C and cured at a temperature of 100 - 400°C to give strongly bonded adherends. In this procedure, a desired quantity of the polyimide containing solution is coated and heated at 30 - 200°C to remove the solvents. The coating can be made insoluble in organic solvents by further heating above 250°C. Such organic solvents include halogenated aliphatic hydrocarbon, phenol, cresol, halophenols, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, sulfolane and N,N-dimethylformamide. In the case c , polyimide films are obtained by casting the polyimide containing solution and heating at 20 - 200°C. Homogenous polyimide films without voids and pinholes can be obtained by using halogenated aliphatic hydrocarbon as solvents in particular. To apply the polyimide films for adhesion, the films are inserted between the adherends and pressed under a pressure of 1 - 1,000 kg/cm 2 at a temperature of 50 - 400°C. The adherends can be strongly bonded by curing at a temperature of 100 - 400°C. The polyimide of the invention can be obtained by polymerizing 4,4'-bis(3-aminophenoxy) biphenyl as the diamine component with one or more tetracarboxylic acid dianhydrides to give a polyamic acid which is further cyclized by dehydration. This polyimide is particularly excellent in processability and high-temperature adhesion. If 4,4'-bis(4-aminophenoxy)biphenyl, ie. an isomer having amino groups at different positions is used in place of 4,4'-bis(3-aminophenoxy)biphenyl, the polyimide obtained by reacting with tetracarboxylic acid dianhydride, for example, pyromellitic dianhydride or 3,3',4,4'-benzophenone tetracarboxylic dianhydride, has no distinct glass transition temperature, almost no or very little bonding strenght and poor processability. Polyimides of this invention are thermoplastic while maintaining the same level of high-temperature stability as conventional polyimides, and thus excellent in processability and high-temperature adhesion. Some polyimides in this invention are very stable at high temperature and can be molded by fusion. Besides this polyimide has characteristics of low water absorption and good transparency in addition to the excellent processability. Therefore polyimide of this invention is very valuable as a raw material for aeronautics and space instruments, electric and electronic appliances, and further as a high-temperature adhesive. This polyimide can be prepared by the following method. Polyamic acid is obtained by polymerizing 4,4'-bis(3-amino-phenoxy)biphenyl with tetracarboxylic acid dianhydride in an organic solvent. In the present invention, the inherent viscosity of the polyamic acid precursor of polyimide preferably is in the range of 0.1 to 4.0 dl/g, more preferably 0.3 to 2.5 dl/g. The inherent viscosity is measured at 35°C with a solution containing 0.5 grams of polyamic acid in 100 ml of N,N-dimethylacetamide solvent. The corresponding polyimide can be obtained from the polyamic acid by thermal dehydration at 100 - 400°C or by chemical dehydration with conventional imidizing agents. A preferred polyimide has repeating units represented by the formula (VI): This polyimide is obtained by polymerizing 4,4'-bis(3-aminophenoxy)biphenyl with pyromellitic dianhydride to give a polyamic acid which is further cyclized by dehydration. This polyimide is thermoplastic yet maintains the same level of high-temperature stability as prior known conventional polyimides. Therefore this polyimide can be molded by fusion and is excellent in processability and high-temperature stability. In addition, this polyimide has further characteristics of low water absorption, high resistance to solvent and alkali, and excellent flexibility. Therefore the polyimides of this invention are very valuable as raw materials for aeronautics and space instruments as well as electric and electronic appliances. This preferred polyimide can be prepared by polymerizing 4,4'-bis(3-aminophenoxy)biphenyl with pyromellitic dianhydride in an organic solvent . The inherent viscosity of the polyamic acid precursor of this preferred polyimide preferably is in the range of 0.1 to 4.0 dl/g, more preferably 0.3 to 2.5 dl/g. The corresponding polyimide can be obtained from the polyamic acid by thermal dehydration at 100 - 400°C or by chemical dehydration with imidizing agents such as acetic anhydride. Furthermore, the polyimide having repeating units of the formula (VI) can also be obtained by suspending or dissolving 4,4'-bis(3-aminophenoxy)biphenyl and pyromellitic dianhydride in an organic solvent, and heating to perform simultaneous generation and dehydrating imidization of polyamic acid which is the precursor of the polyimide. To achieve the excellent adhesion by the polyimides of this invention, an inherent viscosity of 0.05 to 1.5 dl/g is preferred for the polyimide. Adhesive strength is poor at 0.05 or less. Preparation becomes difficult and adhesive strength decreases at 1.5 or more. To apply the polyimide of this invention as an adhesive, polyimide powder can be used as it is, or the solution in polymerization/imidization solvents also can be used as it is. The solution in halogenated aliphatic hydrocarbon is preferably used. When providing cast films or preparing coated layers on a metal surface and further applying them for bonding, strong adhesion can be obtained by dissolving the polyimide of this invention in a halogenated aliphatic hydrocarbon or other organic solvents. Because the cyclizing step by dehydration is not included as in the case of applying an organic solvent solution of a polyamic acid, void generation by foaming and non-uniformity of films do not occur. The halogenated aliphatic hydrocarbon solvents used have relatively low boiling points, evaporate at lower temperatures, and are easy to process without complicated steps for temperature rise. Besides these solvents have low toxicity as compared with cresol and halophenols which are generally used for the solvents of wire varnishes and metal coatings. Therefore this invention is advantageous in the varnish industry from an environmental viewpoint. The polyimide films prepared by casting the halogenated aliphatic hydrocarbon solution of polyimide and curing at above 250°C, or prepared by thermally removing the solvents and imidizing the organic solvent solution of the polyamic acid precursor of polyimide and curing have the characteristic of very high chemical resistance, because the films are insoluble in organic solvents including halogenated aliphatic hydrocarbon, cresol, halophenols, N,N-dimethyl acetamide, N-methyl-2-pyrrolidone, sulfolane, and N,N-dimethyl formamide. The invention will be illustrated further with respect to the following Examples, Comparative Examples and Synthetic Examples, and with reference to accompanying drawings in which: Figures 1 and 3 show the IR absorption spectrum of polyimide powder made according to Examples 1 and 4, respectively; and Figure 2 illustrates the relation between shear rate and melt viscosity of the polyimide prepared according to Example 2. Synthetic Example 1 A 3 liter glass reaction vessel was charged with 186 grams (1.0 mol) of 4,4'-dihydroxybiphenyl, 438 grams (2.6 mols) of m-dinitrobenzene, 363 grams of potassium carbonate and 2.0 liters of N,N-dimethylformamide, and the reaction conducted for 16 hours at 145 - 150°C. After ending the reaction, the resultant mixture was cooled, inorganic salt filtered and the solvent was vacuum distilled from the filtrate. The residue was cooled to 65°C, added to 2.0 liters of methanol and stirred for an hour. The separated crystals were filtered, washed with water and methanol successively, and dried to give 426 grams (99.5% yield) of 4,4'-bis(3-nitrophenoxy)biphenyl as brown crystals. In the next step, 100 grams (0.23 mol) of crude 4,4'-bis(3-nitrophenoxy)biphenyl thus obtained were charged into a 1 liter sealed glass reaction vessel with 1 gram of 5% Pd/C (from Japan Engelhardt Co.) and 350 ml of ethyleneglycol monomethylether. Hydrogen was introduced at 60 - 65°C under vigorous stirring and its absorption was stopped after 8 hours. The resultant mixture was cooled, filtered to remove the catalyst and poured into 500 ml of water. The separated crystals were filtered, and added to 48 grams of 35% hydrochloric acid and 540 ml of 50% isopropyl alcohol, and warmed. The resultant solution was allowed to cool and the hydrochloride of 4,4'-bis(3-aminophenoxy)biphenyl was separated. The separated crystals were filtered and dissolved in 540 ml of 50% isopropyl alcohol by warming, added with 5 grams of active carbon and filtered. The filtrate was neutralized with aqueous ammonia. The separated crystals were filtered, washed with water and dried to give 72.0 grams (85% yield) of desired 4,4'-bis(3-aminophenoxy)biphenyl. Colorless crystals: mp. 144 - 146°C Purity : 99.6% (based on high-speed liquid chromatography) Elementary analysis : C 24 H 20 N 2 O 2 C H N Calculated (%) 78.26 5.43 7.61 Found (%) 78.56 5.21 7.66 MS : 368 (M + ), 340,184 IR (KBr.cm -1 ) : 3400 and 3310 (amino group), 1240 (ether linkage) Example 1 A reaction vessel with a stirrer, reflux condenser and nitrogen inlet tube was charged with 36.8 grams (0.1 mol) of 4,4'-bis-(3-aminophenoxy)biphenyl and 175.8 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 21.8 grams (0.1 mol) of pyromellitic dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for 20 hours at room temperature. The inherent viscosity of the polyamic acid thus obtained was 2.47 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a light yellow and transparent polyimide film having a thickness of 35 µm. The polyimide film obtained had a tensile strength of 14.8 kg/mm 2 and an elongation of 70% in accordance with ASTM D-882, a glass transition temperature of 271°C in accordance with TMA penetration method and a 5% by weight decrease temperature in air of 545°C. Besides the polyimide film was inserted between cold rolled steel panels which were preheated at 130°C, and pressed for 5 minutes at 340°C under a pressure of 20 kg/cm 2 . The lap shear strength of the specimen was 310 kg/cm 2 at room temperature and 205 kg/cm 2 at 240°C. Besides water absorption of the film was 0.52% after immersing for 24 hours at 23.5°C in accordance with ASTM D-570-63. Change in appearance was also not found at all on the film after immersing the film in 30% by weight aqueous sodium hydroxide solution at 70°C. The polyamic acid solution was cast on an electrolytic copper foil and heated for an hour each at 100°C, 200°C and 350°C to give a flexible copper-clad circuit substrate. Thickness of the coated film was about 35 µm. The peel strength of copper foil was 2.8 kg/cm by 90° peel test. Blister was not found at all after immersing in a solder bath at 300°C for 180 seconds. Besides 150 grams of the polyamic acid solution was added with 337.5 grams of N,N-dimethylacetamide and heated to 70°C under nitrogen atmosphere before dropping 26.1 grams (0.26 mol) of acetic anhydride and 9.05 grams (0.09 mol) of triethylamine. After the end of dropping, a yellow powder of polyimide started to precipitate for about 10 minutes. After stirring under heating for 2 hours, the polyimide powder was hot-filtered, washed with methanol and dried in vacuum for 5 hours at 150°C to give 34.5 grams (98% yield) of product. X-ray analysis of this powder results in 21% crystallinity. Besides the IR spectrum of the powder is illustrated in Figure 1. Remarkable absorption was found on this spectrum at around 1780cm -1 and 1720cm -1 of characteristic absorption bands for imide and around 1240cm -1 of the characteristic absorption band for ether linkage. The polyimide powder was quite insoluble in halogenated hydrocarbon solvents such as methylene chloride and chloroform. The polyimide powder had glass transition temperature of 260°C and melting point of 367°C in accordance with DSC method. The specimen which was compression molded at 400°C for 30 minutes under a pressure of 300 kg/cm 2 had a notched Izod impact strength of 18 kg.cm/cm in accordance with ASTM D-256. Comparative Example 1 The polymerization of Example 1 was repeated except 4,4'-bis-(4-aminophenoxy)biphenyl was used in place of 4,4'-bis(3-aminophenoxy)biphenyl. The inherent viscosity of the polyamic acid obtained was 1.50 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a light yellow transparent polyimide film. The film had a tensile strength of 9.0 kg/mm 2 , an elongation of 20%, no distinct glass transition temperature in accordance with TMA penetration method, and a 5% by weight decrease temperature in air of 533°C. The cold rolled steel panels were pressed with the polyimide film by inserting the polyimide powder between cold rolled steel panels which were preheated at 130°C and pressed for 5 minutes at 320°C under a pressure of 20 kg/cm 2 . The lap shear strength of the specimen at room temperature had an inferior value of 50 kg/cm 2 . Example 2 A reaction vessel with a stirrer, reflux condenser and nitrogen inlet tube was charged with 368 grams (1.0 mol) of 4,4'-bis-(3-aminophenoxy)biphenyl and 5,215 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 211.46 grams (0.97 mol) of pyromellitic dianhydride was added by portions with care to avoid temperature rise of the solution and stirred for 20 hours at room temperature. The polyamic acid thus obtained had an inherent viscosity of 0.52 dl/g. The polyamic acid solution was dropped with 404 grams (4 mols) of triethylamine and 612 grams (6 mols) of acetic anhydride at room temperature and under nitrogen atmosphere. Yellow polyimide powder started to precipitate at an hour after the end of dropping. The powder was filtered after stirring for further 20 hours at room temperature, sludged with methanol, filtered and dried at 180°C for 24 hours to give 529 grams (97.3% yield) of polyimide powder. The resultant polyimide powder had the same IR absorption spectrum as Figure 1 and crystallinity of 9.3% according to X-ray analysis. Melt viscosity of the polyimide powder thus obtained was measured with the flow tester of The Society of Polymer Science Japan model (Shimadzu Seisakusho CFT-500) by use of the nozzle having 0.1 cm in diameter and 1 cm in length. Effect of temperature variation on shear rate vs. melt viscosity relationships is shown in Figure 2. The strand obtained was light brown, transparent, tough and very flexible. Brown, transparent and tough strands were extruded from the polyimide powder at 390°C and pelletized. The pellets were molded by injection at 390°C with a pressure of 500 kg/cm 2 to give a brown and transparent molded product. In accordance with ASTM D-638, the molded product had a tensile yield strength of 1,240 kg/cm 2 , tensile strength of 1,110 kg/cm 2 and elongation of 40%. In accordance with ASTM D-648, the molded product had a notched Izod impact strength of 18.2 kg.cm/cm and heat distortion temperature of 250°C. Example 3 A vessel with a stirrer, reflux condenser and nitrogen inlet tube was charged with 3.68 grams (0.01 mol) of 4,4'-bis(3-amino-phenoxy)biphenyl, 2.11 grams (0.0097 mol) of pyromellitic dianhydride and 52.1 grams of m-cresol, and heated with stirring under nitrogen atmosphere. The mixture gave a brown, transparent and uniform solution at around 135°C. The temperature was raised to 150°C and the stirring was continued. Yellow polyimide powder started to precipitate in 10 minutes, stirred for further 2 hours with heating and filtered. The polyimide powder was washed with methanol and acetone, and dried in vacuum at 180°C for 24 hours to give 4.62 grams (85.1% yield) of product. The polyimide powder thus obtained had the same IR absorption spectrum as Figure 1. Example 4 A reaction vessel with a stirrer, reflux condenser and nitrogen inlet tube was charged with 36.8 grams (0.1 mol) of 4,4'-bis-(3-aminophenoxy)biphenyl and 175.8 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 20.71 grams (0.095 mol) of pyromellitic dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for 20 hours at the room temperature. The polyamic acid thus obtained had an inherent viscosity of 0.60 dl/g. The polyamic acid solution was mixed with 160 grams of N,N-dimethylacetamide, warmed to 70°C, and dropped with 20.4 grams (0.2 mol) of acetic anhydride and 7.1 grams (0.07 mol) of triethylamine. Yellow polyimide powder started to precipitate in 10 minutes after the end of dropping. The powder was hot-filtered after stirring for further 2 hours with heating, sludged with methanol, filtered and dried at 150°C for 5 hours to give 53.8 grams (97% yield) of polyimide powder. Figure 3 shows the IR absorption spectrum of the resultant polyimide powder. On this spectrum, remarkable absortion was found at characteristic bands for imide of around 1780 cm -1 and 1720 cm -1 as well as for ether linkage of around 1240 cm -1 . The polyimide thus obtained had a melt viscosity of 5 x 10 3 poise at 400°C by use of 100 kg load and a nozzle having 0.1 cm in diameter. The strand obtained was brown, transparent, tough and very flexible. The polyimide film was inserted between cold rolled steel panels which were preheated at 130°C and pressed for 5 minutes at 340°C under a pressure of 20 kg/cm 2 . The specimen had a lap shear strength of 305 kg/cm 2 at room temperature and 210 kg/cm 2 at 240°C. Example 5 The same reaction vessel as in Example 1 was charged with 18.4 grams (0.05 mol) of 4,4'-bis(3-aminophenoxy)biphenyl and 103.5 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 16.1 grams (0.05 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for about 20 hours. The polyamic acid thus obtained had an inherent viscosity of 1.62 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a light yellow, transparent polyimide film. The polyimide film had a tensile strength of 13.5 kg/mm 2 , elongation of 11%, glass transition temperature of 230°C and a 5% by weight decrease temperature in air of 538°C. Besides the polyimide film was inserted between cold rolled steel panels which were preheated at 130°C and pressed for 5 minutes at 340°C under a pressure of 20 kg/cm 2 . The specimen had a lap shear strength of 280 kg/cm 2 at room temperature. In addition, the polyamic acid solution was applied on a cold rolled steel panel and dried by heating for an hour each at 100°C and 220°C. The coated panel was assembled with another steel panel and pressed for 5 minutes at 300°C under a pressure of 20 kg/cm 2 . The specimen obtained had a lap shear strength of 260 kg/cm 2 at room temperature. Comparative Example 2 The polymerization of Example 5 was repeated except 4,4'-bis-(4-aminophenoxy)biphenyl was used in place of 4,4'-bis(3-aminophenoxy)-biphenyl. The polyamic acid obtained had an inherent viscosity of 1.28 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a light yellow and transparent polyimide film. The polyimide film obtained had no distinct glass transition temperature and the 5% by weight decrease temperature in air was 505°C; the film had a tensile strength of 13.3 kg/mm 2 and an elongation of 8%. Besides cold rolled steel panels were pressed with the polyimide film by the same procedure as in Example 1. The specimen had an inferior lap shear strength of 40 kg/cm 2 . Example 6 The same reaction vessel as Example 5 was charged with 9.2 grams (0.025 mol) of 4,4'-bis(3-aminophenoxy)biphenyl and 50.85 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 7.75 grams (0.025 mol) of bis(3,4-dicarboxyphenyl) ether dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for further 20 hours at room temperature. The polyamic acid thus obtained had an inherent viscosity of 1.70 dl/g. A part of the polyamic acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a colorless and transparent polyimide film having a thickness of about 50 µm. The film had a tensile strength of 15.2 kg/mm 2 , elongation of 10%, glass transition temperature of 208°C and a 5% by weight decrease temperature in air of 503°C. Besides the polyimide film was inserted between cold rolled steel panels which were preheated at 130°C and pressed for 5 minutes at 340°C under a pressure of 20 kg/cm 2 . The specimen had a lap shear strength of 307 kg/cm 2 at room temperature. The polyimide film had a light transmittance of 86% and a haze value of 0.69% in accordance with ASTM D-1003. Example 7 The same reaction vessel as in Example 1 was charged with 9.2 grams (0.025 mol) of 4,4'-bis(3-aminophenoxy)biphenyl and 42.45 grams of N,N-dimethylacetamide. Under nitrogen atmosphere and at room temperature, 4.95 grams (0.025 mol) of 1,2,3,4-butane tetracarboxylic dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for further 20 hours at room temperature. The polyamic acid thus obtained had an inherent viscosity of 0.35 dl/g. A part of the polyamie acid solution was cast on a glass plate and heated for an hour each at 100°C, 200°C and 300°C to give a yellow-orange and transparent polyimide film. The film had a tensile strength of 11.0 kg/mm 2 , elongation of 8%, glass transition temperature of 207°C and the 5% by weight decrease temperature in air was 400°C. Example 8 The same reaction vessel as in Example 1 was charged with 9.2 grams (0.025 mol) of 4,4'-bis(3-aminophenoxy)biphenyl and 42.45 grams of bis(2-methoxyethyl) ether. Under nitrogen atmosphere and at the room temperature, 5.45 grams (0.025 mol) of pyromellitic dianhydride were added by portions with care to avoid temperature rise of the solution and stirred for further 20 hours at room temperature. The polyamic acid thus obtained had an inherent viscosity of 1.55 dl/g. The polyamic acid solution was applied on a cold rolled steel panel which was previously washed with trichloroethylene and dried by heating for an hour each at 100°C and 220°C. The coated panel was assembled with another cold rolled steel panel and pressed for 5 minutes at 300°C under a pressure of 20 kg/cm 2 . The specimen had a lap shear strength of 280 kg/cm 2 at room temperature.

Claims: A polymer having repeating units of the formula: in which Z is: and R is a tetra-valent radical selected from an aliphatic radical having 2 or more carbons, a cyclo-aliphatic radical, a monoaromatic radical, a condensed polyaromatic radical, or a noncondensed polyaromatic radical wherein the aromatic radicals are mutually connected with a bond or a linking function. A polymer as claimed in Claim 1 in which Z is: and R is as defined in Claim 1. A polymer as claimed in Claim 1 in which Z is: A polymer as claimed in Claim 1 in which Z is: Use of a polymer as claimed in any preceding claim as a high-temperature stable adhesive.

Inventors: KAWASHIMA SABURO, OHKOSHI KOUJI, OHTA MASAHIRO YABE, OIKAWA HIDEAKI IIJIMA, SONOBE YOSHIHO IIJIMA, TAMAI SHOJI IIJIMA, YAMAGUCHI AKIHIRO, KAWASHIMA, SABURO, OHKOSHI, KOUJI, OHTA, MASAHIRO, OIKAWA, HIDEAKI, SONOBE, YOSHIHO, TAMAI, SHOJI, YAMAGUCHI, AKIHIRO, KAWASHIMA, SABURO 4-37-14, OYABE, OHKOSHI, KOUJI 4-10-8,, OHTA, MASAHIRO 1541, YABE-CHO, OIKAWA, HIDEAKI 2070, IIJIMA-CHO, SONOBE, YOSHIHO 2070, IIJIMA-CHO, TAMAI, SHOJI 2070, IIJIMA-CHO, YAMAGUCHI, AKIHIRO 1-13-24,
Applicants: MITSUI TOATSU CHEMICALS, MITSUI TOATSU CHEMICALS, INC.
Application year: 1986
Main classification: C08G73
IPC codes: C09J179, C08G73