NOVELTY - Solution of polyamide, comprises an aromatic copolyamide, and a solvent, where the aromatic copolyamide comprises at least two amide repeat units (I) and (II), and at least one of the repeat unit has at least one free carboxylic acid group, and the amount of repeat unit containing the free carboxylic acid group is 1-30 mole% of the total repeat units.    USE - The solution is useful for manufacturing a display element, an optical element, an illumination element (claimed) and a polymer film, which is useful for flexible electronic devices including flexible displays and flexible solar cell panels.    ADVANTAGE - The solution manufactures the lightweight polymer thin film with excellent flexibility and optical transparency even at high temperature, increased thermal stability, oxygen and moisture barrier properties, reduced coefficient of thermal expansion, and good solvent resistance in a cost effective manner.    DETAILED DESCRIPTION - Solution of polyamide, comprises an aromatic copolyamide, and a solvent, where the aromatic copolyamide comprises at least two amide repeat units of formulae (I) and (II), and at least one of the repeat unit has at least one free carboxylic acid group, and the amount of repeat unit containing the free carboxylic acid group is 1-30 mole% of the total repeat units.    n = 1-4;    X, Y1 = copolyamide that is soluble in polar aprotic solvents;    Ar1 = divalent groups of formulae (a1)-(a3);    p = 4;    q = 3;    R1-R10 = alkyl, alkoxy, aryl, alkyl ester (all optionally substituted), H and/or halo;    G1-G3 = covalent bond, CH2 group, C(CH3)2, C(CF3)2, or C(CX3)2;    X = optionally substituted 9,9-fluorene, halo, CO, O, S, SO2, Si(CH3)2, or OZO group;    Z = optionally substituted aryl;    Ar2 = divalent groups of formula (b1) or (b2);    Ar3 = divalent groups of formula (c1) or (c2);    m = 1 or 2; and    t = 1-3.    INDEPENDENT CLAIMS are included for:    (1) manufacturing the solution of an aromatic copolyamide, comprising either (a) forming a mixture of two or more aromatic diamines, where at least one of the diamines contains one or more free carboxylic acid groups, (b) dissolving the aromatic diamine mixture in a solvent, (c) reacting the diamine mixture with at least one aromatic diacid dichloride, where hydrochloric acid and a polyamide solution is generated, and (d) eliminating the hydrochloric acid with a reagent, or reacting a mixture of aromatic diamines with at least one aromatic diacid chloride in a solvent to form a polyamide, where a carboxyl group is incorporated along the polyamide backbone, and at least one of the diamines includes a pendant carboxylic acid groups of formula (NH2-Ar3(COOH)n-NH2) (III); and    (2) a process-I of manufacturing a display element, an optical element or an illumination element, comprising either the steps (a)-(d) as above per se, (e) applying the solution of an aromatic copolyamide onto a base, (f) forming a polyamide film on the base after the applying the step and (g) forming the display element, the optical element or the illumination element on the surface of the polyamide film, or the steps (e1)-(g1) as above per se.