JP3132881B2 - Method for producing liquid crystalline polyester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for producing a liquid crystalline polyester. More specifically, the present invention relates to a method for producing a liquid crystalline polyester having excellent reproducibility, production stability, and productivity. The liquid crystalline polyester according to the present invention has excellent fluidity, melt processability, and mechanical properties (elastic modulus, tensile strength). , Bending strength, impact strength, elongation, etc.).

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for materials having excellent rigidity, strength, elongation and heat resistance, regardless of whether they are fibers, films or molded products. Polyester has been widely accepted for use as a general molded article, but many polyesters are inferior in flexural modulus and flexural strength, and thus are not suitable for applications requiring high modulus and high strength. In recent years, liquid crystalline polyesters have attracted attention as polyesters suitable for applications requiring high elastic modulus and high strength. Of particular interest is the Journal of Polymer Science Polymer Chemistry Edition 14 (1976) 2043
Page, U.S. Pat. No. 3,784,410, U.S. Pat. No. 3,804,805 and JP-B-56-18016. J. Jackson et al. Published a thermo-liquid crystalline polymer composed of polyethylene terephthalate and acetoxybenzoic acid. Among them, Jackson et al. Reported that the thermal liquid crystal polymer exhibited more than five times the rigidity, more than four times the strength, and more than 25 times the impact strength of polyethylene terephthalate, showing a new possibility for a high-performance resin. showed that.

[0003]

However, the polymer of Jackson et al. Has the drawback that it is very brittle and has low strength and low elongation. It is considered that this is mainly because the ratio of the chain of the p-oxybenzoic acid residue represented by the following formula (9) is very large.

Embedded image

The present applicants have previously found a method for producing a copolyester, which improves the elongation at break of the polyester developed by Jackson et al. (JP-A-60-186).
525). The idea there is to reduce the above (10), which is a chain of p-oxybenzoic acid units,
Here is the origin of trying to reduce (10). However, according to this method, decarboxylation occurs, or etherification occurs in situ depending on conditions, and it is difficult to control the amount thereof, and therefore, there is a problem in reproducibility of physical properties and the like. Therefore, Japanese Patent Laid-Open No. 1-30
In 1711, the ether component is added at the time of preparation,
Since the chain component of p-oxybenzoic acid is generated in a block form, the mechanical properties and the like are undesirably reduced.

Further, according to JP-A-64-26632,
Since paraacetoxybenzoic acid is used, the polymerization rate is reduced, the sublimate is frequently generated, and the system is clogged. Also, since the formed polymer has no ether component, its mechanical properties, especially strength, impact strength and elongation are reduced. Is low, the fluidity is deteriorated, and the molding temperature is too high. There is also a problem that hydrolysis resistance is poor. Under such circumstances, the present invention provides a liquid crystalline polyester having excellent fluidity, melt processability (low-temperature moldability), mechanical properties (particularly strength and impact strength) and excellent reproducibility without troubles such as sublimation. It is another object of the present invention to provide a method for producing with good productivity such as high polymerization rate.

[0006]

SUMMARY OF THE INVENTION To solve these problems,
As a result of intensive studies, the present inventors have reached the present invention. That is, in the present invention, in producing a liquid crystalline polyester comprising the following components (1) to (4), (5)
Polycondensation is performed with polyethylene terephthalate and (6) p-hydroxybenzoic acid and (8) acetic anhydride, and polycondensation is performed by adding (6) p-hydroxybenzoic acid and (8) acetic anhydride in the subsequent stage, or In the method of performing polycondensation by adding the reaction product of (6) and (8) to that of the preceding stage, (7) 4- (2-hydroxyethoxy) benzoic acid is added in the preceding stage and / or the latter stage. This is a method for producing a liquid crystalline polyester. (1) Terephthalic acid unit (10 to 20 mol%)

[0007]

Embedded image (2) Ethylene glycol unit (10 to 20 mol%)

[0008]

Embedded image —OCH ₂ CH ₂ O— (3) p-hydroxybenzoic acid unit (55 to 79 mol%)

[0009]

Embedded image (4) 4- (2-hydroxyethoxy) benzoic acid unit (1 to 5 mol%)

[0010]

Embedded image The present invention has the above technical matters as its gist, and the following points are particularly important. (A) 4- (2-hydroxyethoxy) benzoic acid having an ether component at the time of preparation

[0011]

Embedded image Is used. (B) As a raw material, p-hydroxybenzoic acid is used. (C) p-hydroxybenzoic acid is reacted in two stages. In the case of further improving the hydrolysis resistance, 1,2-ethylenebis-4-hydroxybenzoate is used.

[0012]

Embedded image Is added. The present invention will be described in more detail. The (5) polyethylene terephthalate used in the present invention is mainly composed of an ethylene glycol residue and a terephthalic acid residue.

[0013]

Embedded image Having a repeating unit of 25 or more, preferably 50 or more and an intrinsic viscosity of 0.25 or more, preferably 0.40 or more. As the polyethylene terephthalate, any of the so-called (1) direct polymerization method (using terephthalic acid) and (2) transesterification method (using dimethyl terephthalate) may be used. In these cases, the main chain may contain some —OCH ₂ CH ₂ OCH ₂ CH ₂ O— groups. The catalyst may include a usual one as a residue. In addition, the molecular weight of 1 mol unit is 192 with the above-mentioned repeating unit.

In the first stage, (5) polyethylene terephthalate, (6) p-hydroxybenzoic acid and (7) 4-
(2-hydroxyethoxy) benzoic acid

(Equation 1) (Hereinafter, the number of moles to be added is indicated by []). Then, (8) acetic anhydride is added and reacted. At this time, (8) the temperature at which acetic anhydride is added and reacted is 1
The temperature is preferably from 00 to 160 ° C, and the time is preferably from 10 minutes to 1 hour. Thereafter, the temperature is raised to cause a reaction, and in some cases, oligomerization or polymerization is performed under reduced pressure.
Alternatively, since (8) was used, the polymerization rate was improved, and there was almost no occurrence of sublimates, so that there was no production trouble and the production rate could be improved.

The polymer may be extracted from the kettle and formed into chips, or may be kept in the kettle. When it is kept in a kettle, it is preferable to add (6) and (8) to another kettle, react a little in advance, and then put it in the oligomer or polymer in the preceding stage.

The ratio of the first stage charge amount is

(Equation 2) The ratio may be any number as long as it is within the above range.

(Equation 3) Is preferred

(Equation 4) Is most preferred.

[0017]

(Equation 5) In the case of (1), the mechanical properties of the final polymer are deteriorated, and the balance of the quantity ratio between the first and second stages is poor, and the production efficiency is unfavorably deteriorated. (8) Acetic anhydride and p of (6)
-The total amount of hydroxybenzoic acid added was [8],
[6], and the addition amounts in the first stage are [8-1] and [6-1], respectively, and the addition amounts in the second stage are [8-2] and [6-2], respectively.

[0018]

(Equation 6) Preferably

(Equation 7) It is.

In the latter stage,

(Equation 8) Preferably

(Equation 9) It is.

As described above, by adding (8) acetic anhydride, there is no trouble such as sublimation, and the polymerization rate can be improved, that is, the productivity can be improved. Until now (7)
Although the example in which the component (7) is added in the previous stage has been described, the component (7) may be added in the second stage. By adding the component (7) from the outside, not only the quality of the produced polymer is stabilized, but also the bending and tensile strength and the impact strength are improved as compared with the case without (7). Or In addition, fluidity is improved, and low-temperature moldability is improved. (7)
When the addition amount of is expressed by [7],

[0021]

(Equation 10) Is preferred.

[Equation 11] If it is, the strength and impact strength decrease, and the fluidity and low-temperature moldability decrease, which is not preferred. or

(Equation 12) In this case, the crystallinity is lowered and the heat resistance is lowered, which is not preferable. More preferably

(Equation 13) It is.

In order to improve the hydrolysis resistance, (9) 1,2-ethylenebis-4-hydroxybenzoate is further added. In some cases, (11) terephthalic acid is also added to increase the degree of polymerization. The timing of the addition is not particularly limited, but the latter is preferable because the structure of (9) is easily maintained. At this time, if the added amounts of (9) and (11) are [9] and [11], it is preferable that [9]> [11]. In particular

[Equation 14] It is preferable to keep

(Equation 15) In this case, it is preferable not to add (11). By adding (9), not only the block component of (6) is further reduced to improve the mechanical properties, but also the extractability from the kettle is improved, the amount of terminal carboxylic acid is reduced, and the hydrolysis resistance is reduced. There is a merit that the releasability during molding is improved.

The liquid crystalline polyester according to the production method of the present invention exhibits optical anisotropy in the molten phase. In particular, when the melting is started, by slightly increasing the temperature from the starting temperature, the solid portion almost disappears and substantially the entire liquid crystal state can be obtained. Therefore, the fluidity corresponding to the solution viscosity (η _inh ) is the same as the conventional one. It has the feature of being much better than polyester. Therefore, the moldability is good, and it is possible to perform general melt molding such as extrusion molding, injection molding, and compression molding. Therefore, it can be easily processed into molded articles, films, fibers and the like. The melt viscosity of the liquid crystalline polyester according to the production method of the present invention is 30 when measured at a temperature of 290 ° C. and a shear rate of 1000 sec ^−1.
It must be at least poise.

However, since the polyester according to the production method of the present invention exhibits liquid crystallinity, its melt viscosity is generally low. For example, the melt viscosity measured under the above conditions is 5000 poise or less. Therefore, the melt viscosity of the liquid crystal polyester of the present invention is preferably 50 to 3000.
Poise, more preferably 100 to 2500 poise. Most preferably, it is 100 to 1500 poise. Another characteristic of the polyester obtained by the production method of the present invention is that the ratio of the melt viscosity at 275 ° C. to the melt viscosity at 290 ° C. is small.

The liquid crystalline polyester according to the production method of the present invention is particularly suitable for precision molded products and thin-walled molded products due to its feature of high fluidity. For example, parts for automobiles, parts for information materials such as compact disks and floppy disks, parts for electronic materials such as connectors and IC sockets, etc.
In addition, the hydrolysis resistance improving system can be suitably used for a hybrid IC sealing part and the like. Further, the liquid crystalline polyester according to the production method of the present invention, glass fibers, fibers such as carbon fibers, talc, mica, fillers such as calcium carbonate,
By adding fillers and additives such as nucleating agents, pigments, antioxidants, lubricants, other stabilizers, flame retardants and the like, thermoplastic resins and the like, it is possible to impart desired properties to the molded article. Furthermore, by blending or alloying with another polymer, a composition having both advantages of the liquid crystalline polyester and the other polymer according to the production method of the present invention can be obtained.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, physical properties were measured and molded by the following methods. (1) Melt viscosity (η _inh ) The melt viscosity was measured using a mixed solvent of p-chlorophenol / o-dichlorobenzene at a temperature of 30 ° C. and a concentration of 0.5 g / dl. (2) Melt Viscosity The measurement was performed at 290 ° C., and the measurement was performed at a shear rate (r) of 1000 sec ⁻¹ using a flow tester (length / diameter of cylinder nozzle = 20) of Shimadzu Corporation. (3) Optical Anisotropy (Liquid Crystallinity) Observation was performed using a polarizing microscope equipped with a hot stage. (4) Molding Molding was performed using a 0.12 OZ injection molding machine manufactured by Nippon Steel Corporation. (5) Tensile properties Tensile modulus, tensile strength and elongation at break were measured using a TENSILON / UTM (III) L manufactured by Toyo Baldwin Co., Ltd. for the 0.1 OZ molded product obtained by the above molding machine. When the elongation exceeds 3.0%, especially 3.5%
From the above, it can be determined that the polymer is sticky. (6) Hydrolysis resistance A sample molded at 0.1 OZ was placed in a pressure cooker test apparatus and subjected to a test under saturated steam at 121 ° C. and 2 atm. The test sample was evaluated for (i) retention of tensile test strength and (ii) retention of melt viscosity.

Example 1 30.72 g (0.160 mol) of PET 56.99 g (0.413 mol) of p-hydroxybenzoic acid in a glass polymerization tube (A) equipped with a stirring blade, a nitrogen inlet, and a vacuum port. -(2-Hydroxyethoxy) benzoic acid (2.55 g, 0.014 mol) was charged, and the system was subjected to reduced pressure-nitrogen substitution to make the system a nitrogen atmosphere, and then 52.66 g (0.516 mol) of acetic anhydride was added. At 140 ° C. for 1 hour. Thereafter, the temperature was raised to 270 ° C. over 1.5 hours and maintained at 270 ° C. for 1 hour.
Next, the pressure was gradually reduced at 270 ° C. The pressure reduction was performed slowly over 1 hour and 30 minutes so that the pressure became 0.3 mmHg. In another flask (B), p-hydroxybenzoic acid 2
6.67 g (0.215 mol) were charged. Under a nitrogen atmosphere, 27.41 g (0.269 mol) of acetic anhydride was added in the same manner and reacted at 140 ° C. for 1 hour.
Until the reaction.

The glass polymerization tube (A) has a reduced pressure of 0.3 mmH
When the pressure reached g, the inside of the system was returned to normal pressure, and the content of (B) was added to the oligomer (A) while the temperature of the flask (B) was not lowered. Thereafter, the glass polymerization tube (A) was maintained at 270 ° C. for 1 hour, and then heated to 290 ° C., and when the temperature reached 290 ° C., pressure reduction was started.
The pressure was adjusted to 0.3 mmHg in 5 hours. 1.5 hours after the start of the pressure reduction, the torque was sufficiently increased, so that the polymerization was terminated. The withdrawal property was very good. No sublimation was observed. Η _inh of this polymer is 1.165d
1 / g, melt viscosity 290 ° C., 380 at 10 ³ sec ⁻¹
Poise. Tensile properties are as follows: elastic modulus 10.2 × 10 ⁴
kg / cm ² , strength 2,000 kg / cm ² , elongation 4.3
%Met.

Example 2 A glass polymerization tube (A) similar to that of Example 1 was charged with 30.72 g (0.160 mol) of PET and 33.12 g (0.240 mol) of p-hydroxybenzoic acid. After that, 30.6 g of acetic anhydride
(0.300 mol) was added. After reacting at 140 ° C for 1 hour, the temperature was raised to 270 ° C over 1.5 hours,
For one hour. Thereafter, the pressure was reduced and the pressure was adjusted to 0.3 mmHg over 1.5 hours. Another flask (B) was charged with 52.55 g (0.381 mol) of p-hydroxybenzoic acid and 3.49 g (0.019 mol) of 4- (2-hydroxyethoxy) benzoic acid, and the mixture was placed under a nitrogen atmosphere and then dried. Acetic acid 48.58 g
(0.476 mol), reacted at 140 ° C. for 1 hour, reacted at 140 ° C. for 1 hour, and then heated to 220 ° C. and reacted.

The glass polymerization tube (A) has a reduced pressure of 0.3 mmH
When the pressure reaches g, the system is returned to normal pressure and the flask (B)
The content of (B) was added to the oligomeric (A) while not lowering the temperature of. Thereafter, the glass polymerization tube (A) was maintained at 270 ° C. for 1 hour, and then heated to 290 ° C., and when the temperature reached 290 ° C., pressure reduction was started.
The time was adjusted to 0.3 mmHg. 2 after the start of decompression
The polymerization was terminated because the torque increased sufficiently in a time. The withdrawal property was very good. No sublimation was observed. Η _inh of this polymer is 1.158 dl / g,
The melt viscosity was 450 poise at 290 ° C. and 10 ³ sec ⁻¹ . Tensile properties are as follows: elastic modulus 9.5 × 10 ⁴ kg / c
m ² , strength 1830 kg / cm ² , elongation 3.8%.

Example 3 15.55 g (0.081 mol) of PET and 28.84 g (0.209 mol) of p-hydroxybenzoic acid were placed in a glass polymerization tube (A) similar to that of Example 1 to give 4- (2-hydroxyethoxy). ) 3.46 g (0.019 mol) of benzoic acid was charged, and the mixture was placed under a nitrogen atmosphere, and then 26.65 g of acetic anhydride was added.
(0.261 mol) was added. After reacting at 140 ° C for 1 hour, the temperature was raised to 270 ° C over 1.5 hours,
For one hour. Thereafter, the pressure was reduced and the pressure was adjusted to 0.3 mmHg over 1.5 hours. In another flask (B), p-hydroxybenzoic acid 35.74 g (0.259 mol) terephthalic acid 11.12 g (0.067 mol) 1,2-ethylenebis-4-hydroxybenzoate 24.46 g (0.081 mol) ), And the mixture was placed in a nitrogen atmosphere, and then 53.68 g of acetic anhydride was added.
(0.526 mol) was added and reacted at 140 ° C. for 1 hour, then heated to 220 ° C. and reacted.

The glass polymerization tube (A) has a reduced pressure of 0.3 mmH
When the pressure reaches g, the system is returned to normal pressure and the flask (B)
The content of (B) was added to the oligomeric (A) while not lowering the temperature of. Thereafter, the glass polymerization tube (A) was maintained at 270 ° C. for 1 hour, and then heated to 290 ° C., and when the temperature reached 290 ° C., pressure reduction was started.
The time was adjusted to 0.3 mmHg. 1 after the start of decompression
The polymerization was terminated because the torque increased sufficiently in 15 minutes. The withdrawal property was very good. No sublimation was observed. The η _inh of this polymer is 1.185d
l / g, melt viscosity is 400 at 290 ° C. and 10 ³ sec ^-1 .
Poise. Tensile properties are as follows: elasticity 10.3 × 10 ⁴
kg / cm ² , strength 2200 kg / cm ² , elongation 4.7%
Met. In order to evaluate the hydrolysis resistance, a pressure cooker test was conducted at 121 ° C. under 2 atmospheres of saturated steam for 1 hour.
Performed for 2 hours. The sample after the test had a retention of melt viscosity of 90% and a retention of tensile strength of 95%, indicating that the sample was excellent in hydrolyzability.

Example 4 In an autoclave in which two reaction vessels of 20 L scale are located one above the other and connected to each other, the upper reaction vessel is (A)
The lower reaction vessel is designated as (B). 1.152 kg (6.0 mol) of PET 1.242 kg (9.0 mol) of p-hydroxybenzoic acid 131 kg (0.72 mol) of 4- (2-hydroxyethoxy) benzoic acid were charged into the reaction tank (A). After the atmosphere in the system was nitrogen atmosphere, acetic anhydride 1.1
48 kg (11.25 mol) was added and reacted at 140 ° C. for 1 hour. Thereafter, the temperature was raised to 270 ° C. over 1.5 hours and maintained at 270 ° C. for 1 hour. Next, the reaction solution was transferred to the lower reaction tank (B), and pressure reduction was started while the temperature was kept at 270 ° C. 0.3 mmH over 1 hour and 30 minutes
g.

After transferring the above reaction solution, 2.070 kg (15 mol) of p-hydroxybenzoic acid was charged into the reaction tank (B), and 1.913 kg (1 mol) of acetic anhydride was added under a nitrogen atmosphere.
(8.75 mol) was added and reacted at 140 ° C. for 1 hour, then heated to 220 ° C., reacted at 140 ° C. for 1 hour, and then heated to 220 ° C. and reacted. When the reaction tank (B) reached 0.3 mmHg, (B) was returned to normal pressure, and the reaction solution of (A) was transferred to (B). Thereafter, the reaction tank (B) was kept at 270 ° C. for 1 hour, and then heated to 290 ° C., and when the temperature reached 290 ° C., pressure reduction was started.
The pressure was adjusted to 0.3 mmHg in 5 hours. The polymerization was terminated 1.5 hours after the start of the pressure reduction. The withdrawal property was very good. Further, no clogging of the pipe due to sublimation was observed. The η _inh of this polymer was 1.190 dl / g, and the melt viscosity was 520 poise at 290 ° C. and 10 ³ sec ^-1 . Tensile properties were as follows: elastic modulus 10.0 × 10 ⁴ kg / cm ² ,
The strength was 1850 kg / cm ² and the elongation was 3.5%.

Comparative Example 1 A product was produced according to the method described in JP-B-56-18016. The molar ratio between PET and p-acetoxybenzoic acid is 20 /
The mixture was charged into a polymerization tube so as to give a value of 80. After the atmosphere was changed to a nitrogen atmosphere, the temperature was raised to 275 ° C., and an acidolysis reaction was performed while stirring at 275 ° C. for 1 hour. Thereafter, the pressure was reduced while increasing the temperature to 300 ° C., and the pressure was reduced to 0.3 over 1.5 hours.
mmHg. The polymerization was completed 5 hours after the start of the pressure reduction. Sublimation of about 2% was observed at the top of the polymerization tube. The η _inh of this polymer could not be measured because it was insoluble in the viscosity solvent, and the melt viscosity was 850 poise at 290 ° C and 1000 sec ^-1 . The tensile properties of this polymer are as follows: elasticity 6.6 × 10 ⁴ kg / cm ² , strength 1330 kg / c
m ² and elongation 2.3%.

Comparative Example 2 It was produced according to the method described in JP-B-56-18016. As a first step, the polymerization tube was charged so that the molar ratio between PET and p-acetoxybenzoic acid was 40/60. After a nitrogen atmosphere, the temperature was raised to 270 ° C.
The acidolysis reaction was performed while stirring for 0 minutes. afterwards,
Decompression was started so as to become 1 mmHg in 90 minutes, and finally polymerization was performed at 280 ° C. and 0.3 mmHg for 3 hours to obtain chips. In the second step, the polymer obtained in the preceding step and the insufficient p-acetoxybenzoic acid were combined and charged into a polymerization tube so that the composition ratio of the polymer finally became 20/80, the same as in Comparative Example 1. Next, the temperature was raised to 280 ° C., and an acidolysis reaction was performed for 40 minutes.
The pressure was reduced to 0.3 mmHg over 5 hours. The polymerization was completed 4 hours after the start of the pressure reduction. About 0.7% of a sublimate was found at the top of the polymerization tube. Η of this polymer
_inh is 1.104 dl / g, melt viscosity is 290 ° C, 10
It was 790 poise at 00 sec ^-1 . Further, the tensile properties of the polymer were as follows: the elastic modulus was 8.3 × 10 ⁴ kg / cm ² and the strength was 1
It was 550 kg / cm ² and elongation 2.5%.

Comparative Example 3 A product was produced according to the method described in JP-A-1-301711. PET, p-acetoxybenzoic acid and 4- (2-hydroxyethoxy) benzoic acid were charged into a polymerization tube so as to have the same composition ratio as the polymer obtained in Example 1. The polymerization tube was then evacuated and purged with nitrogen three times before
Dry under vacuum for 1 hour. Thereafter, the temperature was raised to 275 ° C. in a nitrogen atmosphere at normal pressure. After reacting at 275 ° C. for 1 hour, the pressure was then reduced to 0.3 mmHg over 1.5 hours. The polymerization was completed 5 hours after the start of the pressure reduction. About 1.3% of a sublimate was observed at the upper part of the polymerization tube. Η _inh of this polymer could not be measured because it was insoluble in the viscosity solvent. The melt viscosity is 68 at 290 ° C. and 1000 sec ⁻¹ .
It was 0 poise. The tensile properties of the polymer are as follows: elasticity: 6.8 × 10 ⁴ kg / cm ² , strength: 1230 kg / c
m ² and elongation 3.0%.

[0038]

As described above, according to the production method of the present invention, a liquid crystalline polyester which is excellent in fluidity, melt processability, mechanical properties and reproducibility is produced without occurrence of trouble due to sublimation or the like. It can be manufactured with good quality.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-110322 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (2)

(57) [Claims] 1. A method for producing a liquid crystalline polyester comprising the following components (1) to (4):
Polycondensation is performed with polyethylene terephthalate and (6) p-hydroxybenzoic acid and (8) acetic anhydride, and polycondensation is performed by adding (6) p-hydroxybenzoic acid and (8) acetic anhydride in the subsequent stage, or In the method of performing polycondensation by adding the product obtained by reacting (6) and (8) to the former product, adding (7) 4- (2-hydroxyethoxy) benzoic acid in the former product and / or the latter product. A method for producing a liquid crystalline polyester. (1) Terephthalic acid unit (10 to 20 mol%) (2) ethylene glycol units (10 to 20 mol%) ## STR2 ## -OCH ₂ CH ₂ O-(3) p-hydroxybenzoic acid unit (55-79 mol%) ## STR3 ## (4) 4- (2-hydroxyethoxy) benzoic acid unit (1 to 5 mol%) 2. The method for producing a liquid crystalline polyester according to claim 1, further comprising (9) 1,
A method for producing a liquid crystalline polyester, wherein polycondensation is performed by adding 2-ethylenebis-4-hydroxybenzoate.