JP2001354733A - Side chain type liquid crystalline polymer and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystalline polymer which has a controllable refraction index or birefringence. SOLUTION: The side chain type liquid crystalline polymer comprises (a) a monomer unit having a liquid crystalline fragmental side chain and (b) a monomer unit having a non-liquid crystalline fragmental side chain of an amomatic ring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a side chain type liquid crystal polymer and a method for producing the same. The side chain type liquid crystal polymer of the present invention has a refractive index characteristic and a birefringence characteristic suitable for an optical element, and is used for various optical elements such as a viewing angle compensator, a retardation plate and a cholesteric reflector.

[0002]

2. Description of the Related Art Since liquid crystal polymers have optically anisotropic properties, many applications to optical applications such as liquid crystal displays have been reported. For example, a liquid crystal polymer is
Utilizing the birefringence phenomenon, it is used for applications such as a viewing angle compensator, a retardation plate, and a cholesteric reflector. In general, a thermotropic liquid crystal polymer can exhibit birefringence by heating the polymer to an appropriate temperature or by cooling from an isotropic phase. Expressed as the difference in light refractive index.

However, since the refractive index and birefringence of the liquid crystal polymer are values unique to the liquid crystal polymer, changing the refractive index and birefringence of the liquid crystal polymer requires changing the material of the liquid crystal polymer itself. It was necessary to confirm the refractive index and birefringence of the liquid crystal polymer.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal polymer capable of controlling the refractive index characteristics or birefringence characteristics.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by the following side chain type liquid crystal polymer. It was completed.

That is, the present invention is characterized in that it comprises a monomer unit (a) containing a liquid crystal fragment side chain and a monomer unit (b) containing a non-liquid crystal aromatic ring fragment side chain. A chain type liquid crystal polymer.

The side chain type liquid crystal polymer of the present invention has a monomer unit (b) containing a non-liquid crystal aromatic ring fragment side chain in addition to a monomer unit (a) containing a liquid crystal fragment side chain. Therefore, by appropriately adjusting the ratio (copolymerization ratio) of the monomer unit (b) to produce a side-chain type liquid crystal polymer, the side-chain type liquid crystal polymer consisting of the monomer unit (a) alone can be produced. Also, by reducing the refractive index, the refractive index of the side chain type liquid crystal polymer can be controlled to a desired value. By controlling the refractive index of the side-chain liquid crystal polymer, the birefringence of the side-chain liquid crystal polymer can also be controlled, and a high-performance optical element can be manufactured.

The fragment side chain in the monomer unit (a) has at least one substituent selected from an alkoxy group, a cyano group, a fluoro group and an alkyl group in parallel with the molecular length axis of the fragment side chain. It is preferable to include (in the object) in any direction. A monomer unit having a fragment side chain having such a substituent exhibits good refractive index characteristics and birefringence characteristics.

The monomer unit (a) includes, for example, a compound represented by the following general formula (a):

Embedded image (However, R ¹ is a hydrogen atom or a methyl group, a is 1 to
A positive integer of 6, X ¹ represents a —CO ₂ — group or —OCO—
R ² represents a cyano group, an alkoxy group, a fluoro group or an alkyl group; b and c each represent an integer of 1 or 2; )). The monomer unit represented by the general formula (a) is preferable in the refractive index characteristics and the birefringence characteristics.

On the other hand, the fragment side chain in the monomer unit (b) is non-liquid crystalline and has an aromatic ring. With the monomer unit having a side chain having such a substituent, the refractive index characteristics and the birefringence characteristics can be controlled. The ordinary light refractive index can be increased and the birefringence can be decreased by increasing the proportion of the monomer unit represented by the general formula (b) having such an aromatic ring fragment side chain.

As the monomer unit (b), for example, a compound represented by the general formula (b):

Embedded image (However, R ³ represents a hydrogen atom or a methyl group, and X ² represents-
R _{2 represents a} CO ₂ — group or —OCO— group, —O— or a single bond, and R ⁴ has the general formula (c):

Embedded image And a substituent represented by )). The monomer unit represented by the general formula (b) is preferable in controlling the refractive index characteristics.

The ratio of the monomer unit (a) to the monomer unit (b) is not particularly limited, and differs depending on the type of the monomer unit. Liquid crystal polymer does not show liquid crystal monodomain alignment,
(B) / {(a) + (b)} = 0.01 to 0.8 (molar ratio) is preferable. Within this range, the ratio of the monomer unit (b) is appropriately changed to control the refractive index characteristics and birefringence characteristics of the side chain type liquid crystal polymer.

The weight average molecular weight of the side chain type liquid crystal polymer is preferably from 2,000 to 100,000. By adjusting the weight average molecular weight in such a range, performance as a liquid crystal polymer is exhibited. If the weight average molecular weight of the side chain type liquid crystal polymer is too small, the film formability as a non-fluidized layer tends to be poor, so the weight average molecular weight is more preferably at least 25,000. On the other hand, if the weight average molecular weight is too large, the orientation as a liquid crystal, especially the monodomain formation via a rubbing alignment film or the like tends to be poor, and it is difficult to form a uniform alignment state, so that the weight average molecular weight is 50,000 or less. More preferably,

The side chain type liquid crystal polymer of the present invention generally has a monodomain orientation, and can have any refractive index and birefringence. It is possible to improve the performance of various optical materials utilizing anisotropy.

Further, the present invention provides a method for producing a monomer (a) by copolymerizing a monomer (a) containing a liquid crystal fragment side chain and a monomer (b) containing a non-liquid crystal aromatic ring fragment side chain. And b) controlling the refractive index characteristic or birefringence characteristic of the liquid crystal fragment side chain.

The side chain type liquid crystal polymer comprises a monomer (b) containing a non-liquid crystal aromatic ring fragment side chain as a copolymerization component of a monomer (a) containing a liquid crystal fragment side chain. By appropriately adjusting the proportion of the monomer (b), the side chain type in which the refractive index characteristic or birefringence characteristic of the liquid crystal fragment side chain of the monomer (a) is controlled to a desired value. Liquid crystal polymers can be manufactured.

Further, according to the present invention, the refractive index characteristic or the birefringence characteristic of the side chain type liquid crystal polymer containing the monomer unit (a) containing the liquid crystal fragment side chain is shared with the side chain type liquid crystal polymer. As a polymerization monomer unit,
The present invention relates to a method for controlling a desired value by containing a monomer unit (b) containing a side chain of a non-liquid crystalline aromatic ring fragment and changing the ratio of the monomer unit (b).

The refractive index characteristics and the birefringence characteristics of the side chain type liquid crystal polymer can be controlled by adjusting the ratio of the monomer unit (b) containing a non-liquid crystalline aromatic ring side chain.

Further, the present invention relates to an optical element comprising the side chain type liquid crystal polymer. Further, the present invention relates to a liquid crystal display using the optical element. The side chain type liquid crystal polymer of the present invention is useful as an optical element and used for a liquid crystal display.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The side chain type liquid crystal polymer of the present invention comprises
The monomer unit (a) and the monomer unit (b)
Can be prepared by copolymerizing an acrylic monomer or a methacrylic monomer corresponding to the above. The monomers corresponding to the monomer units (a) and (b) can be synthesized by a known method. An alkyl group or an alkoxy group which can be a substituent in the monomer unit (a) usually has about 1 to 6 carbon atoms.

The preparation of the copolymer can be carried out in accordance with a conventional polymerization system of acrylic monomers such as a radical polymerization system, a cationic polymerization system, and an anion polymerization system. When the radical polymerization method is applied, various polymerization initiators can be used, but the decomposition temperature of azobisisobutyronitrile or benzoyl peroxide is not high, and decomposes at an intermediate temperature that is not low. Are preferably used.

The obtained side chain type liquid crystal polymer forms a non-fluid layer having nematic liquid crystal alignment by a method according to a conventional alignment treatment. As an alignment treatment method, for example, after forming an alignment film made of polyimide or polyvinyl alcohol on a plastic substrate, rubbing it with a rayon cloth or the like, then developing a liquid crystal polymer on the film, and applying a glass transition temperature or higher, A method in which the liquid crystal polymer molecules are heated to a temperature lower than the isotropic phase transition temperature, cooled to a temperature lower than the glass transition temperature in a state where the liquid crystal polymer molecules are oriented to a glass state, and a solidified layer in which the orientation is fixed is formed. In addition, as a method of aligning the liquid crystal polymer, a method of using a stretched film as an alignment film instead of the above rubbing, a method of irradiating a polymer or polyimide containing cinnamate or azobenzene with polarized ultraviolet light to form an alignment film, a magnetic field, electromagnetic alignment, shear stress An operation or an orientation operation by stretching can be used.

As the substrate, for example, a film made of a plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyethersulfone, or epoxy resin, or an appropriate substrate such as a glass plate Can be used. The non-fluidized layer of the liquid crystal polymer formed on the substrate can be used as it is with the substrate for forming an optical element as it is, or can be peeled off from the substrate and used for forming an optical element composed of a film or the like.

The liquid crystal polymer may be developed by a heating and melting system or may be developed as a solution using a solvent. As the solvent, for example, an appropriate solvent such as methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dioxane, or dimethylsulfoxide can be used. The development can be performed by a suitable coating machine such as a bar coater, a spinner, and a roll coater.

The thickness of the non-fluidized layer of the liquid crystal polymer to be formed is preferably 0.5 to 20 μm. If the thickness is too small, it is difficult to exhibit birefringence characteristics. If the thickness is too large, the birefringence property may not be exhibited due to poor uniform orientation. In addition, it is preferable that the thickness be 10 μm or less because the alignment treatment requires a long time. When forming the optical element, various additives other than the liquid crystal polymer, such as a polymer, a stabilizer, and an inorganic or organic material such as a plasticizer, or a metal can be added as necessary.

Examples of the optical element obtained from the liquid crystal polymer include a viewing angle compensator, a retardation plate, and a color reflector. In any of these optical elements, control of birefringence greatly affects its optical characteristics. An optical element obtained from a liquid crystal polymer whose birefringence is controlled in this way is:
Useful for improving the display quality of liquid crystal displays.

[0027]

EXAMPLES The present invention will be specifically described below with reference to production examples and examples.

Synthesis Example 1 (Synthesis of monomer corresponding to monomer unit (a))

Embedded image A synthetic example of the acrylic monomer represented by the formula (a1) is shown in Chemical formula 7.

276 g (2 mol) of 4-hydroxybenzoic acid and a catalytic amount of potassium iodide were added to a potassium hydroxide solution (300 g of KOH, 700 ml of ethanol and 300 ml of water), and dissolved. While heating, 177 g (2.2 mol) of ethylene chlorohydrin was slowly added, and
Reflux for hours (potassium chloride precipitated with the reaction). After completion of the reaction, ethanol was distilled off, and the reaction solution was added to 2 liters of water. This aqueous solution is treated with diethyl ether 2
After washing twice, the aqueous layer was acidified with 4 × 10 ³ mol / m ³ hydrochloric acid. The obtained precipitate was filtered, dried and then recrystallized from ethanol to obtain 4- (2-hydroxyethoxy) benzoic acid (yield 290 g, yield 82%, purity 98%).

182 g (1 mol) of 4- (2-hydroxyethoxy) benzoic acid, 40 g of hydroquinone, 40 g of p-toluenesulfonic acid and 600 ml of acrylic acid were mixed with 600 ml of a mixed solvent of benzene / toluene = 1/1 (weight ratio).
Was dissolved. The mixture was refluxed using a Dean-Stark tube until the theoretical amount of water was removed from the system (about 15 hours). Next, the reaction solution was placed in 4 liters of diethyl ether and washed with warm water. After washing with a saturated saline solution, the mixture was dried over anhydrous sodium sulfate. The solvent was distilled off, and the obtained solid was recrystallized with a mixed solvent of acetone / hexane = 1/1 (weight ratio) to obtain 4- (2-propenoyloxyethoxy) benzoic acid (153 g, yield: 153 g). Rate 65%, purity 97%).

4- (2-propenoyloxyethoxy)
23.6 g (0.1 mol) of benzoic acid was added to acetone 400
ml. Further, trifluoroacetic anhydride 20.8
ml (0.15 mol) was added and stirred. 19.5 g of 4-cyano-4'-hydroxybiphenyl (0.1 mol
l) was added to the reaction solution and reacted at room temperature for 6 hours. After the reaction solution was distilled off, the residue was dissolved in diethyl ether, washed with water, a saturated aqueous solution of sodium hydrogen carbonate and saturated saline, and dried over anhydrous sodium sulfate. The solvent was distilled off, and the obtained solid was recrystallized from 600 ml of acetonitrile to obtain the desired compound (a).
1) A monomer was obtained (yield 29.3 g, yield 71%, purity 99%).

Synthesis Example 2 (Synthesis of monomer corresponding to monomer unit (b))

Embedded image Formula 8 shows a synthesis example of the acrylic monomer represented by the formula (b1).

7.21 g of 2-naphthol (50 mmo
l), acrylic acid 3.78 g (52 mmol), dimethylaminopyridine 0.8 g (66 mmol, DMA in the formula)
P) and 2,6-di-ter as a small amount of polymerization inhibitor
100 ml of a methylene chloride solution containing t-butyl-p-cresol was charged into a 200 ml eggplant flask to form a suspension, and then 10.52 g of dicyclohexylcarbodiimide (51 m 2) diluted with 10 ml of methylene chloride was added thereto.
mol, DCC in the formula) was added little by little, and the mixture was stirred overnight. The precipitated dicyclohexylurea was filtered off, and the total volume was made up to 300 ml with methylene chloride. I left.
The crude product was purified by silica gel column chromatography (developing solvent: methylene chloride) to obtain an acrylic monomer (b1: 2-naphthyl acrylate) (7.73 g, 78% yield).

Example (Synthesis of Side Chain Type Liquid Crystal Polymer)

Embedded image In Chemical Formula 9, n represents the mole% of the monomer (b1) constituting the side chain type liquid crystal polymer. In Chemical formula 9, the side chain type liquid crystal polymer is represented by a block for convenience.

A predetermined amount of the monomer (a1) shown in Table 1 and 30 ml of a mixed solvent of (b1: 2-naphthyl acrylate) and dimethylacetamide (DMAc) / tetrahydrofuran (THF) = 4/1 (weight ratio) were added to three portions. After charging the flask, the mixture was heated and stirred under a nitrogen stream to completely dissolve the monomers. Azobisisobutyronitrile (AIBN) 1 dissolved in a small amount of the mixed solvent
00 mg was added dropwise. After refluxing for 6 hours, the heating was stopped and the reaction solution was returned to room temperature.
The polymer was re-precipitated by dropping into ml. The polymer was separated by filtration, washed with 50 ml of a mixed solvent of methanol / THF = 3/2 (weight ratio), filtered and dried to obtain a side chain type liquid crystal polymer. The reaction substrate (a1) monomer and (b)
Table 1 shows 1) the amount of the monomer used, (b1) the proportion of the monomer, and the yield, yield, and weight average molecular weight of the obtained side chain liquid crystal polymer.

A polyimide (20% solution of N-methylpyrrolidone) was spin-coated on a lead-containing glass substrate at 2000 rpm for 10 seconds, heated at 300 ° C. for 1 hour, and rubbed to form an alignment film. Next, a solution of the side chain type liquid crystal polymer obtained above in cyclohexanone (concentration 2
6% by weight) was spin-coated on the alignment film, and heated at 160 ° C. to align the side chain type liquid crystal polymer. The thickness of the side chain type liquid crystal polymer was 2.0 to 2.4 μm.

[Measurement of refractive index of ordinary light] Table 1 shows the result of measuring the refractive index of ordinary light of the obtained liquid crystal polymer alignment product. The ordinary light refractive index was measured with an Atago Abbe refractometer 1T type.

[Measurement of Birefringence] From the results of measuring the front retardation (Δnd) and the film thickness (d) of the obtained liquid crystal polymer alignment product, the birefringence (Δn) was calculated by the following equation. Was calculated. The front phase difference (Δn · d) was measured by the Senarmont method. Table 1 shows the results. Birefringence (Δn) = front retardation (Δn · d) / side chain type liquid crystal polymer alignment film thickness (d).

[Measurement of chromatic dispersion of phase difference (Δn · d)]
The wavelength of the measurement light is changed by a monochromator, and the front phase difference (Δn ·
d) was measured. The chromatic dispersion (α) of the phase difference was defined as follows. Table 1 shows the results.

Α = Δn · d (450 nm) / Δn · d
(590 nm).

Incidentally, (b1) a monomer was not contained ((a
1) A side chain type liquid crystal polymer (formed only of a monomer) is also synthesized in the same manner as described above, and the ordinary light refractive index (1.545), the birefringence (0.30), and the wavelength dispersion of the retardation are similarly obtained. (Α: 1.170) was calculated. Table 1 shows the results.

[0042]

[Table 1] From Table 1, it can be seen that the side-chain type liquid crystal polymer of the present invention has an ordinary refractive index of 1.5 by adjusting a monomer containing a non-liquid crystal fragment side chain represented by (b1) monomer.
It is recognized that the control can be continuously performed from 45 to 1.565.

Further, the side chain type liquid crystal polymer of the present invention comprises:
It is recognized that the birefringence characteristic (Δn = 0.30) of the side chain type liquid crystal polymer formed by only the (a1) fragment can be continuously controlled by adjusting the ratio of the (b1) monomer unit. .

In order to improve the display quality of the liquid crystal display, it is considered that it is desirable that the wavelength dispersion of the birefringence (Δn) of the liquid crystal of the liquid crystal display coincides with the wavelength dispersion of the birefringence of the retardation plate. Heretofore, polycarbonate (α: 1.1:
) And polyethersulfone (α: 1.17) are used. As shown in Table 1, the side chain type liquid crystal polymer of the present invention comprises polycarbonate and polyether. The wavelength dispersion of the birefringence (Δn) between the sulfones can be continuously controlled, and it is easy to match the wavelength dispersion of the liquid crystal of the liquid crystal display of the retardation plate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G02F 1/13363 (72) Inventor Shu Mochizuki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Masahiro Yoshioka 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA06 BA42 BB42 BC22 2H091 FA11X FA11Z FA12X FA12Z FA14Z FB02 FD06 4H027 BA13 BD07 4J100 AL08P AL08Q BA02P BA20P BA40P BC43P BC44P BC49Q CA04 DA63 DA66 JA32

Claims (10)

[Claims] 1. A side chain type liquid crystal polymer comprising a monomer unit (a) containing a liquid crystal fragment side chain and a monomer unit (b) containing a non-liquid crystal aromatic fragment side chain. . 2. In the monomer unit (a) containing a liquid crystal fragment side chain, the fragment side chain has at least one substituent selected from an alkoxy group, a cyano group, a fluoro group and an alkyl group,
2. The side chain type liquid crystal polymer according to claim 1, wherein the side chain type liquid crystal polymer is included in a direction parallel to the molecular long axis of the fragment side chain. 3. The monomer unit (a) containing a liquid crystal fragment side chain has a general formula (a): (However, R ¹ is a hydrogen atom or a methyl group, a is 1 to
A positive integer of 6, X ¹ represents a —CO ₂ — group or —OCO—
R ² represents a cyano group, an alkoxy group, a fluoro group or an alkyl group; b and c each represent an integer of 1 or 2; 3. The side chain type liquid crystal polymer according to claim 1, which is a monomer unit represented by the formula: 4. The monomer unit (b) containing a non-liquid crystalline aromatic ring fragment side chain has a general formula (b): (However, R ³ represents a hydrogen atom or a methyl group, and X ² represents-
A CO ₂ — group or —OCO— group, —O— or a single bond, and R ⁴ is a group represented by the general formula (c): And a substituent represented by The side chain type liquid crystal polymer according to any one of claims 1 to 3, which is a monomer unit represented by the formula: 5. The side chain type liquid crystal polymer according to claim 1, wherein the weight average molecular weight is 2,000 to 100,000. 6. The composition according to claim 1, which has a monodomain orientation.
6. The side chain type liquid crystal polymer according to any one of 5. 7. A monomer (a) containing a liquid crystal fragment side chain and a monomer (b) containing a non-liquid crystal aromatic ring fragment side chain are copolymerized to give a liquid crystal property of the monomer (a). 2. The method according to claim 1, wherein the refractive index characteristic or the birefringence characteristic of the side chain of the fragment is controlled.
7. The method for producing a side chain type liquid crystal polymer according to any one of items 1 to 6. 8. The side chain type liquid crystal polymer comprising a monomer unit (a) having a liquid crystal fragment side chain and the side chain type liquid crystal polymer may be provided with a copolymer monomer unit. A method in which a monomer unit (b) containing a side chain of a non-liquid crystalline aromatic ring fragment is contained, and the ratio is controlled to a desired value by changing the ratio of the monomer unit (b). 9. An optical element comprising the side chain type liquid crystal polymer according to claim 1. 10. A liquid crystal display using the optical element according to claim 9.