JPH03149218A - Aromatic polyester - Google Patents

Abstract

PURPOSE:To prepare a melt moldable arom. polyester improved in the heat resistance and mechanical strengths by reacting 4-hydroxybenzoic acid, 3- hydroxybenzoic acid, protocatechuic acid, and a lower acyl ester of 4,4'-biphenol. CONSTITUTION:4-Hydroxybenzoic acid, 3-hydroxybenzoic acid, protocatechuic acid, and a lower acyl ester of 4,4'-biphenol are heated in a nitrogen stream at a temp. between room temp. and 150 deg.C for 30min to 15hr to convert the hydroxyl groups into active esters groups, and then caused to undergo polycondensation reaction at 180-350 deg.C to give an arom. polyester which comprises 10-99mol% repeating units of formula I, 1-90mol% repeating units of formula II, and 0-10mol% repeating units of formula III, forms a thermoplastic liq. crystal phase at 400 deg.C or lower, and has a melt viscosity of 10-100000P measured at a temp. in the range of from the flow switching temp. to 400 deg.C at a shear rate of 10<3>sec<-1>. In the formulas, X<1> to X<6> are each -O-, -NH-, or -CO-; when X is -O- or -NH-, Y is -CO-, while Y is -O- or -NH- when X is -CO-; Ar1 to Ar3 are each a 6-18C arom. group; m is 2 or 3; and n is 1-6.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field The present invention relates to a novel branched thermotropic aromatic polyester. The polyester of the present invention is
Provides a molded product that is melt moldable, has excellent heat resistance, and has good mechanical properties.

<Conventional technology> In recent years, the demand for higher performance plastics has been increasing, and various high-performance plastics have been developed and put on the market. Thermotropic liquid crystal polymers have good heat resistance and processability, and are being used mainly in electrical and electronic materials.

Fully aromatic polyesters are widely known as such liquid crystal polymers, and for example, homopolymers and copolymers of 4-hydroxybenzoic acid are commercially available. However, 4-hydroxybenzoic acid homopolymer has a melting point that is too high to be melt-molded. As a means of lowering the melting point or softening point of such wholly aromatic polyester to improve melt processability, generally,
1) Copolymerization of rigid and linear chains, 2) Introduction of king and crank structures, 3) Introduction of nuclear substituents, and 4) Introduction of aliphatic chains are known. For method 1), for example, terephthalic acid and hydroquinone or 4,41
- A copolymer obtained by copolymerizing biphenol is described in Japanese Patent Publication No. 47870/1983. As the method 2), for example, the above-mentioned publication and JP-A-54-77691 describe the introduction of isophthalic acid or a naphthalene ring. Method 3) is described in Japanese Patent Application Laid-open No. 53-654.
No. 21 describes a liquid crystal polymer composed of terephthalic acid and phenylhydroquinone.

As for method 4), JP-A-51-8395 describes a type of liquid crystal polymer obtained by modifying polyethylene terephthalate with 4-hydroxybenzoic acid.

These polymers are rigid (semi-rigid) linear polymers and have many advantages such as heat resistance, high strength, high elasticity, easy processability, and dimensional stability, but on the other hand, they have large anisotropy in physical properties. , they have problems such as weak weld strength and poor adhesion to metals and other resins. By giving these polymers a branched structure, new properties not found in linear polymers can be expected. As a branched thermotropic liquid crystal polymer, Japanese Patent Publication No. 55-14090 discloses a branched aromatic polymer comprising a cyanuric halide and one or more compounds selected from the group consisting of hydroxybenzoic acid, aromatic diols, and aromatic dicarboxylic acids. family polyesters are described.

Furthermore, JP-A-56-109226 discloses that a copolymer contains a residue formed from a crosslinking reactant, and that the concentration of the residue is determined by shearing at a temperature lower than the decomposition temperature of the polymer using a capillary rheometer. A polymer capable of forming an anisotropic melt characterized in that the melt viscosity measured at a stress of 104 N/m2 is insufficient to produce a fully crosslinked polymer of less than 107 Nsec/m2. Coalescence is described and polyesters consisting of aromatic diols, aromatic dicarboxylic acids and pyrog6-triacetate are exemplified. In addition, in JP-A-58-104924, a hydroxy acid unit and R, (0), or R2 (CO),
A polyester comprising: In such a branched polymer, as described in JP-A-58-104924, all units other than the branching component are hydroxycarboxylic acids, and all the polyfunctional compounds serving as the branching component have the same functional group. It can be divided into star-shaped polymers, and partially crosslinked polymers made of aromatic diols, aromatic dicarboxylic acids, and in some cases further aromatic hydroxycarboxylic acids, and polyfunctional compounds having one or more functional groups. However, an increase in the amount of branched components causes a decrease in physical properties due to a decrease in molecular weight in the case of foot-shaped polymers, and a deterioration in moldability due to the polymer becoming insoluble and infusible due to the progress of crosslinking in the case of partially crosslinked polymers. Therefore, the amount of branched components introduced is limited, and according to the examples in the above publication and studies by the present inventors, the preferred amount of branched components is about 0.1-1 mol% of the total monomer components. OBJECTS OF THE INVENTION An object of the present invention is to provide a novel branched thermosetting aromatic polyester that is easy to melt process. More specifically, it has a plurality of branched units in the main chain, is not crosslinked, is processed by a thermoplastic molding method in a liquid crystal state at a temperature of 400°C or lower, preferably 360°C or lower, and has heat resistance, The goal is to create molded products with excellent mechanical strength.

Means for Solving the Problems As a result of extensive studies, the present inventors have discovered an aromatic polyester having a specific repeating unit that achieves the above object.

That is, the present invention essentially comprises the following (1), (n), (
The repeating unit represented by III) is used as a constituent component, and the unit (I
) is contained in 10-99 mol% of the total, (II) is contained in 1-90 mol% of the total, and (m) is 0-10 mol% of the total.
It forms a thermotropic liquid crystal phase at a temperature lower than 400°C, and has a melt viscosity of 10-1 measured at a shear rate of 103 sec in a temperature range from the starting temperature to 400°C.
00.000 poise aromatic polyester.

X Art Y (1) (X)
, A r 2 Y (II)
(X), A r 3 (III) (However, in the formula, X is -〇-, -NH- or -CO-, and Y is -CO-, X when x is -〇-, -NH-4) When is -CO-, it is -〇-, -NH-.

Ar, %Ar2, Ar3 are each independently an aromatic group having 6-18 carbon atoms, m is 2 or 3, and n is an integer of 1-6) repeating unit (1) The compound to be given is R.

1-4 alkyl group, C1-4 alkoxy group, C6-12 aryl group, halogen), for example, 4-hydroxybenzoic acid, 4-hydroxy-3- Methylbenzoic acid, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxy-3-phenylbenzoic acid, 4-hydroxy-3-chlorobenzoic acid,
3-hydroxybenzoic acid and derivatives thereof, or
Compounds that give repeating units represented by C, aryl groups having 6 to 12 carbon atoms, halogen), such as 4-aminobenzoic acid, 3-aminobenzoic acid, and compounds that give repeating units such as 4-hydroxy Phenylacetic acid, 3-
(4-Hydroxyphenyl)propionic acid and its derivatives, or compounds giving -F-, such as 2-hydroxy-6-naphthoic acid, 3-hydroxy-6-naphthoic acid, -CO-(
B is an alkylene group having 1 to 4 carbon atoms), such as 6-hydroxy-2-naphthyl acetic acid, 3-(6-hydroxy-2-naphthyl)propionic acid, and SO2-, - A compound giving a repeating unit represented by OCH2CH20-, -C(CHi)z-, where n is 0 or 1), such as 4-hydroxy-
4°-carboxybiphenyl, 4-hydroxy-4″-
Carboxybenzophenone, 4-hydroxy-3°-
One or more compounds selected from carboxybenzophenone, 4-hydroxy-4°-carboxydiphenyl ether, and derivatives thereof, preferably two or more, containing 60-99 mol% of 4-hydroxybenzoic acid. is preferred. The amount of these hydroxycarboxylic acids is 10-99 mol% of the total, preferably
40-98 mol%, more preferably 60-95 mol%
is within the range of If the content of the repeating unit (I) is less than 10 mol %, it is not preferable because the heat resistance, thermal stability, etc. will be insufficient and the mechanical strength of the molded article will also decrease.

The repeating unit (II) and X2 are -0-, -NH- or -CO-, and Y
is X, and when X2 is -〇-, -NH-, -CO-,
When 1 and X2 are -CO-, -〇-, -NH-,
Functional groups X1 and Yl or X.

and X2 are in a rose positional relationship. ), for example, protocatechuic acid (3,4-
dihydroxybenzoic acid), 2.4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2.4-dicarboxyphenol, 4-hydroxyphthalic acid, 3,4-
Diaminobenzoic acid, 3-amino-4-hydroxybenzoic acid, and derivatives thereof, or -X, X, -X2, and X3 are -〇-, -NH-? : get
-co-, Y is x, , X2 and X3 are -0-,
When -NH-, -CO-, Xl, X, :Fi and X3 are-
When it is CO-, it is -0-, -NH-. ), for example, 3.4°5-trihydroxybenzoic acid, 2,4.5-)lihydroxybenzoic acid,
and derivatives thereof, or x2ti-o-, -NH-
or -CO-, Y is xl and X2 is -〇-,
-NH- When -CO-, xl and X2 are -CO- 10-, -NH-, and the functional group X and Yl or
l and X2 are 1.4-1st, 2.6-position or 2. It is in a positional relationship of Fu position. ), for example, 2,3-dihydroxy-6-naphthoic acid,
Examples include 2,4-dihydroxy-6-naphthoic acid, 2-hydroxy-5,7-dicarboxynaphthalene, and derivatives thereof, the amount of which is 1-90 mol% of the total, preferably 2-60 mol%, and Preferably 5-40 mol%
It is.

Repeating unit (m) is hydroquinone, resorcinol, 4.
4°-biphenol, 4.4”-dihydroxydiphenyl ether, bisphenol S1 bisphenol A, 2
．． 6-dihydroxynaphthalene, 4-hydroxybiphenyl, β-naphthol, 1,4-phenylenediamine,
1.3.5-trihydroxybenzene, terephthalic acid,
Isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4-
Examples include phenylbenzoic acid, derivatives thereof, or mixtures thereof, and the amount thereof is preferably 0 to 10 mol%, particularly 0.01 to 2.00 mol% of the total. If the content of repeating unit (III) is 10 mol % or more, the physical properties will decrease due to a decrease in molecular weight, but if a small amount is added, the thermal stability during melting will be improved.

According to the studies conducted by the present inventors, in order to introduce multiple branching units into the main chain without a crosslinking reaction, the main constituents are hydroxycarboxylic acid and/or aminocarboxylic acid units (1) and at least two Branching unit (II) having three or more functional groups X and one functional group Y (where X is -0-
, -NH- or -CO-, and y tt x is -0
-, when -NH-, -CO-, when X is -CO-, 10-,
-NH--), and preferably further comprises a unit (III) having one or more functional MX.

Here, the crosslinking reaction refers to a reaction that results in the formation of a so-called insoluble and infusible polymer having a three-dimensional network structure (new edition of the Polymer Dictionary; edited by the Polymer Dictionary Editorial Committee, Japan Society of Polymer Science). Furthermore, in order to express liquid crystallinity, the branching unit (II)
The functional group X or Y of is located linearly, that is, when the unit (Il) contains a benzene ring, the functional group is located at the 1.4-position, and when the functional group contains a naphthalene unit at the 1.4-position, the 1. 41st place, 2.6-th place, or 2. Preferably, it is in the F position.

Therefore, the polyester of the present invention has structural units (1), (I
f), (III), essentially cross-linked anti-12
For the time being, it doesn't come with it. Moreover, (X) is a polyfunctional component.

Even if the amount of -Ar2-Y added is increased, the molecular weight does not decrease, and a polymer having multiple branches in the main chain is produced. Furthermore, since a set of functional groups of the (X)a+Ar2Y component is in a linear relationship, it has a liquid crystal forming ability. Furthermore, surprisingly, by introducing a branched structure, the melting point of the polymer is significantly lowered and good processability is imparted.

The polyester of the present invention exhibits a melt viscosity value of 10-100,000 boas when measured at a shear rate of 10 see under a temperature range from the onset temperature to 400°C,
Particularly preferred are those exhibiting a melt viscosity of 10-50,000 poise. The measurement of the melt viscosity can be carried out using a Koka-type F6-Tester manufactured by Shimadzu Corporation, and a die having a diameter of 0 to 5 mm and a length of 2 mm.

The polyester of the present invention can be produced according to the conventional polycondensation method of aromatic polyester, and there are no particular restrictions on the production method, but typical production methods include, for example, 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, Examples include a method in which lower acyl esters of benzoic acid, protocatechuic acid, and 4.4°-biphenol, preferably acetic esters, are reacted. Acyl esters can also be made in situ and used without isolation.

To be more specific about this reaction, the repeating unit (I
), (II), and (I[) and an active esterifying agent such as acetic anhydride are charged into a polymerization apparatus equipped with a stirrer, a nitrogen gas inlet tube, and a vacuum distillation apparatus, and the mixture is heated at room temperature under a nitrogen stream. −
The mixture is heated at 150° C. for 30 minutes to 15 hours to effect active esterification of hydroxyl groups.

This is followed by a reaction at a temperature of 180-350°C.

Since the rate of the polycondensation reaction generally increases as the temperature rises, it is preferable to carry out the polycondensation at a relatively high temperature.

However, at high temperatures polyester tends to decompose. Further, a higher molecular weight is advantageous for thermal stability.

Therefore, it is generally desirable to start the reaction at a low temperature and to continuously increase the temperature as the reaction progresses. Furthermore, when the reaction rate decreases, the reaction can be carried out under reduced pressure of about 1 mmHg. The obtained product can optionally be subjected to solid state polymerization at a temperature of 200-300°C. This operation increases the molecular weight and significantly improves the properties of the resulting polymer. Additionally, a catalyst can be used to promote the above reaction. Catalysts of this type are known, for example, alkali metal salts, Mn, Mg,
These include Zn, Cd, and Sb compounds. The amount of catalyst is 0.001-1.0, especially 0.001-1.0, based on the amount of total monomers used.
01-0.2% by weight is preferred. Furthermore, the molecular terminals can be sealed by adding a -functional compound.

<Effects of the Invention> The aromatic polyester of the present invention is a novel branched thermotropic aromatic polyester, and the molding temperature is 40°C.
Low temperature below 0℃, suitable for injection molding, extrusion molding, compression molding, and bu 6
- Can be subjected to melt forming such as molding, and can be processed into molded products, fibers, films, etc. Furthermore, this polyester has excellent mechanical strength (especially elastic modulus) because molecular orientation is achieved by shearing during processing.
Gives a molded product with compromised dimensional stability. In addition, additives such as reinforcing agents such as glass fibers and carbon fibers, fillers, nucleating agents, pigments, antioxidants, stabilizers, and other thermoplastic resins are added to the polyester of the present invention during molding. The properties of molded products can be improved.

<Examples> The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited in any way by these Examples. In addition, the temperature at which the outflow starts is the length 10
Using a die with a diameter of 1 mm,
- Under a pressure of 100Kg/cm'' with a tester, 6℃/mi
The temperature was increased by n to give a melt viscosity of 48,000 boads. The melt viscosity of the obtained polymer was 2 mm in length.
The measurement was carried out using a Koka-type F6-Tester using a die having a diameter of 0.5 mm. The anisotropy of the obtained polymer during melting was confirmed using a polarizing microscope equipped with a hot stage. Mechanical properties were determined by ASTM D790 after injection molding with Banashection NM-5211 (manufactured by Matsushita Electric Industrial Co., Ltd.).
．． Measurement was carried out in accordance with D256.

Example 1 151.94 g of 4-hydroxybenzoic acid (1,
10m0 l), 3-hydroxybenzoic acid 13-81
g (0.10 mol), protocatechuic acid 30.83
g (0,20m0 l), 4.4”-biphenol 1
．． After charging 12 g (0,007 m01) and 180.82 g (1,77 m0 l) of acetic anhydride and purging with nitrogen, the polymerization apparatus was heated to 150 m
The temperature was raised to 0.degree. C. and maintained for 2 hours to activate the hydroxy groups. Thereafter, the reaction temperature was increased to 30°C while distilling off the by-product acetic acid.
The temperature was raised to 0°C. The obtained polymer was taken out after cooling the polymerization system.

This polymer showed optical anisotropy in the molten state as measured by polarized light microscopy. The outflow start temperature is 245℃, and the temperature is 27℃.
The melt viscosity measured at 0°C and a shear rate of 1035 ec-'' was 3,040 poise.The bending strength was 1.350 k.
g/Cm2, flexural modulus is 163,000 kg
/ cm”.The obtained white polymer was
It is soluble in p-chlorophenol and pentafluorophenol, and a transparent and tough film was obtained by solvent casting.

Example 2 Into the polymerization apparatus described in Example 1, 116.72 g of 4-hydroxybenzoic acid (0,850 m.

1), 3-hydroxybenzoic acid a 1198g (0,06
5m0 J), protocatechuic acid 20.04g (0
, 130m0 l), 4.4°-biphenol 0.9
7 g (0,005 m0 l) and 131 acetic anhydride
, prepare 0 g (1,29 mol) of fu,
Polymer synthesis was performed in the same manner as in Example 1.
The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 256°C. The melt viscosity measured at a temperature of 270° C. and a shear rate of 10 see − was 5.800 poise. Bending strength is 1.
330 kg/cm, and the flexural modulus was 172.000 kg/cm2.

Example 3 In the polymerization apparatus described in Example 1, 132.60 g (0.96 m01) of 4-hydroxybenzoic acid, 8.29 g (0.06 m01) of 3-hydroxybenzoic acid, and 18.50 g (0.06 m01) of protocatechuic acid were added. ,12m01) ,4.
4-biphenol 1-12g (0,006m0 l
) and acetic anhydride 150-07g (1,47m01)
was charged, and polymer synthesis was performed in the same manner as in Example 1.

After pulverizing the obtained polymer, solid phase polymerization was performed at 200-260°C under reduced pressure.

The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 322°C. The melt viscosity measured at a temperature of 340° C. and a shear rate of 103 sec was 4,200 poise. Bending strength is 108
0 kg/cm2, flexural modulus is 158,
000 kg/cm2.

Example 4 In the polymerization apparatus described in Example 1, 82-88 g (0-60 m0 l) of 4-hydroxybenzoic acid, 30.82 g (0.20 m0 l) of protocatechuic acid, 4.4
- 1.86 g (0,001 m01) of biphenol and 114.00 g (1,12 m01) of acetic anhydride were charged, and polymer synthesis was performed in the same manner as in Example 1.

The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 212°C. The melt viscosity measured at a temperature of 240°C and a shear rate of 10 see-'' was 2,200 poise.The bending strength was 1.
120kg/cm2, flexural modulus is 112,000kg
/cm”.

-20 Example 5 In the polymerization apparatus described in Example 1, 138.13 g (1,00 m01) of 4-hydroxybenzoic acid, 13.81 g (0-10 m0 l) of 3-hydroxybenzoic acid,
4-aminobenzoic acid 13.71g (0.10mol)
, protocatechuic acid 30.83g (0.20m0 l
), 4.4°-biphenol 1.12g (0,00
6 m0 l) and 180.82 g of acetic anhydride (1,7
Polymer synthesis was performed in the same manner as in Example 1.

The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 262°C. The melt viscosity measured at a temperature of 290°C and a shear rate of 103 sec-'' was only 3.00 boads.

The bending strength is 1.250 kg/cm2, and the bending modulus is 168. OOOkg/cm”.

Example Low - In the polymerization apparatus described in Example 1, 151-94 g (1,10 m0 l) of 4-hydroxybenzoic acid and 15.21 g (0,10 m0 l) of 4-hydroxyphenylacetic acid were added.
), protocatechuic acid 30.83g (0.20m0
l), 4-hydroxybiphenyl 1.69g (0
,01m01) and acetic anhydride 180.82g (1,
77 ml) was charged, and polymer synthesis was performed in the same manner as in Example 1. The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 270°C. Temperature 290℃, shear rate 1
The melt viscosity measured at 035 ec- was 6.800 boads. The bending strength was 1.300 kg/cm2, and the bending modulus was 14.700 kg/cm2.

Example 7 In the polymerization apparatus described in Example 1, 151.94 g (1,10 m01) of 4-hydroxybenzoic acid, 13.81 g (L 10 m01) of 3-hydroxybenzoic acid were added.
, 2,5-dihydroxybenzoic acid 30.83g (0
, 20m0 l), 4-hydroxybiphenol 1.
69g (0.01m01) and acetic anhydride 180.8
2g (1,77m01) was charged, and polymer synthesis was performed in the same manner as in Example 1.

The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature of the outflow was 269°C. The melt viscosity measured at a temperature of 300°C and a shear rate of 10 see-'' was 3,300 poise.The bending strength was 1
, 100kg/cm2, flexural modulus is 141.000k
g/cm2.

Example 8 In the polymerization apparatus described in Example 1, 151.94 g (1,10 m0 l) of 4-hydroxybenzoic acid, 13.81 g (0,10 m0 l) of 3-hydroxybenzoic acid were added.
, 4-hydroxyphthalic acid 36.62g (0,20m
0 l), terephthalic acid 1,66 g (0,01 m0
1) and acetic anhydride 180.82°g (1, Fufu m
o l) was charged, and polymer synthesis was performed in the same manner as in Example 1.

The obtained polymer showed optical anisotropy in the molten state by polarizing microscopy measurements. The starting temperature for outflow was 250°C. The melt viscosity measured at a temperature of 270°C and a shear rate of 10 see-'' was 6,300 poise.The bending strength was 1,
310kg/cm2, flexural modulus is 159,000kg
/cm2 ◎ Comparative Example 1 In the polymerization apparatus described in Example 1, 151.94 g (1.10 mol) of 4-hydroxybenzoic acid, 13.81 g (0.10 mol) of 3-hydroxybenzoic acid, and A polymer was synthesized in the same manner as in Example 1 by charging 180.82 g (1,0 mol) of acetic anhydride.

Stirring became difficult at the polymerization temperature of 280°C. The obtained polymer was brittle.

Comparative Example 2 In the polymerization apparatus described in Example 1, 151.94 g (1,10 mol) of 4-hydroxybenzoic acid and 13.81 g (0,10 mol) of 3-hydroxybenzoic acid were added.
, 30-83g of 3,5-dihydroxybenzoic acid (0,
20m01), 4.4-biphenol 1.86g (
0.01 m0 l) and 180-82 g of acetic anhydride (
1.77 ml) was charged, and polymer synthesis was performed in the same manner as in Example 1. The contents solidified at a polymerization temperature of 250°C. The obtained polymer was brittle.

Comparative Example 3 In the polymerization apparatus described in Example 1, 151.94 g (1.10 mol) of 4-hydroxybenzoic acid, 1181 g (0.10 mol) of 3-hydroxybenzoic acid, 1,3.5-)ri Hydroxybenzene 25.21g (0.20m01), 4゜4
°-biphenol 1.86 g (0-01 m0 l) and acetic anhydride 180,82 g (1,) m
ol) was charged, and polymer synthesis was performed in the same manner as in Example 1. Stirring became difficult at the polymerization temperature of 280°C. The obtained polymer was very brittle.

Claims (1)

[Claims] (1) Essentially the repeating units shown below (I), (II), and (III) are the constituent components, and the unit (I) is 1 of the whole.
Contains 0-99 mol%, and (II) is 1-90 mol% of the total
(III) is 0-10 mol% of the total, and 40
Forms a thermotropic liquid crystal phase at a temperature lower than 0°C, and maintains a temperature of 10^3se in a temperature range from the outflow start temperature to 400°C.
Melt viscosity measured at a shear rate of c^-^1 is 10-10
0,000 poise aromatic polyester. -X-Ar_1-Y-(I) -(X)_m-Ar_2-Y-(II) -(X)_n-Ar_3(III) (However, in the formula, X is -O-, -NH- or -CO -, Y is -CO- when X is -O-, -NH-,
When O-, it is -O-, -NH-. Ar_1, Ar_2, Ar_3 are each independently an aromatic group having 6 to 18 carbon atoms, m is 2 or 3,
n is an integer from 1 to 6)