NOVELTY - Polyimide obtained by imidizing polyimide precursor produced by primarily polymerizing 1,2,4,5-cyclohexanetetracarboxylic dianhydride isomers (I) with diamine-based compounds at 10-30 degrees C, and secondarily polymerizing at 30-65 degrees C, is claimed.    USE - The polyimide is useful to produce polyimide film for display substrate (all claimed), preferably flexible substrate of electronic devices (organic light-emitting diode, liquid-crystal display, electronic paper and solar cells).    ADVANTAGE - The polyimide improves permeability, and high heat resistance, excellent mechanical and low isotropic properties of polyimide film.    DETAILED DESCRIPTION - Polyimide obtained by imidizing polyimide precursor produced by primarily polymerizing 1,2,4,5-cyclohexanetetracarboxylic dianhydride isomers of formula (I) with diamine-based compounds at 10-30 degrees C, and secondarily polymerizing at 30-65 degrees C, is claimed.X = tetravalent organic moieties of formulae (IIa)-(IIc).    INDEPENDENT CLAIMS are also included for:    (1) preparing polyimide by the above method;    (2) polyamic acid of formula (VIII); and    (3) manufacturing display substrate, comprising (a) preparing polyimide film-forming composition comprising imide compound or the polyimide precursor, (b) coating the polyimide film-forming composition on one side of a support, and curing to obtain polyimide film, and (c) separating the polyimide film from the support.    X1 = tetravalent organic moieties of formulae (IXa)-(IXf);    A, A' = binding sites of amide groups with X1;    B, B' = binding sites of carboxyl groups with X1;    Y1 = aromatic divalent organic moieties of formulae (VIa)-(VId), alicyclic divalent organic moiety of formula (VIe), (4-18C)-cycloalkanediyl-containing alicyclic divalent organic group, divalent organic moiety of formula (VIf) or silane-containing divalent organic moiety of formula (VIg);    R21-R28 = 1-10C alkyl, halo, OH, carboxy, 1-10C alkoxy or 1-10C fluoroalkyl;    R31-R38 = H, 1-10C alkyl or phenyl;    A21, A22 = single bond, -O-, -CR'R''-, -C(=O)-, -C(=O)O-, -C(=O)NH-, -S-, -SO-, -SO2-, -O(CH2CH2O)y- -NH(C=O)NH-, -NH(C=O)O-, 6-18C monocyclic or polycyclic cycloalkylene or 6-18C monocyclic or polycyclic arylene;    R', R'' = H, 1-10C alkyl or 1-10C haloalkyl;    y = 1-44;    A23 = -(CR'R''-CH2O)z-;    z = 1-8;    b1, b4, b5 = 0-4;    b2 = 0-6;    b3 = 0-3;    b6, b9 = 0 or 1;    b7, b8 = 0-10; and    m, n = 1-15.