JPS63199223A - Production of thermotropic liquid crystalline polyester - Google Patents

Abstract

PURPOSE:To obtain the titled polyester, having excellent heat resistance, color tone, etc., by blending an acyloxy aromatic carboxylic acid with a lower fatty acid ester of an aromatic diol, etc., and a specific amount of an acid anhydride and polymerizing the blend. CONSTITUTION:(A) An acyloxy aromatic carboxylic acid expressed by formula I (Ar1 is aromatic group; R1 is lower acyl) (e.g. 4-hydroxybenzoic acid, etc.) is, e.g. melt blended with (B) a lower fatty acid ester of an aromatic diol expressed by formula II (Ar2 is aromatic group; R2 and R3 are lower acyl) (e.g. hydroquinone acetate, etc.), (C) an aromatic dicarboxylic acid expressed by formula III (Ar3 is aromatic group) (e.g. terephthalic acid, etc.) and (D) an acid anhydride of a 2-5C lower fatty acid (e.g. acetic anhydride, etc.) in an equivalent amount of 0.01-0.50 based on aromatic hydroxyl groups and (E) a polyester, such as polyethylene terephthalate, etc., and polycondensed to afford the aimed polymer.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing thermotropic liquid crystalline polyester, and more specifically to a thermotropic liquid crystalline polyester that has improved heat resistance, excellent color tone, and is free from foreign substances. The present invention relates to a method for manufacturing.

(Prior art) In recent years, regardless of whether it is a ta fiber, a film or a molded product,
There is an increasing demand for materials with excellent rigidity, heat resistance, and chemical resistance. Polyester has come to be widely recognized for its use in general molded products.

Many polyesters have poor mechanical properties such as 2-flexural modulus, so they are not suitable for applications that require high strength.

Therefore, as a polyester suitable for applications requiring high strength, W. J. Jackson published in the Journal of
Thermotropic liquid crystalline polyesters have attracted attention since the publication of thermotropic liquid crystalline polyesters made of polyethylene terephthalate and 4-hydroxybenzoic acid in Polymer Science Polymer Chemistry Edition, Volume 14 (1976), page 2043. I started collecting them. In this document, Jackson reported that this thermotropic liquid crystalline polyester has more than 5 times the stiffness, 4 times the strength, and 25 times the impact strength of polyethylene terephthalate.

This demonstrated new possibilities for highly functional polymers.

However, this thermotropic liquid crystalline polyester had a glass transition temperature of 80° C. or lower and was inferior in heat resistance. Alloying with other polyesters is a way to improve heat resistance.

For example, blending or copolymerization of t-ba2,2-bis(4'-hydroxyphenyl)propane with an aromatic polyester such as a copolyester consisting of terephthalic acid and isophthalic acid (manufactured by Unitika, trade name: U Polymer). is possible.

However, simply blending such a wholly aromatic polyester with the above-mentioned thermotropic liquid crystalline polyester causes phase separation due to the difference in melt viscosity.
It has been difficult to produce thermotropic liquid crystalline polyester free of foreign matter.

(Problems to be Solved by the Invention) As described above, heat resistance was improved and mechanical strength was excellent. It has been extremely difficult to obtain a thermotropic liquid crystalline polyester free of foreign matter.

An object of the present invention is to provide a method for producing a thermotropic liquid crystalline polyester that has a high intrinsic viscosity, is particularly suitable for molded products that require high strength, is free from foreign matter, and has excellent heat resistance. be.

(Means for Solving the Problems) As a result of intensive research into a method for producing thermotropic liquid crystalline polyester that does not have the above problems, the present inventors found that By mixing fatty acid esters, aromatic dicarboxylic acids, and acid anhydrides of lower fatty acids having 2 to 5 carbon atoms with a polyester whose main component is alkylene terephthalate, and then subjecting them to a single polycondensation reaction, it has heat resistance and eliminates foreign substances. The inventors have discovered that the present invention is suitable for producing a thermotropic liquid crystalline polyester that does not require a thermotropic liquid crystalline polyester, and that the color tone of the obtained thermotropic liquid crystalline polyester is also good.

That is, 2 the present invention comprises 9 an acyloxy aromatic carboxylic acid represented by formula (1), 1 a lower fatty acid ester of an aromatic diol represented by formula (II), and 1 an aromatic dicarboxylic acid represented by formula (III). , an acid anhydride of a lower fatty acid having 2 to 5 carbon atoms in an equivalent amount of 0.01 to 0.50 times the aromatic hydroxyl residue, and a polyester whose main component is alkylene terephthalate are mixed and then polycondensed. At least 0.5dj characterized by reacting! The gist of this paper is a method for producing a thermotropic liquid crystalline polyester having an intrinsic viscosity of /g.

R+ OA-+ COH(1) Rz OAr2 0 Ri'(II)H
O-C-A,, -C-OH(III) (in the formula A
r I + A r z + A r x are each 2
represents a valent aromatic group. However, the aromatic ring may be substituted with a substituent.) In the present invention, the obtained thermotropic liquid crystalline polyester has an intrinsic viscosity of 0.5 or more, preferably 0.5
~0. It is more preferably 0.6 to 0.9. If the intrinsic viscosity is less than 0.5, the mechanical properties will be poor, which is not preferable. In addition, if the intrinsic viscosity becomes higher than necessary, the mechanical properties may become saturated and melt processability may deteriorate, so the intrinsic viscosity should be 1.0 or less, preferably 0.
．． It should be about 9 or less.

The acyloxy aromatic carboxylic acid used in the present invention is 9
This is expressed by formula (1). Since the acyloxy aromatic carboxylic acid basically plays the role of a rigid linear chain portion of the thermotropic liquid crystalline polyester to be produced, a substantially para-oriented compound is often selected. Preferred specific examples include 4-hydroxybenzoic acid, 1-hydroxy-4-
naphthoic acid, 4-hydroxy-3-methylbenzoic acid, 4
Examples include lower fatty acid esters such as acetate, propionate, butyrate, isopropionate, and α,α-dimethylteropionate of hydroxy-3-chlorobenzoic acid or 2-hydroxy-6-naphthoic acid. However, 4-acetoxybenzoic acid (4JIBA) and 2-acetoxy-6-naphthoic acid are particularly preferred.As for the acyloxy aromatic carboxylic acid, a mixture of these may be used if necessary, however, if the liquid crystal of the polyester to be produced As long as the properties are not impaired, acyloxy aromatic carboxylic acids having meta- or ortho-ortho-ortho-ortho-, ana-, shrimp-, kata-, peri-, or pro-orthogonal orientations other than para or ansoy orientation can also be used.

The lower fatty acid ester of aromatic diol used in the present invention is represented by formula (II).

Specific examples of lower fatty acid esters of aromatic diols include hydroquinone, resorcinol, 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene,
1.4-Dihydroxynaphthalene.

1.5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1.7-dihydroxynaphthalene, 1.
8-dihydroxynaphthalene, 2゜3-dihydroxynaphthalene, 2.6-dihydroxynaphthalene, 2.7-
Dihydroxynaphthalene, 2.2”-diphenyl, 4
．． 4'-diphenyl, 1.1'-binaphthyl-2,
2′-diol, 2-methyl-1,4-dihydroxynaphthalene, 3.3″, 5.5′-tetramethoxybiphenyl-4,4′-diol, 4. 4′-dihydroxy-diphenyl ether, bis(4- hydroxy-2-methylphenyl)-ether, bis(4-hydroxy-3-chlorophenyl)-ether, bis(4-
hydroxyphenyl)-sulfide, bis(4-hydroxyphenyl)-sulfone, bis(4-hydroxyphenyl)-ketone.

Bis(4-hydroxyphenyl)-methane. Bis(4-
Hydroxy-3-methylphenyl)-methane, bis(4
-hydroxy-3,5-dichlorophenyl)-methane,
Bis(4-hydroxy-3,5-dibromophenyl)-
Methane, bis(4-hydroxy-3,5-difluorophenyl)-methane.

1.1-bis(4′-dihydroxyphenyl)-ethane, 2.2-bis(4′-hydroxy-3′-methylphenyl)propane, 2.2-bis(4”-hydroxy-
3'-chlorophenyl)-propane, 2,2-bis(4
゛ -Hydroxy-3”,5”-dichlorophenyl)-
Propane, 2,2-bis(4′-hydroxyphenyl)
-propane, 2゜2-bis(4'-hydroxy-3'',
5°-dibromophenyl)-propane, 1,1-bis(4°-hydroxyphenyl)-n-butane, bis(4
-hydroxyphenyl)-phenylmethane, bis(4-
hydroxyphenyl)-diphenylmethane.

Bis(4-hydroxyphenyl)-4'-methylphenylmethane, 1,1-bis(4'-hydroxyphenyl)-2,2,2-)dichloroethane.

Bis(4-hydroxyphenyl)-(4'-chlorophenyl)-methane, 1,1-bis(4"-hydroxyphenyl)-cyclohexane, bis(4"-hydroxyphenyl)-cyclohexylmethane.

2.2-Bis(4'-hydroxynaphthyl)-propane, bis(4'-hydroxy-3,5-dimethylphenyl)-methane. Bis(4-hydroxy-3,5-dimethylphenyl)-ketone, bis(4-hydroxy-3,5-
dichlorophenyl)-ketone, bis(4-hydroxy-
3-chlorophenyl)-sulfide, bis(4-hydroxy-3,5-dichlorophenyl)-sulfide, bis(4-hydroxy-3,5-dichlorophenyl) ether, bis(3-hydroxyphenyl) sulfide, bis(3-hydroxy phenyl) sulfone, bis(3-hydroxyphenyl) ether.

3-Hydroxyphenyl-4°-hydroxyphenyl ether, 3.4-bis(4°-hydroxyphenyl)hexane, 1.5-dihydroxyanthracene, 1,
2-dihydroxyphenanthrene.

1.4-dihydroxyphenanthrene, 1.6-dihydroxyphenanthrene, 1,7-dihydroxyphenanthrene, 2.3-dihydroxyphenanthrene, 2.5
-dihydroxyphenanthrene, 2,6-dihydroxyphenanthrene, 2,7-dihydroxyphenanthrene, 3.4-dihydroxyphenanthrene, 3,6-dihydroxyphenanthrene, 3.10-dihydroxyphenanthrene, 9.10-dihydroxyphenanthrene.

1.1-dithiodi-2-naphthol, retin-3,8-
Diol, 3,4-dihydroxyanthrone.

1.8-dihydroxy-3-methylanthrone.

1,2-dihydroxyanthraquinone, 1,8-dihydroxy-3-methylanthraquinone, 1,2-dihydroxy-3-nitroanthraquinone.

1.8-dihydroxy-2,4,5,7-tetranitroanthraquinone, 5,6-dihydroxy-2-anthraquinonecarboxylic acid, 3.4-dihydroxyanthraquinone-2-sulfonic acid, 3.7-cyoxy-10-methylxanthine , dioxyacridone, 1,3-dioxyxanthine, 2,7-cyoxy-9-phenylxanthine,
Hydroquinone, 2゜2
-bis(4'-hydroxyphenyl)-propane (BA
), 4.4''-dihydroxydipheyl acetate is particularly preferably used.

The aromatic dicarboxylic acid used in the present invention is of formula 1 (III
). Preferred specific examples of such aromatic dicarboxylic acids include terephthalic acid (TPA),
Examples include isophthalic acid (IPA).

Examples of the acid anhydrides of lower fatty acids having 2 to 5 carbon atoms used in the present invention include acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, and isobutyric anhydride.

Bivalic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, etc., among which anhydrous Acetic acid, propionic anhydride, and trichloroacetic anhydride are preferred.

Examples of polyesters containing alkylene terephthalate as a main component used in the production of thermotropic liquid crystalline polyesters in the present invention include polyethylene terephthalate, polybutylene terephthalate, and various copolymers thereof. Among these, polyethylene terephthalate is particularly suitable. As polyester, 9 usually has an intrinsic viscosity of 0.2 d//g.
, preferably 1.4 di/g or less, more preferably 0.4 to 1.2 dβ/g.

Particularly preferably, one having an amount of 0.5 to 1.0 dl/g is used.

In the present invention, the amount of acyloxy aromatic carboxylic acid used is preferably 5 to 95 mol%, particularly preferably 30 to 70 mol%, based on the number of moles of units constituting the thermotropic liquid crystalline polyester. The amount of lower fatty acid ester of diol used is preferably 1 to 99 mol%, particularly preferably 1 to 20 mol%, based on the number of moles of units constituting the thermotropic liquid crystalline polyester, which has so-called thermotropic liquid crystallinity. It may be selected appropriately so that polyester can be obtained.

In the present invention, the amount of aromatic dicarboxylic acid used is preferably equivalent to the lower fatty acid ester of aromatic diol.

In the present invention, the amount of the acid anhydride of lower fatty acid used is 0.01 to 0.05 times equivalent to the aromatic hydroxyl residue derived from the lower fatty acid ester of the acyloxy aromatic carboxylic acid and aromatic diol, that is, the acyloxy group. , preferably 0.01 to 0.2 times equivalent.

If the amount added is less than 0.01 times equivalent, the addition effect will not be substantially expressed, while if it is added in excess of 0.05 times equivalent, not only will the effect become saturated, but the color tone of the obtained polyester will be unnecessarily changed. Both are undesirable because they only cause damage.

Thermotropic liquid crystalline polyester can be produced by the method of the present invention as follows.

First, an acyloxyaromatic carboxylic acid represented by the formula (1), a lower fatty acid ester of an aromatic diol represented by the formula (n), and an acid of an aromatic dicarboxylic acid and a lower fatty acid represented by the formula (III). with anhydrous.

A polyester whose main component is alkylene terephthalate is mixed.

At this time, you can mix everything at the same time.

It is preferable to mix the acyloxy aromatic carboxylic acid, the lower fatty acid ester of the aromatic diol, the aromatic dicarboxylic acid, and the acid anhydride of the lower fatty acid in advance, and then mix the mixture with the polyester containing alkylene terephthalate as a main component. The mixing at each stage here means heating and melting the mixture under an inert atmosphere until it becomes homogeneous. Heat dissolution is usually carried out at 210 to 300°C for several minutes to several hours, preferably at 250 to 300°C for 5 to 120 minutes, and optimally at 250 to 280°C for 30 to 60 minutes. When the champion is mixed at a temperature lower than 210°C, it is preferable to raise the temperature to 250 to 280°C over time and heat and melt until a uniform state is obtained. In this case, if the heating time to 250 to 280°C exceeds 5 hours, a copolymer of oxyaromatic carboxylic acid, aromatic diol, and aromatic dicarboxylic acid is preferentially produced.

This is not preferable since it may cause a problem of remaining as foreign matter in the polymer. Then, 1 polycondensation reaction is 1 usually 2
Single polycondensation is carried out at a temperature of 00 to 300°C, preferably 250 to 300°C, gradually reducing the pressure, and finally under reduced pressure of less than 10 torr, preferably 1, Q torr, for several tens of minutes to several hours. All you have to do is complete the reaction. Furthermore, by using an appropriate catalyst during the single polycondensation reaction, the reaction can be carried out efficiently. As the catalyst, one or more compounds such as various metal compounds or organic sulfonic acid compounds can be used. As a metal compound.

antimony, titanium, germanium, tin, zinc.

aluminum, magnesium, calcium, manganese,
Compounds such as sodium or cobalt are used,
On the other hand, as the organic sulfonic acid compound, compounds such as sulfosalicylic acid and O-sulfobenzoic anhydride (O3B) are used, and antimony dioxide (CA) and O3B are particularly preferably used. The amount of catalyst added is usually 0.9 to 1 mole of the polyester structural unit. IX10-
'~100XIO-' mole, preferably 0.5xlO-
'~50 Xl0-'-E/l/.

Optimally, 1X10-' to 10 X10-' moles are used.

(Function) The reason why the production method of the present invention exhibits an excellent effect on the production of thermotropic liquid crystalline polyester that is homogeneous and has excellent color tone is still unclear.

It is presumed that this is due to the following effects. That is,
■ Acyloxy aromatic carboxylic acid, lower fatty acid ester of aromatic diol, and aromatic dicarboxylic acid are used as monomers, and when these are melted, the melt viscosity is very low, and the main component is alkylene lentile refrate. Since the acidolysis reaction and the transesterification reaction with the polyester are performed uniformly, blocking of aromatic components is less likely to occur. (2) Acid anhydrides of lower fatty acids not only promote uniform acidolysis reactions and transesterification reactions, but also suppress the generation of phenolic hydroxyl groups with low reactivity.

(Example) Hereinafter, the present invention will be described in more detail with reference to Examples.

The intrinsic viscosity of the polymer in one example was determined from the solution viscosity measured at 20° C. using a mixed solvent of equal weights of phenol and tetrachloroethane. In addition, thermotropic liquid crystal properties are
Confirmation was made using a Leitz polarizing microscope equipped with a hot stage. Also, what is the composition of the polymer?

After metatrilysis, it was quantified by gas chromatography.
confirmed. In addition, regarding the color tone of the polymer, the L value is 70
Those with a b value of about 15 or above and a b value of about 15 or less were judged as good.

Example 1 Terephthalic acid and ethylene glycol were esterified by a conventional method to obtain an esterified product with an esterification reaction rate of 95%. This esterified product was charged into a polycondensation reactor, 2×10-' mol of antimony dioxide was added per 1 mol of the acid component, and the polycondensation reaction was carried out under reduced pressure at 270''C with stirring for 3 hours. The intrinsic viscosity [η] was measured and found to be 0.63 di/
It was g.

This polyester and 4-acetoxybenzoic acid (4HB
A-A), 2,2-bis(4°-acetoxyphenyl)-propane (BA-A), TPA and acetic anhydride (A
C20) at a molar ratio of 5:4:1:1:0.6 and stirred at 270° C. for 1 hour under a nitrogen atmosphere, the reaction mixture became a homogeneous solution. Then, the pressure was gradually reduced, and finally the polycondensation reaction was carried out at 1.0 torr for 5 hours.

The intrinsic viscosity of the obtained polymer was 0.72 dl! /
g.

The color tone has an L value of 74.3. The a value was -1.3 and the b value was 12.9, indicating thermotropic liquid crystallinity. Also.

The composition of the obtained polymer is a polyethylene terephthalate component and a 4-hydroxybenzoic acid component.

The molar ratio of the 2.2-bis(4'-hydroxyphenyl)propane components was 5:4:1, which was consistent with the charging composition.

Furthermore, the solution for viscosity measurement was completely transparent, and no insoluble matter was observed.

Examples 2-15 Intrinsic viscosity of polyethylene terephthalate (PET), 4
1 (molar ratio of BA-A, BA-A, TPA and ActO, polyethylene terephthalate and 4HBA-A and BA-
A thermotropic liquid crystalline polyester was obtained in the same manner as in Example 1, except that the heating temperature of A, TPA, IPA, and AczO was changed as shown in Table 1.

The results of Examples 1 to 15 are listed in Table 1.

Example 16 4HBA-A, BA-A, TPA, A, 20 were charged into a reaction tank at a molar ratio of 4:1:1:0.6, heated for 15 minutes,
A mixture was obtained by melting (mixture A).

After mixing the polyester with [η] of 0.63 used in Example 1 and Mixture A at a molar ratio of polyester, 4HBA-A, BA-A, and TPA of 5:4:1:1. , and stirred for 1 hour at 270'C under nitrogen atmosphere. Then, the pressure was gradually reduced, and finally the polycondensation reaction was carried out at 1.0 tOtt for 5 hours.

In addition, the intrinsic viscosity of the obtained polymer was 0.75 dn/g
The color tone was L value 74.8, a value -0.9, and b value 12.1, indicating thermotropic liquid crystallinity.

The composition of the obtained polymer is a polyethylene terephthalate component, a 4-hydroxybenzoic acid component, and a 2,2-
The molar ratio of bis(4'-hydroxyphenyl)propane components was 5:4:1, which was consistent with the charging composition.

Furthermore, the solution for viscosity measurement was completely transparent, and no insoluble matter was observed.

Examples 17-30 4HBA-A, BA-A, TPA, AC20 and molar ratio,
A thermotropic liquid crystalline polyester was obtained in the same manner as in Example 12, except that the mixing temperature of polyethylene terephthalate (PET) and mixture A and the heating time to 270° C. were changed as shown in Table 2.

Example 31 Terephthalic acid and ethylene glycol were esterified by a conventional method to obtain an esterified product with an esterification reaction rate of 95%. This esterified product was charged into a polycondensation reactor, 2×10 −' mol of antimony trioxide was added per 1 mol of the acid component, and a polycondensation reaction was carried out at 270° C. under tJli pressure for 3 hours with stirring. This was paid out in the form of chips using a conventional method. The intrinsic viscosity (?) of the obtained polyester was measured.

It was 0.64 dll/g.

This polyester chip and 4HBA were added to another polycondensation reactor.
-A, BA-A, TPA, A, o in a molar ratio of 5:4:1
:1:0.6 at 150°C, and the temperature was raised to 270°C over 3 hours with stirring under a nitrogen atmosphere, and the 9 reaction vessels became a homogeneous solution. Then, the pressure was gradually reduced, and finally the polycondensation reaction was carried out at 1, Q torr for 5 hours.

The intrinsic viscosity of the obtained polymer was 0.73dj! /g.

The color tone has an L value of 75.1. The a value was -1.3 and the b value was 14.3, indicating thermotropic liquid crystallinity. In addition, the composition of the obtained polymer was a polyethylene terecrate component and 4
-Hydroxybenzoic acid component and 2,2-bis(4''-hydroxyphenyl)propane component had a molar ratio of 5:4:1, which matched the composition of the charge.

Furthermore, the solvent for viscosity measurement was completely transparent, and no insoluble matter was observed.

The results of Examples 16 to 31 are listed in Table 2.

Examples 32 to 36 Thermotropic liquid crystalline polyesters were obtained in the same manner as in Example 1, except that diacetate of another aromatic diol was used instead of 2.2-bis(4'-acetoxy)propane.

Example 37 Instead of using 4-acetoxybenzoic acid alone, 3-
Acetoxybenzoic acid and 4-acetoxybenzoic acid at 20/
A thermotropic liquid crystalline polyester was obtained in the same manner as in Example 1 except that a molar ratio of 80 was used.

Example 38 Instead of 4-acetoxybenzoic acid, 2-acetoxy-
In the same manner as in Example 1 except that 6-naphthoic acid was used,
A thermotropic liquid crystalline polyester was obtained.

Example 39 Dimethyl ester of TPA and 1
．． After charging 4-butanediol and performing a transesterification reaction at a temperature of 220"C to distill methanol, the reaction product was charged into a batch polymerization reactor, and TBT (tetrabutyl titanate) was used as a catalyst to convert the polyester into Add 5X10-' moles to 1 mole of structural unit + 1.
The reaction was carried out at 240° C. for 3 hours under reduced pressure of 0 torr. A portion of the produced polyester was sampled and its intrinsic viscosity was measured.

It was 0.82 dl/g.

This polyester, 4HBA-A, BA-A, TPA, and ^C20 were mixed in a molar ratio of 5:4:1:1:0.6,
After stirring for 1 hour at 270° C. under a nitrogen atmosphere, the reaction mixture became a homogeneous solution.

Then, the pressure is gradually reduced, and finally 1. The polycondensation reaction was carried out at Qtorr for 5 hours.

The intrinsic viscosity of the obtained polymer was 0.19 dl/g.

The color tone has an L value of 75.1. The a value is -1.0 and the b value is 12.7.

It exhibited motropic liquid crystallinity. In addition, the composition of the obtained polymer was polybutylene terephthalate (PBT
) component, 4-hydroxybenzoic acid component, and 2,2-bis(
The molar ratio of the 4'-hydroxyphenyl)-propane components was 5:4:1, which was consistent with the charged composition.

Furthermore, the solution for viscosity measurement was completely transparent, and no insoluble matter was observed.

The results of Examples 32 to 38 are listed in Table 3.

Comparative Example I A polyester was obtained in the same manner as in Example 1 except that a polymer composed of BA and TPA with an intrinsic viscosity of 0.9 df/g was used instead of BA-A and TPA, but a large amount of crystals precipitated. However, when it was dissolved in a mixed solvent of phenol and tetrachloroethane, a large amount of undissolved matter remained, making it unusable for practical use.

Comparative Example 2 Instead of using BA-A and TPA, BA, TPA and I
PA (TPA/I PA=50150) with an intrinsic viscosity of 0.8dj! A liquid crystalline polyester was obtained in the same manner as in Example 1, except that a polymer of A residue was left behind and it could not be put to practical use.

Comparative Example 3 A liquid crystalline polyester was obtained in the same manner as in Example 1 except that acetic anhydride was not used, but some crystals were precipitated, and when dissolved in a mixed solvent of phenol and tetrachloroethane, some insolubility was observed. The material remains and the intrinsic viscosity is 0.3dj! /g was not suitable for practical use.

(Effect of the invention) According to the method of the invention, it has a high intrinsic viscosity.

Furthermore, it has become possible to produce a homogeneous thermotropic liquid crystalline polyester with excellent color tone and heat resistance.

Claims (4)

[Claims] (1) Acyloxy aromatic carboxylic acid represented by formula (I), lower fatty acid ester of aromatic diol represented by formula (II), aromatic dicarboxylic acid represented by formula (III), and aromatic 0.01-0.5 for group hydroxyl residues
The limit of at least 0.5 dl/g, characterized by mixing 0 times equivalent of an acid anhydride of a lower fatty acid having 2 to 5 carbon atoms and a polyester whose main constituent is alkylene terephthalate, and then subjecting the mixture to a polycondensation reaction. A method for producing a thermotropic liquid crystalline polyester having viscosity. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) R_2-O-Ar_2-O-R_3(II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(III) (In the formula, Ar_1, Ar_2, Ar_3 are each 2 The aromatic groups R_1, R_2, and R_3 represent lower acyl groups.However, the aromatic ring may be substituted with a substituent.) (2) The acyloxy aromatic carboxylic acid is 4-acetoxybenzoic acid, the lower fatty acid ester of the aromatic diol is 2,2-bis(4'-acetoxyphenyl)-propane, and the acid anhydride of the lower fatty acid is anhydride. The manufacturing method according to claim 1, wherein the acetic acid is acetic acid. (3) Claim 1 in which a mixture of an acyloxy aromatic carboxylic acid, a lower fatty acid ester of an aromatic diol, and an acid anhydride of an aromatic dicarboxylic acid and a lower fatty acid is mixed with a polyester whose main constituent is alkylene terephthalate. Manufacturing method described in section. (4) Claim 3: Mixing at 150-300°C
Manufacturing method described in section.