Aromatic diamine and polyimide, and preparation process of same

Abstract: This invention relates to fluorine containing polyimide, a novel aromatic diamine which has a perfluoroalkyl radical and can be used as a raw material monomer of the polyimide, and a process for preparing the same. The polyimide comprise a requisite structural unit having one or more recurring structural units of the formula: such as the structural units of the formula Further, the present invention relates to a novel aromatic diamine which has a perfluoro radical and can be used as a raw material monomer of the polyimide, and a process for preparing the same. The present invention can provide polyimide which has an extremely low dielectric constant and is colorless, transparent and excellent in processability and heat resistance, and also provides an aromatic diamine which is useful as a raw material monomer of the polyimide or a raw material of other various engineering plastics.

Description: The present invention relates to fluorine containing polyimide, a novel aromatic diamine which has a perfluoro alkyl radical and can be used as a raw material monomer of the polyimide, and a process for preparing the same. Preferred embodiments relate to a novel thermoplastic polyimide which contains fluorine, has extremely low dielectric constant and hygroscopic property, and is excellent in processability ; a preparation process of the thermoplastic polyimide ; a novel aromatic diamine compound which has a perfluoroalkyl radical such as trifluoromethyl and is useful for a raw material monomer of the polyimide, for a starting material of polyamide, polyamideimide, bismaleimide and epoxy resin, and for a raw material of organic chemicals; and a preparation process of the aromatic diamine compound. Polyimide is prepared by reaction of tetracarboxylic dianhydride with diamine. Conventionally Known polyimide has an essential characteristic of high heat resistance, is additionally excellent in mechanical strengths, chemical resistance and dimensional stability, and also has flame retardance and electrical insulation property. Consequently, polyimide has been used in electric and electronic fields, particularly in the field where heat resistance is required, and is expected for future extension of application field and amount in use. Polyimide having excellent characteristics has conventionally been developed. However, conventionally known polyimide has no distinct glass transition temperature though excellent in heat resistance and hence must be processed by such means as sintering in the case of using as a molded article. In other cases, polyimide is soluble in halogenated hydrocarbon solvents and causes problems on solvent resistance though excellent in processability. Thus, both merits and drawbacks have been found in the properties of polyimide. Recently, polyimide having improved properties or being provided a novel performance has been developed in order to extend the utilization field of polyimide. For example, it has been known thermoplastic polyimide of the formula (A) : The polyimide has been disclosed by Proger et al. as a heat resistant adhesive in USP 4,065,345. Ohta et al. have provided the polyimide with a new performance of injection ability by controlling the molecular weight of polymer and capping the reactive end of polymer chain in Japanese Laid-Open Patent Hei 2-018419. Development in microelectronics has recently been remarkable in the electric and electronic field. Development research has been extensively conducted in particular on the insulation material for use in a multi-layered circuit substrate. In organic materials applied to the field, polyimide in particular is used as a suitable material for insulation because of excellent heat resistance and dimensional stability and a low dielectric constant as compared with inorganic materials. The dielectric constant of presently marketed polyimide resin is, however, unsatisfactory. For example, Polyimide KAPTON (Trade Mark) prepared from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride has a dielectric constant of 3.6 at 1 KHz, polyimide UPILEX (Trade Mark) prepared from 4,4'-diaminodiphenyl ether and biphenyltetracarboxylic dianhydride has a dielectric constant of 3.5 at 1 MHz, and polyimide LARC-TP1 (Trade Mark) prepared from 3,3'-diaminobenzophenone and benzophenonetetracarboxylic dianhydride has a dielectric constant of 3.7 at 1 MHz. Polyimide resin has already been used for an insulation material of a flexible printed-circuit substrate. High integration of an electronic circuit has recently been more extended, and accordingly, improvement in electrical characteristics, for example, lowering of the dielectric constant has been strongly desired. Practically, insulation materials having a low dielectric constant of 3.0 or less, preferably about 2.8 have been desired. Particularly in large-sized computers, high speed transfer of signals by use of 2 multi-layered circuit substrate is inevitable. However, high dielectric constant of the circuit material leads to transfer lag of signals and inhibits high speed transfer. Polyimide is used for an interlayer insulation film in multi-layered wiring. Accordingly, attention has been focused to develop polyimide having a low dielectric constant in particular in addition to the above characteristics of conventional polyimide. Teflon resin has been known as a resin having a low dielectric constant. Investigations for decreasing the dielectric constant has also been carried out on polyimide having heat resistance and other various excellent properties as an engineering polymer. Reduction of a dielectric constant by introduction of fluorine or a fluoro radical into the structure of polyimide has been reported, for example, in A.K. st. Clair et al. Polymeric Materials Science and Engineering, 59, 28 to 32 (1988) and EP 0299865. That is, introduction of a fluorine atom into the molecular unit of polyimide has been known as a means of reducing the dielectric constant of polyimide. In order to achieve such object, an aromatic diamino compound having a hexafluoroisopropylidene radical has been disclosed as a polyimide monomer used for preparing materials of low dielectric constant (Japanese Laid-open Patent Hei 1-190652). These aromatic diamine compounds, however, require many steps in preparation and also have problems in industry that the resultant polyimide resin has insufficient melt-flowability in processing. An aromatic diamino compound which has biphenyl structure and a trifluoromethyl radical in the molecule is, for example, 4,4'-bis(3-trifluoromethyl-4-aminophenoxy) biphenyl of the formula (B) : The compound, however, has an electron absorbing trifluoromethyl radical on the ortho position to an amino radical and is hence known that the compound is difficult to react with acid anhydride due to an electric factor and is difficult to increase polymerization degree. Since the amino group is located on the para position to the connecting radical, the resulting polyimide has rigid structure and causes a problem of difficulty or processing. Other fluorine containing polyimides having low dielectric constant have conventionally been proposed, for example, in Japanese Laid-Open Patent Hei 1-182324, 2-60933, 2-281037 and 4-122729. These polyimide are very expensive or difficult to manufacture in industry and it is hence desired to develop polyimide which is free from these disadvantages and has a low dielectric constant. Development of plastics having excellent transparency in addition to a low dielectric constant has also been carried out extensively in order to obtain engineering plastics applied to an electric and electronic field. A plastic which has excellent transparency and is widely used is polycarbonate of the formula (C) : The plastic, however, has low glass transition temperature of about 150 °C and hence heat resistance is unsatisfactory. Another Known transparent resin is polyether sulfone of the formula (D) : The resin, however, has a sulfonyl radical which has a high hygroscopic property and thus cannot be used for electric and electronic materials which must be free from moisture. Further, various kinds of transparent polyimide have also been developed. For example, polyimide having excellent yellowness index has been disclosed in Japanese Laid-Open patent Hei 1-182324 and has the formula (E) : However, the polyimide also has a problem of hygroscopic property due to the presence of a sulfonyl radical as the case of the above polyether sulfone. Problems generally found on polyimide resin have been coloration and higher dielectric constant than other resin such as Teflon which has a low dielectric constant. Coloration is a very important problem in the development of optical communication cables and optical materials such as filters and liquid crystal which are used for construction of a highly heat-resistant and reliable communication system. Practically, yellowness index (hereinafter referred to as YI) is used as a parameter of yellowness. YI is 129 on polyimide KAPTON (Trade Mark) prepared from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, 125 on polyimide UBILEX (Trade Mark) prepared form 4,4'-diaminodiphenyl ether and biphenyltetracarboxylic dianhydride, and 50 on polyimide LARC-TPI (Trade Mark) prepared from 3,3'-diamino benzophenone and benzophenonetetracarboxylic dianhydride. Any of these YI values are too high. YI of 10 or less is desired for use in the above optical materials. Polyimide resin is desired to have YI of 4 to 8 which is equal to that of polycarbonate for present optical application. EP-A-0,382,198 (Occidental Chemical Corporation) discloses the preparation of polyimidesiloanes from certain diamines each of whose terminal aryl groups carries, in addition to an amine group, a trifluoromethyl group. Such polyimides are said to have enhanced solubility in diglyme. GB-A-2,229,180 (The British Petroleum Company plc) discloses the production of the polyimides from diamines including three linked aryl groups. The three aryl groups are linked by two linkage groups which must, according to the reference, bedifferent from each other. The polyimides are suitable for use as gas spearation membranes. EP-A-0,495,425 was published between the earliest claimed priority date and European filing date of the present patent and discloses a preparation process for diphenyl ethers. One such ether is 1,3-di(oxy-3-trifluoromethyl-5-aminophenyl)-5-trifluoromethylbenzene, which may, in turn, be used for the preparation of certain polyimides. Such polyimides are outside the scope of the claims appended hereto. Embodiments of the invention may enable one to attain one or more of the following objects: to provide polyimide having a low dielectric constant and excellent processability, and a process for preparing the polyimide ; to provide polyimide having good transparency and a preparation process of the polyimide; to provide a novel fluorine containing aromatic diamine which is useful as a raw material monomer of the polyimide and a process for preparing the same. As a result of an intensive investigation, the present inventors have found that polyimide having a low dielectric constant and excellent transparency can be obtained by using an aromatic diamine monomer wherein the molecule comprises 3 to 4 aromatic rings, two amino radicals are individually located on each terminal benzene ring on the meta position to the molecular chain connecting radical, and one or more perfluoro radicals are located on each aromatic ring. They have also found a novel fluorine containing aromatic diamine which is useful for the monomer of polyimide having the above properties, and have succeeded in the preparation of the novel diamine. Thus, the invention has been completed. That is, the present-invention is : (1) A polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO- and -C(CH 3 ) 2 - and each X 1 is the same, m is an integer of 1 to 6, n is individually 0 or an intager of 1 to 4, R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of aliphatic radical, alicyclic radical, monoaromatic radical, comdensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is individually 0 or an integer of 1 to 4, or an integer of 1 to 4 when n is 0 in the formula (1) with the proviso that said polyimide (1) is not one having one or more recurring structural units of formula wherein R 1 is a tetravalent radical selected from WHERE AR 3 IS or The polyimide of the formula (1) practically includes below described polyimide : (2) An aromatic polyimide comprising a requisite structural units having one or more recurring structural units of the formula (2) : wherein n and p are 0 (simultaneously 0, exclusive) or an integer of 1 to 4, and R is the same as in the formula (1). (3) An aromatic polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (3) : wherein n is an integer of 1 to 4 and R is the same as in the formula (1). (4) An aromatic polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (4) : wherein p is an integer of 1 to 4 and R is the same as in the formula (1). The polyimide of the formulas (2), (3) and (4) more practically includes below described polyimide : (5) An aromatic polyimide comprising a requisite structural units having one or more recurring structural units selected from the group consisting of the formulas (5),(6),(7),(8),(9) and (10) : wherein R is the same as above. (6) An aromatic polyimide comprising a requisite structural units having one or more recurring structural units of the formula (11) : wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, n and p are 0 (simultaneously 0, exclusive) or an integer of 1 to 4, and R is the same as in the formula (1). (7) An aroamtic polyimide comprising a requisite structural units having one or more recurring structural units of the formula (12) : wherein R is the same as in the formula (1). (8) A capped polyimide having at the polymer chain end an aromatic ring unsubstituted or substituted with a radical having no reactivity for amine and dicarboxylic anhydride. Capped polyimides of the invention are set out in the appended claims 2, 7, 25 and 26, and include aromatic polyimides of formulae (1) to (7) which are capped. That is, a capped aromatic polyimide obtained by capping the polymer chain end with aromatic dicarboxylic anhydride of the formula (15) : wherein Z is a divalent radical having 6 to 15 carbon atoms and being selected the group consisting of a monoaromatic radical condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member and/or aromatic monoamine of the formula (16) : Z 1 - NH 2 wherein Z 1 is a monovalent radical having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, preferably by capping with phthalic anhydride or aniline. Another invention is a preparation process of polyimide, that is: (9) A preparation process of polyimide comprising a requisite structural units having one or more recurring structural units of the formula (1) wherein X 1 Ar, m, n, and R are the same as above each X 1 being the same, which comprises reacting an aromatic diamine having one or more principal ingredients of the formula (13): Wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO-, and -C(CH 3 ) 2 -, the two X 1 being the same, m is an integer of 1 to 6 n is 0 or an integer of 1 to 4, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is individually 0 or an integer 1 to 4 and an integer of 1 to 4 when n is 0 in the formula (13), with one or more tetracarboxylic dianhydride principally represented by the formula (14) : wherein R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and thermally or chemically imidizing the resulting polyamic acid; with the proviso that said polyimide (1) is not one having one or more recurring structural units of formula wherein R 1 is a tetravalent radical selected from WHERE AR 3 IS (10) A preparation process of capped aromatic polyimide having recurring structural units of the formula (1) : wherein X 1 , Ar, m, n and R are the same as above except that X 1 may be the same or different, and having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for amine and dicarboxy anhydride, comprising reacting aromatic diamine having one or more principal ingredients of the formula (13): wherein X 1 , Ar, m and n are the same as above and the two X 1 may be the same or different, with one or more tetracarboxylic dianhydride principally represented by the formula (14) wherein R is the same as above, in the presence of aromatic dicarboxylic anhydride of the formula (15) : wherein Z is the same as above, and/or aromatic monoamine of the formula (16): Z 1 - NH 2 wherein Z 1 is the same as above, and thermally or chemically imidizing the resulting polyamic acid. (11) The preparation processes above wherein the aromatic diamine has the formula (18) : wherein n and p are 0 or an integer of 1, and are not simultaneously 0. (12) The preparation processes above wherein the aromatic diamine has the formula (19) : wherein n is an integer of 1 to 4. (13) The preparation processes above wherein the aromatic diamine has the formula (20) : wherein p is an integer of 1 to 4. (14) The preparation processes above wherein the aromatic diamine is one or more compounds selected from the group consisting of 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 1,3-bis(3-aminophenoxy)-5-trifluoromethylbenzene, 1,3-bis(3-amino-5-trifluoromethylphenoxy)benzene, 1,4-bis(3-amino-5-trifluoromethylphenoxy)benzene, and 1,3-bis(3-amino-5-trifluoromethylphenoxy)-5-trifluoromethylbenzene (15) The preparation processes above wherein the aromatic diamine has the formula (21) : wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, and n and p are individually 0 or an integer of 1 to 4 and are not simultaneously 0. (16) The preparation processes above wherein the aromatic diamine has the formula (22) : A still another invention is a novel aromatic diamine which is useful for preparing the above polyimide having a low dielectric constant, that is : (17) An aromatic diamine having the formula (17) : wherein Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is an integer of 1 to 4. (18) An aromatic diamine having the formula (18) : wherein p is an integer of 1 to 4. (20) An aromatic diamine having the formula (20) : wherein p is integer of 1 to 4. (21) An aromatic diamine selected from 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, or 1,3-bis(3-aminophenoxy)-5-trifluoromethylbenzene, (22) An aromatic diamine wherein the aromatic diamine of the formula (17) has the formula (21) : wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 - and p is an integer of 1 to 4. A further invention is a preparation process of the above aromatic diamine, that is : (25) A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar, m and n are the same as above, comprising reacting a dihalogeno or dinitro compound of the formula (23) : Y - Ar - Y wherein Y is a halogen atom or a nitro radical, and Ar is a divalent radical radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is 0 or an integer of 1 to 4, with a m-nitrophenol derivative of the formula (24) : wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and is an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of a base and successively reducing the resultant aromatic dinitro compound. (26) A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar, m and n are the same as above, comprising reacting a dihydroxy compound of the formula (25) : HO - Ar - OH wherein Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 ∼ 6, and p is 0 or an integer of 1∼4, with a m-dinitro or m-nitrohalogeno compound of the formula (26) : wherein Y is a halogen atom or a nitro radical, at 100 to 250 °C in an aprotic solvent in the presence of a base and successively reducing the resultant aromatic dinitro compound. (27) A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar, m and n are the same as above, comprising reacting a dihalogeno or dinitro compound of the formula (23) : Y - Ar - Y wherein Y is a halogen atom or a nitro radical, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -C-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, is 0 or an integer of 1 to 4, with a m-aminophenol derivative of the formula (27) : wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of a base. A still further invention is a polyimide wherein the polyamic acid, the precursor of the polyimide, has an inherent viscosity of 0.01 to 3.0 d ℓ/g at a concentration of 0.5 g/ d ℓ in a dimethylacetamide solution at 35°C, or a polyimide wherein a solution of the polyimide powder at a concentration of 0.5 g/ d ℓ in a solvent mixture composed of 9 parts by weight of p-chlorophenol and 1 part by weight of phenol has an inherent viscosity of 0.01 to 3.0 d ℓ/g at 35°C. The present invention can provide polyimide which has an extremely low dielectric constant and is colorless, transparent and excellent in processability and heat resistance. The invention also provides an aromatic diamine which is useful as a raw material monomer of the polyimide or a raw material of other various engineering plastics. The polyimide of the invention has excellent characteristics and thus wide utilization is expected in industry, particularly in the field of electric and electronic materials and optical materials. Brief Description of the Drawing Figure 1 illustrates an infrared absorption spectrum of the polyimide powder obtained in Example 8. Figure 2 is a drawing illustrating the relationships between the viscosity and the residence time of the polyimide powder obtained in Example 8 in the cylinder of a flow tester. Figure 3 illustrates an infrared absorption spectrum of the polyimide powder obtained in Example 22. Figure 4 is a drawing illustrating the relationships between the viscosity and the residence time of the polyimide powder obtained in Example 22 in the cylinder of a flow tester. Figure 5 illustrates an infrared absorption spectrum of the polyimide powder obtained in Example 34. Figure 6 is a drawing illustrating relationships between the viscosity and the residence time of the polyimide powder obtained in Example 34 in the cylinder of a flow tester. Figure 7 illustrates an infrared absorption spectrum of the polyimide powder obtained in Example 43. Figure 8 is a drawing illustrating the relationships between the viscosity and the residence time of the polyimide powder obtained in Example 43 in the cylinder of a flow tester. Detailed Description of the Invention The polyimide of the invention comprises a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO-, and -C(CH 3 ) 2 - and each X 1 is the same, m is an integer of 1 to 6, n is individually 0 or an integer of 1 to 4, R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is indivisually 0 or an integer of 1 to 4, or in integer of 1 to 4 when n is 0 in the formula (1) ; with the proviso that said polyimide (1) is not one having one or more recurring structural units of formula wherein R 1 is a tetravalent radical selected from WHERE AR 3 IS That is, the invention is a polyimide comprising a requisite structural unit having recurring structural units of the formula (1), and more specifically, can be a homopolymer having one of the recurring structural units of the formula (1) or can be a copolymer having two or more of the recurring structural units. The polyimide of the invention can also be a copolymer of recurring structural units of the formula (1) and other recurring structural units of polyimide in the range giving no adverse effect on the properties of polyimide of the invention. Further, the polyimide of the invention and others - see appendend claims 2, 7, 25 and 26 can have at the polymer chain end an aromatic ring which is essentially unsubstitued or substituted with a radical having no reactivity for amine and dicarboxylic anhydride. That is, the polyimide of the invention can be capped at the polymer chain end thereof with an aromatic dicarboxylic anhydride of the formula (15) : wherein Z is a divalent radical having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and/or aromatic monoamine of the formula (16) : Z 1 - NH 2 wherein Z 1 is a monovalent radical having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, preferably by capping with phthalic anhydride or aniline. The polyimide of the invention includes a polyimide homopolymer having one of the above recurring structural units, a polyimide copolymer having two or more of the above recurring structural units, a mixture of two or more of said polyimide homopolymer and/or said polyimide copolymers, a polyimide copolymer having-the recurring structural units of the formula (1) and other recurring structural units which are comprised in a proportion giving no adverse effect on the essential properties of polyimide, and a mixture of polyimide having one or more recurring structural units of the formula (1) and polyimide having said other recurring structural units. Consequently, when the polyimide of the invention-is a polyimide copolymer having two or more recurring structural units of the formula(1) or a mixture of polyimide, the polyimide has two or more recurring structural units wherein one or more radicals selected from X 1 , X 2 , Ar and R in the formula (1) are different each other. The polyimide of the invention can be prepared by reacting the raw material monomers, fluorine containing aromatic diamine and aromatic tetracarboxylic dianhydride in the absence or presence of aromatic dicarboxylic anhydride and/or aromatic monoamine and by thermally or chemically imidizing the resulting polyamic acid. The aromatic diamine which can be used for preparing the polyimide or capped polyimide of the invention comprises one or more principal ingredients of the formula (13) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO-, and -C(CH 3 ) 2 -, two X 1 may be the same or different, m is an integer of 1 to 6, n is 0 or an integer of 1 to 4, Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is individually 0 or an integer of 1 to 4 and an integer of 1 to 4 when n is 0 in the formula (13). Preferred aromatic diamine has the formula (17) : wherein Ar, m and n are the same as in the formula (13), and the formula (21) : wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO-, and -C(CH 3 ) 2 -, and n and p are individually 0 or an integer of 1 to 4 and are not simultaneously 0. More preferred aromatic diamine has the formulas (18), (19), (20) and (22) : wherein n and p are 0 or an integer of 1 and are not simultaneously 0. wherein n is an integer of 1 to 4. wherein p is an integer of 1 to 4. Exemplary aromatic diamines include following groups. Group A which can be generally used are : [Aromatic diamines of the formula (13) having 3 benzene rings] ; 3,3'-diamine-mono∼dodeca-perfluoroalkylterphenyls, mono∼tetra-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy)benzenes, mono∼tetra-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylthiophenyl)benzenes, mono∼tetra-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylbenzenes, and mono∼tetra-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkyl-α, α-dimethylbenzyl)benzenes, [Aromatic diamines of the formula (13) having 4 benzene rings] ; 3,3"-diamino-di ∼ hexadeca-perfluoroalkylquaterphenyls, Di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) biphenyls, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylbenzoyl) biphenyls, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)biphenyls, bis(3-amino-di∼octa-perfluoroalkylbiphenyl-yl)ethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) diphenyls ethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylbenzoyl) diphenyls ethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)diphenyl ethers, bis(3-amino-di∼octa-perfluoroalkylbiphenyl-yl)thioethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) diphenyl thioethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylbenzoyl) diphenyl thioethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)diphenyl thioethers, bis(3-amino-di∼octa-perfluoroalkylbiphenyl-yl)ketones, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) benzophenones, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylbenzoyl) benzophenones, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)benzophenones, 2,2-bis[mono∼tetra-perfluoroalkyl-bis(3-amino-mono∼octa-perfluoroalkylbiphenyl-yl)phenyl]propanes, 2,2-bis[mono∼tetra-perfluoroalkyl-bis(3-amino-mono ∼tetra-perfluoroalkylphenoxy)phenyl]propanes, 2,2-bis[mono∼tetra-perfluoroalkyl-bis(3-amino-mono ∼tetra-perfluoroalkylbenzoyl)phenyl]propanes, and 2,2-bis[mono∼tetra-perfluoroalkyl-bis(3-amino-mono ∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)phenyl]propanes, [Aromatic diamines of the formula (13) having 4 benzene rings and a naphthalene ring as the Ar radical] ; di∼hexa-perfluoroalkyl-bis(3'-amino-mono ∼tetra-perfluoroalkylphenyl) naphthalenes, di∼hexa-perfluoroalkyl-bis(3'-amino-mono ∼tetra-perfluoroalkylphenoxy) naphthalenes. di∼hexa-perfluoroalkyl-bis(3'-amino-mono ∼tetra-perfluoroalkylthiophen yl)naphthalenes, di∼hexa-perfluoroalkyl-bis(3'-amino-mono ∼tetra-perfluoroalkylbenzoyl) naphthalenes, and di∼hexa-perfluoroalkyl-bis(3'-amino-mono ∼tetra-perfluoroalkyl-α,α-dimethylbenzyl)naphthalenes. Group B which can be preferable used are : [Aromatic diamines of the formula (17) having 3 benzene rings] ; mono∼tetra-perfluoroalkyl-bis(3-amino-mono ∼tetra-perfluoroalkylphenox y)benzenes, [Aromatic diamines of the formula (17) having 4 benzene rings] ; di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) biphenyls, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) diphenyl ethers, di∼octa-perfluoroalkylphenoxy diphenyl thioethers, di∼octa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) benzophenones, and 2,2-bis[mono∼tetra-perfluoroalkyl-bis(3-amino-mono ∼tetra-perfluoroalkylphenoxy)phenyl]propanes, [Aromatic diamines of the formula (17) having 4 benzene rings and a naphthalene ring as a divalent radical] ; di∼hexa-perfluoroalkyl-bis(3-amino-mono∼tetra-perfluoroalkylphenoxy) naphthalenes. Group C which can be more preferable used are : [Aromatic diamines of the formula (18)] ; mono∼tetra-trifluoromethyl-bis(3-amino-mono∼tetratrifluoromehylphenoxy )benzenes, [Aromatic diamines of the formula (19)] ; bis(3-amino-mono∼tetra-trifluoromethylphenoxy)benzenes, and mono ∼ tetra-trifluoromethyl-bis(3-aminophenoxy)benzenes, [Aromatic diamines of the formula (21)] ; di∼octa-trifluoromethyl-bis(3-amino-mono∼tetra-trifluoromethylphenoxy )bisphenyls, di∼octa-trifluoromethyl-bis(3-amino-mono∼tetra-trifluoromethylphenoxy )diphenyl ethers, di∼octa-trifluoromethyl-bis(3-amino-mono∼tetra-trifluoromethylphenoxy )diphenyl thioethers, di∼octa-trifluoromethyl-bis(3-amino-mono∼tetra-trifluoromethylphenoxy )diphenyl benzophenones, and 2,2-bis[di∼tetra-trifluoromethyl(3-amino-mono∼tetra trifluoromethylphe noxy)phenyl]propanes, [Aromatic diamines of the formula (22)] ; 4,4'-bis[3-amino∼tatra-trifluoromethylphenoxy)biphenyl. Group D which can be most preferably used is : 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 1,3-bis(3-aminophenoxy)-5-trifluoromethylbenzene, 1,3-bis(3-amino-5-trifluoromethylphenoxy)benzene, 1,4-bis(3-amino-5-trifluoromethylphenoxy)benzene, 1,3-bis(3-amino-5-trifluorcmethylphenoxy)-5-trifluoromethylbenzene, 1,3-bis(3-amino-5-trifluoromethylphenoxy)-4-trifluoromethylbenzene, and 4,4'-bis(3-amino-5-trifluoromethylphenoxy)biphenyl. These aromatic diamines can be used singly or as a mixture. These fluorine containing aromatic diamines can be prepared by the following processes. 1 ○ A process for reacting a dihalogeno or dinitro compound of the formula (23) : Y-Ar-Y wherein Y is a halogen atom or a nitro radical, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is 0 or an integer of 1 to 4, with a m-nitrophenol derivative of the formula (24) wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and is an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of a base and successively reducing the resultant aromatic dinitro compound. 2 ○ A process for reacting a dihydroxy compound of the formula (25) : HO - Ar - OH wherein Ar is the same as in the formula (23), with a m-dinitro or m-nitrohalogeno compound of the formula (26) : wherein Y is a halogen atom or a nitro radical, m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and is an integer of 1 to 4 when p is 0 in the formula (25), at 100 to 250 °C in an aprotic solvent in the presence of a base and successively reducing the resultant aromatic dinitro compound. 3 ○ A process for reacting a dihalogeno compound or dinitro compound of the formula (23) Y - Ar - Y wherein Y and Ar are the same as above, with a m-aminophenol derivative of the formula (27) : wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of base. These processes will hereinafter be illustrated in detail. In the processes 1 ○, 1,3-bis(3-aminophenoxy)-5-trifluoromethylben zene is prepared in high yield by carrying out condensation of 3,5-dinitrobenzotrifluoride and m-nitrophenol in an aprotic polar solvent in the presence of a base to obtain 1,3-bis(3-nitrophenoxy)-5-trifluoromethylbenzene and successively reducing the same. One of the raw material, 3,5-dinitrobenzotrifluoride, can be obtained by reacting benzotrifluoride with mixed acid according to a known method as described in J. Am. Chem. Soc., 74 , 3011-14. Two or more mols of m-nitrophenol is used in the reaction for a mol of 3,5-dinitrobenzotrifluoride. Preferred amount is 2-2.5 mols in view of complex post-treatment and cost. Bases which can be used are carbonate, hydrogen carbonate, hydroxide and alkoxide of alkali metals, and include, for example, potassium carbonate, potassium hydrogen carbonate, potassium hydroxide, sodium carbonate, sodium hydroxide, sodium hydrogen carbonate, lithium carbonate, lithium hydroxide, sodium methoxide and potassium isopropoxide. The amount of these bases is one equivalent or more, preferably 1 to 2 equivalents to the hydroxyl group of the biphenol raw material. Exemplary aprotic polar solvents used include N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide and sulfolane. No particular limitation is imposed upon the amount of these solvents and the amount of 1-10 times by weight of the raw materials is usually sufficient. Catalysts which can be used for accelerating the reaction are copper powder, copper compounds and phase transfer catalysts such as crown ether, polyethylene glycol, quaternary ammonium base and quaternary phosphonium base. Reaction temperature is usually in the range of 80 to 250 °C, preferably in the range of 100-200°C. In a common method for carrying out the reaction, prescribed amounts of m-nitrophenol, the base and the aprotic polar solvent are charged to form an alkali metal salt of m-nitrophenol and then 3,5-dinitrobenzotrifluoride is added and reacted. Alternatively, the whole materials including 3,5-dinitrobenzotrifluoride are previously charged at one time and the mixture is heated as intact to carry out the reaction. The method is not limited to these procedures and other methods can be suitably carried out. When water is present in the reaction system, water is removed out of the reaction system by ventilating nitrogen gas during the reaction. However, a method for generally carried out is to azeotropically distill off water by addition of a small amount of benzene, toluene xylene and chlorobenzene. End point of the reaction can be determined by decrease of the raw materials according to thin layer chromatography or high performance liquid chromatography. After finishing the reaction, the reaction mixture is poured as intact or after concentration into water to obtain the crude dinitro compound. The crude compound can be purified by recrystallization from or sludging in a solvent. The dinitro compound thus obtained is reduced to prepare corresponding diamino compound. No particular restriction is placed upon the reduction method of dinitro compound. A method for reducing a nitro radical to an amino radical described, for example, in Shin Jikken Kagaku Koza, vol. 15, Oxidation and Reduction II, Published from Maruzen (1977), can be usually applied. Catalytic reduction is preferred in industry. Exemplary reducing catalysts which can be used include metal catalysts used generally for catalytic reduction, for example, nickel, palladium, platinum, rhodium, ruthenium, cobalt and copper. Palladium catalysts are preferred in industry. These catalysts are generally used, though can be used in the state of metal, by supporting on the surface of a carrier such as carbon, barium sulfate, silica gel, alumina and cerite, or also used in the form of a Raney catalyst of nickel, cobalt or copper. No particular limitation is put upon the amount of these catalysts. The amount is in the range of 0.01-10 % by weight for the raw material dinitro compound, usually 2-8 % by weight in the form of metal and 0.1-5 % by weight when supported on the carrier. No particular restriction is imposed upon the solvents used in the reduction so long as inactive for the reaction. Preferred solvents include, for example, methanol, ethanol, isopropyl alcohol and other alcohols ; ethylene glycol, propylene glycol and other glycols ; ether, dioxane, tetrahydrofuran, methyl cellosolve and other ethers. Other solvents which can also be used in some cases are hexane, cyclohexane and other aliphatic hydrocarbons ; benzene, toluene, xylene and other aromatic hydrocarbons ; ethyl acetate, butyl acetate and other esters ; dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,2-trichloroethane, tetrachloroethane and other halogenated hydrocarbons : and N,N-dimethylformamide. No particular limitation is placed upon the amount of these solvents. These solvents are used in an amount enough to suspend or completely dissolve raw materials, that is, usually 0.5-10 times by weight for the weight of raw materials. No particular limitation is placed on the reaction temperature. The reaction temperature is in the range of usually 20-200 °C, preferably 20-100 °C. Reaction pressure is in the range of atmospheric pressure to 50 atm. Reducing reaction is usually carried out by suspending or dissolving the dinitro compound in a solvent, adding the catalyst and introducing hydrogen into the reaction system with stirring at a prescribed temperature. End point of the reaction can be determined by the amount of hydrogen, thin layer chromatography or high performance liquid chromatography. After finishing the reaction, the catalyst is removed by filtration and the solvent is distilled out of the filtrate to obtain the desired product. In the process 2 ○, 4,4'-bis(3-amino-5-trifluoromethylphenoxy) biphenyl, or 1,3- or 1,4-bis(3-amino-5-trifluoromethylphenoxy)benzene can be prepared in high yield by reacting 3,5-dinitrobenzotrifluoride and biphenol, or 3,5-dinitrobenzotrifluoride and resorcinol or hydroquinone in an aprotic solvent in the presence of the base and by reducing the resulting dinitro compound. 3,5-Dinitrobenzotrifluoride used in the reaction can be prepared by the process described in J. Am. Chem, Soc. , 74, 3011-14, for example, by reaction of benzotrifluoride with a mixed acid. Biphenol, resorcinol and hydroquinone are available with ease from the market. The amount of 3,5-dinitrobenzotrifluoride used in the reaction is 2 equivalents or more per equivalent of biphenol, resorcinol or hydroquinone. Preferred amount is 2-2.5 equivalents is view of complex post-treatment and cost. Bases used are the same is in the case of the process 1 ○ and are carbonate, hydrogen carbonate, hydroxide and alkoxide of alkali metals. The amount of these bases is one equivalent or more, preferably 1-2 equivalents per equivalent of hydroxy radicals in the biphenol, resorcinol or hydroquinone as raw material. Aprotic polar solvents which can be used are also the same as in the case of the process 1 ○. No particular limitation is imposed upon the amount of solvents. The amount of 1-10 times by weight for the raw materials is sufficient to carry out the reaction. Reaction temperature is usually in the range of 40-250°C, preferably in the range of 80-180 °C . The same catalysts as used in the process 1 ○ can be used without any trouble for accelerating the reaction. In a common reaction method, prescribed amounts of biphenol, resorcinol or hydroquinone, a base and a solvent are charged to form alkali metal salts of biphenol and resorcinol or hydroquinone, and then 3,5-dinitribenzotrifluoride is added and reacted. Alternatively, the whole materials including 3,5-dinitrobenzotrifluoride are previously charged at one time and the mixture was heated as such to carry out the reaction. The method is not limited to these procedures and other methods can be be suitably carried out. when water is present in the reaction system, water is removed out of the reaction system by ventilating nitrogen gas during the reaction. However, a method generally carried out is to azeotropically distill off water by addition of a small amount of benzene, toluene, xylene and chlorobenzene. End point of the reaction can be determined by decrease of the raw materials according to thin layer chromatography or high performance liquid chromatography. After finishing the reaction, the reaction mixture is poured as intact or after concentration into water to obtain the crude dinitro compound. The compound can be purified by recrystallization from or sludging in a solvent. The dinitro compound thus obtained is reduced to prepare corresponding diamino compound. Reduction of the dinitro compound can be carried out by the same method as in the process 1 ○. In the reducing reaction, almost the same materials and means as in the process 1 ○ can be used on the catalyst, form and amount thereof, the solvent and amount thereof, and the addition of common phase transfer catalysts such as quaternary ammonium base and quaternary phosphonium base in order to accelerate the reaction. No particular limitation is placed on the reaction temperature. The reaction temperature is usually in the range of 20-200 °C, preferably in the range of 20-100 °C. Reaction pressure is in the range of atmospheric pressure to 50 atm. Reducing reaction is usually carried out by suspending or dissolving the dinitro compound in a solvent, adding the catalyst and introducing hydrogen into the the reaction system with stirring at a prescribed temperature. End point of the reaction can be determined by the amount of hydrogen, thin layer chromatography or high performance liquid chromatography. After finishing the reaction, the catalyst is removed by filtration and the solvent is distilled out of the filtrate to obtain the desired product. In the process 3 ○, 3,5-bis(3-amino-5-trifluoromethylphenoxy)trifluoromethylbenzene and 2,4-bis(3-amino-5-trifluoromethylphenoxy)trifluoromethylbenzene can be prepared in high yield by reacting 3,5-dihalogenobenzotrifluoride, 3,5-dinitrobenzotrifluoride, 2,4-dihalogenobenzotrifluoride or 2,4-dinitrobenzotrifluoride(hereinafter referred to as the benzotrifluoride derivative) with 3-amino-5-trifluoromethylphenol in an aprotic polar solvent in the presence of a base. One of the raw material, the trifluoromethylbenzene derivative, can be obtained, for example, by reacting benzotrifluoride with a mixed acid according to a known method as described in J. Am. Chem, Soc., 74, 3011-14. 3-Amino-5-trifluoromethyl phenol can also be prepared by a know method described in J. Am. Chem, Soc., 1949, 3016-20. Two or more equivalents of 3-amino-5-trifluoromethyl is used in the reaction for one equivalent of the trifluoroethylbenzene derivative. Preferred amount is 2-2.5 equivalents in view of complex post-treatment and cost. Bases which can be used include carbonate, hydrogen carbonate, hydroxide and alkoxide of alkali metals as in other processes. The amount of these bases is one equivalent or more, preferably 1-2 equivalents to the hydroxyl group of the biphenol raw material. Aprotic polar solvents used are the same as in other processes. No particular limitation is imposed upon the amount of these solvents. The amount of 1 to 10 times by weight for the weight of raw materials is usually sufficient to carry out the reaction. Reaction temperature is usually in the range of 40-250°C, preferably in the range of 80-180 °C. Catalysts such as copper and copper derivatives, and phase transfer catalysts such as crown ether, polyethylene glycol, quaternary ammonium bases and quaternary phosphonium bases can be used for accelerating the reaction. In a common method for carrying out the reaction, prescribed amounts of 3-amino-5-trifluoromethylphenol, the base and the solvent are charged to form an alkali metal salt of 3-amino-5-trifluoromethylphe nol, and then the trifluoromethylbenzene derivative is added and reacted. Alternatively, the whole materials including the trifluoromethylbe nzene derivative are previously charged at one time and the mixture is heated as intact to carry out the reaction. The method is not limited to these procedures and other methods can be suitably carried out. When water is present in the reaction system, water is removed out of the reaction system by ventilating nitrogen gas during the reaction. However a method generally carried out is to azeotropically distill off water by addition of a small amount of benzene, toluene, xylene and chlorobenzene. End point of the reaction can be determined by decrease of the raw materials according to thin layer chromatography or high performance liquid chromatography. After finishing the reaction. The reaction mixture is poured as intact or after concentration into water to obtain the crude dinitro compound. The crude compound can be purified by recrystallization from or sludging in a solvent. Reducing reaction is carried out by the same procedures as in the process 2 ○. After finishing the reaction, the catalyst is removed from the reaction mixture by filtration, and the filtrate is concentrated to obtain the desired product. Further, in the process 3 ○, 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene can be prepared by reacting 2,4-dichlorobenzotrifluoride with m-aminophenol in an aprotic polar solvent in the presence of a base. 2,4-Dichlorobenzotrifluoride and m-aminophenol are available with ease from the market. The amount of m-aminophenol used in the reaction is 2 equivalents or more per equivalent of 2,4-dichlorobenzotrifluoride. Preferred amount is 2-2.5 equivalents in view of complex post-treatment and cost. Bases and aprotic polar solvents which can be used in the reaction include the same as used in the process 2 ○. The amount of these bases is one equivalent or more, preferably 1-2 equivalents per equivalent of m-aminophenol raw material. No particular limitation is placed on the amount of solvents. The amount of 1-10 times by weight for the weight of the raw materials is sufficient to carry out the reaction. Catalysts such as copper powder and copper and copper compounds and phase transfer catalysts such as crown ether, polyetherglycol, quaternary ammonium base and quaternary phosphonium base can be used without any trouble to accelerate the reaction. Reaction temperature is usually in the range of 40-250°C, preferably in the range of 80-180 °C. In a common reaction method, prescribed amounts of m-aminophenol, the base and the aprotic polar solvent are charged to form an alkali metal salt of m-aminophenol, and then 2,4-dichlorobenzotrifluoride is added and reacted. Alternatively, the whole materials including 2,4-dichlorobenzotrifluoride are previously charged at one time and heated as intact to carry out the reaction. The method is not limited to these procedures and other methods can be suitably carried out. When water is present in the reaction system, water is removed out of the reaction system by ventilating nitrogen gas during the reaction. However, a method generally carried out is to azeotropically distill off water by addition of a small amount of benzene, toluene, xylene and chlorobenzene. End point of the reaction can be determined by the same means as in the process 2 ○. Exemplary polyimides obtained by using these preferred aromatic diamines include those comprising a fundamental skeleton having recurring structural units of the formula (2) : the formula (3) : the formula (4) : the formula (5) : the formula (6) : the formula (7) : the formula (8) : the formula (9) : the formula (10) : wherein m, n, p and R are the same as above. The polyimide of the invention is prepared by using the above aromatic diamines for the requisite raw material monomer. Other aromatic diamines can be used in combination with these diamines so long as giving no adverse effect on the good properties of the polyimide. Other aromatic diamines which can be used in combination include, for example, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, bis(3-aminophenyl)sulfide, (3-aminophenyl)(4-aminophenyl)sulfide, bis(4-aminophenyl)sulfide, bis(3-aminophenyl)sulfoxide, (3-aminophenyl)(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, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 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-(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, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethybenzyl)benzene, 1,3-bis(4-amino-α,α-dimethybenzyl)benzene, 1,4-bis(3-amino-α,α-dimethybenzyl)benzene, 1,4-bis(4-amino-α,α-dimethybenzyl)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-(3-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, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[3-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethybenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethybenzyl)phenoxy]diphenyl sulfone, bis[4- {4-(4-aminophenoxy) phenoxy} phenyl]sulfone, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethybenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethybenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethybenzyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethybenzyl]benzene, 3,3'-diamino-4,4'-difluorobenzophenone, 3,3'-diamino-5,5'-bis(trifluoromethyl)diphenyl ether, and 4,4'diamino-5,5'-bis (trifluoromethyl)diphenyl ether. These aromatic diamines can be used singly or as a mixture. Aromatic tetracarboxylic dianhydride which can be used in the invention is one or more of compounds of the formula (14) wherein R is a tetravalent radical having 2-27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member. In the aromatic tetracarboxylic dianhydride of the formula (14), R is specifically a tetravalent radical selected from the group consisting of an aliphatic radical having 2-10 carbon atoms, alicyclic radical having 4-10 carbon atoms, monoaromatic radical of the formula (a) : condensed polyaromatic radical of the formula (b) : and noncondensed aromatic radical being connected each other with a direct bond or a bridge member and having the formula (c) : wherein X is a direct bond, -CO-, -O-, -S-, -SO 2 -, -CH 2 -, -C(CH 3 ) 2 -, -C(CF 3 ) 2 -, or wherein Y is a direct bond, -CO-, -O-, -S-, -SO 2 -, -CH 2 -, -C(CH 3 ) 2 - or -C(CF 3 ) 2 -. Exemplary tetracarboxylic dianhydride of the formula (4) which can be used in the invention include, ethylenetetracarboxylic 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, 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, 2,2-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, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-bis[4 {4-(1,2-dicarboxy)benzoyl} phenyl]propane dianhydride, 2,2-bis[4 {3-(1,2-dicarboxy)phenoxy} phenyl]propane dianhydride, bis[4- {4-(1,2-dicarboxy)phenoxy} phenyl]Ketone dianhydride, bis[4- {3-(1,2-dicarboxy)phenoxy} phenyl]Ketone dianhydride, 4,4'-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4'-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis[4- {4-(1,2-dicarboxy)phenoxy} phenyl]ketone dianhydride, bis[4- {3-(1,2-dicarboxy)phenoxy} phenyl]ketone dianhydride, bis[4- {4-(1,2-dicarboxy)phenoxy} phenyl]sulfone dianhydride, bis[4- {3-(1,2-dicarboxy)phenoxy} phenyl]sulfone dianhydride, bis[4- {4-(1,2-dicarboxy)phenoxy} phenyl]sulfide dianhydride, bis[4- {3-(1,2-dicarboxy)phenoxy} phenyl]sulfide dianhydride, 2,2-bis[4- {4-(1,2-dicarboxy)phenoxy} phenyl]-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[4-(3-(1,2-dicarboxy)phenoxy} phenyl]-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic dianhydride. These dianhydrides can be used singly or as a mixture. The polyimide of the invention prepared by using the above aromatic diamine and aromatic tetracarboxylic dianhydride as monomer components comprises a requisite structural unit primarily having recurring structural units of the formula (1). That is, the invention includes polyimide which is derived from a selected aromatic diamine and a selected aromatic tetracarboxylic dianhydride in the above enumerated raw materials of the invention and has recurring structural units of the formula (1) to (12), a polyimide copolymer which is derived from one or more selected aromatic diamines and one or more selected aromatic tetracarboxylic dianhydrides (both one, exclusive) in the above enumerated raw materials of the invention, and a polyimide copolymer which is derived from one or more selected aromatic diamines and one or more selected aromatic tetracarboxylic dianhydride in the above enumerated raw materials of the invention in combination with other diamines added in the range of giving no adverse effect on the properties of resulting polyimide. The invention also includes capped polyimide having at the polymer chain end thereof an aromatic ring which is unsubstituted or substituted with a radical having no reactivity for amine and dicarboxylic anhydride. Further, the invention includes composition of these polyimides. Compositions have better properties than polyimides as such in some cases. The capped polyimide having at the polymer chain end thereof an aromatic ring unsubstituted or substituted with a radical having no reactivity for amine and dicarboxylic anhydride can be obtained by capping with aromatic dicarboxylic anhydride of the formula (15) : wherein Z is the same as above, and/or aromatic monoamine of the formula (16) : Z 1 - NH 2 wherein Z 1 is the same as above, preferably phthalic anhydride and/or aniline. The capped polyimide can be prepared by reacting an aromatic diamine component with an aromatic tetracarboxylic dianhydride component in the presence of the aromatic dicarboxylic anhydride of the formula (15) and/or the aromatic monoamine of the formula (16) and thermally or chemically imidizing the resulting polyamic acid. Exemplary aromatic dicarboxylic anhydrides of the formula (15) include 2,3-benzophenonedicarboxylic anhydride, 3,4--benzophenonedicarboxylic anhydride, 2,3-dicarboxyphenylphenyl ether anhydride, 3,4-dicarboxyphenyl phenyl ether anhydride, 2,3-biphenyldicarboxylic anhydride, 3,4-biphenyldicarboxylic anhydride, 2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxyphenyl phenyl sulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride, 1,2-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,8-naphthalenedicarboxylic anhydride, 1,2-anthracenedicarboxylic anhydride, 2,3-anthracenedicarboxylic anhydride, and 1,9-anthracenedicarboxylic anhydride. These dicarboxylic anhydrides can be substituted with a radical having no reactivity for amine and dicarboxylic anhydride. Phthalic anhydride is most preferred in these dicarboxylic anhydrides in view of properties of resulting polyimide and practical use. Polyimide prepared in the presence of phthalic anhydride has excellent heat stability in high temperature processing has dominant chemical resistance and is very useful for a material of space and aeronautic instruments and electric and electronic devices. A portion of phthalic anhydride can be replaced with other dicarboxylic anhydrides in the range giving no adverse effect on the good properties of polyimide. The amount of dicarboxylic anhydride is 0.001-1.0 mol per mol of the aromatic diamine component. The amount less than 0.001 mol leads to viscosity increase in the high temperature processing and causes reduction of processability. On the other hand, the amount exceeding 1.0 mol lowers mechanical strengths of the product. Thus, preferred range is 0.001-0.5 mol. Aromatic monoamines which can be used include, for example, o-toluidine, m-toluidine, p-toluidine, 2,3-xylidine, 2,6-xylidine, 3,4-xylidine, 3,5-xylidine, o-chloroaniline, m-chloroaniline, p-chloroaniline, o-bromoaniline, m-bromoaniline, p-bromoaniline, m-nitroaniline, p-nitroaniline, o-aminophenol, m-aminophenol, p-aminophenol, o-anisidine, m-anisidine, p-anisidine, o-phenetidine, m-phenetidine, p-phenetidine, o-aminobenzaldehyde, m-aminobenzaldehyde, p-aminobenzaldehyde, o-aminobenzonitrile, m-aminobenzonitrile, p-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl, 2-aminophenyl phenyl ether, 3-aminophenyl phenyl ether, 4-aminophenyl phenyl ether, 2-aminobenzophenone, 3-aminobenzophenone, 4-aminobenzophenone, 2-aminophenyl phenyl sulfide, 3-aminophenyl phenyl sulfide, 4-aminophenyl phenyl sulfide, 2-aminophenyl phenyl sulfone, 3-aminophenyl phenyl sulfone, 4-aminophenyl phenyl sulfone, α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol, 2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino-1-naphthol, 5-amino-2-naphthol, 7-amino-2-naphthol, 8-amino-1-naphthol, 8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene and 9-aminoanthracene. These aromatic monoamines can be substituted with a radical having no reacting for amine and dicarboxylic anhydride. The amount of aromatic monoamine is 0.001 to 1.0 mol per mol of the aromatic tetracarboxylic dianhydride component. The amount less than 0.001 mol leads to viscosity increase in the high temperature processing and causes reduction of processability. On the other hand, the amount exceeding 1.0 mole lowers mechanical strengths of the product. Thus, preferred range is 0.001 to 0.5 mol. Consequently, preparation of capped polyimide of the invention which is terminated with an unsubstituted or substituted aromatic ring is carried out by using 0.9-1.0 mol of aromatic diamine and 0.001-1.0 mol of dicarboxylic anhydride or aromatic monoamine per mol of tetracarboxylic dianhydride. In the preparation of polyimide, the molar ratio of tetracarboxylic dianhydride to aromatic diamine is usually controlled in order to adjust molecular weight of formed polyimide. In order to obtain polyimide having good melt-flowability in the process of the invention, the molar ratio of aromatic diamine to tetracarboxylic dianhydride is suitably in the range of 0.9-1.0. Any process preparing polyimide including known processes can be applied to the preparation of polyimide in the invention. Particularly preferred process is to carry out the reaction in an organic solvent. Exemplary solvent which can be used for the reaction 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, tetrahydroxyfluoran, 1,3-dioxane, 1,4-dioxane, pyridine, picoline, dimethyl sulfoxide, dimethyl sulfone, tetramethylurea, hexamethylphosphoramide, phenol, o-cresol, m-cresol, p-cresol, m-cresylic acid, p-chlorophenol and anisole. These organic solvents can be used singly or as a mixture. In the process of the invention, the reaction is carried out by the addition of aromatic diamine, aromatic tetracarboxylic dianhydride and aromatic dicarboxylic anhydride or aromatic monoamine to the organic solvent according to the following procedures. (A) After reacting aromatic tetracarboxylic dianhydride with aromatic diamine, aromatic dicarboxylic anhydride or aromatic monoamine is added to continue the reaction. (B) After reacting aromatic diamine with aromatic dicarboxylic anhydride, aromatic tetracarboxylic dianhydride is added to continue the reaction. (C) After reacting aromatic tetracarboxylic dianhydride with aromatic monoamine, aromatic diamine is added to continue the reaction. (D) Aromatic tetracarboxlic dianhydride, aromatic diamine and aromatic dicarboxylic anhydride or aromatic monoamine are added at one time and the reaction is carried out. Any of the above addition procedures can be conducted. Reaction temperature is usually 250 °C or less, preferably 50 °C or less. No particular limitation is imposed upon the reaction pressure. Atmospheric pressure is satisfactory for carrying out the reaction. Reaction time differs depending upon the tetracarboxylic dianhydride, solvent and reaction temperature and sufficient time for carrying out the reaction is usually 4-24 hours. Further, polyamic acid thus obtained is thermally imidized by heating at 100-400°C or chemically imidized by using an imidizing agent such as acetic anhydride to give polyimide having recurring structural units corresponding to those of polyamic acid. Alternatively, formation and imidization of the polyamic acid precursor can be simultaneously carried out to obtain polyimide of the invention by suspending or dissolving in the organic solvent aromatic tetracarboxylic dianhydride, aromatic diamine and optionally aromatic dicarboxylic anhydride or aromatic monoamine in the case of capping the polyimide chain end and successively heating the resulting mixture. The polyamic acid precursor of the polyimide of the invention has an inherent viscosity of 0.01-3.0 d ℓ/g at 35°C in a dimethylacetamide solution at a concentration of 0.5 g/ d ℓ. The polyimide has an inherent viscosity of 0.01-3.0 d ℓ/g at 35°C at a concentration of 0.5 g/ d ℓ in a solvent mixture consisting of 9 parts by weight of p-chlorophenol and 1 part by weight of phenol. Polyimide film of the invention can be prepared by casting a solution of the polyamic acid precursor on a glass plate and carrying out thermal imidization or by directly hot-pressing polyimide powder. That is, films and powder of polyimide can be prepared by known methods. In the case of melt-processing the polyimide of the invention, other thermoplastic resins can be blended in a suitable amount depending upon the object for use so long as giving no adverse effect on the good properties of polyimides. Thermoplastic resin which can be blended include, for example, polyethylene, polypropylene, polycarbonate, polyarylate, polyamide, polysulfone, polyether sulfone, polyether ketone, polyphenylene sulfide, polyamideimide, polyetherimide, modified polyphenylene oxide and other kind of polyimide. Fillers which are used for common resin compositions can be added in the range not impairing the object of the invention. Exemplary fillers include graphite, carborundum, silica powder, molybdenum disulfide, fluoro resin and other wear resistance improvers; glass fiber, carbon fiber and other reinforcements; antimony trioxide, magnesium carbonate, calcium carbonate and other flame retardance improvers; clay, mica and other electrical property improvers; asbestos, silica, graphite and other tracking resistance improvers; barium sulfide, silica, calcium metasilicate and other acid resistance improvers; iron powder, zinc powder, aluminum powder, copper powder and other thermal conductivity improvers; and other miscellaneous materials such as glass beads, glass balloons, talc, diatomaceous earth, alumina, silicate balloons, hydrated alumina, metal oxides and colorants. The invention will hereinafter be illustrated in detail by way of examples. However, these examples are not to be construed to limit the scope of the invention. Example 1 To a four necked flask equipped with a thermometer, reflux condenser and stirrer, 250 m ℓ of N,N-dimethylformamide(DMF), 30 m ℓ of toluene, 30 g (0.127 mol) of 3,5-dinitrobenzotrifluoride, 11.83 g (0.0635 mol) of 4,4'-dihydroxybiphenyl and 17.56 g (0.127 mol) of potassium carbonate were charged. The mixture was heated to 110 °C with stirring and aged for 4 hours at 110 °C. After finishing the reaction, the reaction mixture was cooled to 80 °C and filtered to remove inorganic salts. The filtrate was mixed with 30 m ℓ of water and cooled to the room temperature to precipitate the desired product. Precipitated crystals were filtered and sludged with methanol to obtain 34.4g (96 % yield) of desired 4,4'-bis(3-nitro-5-trifluoromethylphenoxy) biphenyl having a melting point of 148.2∼ 149.3. Elementary analysis (C 26 H 14 N 2 O 6 F 6 ) C H N F Calculated (%) 55.33 2.50 4.96 20.20 Found (%) 55.14 2.62 4.90 20.08 1 H-NMR δ (CDCl 3 , ppm) 7.19 ( (1)-4H, d ) 7.63 ( (2)-2H, s ) 7.68 ( (3)-4H, d ) 7.99 ( (4)-2H, s ) 8.19 ( (5)-2H, s ) wherein (1) ∼ (5) indicate positions on the following formula. Example 2 To a reducing apparatus equipped with a themometer, reflux condenser and stirrer, 33 g (0.0585 mol) of 4,4'-bis(3-nitro-5-trifluoromethylphenoxy) biphenyl, 100 m ℓ of methyl cellosolve and 1.7 g of 5 %-pd/c having a moisture content of 50 % were charged and reacted in a hydrogen atmosphere at 70 to 80 °C for 4 hours. After finishing the reaction, the catalyst was filtered off. The filtrate was concentrated under reduced pressure to obtain 4,4'-bis(3-amino-5-trifluoromethylphenoxy) biphenyl as light yellow crystals. The product was 34.4 g (96 % yield) and had a melting point of 130.4 to 132.9 °C. Elementary analysis (C 26 H 18 N 2 O 2 F 6 ) C H N F Calculated (%) 61.91 3.60 5.55 22.60 Found (%) 62.02 3.63 5.31 22.41 1 H-NMR δ (CDCl 3 , ppm) 3.86 ( (1) - 4H, s ) 6.45 ( (2)- 2H, m ) 6.63 ( (3)- 4H, s ) 7.08 ( (4)- 4H, m ) 7.59 ( (5)- 4H, m ) wherein (1) to (5) indicate positions on the following formula. Example 3 To a four necked flask equipped with a thermometer, reflux condenser and stirrer, 150 g of N,N-dimethylimidazolidinone (DMI), 30 g of o-xylene, 37 g (0.172 mol) of 2,4-dichlorobenzotrifluoride, 39.4 g (0.361 mol) of m-aminophenol and 25.5 g (0.185 mol) of potassium carbonate were charged. The mixture was heated to 200°C with stirring and reacted for 30 hours at 200 °C . At the end of reaction, 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene (APTFB) had purity of 83 % by HPLC. The reaction mixture was cooled after finishing the reaction and filtered to remove inorganic salts. DMI was distilled off from the filtrate under reduced pressure. The residue was dissolved by adding 100 g of isopropanol (IPA) and 200 g of 36 % hydrochloric acid was added to the resultant solution to precipitate the desired product in the form of hydrochloride. APTFB hydrochloride thus obtained was suspended in a mixture of 150 g of water and 200 g of 1,2-dichloroethane (EDC), neutralized with a 28 % aqueous ammonia solution and separated. The EDC layer was washed with water. Solvent was distilled off from the EDC solution to obtain desired APTFB as a red brown viscous liquid. The product was 35.6 g (57.4 % yield). 1 H-NMR δ (CDCl 3 , ppm) 3.53 ( 4H (1), s ) 6.26 to 6.45 ( 6H (2), m ) 6.61 to 6.71 ( 2H (3), m ) 6.99 to 7,24 ( 2H (4), m ) 7.53 ( 1H (5), d ) wherein (1) to (5) indicate positions on the following formula. Elementary analysis (C 19 H 15 N 2 O 2 F 3 ) C H N F Calculated (%) 63.33 4.20 7.77 15.82 Found (%) 63.30 4.24 7.81 15.77 Example 4 To a four necked flask equipped with a thermometer, reflux condenser and stirrer, 250 g of N,N-dimethylformamide(DMF), 25 g of toluene, 40 g (0.169 mol) of 3,5-dinitrobenzotrifluoride, 48.3 g (0.347 mol) of m-nitrophenol and 28 g (0.203 mol) of potassium carbonate were charged. The mixture was heated to 150 °C and reacted for 25 hours at 150°C . At the end of reaction, 1,3-bis(3-nitrophenoxy)-5-trifluoromethydbenzene had purity of 80% by HPLC. After finishing the reaction, the reaction mixture was cooled to 90 °C and filtered to remove inorganic salt. The filtrate was mixed with 190 m ℓ of water and cooled to the room temperature. Precipitated crystals were filtered and recrystallized from methyl cellosolve to obtain 1,3-bis(3-nitrophenoxy) -5-trifluoromethylbenzene as light yellow solid. The product was 54.9 g (77 % yield) and had a melting point of 117.6 to 118.5 °C. Elementary analysis (C 19 H 11 N 2 O 6 F 3 ) C H N F Calculated (%) 54.30 2.64 6.67 13.56 Found (%) 54.14 2.62 6.59 13.51 To a reducing apparatus equipped with a thermometer, reflux condenser and stirrer, 55 g (0.131 mol) of 1,3-bis(3-nitrophenoxy)-5-trifluoromethylbenzene, 150 g of methyl cellosolve and 5 g of 5% Pd/c having a moisture content of 50 % were charged and reacted in a hydrogen atmosphere at 70 to 80 °C for 4 hours. After finishing the reaction, the catalyst was filtered off. The filtrate was heated to 90 °C, mixed with 140 g of water and cooled to the room temperature. The precipitated crystals were filtered and dried under reduced pressure to obtain 1,3-bis (3-aminophenoxy)-5-trifluoromethyl benzene as colorless solid. The product was 41 g (87 % yield) and had a melting point of 98.0 to 98.6 °C. 1 H-NMR δ (CDCl 3 , ppm) 3.56 ( 4H (1), s ) 6.31 to 6.51 ( 6H (2), m ) 6.81 to 7.24 ( 5H (3), m ) wherein (1)∼(3) indicate positions on the following formula. Elementary analysis (C 19 H 15 N 2 O 2 F 3 ) C H N F Calculated (%) 63.33 4.20 7.77 15.82 Found (%) 63.38 4.26 7.75 15.79 Example 5 To a four necked flask equipped with a thermometer, reflux condenser and stirrer, 500 m ℓ of DMF, 50 m ℓ of toluene, 80 g (0.339 mol) of 3,5-dinitrobenzotrifluoride, 18.7 g (0.169 mol) of resorcinol and 28.1 g (0.203 mol) of potassium carbonate were charged. The mixture was heated to 110 °C with stirring and aged for 5 hours at 110 °C. After finishing the reaction, the reaction mixture was cooled to the room temperature and filtered to remove inorganic salts. The filtrate was concentrated to obtain desired 1,3-bis(3-nitro-5-trifluoromethylphenoxy)benzene. The product was 72 g (87 % yield). Elementary analysis (C 20 H 10 N 2 O 6 F 6 ) C H N F Calculated (%) 49.20 2.06 5.74 23.34 Found (%) 49.17 2.10 5.78 23.29 1 H-NMR δ (CDCl 3 , ppm) 6.82 to 6.96 ( 2H (1), m ) 7.02 to 7.04 ( 2H (2), m ) 7.45 to 7.54 ( 1H (3), m ) 7.61 to 7.63 ( 1H (4), m ) 7.98 to 8.03 ( 2H (5), m ) 8.23 to 8.35 ( 2H (6), m ) wherein (1) to (6) indicate positions on the following formula. To a reducing apparatus equipped with a thermometer, reflux condenser and stirrer, 72 g (0.147 mol) of 1,3-bis(3-nitro-5-trifluoromethylphenoxy)benzen, 500 m ℓ of isopropyl alcohol and 7.2 g of 5 % Pd/c having a moisture content of 50 % were charged and reacted in a hydrogen atmosphere at 50 °C for 5 hours. After finishing the reaction, the catalyst was filtered off. The filtrate was concentrated under reduced pressure. The residue was dissolved in 200 g of isopropyl alcohol. The resulting solution was mixed with 400 g of 36 % hydrochloric acid to precipitate the desired product in the form of hydrochloride. The hydrochloride thus obtained was suspended in a mixture of 150 g of water and 200 g of 1,2-dichloroethane(EDC) and neutralized with a 28% aqueous ammonia solution. The EDC layer was separated, washed with water, and distilled off the solvent to obtain 1,3-bis(3-amino-5-trifluoromethylphenoxy) benzene as a brown viscous liquid. The product was 33.8 g (53.7 % yield). Elementary analysis (C 20 H 14 N 2 O 6 F 6 ) C H N F Calculated (%) 56.08 3.29 6.54 26.61 Found (%) 56.12 3.26 6.57 26.57 1 H-NMR δ (CDCl 3 , ppm) 3.85 ( 4H (1), s ) 6.41 - 6.45 ( 2H (2), m ) 6.61 - 6.70 ( 4H (3), m ) 6.73 - 6.77 ( 2H (4), m ) 6.82 - 6.96 ( 1H (5), m ) 7.16 - 7.40 ( 1H (6), m ) wherein (1) - (6) indicate positions on the following formula. Example 6 To a four necked flask equipped with a thermometer, reflux condenser and stirrer, 250 m ℓ of DMF, 50 m ℓ of toluene, 50 g (0.212 mol) of 3,5-dinitrobenzotrifluoride, 11.7 g (0.106 mol) of hydroquinone and 17.6 g (0.127 mol) of potassium carbonate were charged. The mixture was heated to 120 °C with stirring and aged for 8 hours at 120 °C. After finishing the reaction, the reaction mixture was cooled to 80 °C and filtered to remove inorganic salts. The filtrate was mixed with 180 m ℓ of water and cooled to the room temperature to crystallize the desired product. Precipitated crystals were filtered and recrystallized from isopropyl alcohol. 1,4-Bis(3-nitro-5-trifluoromethylphenoxy)benzene thus obtained was 36.5 g (70.5 % yield) and had a melting point of 162.8 - 163.3 °C . 1 H-NMR δ (CDCl 3 , ppm) 7.20 ( 4H (1), s ) 7.60 - 7.62 ( 2H (2), m ) 7.69 - 8.01 ( 1H (3), m ) 7.21 ( 2H (4), s ) wherein (1) - (6) indicate positions on the following formula. To a reducing apparatus equipped with a thermometer, reflux condenser and stirrer, 36.5 g (0.0747 mol) of 1,4-bis(3-nitro-5-trifluoromethylphenoxy)benzene, 250 m ℓ of N,N-dimethylformamide and 1.8 g Pd-alumina were charged and reacted in a hydrogen atmosphere at 50°C for 6 hours. After finishing the reaction, the catalyst was filtered and the filtrate was concentrated under reduced pressure to obtain 1,4-bis(3-amino-5-trifluoromethylphenoxy)benzene as colorless crystals. The product was 36.5 g (70.5 % yield) and had a melting point of 157.4-158.0 °C. Elementary analysis (C 20 H 14 N 2 O 2 F 6 ) C H N F Calculated (%) 56.08 3.29 6.54 26.61 Found (%) 56.04 3.32 6.56 26.56 1 H-NMR δ (DMSO, ppm) 5.72 ( 4H (1), s ) 6.39 - 6.41 ( 4H (2), m ) 6.63 ( 2H (3), m ) 7.12 ( 4H (4), m ) wherein (1)-(4) indicate positions on the following formula. Example 7 To a reducing apparatus equipped with a thermometer, reflux condenser and stirrer, 36.9 g (0.156 mol) of 3,5-dinitrobenzotrifluoride , 60 g (0.329 mol) of 3-amino-5-trifluoromethylphenol, 290 g of N,N-dimethylformamide and potassium carbonate were charged. The mixture was heated to 145°C with stirring and aged for 14 hours at 145°C. At the end of reaction, desired product had purity of 63% by HPLC. The reaction mixture was cooled after finishing the reaction and filtered to remove inorganic salts. 400 g of water was added to separate organic layer. 400g of toluene was added to the separated organic layer and the resultant solution was washed by aqueous solution containing 2 % NaOH. The residue obtained by distilling off toluene was purified by column chromatography to obtain 1,4-bis(3-amino-5-trifluoromethylphenoxy)-5-trifluoromethylbenzene as light yellow crystals. The product was 32 g (41.3 % yield) and had a melting point of 82 - 84 °C. 1 H-NMR δ (CDCl 3 , ppm) 3.93 ( 4H (1), s ) 6.42 - 6.47 ( 2H (2), t ) 6.62 - 6.68 ( 4H (3), m ) 6.77 - 7.82 ( 2H(4), t ) 6.99 - 7.01 ( 2H(5), d ) wherein (1) - (5) indicate positions on the following formula. Properties of polyimide in the examples below were measured by the following methods. Tg, Tc and Tm : Measured by DSC with Shimadzu DT-40 series, Model DSC-41M. 5% Weight loss temperature : Measured by DTG with Shimadzu DT-40 series, Model DTG-40M. Dielectric constant : Measured in accordance with ASTM D 150-87. Melt viscosity : Measured with a Shimazsu Koka type flow tester. Model CFT-500A under 100 Kg load. Saturated moisture content : Measured after allowed to stand for 24 hours at 23 °C in 85 % RH. Melt initiation temperature : Measured with a Shimazsu Koka type flow tester. Model CFT-500A under 100 Kg load at a temperature rise rate of 5 °C/min. Yellowness index : Measured by a transmission method with a direct-reading color difference computer, model CDE-SCH-3 (manufactured by Suga Test Machine Co.) in accordance with JIS K-7103. Light transmittance : Measured with a Hitachi self-recording spector-photometer, model 3400. Inherent viscosity : Measured at 35 °C in a concentration of 0.5 g/dl after individually dissolving polyamic acid in N,N-dimethylacetamide and polyimide in a mixture of p-chlorophenol/phenol at a ratio of 9/1 by weight. Mechanical properties of film : Measured in accordance with ASTM D-822. Example 8 To a reaction vessel equipped with a stirrer, reflux condenser, water separator and nitrogen inlet tube, 50.45 g (0.1 mol) of 4,4'-bis(3-amino-5-trifluoromethylphenoxy)biphenyl, 21.38 g (0.098 mol) of pyromellitic dianhydride, 0.592 g (4 × 10 -3 mol) of phthalic anhydride, 1.4 g of γ-picoline and 287.3 g of m-cresol were charged. The mixture was heated to 145°C with stirring in a nitrogen atmosphere while distilled out about 3.5 mℓ water. The reaction was further continued for 4 hours at 140 - 150 °C. The reaction mixture was then cooled to the room temperature and poured into about 1.5 ℓ of methyl ethyl ketone. Precipitated polyimide powder was filtered, washed with methyl ethyl ketone and dried at 180°C for 24 hours under reduced pressure to obtain 67.45 g (98.0% ) polyimide powder. The polyimide powder thus obtained had an inherent viscosity of 0.47 d ℓ/g, a glass transition temperature of 251 °C by DSC method, and a 5 % weight loss temperature of 553 °C in the air. An infrared absorption spectrum of the polyimide powder is illustrated in Figure 1. The spectrum atlas clearly indicates characteristic absorption bands of imide in around 1780 cm -1 and 1720 cm -1 , and also indicates characteristic absorption bands of a trifluoromethyl group in around 1130 cm -1 . Results of elementary analysis on the polyimide powder thus obtained were as follows. Elementary analysis C H N F Calculated (%) 62.98 2.35 4.08 16.61 Found (%) 62.87 2.40 4.04 16.51 Melt viscosity of the polyimide was measured with a Koka type flow tester under 100 Kg load by using an oriffice having a diameter of 0.1 cm and a length of 1 cm. Melt flow initiation temperature was 320°C, melt viscosity was 6950 poise at 400°C, and the strand obtained was red brown, transparent and very flexible. Processing stability of the polyimide in the examples was measured by changing the residence time in the cylinder of the flowtester. The measurement was carried out at 400 °C with a load of 100 Kg. Results are illustrated in Figure 2. Melt viscosity is almost constant even thought residence time in the cylinder was extended, which indicates good heat stability. The polyimide powder was hot-pressed at 380 °C under pressure of 300 psi to form a film having a thickness of about 50 µm. The polyimide film obtained had dielectric constant of 3.36 at frequency of 60 Hz, 3.32 at 3 KHz and 3.24 at 1 MHz. Comparative Example 1 The same procedures as described in Example 8 were carried out except that 36.84 g (0.1 mol) of 4,4-bis(3-aminophenoxy)biphenyl was used in place of 50.45 g (0.1 mol) of 4,4-bis(3-amino-5-trifluoromethylphenoxy)biphenyl to obtain 54.3 g (98.7 % yield) of polyimide powder. The polyimide powder had an inherent viscosity of 0.46 d ℓ/g, glass transition temperature of 248 °C and a 5 % weight loss temperature of 561 °C in the air. Melt flow initiation temperature was 395 °C and melt viscosity was 9000 poise at 400 °C. Polyimide film having a thickness of 50 µm was prepared by the same procedure as described in Example 1. The film had dielectric constant of 3.42 at frequency of 60 Hz, 3.40 at 3 KHz, and 3.34 at 1 MHz. Example 9 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 50.45 g (0.1 mol) of 4,4'-bis(3-amino-5-trifluoromethylphenoxy)biphenyl obtained in Example 2 and 168.6 g of N,N-dimethylacetamide were charged. To the mixture, 21.81 g (0.1 mol) of pyromellitic dianhydride was added by portions with caution to prevent temperature rise of the solution and stirred for 30 hours at the room temperature. Polyamic acid thus obtained had an inherent viscosity of 0.97 d ℓ/g. A portion of the polyamic acid solution was cast on a glass plate and heated successively at 100 °C, 200 °C and 300 °C for an hour each to obtain a film having a thickness of 50 µm. Polyimide film thus obtained had a glass transition temperature of 263 °C and 0.5 % weight loss temperature of 556 °C in the air. The film also had a tensile strength of 9.6 Kg/mm 2 , tensile elastic modulus of 238 Kg/mm 2 , and elongation of 56 % in accordance with ASTM D-822. The film had dielectric constant of 3.34 at frequency of 60 Hz, 3.32 at 3 KHz, and 3.22 at 1 MHz. Examples 10 - 12 The same procedures as described in Example 8 were carried out by using a tetracarboxylic dianhydride illustrated in Table 1 in an amount shown in Table 1 to prepare polyimide powder, respectively. The yield, inherent viscosity, glass transition temperature (Tg), 5 % weight loss temperature (Td 5.0) and values of elementary analysis on the polyimide powder thus obtained are summarized in Table 1. Further, polyimide films were prepared by the same procedures as described in Example 8 and dielectric constant of these films was measured at frequency of 60 KHz and 1 MHz, respectively. Results are summarized in Table 3. Examples 13 - 15 The same procedures as described in Example 9 were carried out by using a tetracarboxylic dianhydride illustrated in Table 2 in an amount shown in Table 2 to prepare polyamic acid, respectively. Further, polyimide films were prepared from these polyamic acid by using the same procedures from these polyamic acids by using the same procedures as described in Example 9. The inherent viscosity of these polyamic acids and glass transition temperatures (Tg), 5 % weight loss temperature (Td 5.0) and mechanical properties of these polyimide films are illustrated in Table 2. Further, dielectric constant of each polyimide film was measured at frequency of 60 Hz, 3Khz and 1 MHz, respectively. Results are summarized in Table 3. Example 16 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 36.04 g (0.1 mol) of 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene obtained in Example 3 and 187.8 g of N,N-dimethylacetamide were charged. To the solution obtained, 44.43 g (0.1 mol) of 2,2-bis (3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride was added in a nitrogen atmosphere by portions with caution to prevent temperature rise of the solution and stirred for 30 hours at the room temperature. Polyamic acid thus obtained had an inherent viscosity of 0.82 d ℓ/g. A portion of the polyamic acid was cast on a glass plate and heated successively at 100 °C, 200 °C and 300 °C each for an hour to obtain a film having a thickness of about 50 µm. The polyimide film thus obtained had a glass transition temperature of 211 °C, tensile strength of 9.12 Kg/mm 2 , elongation of 3 % and tensile modulus of 372 Kg/mm 2 . Dielectric constant of the film was 2.90 at frequency of 60 Hz, 2.87 at 3 KHz and 2.83 at 1 MHz. The film also had an yellowness index (YI) of 8, light transmittance (T % ) of 86.5 %, and moisture absorption of 0.55 % . Examples 17 - 21 and Comparative Examples 2 - 3 The same procedures as Example 16 were carried out by using diamine components and tetracarboxylic dianhydride components illustrated in Table 4 to obtain various polyimide films. Table 4 summarizes diamine components, tetracarboxylic dianhydride components, inherent viscosity of polyamic acids, Tg, mechanical properties of films, dielectric constants, yellowness indexes, light transmittance at 500 nm and moisture absorption, together with the results of Example 16. Example 22 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 36.04 g (0.1 mol) of 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene obtained in Example 5, 43.09 g (0.097 mol) of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3,-hexafluoropropane dianhydride, 0.8887 g (0.006 mol) of phthalic anhydride, 1.40 g of γ-picoline and 316.5 g of m-cresol were charged. The mixture was heated to 150 °C with stirring in a nitrogen atmosphere and successively reacted at 150 °C for 4 hours while distilling out about 3.6 m ℓ of water. After finishing the reaction, the reaction mixture was cooled to the room temperature and poured into about 2 ℓ of isopropanol. The precipitated polyimide powder was filtered, washed with isopropanol and dried in the air at 50 °C for 24 hours and thereafter at 200 °C for 4 hours to obtain 77.34 g (96.7 % yield) of polyimide powder. The polyimide powder thus obtained had an inherent viscosity of 0.48 d ℓ/g, glass transition temperature of 206 °C and 5 % weight loss temperature of 512 °C. Figure 3 illustrates an infrared absorption spectrum of the polyimide powder. The spectrum atlas has a remarkable absorption at around 1780 -1 and 1720cm -1 which are characteristic absorption bands of imide. Elementary analysis results of the polyimide powder was as follows. C H N F Calculated (%) 59.38 2.23 3.65 22.25 Found (%) 58.46 2.16 3.88 22.29 The polyimide powder had flow initiation temperature of 280°C by the Koka type flow tester and melt viscosity of 8600 poise at 350°C. Processing stability of the polyimide was measured by changing residence time in the cylinder of the flow tester. Results at 360 °C under 100 Kg load are illustrated in Figure 4. Melt viscosity was almost unchanged although residence time was extended in the cylinder. Thus, processing stability was good. The polyimide powder thus obtained was dissolved in N,N-dimethylacetamide in a concentration of 20% % by weight, cast on a glass plate and removed the solvent at 200°C to obtain a film having a thickness of about 50 µm. The film had dielectric constant of 2.93 at frequency of 60 Hz, 2.88 at 3KHz, and 2.86 at 1 MHz. The film also had YI of 10, light transmittance of 84 % at 50 nm and moisture absorption of 0.60 %. Comparative Example 4 The same procedures as described in Example 22 were carried out except that 29.24 g (0.1 mol) of 1,4-bis(3-aminophenoxy)benzene was used in place of 36.04 g (0.1 mol) of 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene to obtaine 68.0 g (99.0 % yield) of polyimide powder. The polyimide powder had an inherent viscosity of 0.49 d ℓ/g, glass transition temperature of 210 °C and a 5 % weight loss temperature of 541 °C in the air. Melt flow initiation temperature was 270 °C and melt viscosity was 9500 poise at 350 °C. Polyimide film having a thickness of 50 µm was prepared by the same procedure as described in Example 22. The film had dielectric constant of 3.25 at frequency of 60 Hz, 2.21 at 3KHz, and 3.20 at 1 MHz. Examples 23 - 27 The same procedures as described in Example 22 were carried out by using diamine components and tetracarboxylic dianhydride components as illustrated in Table 5 to obtain various polyimide powder. Further, polyimide films were prepared by the same procedures as described in Example 22. Table 5 illustrated diamine components, tetracarboxylic dianhydride components, inherent viscosity of polyamic acids, Tg, melt viscosity at 350 °C, dielectric constant, YI, light transmittance at 500 nm and moisture absorption, together with the results of Example 22. Example 28 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 42.84 g (0.1 mol) of 1,3-bis(3-amino-5-trifluoromethylphenoxy)benzene obtained in Example 5 and 203.6 g of N,N-dimethylacetamide were charged. To the solution obtained, 44.43 g (0.1 mol) of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride was added by portions in a nitrogen atmosphere with caution to prevent temperature rise of the solution and stirred for 30 hours at the room temperature. The polyamic acid thus obtained had an inherent viscosity of 0.72 d ℓ/g. A portion of the polyamic acid was cast on a glass plate and successively heated at 100 °C, 200 °C and 300 °C each for an hours to obtain a film having a thickness of about 50 µm. The polyimide film thus obtained had a glass transition temperature of 194 °C, tensile strength of 8.76 Kg/mm 2 , elongation of 3.6 % and tensile modulus of 283 Kg/mm 2 . The polyimide film had dielectric constant of 2.84 at frequency of 60 Hz, 2.81 at 3 KHz, and 2.79 at 1 MHz. The film also had yellowness index (YI) of 7, light transmittance (T) of 88.8 % at 500 nm, and moisture absorption of 0.36 %. Examples 29 - 33 and Comparative Examples 5 - 8 The same procedures as described in Example 28 were carried out by using diamine components and tetracarboxylic dianhydride components as illustrated in Table 6 to obtain various films. Table 6 illustrates diamine components, tetracarboxylic dianhydride components, inherent viscosity of polyamic acids, Tg, mechanical properties of films, dielectric constant, yellowness index, light transmittance at 500 nm and moisture absorption, together with results of Example 28. Example 34 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 42.84 (0.1 mol) of 1,3-bis(3-amino-5-trifluoromethylphenoxy)benzene obtained in Example 5, 43.09 g (0.097 mol) of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 0.8887 g (0.006 mol) of phthalic anhydride, 1.40 g of γ -picoline, and 316.5 g of m-cresol were charged. The mixture was heated to 150°C with stirring in a nitrogen atmosphere and reacted at 150°C for 4 hours while distilling out about 3.6 m ℓ of water. After finishing the reaction, the reaction mixture was cooled to the room temperature and poured into about 2 ℓ of isopropanol. The precipitated polyimide powder was filtered, washed with isopropanol and dried in the air at 50°C for 24 hours and successively at 200°C for 4 hours. The polyimide powder thus obtained was 79.84 g (96.0 % yield) and had an inherent viscosity of 0.47 d ℓ/g, glass transition temperature of 191 °C and 5 % weight loss temperature of 509 °C. The infrared absorption spectrum of the polyimide powder is illustrated in Figure 5. The spectrum atlas remarkably exhibits absorption around 1780 and 1720 cm -1 which are characteristic absorption bands of imide. Following results were obtained on the elementary analysis of the polyimide powder. C H N F Calculated (%) 59.38 2.23 3.65 22.25 Found (%) 58.46 2.16 3.88 23.29 Flow initiation temperature was measured with a Koka type flow tester. The polyimide powder had flow initiation temperature of 280 °C and melt viscosity of 7240 poise at 350°C. Processing stability of the polyimide was measured by changing the residence time in the cylinder of the flow tester. Results measured at 360 °C under 100 kg load was illustrated in Figure 6. Melt viscosity was almost unchanged even though residence time in the cylinder was extended. Thus processing stability was good. The polyimide powder was dissolved in N,N-dimethylacetamide in a concentration of 20 % by weight, cast on a glass plate and removed the solvent at 200 °C to obtain a film having a thickness of about 50 µm. The polyimide film had dielectric constant of 2.87 at frequency of 60 Hz, 2.84 at 3 KHz and 2.82 at 1 MHz. The film also had YI of 9, light transmittance of 86.5 % at 500 nm, and moisture absorption of 0.42 % . Examples 35 - 39 The same procedures as described in Example 34 were carried out by using diamine components and tetracarboxylic dianhydride components illustrated in Table 7 to obtain various polyimide powder. Further, polyimide films were prepared by the same procedures as described in Example 34. Table 7 illustrates diamine components, tetracarboxylic dianhydride components, inherent viscosity of the polyimide powder, Tg, melt viscosity at 350 °C, dielectric constant, YI, light transmittance at 500 nm, and moisture absorption, together with the results of Example 34. Example 40 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 49.64 g (0.1 mol) of 1,3-bis(3-amino-5-trifluoromethylphenoxy)-5-trifluoromethylbenzene obtained in Example 7 and 219.5 g of N,N-dimethylacetamide were charged. To the solution obtained, 44.43 g (0.1 mol) of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride was added by portions in a nitrogen atmosphere with caution to prevent temperature rise of the solution and stirred for 30 hours at the room temperature. The polyamic acid thus obtained had an inherent viscosity of 0.54 d ℓ/g. A portion of the polyamic acid was cast on a glass plate and successively heated at 100 °C, 230 °C and 300 °C each for an hours to obtain a film having a thickness of about 50 µm. The polyimide film thus obtained had a glass transition temperature of 190 °C, tensile strength of 8.94 Kg/mm 2 , elongation of 4.4 % and tensile modulus of 288 Kg/mm 2 . The polyimide film had dielectric constant of 2.83 at frequency of 60 Hz, 2.81 at 3 KHz, and 2.79 at 1 MHz. The film also had yellowness index (YI) of 7, light transmittance (T) of 88.6 % at 500 nm, and moisture absorption of 0.26 %. Examples 41 - 42 The same procedures as described in Example 40 were carried out by using diamine components and tetracarboxylic dianhydride components as illustrated in Table 8 to obtain various films. Table 8 illustrates diamine components, tetracarboxylic dianhydride components, inherent viscosity of polyamic acids, Tg, mechanical properties of films, dielectric constant, yellowness index, light transmittance at 500 nm and moisture absorption, together with results of Example 40. Example 43 To a reaction vessel equipped with a stirrer, reflux condenser and nitrogen inlet tube, 49.64 g (0.1 mol) of 1,3-bis(3-amino-5-trifluoromethylphenoxy)-5-trifluoromethylbenzene, 43.09 g (0.097 mol) of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 0.8887 g (0.006 mol) of phthalic anhydride, 1.40 g of γ-picoline, and 316.5 g of m-cresol were charged. The mixture was heated to 150 °C with stirring in a nitrogen atmosphere and reacted at 150°C for 4 hours while distilling out about 3.6 m ℓ of water. After finishing the reaction, the reaction mixture was cooled to the room temperature and poured into about 2 ℓ of isopropanol. The precipitated olyimide powder was filtered, washed with isopropanol and dried in the air at 50°C for 24 hours and successively at 200°C for 4 hours. The polyimide powder thus obtained was 86.02 g (95.6 % yield) and had an inherent viscosity of 0.43 d ℓ/g, glass transition temperature of 188 °C and 5 % weight loss temperature of 505 °C. The infrared absorption spectrum of the polyimide powder is illustrated in Figure 7. The spectrum atlas remarkably exhibits absorption around 1780 and 1720 cm -1 which are characteristic absorption bands of imide. Following results were obtained on the elementary analysis of the polyimide powder. C H N F Calculated (%) 59.38 2.23 3.65 22.25 Found (%) 58.46 2.16 3.88 23.29 Flow initiation temperature was measured with a Koka type flow tester. The polyimide powder had flow initiation temperature of 275 °C and melt viscosity of 6620 poise at 350°C. Processing stability of the polyimide was measured by changing the residence time in the cylinder of the flow tester. Results measured at 360 °C under 100 kg load was illustrated in Figure 8. Melt viscosity was almost unchanged even though residence time in the cylinder was extended. Thus processing stability was good. The polyimide powder was dissolved in N,N-dimethylacetamide in a concentration of 20 % by weight, cast on a glass plate and removed the solvent at 200 °C to obtain a film having a thickness of about 50 µm. The polyimide film had dielectric constant of 2.85 at frequency of 60 Hz, 2.82 at 3 KHz and 2.80 at 1 MHz. The film also had YI of 7, light transmittance of 88.1 % at 500 nm, and moisture absorption of 0.31 %. Examples 44 - 45 The same procedures as described in Example 43 were carried out by using diamine components and tetracarboxylic dianhydride components illustrated in Table 9 to obtain various polyimide powder. Further, polyimide films were prepared by the same procedures as described in Example 43. Table 9 illustrates diamine components, tetracarboxylic dianhydride components, inherent viscosity of the polyimide powder, Tg, melt viscosity at 350 °C, dielectric constant, YI, light transmittance at 500 nm, and moisture absorption, together with the results of Example 43. Examples 46 - 60 The same procedures as described in Example 16 were carried out by using diamine components and tetracarboxylic dianhydride components illustrated in Table 10 to obtain various polyimide powder. Further, polyimide films were prepared by the same procedures as described in Example 16. Table 10 illustrates diamine components, tetracarboxylic dianhydride components, inherent viscosity of the polyimide powder, Tg, melt viscosity at 350°C, dielectric constant, YI, light transmittance at 500 nm, and moisture absorption. In table 10, diamine components are as follows. A: 1,3-bis(4-amino-5-trifluoromethyl-α,α-dimethylbenzyl)benzene B: 1,3-bis(4-amino-4-trifluoromethylbenzoyl)benzene C: 1,3-bis(3-amino-4-trifluoromethylbenzoyl D: 1,3-bis(3-amino-5-trifluoromethylphenyl)benzene E: 1,3-bis(3-amino-4-pentafluoromethylbenzoyl)benzene F: 4,4'-bis(3-amino-5-trifluoromethylphenoxy)benzophenone G: 2,2-bis[4-(3-amino-5-trifluoromethylphenoxy)phenyl]propane H: 4,4'-bis(3-amino-5-trifluoromethylbenzoyl)diphenylether I: 4,4'-bis(3-amino-5-trifluoromethylbenzoyl)biphenyl J : 4,4'-bis(3-amino-5-trifluoromethylphenyl)diphenylether K: 2,2-bis[4-(3-amino-5-pentafluoromethylphenoxy)phenyl]propane Examples 60 - 69 The same procedures as described in Example 16 were carried out by using diamine components and tetracarboxylic dianhydride components illustrated in Table 11 to obtain various polyimide copolymer powder. Further, polyimide copolymer films were prepared by the same procedures as described in Example 16.

Claims: A polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO- and -C(CH 3 ) 2 - and each X 1 is the same, m is an integer of 1 to 6, n is individually 0 or an integer of 1 to 4, R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is individually 0 or an integer of 1 to 4, or an integer of 1 to 4 when n is 0 in the formula (1) with the proviso that said polyimide (1) is not one having one or more recurring structural units of formula wherein R 1 is a tetravalent radical selected from WHERE AR 3 IS A capped polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO- and -C(CH 3 )- and two X 1 may be the same or different each other, m is an integer of 1 to 6, n is individually 0 or an integer of 1 to 4, R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is individually 0 or an integer of 1 to 4, or an integer of 1 to 4 when n is 0 in the formula (1), and having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for amine and dicarboxylic anhydride. The polyimide of claim 1 or claim 2 wherein the polyimide having the recurring structural units of the formula (1) is derived from the polyamic acid precursor having an inherent viscosity of 0.01 to 3.0 d ℓ/g at a concentration of 0.5 g/ d ℓ in a dimethylacetamide solution at 35°C A polyimide of claim 1 or claim 2 wherein the polyimide having reccuring structural units of the formula (1) has an inherent viscosity of 0.01 to 3.0 d ℓ/g at 35°C at a concentration of 0.5 g/ d ℓ in a solvent mixture composed of 9 parts by weight p-chlorophenol and 1 part by weight of phenol. An aromatic polyimide of claim 1 comprising a requisite structural unit having one or more recurring structural units of the formula (2) : wherein n and p are 0 or an integer of 1 to 4, and are not simultaneously 0, and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member; and/or one or more recurring structural units of the formula (3) : wherein n is an integer of 1 to 4 and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, mono aromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member ; and/or one or more recurring structural units of the formula (4) : wherein n is an integer of 1 to 4 and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member. An aromatic polyimide of claim 1 comprising a requisite structural unit having one or more recurring structural units selected from the group consisting of the formulas (5), (6), (7), (8), (9) and (10) : wherein R is a tetravalent radical having 2-27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member. An aromatic polyimide or a capped aromatic polyimide having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for dicarboxylic anhydride, comprising a requisite structural unit having one or more recurring structural units of the formula (11) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, n and p are 0 or an integer of 1 to 4 and are not simultaneously 0, and R is a tetravalent radical having 2-27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member; and/or one or more recurring structural units of the formula (12) : wherein R is a tetravalent radical having 2 to 27 carbon atoms and being selected form the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member. A preparation process of polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO- and -C(CH 3 ) 2 -, each X 1 is the same, m is an integer of 1 to 6, n is O or an integer of 1 to 4, and Ar is a divalent radical delected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p individually O or an integer of 1 to 4, and an integer of 1 to 4 when n=O in the formula (13), R is tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each with a direct bond or a bridge member, which comprises reacting an aromatic diamine having one or more principal ingredients of the formula (13) : wherein X 1 , Ar, m and n are the same as above, with one or more tetracarboxylic dianhydide principally represented by the formula (14) : wherein R are the same as above, and thermally or chemically imidizing the resulting polyamic acid; with the proviso that said polyimide (1) is not one having one or more recurring structural units of formula wherein R 1 is a tetravalent radical selected from WHERE AR 3 IS A preparation process of capped aromatic polyimide comprising a requisite structural unit having one or more recurring structural units of the formula (1) : wherein X 1 is a divalent radical selected from the group consisting of a direct bond, -O-, -CO- and -C(CH 3 ) 2 -, two X 1 may be the same or different, m is an integer of 1 to 6, n is O or an integer of 1 to 4, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p individually O or an integer of 1 to 4, and an integer of 1 to 4 when n=O in the formula (13), R is tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each with a direct bond or a bridge member, and having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for amine and dicarboxylic anhydride, comprising reacting aromatic diamine having one or more principal ingredients of the formula (13) : wherein X 1 , Ar, m, and n are the same as above, with one or more tetracarboxylic dianhydride principally represented by the formula (14) wherein R is the same as above, in the presence of aromatic dicarboxylic anhydride of the formula (15) : wherein Z is a divalent having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and/or aromatic monoamine of the formula(16) Z 1 - NH 2 wherein Z 1 is a monovalent radical having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member, and thermally or chemically imidizing the resulting polyamic acid. The preparation process of claim 9 wherein the aromatic dicarboxylic anhydride is phthalic anhydride. The preparation process of claims 9 or 10 wherein the aromatic monoamine is aniline. The preparation process of claim 9, 10 or 11 wherein the amount of the aromatic dicarboxylic anhydride is 0.001 to 1.0 mol per mol of the aromatic diamine. The preparation process of claim 12 wherein the amount of phthalic anhydride is 0.001 to 1.0 mol per mol of the aromatic diamine. The preparation process of any of claims 9 to 13 wherein the amount of the aromatic monoamine is 0.001 to 1.0 mol per mol of the tetracarboxylic dianhydride. The preparation process of claim 14 wherein the amount of aniline is 0.001 to 1.0 mol per mol of the tetracarboxylic dianhydride. The preparation process of any of claims 8 to 15 wherein the aromatic diamine comprises one or more of: the diamine of formula (17): wherein m is an integer of 1 to 6, n is 0 or an integer of 1 to 4, and Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is O or an integer of 1 to 4 and is an integer of 1 to 4 when n is 0 in the formula (17); the diamine of formula (18): wherein n and p are O or an integer of 1, and are not simultaneously O; the diamine of formula (19): wherein n is an integer of 1 to 4 ; the diamine of formula (20): wherein p is an integer of 1 to 4 ; the diamine of formula (21): wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, and n and p are individually 0 or an integer of 1 to 4 and are not simultaneously 0; the diamine of formula (22): The preparation process of any of claims 8 to 15 wherein the aromatic diamine is 4,4-bis (3-amino-5-fluoromethylphenoxy)biphenyl or one or more compounds selected from 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 1,3-bis(3-aminophenoxy)-5-trifluoromethylbenzene, 1,3-bis(3-amino-5-trifluoromethylphenoxy)benzene, and 1,4-bis(3-amino-5-trifluoromethylphenoxy)benzene. A composition comprising the polyimide of any one of claims 1 to 7. A polyimide film comprising the polyimide of any one of claims 1 to 7. An aromatic diamine having the formula (17) : wherein Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is an integer of 1 to 4; said amine preferably having the formula (21) : wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 - and p is an integer of 1∼4. An aromatic diamine having the formula (18) : wherein p is an integer of 1∼4; said diamine of formula (18) preferably being of the formula (20) : and preferably being selected from 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 1,3-bis(3-aminophenoxy)-5-trifluoromethylbenzene, A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar is a divalent radical selected from the group consisting of Wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is 0 or an integer of 1 to 4, comprising reacting a dihalogen or dinitro compound of the formula (23) : Y - Ar - Y wherein Y is a halogen atom or a nitro radical, and Ar is the same as above, with a m-nitrophenol derivative of the formula (24) : wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and is an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of a base and successively reducing resultant aromatic dinitro compound. A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar is a divalent radical selected from the group consisting of Wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 - m is an integer of 1 to 6, and p is 0 or an integer of 1 to 4, comprising reacting a dihydroxy compound of the formula (25) : HO - Ar - OH wherein Ar is the same as above, with a m-dinitro or m-nitrohalogeno compound of the formula (26) : wherein Y is s halogen atom or a nitro radical, at 100 to 250 °C in an aprotic solvent in the presence of a base and successively reducing the resultant aromatic dinitro compound. A preparation process of an aromatic diamine compound of the formula (17) : wherein Ar is a divalent radical selected from the group consisting of wherein X 2 is a divalent radical selected from the group consisting of a direct bond, -O-, -S-, -CO- and -C(CH 3 ) 2 -, m is an integer of 1 to 6, and p is 0 or an integer of 1 to 4, comprising reacting a dihalogeno or dinitro compound of the formula (23) : Y - Ar - Y wherein Y is a halogen atom or a nitro radical and Ar is the same as above, with a m-aminophenol derivative of the formula (27) : wherein m is an integer of 1 to 6, and n is 0 or an integer of 1 to 4 and an integer of 1 to 4 when p is 0 in the formula (23), at 100 to 250 °C in an aprotic polar solvent in the presence of a base. A capped aromatic polyimide having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for dicarboxylic anhydride, comprising a requisite structural unit having one or more recurring structural units of the formula (2) : wherein n and p are 0 or an integer of 1 to 4, and are not simultaneously 0, and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member; and/or one or more recurring structural units of the formula (3) : wherein n is an integer of 1 to 4 and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, mono aromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member ; and/or one or more recurring structural units of the formula (4) : wherein n is an integer of 1 to 4 and R is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member. A capped aromatic polyimide having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity for dicarboxylic anhydride, comprising a requisite structural unit having one or more recurring structural units selected from the group consisting of the formulas (5), (6), (7), (8), (9) and (10) : wherein R is a tetravalent radical having 2-27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected each other with a direct bond or a bridge member.

Inventors: ASANUMA TADASHI, ISHIDA TSUTOMU, KATAOKA TOSHIYUKI, MATSUO MITSUNORI, OIKAWA HIDEAKI, OKAWA YUICHI, SAKATA YOSHIHIRO, YAMAGUCHI AKIHIRO, YAMAGUCHI KEIZABURO, YAMASHITA WATARU, ASANUMA, TADASHI, ISHIDA, TSUTOMU, KATAOKA, TOSHIYUKI, MATSUO, MITSUNORI, OIKAWA, HIDEAKI, OKAWA, YUICHI, SAKATA, YOSHIHIRO, YAMAGUCHI, AKIHIRO, YAMAGUCHI, KEIZABURO, YAMASHITA, WATARU
Applicants: MITSUI TOATSU CHEMICALS, MITSUI TOATSU CHEMICALS, INC.
Application year: 1993
Main classification: C08G73
IPC codes: C08G73, H05K1, C07C217