Abstract: A flexible printing base comprising a metal foil having formed thereon a polyimide layer is disclosed, wherein said metal foil has a centerline average roughness of not more than 0.7 .mu.m, and said polyimide mainly comprises a repeating unit represented by formula (I): ##STR1## and a repeating unit represented by formula (II): ##STR2## wherein l:m=x:y, wherein x represents a number not less than 45 and less than 70; y represents a number more than 30 and not more than 55; and x+y=100, said polyimide layer is formed by applying a solution of a polyamic acid mainly comprising a repeating unit represented by formula (III): ##STR3## and a repeating unit represented by formula (IV): ##STR4## wherein l and m are as defined above, in N,N'-dimethylformamide and/or N,N'-dimethylacetamide on a metal foil, followed by imidation. The flexible printing base is quite free from curling either in the state of a composite laminate but also in the state where the metal foil has been removed by etching.

Abstract: A polyamide acid solution is disclosed, comprising a polyamide acid comprising as main components at least one recurring unit selected from the recurring units of the formulae (I) to (IV) and a recurring unit of formula (V), dissolved in an organic solvent comprising as a main component an amide type polar solvent having a boiling point of 170.degree. C. or less. The solution is capable of forming a polyimide film which has colorless transparency free from coloration and strong adhesion to a substrate for liquid crystal cell enough to prevent penetration of water into interface between the substrate and film. The solution is particularly useful for forming a liquid crystal oriented film.

Abstract: A colorless transparent polyimide shaped article having as a main component at least one recurring unit selected from the recurring units of the formulae (I) to (IX). It is useful, for example, as an oriented film in liquid crystal display devices. The polyimide shaped article is produced by a process which comprises preparing a solution of a polyamide acid having as a main component at least one recurring unit selected from the recurring units of the formulae (V) to (VIII) in an amide-type organic polar solvent, forming a shaped article of the polyamide acid from the solution, and imidizing the resulting shaped article of the polyamide acid.

Abstract: A colorless transparent polyimide shaped article having as a main component at least one recurring unit selected from the recurring units of the formulae (I) to (III), which is useful, for example, as an oriented film in liquid crystal display devices. The polyimide shaped article is produced by a process which comprises preparing a solution of (A) a polyimide precursor obtained by reacting a diamino compound comprising as a main component at least one aromatic diamine having amino groups at the m-position selected from diamines of formulae (IV) to (VI) with a tetracarboxylic acid compound comprising as a main component a tetracarboxylic acid dianhydride of formula (VII) dissolved in (B) at least one organic polar solvent selected from N,N-dimethylacetamide, N,N-dimethylformamide, bis(2-methoxyethyl)ether, cresol and halogenated phenols; forming a shaped article of the polyimide precursor from the solution; and imidizing the resulting shaped article.

Abstract: A polyimide molding powder and a process for producing the same are disclosed, said powder comprising an aggregate of polyimide particles, in which the whole or a large portion of said powder comprises polyimide particles composed of a particulate filler coated with a polyimide resin and/or polyimide particles composed of a fibrous filler coated with a polyimide resin, and said process comprising reacting an aromatic tetracarboxylic acid dianhydride and an aromatic diamino compound in an organic solvent to synthesize a polyimide precursor and imidating the polyimide precursor to precipitate polyimide particles, wherein a particulate filler and/or a fibrous filler dispersed in a prescribed amount of an organic solvent is or are added to the reaction system at any stage before the imidation of the polyimide precursor. The molding powder produces polyimide molded products free from brittleness and excellent in appearance, as well as various performance characteristics due to the improving effects of the filler.

Abstract: A polyimide powder which can provide a molding having excellent both strength and heat resistance by heat-press molding, and a method for producing such polyimide powder are disclosed. The polyimide powder comprises spherical polyimide particles having a particle size distribution of from 0.5 to 20 .mu.m and a mean particle diameter of from 1 to 15 .mu.m, and comprising a repeating unit represented by the formula ##STR1## wherein Ar represents an aromatic diamine residue.

Abstract: A polyimide/metallic foil composite film having a curvature radius of at least 25 cm and which is substantially free from curling is described, comprising coating a solution of a polyimide precursor in an organic polar solvent on a 1 to 500 .mu.m thick metallic foil, the polyimide precursor being prepared by reacting a diamine component comprising p-phenylenediamine and an aromatic tetracarboxylic acid component comprising 3,3',4,4'-biphenyltetracarboxylic dianhydride or its derivative; heat-drying the above-prepared coating in the state that the metallic foil is fixed; and then heating it at a high temperature to form a 5 to 200 .mu.m thick polymide film. This composite film does not substantially curl in either the lengthwise and widthwise directions and is very suitable for use in the production of an electrical circuit board.

Abstract: A process for producing a polyimide/metallic foil composite film having a curvature radius of at least 25 cm and which is substantially free from curling is described, comprising coating a solution of a polyimide precursor in an organic polar solvent on a 1 to 500 .mu.m thick metallic foil, the polyimide precursor being prepared by reacting a diamine component comprising p-phenylenediamine and an aromatic tetracarboxylic acid component comprising 3,3',4,4'-biphenyltetracarboxylic dianhydride or its derivative; heat-drying the above-prepared coating in the state that the metallic foil is fixed; and then heating it at a high temperature to form a 5 to 200 .mu.m thick polyimide film. This composite film does not substantially curl in either the lengthwise and widthwise directions and is very suitable for use in the production of an electric circuit board.

Abstract: A selective permeable membrane comprising a polyquinazolone-based polymer including a repeating unit represented by the formula ##STR1## wherein R.sup.1 is a tetravalent aromatic group, R.sup.2a and R.sup.2b are each independently, an alkyl group or aromatic group, and R.sup.3 is a divalent organic group.

Abstract: A spherical porous polyimide powder which is thermally infusible and is insoluble in an organic solvent, comprising spherical porous particles of a weight average particle diameter of 1 to 20 .mu.m comprising an aromatic polyimide having an inherent viscosity measured in sulfuric acid at a concentration of 0.5 g/dl at temperature of 30.+-.0.01.degree. C. of 0.1 to 2.0, wherein a packed bulk density is 100 to 600 g/l and a specific surface area measured by a nitrogen absorption method is 1 m.sup.2 /g or more.

Abstract: Spherical porous polyimide powder having an average particle diameter of 1 to 20 .mu.m which is infusible and insoluble in organic solvents is produced by polymerizing an aromatic tetracarboxylic acid dianhydride and an aromatic polyisocyanate in an organic solvent at a temperature of 100.degree. to 200.degree. C. and in the presence of a tertiary amine catalyst to form polyimide particles in the form of slurry, filtering or centrifuging said polyimide particles, and washing the resulting polyimide particles with an organic solvent.

Abstract: A process for the production of polyquinazolone-based polymers by reacting bisquinazolone with a diamine or a diamine substituted with a carboxylic acid, sulfonic acid or metal salt thereof in the presence of a Lewis acid catalyst or a phosphorus-containing dehydrating agent, where the polymers are useful to produce permselective membranes.

Abstract: A water-solubilized resin composition for forming a thermally stable polyimide polymer prepared by mixing(I) a nitrogenous base salt of a polyimide precursor containing an amino group at both terminals of the molecule and having a residual acid value ratio of about 50 to about 5% obtained by reacting 1,2,3,4-butanetetracarboxylic acid and a molar excess of a diamine in water, or in a water-soluble solvent or in the presence of both a water-soluble solvent and water with(II) a nitrogenous base salt of a 3,3',4,4'-benzophenonetetracarboxylic acid diester whose ester linkage is positioned at either one of the adjoining two carboxyl groups in the same benzene nucleus thereof.

Abstract: A heat resistant resin solution comprising (1) at least one solvent selected from the group consisting of alcohols, polyhydric alcohols, polyhydric alcohol derivatives, ketones, ethers and esters, (2) aqueous ammonia and (3) a polymer having a residual acid value of about 5 to 40% obtained by reaction of a 1,2,3,4-butanetetracarboxylic acid, an aromatic tricarboxylic acid anhydride and a diamine in the presence of a polyhydric alcohol and a method of preparation of the heat resistant resin solution.

Abstract: A concentrated solution suitable for forming thermal resisting polymers having a high degree of polymerization comprising a mixture of a prepolymer solution prepared by the reaction of an organic diisocyanate or diamine and a molar excess of 1,2,3,4-butanetetracarboxylic acid or an anhydride of the acid, and a blocked polyisocyanate.