COPOLYMER FOR LIQUID CRYSTAL ALIGNMENT AGENT, LIQUID CRYSTAL ALIGNMENT AGENT INCLUDING THE SAME, AND LIQUID CRYSTAL ALIGNMENT FILM AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME

Abstract

A polymer having excellent liquid crystal alignment and electrical properties and thus is suitable for use as a liquid crystal alignment agent, a liquid crystal alignment agent including the same, a liquid crystal alignment film formed from the liquid crystal alignment agent, and a liquid crystal display device including the liquid crystal alignment film are provided.

Claims

1. A copolymer for a liquid crystal alignment agent comprising: one or more repeating units selected from the group of a repeating unit represented by Chemical Formula 1, a repeating unit represented by Chemical Formula 2, and a repeating unit represented by Chemical Formula 3; and one or more repeating units selected from the group of a repeating unit represented by Chemical Formula 4, a repeating unit represented by Chemical Formula 5, and a repeating unit represented by Chemical Formula 6: ##STR00020## wherein, in the Chemical Formulae 1 to 6, R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are each independently hydrogen or a C.sub.1-10 alkyl, provided that R.sup.1 and R.sup.2 are not both hydrogen, and that R.sup.3 and R.sup.4 are not both hydrogen, X.sup.1, X.sup.3, and X.sup.5 are each independently a tetravalent organic group represented by Chemical Formula 7: ##STR00021## wherein, in the Chemical Formula 7, R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are each independently hydrogen or a C.sub.1-6 alkyl, X.sup.2, X.sup.4, X.sup.6, X.sup.7, X.sup.8, and X.sup.9 are each independently a tetravalent organic group derived from a hydrocarbon having 4 to 20 carbon atoms or a tetravalent organic group, wherein in the tetravalent organic group, one or more of H is substituted with a halogen or one or more of CH.sub.2 is substituted with O, CO, S, SO, SO.sub.2, or CONH to prevent direct binding with oxygen or sulfur atoms, in Chemical Formulae 1 to 3, Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4, Y.sup.5, and Y.sup.6 are each independently a divalent organic group represented by Chemical Formula 8: ##STR00022## wherein, in the Chemical Formula 8, R.sup.9 and R.sup.10 are each independently a halogen, a cyano, a C.sub.1-10 alkyl, a C.sub.2-10 alkenyl, a C.sub.1-10 alkoxy, a C.sub.1-10 fluoroalkyl, or a C.sub.1-10 fluoroalkoxy, p and q are each independently an integer of 0 to 4, L.sup.1 is a single bond, O, CO, S, SO.sub.2, C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, CONH, COO, (CH.sub.2).sub.z, O(CH.sub.2).sub.zO, O(CH.sub.2).sub.z, OCH.sub.2C(CH.sub.3).sub.2CH.sub.2O, COO(CH.sub.2).sub.zOCO, or OCO(CH.sub.2).sub.zCOO, wherein each z is independently an integer of 1 to 10, k and m are each independently an integer of 0 to 3, and n is an integer of 0 to 3, in the Chemical Formulae 4 to 6, Z.sup.1, Z.sup.2, and Z.sup.3 are each independently a divalent organic group represented by Chemical Formula 9: ##STR00023## wherein, in the Chemical Formula 9, A.sup.1 is oxygen, sulfur, selenium, tellurium or polonium, R.sup.11 is hydrogen or a C.sub.1-10 alkyl, a is an integer of 0 to 3, and A.sup.2, A.sup.3, A.sup.4, and A.sup.5 are nitrogen or carbon, provided that at least one of A.sup.2 to A.sup.5 is nitrogen and the rest are carbon.

2. The copolymer for a liquid crystal alignment agent according to claim 1, wherein X.sup.2, X.sup.4, X.sup.6, X.sup.7, X.sup.8, and X.sup.9 each independently include a tetravalent organic group represented by Chemical Formula 10: ##STR00024## wherein, in the Chemical Formula 10, R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are each independently hydrogen or a C.sub.1-6 alkyl, R.sup.12 and R.sup.13 are each independently hydrogen or a C.sub.1-10 alkyl, L.sup.2 is a single bond, O, CO, S, SO, SO.sub.2, CR.sup.14R.sup.15, CONH, COO, (CH.sub.2).sub.b, O(CH.sub.2).sub.bO, COO(CH.sub.2).sub.bOCO, HN(CH.sub.2).sub.bNH, R.sup.14N(CH.sub.2).sub.bNR.sup.15, phenylene, and combinations thereof, wherein each of R.sup.14 and R.sup.15 is independently hydrogen, a C.sub.1-10 alkyl, or a C.sub.1-10 fluoroalkyl, and each b is independently an integer of 1 to 10.

3. The copolymer for a liquid crystal alignment agent according to claim 1, wherein the Chemical Formula 8 is a divalent organic group represented by Chemical Formula 11 or Chemical Formula 12: ##STR00025## wherein, in Chemical Formula 12, L.sup.3 is a single bond, O, SO.sub.2, or CR.sup.16R.sup.17, wherein R.sup.16 and R.sup.17 are each independently hydrogen or a C.sub.1-10 alkyl.

4. The copolymer for a liquid crystal alignment agent according to claim 1, wherein in the Chemical Formula 9, one of A.sup.2 to A.sup.5 is nitrogen and the rest are carbon.

5. The copolymer for a liquid crystal alignment agent according to claim 1, wherein in the Chemical Formula 9, one of A.sup.2 and A.sup.5 is nitrogen and the other is carbon, and A.sup.3 and A.sup.4 are carbon.

6. The copolymer for a liquid crystal alignment agent according to claim 1, wherein in the Chemical Formula 9, A.sup.1 is oxygen and a is 0.

7. The copolymer for a liquid crystal alignment agent according to claim 1, wherein the Chemical Formula 9 includes one or more repeating units selected from the group of Chemical Formula 9-1, Chemical Formula 9-2, and Chemical Formula 9-3: ##STR00026## wherein, in the Chemical Formulae 9-1 to 9-3, A.sup.1 to A.sup.5, R.sup.11, and a are as defined in claim 1.

8. The copolymer for a liquid crystal alignment agent according to claim 1, comprising one or more repeating units selected from the group of repeating units represented by Chemical Formulae 13 to 21: ##STR00027## ##STR00028## wherein, in the Chemical Formulae 13 to 21, R.sup.1 to R.sup.4, X.sup.1 to X.sup.9, Y.sup.1 to Y.sup.6, and Z.sup.1 to Z.sup.3 are as defined in claim 1, and m.sup.1 to m.sup.18 are each independently an integer of 1 to 500.

9. The copolymer for a liquid crystal alignment agent according to claim 1, wherein the copolymer for a liquid crystal alignment agent has a weight average molecular weight of 1000 g/mol to 200,000 g/mol.

10. A liquid crystal alignment agent comprising the copolymer for a liquid crystal alignment agent according to claim 1.

11. A method of producing a liquid crystal alignment film, the method comprising the steps of: coating the liquid crystal alignment agent of claim 10 onto a substrate to form a coating film; drying the coating film; irradiating the coating film with light or rubbing the coating film immediately after the drying step to perform an alignment treatment; and heat-treating and curing the alignment-treated coating film.

12. The method of producing a liquid crystal alignment film according to claim 11, wherein the liquid crystal alignment agent is dissolved or dispersed in an organic solvent.

13. The method of producing a liquid crystal alignment film according to claim 11, wherein the step of drying the coating film is performed at 50 C. to 150 C.

14. The method of producing a liquid crystal alignment film according to claim 11, wherein in the alignment treatment step, the light irradiation is performed by irradiating polarized ultraviolet rays having a wavelength of 150 nm to 450 nm.

15. The method of producing a liquid crystal alignment film according to claim 11, wherein in the step of heat-treating and curing the coating film, the heat treatment temperature is 150 C. to 300 C.

16. A liquid crystal alignment film produced by the method of claim 11.

17. A liquid crystal display device comprising the liquid crystal alignment film according to claim 16.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0129] Hereinafter, the present invention will be described in more detail in the following examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not intended to be limited by the following examples.

PREPARATION EXAMPLES 12

Preparation of Diamine

Preparation Example 1

[0130] ##STR00016##

[0131] After 17.1 g (100 mmol) of 2-chloro-5-nitropyridine (compound 1) and 12.5 g (98.6 mmol) of 4-nitrophenol (compound 2) were completely dissolved in about 200 mL of dimethyl sulfoxide (DMSO), 27.2 g (200 mmol) of potassium carbonate (K.sub.2CO.sub.3) was added thereto, and the mixture was stirred at room temperature for 16 hours. When the reaction was completed, the reaction product was charged into a container containing about 500 mL of water and stirred for about 1 hour. A solid obtained by filtration thereof was washed with about 200 mL of water and about 200 mL of ethanol to synthesize 16 g (61.3 mmol) of a compound 3 (yield: 57%).

##STR00017##

[0132] The compound 3 was dissolved in about 200 mL of a 1:1 mixed solution of ethyl acetate (EA) and THF, 0.8 g of palladium (Pd)/carbon (C) was added thereto, and the mixture was stirred for about 12 hours under a hydrogen atmosphere. After completion of the reaction, the reaction mixture was filtered through a pad of Celite and then concentrated to obtain 11 g of a diamine (pODA) compound 4 (yield: 89%).

[0133] .sup.1H NMR (500 MHz, DMSO-d6) 7.48 (dd, J=3.0, 0.7 Hz, 1H), 7.01 (dd, J=8.6, 3.0 Hz, 1 H), 6.70-6.66 (m, 2H), 6.58 (dd, J=8.6, 0.6 Hz, 1 H), 6.55-6.50 (m, 2H), 4.92 (s, 2H), 4.85 (s, 2H).

Preparation Example 2

[0134] ##STR00018##

[0135] 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA, compound 5) and 4-nitroaniline were dissolved in dimethylformamide (DMF) to prepare a mixture. Subsequently, the mixture was allowed to react at about 80 C. for about 12 hours to prepare polyamic acid of compound 6. Next, the polyamic acid was dissolved in DMF, and acetic acid anhydride and sodium acetate were added to prepare a mixture. Then, polyamic acid of compound 6 included in the mixture was imidized at about 90 C. for about 4 hours to obtain a compound 7. The imide of compound 7 thus obtained was dissolved in dimethylacetamide (DMAc), and then Pd/C was added to prepare a mixture. The mixture was reduced at about 45 C. under a hydrogen atmosphere of about 6 bar for 20 hours to prepare a diamine compound 8 (DMICPD).

SYNTHESIS EXAMPLES 18 AND COMPARATIVE SYNTHESIS EXAMPLES 14

Synthesis of Polymer For Liquid Crystal Alignment Agent

Synthesis Example 1

[0136] 1.930 g (0.010 mol) of the diamine (pODA) prepared in Preparation Example 1 and 34.918 g (0.086 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 322.144 g of anhydrous N-methyl pyrrolidone (NMP).

[0137] Then, under an ice bath, 20.0 g (0.089 mol) of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-1 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 24,000 g/mol.

Synthesis Example 2

[0138] 7.239 g (0.036 mol) of the diamine (pODA) prepared in Preparation Example 1 and 14.549 g (0.036 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 208.469 g of anhydrous N-methyl pyrrolidone (NMP).

[0139] Then, under an ice bath, 15.0 g (0.067 mol) of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-2 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 25,000 g/mol.

Synthesis Example 3

[0140] 1.984 g (0.010 mol) of the diamine (pODA) prepared in Preparation Example 1 and 35.887 g (0.089 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 327.936 g of anhydrous N-methyl pyrrolidone (NMP).

[0141] Then, under an ice bath, 20.0 g (0.092 mol) of pyromellitic dianhydride (PMDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-3 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 24,500 g/mol.

Synthesis Example 4

[0142] 7.440 g (0.037 mol) of the diamine (pODA) prepared in Preparation Example 1 and 14.953 g (0.037 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 211.894 g of anhydrous N-methyl pyrrolidone (NMP).

[0143] Then, under an ice bath, 15.0 g (0.069 mol) of pyromellitic dianhydride (PMDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-4 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 25,500 g/mol.

Synthesis Example 5

[0144] 1.471 g (0.007 mol) of the diamine (pODA) prepared in Preparation Example 1 and 26.605 g (0.066 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 272.429 g of anhydrous N-methyl pyrrolidone (NMP).

[0145] Then, under an ice bath, 20.0 g (0.068 mol) of biphenyl tetracarboxylic dianhydride (BPDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-5 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 25,500 g/mol.

Synthesis Example 6

[0146] 7.354 g (0.037 mol) of the diamine (pODA) prepared in Preparation Example 1 and 14.780 g (0.037 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 238.763 g of anhydrous N-methyl pyrrolidone (NMP).

[0147] Then, under an ice bath, 20.0 g (0.068 mol) of biphenyl tetracarboxylic dianhydride (BPDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-6 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 24,000 g/mol.

Synthesis Example 7

[0148] 1.930 g (0.010 mol) of the diamine (pODA) prepared in Preparation Example 1 and 34.918 g (0.086 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 322.144 g of anhydrous N-methyl pyrrolidone (NMP).

[0149] Then, under an ice bath, 20.0 g (0.089 mol) of cyclohexane dianhydride (CHDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-7 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 26,000 g/mol.

Synthesis Example 8

[0150] 9.652 g (0.048 mol) of the diamine (pODA) prepared in Preparation Example 1 and 19.399 g (0.048 mol) of the diamine (DMICPD) prepared in Preparation Example 2 were completely dissolved in 277.958 g of anhydrous N-methyl pyrrolidone (NMP).

[0151] Then, under an ice bath, 20.0 g (0.089 mol) of cyclohexane dianhydride (CHDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a copolymer P-8 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 25,000 g/mol.

Comparative Synthesis Example 1

[0152] 10.374 g (0.096 mol) of p-phenylenediamine (p-PDA) was completely dissolved in 172.121 g of anhydrous N-methyl pyrrolidone (NMP).

[0153] Then, under an ice bath, 20.0 g (0.089 mol) of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a polymer R-1 for a liquid crystal alignment agent. The molecular weight of the polymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 25,000 g/mol.

Comparative Synthesis Example 2

[0154] 19.399 g (0.048 mol) of the diamine (DMICPD) prepared in Preparation Example 2 and 9.510 g (0.048 mol) of methylene diphenyl diamine (MDA) were completely dissolved in 277.154 g of anhydrous N-methyl pyrrolidone (NMP).

[0155] Then, under an ice bath, 20.0 g (0.089 mol) of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a polymer R-2 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 27,000 g/mol.

Comparative Synthesis Example 3

[0156] 9.652 g (0.048 mol) of the diamine (pODA) prepared in Preparation Example 1 and 5.187 g (0.048 mol) of p-phenylenediamine (p-PDA) were completely dissolved in 197.424 g of anhydrous N-methyl pyrrolidone (NMP).

[0157] Then, under an ice bath, 20.0 g (0.089 mol) of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (DMCBDA) was added to the solution and stirred at room temperature for about 16 hours to prepare a polymer R-3 for a liquid crystal alignment agent. The molecular weight of the copolymer was confirmed by GPC, and as a result, the weight average molecular weight (Mw) was 23,500 g/mol.

Comparative Synthesis Example 4

[0158] A copolymer S-1 for a liquid crystal alignment agent was prepared in the same manner as in Synthesis Example 1, except that 2,6-bis(trifluroromethyl)-4,4-diaminodiphenyl ether represented by the following Chemical Formula A was used instead of the diamine (pODA) compound 4 prepared in Preparation Example 1.

##STR00019##

EXAMPLES 18 AND COMPARATIVE EXAMPLES 14

Preparation of Liquid Crystal Alignment Agent

Example 1

[0159] 20 g of the copolymer (P-1) for a liquid crystal alignment agent of Synthesis Example 1 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of -butyrolactone (GBL), and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-1.

Example 2

[0160] 20 g of the copolymer (P-2) for a liquid crystal alignment agent of Synthesis Example 2 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-2.

Example 3

[0161] 20 g of the copolymer (P-3) for a liquid crystal alignment agent of Synthesis Example 3 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-3.

Example 4

[0162] 20 g of the copolymer (P-4) for a liquid crystal alignment agent of Synthesis Example 4 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-4.

Example 5

[0163] 20 g of the copolymer (P-5) for a liquid crystal alignment agent of Synthesis Example 5 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-5.

Example 6

[0164] 20 g of the copolymer (P-6) for a liquid crystal alignment agent of Synthesis Example 6 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-6.

Example 7

[0165] 20 g of the copolymer (P-7) for a liquid crystal alignment agent of Synthesis Example 7 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-7.

Example 8

[0166] 20 g of the copolymer (P-8) for a liquid crystal alignment agent of Synthesis Example 8 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent A-3.

Comparative Example 1

[0167] 20 g of the copolymer (R-1) for a liquid crystal alignment agent of Comparative Synthesis Example 1 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent R-1.

Comparative Example 2

[0168] 20 g of the copolymer (R-2) for a liquid crystal alignment agent of Comparative Synthesis Example 2 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent R-2.

Comparative Example 3

[0169] 20 g of the copolymer (R-3) for a liquid crystal alignment agent of Comparative Synthesis Example 3 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent R-3.

Comparative Example 4

[0170] 20 g of the copolymer (S-1) for a liquid crystal alignment agent of Comparative Synthesis Example 4 was dissolved in a mixed solvent of 8.65 g of NMP, 19.95 g of GBL, and 11.4 g of 2-butoxyethanol to obtain a 5 wt % solution. Then, the solution thus obtained was subjected to pressure filtration using a filter having a pore size of 0.1 m and made of poly(tetrafluoroethylene) to prepare a liquid crystal alignment agent S-1.

Experimental Example

Measurement of Physical Properties of Liquid Crystal Alignment Agent

[0171] 1) Preparation of Liquid Crystal Alignment Cell

[0172] Each of the liquid crystal alignment agents obtained in Examples 1 to 8 and Comparative Examples 1 to 4 was used to prepare a liquid crystal alignment cell.

[0173] Specifically, the liquid crystal alignment agent was coated onto the upper and lower substrates for a voltage holding ratio (VHR) in which ITO electrodes with a thickness of 60 nm and an area of 1 cm1 cm were patterned on a square glass substrate with a size of 2.5 cm2.7 cm by a spin coating method, respectively. Then, the substrates coated with the liquid crystal alignment agent were placed on a hot plate at about 70 C. and dried for 3 minutes to evaporate the solvent. For alignment treatment of the coated substrates thus obtained, each of upper and lower coated substrates was irradiated with UV of 254 nm using an exposure equipped with a line polarizer. Thereafter, the alignment-treated upper and lower substrates were baked (cured) in an oven at about 230 C. for about 30 minutes to obtain a coating film with a thickness of 0.1 m. Thereafter, a sealing agent impregnated with ball spacers with a size of 4.5 m was coated onto the edges of the upper substrate excluding a liquid crystal inlet. The alignment films formed on the upper and lower substrates were then aligned such that they faced each other and the alignment directions were aligned with each other, and the upper and lower substrates were bonded together and the sealing agent was cured with UV and heat to prepare an empty cell. Then, a liquid crystal was injected into the empty cells, and the inlet was sealed with a sealing agent to prepare a liquid crystal alignment cell.

[0174] 2) Measurement of Voltage Holding Ratio (VHR)

[0175] The voltage holding ratio (VHR) which is an electrical property of the liquid crystal alignment cell thus prepared was measured using 6254C equipment manufactured by TOYO Corporation. The voltage holding ratio (VHR) was measured at 1 Hz and 60 C. (VHR 60 degrees 1 Hz n-LC conditions). The results of measuring the voltage holding ratios (VHR) of the liquid crystal alignment cells are shown in the following Table 1.

[0176] 3) Evaluation of Liquid Crystal Alignment Characteristics (Alternating Current (AC) Afterimage)

[0177] Polarizing plates were attached to the upper and lower substrate plates of the above prepared liquid crystal alignment cell so as to be perpendicular to each other. The polarizing plate-attached liquid crystal alignment cell was attached on a backlight having luminance of 7000 cd/cm.sup.2, and the luminance in a black state was measured using a luminance measuring instrument PR-880. Then, the liquid crystal cell was operated at room temperature with an alternating voltage of 5 V for 24 hours. Thereafter, in the voltage-off state of the liquid crystal cell, luminance in the black state was measured as described above. A difference between the initial luminance (L.sub.0) measured before operation of the liquid crystal cell and the later luminance (L.sub.1) measured after operation was divided by the initial luminance (L.sub.0), and then multiplied by 100 to calculate a luminance fluctuation rate. When the calculated luminance fluctuation rate is close to 0%, it means that the alignment stability is excellent.

[0178] Through the measurement results of the luminance fluctuation rate, the afterimage level was evaluated under the following criteria. It is preferable to minimize an AC afterimage. According to the measurement results, when the luminance fluctuation rate was less than 10%, it was evaluated as excellent, when the luminance fluctuation rate was 10% to 20%, it was evaluated as ordinary, and when the luminance fluctuation rate was more than 20%, it was evaluated as poor. The results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Evaluation of physical property of liquid First diamine Second diamine Dianhydride liquid crystal crystal Content Content Content cell* agent Type (mmol) Type (mmol) Type (mmol) AC afterimage VHR (%) Example 1 A-1 PODA 10 DMICPD 86 DMCBDA 89 Excellent 73 Example 2 A-2 PODA 36 DMICPD 36 DMCBDA 67 Excellent 71 Example 3 A-3 PODA 10 DMICPD 89 PMDA 92 Excellent 68 Example 4 A-4 PODA 37 DMICPD 37 PDMA 69 Excellent 70 Example 5 A-5 PODA 7 DMICPD 66 BPDA 68 Excellent 70 Example 6 A-6 PODA 37 DMICPD 37 BPDA 68 Excellent 69 Example 7 A-7 PODA 10 DMICPD 86 CHDA 89 Excellent 72 Example 8 A-8 PODA 48 DMICPD 48 CHDA 89 Excellent 71 Comparative R-1 PDA 96 DMCBDA 89 Poor 37 Example 1 Comparative R-2 MDA 48 DMICPD 48 DMCBDA 89 Excellent 34 Example 2 Comparative R-3 PODA 48 PDA 48 DMCBDA 89 Poor 70 Example 3 Comparative S-1 Chemical 10 DMICPD 86 DMCBDA 89 Poor 33 Example 4 Formula A *Measured under an exposure dose of 0.1 to 0.5 J/cm.sup.2

[0179] As shown in Table 1, it was confirmed that since each of the liquid crystal alignment agents of Examples 1 to 8 includes the copolymer produced from the reaction product containing the imide-containing first diamine having a specific structure along with the second diamine having a specific asymmetric structure, an excellent alignment property may be obtained without an initial thermosetting process, the voltage holding ratio (VHR) may be improved to as high as about 68% to about 73%, and the AC afterimage may be maintained at an equivalent level or more.

[0180] Particularly, the liquid crystal alignment agents of Examples 1 to 8 may exhibit an excellent coating property to implement a high imidization rate while having excellent processing properties, and may also exhibit excellent effects in terms of electrical properties such as voltage holding ratio and direct current (DC) afterimage generated by the direct current/alternating voltage.

[0181] In contrast, in the case of the liquid crystal alignment agents of Comparative Examples 1 to 4, none of the imide-containing diamine having a specific structure and the diamine having a specific asymmetric structure were included or one of them was included in the reaction product during the preparation of the polymer, and as a result, electrical properties or alignment properties of the liquid crystal cells were remarkably deteriorated.

[0182] In particular, in the case of Comparative Example 1, the polymer including only para-phenylenediamine (p-PDA) as the diamine component was used, and as a result, it showed a remarkably reduced voltage holding ratio (VHR) of about 37% and also showed a luminance fluctuation rate of more than 20%, and was thus evaluated as poor in the AC afterimage test. In the case of Comparative Example 2, of the copolymers, diamine (DMICPD) having a specific asymmetric structure was used, but methylene diphenyl diamine (MDA) was used instead of the imide-containing first diamine. As a result, there was no problem in the liquid crystal alignment properties, but it showed a remarkably reduced voltage holding ratio (VHR) of about 34%. In the case of Comparative Example 3, of the copolymers, the imide-containing diamine (p-ODA) having a specific structure was used, but para-phenylenediamine (p-PDA) was used instead of the second diamine having a specific asymmetric structure. As a result, the voltage holding ratio (VHR) may be maintained at the equivalent level or more, but there was a problem that a luminance fluctuation rate of more than 20% was observed, and thus was evaluated as poor in the AC afterimage test.