Methods for preparing mixed polyamides, polyimides and polyamideimides under hydrothermal polymerization conditions are provided. The methods are based on suitable mixtures of poly carboxylic acids, poly carboxylic dianhydrides or poly carboxylic acid chloride anhydrides and polyamines and provide routes to low cost structural polymers useful in, for example, infrastructure applications.

A polyimide is provided, which contains at least one repeating unit selected from a group consisting of the following general formulas, M, N, and O:

##STR00001##

X is a residue derived from TCA represented by formula I. Y.sub.1 is a residue derived from a diamine with a cardo structure. Y.sub.2 is a residue derived from a diamine with the structure of a benzene ring, biphenyl, phenylbenzimidazole or phenylbenzoxazole. Y.sub.3 is a residue derived from a diamine with an ether or an ester group.

##STR00002##

A diamine monomer compound with reduced dielectric losses for better integrity and stability in digital transmissions is represented by a structural formula of

##STR00001##

wherein n.sub.1 is an integer greater than 1. A method for preparing the diamine monomer compound and a polyimide resin developed therefrom are disclosed. The diamine monomer compound introduces a long even numbered carbon chain and a liquid crystal unit structure, the long even numbered carbon chain giving flexibility, which reduces the regularity and rigidity of the molecular chain and facilitates film-forming processing. Dimensional stability is improved, and the coefficient of thermal expansion of the materials is reduced, the materials have good mechanical and heat-tolerant thermal properties, the loss factor and the coefficient of thermal expansion of the materials being reduced. A flexible film of the resin and an electronic device are also disclosed.

The present invention relates to the production of a polyimide precursor, whereby, by using an amide-based organic solvent having a positive-number partition coefficient (Log P) and a density of at most 1 g/cm3, an interaction between the organic solvent and polyamic acid, which is a polyimide precursor, may be mitigated, thereby enabling the decrease of the viscosity of a polyimide precursor solution, and thus enabling a polyimide precursor solution having high solid content and low viscosity to be obtained.

A polyimide precursor solution includes: a polyimide precursor; polyester resin particles containing a polyester resin and having a volume average particle diameter of from 3 μm to 50 μm inclusive and an average circularity of 0.970 or more; and a solvent.

A polyimide precursor solution includes a polyimide precursor having a glass transition temperature Tg of equal to or higher than 300° C. after imidization, an aqueous solvent containing water, an organic amine compound, and resin particles having a volume average particle size of equal to or less than 100 nm.

A polyimide precursor solution includes an aqueous solvent including water, a polyimide precursor, resin particles, and an ionization agent X having a boiling point of 100° C. or more and 130° C. or less and an ionization agent Y having a boiling point of 250° C. or more and 300° C. or less.

A polyimide precursor solution includes: a polyimide precursor that is a polymer of a tetracarboxylic dianhydride and a diamine compound; particles; a solvent; and a compound having at least four carboxy groups per molecule.

The present disclosure relates to a polyimide-based polymer film comprising a polyimide-based polymer containing a polyimide repeating unit synthesized by the reaction of an acid anhydride compound having a specific structure and a diamine compound, wherein an average transmittance at a wavelength of 380 nm or more and 780 nm or less is 60% or more, and a thickness direction retardation value at a thickness of 10 pm is 150 nm or less, and a substrate for a display device, a circuit board, an optical device, and an electronic device using the same.

The present disclosure provides a polyimide polymer, which includes a repeating unit represented by formula (I). Formula (I) is defined as in the specification. The present disclosure further provides a polyimide mixture and a polyimide film, wherein the polyimide mixture is prepared by the polyimide polymer, and the polyimide film is prepared by the polyimide mixture.