Polyimide film for display substrate

A polyimide film for a flexible display substrate comprising a polyimide, which has a thickness of 5 to 20 μm, and has a stress variation of 0 to 5, wherein the stress variation is a difference in values of residual stress at a temperature of 350° C. and at a temperature of 500° C. while the film on a silicon wafer is subject to heating and cooling at a temperature ranging from 350 to 500° C.

• wherein the polyimide comprises an end-capped polyimide including a polymerization product of a diamine, an acid dianhydride and an end-capping agent, and
• the end capping agent is in an amount of 1 to 10 parts by weight based on 100 parts weight of the sum of the acid dianhydride and the diamine,
• wherein the polyimide film comprises a heat-cured product of a polyimide precursor solution comprising a polyimide precursor and an organic solvent having a positive value of LogP, and the organic solvent having a positive value of Log P comprises diethylpropionamide (DEPA), and
• wherein the polyimide has a repeat unit of formula 6 and a repeat unit of formula 6a:
• wherein, R1, R2 and R3 are hydrogen atom;
• wherein, R4 and R5 are hydrogen atom and R6 and R7 are each independently C1-10 fluoroalkyl, and
• wherein the repeat unit of formula 6 is formed from p-phenylene diamine (p-PDA), the repeat unit of formula 6a is formed from bis(trifluoromethyl)benzidine (TFMB), and a ratio of p-PDA to TFMB is 90:10 to 95:5.