Polyimide-based polymer film, substrate for display device, and optical device using the same

A polyimide-based resin film comprising a polyimide-based resin including a polyimide repeating unit represented by Chemical Formula 1 and a polyimide repeating unit represented by Chemical Formula 5,

• wherein a coefficient of thermal expansion over the range of 100° C. or more and 430° C. or less is 20 ppm/° C. or less:
• in the Chemical Formula 1, X1 is a tetravalent functional group represented by Chemical Formula 2,
• Y1 is the same as or different from Y2 and is an aromatic divalent functional group having at least 15 carbon atoms in which at least one electron-withdrawing group is substituted,
• in the Chemical Formula 2, Ar is a polycyclic aromatic divalent functional group,
• in the Chemical Formula 5,
• X2 is one of the tetravalent functional groups represented by the following Chemical Formula 6, and
• Y2 is the same as or different from Y1 and is an aromatic divalent functional group having at least 15 carbon atoms in which at least one electron-withdrawing group is substituted,
• in the Chemical Formula 6, R1 to R6 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, each L is independently a single bond, —O—, —CO—, —COO—, —S—, —SO—, —SO2—, —CR7R8—, —(CH2)t—, —O(CH2)tO—, —COO(CH2)tOCO—, —CONH—, or phenylene, where R7 and R8 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, or a haloalkyl group having 1 to 10 carbon atoms, and t is an integer of 1 to 10, and
• wherein the aromatic divalent functional group of Y1 includes a functional group represented by Chemical Formula 3:
• in the Chemical Formula 3,
• T1 to T3 are the same as or different from each other, and each independently, an electron-withdrawing group,
• m1 to m3 are the same as or different from each other, at least one of m1 to m3 is an integer of 1 to 4, the rest are an integer of 0 to 4, and
• n is an integer of 1 to 10.