Poly(amide-imide) copolymer film, window for display device, and display device

1. A poly(amide-imide) copolymer film having a tensile modulus of greater than or equal to 5.4 gigapascals, and a yellowness index of less than or equal to 3.6,

wherein the poly(amide-imide) copolymer film is a reaction product of an aromatic dianhydride comprising biphenyl tetracarboxylic dianhydride in an amount of greater than or equal to 10 mole percent and less than or equal to 45 mole percent and 4,4′-hexafluoroisopropylidene diphthalic dianhydride in an amount of greater than or equal to 10 mole percent and less than or equal to 30 mole percent, an aliphatic dianhydride comprising 1,2,3,4-cyclobutane tetracarboxylic dianhydride in an amount of greater than or equal to 5 mole percent and less than or equal to 45 mole percent, an aromatic dicarbonyl compound comprising terephthaloyl dichloride in an amount of greater than or equal to 25 mole percent and less than or equal to 75 mole percent, and an aromatic diamine comprising 2,2-bis(trifluoromethyl) benzidine, wherein the mole percent for each of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound is based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

2. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of 1,2,3,4-cyclobutane tetracarboxylic dianhydride is greater than or equal to 10 mole percent and less than or equal to 25 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

3. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of 1,2,3,4-cyclobutane tetracarboxylic dianhydride is greater than or equal to 10 mole percent and less than or equal to 45 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

4. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of terephthaloyl dichloride is greater than or equal to 30 mole percent and less than or equal to 70 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

5. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of terephthaloyl dichloride is greater than or equal to 30 mole percent and less than or equal to 65 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

6. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of biphenyl tetracarboxylic dianhydride is greater than or equal to 10 mole percent and less than or equal to 21.7 mole percent based on 100 mole percent of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

7. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of 4,4′-hexafluoroisopropylidene diphthalic dianhydride is greater than or equal to 10 mole percent and less than or equal to 16.5 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

8. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of 4,4′-hexafluoroisopropylidene diphthalic dianhydride is greater than or equal to 10.5 mole percent and less than or equal to 15 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

9. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount of 1,2,3,4-cyclobutane tetracarboxylic dianhydride is greater than or equal to 10 mole percent and less than or equal to 45 mole percent, and the amount of terephthaloyl dichloride is greater than or equal to 30 mole percent and less than or equal to 70 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

10. The poly(amide-imide) copolymer film according to claim 1 , wherein biphenyl tetracarboxylic dianhydride comprises at least one of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,3,3′,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, or a combination thereof.

11. The poly(amide-imide) copolymer film according to claim 1 , wherein the film has a light transmittance of greater than or equal to 88% in a wavelength range of 380 nanometers to 780 nanometers.

12. The poly(amide-imide) copolymer film according to claim 1 , wherein the amount terephthaloyl dichloride is greater than or equal to 30 mole percent and less than or equal to 65 mole percent, the amount of biphenyl tetracarboxylic dianhydride is greater than or equal to 10 mole percent and less than or equal to 21.7 mole percent, and the amount of 4,4′-hexafluoroisopropylidene diphthalic dianhydride is greater than or equal to 10 mole percent and less than or equal to 16.5 mole percent based on the total mole number of the aromatic dianhydride, the aliphatic dianhydride, and the aromatic dicarbonyl compound.

13. The poly(amide-imide) copolymer film according to claim 1 , wherein the tensile modulus is greater than or equal to 5.4 gigapascals and less than or equal to 7.5 gigapascals, and wherein the yellowness index of from is greater than or equal to 2.8 and less than or equal to 3.6.

14. A window for a display device comprising the poly(amide-imide) copolymer film according to claim 1 .

15. The window according to claim 14 , wherein the window further comprises a hard coating layer disposed on at least one surface of the poly(amide-imide) copolymer film.

16. The window according to claim 15 , wherein the hard coating layer comprises at least one selected from an acrylate polymer, a polycaprolactone, a urethane-acrylate copolymer, a polyrotaxane, an epoxy polymer, an organosilicone material, an inorganic hard coating material, or a combination thereof.

17. A display device comprising the window for a display device according to claim 14 .

18. The display device according to claim 17 , wherein the display device is a flexible display device.