NOVELTY - A copolyimide precursor consists of amide-containing unit structures (I) and (II).    USE - Copolyimide precursor is used for manufacturing solution compositions and manufacturing (co)polyimide used for manufacturing varnish (all claimed) and for transparent substrates of flexible displays and touch panels, and substrates of solar cells. Can also be used for liquid-crystal aligning films of display apparatus, optical fibers, optical waveguides, protective films of color filters, vapor-deposition substrates, transistors, and photoelectric elements.    ADVANTAGE - The copolyimide precursor enables manufacture of highly transparent polyimide having excellent mechanical strength, dimensional stability, solvent resistance, heat resistance, and bending tolerance, and low linear expansion coefficient.    DETAILED DESCRIPTION - A copolyimide precursor consists of amide-containing unit structures of formulae (I) and (II).    R1,R4=H or 1-4C alkyl;    R2,R3,R5,R6=H, 1-6C alkyl, or 3-9C alkylsilyl;and    X=tetravalent group other than group formula (i) or (ii).    INDEPENDENT CLAIMS are included for the following:    (1) manufacture of copolyimide precursor, which involves reacting a diamine component and a tetracarboxylic-acid component at 100 degrees C or less in a solvent;    (2) manufacture of copolyimide precursor solution composition, which involves adding carboxylic acid derivative to polyimide precursor obtained by reacting diamine component in excess molar ratio with tetracarboxylic-acid component, in a quantity corresponding to the number-of-moles of excess diamine. The molar ratio of total amount of diamine component and tetracarboxylic acid, and carboxylic acid derivative closely approaches to equivalence;    (3) copolyimide having unit structures of formulae (III) and (IV);    (4) polyimide precursor consisting of a unit structure of formula (V), in which at least one of R2 and R3 is 3-9C alkylsilyl;    (5) polyimide obtained by imidating the polyimide precursor;    (6) 2,3,3',4'-biphenyl tetracarboxylic dianhydride powder having a light transmittance of 85% or more at a wavelength of 400 nm with respect to a solution obtained by dissolving the powder in 2N sodium hydroxide aqueous solution in a concentration of 10 %mass at an optical path lengths of 1 cm;    (7) purification of 3,3',4,4'-biphenyl tetracarboxylic dianhydride powder, which involves mixing a solvent having a solubility of 0.1 g/100 g or more at 25 degrees C with respect to 3,3',4,4'-biphenyl tetracarboxylic dianhydride, and 3,3',4,4'-biphenyl tetracarboxylic dianhydride powder in nonuniform state with at least 1 portion of 3,3',4,4'-biphenyl tetracarboxylic dianhydride powder not being dissolved, and separating and recovering undissolved 3,3',4,4'-biphenyl tetracarboxylic dianhydride powder from the liquid mixture;    (8) trans-1,4-diaminocyclohexane powder having a light transmittance of 90% or more at a wavelength of 400 nm with respect to a solution obtained by dissolving trans-1,4-diaminocyclohexane powder in pure water in a concentration of 10 %mass at an optical path length of 1 cm;    (9) 2,2',3,3'-biphenyl tetracarboxylic dianhydride powder having a light transmittance of 80% or more at a wavelength of 400 nm with respect to a solution obtained by dissolving in 2N sodium hydroxide aqueous solution in a concentration of 10 %mass at an optical path length of 1 cm; and    (10) manufacture of varnish containing an organic solvent, and polyimide precursor of formula (VI) or polyimide of formula (VII). The organic solvent has a light transmittance of 89% or more at a wavelength of 400 nm and an optical path length of 1 cm.    A1,A2=tetravalent aliphatic group or aromatic group;and    B1,B2=bivalent aliphatic group or aromatic group.