Copolymer and optical film using same

Abstract

A novel copolymer suitable for an optical film which is excellent in optical characteristics and has high retardation even in a thin film state, and an optical film containing the same are provided. A copolymer excellent in optical characteristics and easy to form a composite with a different polymer, and an optical film composed of the same are also provided.

Claims

1. A copolymer, comprising: a residue unit A of formula (1); and a residue unit B of formula (2): ##STR00012## wherein R.sub.1 and R.sub.2 each independently represent hydrogen provided that the case where R.sub.1 and R.sub.2 are both hydrogen is excluded, a cyano group, an ester group (—C(═O)OX.sub.1), an amide group (—C(═O)N(X.sub.2)(X.sub.3)), or an acyl group (—C(═O)X.sub.4), where X.sub.1 to X.sub.3 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and X.sub.4 represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms; R.sub.3 to R.sub.7 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, a cyclic group having 3 to 14 carbon atoms, a halogen, a hydroxy group, a carboxy group, a nitro group, a cyano group, an alkoxy group (—OX.sub.5), an ester group (—C(═O)OX.sub.6), an amide group (—C(═O)N(X.sub.7)(X.sub.8)), an acyl group (—C(═O)X.sub.9), an amino group (—N(X.sub.10)(X.sub.11)), or a sulfonyl group (—SOOX.sub.12), where X.sub.5 to X.sub.8 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and X.sub.9 to X.sub.12 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms; at least one of R.sub.3 to R.sub.7 is a hydroxy group; and adjacent substituents among R.sub.3 to R.sub.7 may form a fused ring structure each other, ##STR00013## wherein R.sub.8 represents an m-membered heterocyclic residue including one or more heteroatoms or a 5-membered or 6-membered ring residue containing no heteroatom, and m represents an integer of 5 to 10; and the m-membered heterocyclic residue, the 5-membered ring residue, and the 6-membered ring residue may form a fused ring structure with another cyclic structure.

2. The copolymer according to claim 1, wherein R.sub.1 is selected from the group consisting of a cyano group, an ester group, an amide group, and an acyl group.

3. The copolymer according to claim 1, wherein R.sub.2 is a cyano group.

4. The copolymer according to claim 1, wherein R.sub.8 is a 5-membered heterocyclic residue or a 6-membered heterocyclic residue including at least one nitrogen atom or oxygen atom as a heteroatom, and the 5-membered heterocyclic residue and the 6-membered heterocyclic residue may form a fused ring structure with another cyclic structure.

5. The copolymer according to claim 1, wherein the residue unit A of the formula (1) is at least one selected from the group consisting of an α-cyanocinnamate ester residue unit, a benzalmalononitrile residue unit, a nitrobenzalmalononitrile residue unit, a cinnamonitrile residue unit, a chalcone residue unit, an alkoxychalcone residue unit, a benzylidenemalonate diester residue unit, and an N,N-dialkylcinnamamide residue unit.

6. The copolymer according to claim 1, wherein the residue unit B is a residue unit of formula (3) and/or a residue unit of formula (4): ##STR00014## wherein R.sub.9 to R.sub.16 each independently represent hydrogen, a halogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, a cyclic group having 3 to 14 carbon atoms, a cyano group, a nitro group, a hydroxy group, a carboxy group, a thiol group, an alkoxy group (—OX.sub.13), an ester group (—C(═O)OX.sub.14 or —CO(═O)—X.sub.15), an amide group (—C(═O)N(X.sub.16)(X.sub.17) or —NX.sub.18C(═O)X.sub.19), an acyl group (—C(═O)X.sub.20), or an amino group (—N(X.sub.21)(X.sub.22)), where X.sub.13 to X.sub.15 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms, X.sub.16 to X.sub.22 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms; adjacent substituents among R.sub.9 to R.sub.16 may form a fused ring structure each other; and R.sub.9 and R.sub.15, and, R.sub.10 and R.sub.16 may consist of the same atoms and may form a ring structure, ##STR00015## wherein R.sub.17 to R.sub.20 each independently represent hydrogen, a halogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, a cyclic group having 3 to 14 carbon atoms, a cyano group, a nitro group, a hydroxy group, a carboxy group, a thiol group, an alkoxy group (—OX.sub.23), an ester group (—C(═O)OX.sub.24 or —CO(═O)—X.sub.25), an amide group (—C(═O)N(X.sub.26)(X.sub.27) or —NX.sub.28C(═O)X.sub.29), an acyl group (—C(═O)X.sub.30), or an amino group (—N(X.sub.31)(X.sub.32)), where X.sub.23 to X.sub.25 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms, X.sub.26 to X.sub.32 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms; adjacent substituents among R.sub.17 to R.sub.20 may form a fused ring structure each other; and R.sub.17 and R.sub.18, and, R.sub.19 and R.sub.20 may consist of the same atoms and may form a ring structure.

7. The copolymer according to claim 1, wherein a molar ratio AB of the residue unit A of the formula (1) to the residue unit B of the formula (2) falls within the range of 0.05 to 6.

8. The copolymer according to claim 6, wherein the copolymer has a number-average molecular weight of 3,000 to 500,000 in terms of standard polystyrene when the residue unit B is a residue unit B of other than the formula (4) or in terms of standard pullulan when the residue unit B is a residue unit of the formula (4).

9. A process for producing the copolymer of claim 1, comprising: conducting polymerization of a monomer of formula (5): ##STR00016## wherein R.sub.1 and R.sub.2 each independently represent hydrogen, provided that the case where R.sub.1 and R.sub.2 are both hydrogen is excluded, a cyano group, an ester group (—C(═O)OX.sub.1), an amide group (—C(═O)N(X.sub.2)(X.sub.3)), or an acyl group (—C(═O)X.sub.4), where X.sub.1 to X.sub.3 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and X.sub.4 represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms; R.sub.3 to R.sub.7 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, a cyclic group having 3 to 14 carbon atoms, a halogen, a hydroxy group, a carboxy group, a nitro group, a cyano group, an alkoxy group (—OX.sub.5), an ester group (—C(═O)OX.sub.6), an amide group (—C(═O)N(X.sub.7)(X.sub.8)), an acyl group (—C(═O)X.sub.9), an amino group (—N(X.sub.10)(X.sub.11)), or a sulfonic acid group (—SOOX.sub.12), where X.sub.5 to X.sub.8 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, X.sub.9 to X.sub.12 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms; at least one of R.sub.3 to R.sub.7 is a hydroxy group; and adjacent substituents among R.sub.3 to R.sub.7 may form a fused ring structure each other.

10. An optical film, comprising: the copolymer of claim 1.

11. A retardation film, comprising: the optical film of claim 10, wherein the retardation film satisfies nx≅ny<nz, where nx is a refractive index in a fast axis direction in a film plane, ny is a refractive index in a direction orthogonal to the fast axis direction in the film plane, and nz is a refractive index in a thickness direction of the film.

12. A resin composition, comprising: the copolymer of claim 11; and a resin having positive intrinsic birefringence.

13. An optical compensation film, comprising: the resin composition of claim 12, wherein an in-plane retardation (Re) of formula (b) is 50 to 500 nm; an Nz coefficient of formula (c) is 0≤Nz≤1.0; and a ratio Re(450)/Re(550) of the in-plane retardation (Re) at a light wavelength of 450 nm to the in-plane retardation (Re) at a light wavelength of 550 nm is 0.60<Re(450)/Re(550)<1.10:
Re=(nx−ny)×d  (b)
Nz=(nx−nz)/(nx−ny)  (c) wherein nx represents a refractive index in a stretching axis direction in the film plane, ny represents a refractive index in a direction perpendicular to the stretching axis in the film plane, nz represents a refractive index of a thickness direction of the film, and d represents film thickness.

14. The copolymer according to claim 1, wherein the residue unit B of the formula (2) is 9-vinylcarbazole residue units.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described by way of Examples, but the present invention is not limited to these Examples.

(2) Incidentally, the various physical properties shown by Examples were measured by the following method.

(3) <Composition of Copolymer>

(4) It was determined from proton nuclear magnetic resonance (.sup.1H-NMR) spectroscopy using a nuclear magnetic resonance measurement apparatus (manufactured by JEOL Ltd., trade name: JNM-ECZ400S/L1). Further, those which are difficult to determine by .sup.1H-NMR spectroscopy were determined by CHN elemental analysis.

(5) <Measurement of Number-Average Molecular Weight>

(6) It was measured at 40° C. using tetrahydrofuran or N,N-dimethylformamide as a solvent and using a gel permeation chromatography (GPC) apparatus (manufactured by Tosoh Corporation, trade name: HLC8320GPC (equipped with a column of GMHHR-H)), and was determined as a value in terms of standard polystyrene or standard pullulans.

(7) <Evaluation Method of Transparency>

(8) The total light transmittance and haze of a film were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: NDH5000).

(9) <Measurement of Refractive Index>

(10) The measurement was performed using an Abbe refractometer (manufactured by Atago) in accordance with JIS K 7142 (1981).

(11) <Measurement of Retardation and Three-Dimensional Refractive Index of Film>

(12) Measurement was performed using a fully automatic birefringence meter (manufactured by Oji Scientific Instruments, trade name: KOBRA-WPR.

Example 1 (Synthesis of Cinnamonitrile/1-Vinylindole Copolymer)

(13) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.039 mol) of cinnamonitrile, 5.6 g (0.039 mol) of 1-vinylindole, and 0.28 g (0.00065 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.1 g of a cinnamonitrile/1-vinylindole copolymer (yield: 48%).

(14) The number-average molecular weight of the obtained cinnamonitrile/1-vinylindole copolymer was 14,000 in terms of standard polystyrene.

(15) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: cinnamonitrile residue unit/1-vinylindole residue unit=34/66 (mol %) (residue unit A/residue unit B=0.52).

Example 2 (Synthesis of Cinnamonitrile/9-Vinylcarbazole Copolymer)

(16) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.039 mol) of cinnamonitrile, 7.5 g (0.039 mol) of 9-vinylcarbazole, and 0.28 g (0.00065 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 8.0 g of a cinnamonitrile/9-vinylcarbazole copolymer (yield: 64%).

(17) The number-average molecular weight of the obtained cinnamonitrile/9-vinylcarbazole copolymer was 25,000 in terms of standard polystyrene.

(18) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: cinnamonitrile residue unit/9-vinylcarbazole residue unit=38/62 (mol %) (residue unit A/residue unit B=0.61).

Example 3 (Synthesis of Methyl α-Cyanocinnamate/9-Vinylcarbazole Copolymer)

(19) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.027 mol) of methyl α-cyanocinnamate, 5.2 g (0.027 mol) of 9-vinylcarbazole, 0.19 g (0.00044 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 1.0 g of toluene. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 24 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 6.9 g of a methyl α-cyanocinnamate/9-vinylcarbazole copolymer (yield: 68%).

(20) The number-average molecular weight of the obtained methyl α-cyanocinnamate/9-vinylcarbazole copolymer was 33,000 in terms of standard polystyrene.

(21) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: methyl α-cyanocinnamate residue unit/9-vinylcarbazole residue unit=29/71 (mol %) (residue unit A/residue unit B=0.41).

Example 4 (Synthesis of Methyl α-Cyanocinnamate/N-Vinylsuccinimide Copolymer)

(22) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.027 mol) of methyl α-cyanocinnamate, 3.4 g (0.027 mol) of N-vinylsuccinimide, and 0.19 g (0.00044 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of N,N-dimethylformamide. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 4.5 g of a methyl α-cyanocinnamate/N-vinylsuccinimide copolymer (yield: 54%).

(23) The number-average molecular weight of the obtained methyl α-cyanocinnamate/N-vinylsuccinimide copolymer was 21,000 in terms of standard pullulan.

(24) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: methyl α-cyanocinnamate residue unit/N-vinylsuccinimide residue unit=42/58 (mol %) (residue unit A/residue unit B=0.72).

Example 5 (Synthesis of Ethyl α-Cyanocinnamate/N-Vinylphthalimide Copolymer)

(25) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.025 mol) of ethyl α-cyanocinnamate, 4.3 g (0.025 mol) of N-vinylphthalimide, 0.18 g (0.00042 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 1.0 g of toluene. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 2 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of N,N-dimethylformamide. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 6.7 g of an ethyl α-cyanocinnamate/N-vinylphthalimide copolymer (yield: 72%).

(26) The number-average molecular weight of the obtained ethyl α-cyanocinnamate/N-vinylphthalimide copolymer was 25,000 in terms of standard pullulan.

(27) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl α-cyanocinnamate residue unit/N-vinylphthalimide residue unit=44/56 (mol %) (residue unit A/residue unit B=0.79).

Example 6 (Synthesis of Ethyl α-Cyanocinnamate/2-Vinylbenzofuran Copolymer)

(28) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.025 mol) of ethyl α-cyanocinnamate, 3.6 g (0.025 mol) of 2-vinylbenzofuran, and 0.18 g (0.00042 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 3.9 g of an ethyl α-cyanocinnamate/2-vinylbenzofuran copolymer (yield: 45%).

(29) The number-average molecular weight of the obtained ethyl α-cyanocinnamate/2-vinylbenzofuran copolymer was 17,000 in terms of standard polystyrene.

(30) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl α-cyanocinnamate residue unit/2-vinylbenzofuran residue unit=32/68 (mol %) (residue unit A/residue unit B=0.47).

Example 7 (Synthesis of n-Propyl α-Cyanocinnamate/2-Vinylquinoline Copolymer)

(31) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.023 mol) of n-propyl α-cyanocinnamate, 3.6 g (0.023 mol) of 2-vinylquinoline, and 0.17 g (0.00039 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of n-hexane for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 4.2 g of an n-propyl α-cyanocinnamate/2-vinylquinoline copolymer (yield: 49%).

(32) The number-average molecular weight of the obtained n-propyl α-cyanocinnamate/2-vinylquinoline copolymer was 21,000 in terms of standard polystyrene.

(33) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: n-propyl α-cyanocinnamate residue unit/2-vinylquinoline residue unit=30/70 (mol %) (residue unit A/residue unit B=0.43).

Example 8 (Synthesis of Benzalmalononitrile/N-Vinylphthalimide Copolymer)

(34) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.032 mol) of benzalmalononitrile, 5.5 g (0.032 mol) of N-vinylphthalimide, 0.23 g (0.00053 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 1.0 g of toluene. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 24 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of N,N-dimethylformamide. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 7.6 g of a benzalmalononitrile/N-vinylphthalimide copolymer (yield: 72%).

(35) The number-average molecular weight of the obtained benzalmalononitrile/N-vinylphthalimide copolymer was 24,000 in terms of standard pullulan.

(36) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: benzalmalononitrile residue unit/N-vinylphthalimide residue unit=32/68 (mol %) (residue unit A/residue unit B=0.47).

Example 9 (Synthesis of Benzalmalononitrile/9-Vinylcarbazole Copolymer)

(37) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.032 mol) of benzalmalononitrile, 6.2 g (0.032 mol) of 9-vinylcarbazole, 0.23 g (0.00053 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 1.2 g of toluene. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 6 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.9 g of a benzalmalononitrile/9-vinylcarbazole copolymer (yield: 53%).

(38) The number-average molecular weight of the obtained benzalmalononitrile/9-vinylcarbazole copolymer was 90,000 in terms of standard polystyrene.

(39) In addition, by CHN elemental analysis, the copolymer composition was confirmed as follows: benzalmalononitrile residue unit/9-vinylcarbazole residue unit=43/57 (mol %) (residue unit A/residue unit B=0.75).

Example 10 (Synthesis of 4-Nitrobenzalmalononitrile/2-Vinylbenzofuran Copolymer)

(40) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.025 mol) of 4-nitrobenzalmalononitrile, 3.6 g (0.025 mol) of 2-vinylbenzofuran, 0.18 g (0.00042 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 5.0 g of N,N-dimethylformamide. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 3.9 g of a 4-nitrobenzalmalononitrile/2-vinylbenzofuran copolymer (yield: 45%).

(41) The number-average molecular weight of the obtained 4-nitrobenzalmalononitrile/2-vinylbenzofuran copolymer was 26,000 in terms of standard polystyrene.

(42) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: 4-nitrobenzalmalononitrile residue unit/2-vinylbenzofuran residue unit=33/67 (mol %) (residue unit A/residue unit B=0.49).

Example 11 (Synthesis of N,N-Diethylcinnamamide/2-Vinylfuran Copolymer)

(43) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.025 mol) of N,N-diethylcinnamamide, 2.4 g (0.025 mol) of 2-vinylfuran, and 0.18 g (0.00042 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 3.7 g of an N,N-diethylcinnamamide/2-vinylfuran copolymer (yield: 50%).

(44) The number-average molecular weight of the obtained N,N-diethylcinnamamide/2-vinylfuran copolymer was 8,000 in terms of standard polystyrene.

(45) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: N,N-diethylcinnamamide residue unit/2-vinylfuran residue unit=31/69 (mol %) (residue unit A/residue unit B=0.45).

Example 12 (Synthesis of Chalcone/2-Vinylquinoline Copolymer)

(46) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.024 mol) of chalcone, 3.7 g (0.024 mol) of 2-vinylquinoline, and 0.17 g (0.00039 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of n-hexane for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 4.1 g of a chalcone/2-vinylquinoline copolymer (yield: 47%).

(47) The number-average molecular weight of the obtained chalcone/2-vinylquinoline copolymer was 9,000 in terms of standard polystyrene.

(48) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: chalcone residue unit/2-vinylquinoline residue unit=29/71 (mol %) (residue unit A/residue unit B=0.41).

Example 13 (Synthesis of Methyl α-Cyanocinnamate/9-Vinylcarbazole Copolymer)

(49) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.027 mol) of methyl α-cyanocinnamate, 5.2 g (0.027 mol) of 9-vinylcarbazole, 0.39 g (0.00091 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 1.0 g of toluene. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 24 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 7.1 g of a methyl α-cyanocinnamate/9-vinylcarbazole copolymer (yield: 70%).

(50) The number-average molecular weight of the obtained methyl α-cyanocinnamate/9-vinylcarbazole copolymer was 15,000 in terms of standard polystyrene.

(51) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: methyl α-cyanocinnamate residue unit/9-vinylcarbazole residue unit=31/69 (mol %) (residue unit A/residue unit B=0.45).

Example 14 (Synthesis of Isobutyl 4-Hydroxy-α-Cyanocinnamate/9-Vinylcarbazole Copolymer)

(52) In a glass ampoule having a volume of 50 mL were charged 5.0 g (0.020 mol) of isobutyl 4-hydroxy-α-cyanocinnamate, 3.9 g (0.020 mol) of 9-vinylcarbazole, 0.14 g (0.00033 mol) of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.0 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of a mixed solvent of methanol/water=80/20 (volume %/volume %) for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 7.5 g of an isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer (yield: 84%).

(53) The number-average molecular weight of the obtained isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer was 16,000 in terms of standard polystyrene.

(54) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: isobutyl 4-hydroxy-α-cyanocinnamate residue unit/9-vinylcarbazole residue unit=46/54 (mol %) (residue unit A/residue unit B=0.85).

Example 15 (Synthesis of Ethyl α-Cyano-4-Hydroxycinnamate/9-Vinylcarbazole Copolymer)

(55) In a glass ampoule having a volume of 50 mL were charged 5.0 g of ethyl α-cyano-4-hydroxycinnamate, 4.4 g of 9-vinylcarbazole, 8.5 g of tetrahydrofuran as a polymerization solvent, and 0.17 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution was performed, the ampoule was melt-sealed in a reduced pressure state. The glass ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the vessel and added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 80° C. for 10 hours to obtain 7.7 g of an ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer (yield: 82%).

(56) The number-average molecular weight of the obtained ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer was 22,000 in terms of standard polystyrene.

(57) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl α-cyano-4-hydroxycinnamate residue unit/9-vinylcarbazole residue unit=42/58 (mol %) (residue unit A/residue unit B=0.72).

Example 16 (Synthesis of 4-Hydroxybenzalmalononitrile/2-Vinylnaphthalene Copolymer)

(58) In a glass ampoule having a volume of 50 mL were charged 5.0 g of 4-hydroxybenzalmalononitrile, 4.5 g of 2-vinylnaphthalene, 10 g of tetrahydrofuran as a polymerization solvent, and 0.21 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution was performed, the ampoule was melt-sealed in a reduced pressure state. The glass ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the vessel and added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 80° C. for 10 hours to obtain 6.2 g of a 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer (yield: 65%).

(59) The number-average molecular weight of the obtained 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer was 12,000 in terms of standard polystyrene.

(60) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: 4-hydroxybenzalmalononitrile residue unit/2-vinylnaphthalene residue unit=43/57 (mol %) (residue unit A/residue unit B=0.75).

Example 17 (Synthesis of 4-Carboxybenzalmalononitrile/N-Vinylphthalimide Copolymer)

(61) In a glass ampoule having a volume of 50 mL were charged 5.3 g of 4-carboxybenzalmalononitrile, 4.7 g of N-vinylphthalimide, 12.5 g of N,N-dimethylformamide as a polymerization solvent, and 0.19 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution was performed, the ampoule was melt-sealed in a reduced pressure state. The glass ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the vessel and added dropwise into 200 mL of methanol for precipitation, and then vacuum drying was performed at 80° C. for 10 hours to obtain 4.5 g of a 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer (yield: 45%).

(62) The number-average molecular weight of the obtained 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer was 13,000 in terms of standard pullulan.

(63) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: 4-carboxybenzalmalononitrile residue unit/N-vinylphthalimide residue unit=35/65 (mol %) (residue unit A/residue unit B=0.54).

Synthesis Example 1 (Synthesis of Cinnamonitrile/Styrene Copolymer)

(64) In a 50 mL glass ampoule were charged 5.0 g (0.039 mol) of cinnamonitrile, 4.1 g (0.039 mol) of styrene, and 0.28 g (0.00065 mol) of 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.4 g of a cinnamonitrile/styrene copolymer (yield: 59%).

(65) The number-average molecular weight of the obtained cinnamonitrile/styrene copolymer was 46,000 in terms of standard polystyrene.

(66) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: cinnamonitrile residue unit/styrene residue unit=27/73 (mol %) (residue unit A/residue unit B=0.37).

Synthesis Example 2 (Synthesis of Ethyl α-Cyanocinnamate/Methyl Acrylate Copolymer)

(67) In a 50 mL glass ampoule were charged 5.0 g (0.025 mol) of ethyl α-cyanocinnamate, 2.2 g (0.026 mol) of methyl acrylate, and 0.18 g (0.00042 mol) of 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 2.5 g of an ethyl α-cyanocinnamate/methyl acrylate copolymer (yield: 35%).

(68) The number-average molecular weight of the obtained ethyl α-cyanocinnamate/methyl acrylate copolymer was 13,000 in terms of standard polystyrene.

(69) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl α-cyanocinnamate residue unit/methyl acrylate residue unit=11/89 (mol %) (residue unit A/residue unit B=0.12).

Synthesis Example 3 (Synthesis of Benzalmalononitrile/Styrene Copolymer)

(70) In a 50 mL glass ampoule were charged 5.0 g (0.032 mol) of benzalmalononitrile, 3.3 g (0.032 mol) of styrene, and 0.23 g (0.00053 mol) of 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.8 g of a benzalmalononitrile/styrene copolymer (yield: 70%).

(71) The number-average molecular weight of the obtained benzalmalononitrile/styrene copolymer was 93,000 in terms of standard polystyrene.

(72) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: benzalmalononitrile residue unit/styrene residue unit=36/64 (mol %) (residue unit A/residue unit B=0.56).

Synthesis Example 4 (Synthesis of Acrylonitrile/1-Vinylindole Copolymer)

(73) In a 50 mL glass ampoule were charged 2.5 g (0.047 mol) of acrylonitrile, 6.7 g (0.047 mol) of 1-vinylindole, and 0.34 g (0.00079 mol) of 2,5-dimethyl-2,5-di (2-ethylhexanoylperoxy)hexane that was a polymerization initiator. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 4.9 g of an acrylonitrile/1-vinylindole copolymer (yield: 53%).

(74) The number-average molecular weight of the obtained acrylonitrile/1-vinylindole copolymer was 12,000 in terms of standard polystyrene.

(75) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: acrylonitrile residue unit/1-vinylindole residue unit=31/69 (mol %) (residue unit A/residue unit B=0.45).

Example 18

(76) The cinnamonitrile/1-vinylindole copolymer obtained in Example 1 was dissolved in cyclopentanone to obtain a 35% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 60° C. for 60 minutes to obtain a 10.1 μm-thick film using the cinnamonitrile/1-vinylindole copolymer.

(77) The obtained film had a total light transmittance of 87%, a haze of 0.6%, and a refractive index of 1.648.

(78) The three-dimensional refractive index was as follows: nx=1.6421, ny=1.6421, and nz=1.6588, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx ny<nz. The out-of-plane retardation Rth was negatively as large as −169 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 16.7 nm/film thickness (μm).

(79) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 19

(80) The cinnamonitrile/9-vinylcarbazole copolymer obtained in Example 2 was dissolved in cyclopentanone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 60° C. for 60 minutes to obtain an 8.8 μm-thick film using the cinnamonitrile/9-vinylcarbazole copolymer.

(81) The obtained film had a total light transmittance of 87%, a haze of 0.5%, and a refractive index of 1.655.

(82) The three-dimensional refractive index was as follows: nx=1.6445, ny=1.6445, and nz=1.6774, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −290 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 32.9 nm/film thickness (μm).

(83) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 20

(84) The methyl α-cyanocinnamate/9-vinylcarbazole copolymer obtained in Example 3 was dissolved in cyclopentanone to obtain a 20% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 130° C. for 10 minutes to obtain a 12.2 μm-thick film using the methyl α-cyanocinnamate/9-vinylcarbazole copolymer.

(85) The obtained film had a total light transmittance of 87%, a haze of 0.6%, and a refractive index of 1.653.

(86) The three-dimensional refractive index was as follows: nx=1.6432, ny=1.6432, and nz=1.6740, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −376 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 30.8 nm/film thickness (μm).

(87) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 21

(88) The methyl α-cyanocinnamate/N-vinylsuccinimide copolymer obtained in Example 4 was dissolved in N,N-dimethylformamide to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and vacuum-dried at 60° C. for 3 hours to obtain a 10.5 μm-thick film using the methyl α-cyanocinnamate/N-vinylsuccinimide copolymer.

(89) The obtained film had a total light transmittance of 89%, a haze of 0.4%, and a refractive index of 1.575.

(90) The three-dimensional refractive index was as follows: nx=1.5679, ny=1.5679, and nz=1.5881, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −212 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 20.2 nm/film thickness (μm).

(91) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 22

(92) The ethyl α-cyanocinnamate/N-vinylphthalimide copolymer obtained in Example 5 was dissolved in N,N-dimethylformamide to obtain a 20% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and vacuum-dried at 60° C. for 3 hours to obtain a 9.2 μm-thick film using the ethyl α-cyanocinnamate/N-vinylphthalimide copolymer.

(93) The obtained film had a total light transmittance of 88%, a haze of 0.6%, and a refractive index of 1.613.

(94) The three-dimensional refractive index was as follows: nx=1.6042, ny=1.6042, and nz=1.6310, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −247 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 26.8 nm/film thickness (μm).

(95) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 23

(96) The ethyl α-cyanocinnamate/2-vinylbenzofuran copolymer obtained in Example 6 was dissolved in toluene to obtain a 35% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 60° C. for 60 minutes to obtain an 8.8 μm-thick film using the ethyl α-cyanocinnamate/2-vinylbenzofuran copolymer.

(97) The obtained film had a total light transmittance of 87%, a haze of 0.3%, and a refractive index of 1.634.

(98) The three-dimensional refractive index was as follows: nx=1.6294, ny=1.6294, and nz=1.6438, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx ny<nz. The out-of-plane retardation Rth was negatively as large as −127 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 14.4 nm/film thickness (μm).

(99) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 24

(100) The n-propyl α-cyanocinnamate/2-vinylquinoline copolymer obtained in Example 7 was dissolved in cyclopentanone to obtain a 35% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 11.0 μm-thick film using the n-propyl α-cyanocinnamate/2-vinylquinoline copolymer.

(101) The obtained film had a total light transmittance of 88%, a haze of 0.3%, and a refractive index of 1.635.

(102) The three-dimensional refractive index was as follows: nx=1.6291, ny=1.6291, and nz=1.6464, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −190 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 17.3 nm/film thickness (μm).

(103) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 25

(104) The benzalmalononitrile/N-vinylphthalimide copolymer obtained in Example 8 was dissolved in N,N-dimethylformamide to obtain a 20% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and vacuum-dried at 60° C. for 3 hours to obtain a 12.6 μm-thick film using the benzalmalononitrile/N-vinylphthalimide copolymer.

(105) The obtained film had a total light transmittance of 87%, a haze of 0.5%, and a refractive index of 1.638.

(106) The three-dimensional refractive index was as follows: nx=1.6301, ny=1.6301, and nz=1.6535, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx≈ny<nz. The out-of-plane retardation Rth was negatively as large as −295 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 23.4 nm/film thickness (μm).

(107) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 26

(108) The benzalmalononitrile/9-vinylcarbazole copolymer obtained in Example 9 was dissolved in tetrahydrofuran to obtain a 20% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 130° C. for 10 minutes to obtain a 11.8 μm-thick film using the benzalmalononitrile/9-vinylcarbazole copolymer.

(109) The obtained film had a total light transmittance of 87%, a haze of 0.4%, and a refractive index of 1.652.

(110) The three-dimensional refractive index was as follows: nx=1.6410, ny=1.6410, and nz=1.6732, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx ny<nz. The out-of-plane retardation Rth was negatively as large as −380 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 32.2 nm/film thickness (μm).

(111) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 27

(112) The 4-nitrobenzalmalononitrile/2-vinylbenzofuran copolymer obtained in Example 10 was dissolved in methyl ethyl ketone to obtain a 35% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 60° C. for 60 minutes to obtain a 9.8 μm-thick film using the 4-nitrobenzalmalononitrile/2-vinylbenzofuran copolymer.

(113) The obtained film had a total light transmittance of 87%, a haze of 0.5%, and a refractive index of 1.642.

(114) The three-dimensional refractive index was as follows: nx=1.6357, ny=1.6357, and nz=1.6550, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −189 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 19.3 nm/film thickness (μm).

(115) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 28

(116) The N,N-diethylcinnamamide/2-vinylfuran copolymer obtained in Example 11 was dissolved in cyclopentanone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 12.2 μm-thick film using the N,N-diethylcinnamamide/2-vinylfuran copolymer.

(117) The obtained film had a total light transmittance of 89%, a haze of 0.5%, and a refractive index of 1.577.

(118) The three-dimensional refractive index was as follows: nx=1.5741, ny=1.5741, and nz=1.5837, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −117 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 9.6 nm/film thickness (μm).

(119) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 29

(120) The chalcone/2-vinylquinoline copolymer obtained in Example 12 was dissolved in cyclopentanone to obtain a 35% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 7.9 μm-thick film using the chalcone/2-vinylquinoline copolymer.

(121) The obtained film had a total light transmittance of 87%, a haze of 0.6%, and a refractive index of 1.651.

(122) The three-dimensional refractive index was as follows: nx=1.6476, ny=1.6476, and nz=1.6568, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −73 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 9.2 nm/film thickness (μm).

(123) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 30

(124) The methyl α-cyanocinnamate/9-vinylcarbazole copolymer obtained in Example 13 was dissolved in cyclopentanone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 130° C. for 10 minutes to obtain a 11.9 μm-thick film using the methyl α-cyanocinnamate/9-vinylcarbazole copolymer.

(125) The obtained film had a total light transmittance of 87%, a haze of 0.3%, and a refractive index of 1.650.

(126) The three-dimensional refractive index was as follows: nx=1.6431, ny=1.6431, and nz=1.6650, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx ny<nz. The out-of-plane retardation Rth was negatively as large as −261 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 21.9 nm/film thickness (μm).

(127) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 31

(128) The isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer obtained in Example 14 was dissolved in ethyl acetate to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 12.4 μm-thick film using the isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer.

(129) The obtained film had a total light transmittance of 88%, a haze of 0.5%, and a refractive index of 1.613.

(130) The three-dimensional refractive index was as follows: nx=1.6060, ny=1.6060, and nz=1.6270, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx≈ny<nz. The out-of-plane retardation Rth was negatively as large as −260 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 21.0 nm/film thickness (μm).

(131) When the same film was measured one month later, the out-of-plane retardation was maintained, and thus the film was excellent in stability.

Example 32

(132) The ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer obtained in Example 15 was dissolved in tetrahydrofuran and the solution was cast on a glass substrate by means of a coater and vacuum-dried at 60° C. for 10 hours to obtain a 15.2 μm-thick film using the ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer.

(133) The obtained film had a total light transmittance of 87%, a haze of 0.4%, and a refractive index of 1.689.

(134) The three-dimensional refractive index was as follows: nx=1.681, ny=1.681, and nz=1.704, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx≈ny<nz. The out-of-plane retardation Rth was negatively as large as −350 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 23.0 nm/film thickness (μm).

(135) Into 10 g of tetrahydrofuran were dissolved 0.5 g of the obtained ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer and 0.5 g of polymethyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd., number-average molecular weight: 270,000). The solution was applied on a glass substrate by means of a spin coater and vacuum-dried at 60° C. for 10 hours to form a good film having a haze of 0.7%, and therefore the ethyl α-cyano-4-hydroxycinnamate/9-vinylcarbazole copolymer was a polymer excellent in compatibility.

Example 33

(136) Into 4 g of tetrahydrofuran were dissolved 0.5 g of the 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer obtained in Example 16 and 0.5 g of polyethylene glycol (manufactured by Tokyo Kasei Co., Ltd., number-average molecular weight: 3,000). The solution was applied on a glass substrate by spin coating and vacuum-dried at 60° C. for 10 hours to obtain a 12.4 μm-thick film using the 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer.

(137) The obtained film had a total light transmittance of 86%, a haze of 0.4%, and a refractive index of 1.645.

(138) The three-dimensional refractive index was as follows: nx=1.634, ny=1.633, and nz=1.668, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −425 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 34.3 nm/film thickness (μm).

(139) Into 9 g of cyclohexanone were dissolved 0.8 g of the obtained 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer and 0.2 g of polymethyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd., number-average molecular weight: 270,000). The solution was applied on a glass substrate by means of a spin coater and vacuum-dried at 100° C. for 10 hours to form a good film having a haze of 0.8%, and therefore the 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer was a polymer excellent in compatibility.

Example 34

(140) The 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer obtained in Example 17 was dissolved in N,N-dimethylformamide and the solution was applied on a glass substrate by spin coating and vacuum-dried at 60° C. for 180 minutes to obtain a 13.0 μm-thick film using the 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer.

(141) The obtained film had a total light transmittance of 87%, a haze of 0.5%, and a refractive index of 1.633.

(142) The three-dimensional refractive index was as follows: nx=1.626, ny=1.626, and nz=1.647, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx-ny<nz. The out-of-plane retardation Rth was negatively as large as −274 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 21.1 nm/film thickness (μm).

(143) Into 4 g of N,N-dimethylformamide were dissolved 0.7 g of the obtained 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer and 0.3 g of polyvinyl acetate (manufactured by Aldrich, number-average molecular weight: 53,000). The solution was applied on a glass substrate by means of a spin coater and vacuum-dried at 60° C. for 10 hours to form a good film having a haze of 0.8%, and therefore the 4-carboxybenzalmalononitrile/N-vinylphthalimide copolymer was a polymer excellent in compatibility.

Example 35 (Polymerization of 4-Carboxybenzalmalononitrile/1-Vinylindole Copolymer and Preparation of Optical Compensation Film Using Resin Composition Containing the Copolymer)

(144) In a glass ampoule having a volume of 50 mL were charged 5.0 g of 4-carboxybenzalmalononitrile, 3.6 g of 1-vinylindole, 0.18 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.5 g of N,N-dimethylformamide. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.0 g of a 4-carboxybenzalmalononitrile/1-vinylindole copolymer (yield: 58%).

(145) The number-average molecular weight of the obtained 4-carboxybenzalmalononitrile/1-vinylindole copolymer was 23,000 in terms of standard polystyrene.

(146) In addition, by CHN elemental analysis, the copolymer composition was confirmed as follows: 4-carboxybenzalmalononitrile residue unit/1-vinylindole residue unit=33/67 (mol %) (residue unit A/residue unit B=0.49).

(147) Then, 1.5 g of the obtained 4-carboxybenzalmalononitrile/1-vinylindole copolymer and 10 g of cellulose acetate butyrate as a resin having positive intrinsic birefringence (molecular weight Mn=72,000, acetyl group=15 mol %, butyryl group=70 mol %, total degree of substitution DS=2.55) were dissolved into a solution of toluene/methyl ethyl ketone=6/4 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 15° C., a film having a width of 150 mm was obtained (ethyl cellulose: 87% by weight, 4-carboxybenzalmalononitrile/1-vinylindole copolymer: 13% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 140° C. by 1.8 times (thickness after stretching: 80 μm).

(148) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 shows the results.

(149) TABLE-US-00001 TABLE 1 Total light trans- mittance Haze Re Rth Nz Re(450)/ (%) (%) (nm) (nm) coefficient Re(550) Example 35 91 0.5 315 −30 0.40 0.89 Example 36 90 0.5 293 16 0.56 0.79 Example 37 90 0.6 248 24 0.60 0.81 Example 38 90 0.6 299 −1 0.50 0.89 Example 39 91 0.4 301 25 0.58 0.82 Example 40 91 0.5 301 −13 0.46 0.85 Example 41 88 0.6 243 −32 0.37 0.87

(150) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 36 (Polymerization of Ethyl 4-Hydroxy-α-Cyanocinnamate/9-Vinylcarbazole Copolymer and Preparation of Optical Compensation Film Using Resin Composition Containing the Copolymer)

(151) In a glass ampoule having a volume of 50 mL were charged 5.0 g of ethyl 4-hydroxy-α-cyanocinnamate, 4.4 g of 9-vinylcarbazole, 0.17 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.5 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 7.7 g of an ethyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer (yield: 82%).

(152) The number-average molecular weight of the obtained ethyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer was 22,000 in terms of standard polystyrene.

(153) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl 4-hydroxy-α-cyanocinnamate residue unit/9-vinylcarbazole residue unit=42/58 (mol %) (residue unit A/residue unit B=0.89).

(154) Then, 1.5 g of the obtained ethyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer and 10 g of ethyl cellulose as a resin having positive intrinsic birefringence (ETHOCEL standard 100 manufactured by Dow Chemical Company, molecular weight Mn=55,000, molecular weight Mw=176,000, Mw/Mn=3.2, total degree of substitution DS=2.5) were dissolved into a solution of toluene/ethyl acetate=4/6 (weight ratio) to obtain a 15 wt % resin solution, which was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 87% by weight, ethyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer: 13% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 145° C. by 1.5 times (thickness after stretching: 40 μm).

(155) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(156) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 37 (Polymerization of 4-Hydroxybenzalmalononitrile/2-Vinylnaphthalene Copolymer and Preparation of Optical Compensation Film Using Resin Composition Containing the Copolymer)

(157) In a glass ampoule having a volume of 50 mL were charged 5.0 g of 4-hydroxybenzalmalononitrile, 4.5 g of 2-vinylnaphthalene, 0.21 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 10 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 6.2 g of a 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer (yield: 65%).

(158) The number-average molecular weight of the obtained 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer was 12,000 in terms of standard polystyrene.

(159) In addition, by CHN elemental analysis, the copolymer composition was confirmed as follows: 4-hydroxybenzalmalononitrile residue unit/2-vinylnaphthalene residue unit=43/57 (mol %) (residue unit A/residue unit B=0.75).

(160) Then, 2.0 g of the obtained 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer and 10 g of ethyl cellulose as a resin having positive intrinsic birefringence (ETHOCEL standard 100 manufactured by Dow Chemical Company, molecular weight Mn=55,000, molecular weight Mw=176,000, Mw/Mn=3.2, total degree of substitution DS=2.5) were dissolved into a solution of toluene/ethyl acetate=4/6 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 83% by weight, 4-hydroxybenzalmalononitrile/2-vinylnaphthalene copolymer: 17% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 140° C. by 1.3 times (thickness after stretching: 40 μm).

(161) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(162) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 38 (Polymerization of Isobutyl 4-Hydroxy-α-Cyanocinnamate/N-Vinylsuccinimide Copolymer)

(163) In a glass ampoule having a volume of 50 mL were charged 5.0 g of isobutyl 4-hydroxy-α-cyanocinnamate, 2.6 g of N-vinylsuccinimide, 0.15 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.5 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of N,N-dimethylformamide. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 5.5 g of an isobutyl 4-hydroxy-α-cyanocinnamate/N-vinylsuccinimide copolymer (yield: 73%).

(164) The number-average molecular weight of the obtained isobutyl 4-hydroxy-α-cyanocinnamate/N-vinylsuccinimide copolymer was 16,000 in terms of standard pullulan.

(165) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: isobutyl 4-hydroxy-α-cyanocinnamate residue unit/N-vinylsuccinimide residue unit=46/54 (mol %) (residue unit A/residue unit B=0.85).

(166) Then, 2.0 g of the obtained isobutyl 4-hydroxy-α-cyanocinnamate/N-vinylsuccinimide copolymer and 10 g of cellulose acetate propionate as a resin having positive intrinsic birefringence (molecular weight Mn=75,000, acetyl group=5 mol %, propionyl group=80 mol %, total degree of substitution DS=2.55) were dissolved into a solution of toluene/methyl ethyl ketone=6/4 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 83% by weight, isobutyl 4-hydroxy-α-cyanocinnamate/N-vinylsuccinimide copolymer: 17% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 140° C. by 1.7 times (thickness after stretching: 60 μm).

(167) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(168) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 39 (Polymerization of Ethyl 3,4-Dihydroxy-α-Cyanocinnamate/N-Vinylphthalimide Copolymer)

(169) In a glass ampoule having a volume of 50 mL were charged 5.0 g of ethyl 3,4-dihydroxy-α-cyanocinnamate, 3.7 g of N-vinylphthalimide, 0.15 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.5 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of N,N-dimethylformamide. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 6.4 g of an ethyl 3,4-dihydroxy-α-cyanocinnamate/N-vinylphthalimide copolymer (yield: 73%).

(170) The number-average molecular weight of the obtained ethyl 3,4-dihydroxy-α-cyanocinnamate/N-vinylphthalimide copolymer was 21,000 in terms of standard pullulan.

(171) In addition, by .sup.1H-NMR measurement, the copolymer composition was confirmed as follows: ethyl 3,4-dihydroxy-α-cyanocinnamate residue unit/N-vinylphthalimide residue unit=41/59 (mol %) (residue unit A/residue unit B=0.69).

(172) Then, 1.5 g of the obtained ethyl 3,4-dihydroxy-α-cyanocinnamate/N-vinylphthalimide copolymer and 10 g of ethyl cellulose as a resin having positive intrinsic birefringence (ETHOCEL standard 100 manufactured by Dow Chemical Company, molecular weight Mn=55,000, molecular weight Mw=176,000, Mw/Mn=3.2, total degree of substitution DS=2.5) were dissolved into a solution of toluene/ethyl acetate=6/4 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 87% by weight, ethyl 3,4-dihydroxy-α-cyanocinnamate/N-vinylphthalimide copolymer: 13% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 145° C. by 1.5 times (thickness after stretching: 40 μm).

(173) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(174) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 40 (Polymerization of 4-Carboxy-3-Hydroxybenzalmalononitrile/2-Vinylfuran Copolymer)

(175) In a glass ampoule having a volume of 75 mL were charged 15 g of 4-carboxy-3-hydroxybenzalmalononitrile, 6.6 g of 2-vinylfuran, 0.50 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 30 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 75 g of tetrahydrofuran. The polymer solution was added dropwise into 1,500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 12.6 g of a 4-carboxy-3-hydroxybenzalmalononitrile/2-vinylfuran copolymer (yield: 58%).

(176) The number-average molecular weight of the obtained 4-carboxy-3-hydroxybenzalmalononitrile/2-vinylfuran copolymer was 15,000 in terms of standard polystyrene.

(177) In addition, by CHN elemental analysis, the copolymer composition was confirmed as follows: 4-carboxy-3-hydroxybenzalmalononitrile residue unit/2-vinylfuran residue unit=36/64 (mol %) (residue unit A/residue unit B=0.56).

(178) Then, 2.0 g of the obtained 4-carboxy-3-hydroxybenzalmalononitrile/2-vinylfuran copolymer and 10 g of ethyl cellulose as a resin having positive intrinsic birefringence (ETHOCEL standard 100 manufactured by Dow Chemical Company, molecular weight Mn=55,000, molecular weight Mw=176,000, Mw/Mn=3.2, total degree of substitution DS=2.5) were dissolved into a solution of toluene/ethyl acetate=6/4 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 83% by weight, 4-carboxy-3-hydroxybenzalmalononitrile/2-vinylfuran copolymer: 17% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 140° C. by 1.2 times (thickness after stretching: 40 μm).

(179) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(180) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Example 41 (Polymerization of Isobutyl 4-Hydroxy-α-Cyanocinnamate/9-Vinylcarbazole Copolymer)

(181) In a glass ampoule having a volume of 50 mL were charged 5.0 g of isobutyl 4-hydroxy-α-cyanocinnamate, 3.9 g of 9-vinylcarbazole, 0.14 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane that was a polymerization initiator, and 8.0 g of tetrahydrofuran. After nitrogen substitution and pressure reduction were repeated, the ampoule was melt-sealed in a reduced pressure state. The ampoule was placed in a thermostatic chamber at 62° C. and held for 48 hours to perform radical polymerization. After completion of the polymerization reaction, a polymerized product was taken out of the ampoule and dissolved in 25 g of tetrahydrofuran. The polymer solution was added dropwise into 500 mL of methanol for precipitation, and then vacuum drying was performed at 60° C. for 10 hours to obtain 7.5 g of an isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer (yield: 85%).

(182) The number-average molecular weight of the obtained isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer was 12,000 in terms of standard polystyrene.

(183) In addition, by CHN elemental analysis, the copolymer composition was confirmed as follows: isobutyl 4-hydroxy-α-cyanocinnamate residue unit/9-vinylcarbazole residue unit=46/54 (mol %) (residue unit A/residue unit B=0.85).

(184) Then, 2.0 g of the obtained isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer and 10 g of ethyl cellulose as a resin having positive intrinsic birefringence (ETHOCEL standard 100 manufactured by Dow Chemical Company, molecular weight Mn=55,000, molecular weight Mw=176,000, Mw/Mn=3.2, total degree of substitution DS=2.5) were dissolved into a solution of toluene/ethyl acetate=6/4 (weight ratio) to obtain a 15% by weight resin solution. The resin solution was cast on a polyethylene terephthalate film by means of a coater. After two-stage drying at a temperature of 40° C. and then at 150° C., a film having a width of 150 mm was obtained (ethyl cellulose: 83% by weight, isobutyl 4-hydroxy-α-cyanocinnamate/9-vinylcarbazole copolymer: 17% by weight). The obtained film was cut into 50 mm square, and uniaxially stretched at 150° C. by 1.5 times (thickness after stretching: 40 μm).

(185) The total light transmittance, haze, retardation characteristics, and wavelength dispersion characteristics of the obtained optical compensation film were measured. Table 1 collectively shows the results.

(186) The obtained optical compensation film had high light transmittance, excellent transparency, small haze, and objective optical characteristics of the in-plane retardation (Re), the wavelength dispersion characteristics (Re (450)/Re (550)), and the Nz coefficient.

Comparative Example 1

(187) The cinnamonitrile/styrene copolymer obtained in Synthesis Example 1 was dissolved in methyl ethyl ketone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 60° C. for 60 minutes to obtain a 12.5 μm-thick film.

(188) The obtained film had a total light transmittance of 88%, a haze of 0.5%, and a refractive index of 1.604.

(189) The three-dimensional refractive index was as follows: nx=1.6021, ny=1.6021, and nz=1.6065, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz, but the out-of-plane retardation Rth was as small as −55 nm and the ratio of the absolute value of the out-of-plane retardation to the film thickness was also as small as 4.4 nm/film thickness (μm).

(190) From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was small and retardation characteristics were poor in a thin film state.

Comparative Example 2

(191) The ethyl α-cyanocinnamate/methyl acrylate copolymer obtained in Synthesis Example 2 was dissolved in cyclopentanone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 9.5 μm-thick film.

(192) The obtained film had a total light transmittance of 88%, a haze of 0.3%, and a refractive index of 1.597.

(193) The three-dimensional refractive index was as follows: nx=1.5951, ny=1.5951, and nz=1.6001, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz, but the out-of-plane retardation Rth was as small as −48 nm and the ratio of the absolute value of the out-of-plane retardation to the film thickness was also as small as 5.0 nm/film thickness (μm).

(194) From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was small and retardation characteristics were poor in a thin film state.

Comparative Example 3

(195) The benzalmalononitrile/styrene copolymer obtained in Synthesis Example 3 was dissolved in methyl ethyl ketone to obtain a 20% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 9.1 m-thick film.

(196) The obtained film had a total light transmittance of 88%, a haze of 0.5%, and a refractive index of 1.623.

(197) The three-dimensional refractive index was as follows: nx=1.6213, ny=1.6213, and nz=1.6270, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz, but the out-of-plane retardation Rth was as small as −52 nm and the ratio of the absolute value of the out-of-plane retardation to the film thickness was also as small as 5.7 nm/film thickness (μm).

(198) From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was small and retardation characteristics were poor in a thin film state.

Comparative Example 4

(199) The acrylonitrile/1-vinylindole copolymer obtained in Synthesis Example 4 was dissolved in cyclopentanone to obtain a 30% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain an 8.3 μm-thick film.

(200) The obtained film had a total light transmittance of 87%, a haze of 0.4%, and a refractive index of 1.630.

(201) The three-dimensional refractive index was as follows: nx=1.6291, ny=1.6291, and nz=1.6331, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz, but the out-of-plane retardation Rth was as small as −33 nm and the ratio of the absolute value of the out-of-plane retardation to the film thickness was also as small as 4.0 nm/film thickness (μm).

(202) From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction, but the out-of-plane retardation was small and retardation characteristics were poor in a thin film state.

Comparative Example 5

(203) Poly(9-vinylcarbazole) (number-average molecular weight: 264,000, manufactured by Tokyo Kasei Co., Ltd.) was dissolved in cyclopentanone to obtain a 15% by weight resin solution. The resin solution was cast on a glass substrate by means of a coater and dried at 100° C. for 10 minutes to obtain a 13.2 μm-thick film using the poly(9-vinylcarbazole).

(204) The obtained film had a total light transmittance of 87%, a haze of 0.6%, and a refractive index of 1.685.

(205) The three-dimensional refractive index was as follows: nx=1.6785, ny=1.6785, and nz=1.6990, and the obtained film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz. The out-of-plane retardation Rth was negatively as large as −271 nm. Further, the ratio of the absolute value of the out-of-plane retardation to the film thickness was 20.5 nm/film thickness (μm).

(206) From these results, the obtained film had negative birefringence and a large refractive index in the thickness direction. Further, the out-of-plane retardation was negatively large and the film had high retardation even in a thin film state. However, when the same film was again measured after 5 days, the three-dimensional refractive index was as follows: nx=1.6849, ny=1.6849, and nz=1.6866, and thus the film exhibited a large value of the refractive index in the thickness direction of the film, which is nx=ny<nz. However, the out-of-plane retardation Rth and the ratio of the absolute value of the out-of-plane retardation to the film thickness were greatly decreased to −22 nm and 1.7 nm/film thickness (μm), respectively, so that the film was not suitable for a retardation film because of its poor stability.

(207) The entire contents of the description, claims, and abstract of Japanese Patent Application No. 2016-23 7864 filed on Dec. 7, 2016, Japanese Patent Application No. 2017-137230 filed on Jul. 13, 2017, Japanese Patent Application No. 2017-137231 filed on Jul. 13, 2017, Japanese Patent Application No. 2017-222844 filed on Nov. 20, 2017, and Japanese Patent Application No. 2017-223986 filed on Nov. 21, 2017 are incorporated herein by reference and incorporated as a disclosure of the description of the present invention.