JPH07188402A - Liquid crystalline polyester - Google Patents

Abstract

PURPOSE:To provide a liq. crystalline polyester which enables the alignment of a liq. crystal to be easily fixed by glassification, provides large wavelength dispersion of birefringence and is favorably applicable to optical devices by introducing particular structural units into its molecule. CONSTITUTION:This liquid crystalline polyester comprises structural units of the formulae [wherein X and Y represent each H, Cl, Br, or a C1 to C4 alkyl group. The A to (C+D) molar ratio is (45:55) to (55:45), the A to B molar ratio is (49:1) to (20:30), and the C to D molar ratio is (10:40) to (45:5)]. In the structural units, the unit A is one derived from a polyester forming deriv., e.g. terephthalic acid, the unit B is one derived from a polyester forming deriv., e.g. 4-hydroxycinnamic acid, the unit C is one based on a polyester forming deriv., e.g. hydroquione, and the unit D is one based on a polyester forming deriv., e.g. catechol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystalline polyester which is suitable for application to an optical element, in which glass for liquid crystal orientation is easily fixed and birefringence has a large wavelength dispersion.

[0002]

2. Description of the Related Art In recent years, polymer liquid crystals have been used in the field of high-performance materials utilizing high heat resistance and moldability, and functional properties utilizing the change of the liquid crystal phase structure due to external fields such as heat or electric field and phase fixation. It has been actively researched and developed in the materials field, and has already been commercialized in the high performance materials field. On the other hand, in the field of functional materials, active research is being conducted with the aim of application to optical recording, nonlinear optical materials, liquid crystal alignment films, optical fibers, optical elements for liquid crystal display devices, etc., but none have been commercialized yet. When polymer liquid crystals are applied to functional materials, they can be broadly divided into applications that utilize dynamic changes in the phase transition of liquid crystals and applications that use the liquid crystal's unique molecular orientation as static elements. Most of them use the property of liquid crystal for light. The important requirements for polymer liquid crystals that can be applied to the latter liquid crystal alignment-fixed optical element are that the liquid crystal alignment is easy to fix and that the liquid crystal alignment is stable after fixation, and the property against light, that is, refraction It is possible to freely control the index, birefringence, wavelength dispersion of birefringence, and the like. In particular, if an optical element with a large wavelength dispersion of birefringence, which has recently been strongly demanded in the display field, can be manufactured from a polymer liquid crystal, it will be an epoch-making optical element together with the unique polarization property of a fixed liquid crystal alignment structure. Can be manufactured. However, there is no example of the development of a polymer liquid crystal that has a large wavelength dispersion of birefringence and can stably fix the liquid crystal alignment, which can be a material for such an optical element, and there are few research examples. It was the current situation.

[0003]

DISCLOSURE OF THE INVENTION The inventors of the present invention have used a liquid crystalline polyester having a glass phase at a temperature below a liquid crystal transition point as a polymer liquid crystal which can be easily fixed in orientation and can be easily manufactured industrially at a low cost. As a result of searching for a unique structure that can realize the required wavelength dispersion of large birefringence, a polyester containing a catechol unit and a 4-hydroxycinnamic acid unit as a constitutional unit in the molecule satisfies these requirements. Finally, the present invention was finally reached.

[0004]

That is, the present invention relates to a liquid crystalline polyester comprising a structural unit represented by the following general formula.

[0005]

[Chemical 2]

(Where X and Y are hydrogen atoms, Cl, Br
Alternatively, it represents an alkyl group having 1 to 4 carbon atoms, and the composition represented by the molar ratio has A / (C + D) of 45/55 to 55/45.
, A / B in the range 49/1 to 20/30 and C / D in the range 10/40 to 45/5).

The polymer of the present invention comprises a terephthalic acid unit represented by the above general formula, a 4-hydroxycinnamic acid unit, a hydroquinone or a substituted hydroquinone unit and a catechol or a substituted catechol unit. Many liquid crystalline polyesters composed of aromatic compounds are known, but no polymer containing 4-hydroxycinnamic acid units and catechol units in the same polymer is known at all. In general, a rigid and highly linear molecule is preferable in order to exhibit good liquid crystallinity, but since the catechol unit acts in a direction that disturbs the linearity of the molecule, it lowers the melting point of the polymer or improves the solubility. For the purpose of introduction (for example, F. Navarro et al, J. Polym.
Sci. , Polym. Chem. Ed. , 1992,
30, 1789), but is not commonly used. Further, 4-hydroxycinnamic acid is an example introduced to impart photoreactivity to a polymer (for example, WRK).
rigbaum et al. Polym. Sc
i. , Polym. Phy. Ed. , 1983, 21,
1851) is observed, but it is usually rarely used in terms of stability. The present inventors intentionally introduced both of these units, which are normally avoided, into the same molecule for the purpose of synthesizing a polymer liquid crystal capable of fixing the liquid crystal orientation and having a large wavelength dispersion of birefringence. It was found that these polymers become a glass phase at a temperature below the liquid crystal transition point (that is, the glass transition point Tg) without impairing the liquid crystallinity, can fix the liquid crystal structure, and have large wavelength dispersion of birefringence. The present invention has been completed.

The A unit is usually a unit derived from a polyester-forming functional derivative such as terephthalic acid or dimethyl terephthalate, and the B unit is usually a polyester-forming functional derivative such as 4-hydroxycinnamic acid or 4-acetoxycinnamic acid. It is a more guided unit. The C unit is usually a unit based on a hydroquinone or a substituted hydroquinone or a polyester-forming functional derivative thereof such as diacetate, and X is a hydrogen atom, Cl, Br or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, an i-propyl group, a butyl group and a t-butyl group. Among them, a methyl group,
Ethyl and t-butyl groups are particularly preferred. The D unit is usually a unit based on catechol or a substituted catechol or a polyester-forming functional derivative thereof such as diacetate, and Y is a hydrogen atom, Cl, Br or an alkyl group having 1 to 4 carbon atoms. As the alkyl group, a methyl group, an ethyl group, an i-propyl group, a butyl group and t
-Butyl group and the like are mentioned, and among them, methyl group, ethyl group and t-butyl group are particularly preferable. Of course, the arrangement of each structural unit may be either block or random.

The composition of these units in the polymer is A / (C + D) of 45/55 to 55 when expressed in terms of molar ratio.
/ 45, preferably 48/52 to 52 /
It is in the range of 48, particularly preferably 50/50.
Further, A / B is preferably in the range of 49/1 to 20/30, and particularly preferably in the range of 48/2 to 25/25. When this value is less than 20/30, that is, when the amount of 4-hydroxycinnamic acid is too large, unfavorable effects such as the inhibition of the expression of liquid crystallinity and the deterioration of the stability of the polymer occur. On the contrary, when it is larger than 49/1, that is, when the amount of terephthalic acid is too large, the wavelength dispersion of birefringence becomes small and the desired effect cannot be obtained.

The value of C / D is 10/40 to 45/5.
Is preferable, and a range of 15/35 to 40/10 is particularly preferable. When this value is less than 10/40, that is, when the amount of catechol units is too large, the liquid crystallinity is impaired, which is not preferable. When it is more than 45/5, that is, when the amount of hydroquinone units is too large, the polymer is Since it has a crystal phase, the liquid crystal orientation cannot be fixed, which is not preferable.

The molecular weight of the polymer is 30 ° C. in a phenol / tetrachloroethane mixed solvent (60/40 weight ratio).
The value of ηinh measured in (1) is preferably 0.05 to 3.0, and particularly preferably 0.07 to 2.0. ηin
If the value of h is less than 0.05, the strength of the device may be weakened, which is not preferable. If the value of h is greater than 3.0, the melt viscosity may be too high and the liquid crystal orientation may be deteriorated. Not preferable. The Tg of these polymers is preferably 50 ° C. or higher, particularly preferably 70 ° C. or higher, and the upper limit is not particularly limited, but is usually preferably 300 ° C. or lower. If the Tg is lower than 50 ° C., even if the liquid crystal alignment is once fixed, the reliability at high temperature becomes poor, and it may be difficult to use it stably as an industrial material.

The method for synthesizing the polymer of the present invention is not particularly limited, and the polymer can be synthesized by a polymerization method known in the art, for example, a melt polymerization method or a solution polymerization method using a corresponding dicarboxylic acid chloride. In the case of synthesizing by melt polycondensation method, one example is terephthalic acid (A ¹ component),
4-acetoxycinnamic acid (B ¹ component), hydroquinone diacetates represented by the general formula (1) (where X is the same as described above).
C ¹ component) and catechol diacetates represented by the general formula (2) (Y is the D ¹ component as described above) at high temperature,
It can be produced by polymerizing under reduced pressure or high vacuum.

[0013]

[Chemical 3]

Examples of the hydroquinone diacetates include hydroquinone diacetate, methylhydroquinone diacetate, ethylhydroquinone diacetate, t-butylhydroquinone diacetate, chlorohydroquinone diacetate and bromohydroquinone diacetate. Examples of the catechol diacetates include catechol diacetate, methyl catechol diacetate, ethyl catechol diacetate, propyl catechol diacetate, t-butyl catechol diacetate, bromocatechol diacetate and chlorocatechol diacetate.

The molecular weight can be easily controlled by controlling the polymerization time or the charge composition. The polymerization conditions in that case are not particularly limited, but a normal temperature is 150 ° C.
To 350 ° C., preferably 200 ° C. to 300 ° C., the reaction time is 30 minutes or longer, preferably about 1 hour to 20 hours, and the reaction can be carried out under normal pressure or reduced pressure. The charging composition (molar ratio) of each raw material component A ^{1 to} D ¹ is A ¹ / (C ¹
The value of + D ¹ ) is usually 40/60 to 60/40, preferably 45/55 to 55/45, more preferably 48.
/ 52 to 52/48, particularly preferably 50/50.

The value of A ¹ / B ¹ is 49/1 to 20/30
Is preferable, and a range of 48/2 to 25/25 is particularly preferable, and the value of C ¹ / D ¹ is 10/40 to 45.
A range of / 5 is preferred, especially 15/35 to 40/10
Is preferred. In order to accelerate the polymerization reaction, conventionally known metal salts such as sodium acetate and zinc acetate, or organic amines can be used.

When the liquid crystalline polyester of the present invention is produced by the solution polymerization method, terephthalic acid dihalide (A ²
Component), 4-hydroxycinnamic acid chloride, 4-hydroxycinnamic acid halide such as 4-hydroxycinnamic acid bromide (B ² component), hydroquinones (C ² component) represented by the general formula (3), and general formula ( The target polyester can be easily obtained by dissolving the catechol represented by 4) (D ² component) in a solvent and heating in the presence of an acid acceptor such as pyridine.

[0018]

[Chemical 4]

Examples of the terephthalic acid dihalide include terephthalic acid dichloride and terephthalic acid dibromide. The hydroquinones include hydroquinone, methylhydroquinone, ethylhydroquinone, t-
Butylhydroquinone, chlorohydroquinone, bromohydroquinone and the like, and the catechols,
Examples thereof include catechol, methylcatechol, ethylcatechol, propylcatechol, t-butylcatechol, chlorocatechol, bromocatechol and the like.

The solvent used is not particularly limited, but for example, halogen solvents such as o-dichlorobenzene, dichloroethane and tetrachloroethane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and N.
Examples thereof include polar solvents such as methylpyrrolidone (NMP) and ether solvents such as tetrahydrofuran (THF) and dioxane. Further, the acid acceptor is not particularly limited, but examples thereof include pyridine, triethylamine, and tripropyriamine.

The conditions for solution polymerization are not particularly limited, but the temperature is usually 50 ° C. to 200 ° C., preferably 60 ° C. to 150 ° C., and the reaction time is usually 1 hour to 10 hours, preferably 2 hours to 7 hours. . Each raw material component A ^{2 to} D ²
The charging composition (molar ratio) of A ² / (C ² + D ² ) is usually 40/60 to 60/40, preferably 45 /
55 to 55/45, more preferably 48/52 to 52/48, and particularly preferably 50/50. A ² /
The value of B ² is preferably in the range of 49/1 to 20/30,
Particularly, the range of 48/2 to 25/25 is preferable, and C
The value of ² / D ² is preferably in the range of 10/40 to 45/5, and particularly preferably in the range of 15/45 to 40/10.

The wavelength dispersion value of birefringence is represented by the K value, which is the ratio of the birefringence (Δn) when the wavelength of light is 450 nm and the birefringence when the wavelength is 600 nm, which is expressed by the equation (5). K = Δn (450 nm) / Δn (600 nm) (5) The K value of the liquid crystalline polyester of the present invention is governed mainly by the amount of 4-hydroxycinnamic acid units introduced into the polymer, but is 1.14. As described above, it is usually in the range of 1.14 to 1.35, and when the amount of 4-hydroxycinnamic acid units increases, K
The value also increases. Therefore, the polyester of the present invention is 4-
By controlling the amount of hydroxycinnamic acid units, the K value can be controlled freely.

[0023]

EXAMPLES Examples will be given below, but the present invention is not limited thereto. The analytical methods used in the examples are as follows. (1) Determination of polymer composition The polymer was dissolved in deuterated chloroform or deuterated trifluoroacetic acid, and measured and determined by ¹ H-NMR (400 nm) of 1H-NMR (JNM-GX400 manufactured by JEOL Ltd.). (2) Measurement of logarithmic viscosity It was measured at 30 ° C. in a phenol / tetrachloroethane (60/40 weight ratio) mixed solvent using an Ubbelohde viscometer. (3) Measurement of DSC DuPont990 Thermal Analyze
It was measured using r. (4) Observation with optical microscope Observation was performed using a BH2 polarization microscope manufactured by Olympus Optical Co., Ltd. (5) Measurement of wavelength dispersion of birefringence Measurement of birefringence at each wavelength of a film sample, which was heat-treated on a glass with a rubbing polyimide alignment film and then cooled and fixed, was measured for each wavelength emitted from a monochromator. The Senarmont method was performed using monochromatic light. The obtained data was fitted by Cauchy's formula to obtain the wavelength dispersion.

Example 1 100 mmol of terephthalic acid, 2-acetoxycinnamic acid 2
0 mmol, hydroquinone diacetate 40 mmol and catechol diacetate 60 mmol to 300 m
In a 1-liter flask equipped with an acetic acid outflow cooling tube, the polymer was synthesized by heating and stirring under a nitrogen stream at 270 ° C. for 8 hours. The obtained polymer was dissolved in tetrachloroethane and poured into a large amount of methanol to purify the polymer. The structural unit composition and ηinh of the obtained polymer are shown in Table 1. From DSC measurement and polarization microscope observation, Tg
Had a glass phase at 101 ° C. and exhibited a nematic liquid crystal phase at higher temperatures. A small amount of polymer was placed on a slide glass, a cover glass was placed on it, heated on a hot plate at 220 ° C for 10 minutes, and after adding a drop of water, the sample was taken down from the hot plate and cooled. The liquid crystal phase was completely fixed. The K value of this polymer is 1.1.
9 was shown as a large value, and it was found that the polymer of this example had a wavelength dispersion with a large birefringence.

Comparative Example 1 100 mmol of terephthalic acid, 40 mmol of hydroquinone diacetate and 60 mm of catechol diacetate
In the same manner as in Example 1, ol was heated and stirred in a 300 ml flask with an acetic acid outflow cooling tube under a nitrogen stream at 270 ° C. for 8 hours to synthesize a polymer. The obtained polymer was dissolved in tetrachloroethane and poured into a large amount of methanol to purify the polymer. The composition and ηinh of the structural units of the obtained polymer are shown in Table 1.
From DSC measurement and polarization microscope observation, Tg had a glass phase at 104 ° C. and showed a nematic liquid crystal phase at a higher temperature. A small amount of polymer was placed on a slide glass, a cover glass was placed on it, heated on a hot plate at 220 ° C for 10 minutes, added with a chill, a sample was taken down from the hot plate and cooled, and the sample was transparent. The liquid crystal phase was completely fixed. However, the K value of this polymer was 1.13, and the wavelength dispersion of birefringence was smaller than that of the polymer of Example 1.

Example 2 50 mmol of terephthalic acid dichloride, 50 mmol of 4-hydroxycinnamic acid chloride, 40 mmol of methylhydroquinone and 60 mmol of catechol were added.
It was dissolved in 0 ml of o-dichlorobenzene, 50 ml of pyridine was added as an acid acceptor, and the mixture was heated and stirred at 70 ° C. for 4 hours under a nitrogen stream to synthesize a polymer. The reaction solution was poured into a large amount of methanol to collect the precipitated polymer. The structural unit composition and ηinh of the obtained polymer are shown in Table 1. From DSC measurement and polarization microscope observation, Tg
Had a glass phase at 94 ° C. and showed a nematic liquid crystal phase at higher temperatures. A small amount of the polymer was placed on a slide glass, a cover glass was placed on the slide glass, heated on a hot plate at 190 ° C for 15 minutes, and a chill was added, and the sample was taken down from the hot plate and cooled. The liquid crystal phase was completely fixed. The K value of this polymer is 1.2.
It showed a large value of 1 and it was found that the polymer of this example had a wavelength dispersion with a large birefringence.

Examples 3 to 8 The polymers of Examples 3, 4 and 6 were prepared according to Example 1,
Further, the polymers of Examples 5, 7 and 8 were synthesized according to Example 2. The properties of the obtained polymers are shown in Table 1. All of them had a nematic liquid crystal phase at Tg or higher and no crystal phase. After heat treatment and orientation in the same manner as in Example 1, the liquid crystal state was cooled to a temperature not higher than Tg to obtain a highly transparent film in which the nematic orientation state during liquid crystal was fixed. Further, the K value of these polymers was as high as 1.17 to 1.23, and it was found that the wavelength dispersion of birefringence of these polymers was very large.

Comparative Example 2 100 mmol of terephthalic acid, 3-acetoxycinnamic acid 3
0 mmol, and hydroquinone diacetate 100 m
The polymer shown in Table 1 was synthesized in the same manner as in Example 1 using mol. This polymer showed a nematic phase in the liquid crystal state by DSC measurement and a polarization microscope observation, but showed a clear crystal phase without a glass phase at a temperature below the liquid crystal transition point. Take a small amount of polymer on a slide glass,
220 on the hot plate with the cover glass on top
The sample, which had been heated at 10 ° C. for 10 minutes and then lowered from the hot plate and cooled, was clouded due to crystallization, and the nematic liquid crystal phase could not be immobilized. In addition, the K value could not be measured because the obtained film was extremely cloudy.

[0029]

[Table 1]

[0030]

The liquid crystalline polyester of the present invention exhibits large birefringence and wavelength dispersion characteristics, and has a crystal phase and a glass phase directly at a temperature lower than the liquid crystal transition point. By cooling to a temperature below the liquid crystal transition point (glass transition point), the alignment structure in the liquid crystal state can be fixed. The material thus obtained which is transparent and retains the liquid crystal alignment structure is industrially extremely valuable because it can be suitably used for various functional materials, particularly optical elements.

[Brief description of drawings]

FIG. 1 ¹ H-of the polymer obtained in Example 1 of the present invention.
An NMR spectrum is shown.

FIG. 2 ¹ H-of the polymer obtained in Example 2 of the present invention.
An NMR spectrum is shown.

FIG. 3 ¹ H-of the polymer obtained in Example 4 of the present invention.
An NMR spectrum is shown.

Claims (1)

[Claims] 1. A liquid crystalline polyester comprising a structural unit represented by the following general formula: (In the formula, X and Y represent a hydrogen atom, Cl, Br, or an alkyl group having 1 to 4 carbon atoms, and the composition represented by the molar ratio is A.
/ (C + D) is in the range of 45/55 to 55/45, A / B is in the range of 49/1 to 20/30, and C
/ D is in the range of 10/40 to 45/5).