A poly(amide-imide) copolymer, a composition for a thin film, and a thin film are provided. The poly(amide-imide) copolymer is synthesized by polymerization, dehydration cyclization, and hydrolysis condensation of an aromatic diamine monomer, a diacyl chloride monomer, a tetracarboxylic dianhydride monomer, and a silane compound having an alkoxy group as an end-capping agent. The aromatic diamine monomer includes 2,2-bis(trifluoromethyl)benzidine. Based on a usage amount of 100 mol % of the aromatic diamine monomer, a usage amount of the 2,2-bis(trifluoromethyl)benzidine is 70 mol % or more.

A poly(amide-imide) copolymer that is a reaction product of a diamine represented by Chemical Formula 1, a tetracarboxylic acid dianhydride including a compound represented by Chemical Formula 2, and a compound represented by Chemical Formula 3:

##STR00001## wherein, in Chemical Formulae 1 to 4, R.sup.1 to R.sup.4, A, and X are the same as defined in the specification.

A crosslinked polyimide, a polyimide film and a method for preparing thereof, an organic light emitting diode (OLED) device. 4,40-diamino-400-N-carbazolyltriphenylamine and 1,2,4,5-cyclohexanetetracarboxylic dianhydride and a p-xylylenediamine crosslinker are introduced in the present invention. The introduction of a diamine monomer with a large volume of pendant groups increases an asymmetry of the polyimide, destroys a close structure of the polymer, and reduces crystallization properties of the polypolymer, thereby effectively increasing its transmissibility. At the same time, a cross-linked agent, p-xylylenediamine, is introduced, and the cross-linked agent widens a molecular chain spacing, so that the polyimide molecule has a larger free volume. At the same time, the formation of cross-linked is beneficial to reduce a polarizability of the molecule, thereby reducing a dielectric constant of the material. An OLED device with a novel low dielectric constant and high transmittance is prepared in this way.

A polyamide acid which contains at least one diamine compound selected from among diamine compounds represented by general formula (8) within the range of 3-60 parts by mole in total per 100 parts by mole of all diamine components, while containing a biphenyl tetracarboxylic acid dianhydride within the range of 40-100 parts by mole and a pyromellitic acid dianhydride within the range of 0-60 parts by mole per 100 parts by mole of all acid anhydride components; and a thermoplastic polyimide which is obtained curing this polyamide acid. ##STR00001##
(In formula (8), linking group X represents a single bond or a divalent group selected from among CONH; each Y independently represents a hydrogen atom, a monovalent hydrocarbon group having 1-3 carbon atoms or an alkoxy group; n represents an integer of 0-2; and each of p and q independently represents an integer of 0-4.)

A low dielectric polyimide composition comprises an aliphatic anhydride, a long chain diamine, and an ester diamine. A polyimide made of such low dielectric polyimide composition has low polarizability group, thus the dielectric constant of the polyimide is lower. A polyimide made of the low dielectric polyimide composition, a polyimide film using the polyimide, and a copper clad laminate using the polyimide film are also provided.

A resin composition for display substrates includes the following: the resin (a): a resin containing, as a main component, a repeating unit represented by the chemical formula (1), wherein the resin contains the total of 95 mass % or more of a tetracarboxylic acid residue A, having 2 or more carbon atoms and an SP value of 15 or more and 17 or less and a diamine residue having an SP value of 11 or more and 13 or less with respect to the total of 100 mass % of A and B contained in the resin; the solvent (b): a solvent having an SP value of 7.5 or more and less than 9.5; and the solvent (c): a solvent having an SP value of 9.5 or more and 14.0 or less;

##STR00001##

wherein R.sup.1 and R.sup.2 independently represent a hydrogen atom, hydrocarbon group having 1 to 10 carbon atoms, alkylsilyl group having 1 to 10 carbon atoms, alkali metal ion, ammonium ion, imidazolium ion, or pyridinium ion.

A method of making a polyetherimide comprises: combining a bisphenol A dianhydride, p-phenylene diamine and a halogenated aromatic solvent to form a reactant solution; heating the reactant solution to a temperature of 205 C. to 330 C. at a pressure sufficient to prevent boiling to afford a reaction solution; removing water from the reaction solution; maintaining the reaction solution at a temperature of 205 C. to 330 C. and a pressure sufficient to prevent boiling for 10 minutes to 5 hours to form a product mixture comprising the polyetherimide and solvent; and isolating the polyetherimide.

A polyimide polymer that includes the reaction product of: (a) at least one diamine selected from the group consisting of a diamine of Structure (I) ##STR00001##
(b) at least one tetracarboxylic acid dianhydride, and optionally (c) at least one compound containing a first functional group reactive with an amine or an anhydride and at least one second functional group selected from the group consisting of an unsubstituted alkenyl group and an unsubstituted alkynyl group. Each variable in the above formula is defined in the specification.

An LED filament and an LED light bulb applying the same are provided. The LED filament includes a conductive section including a conductor; two or more LED sections connected to each other by the conductive section, and each of the LED sections includes two or more LED chips electrically connected to each other through a wire; two electrodes, electrically connected to the LED section; and a light conversion layer with a top layer and a base layer, covering the LED sections, the conductive section and the two electrodes, and a part of each of the two electrodes is exposed respectively. The LED filament is supplied with electric power no more than 8 W, when the LED filament is lit, at least 4 lm of white light is emitted per millimeter of filament length.

A polyimide precursor including at least one repeating unit represented by the following chemical formula (1): ##STR00001## in which A is an arylene group; and X.sub.1 and X.sub.2 are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms, and a polyimide obtained from the polyimide precursor has a coefficient of linear thermal expansion from 50 C. to 400 C. of 100 ppm/K or less.