Polyimide-based block copolymer and polyimide-based film comprising the same

Abstract

The present disclosure relates to a polyimide-based block copolymer and a polyimide-based film including the same. The polyimide-based block copolymer according to the present disclosure makes it possible to provide a polyimide-based film exhibiting excellent mechanical properties while being colorless and transparent. The polyimide-based film may be used as a cover film of various flexible or foldable devices.

Claims

1. A polyimide-based block copolymer including a first repeating unit represented by Chemical Formula 1, a second repeating unit represented by Chemical Formula 2, and a third repeating unit represented by Chemical Formula 3: ##STR00023## in Chemical Formula 1, each R.sup.11 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).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CF.sub.3).sub.2, C(O)NH, or a C6 to C30 divalent aromatic organic group; each R.sup.12 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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 independently an integer of 0 to 3; each Y.sup.10 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, and the divalent 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 fluorenyl group, O, S, C(O), CH(OH), S(O).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or C(O)NH to form a divalent organic group; E.sup.11, E.sup.12, and E.sup.13 are independently a single bond or NH; and each Z.sup.10 is the same as or different from each other in each repeating unit, and each is independently a trivalent linking group derived from at least one compound selected from the group consisting of triacyl halide, tricarboxylic acid, and tricarboxylate,
*E.sup.21-Y.sup.20-E.sup.22-Z.sup.20-E.sup.23*[Chemical Formula 2]
*E.sup.31-Y.sup.30-E.sup.32-Z.sup.30-E.sup.33*[Chemical Formula 3] in Chemical Formulae 2 and 3, Y.sup.20 and Y.sup.30 are the same as or different from each other in each repeating unit, and each independently includes a C6 to C30 divalent aromatic organic group, and the divalent 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 fluorenyl group, O, S, C(O), CH(OH), S(O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or C(O)NH to form a divalent organic group; E.sup.21, E.sup.22, E.sup.23, E.sup.31, E.sup.32, and E.sup.33 are independently a single bond or NH; Z.sup.20 and Z.sup.30 are the same as or different from each other in each repeating unit, and each is independently a divalent linking group of a C(O)-A-C(O) form derived from at least one compound selected from the group consisting of diacyl halide, dicarboxylic acid, and dicarboxylate; in Z.sup.20 and Z.sup.30, A is a C6 to C20 divalent aromatic organic group, a C4 to C20 divalent heteroaromatic group, a C6 to C20 divalent alicyclic group, or a divalent organic group in which two or more of the organic groups are linked by a single bond, a fluorenyl group, O, S, C(O), CH(OH), S(O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or C(O)NH; two carbonyl groups linked to both sides of A in the Z.sup.20 are bonded to the meta position with respect to A; and two carbonyl groups linked to both sides of A in the Z.sup.30 are bonded to the para position with respect to A.

2. The polyimide-based block copolymer of claim 1, wherein the first repeating unit comprises a repeating unit represented by Chemical Formula 1-a: ##STR00024## in Chemical Formula 1-a, each R.sup.11 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).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(O)NH, or a C6 to C30 divalent aromatic organic group; R.sup.12 and R.sup.14 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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 independently an integer of 0 to 3; n2 and m2 are independently an integer of 1 to 4; E.sup.11, E.sup.12, and E.sup.13 are independently a single bond or NH; and each Z.sup.10 is the same as or different from each other in each repeating unit, and each is independently a trivalent linking group derived from at least one compound selected from the group consisting of triacyl halide, tricarboxylic acid, and tricarboxylate.

3. The polyimide-based block copolymer of claim 2, wherein R.sup.11 and R.sup.13 are the same as or different from each other in each repeating unit, and each is independently a single bond or C(CF.sub.3).sub.2; and Z.sup.10 is a trivalent linking group derived from at least one compound selected from the group consisting of 1,3,5-benzenetricarbonyl trichloride, 1,2,4-benzenetricarbonyl trichloride, 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, trimethyl benzenetricarboxylate, and trimethyl 1,2,4-benzenetricarboxylate.

4. The polyimide-based block copolymer of claim 1, wherein the first repeating unit comprises repeating units represented by Chemical Formula 1-b and 1-c: ##STR00025## in Chemical Formulae 1-b and 1-c, R.sup.12 and R.sup.14 are independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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 independently an integer of 0 to 3; and n2 and m2 are independently an integer of 1 to 4.

5. The polyimide-based block copolymer of claim 1, wherein Z.sup.30 is selected from the group represented by the following structural formulae: ##STR00026## in the structural formulae, R.sup.21 is H, F, Cl, Br, I, 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; a1 is an integer of 0 to 3; and a2 is an integer of 0 to 2.

6. The polyimide-based block copolymer of claim 1, wherein the second repeating unit comprises a repeating unit represented by Chemical Formula 2-a: ##STR00027## each R.sup.22 is the same as or different from each other in each repeating unit, and each is independently a single bond, a fluorenyl group, O, S, C(O), CH(OH), S(O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or C(O)NH; each R.sup.23 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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; n3 and m3 are independently an integer of 1 to 4; E.sup.21, E.sup.22, and E.sup.23 are independently a single bond or NH; and Z.sup.20 is selected from the group represented by the following structural formulae, ##STR00028##

7. The polyimide-based block copolymer of claim 1, wherein the second repeating unit comprises a repeating unit represented by Chemical Formula 2-b: ##STR00029## in Chemical Formula 2-b, each R.sup.23 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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; and n3 and m3 are independently an integer of 1 to 4.

8. The polyimide-based block copolymer of claim 1, wherein Z.sup.30 is selected from the group represented by the following structural formulae: ##STR00030## in the structural formulae, R.sup.31 and R.sup.32 are independently H, F, Cl, Br, I, 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; b1 and b2 are independently an integer of 0 to 3; and b3 is an integer of 0 to 2.

9. The polyimide-based block copolymer of claim 1, wherein the third repeating unit comprises a repeating unit represented by Chemical Formula 3-a: ##STR00031## in Chemical Formula 3-a, each R.sup.33 is the same as or different from each other in each repeating unit, and each is independently a single bond, a fluorenyl group, O, S, C(O), CH(OH), S(O).sub.2, Si(CH.sub.3).sub.2, (CH.sub.2).sub.p (wherein 1p10), (CF.sub.2).sub.q (wherein 1q10), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, or C(O)NH; each R.sup.34 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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; n4 and m4 are independently an integer of 1 to 4; E.sup.31, E.sup.32, and E.sup.33 are independently a single bond or NH; and Z.sup.30 is selected from the group represented by the following structural formulae, ##STR00032##

10. The polyimide-based block copolymer of claim 1, wherein the third repeating unit comprises a repeating unit represented by Chemical Formula 3-b or 3-c: ##STR00033## in Chemical Formulae 3-b and 3-c, each R.sup.32 is independently H, F, Cl, Br, I, CF.sub.3, CCl.sub.3, CBr.sub.3, CI.sub.3, NO.sub.2, CN, COCH.sub.3, CO.sub.2C.sub.2H.sub.5, 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; n4 and m4 are independently an integer of 1 to 4.

11. The polyimide-based block copolymer of claim 1, wherein the copolymer exhibits a .sup.1H NMR (300 MHz, DMSO-d6, TMS as standard material) spectrum having at least one peak within a range of 10.80 ppm to 11.00 ppm, and at least one peak within a range of 10.60 ppm to less than 10.80 ppm.

12. The polyimide-based block copolymer of claim 1, wherein a molar ratio of the first repeating unit:the second repeating unit is 1:0.1 to 1:10, and a molar ratio of the second repeating unit:the third repeating unit is 1:0.5 to 1:2.

13. The polyimide-based block copolymer of claim 1, wherein a weight average molecular weight is 100,000 to 5,000,000 g/mol.

14. A polyimide-based film comprising the polyimide-based block copolymer according to claim 1.

15. The polyimide-based film of claim 14, wherein pencil hardness is at least an HB grade, as measured in accordance with ASTM D3363.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an NMR spectrum of the polyimide-based copolymer obtained in Example 1.

(2) FIG. 2 is an NMR spectrum of the polyimide-based copolymer obtained in Comparative Example 1.

(3) FIG. 3 is an NMR spectrum of the polyimide-based copolymer obtained in Comparative Example 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) Hereinafter, preferred examples are provided for better understanding. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

Example 1

(5) 4.851 g (1.01 eq., 0.01515 mol) of 2,2-bis(trifluoromethyl)benzidine; 2.665 g (0.4 eq., 0.006 mol) of 4,4-(hexafluoroisopropylidene)diphthalic anhydride; 2.570 g (0.5825 eq., 0.008738 mol) of 3,3,4,4-biphenyltetracarboxylic dianhydride; 0.020 g (0.005 eq., 0.000075 mol) of 1,3,5-benzenetricarbonyl trichloride; and 73 ml of N,N-dimethylacetamide were placed to a 500 mL round flask equipped with a Dean-Stark apparatus and a condenser, and the mixture was stirred at 0 C. under a nitrogen atmosphere to carry out the polymerization reaction.

(6) After 4 hours, 4.755 g (0.99 eq., 0.01485 mol) of 2,2-bis(trifluoromethyl)benzidine; 1.553 g (0.51 eq., 0.00765 mol) of isophthaloyl dichloride; 2.093 g (0.5 eq., 0.0075 mol) of [1,1-biphenyl]-4,4-dicarbonyl dichloride; and 66 ml of N,N-dimethylacetamide were added to the product of the polymerization reaction, and the mixture was stirred at room temperature for 4 hours under a nitrogen atmosphere to carry out the polymerization reaction.

(7) 14 ml of acetic anhydride and 12 ml of pyridine were added to the polyamic acid solution obtained by the polymerization reaction, and the mixture was stirred in an oil bath at 40 C. for 15 hours to carry out the chemical imidization reaction.

(8) After completion of the reaction, the solid content was precipitated with water and ethanol, and the precipitated solid was filtered and dried at 100 C. for more than 6 hours under vacuum to obtain a polyimide-based block copolymer having the following repeating units (weight average molecular weight: 250,000 g/mol). The .sup.1H NMR (300 MHz, DMSO-d6, TMS as standard material) spectrum of the polyimide-based block copolymer is shown in FIG. 1.

(9) ##STR00019##

Example 2

(10) A polyimide-based copolymer was obtained in the same manner as in Example 1, except that the content of the monomers in the polymerization reaction was changed to 0.944 g (0.31 eq., 0.00465 mol) of isophthaloyl dichloride and 2.93 g (0.7 eq., 0.0105 mol) of [1,1-biphenyl]-4,4-dicarbonyl dichloride (weight average molecular weight: 600,000 g/mol).

Comparative Example 1

(11) 3.203 g (1.01 eq., 0.0101 mol) of 2,2-bis(trifluoromethyl)benzidine; 4.3647 g (0.9825 eq., 0.009825 mol) of 4,4-(hexafluoroisoproylidene)diphthalic anhydride; 0.0133 g (0.005 eq., 0.00005 mol) of 1,3,5-benzenetricarbonyl trichloride; and 73 ml of N,N-dimethylacetamide were placed to a 250 mL round flask equipped with a Dean-Stark apparatus and a condenser, and the mixture was stirred at 0 C. under a nitrogen atmosphere to carry out the polymerization reaction.

(12) After 4 hours, 9.575 g (2.99 eq., 0.0299 mol) of 2,2-bis(trifluoromethyl)benzidine; 6.1109 g (3.01 eq., 0.0301 mol) of isophthaloyl dichloride; and 66 ml of N,N-dimethylacetamide were added to the product of the polymerization reaction, and the mixture was stirred at room temperature for 4 hours under a nitrogen atmosphere to carry out the polymerization reaction.

(13) 14 ml of acetic anhydride and 12 ml of pyridine were added to the polyamic acid solution obtained by the polymerization reaction, and the mixture was stirred in an oil bath at 40 C. for 15 hours to carry out the chemical imidization reaction.

(14) After completion of the reaction, the solid content was precipitated with water and ethanol, and the precipitated solid was filtered and dried at 100 C. for more than 6 hours under vacuum to obtain a polyimide-based block copolymer having the following repeating units (weight average molecular weight: 700,000 g/mol). The .sup.1H NMR (300 MHz, DMSO-d6, TMS as standard material) spectrum of the polyimide-based block copolymer is shown in FIG. 2.

(15) ##STR00020##

Comparative Example 2

(16) 4.851 g (1.01 eq., 0.01515 mol) of 2,2-bis(trifluoromethyl)benzidine; 2.665 g (0.4 eq., 0.006 mol) of 4,4-(hexafluoroisopropylidene)diphthalic anhydride; 2.570 g (0.5825 eq., 0.008738 mol) of 3,3,4,4-biphenyltetracarboxylic dianhydride; 0.0199 g (0.005 eq., 0.000075 mol) of 1,3,5-benzenetricarbonyl trichloride; and 58 ml of N,N-dimethylacetamide were placed to a 250 mL round flask equipped with a Dean-Stark apparatus and a condenser, and the mixture was stirred at 0 C. under a nitrogen atmosphere to carry out the polymerization reaction.

(17) After 4 hours, 4.755 g (0.99 eq., 0.01485 mol) of 2,2-bis(trifluoromethyl)benzidine; 3.075 g (1.01 eq., 0.0101 mol) of terephthaloyl chloride; and 120 ml of N,N-dimethylacetamide were added to the product of the polymerization reaction, and the mixture was stirred at room temperature for 4 hours under a nitrogen atmosphere to carry out the polymerization reaction.

(18) 14 ml of acetic anhydride and 12 ml of pyridine were added to the polyamic acid solution obtained by the polymerization reaction, and the mixture was stirred in an oil bath at 40 C. for 15 hours to carry out the chemical imidization reaction.

(19) After completion of the reaction, the solid content was precipitated with water and ethanol, and the precipitated solid was filtered and dried at 100 C. for more than 6 hours under vacuum to obtain a polyimide-based block copolymer having the following repeating units (weight average molecular weight: 300,000 g/mol). The .sup.1H NMR (300 MHz, DMSO-d6, TMS as standard material) spectrum of the polyimide-based block copolymer is shown in FIG. 3.

(20) ##STR00021##

Comparative Example 3

(21) 4.80 g (1 eq., 0.015 mol) of 2,2-bis(trifluoromethyl)benzidine; 6.56 g (0.985 eq., 0.0148 mol) of 4,4-(hexafluoroisopropylidene)diphthalic anhydride; 1.5227 g (0.5 eq., 0.0075 mol) of isophthaloyl dichloride; 0.039 g (0.01 eq., 0.00015 mol) of benzene-1,3,5-tricarbonyl trichloride; and 70 ml of N,N-dimethylacetamide were placed to a 250 mL round flask equipped with a Dean-Stark apparatus and a condenser, and the reaction was initiated at room temperature.

(22) 14 ml of acetic anhydride and 12 ml of pyridine were added to the mixture, and then stirred in an oil bath at 40 C. for 15 hours to carry out the chemical imidization reaction.

(23) After completion of the reaction, the solid content was precipitated with water and ethanol, and the precipitated solid was filtered and dried at 100 C. for more than 6 hours under vacuum to obtain a polyimide-based block copolymer having the following repeating units (weight average molecular weight: 160,000 g/mol).

(24) ##STR00022##

(25) .sup.1H NMR (CDCl.sub.3, TMS as standard material) (ppm): 10.854(s), 8.644(s), 8.256(m), 8.162(d), 8.044(s), 8.017(d), 7.851(d), 7.816(m), 7.7(d), 7.430(d)

Example 3

(26) The copolymer obtained in Example 1 was dissolved in N,N-dimethylacetamide to prepare a polymer solution of about 25% (w/V). The polymer solution was poured on a glass plate, casted to a thickness of 335 m using a film applicator, and dried with hot air at 80 C. for 10 minutes (repeated twice). It was then slowly heated from 100 C. to 250 C. for 2 hours while flowing nitrogen therein, maintained at 250 C. for 30 minutes, and then gradually cooled down to obtain a film having a thickness of 302 m after being peeled off from the glass plate.

(27) Separately, a film having a thickness of 502 m was obtained by the above-described method using the polymer solution.

Example 4

(28) A film having a thickness of 302 m and a film having a thickness of 502 m were obtained respectively in the same manner as in Example 3, except that the copolymer obtained in Example 2 was used in place of the copolymer obtained in Example 1.

Comparative Example 4

(29) A film having a thickness of 302 m and a film having a thickness of 502 m were respectively obtained in the same manner as in Example 3, except that the copolymer obtained in Comparative Example 1 was used in place of the copolymer obtained in Example 1.

Comparative Example 5

(30) A film having a thickness of 302 m and a film having a thickness of 502 m were respectively obtained in the same manner as in Example 3, except that the copolymer obtained in Comparative Example 2 was used in place of the copolymer obtained in Example 1.

Comparative Example 6

(31) A film having a thickness of 302 m and a film having a thickness of 502 m were respectively obtained in the same manner as in Example 3, except that the copolymer obtained in Comparative Example 3 was used in place of the copolymer obtained in Example 1.

Experimental Examples

(32) The following characteristics were evaluated for the films obtained in the above examples and comparative examples, and the results are shown in Table 1 below.

(33) (1) Pencil Hardness

(34) The pencil hardness of the films having a thickness of 302 m were measured in accordance with ASTM D3363 (750 gf) using a Pencil Hardness Tester.

(35) Specifically, varying hardness values of pencils were fixed to the tester and scratched on the film, and the degree of occurrence of a scratch on the film was observed with the naked eye or with a microscope. When more than 70% of the total number of scratches were not observed, a value corresponding to the hardness of the pencil was evaluated as the pencil hardness of the film.

(36) (2) Mechanical Properties

(37) The elastic modulus (EM, GPa), the ultimate tensile strength (TS, MPa), and the tensile elongation (TE, %) of the films having a thickness of 302 m were measured in accordance with ASTM D 882 using a universal testing machine.

(38) (3) Yellow Index (Y.I.)

(39) The yellow index of the films having a thickness of 302 m was measured in accordance with ASTM D1925 using a UV-2600 UV-Vis Spectrometer (SHIMADZU).

(40) (4) Haziness

(41) The haziness of the films having a thickness of 302 m was measured in accordance with ASTM D1003 using a COH-400 Spectrophotometer (NIPPON DENSHOKU INDUSTRIES).

(42) (5) Folding Endurance

(43) The folding endurance of the films was evaluated using an MIT type folding endurance tester. Specifically, a specimen (1 cm7 cm) of the film was loaded into the folding endurance tester, and folded to an angle of 135 at a rate of 175 rpm on the left and right sides of the specimen, with a radius of curvature of 0.8 mm and a load of 250 g, until the specimen was fractured. The number of reciprocating bending cycles was measured as the folding endurance.

(44) (6) Processability

(45) The degree of transparency of the film having a thickness of 502 m was observed with the naked eye as compared with the film having a thickness of 302 m. When the transparency indicated by the film having a thickness of 502 m was equal to that of the film having a thickness of 302 m, the film was evaluated as having good processability (0), and when the transparency was degraded (for example, was blurry), the film was evaluated as having bad processability (X).

(46) TABLE-US-00001 TABLE 1 Film Comparative Comparative Comparative Example 3 Example 4 Example 4 Example 5 Example 6 Copolymer Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Pencil hardness HB H 4B HB 4B EM (GPa) 3.31 4.99 2.53 3.42 TS (MPa) 142 205 95 148 TE (%) 13 15 16.7 12 Y.I. 2.51 3.23 1.98 2.96 2.5 Haziness 0.38 0.47 0.61 1.23 Folding (cycle) 310,000 310,000 250,000 20,000 58,000 Processability X

(47) Referring to Table 1, it was confirmed that the films of Examples 2 and 3 had low yellow index and haziness, thereby exhibiting excellent mechanical properties and high pencil hardness while being colorless and transparent. The copolymers of Examples 1 and 2 also exhibited transparency equivalent to the film having a thickness of 302 m even when formed into a film having a thickness of 502 m, thus it was confirmed that the processability was good.

(48) The film of Comparative Example 4 showed colorlessness and transparency similar to that of the films according to the examples, but it showed low pencil hardness and poor mechanical properties.

(49) The film of Comparative Example 5 showed pencil hardness and mechanical properties similar to that of the films according to the examples, but it showed poor folding endurance. Further, it was confirmed that the copolymer of Comparative Example 2 had poor processability, because when the copolymer was molded into the film having a thickness of 502 m, it became very hazy compared with the film having a thickness of 302 m.

(50) The film of Comparative Example 6 showed a similar yellow index to that of the films according to the examples, but it showed poor pencil hardness and folding endurance.