Cover window for flexible display device and flexible display device

A cover window for a flexible display device, comprising:

• a polymer substrate comprising a polyamideimide block copolymer having a repeating unit containing an aromatic group;
• and
• a hard coating layer formed on at least one surface of the polymer substrate and having a pencil hardness of at least 5H under a load of 750 g,
• wherein no crack occurs on the cover window when the cover window is wound on a mandrel having a diameter of 3 mm,
• wherein the polyamideimide block copolymer comprises an imide block having a first repeating unit represented by Chemical Formula 1;
• and
• an amide block having a second repeating unit represented by Chemical Formula 2 and a third repeating unit represented by Chemical Formula 3:
• in the Chemical Formula 1,
• each R1 is the same as or different from each other in each repeating unit, and each is independently a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)2—, —Si(CH3)2—, —(CH2)p— (wherein, 1=p≤=10), —(CF2)q— (wherein, 1=q≤=10), —C(CH3)2—, —C(CF3)2—, —C(═O)NH—, or a C6 to C30 divalent aromatic organic group;
• each R2 is the same as or different from each other in each repeating unit, and each is independently —H, —F, —Cl, —Br, —I, —CF3, —CCl3, —CBr3, —Cl3, —NO2, —CN, —COCH3, —CO2C2H5, a silyl group containing three C1 to C10 aliphatic organic groups, a C1 to C10 aliphatic organic group, or a C6 to C20 aromatic organic group;
• n1 and m1 are each independently an integer of 0 to 3;
• each Y1 is the same as or different from each other in each repeating unit, and each independently comprises a C6 to C30 divalent aromatic organic group containing at least one trifluoromethyl group (—CF3);
• and the aromatic organic group exists alone, or two or more aromatic organic groups are bonded to each other to form a divalent condensed ring, or two or more aromatic organic groups are linked by a single bond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)2—, —Si(CH3)2—, —(CH2)1— (wherein, 1=p≤=10), —(CF2)q— (wherein, 1=q≤=10), —C(CH3)2—, —C(CF3)2—, or —C(═O)NH—;
• and
• each E1 is independently a single bond, or —NH—;
• in the Chemical Formulae 2 and 3,
• Y2 and Y2′ are the same as or different from each other in each repeating unit, and each is independently a C6 to C30 divalent aromatic organic group containing at least one trifluoromethyl group (—CF3);
• and the aromatic organic group exists alone, or two or more aromatic organic groups are bonded to each other to form a divalent condensed ring, or two or more aromatic organic groups are linked by a single bond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)2—, —Si(CH3)2—, —(CH2)p— (wherein, 1=p≤=10), —(CF2)q— (wherein, 1=q≤=10), —C(CH3)2—, —C(CF3)2—, or —C(═O)NH—;
• and
• E2, E2′, E3, E3′, E4 and E4′ are independently a single bond, or —NH—, and
• wherein a molar ratio of the imide block:the amide block is 3:7 to 4:6, and a molar ratio of the second repeating unit:
• the third repeating unit is 30:70 to 45:55.