HIGH MODULUS COLORLESS POLYIMIDE FILM AND METHOD OF PREPARATION

Abstract

A polyimide precursor solution is disclosed, and a colorless transparent polyimide film manufactured from the polyimide precursor solution. The polyimide precursor solution has diamines, a first dianhydride represented by biphenyl dianhydride, a second dianhydride represented by rigid alicyclic dianhydride, a third dianhydride represented by non-alicyclic dianhydrides and organic solvent. The colorless polyimide films have a modulus of 4.5 GPa or higher, a glass-transition temperature (T.sub.g) of 370° C. or higher, and a yellow index of 3.0 or lower. These polyimide films can be used as substrates for thin film transistor (TFT), touch sensor panel (TSP), and cover window applications in flexible display such as organic light-emitting diode (OLED), flexible liquid crystal display (LCD) and other fields.

Claims

1. A polyimide precursor solution manufactured by reacting, in an organic solvent: one or more diamines; a first dianhydride represented by biphenyl dianhydride; a second dianhydride represented by rigid alicyclic dianhydride, and a third dianhydride represented by non-alicyclic dianhydride; wherein relative to all dianhydrides which can be considered as 100 mol %, the first dianhydride containing biphenyl structure is in an amount of 10 to 80 mol %; the second dianhydride represented by rigid alicyclic dianhydride is in an amount of 10 to 80 mol %; and the third dianhydride represented by non-alicyclic dianhydride is in an amount of 10 to 80 mol %.

2. The polyimide precursor solution of claim 1, wherein: the one or more diamines are selected from the group consisting of: 1,3-diamino-2,4,5,6-tetrafluorobenzene, 2-(trifluoromethyl) benzene-1,4-diamine, 4,4′-diaminooctafluorobiphenyl, 2,2′-bis(trifluoromethyl) benzidine and combinations thereof.

3. The polyimide precursor solution of claim 1, wherein: the first dianhydride comprises biphenyl dianhydrides which can be represented by Structural Formula (I): ##STR00004## such that R.sub.1 and R.sub.2 are each independently selected from a hydrogen (—H), a halogen atom such as —F, —Cl, —Br, —I, a nitro group (—NO.sub.2), a C.sub.1-4 halogenoalkoxyl group, a C.sub.1-10 alkyl group, a C.sub.1-10 halogenoalkyl group, a C.sub.6-20 aryl group and a C.sub.1-10 alkyl group; the second dianhydride comprises rigid alicyclic dianhydrides represented by Structural Formula (II): ##STR00005## wherein the Ac is selected from any of the following groups: ##STR00006## and the third dianhydride comprises one or more selected from the group consisting of: 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(phthalic anhydride) fluorene, 4,4′-(4,4′-isopropylidenediphenoxy)diphthalic anhydride, 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride and 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride.

4. The polyimide precursor solution of claim 1, wherein the organic solvent is selected from the group consisting of: N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), m-cresol, ethyl acetate, acetone, γ-butyrolactone and combinations thereof.

5. A colorless and transparent polyimide film manufactured from the polyimide precursor solution of claim 1.

6. The polyimide film of claim 5, having at least the following features: a yellow index of 3.0 or less; a Young's modulus of 4.5 GPa or higher, with a tensile strength exceeding 110 MPa; a glass-transition temperature (T.sub.g) of at least 370° C.; and a transmittance of at least 89% at 550 nm, with a haze not exceeding 1.0%.

7. A method for manufacturing the transparent polyimide film of claim 5, comprising a thermal imidization process, a chemical imidization process or some other imidization processes.

8. The method of claim 7, wherein the chemical imidization process comprises the steps of: mixing the polyimide precursor solution of claim 1 with a catalyst and a dehydrant and stirring for 1 to 12 hours to obtain a mixture; casting the mixture on a glass plate or other substrate, and drying to remove the solvent, obtaining a semi-dried film; and producing the transparent polyimide film from the semi-dried film.

9. The method of claim 8, wherein the step of drying to remove the solvent is achieved at a temperature of 50 to 180° C. for 8 to 60 minutes.

10. The method of claim 8, wherein the step of obtaining the transparent polyimide film is achieved by directly heating the film again at a high temperature.

11. The method of claim 8, wherein the step of obtaining the transparent polyimide film is achieved by peeling the film off of the glass substrate, fixing the film on a stainless-steel frame, and heating the peeled film at the highest temperature range of 250 to 500° C. for a time of 10 to 120 minutes.

12. The method of claim 8, wherein: the catalyst is selected from the group consisting of: pyridine, isoquinoline compounds, quinolone compounds, imidazole compounds, benzimidazole compounds, and combinations thereof; and the dehydrant is selected from the group consisting of: acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, and combinations thereof.

13. A flexible display and cover window, comprising: a substrate of the colorless and transparent polyimide film of claim 5.

Description

BEST MODE

[0038] Hereinafter, the present invention will be described more fully with reference to the following embodiments. Furthermore, the embodiments are not limited to the aspects described in the present description.

[0039] The chemical reagents used in the embodiment are all commercial products.

[0040] The methods involved in the embodiments for measuring the properties are as described as below:

(1) Light Transmittance, b*, Yellow Index and Haze

[0041] The Light Transmittance, b value, yellow index and Haze of polyimide films were measured using a spectrophotometer (X-rite Ci7800), all the values were averaged.

(2) Glass-Transition Temperature (T.SUB.g.)

[0042] The glass-transition temperature of polyimide films were measured with method of Dynamic Mechanical Analyzer (DMA850) under the conditions of load of 0.05N, a heating rate of 3° C./min and a nitrogen atmosphere at 200° C. to 500° C., and then an inflection point of a curve with the max value was recorded as a glass-transition temperature.

(3) The Thermal Expansion Coefficient (CTE)

[0043] The thermal expansion coefficient of polyimide films were measured two times in the range of 50˜250° C. with the method of Thermomechanical Analyzer (TMA 7100C) under the conditions of a load of 20 mN, a heating rate of 10° C./min with the first test, and a heating rate of 5° C./min with the second test.

(4) Mechanical Properties (Elongation, Tensile Stress, Young's Modulus)

[0044] The mechanical properties including tensile stress, elongation and Young's modulus of polyimide films were measured using an electronic universal testing machine (CMT2103) at a rate of 100 mm/min.

EXAMPLE 1

[0045] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 226.158 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 11.7688 g (0.04 mol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 9.8055 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0046] The polyimide film can be obtained by imidizing the polyimide precursor solution with the method of thermal imidization and chemical imidization.

[0047] Thermal imidization was described in detail as the following steps: the polyimide precursor solution above was cast and spread on a glass support, then heated in an oven with the temperature of 100° C. for 12 min to remove most of the solvent, and then heated at a temperature of 300° C. again to finish the imidization or peeled off from the glass support and fixed on stainless steel frame, then placed the stainless steel frame with the film above into a nitrogen oven and heated from 150° C. to 300° C. at a rate of 5° C./min, and kept at 300° C. for 15 min, then slowly cooled and separated from the frame, thus obtaining the polyimide film.

[0048] Chemical imidization was described in detail as the following steps: 6.29 g of pyridine and 8.12 g of acetic anhydride were added to 100 g of polyimide precursor solution with stirring for 2-12 hr. Then the mixture was cast and spread on a glass substrate and dried in an oven at a temperature of 100° C. for 12 min to remove most of the solvent, and then heated at a temperature of 300° C. again to finish the imidization, or peeled off from the glass support and fixed on a stainless steel frame, then placed the stainless steel frame with the film above into a nitrogen oven and heated from 150° C. to 300° C. at a rate of 5° C./min and kept at 300° C. for 15 min, then slowly cooled and separated from the frame, thus obtaining the polyimide film.

EXAMPLE 2

[0049] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 240.236 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 13.3272 g (0.03 mol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 11.767 g (0.06 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0050] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.55 g of pyridine and 8.46 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 3

[0051] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 230.31 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 8.8848 g (0.02 mol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 13.73 g (0.07 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0052] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.84 g of pyridine and 8.83 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 4

[0053] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 273.42 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 27.5058 g (0.06 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 5.8833 g (0.03 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0054] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 5.76 g of pyridine and 7.43 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 5

[0055] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 252.43 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 18.3372 g (0.04 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 9.8055 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0056] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.24 g of pyridine and 8.05 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 6

[0057] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 231.446 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 9.1686 g (0.02 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF), 2.9422 g (0.01 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 13.73 g (0.07 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0058] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.8 g of pyridine and 8.78 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 7

[0059] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 252.388 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 11.46 g (0.025 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF), 14.711 g (0.05 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 4.903 g (0.025 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0060] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.49 g of pyridine and 8.38 g of acetic anhydride to the 100 g of polyimide precursor solution.

EXAMPLE 8

[0061] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 242.596 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 11.46 g (0.025 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF), 7.356 g (0.025 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 9.81 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0062] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 6.24 g of pyridine and 8.05 g of acetic anhydride to the 100 g of polyimide precursor solution.

COMPARATIVE EXAMPLE 1

[0063] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 305.788 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 44.424 g (0.1 mol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0064] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 5.14 g of pyridine and 6.64 g of acetic anhydride to the 100 g of polyimide precursor solution.

COMPARATIVE EXAMPLE 2

[0065] The nitrogen was passed through a 500 mL three-neck round bottom flask reactor which was equipped with a stirrer, a nitrogen inlet and a thermometer, 311.264 g of N,N-dimethylacetamide (DMAc) was placed in the reactor as a solvent. Then 32.023 g (0.1 mol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) was dissolved therein. Thereafter, 45.843 g (0.1 mol) of 9,9′-bis(phthalic anhydride) fluorene (BPAF) was added thereto. The resulting solution was kept at room temperature and reacted for 8-48 hr., thus obtaining a polyimide precursor solution with the solid content of 20 wt. %.

[0066] The polyimide film was formed in the same way as in example 1 with the method of thermal imidization and chemical imidization. Wherein, the chemical imidization was carried out by adding 5.05 g of pyridine and 6.52 g of acetic anhydride to the 100 g of polyimide precursor solution.

[0067] The following properties of the polyimide films manufactured in examples and comparative examples above were measured: (1) Light Transmittance, b*, yellow index and Haze; (2) Glass-Transition Temperature (Tg); (3) The Thermal Expansion Coefficient (CTE); (4) Mechanical Properties (elongation, tensile stress, Young's modulus); (5) 5% weight loss temperature. Data from the above experiments are presented below in Tables 1 through 3. In Tables 1 and 2, the symbol “/” means that the film produced was very brittle and unable to be measured.

[0068] Properties of the films from thermal imidization and chemical imidization methods are shown in Tables 1 to 3, respectively. According to these results, the polyimide films of Examples 1 to 8 have high transparency, a yellow index of 3 or less, a Young's modulus of 4.5 GPa or more, and a tensile strength of 110 MPa or higher. In addition, the polyimide films according to the present invention also have glass-transition temperatures (T.sub.g) of 370° C. or higher. Besides, the Examples 1 to 8 in Tables 1 to 3 show that the Young's modulus of polyimide films can be increased by introducing biphenylene and rigid alicyclic structure contents, and when these structural contents increased, polyimide films modulus were also increased. Therefore, by comparing Comparative Example 1 with Examples 1 through 3, and Comparative Example 2 with Examples 4 through 8, when biphenylene and rigid alicyclic structures were introduced, the Young's modulus have been significantly increased.

[0069] Further, and as demonstrated in Tables 1 to 3 described above, the Examples and comparative Examples show that the polyimide films made with the method of thermal imidization method are colored and more brittle with poor mechanical and thermal properties, compared to the films made with the chemical imidization method. The polyimide films of the present invention made by the chemical imidization method show better properties.

[0070] In conclusion, the polyimide films according to the present invention can improve Young's modulus by the introduction of biphenylene and rigid alicyclic structures into the backbone of the polymer, that also possess high heat resistance and transparency at the same time. In addition, in the present invention the transparent polyimide films with better properties can only be manufactured by the method of chemical imidization, and thus achieved these excellent optical, mechanical properties and thermal properties required for the display applications.

TABLE-US-00001 TABLE 1 Thermal imidization method Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 1 Ex. 2 diamine TFMB 100 100 100 100 100 100 100 100 100 100 dianhydride 6FDA 40 30 20 100 s-BPDA 10 10 10 10 10 10 25 50 BPAF 60 40 20 25 25 100 CBDA 50 60 70 30 50 70 50 25 film thickness (μm) 22 23.5 22.5 / / / / / 20 / Transmittance 400-700 nm 89.4 89.3 89.2 / / / / 88.9 / / (%) 550 nm 90.5 90.4 90.3 / / / / 90.26 / / b* 1.6 1.6 1.7 / / / / / 1.7 / YI 2.7 2.8 3.0 / / / / / 2.3 / Elongation (%) / / / / / / / / 9.03 / Tensile strength (Mpa) / / / / / / / / 123.0 / Young's modular (Gpa) 4.5 / / / / / / / 3.6 / Haze (%) 0.1 0.1 0.0 / / / / / 0.3 / T.sub.g (° C.) / / / / / / / / 337 / CTE 1.sup.st scan 34.45 31.4 27.5 / / / / / 39 / (ppm/° C.; 50-250 C.) CTE 2.sup.nd scan 63.4 53.4 51.1 / / / / / 65.94 / (ppm/° C.; 50-250 C.) 5% weight loss temperature/° C. 459.7 470.7 480.3 / / / / / 477.2 /

TABLE-US-00002 TABLE 2 Chemical imidization method (polymer cured on stainless steel frame) Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 1 Ex. 2 Diamine TFMB 100 100 100 100 100 100 100 100 100 100 dianhydride 6FDA 40 30 20 100 s-BPDA 10 10 10 10 10 10 25 50 BPAF 60 40 20 25 25 100 CBDA 50 60 70 30 50 70 50 25 film thickness (μm) 20 21 31.5 27.5 27.0 21.5 22 23 25.0 29.0 Transmittance 400-700 nm 89.8 89.2 88.7 88.5 88.3 88.4 88.2 88.0 90.7 88.5 (%) 550 nm 90.4 89.9 89.6 89.4 89.1 89.3 89.1 89.0 90.9 89.0 b* 0.8 1.0 1.3 0.9 1.0 1.2 1.4 1.3 0.4 0.8 YI 1.4 1.8 2.2 1.7 1.8 2.1 2.5 2.4 1.4 1.5 Elongation (%) 11.9 12.5 16.2 4.3 5.3 11.2 10.8 11.1 6.9 3.5 Tensile strength (Mpa) 153.6 173.5 193.4 114.6 131.1 223.7 157.5 158.1 132.9 107.9 Young's modulus (Gpa) 4.9 5.7 6.3 4.6 4.9 6.8 5.8 5.7 3.3 3.8 Haze (%) 0.3 0.3 0.5 0.4 0.4 0.6 0.2 0.3 0.4 0.8 T.sub.g (° C.) 376.5 373.7 373.9 385.3 389.3 387.6 377.8 375.5 340.7 414.3 CTE 1.sup.st scan 15.9 9.5 10.8 19.9 12.4 2.0 5.2 3.9 30 39.7 (ppm/° C.; 50-250 C.) CTE 2.sup.nd scan 38.6 27.3 22.2 40.6 33.5 17.9 21.0 19.6 62.3 54.5 (ppm/° C.; 50-250 C.) 5% weight loss temperature/° C. 484.5 490.8 500.5 479.2 525.2 541.7 544.2 545.7 479.8 573.9

TABLE-US-00003 TABLE 3 Chemical imidization method (polymer cured on glass plate) Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 1 Ex. 2 diamine TFMB 100 100 100 100 100 100 100 100 100 100 dianhydride 6FDA 40 30 20 100 s-BPDA 10 10 10 10 10 10 25 50 BPAF 60 40 20 25 25 100 CBDA 50 60 70 30 50 70 50 25 film thickness (μm) 10 10 10 10 10 10 10 10 10 10 Transmittance 400-700 nm 89.7 89.5 89.5 88.7 89.0 89.0 88.9 89.0 90.9 88.5 (%) 550 nm 90.2 90.0 89.9 89.1 89.4 89.3 89.4 89.4 91.2 88.8 b* 0.7 0.7 0.8 0.7 0.7 0.9 1.1 1.1 0.3 0.7 YI 1.2 1.3 1.4 1.3 1.3 1.7 1.8 1.8 1.2 1.3 Elongation (%) 3.5 5.8 5.5 4.7 4.8 5.7 5.1 5.8 3.5 4.1 Tensile strength (Mpa) 114.1 173.8 176.9 142.7 150.6 206.7 160.4 161.2 129.3 108.1 Young's modulus (Gpa) 5.0 6.3 6.7 4.9 5.5 6.9 5.9 5.8 3.5 4.0 Haze (%) 0.0 0.1 0.1 0.0 0.0 0.1 0.0 0.1 0.0 0.0 T.sub.g (° C.) 375.3 376.1 372.4 388.7 387.4 389.0 388.1 387.9 341.5 415.7 CTE 1.sup.st scan 8.3 7.1 7.1 13.9 4.5 1.7 3.9 2.1 27.2 36.1 (ppm/° C.; 50-250 C.) CTE 2.sup.nd scan 36.8 24.2 19.2 39.3 30.7 15.3 19.1 17.2 59.7 51.7 (ppm/° C.; 50-250 C.) 5% weight loss temperature/° C. 483.1 491.2 499.7 480.3 527.4 540.3 546.1 547.2 480.1 574.1