Abstract: A method of efficiently removing a low molecular weight substance from a polyimide precursor or polyimide in which the low molecular weight substance is dispersed as micro-domains, without using a large amount of an organic solvent. The method of removing a low molecular weight substance comprises subjecting either a polymer composition having a micro-domain structure made up of a continuous phase comprising a polyimide precursor and, dispersed therein, a discontinuous phase comprising a low molecular weight substance or a polyimide composition obtained from the polymer composition by converting the polyimide precursor into a polyimide to extraction with a combination of supercritical carbon dioxide and a co-solvent to thereby remove the low molecular weight substance. The co-solvent is preferably an aprotic polar solvent, more preferably a nitrogen compound solvent or a sulfur compound solvent.

Abstract: A porous polyimide having a finely cellular structure and having a low dielectric constant and heat resistance. The porous polyimide can be produced by a process comprising adding a dispersible compound to a polyimide precursor to form a micro-domain structure in which the dispersible compound is dispersed in the polymer so as to have a size smaller than 10 &mgr;m and then removing the dispersible compound by extraction with supercritical carbon dioxide to thereby make the precursor porous, wherein the interaction parameter &khgr;AB between the polyimide precursor A and the dispersible compound B is larger than 3. This porous polyimide has an average cell diameter smaller than 5 &mgr;m and a dielectric constant of 3 or lower.

Abstract: A porous article having excellent heat resistance, a finely cellular structure, and a low dielectric constant; and a process for producing the porous article which comprises subjecting a polymer composition having a micro-domain structure comprising a continuous polymer phase and dispersed therein a discontinuous phase having an average diameter smaller than 10 &mgr;m to a treatment for removing the ingredient constituting the discontinuous phase by at least one operation selected from vaporization and decomposition and by an extraction operation to thereby make the polymer porous. The ingredient constituting the discontinuous phase has a weight average molecular weight of, e.g., 10,000 or lower. Liquefied carbon dioxide, supercritical carbon dioxide, or the like can be used as an extraction solvent for the ingredient constituting the discontinuous phase.

Abstract: A porous polyimide having a finely cellular structure and having a low dielectric constant and heat resistance. The porous polyimide can be produced by a process comprising adding a dispersible compound to a polyimide precursor to form a micro-domain structure in which the dispersible compound is dispersed in the polymer so as to have a size smaller than 10 &mgr;m and then removing the dispersible compound by extraction with supercritical carbon dioxide to thereby make the precursor porous, wherein the interaction parameter &khgr;AB between the polyimide precursor A and the dispersible compound B is larger than 3. This porous polyimide has an average cell diameter smaller than 5 &mgr;m and a dielectric constant of 3 or lower.

Abstract: The polyamic acid of the invention can be obtained by the reaction of an acid anhydride component comprising pyromellitic anhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane with 2,2′-di-substituted-4,4′-diaminobiphenyls as a first aromatic diamine and any aromatic diamine component, as a second aromatic diamine, of 2,2-bis(4-aminophenoxyphenyl)propanes, 1,1-bis(4-(4-aminophenoxy)-3-t-butyl-6-methylphenyl)butane, 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane and &agr;,&agr;′-bis(4-aminophenyl)diisopropylbenzenes in an organic solvent. The polyimide resin of the invention can be obtained by heating such a polyamic acid solution. In the production of a circuit board, by using a photosensitive polyamic acid having a sensitizer incorporated in such a polyamic acid solution, a patterned polyimide resin layer can be provided as an insulation layer on a metal foil.

Abstract: An ultraviolet curing pressure-sensitive adhesive sheet prepared by forming an ultraviolet curing pressure-sensitive adhesive layer on at least one surface of a substrate film and adhering a separator to the surface of the ultraviolet curing pressure-sensitive adhesive layer, wherein the separator has an ultraviolet transmittance at a wavelength of 300 to 400 nm of 65% or lower. The separator is obtained by forming a layer containing an ultraviolet absorber on the surface of the substrate film opposite the surface adhering to the pressure-sensitive adhesive layer or incorporating an ultraviolet absorber in the film. The ultraviolet curing pressure-sensitive adhesive sheet is useful as a semiconductor-protective pressure-sensitive adhesive sheet and a semiconductor wafer-fixing sheet, which can be used without causing a curing reaction with the exposure of a slight amount of ultraviolet rays from a surrounding environment at the standby for adhering wafers.

Abstract: An aromatic polycarbodiimide comprising a structure represented by the following formula (1) has high solubility in organic solvents, good processability, excellent moisture resistance, and water repellency: wherein n is an integer of 2 to 300, and R represents an organic group.

Abstract: An aromatic polycarbodiimide having a structural repeating unit represented by the following formula (I): ##STR1## wherein R represents a hydrogen atom or an alkyl group and n is an integer of 3 to 600,which has excellent solubility and heat resistance and also has excellent adhesion, low-temperature workability and moisture resistance, is provided.

Abstract: Disclosed is a gas separating membrane comprising a layer made of a polycarbodiimide resin having repeating units represented by formula (I): ##STR1## wherein R represents a divalent organic group. The gas separating membrane available according to the present invention has high permeability and separation selectivity as well as excellent permeating performance, and further has excellent heat resistance, chemical resistance and durability.

Abstract: A polycarbodiimide having excellent heat resistance and humidity resistance, which comprises a structural unit represented by the following formula (A) ##STR1## wherein R represents a divalent organic group represented by any one of the following formulae (I) and (II), n is an integer of 2 to 400 ##STR2## wherein X.sub.1 to X.sub.4 independently represent a hydrogen or an alkyl group having 1 to 3 carbon atoms.

Abstract: An aromatic polycarbodiimide comprising a structural repeating unit represented by the following formula (I): ##STR1## wherein n is an integer of 2 to 200.