JP2599713B2 - Wholly aromatic thermotropic liquid crystal polyester - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a wholly aromatic thermotropic liquid crystalline polyester having excellent moldability and processability which provides various molded articles having excellent mechanical performance and thermal performance.

[Conventional technology]

In recent years, there has been an increasing demand from the industry for higher performance of induced polymer materials, and various types of fibers, films, injection molded products, etc., with excellent mechanical performance such as strength and elasticity and thermal performance such as heat resistance, etc. Molded articles are strongly desired.

As a polymer material satisfying the above requirements, polyesters that form an optically anisotropic molten phase, so-called so-called thermootropic liquid crystal polyesters, have been noticed, and thermotropic liquid crystal polyesters having many structures have already been proposed. Some of them have been industrially manufactured in recent years.

In such a polymer, since the molecular chains are easily arranged in one direction, various molded articles having high mechanical performance and highly oriented can be obtained from the polymer. Further, it is known that various molded articles obtained from a wholly aromatic thermotropic liquid crystal polyester composed only of an aromatic ring have extremely good heat resistance.

[Problems to be solved by the invention]

Such a wholly aromatic liquid crystal polyester is excellent as a high-performance material. In particular, a wholly aromatic polyester derived from p-hydroxybenzoic acid, terephthalic acid and a 4,4′-dihydroxyphenyl derivative is: Under the trade name Xydar, it has recently been industrially manufactured. However, a wholly aromatic polyester composed of p-hydroxybenzoic acid, terephthalic acid and a 4,4′-dihydroxydiphenyl derivative has a remarkably high transition temperature to a liquid crystal phase, that is, a melting point of 400 ° C. or higher.
Melt molding requires a high temperature of 400 ° C or higher and cannot be molded with conventional ordinary molding machines. A special molding machine is required. In order to achieve the above, a method of copolymerizing a small amount of 2-hydroxy-6-naphthoic acid (Japanese Patent Laid-Open No. 59-62630) or a method of copolymerizing a non-linearly oriented compound such as isophthalic acid (Japanese Patent Laid-open No. -191
No. 219) has already been proposed.

In addition, various molded products obtained from conventionally proposed polyesters have high mechanical performance in the direction (flow direction) because rigid molecular chains are highly oriented in one direction, but are orthogonal to the flow direction. The mechanical performance in the direction is small, and the mechanical performance anisotropy is large. Further, the elongation at break of the molded product is usually extremely small, that is, 5% or less. In addition, since rigid molecules are highly oriented in one direction, the molded article has poor toughness and impact resistance is not always sufficient.

For these reasons, thermotropic liquid crystal polyester is a very suitable material as a high-performance fiber that mainly requires unidirectional strength, but it is not necessarily satisfactory in all respects as a film or injection molded product. Not something you can do. That is, when a film is obtained from the polyester by ordinary melt extrusion, since the strength in the direction perpendicular to the extrusion direction is extremely small, the frame has the property of easily tearing along the flow direction.

[Means for solving the problem]

The present inventors have conducted intensive studies on obtaining a wholly aromatic thermotropic liquid crystal polyester which is excellent in moldability and provides various molded articles having well-balanced physical properties and thermal properties. As a result, the present invention has been completed. In the present invention, for example, the following repeating units I, I
Consisting of I, III and IV, II-OC-A-CO- (wherein A is a 1,4-phenylene group and / or 4,4'-
Represents a diphenylene group and / or a 2,6-naphthalene group, and the proportions of the 1,4-phenylene group, 4,4′-diphenylene group and 2,6-naphthalene group in A are a mol% and b It is assumed that the following relational expression is satisfied when mol% and c mol% are satisfied) a + b + c = 100 0 ≦ a <600 0 ≦ b ≦ 100 0 ≦ c ≦ 100 Unit I is 40-80 mol%, Unit II is 10-30 mol%, unit
III is present in an amount within the range of 5 to 30 mol%, unit IV is present in an amount within the range of 0 to 25 mol%, and the sum of the number of moles of unit III and unit IV is equal to the number of moles of unit II; Medium, has a logarithmic viscosity in the range of 0.5 to 10 dl / g when measured at 60 ° C. at a concentration of 0.1% w / v and forms an optically anisotropic molten phase at temperatures below 400 ° C. A wholly aromatic polyester is formed.

Unit I is a 4-oxybenzoyl moiety, which can be derived from 4-hydroxybenzoic acid and its derivatives. The unit I is 40 to 80 mol%, preferably 45 to 70 mol% in the polyester.
It is present at a concentration in the range of mole%.

Unit II is an aromatic dicarboxyl moiety represented by -OC-A-CO-, and A is a 1,4-phenylene group and / or a 4,4'-diphenyl group and / or a 2,6-naphthalene group. Wherein 1,4-phenylene groups in A are less than 60 mol%, and terephthalic acid and / or
It can be derived from 4'-diphenyldicarboxylic acid and / or 2,6-naphthalenedicarboxylic acid and their derivatives. Unit II is present in the polyester at a concentration in the range of 10 to 30 mol%, preferably 15 to 27.5 mol%.

Unit III is a 4,4'-dioxydiphenyl ether moiety and can be derived from 4,4'-dihydroxydiphenyl ether and its derivatives. Unit III is present in the polyester in an amount ranging from 5 to 30 mol%, preferably from 7 to 25 mol%.

In the present invention, a 4,4'-dioxydiphenyl moiety represented by the unit IV may be present in addition to the essential components of the units I, II and III. Unit IV is 4,4 '
From 0 to 25 mol%, preferably from 0 to 25 mol% in the polyester derived from dihydroxydiphenyl and its derivatives.
It is present in an amount in the range of 2020 mol%.

However, the total amount of the unit III and the unit IV needs to be substantially equal to the unit II.

In each of the aromatic rings of units I to IV described above, at least a part of the hydrogen base paper bonded to the aromatic ring is an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, or phenyl. It may be substituted with a group or the like. However, in the normal case, it is preferable that the ring substituents do not coexist because the resulting polyester has high crystallinity and various molded articles obtained from the polyester have excellent physical properties.

The polyesters of the present invention have units I to IV present in amounts within the ranges specified above and a concentration of 0.1 dl / g in pentafluorophenol at a concentration of 0.1% w / v, measured at 60 ° C., of at least 0.5 dl / g. It is necessary to form an optically anisotropic molten phase at a temperature of 400 ° C. or less having a logarithmic viscosity. When the logarithmic viscosity is smaller than 0.5 dl / g, the mechanical properties of various molded articles obtained from the polyester are unfavorably low.
Preferably, the logarithmic viscosity is 1.0 dl / g or more. The upper limit of the logarithmic viscosity is usually 10 dl / g or less, preferably 7.5 dl / g or less, such as ease of polymerization, ease of molding of the obtained polyester, and physical properties of the obtained various molded articles. It is desirable in terms of.

In the present invention, it is necessary that the 4,4'-dioxydiphenyl ether moiety of the unit III is present in the polyester in an amount within the range of 5 to 30 mol%, and this means that, for the first time, the fluidity is reduced. A thermotropic liquid crystal polyester which is favorable, easily melt-polymerized, and has excellent moldability is obtained.

When the repeating unit consists of only I, II and III, the unit III must be present in the polyester in an amount of 10 to 30 mol%, preferably in an amount in the range of 12.5 to 27.5 mol%. Is desirable. In this case, the molded article obtained from the polyester has excellent toughness as compared with the molded article obtained from the conventionally proposed liquid crystal polyester. That is, in the case of an injection molded product,
The impact strength is extremely high, and in the case of an extruded film, the breaking elongation becomes large. Furthermore, the molded product obtained from the conventionally proposed thermotropic liquid crystal polyester has a large mechanical anisotropy and the surface is easily fibrillated, but the molded product in the above case of the present invention eliminates these disadvantages. You. When the ratio of the unit III is less than 10 mol% or 3
When the amount exceeds 0 mol%, it becomes difficult to obtain a uniform polymer by melt polymerization, and an optically anisotropic molten phase is not formed at a temperature of 400 ° C. or less.

In the present invention, as described above, in addition to the units I, II and III, the 4,4'-dioxydiphenyl moiety represented by IV can be coexisted in an amount not exceeding 25 mol%. As a result, the strength and elastic modulus of various molded articles obtained from the polyester can be significantly increased as compared with the case where the unit IV is not present. When the unit IV is present, the unit III may be present in the polyester in an amount of 5 mol% or more. As the amount of the unit IV increases, the strength and elastic modulus of various molded articles obtained from the polyester increase, but the impact strength and elongation at break decrease and the mechanical anisotropy increases. Therefore, when an injection-molded article or fiber is obtained, a desirable result is obtained when the amount of the unit IV is relatively large, and when an extruded film is obtained, the amount of the unit IV is relatively small.

When 60 mol% or more of A in the aromatic dicarboxyl moiety represented by —OC—A—CO— of the unit II is a 1,4-phenylene group, depending on the composition ratio of the other moiety, the present invention may be used. Polyester which forms an optically anisotropic molten phase at a temperature of 400 ° C. or less, which is a feature of the present invention, and which gives various molded articles having excellent melt moldability and excellent toughness may not be obtained. In addition, a small amount of other aromatic residues, for example, a 1,3-phenylene group, may coexist as A in addition to the 1,4-phenylene group, the 4,4'-diphenyl group and the 2,6-naphthalene group.

It is already known that by partially copolymerizing the 4,4'-dioxydiphenyl ether component, the melting point of the thermootropic liquid crystal polyester decreases. For example, Th
e WJJackson Jr.'s dissertation, beginning on page 154 of the British Polymer Journal, December 1980, It is stated that bisphenols represented by X = CH ₂ , (CH ₃ ) ₂ C, C = O, S, O have an effect of lowering the melting point of polyester. However, at the same time, it is described in the article that the tensile properties and the bending properties are reduced by the addition of the above bisphenols. Also, JIJ, starting from page 132 of the same magazine, December 1980,
In et al.'s paper showed that chlorohydroquinone and terephthalic acid It has been reported that the melting point is lowered by copolymerizing bisphenols represented by X = (CH ₃ ) ₂ C, SO ₂ , CH ₂ , S, O. In addition, Japanese Patent Publication No. 55-482 discloses a thermotropic liquid crystal polyester composed of hydroquinone having a substituent such as chlorohydroquinone and methylhydroquinone, 4,4'-dihydroxydiphenyl ether and terephthalic acid. Are illustrated for the fibers to be obtained. However, a certain proportion of the 4-oxybenzoyl moiety, 1,4-phenylene and / or 4,4'-bisphenyl, and / or 2,6
An aromatic dicarboxyl moiety, a 4,4'-dioxydiphenyl ether moiety, and optionally a 4,4'- Polyester consisting of a dioxydiphenyl moiety and forming an optically anisotropic molten phase at a temperature of 400 ° C. or less has excellent melt moldability, and various molded articles obtained from the polyester have strength, elasticity, Excellent mechanical performance such as rate and impact characteristics cannot be expected at all.

The liquid crystal polyester of the present invention can be produced by various ester formation reactions, but is usually produced by melt polymerization. Unit I, Unit III in normal case
So-called acidolysis in which the hydroxyl groups of 4-hydroxybenzoic acid, 4,4'-dihydroxydiphenyl ether and 4,4'-dihydroxydiphenyl which are the starting material compounds which give the units IV and IV are converted to the form of lower alkyl esters. The polymerization is carried out by the method. In this case, the lower alkyl ester is most preferably an acetate ester.

In the polymerization, when a known transesterification catalyst is used in an amount in the range of about 0.001 to 1% by weight, preferably about 0.005 to 0.5% by weight of the total monomer weight, favorable results are obtained in terms of the polymerization rate. . Specific examples of the transesterification catalyst include alkali or alkaline earth metal salts of carboxylic acids, alkyltin oxide, diaryltin oxide, alkylstannic acid, titanium dioxide, alkoxytitanium silicate, titanium alkoxide, Lewis acid, hydrogen halide, and the like. be able to. Melt polymerization is usually 200-400 ° C
Is carried out in an atmosphere of an inert gas such as nitrogen or argon, preferably under a flow of the gas or under reduced pressure. As the polymerization proceeds, depending on the type of the esterified compound of the starting hydroxy compound, for example, when acetic acid ester is used, acetic acid is distilled off. The reaction temperature is increased stepwise, and the degree of reduced pressure is adjusted. The polymerization time is usually in the range of 1 to 10 hours. After the completion of melt polymerization,
The polymer may be finely pulverized, and the polymerization may be further advanced in the solid phase at a temperature equal to or lower than the melting point to increase the degree of polymerization.

The polymer thus obtained is a linear polyester having repeating units of substantially the same composition as each of the charged raw materials.

As is well known to those skilled in the art, the confirmation of the formation of the optically anisotropic molten phase of the polymer obtained in this manner was confirmed by a polarizing microscope equipped with a heating device and a sample fragment under crossed Nicols. It can be performed by observing a thin section of preferably about 5 to 20 μm at a constant heating rate and observing that light is transmitted at a constant temperature or higher. In this observation, the transmission of polarized light can be observed more reliably by applying a slight pressure to the sample sandwiched between the cover glasses or moving the cover class under high temperature. In this observation, the temperature at which polarized light starts to pass is the transition temperature to the optically anisotropic molten phase. The transition temperature is determined by using a differential scanning calorimeter (DSC) at a constant heating rate, usually 10 to 20 ° C.
The temperature can be determined by the position of the endothermic peak when the temperature is raised at a rate of / min and the thermal behavior of the sample is observed. Since the endothermic peak observed by the differential scanning calorimeter of the thermootropic liquid crystal polyester of the present invention is very small compared to the crystal melting peak of the crystalline polymer into the isotropic phase, care should be taken in the measurement. You need to pay. Although one or more endothermic peaks may be represented, the temperature giving the largest peak may be considered the transition temperature.

Transition temperature determined by observation with a polarizing microscope,
Although the transition temperature by DSC measurement may not be the same, in such a case, the higher temperature is regarded as the transition temperature to the anisotropic molten phase of the present invention.

It is necessary that the polyester of the present invention has a transition temperature to the anisotropic molten phase of 400 ° C. or less, preferably 375 ° C. or less, from the viewpoint of moldability and mechanical properties of the resulting molded article.

In order to more quantitatively confirm that an optically anisotropic molten phase has been formed, in the observation of the molten state of the sample with the above-mentioned polarizing microscope, a known method such as that disclosed in
According to the method described in JP-A-38425, the amount of transmitted polarized light of a sample can be determined by a photomultiplier. In the present invention, the polyester that forms an optically anisotropic molten phase is a thin section of a sample under orthogonal Nicols when the amount of light transmission under parallel Nicols in the absence of the sample is 100. The light transmission amount is 3 or more, preferably 5 or more. Here, no external force is actively applied to the sample.

The polyester of the present invention is prepared by melting the polyester at a temperature equal to or higher than the transition temperature to the optically anisotropic molten phase measured by the above method, usually within a temperature range of 5 to 100 ° C. higher than the temperature. By the method described above, it can be easily formed into various molded products such as fibers, films, and injection molded products. The above-mentioned various molded products obtained as described above have tensile strength and flexural strength as they are, tensile and flexural modulus, or impact strength in the case of injection molded products. Further, in the case of the above-mentioned various molded articles, especially in the case of fibers and films, heat treatment is performed for a certain period of time under a flow of an inert gas or under reduced pressure at a temperature not higher than a temperature at which the fibers or films do not adhere to each other. Thus, the mechanical strength can be further increased. In this case, the heat treatment time is selected from a range of about 1 minute to 50 hours.

The polyester of the present invention can also be added with various fillers and reinforcing agents to enhance the properties of the resulting molded article. For example, by using glass fiber or carbon fiber, the strength and elastic modulus of a molded product, for example, an injection molded product are improved. This reinforcing agent can be used in amounts up to 60% by weight in the polyester. Also antioxidants,
Additives such as UV stabilizers can also be added. Such additives are usually used in an amount of 0.1 to 10% by weight, preferably 0.2 to 2% by weight in the polyester.

Hereinafter, the present invention will be described specifically with reference to Examples.
The present invention is not limited only to the following examples.

Example 1 226.8 g (1.26 mol) of 4-acetoxybenzoic acid, 101.64 g (0.42 mol) of 4,4'-diphenyldicarboxylic acid were placed in a separable flask of the content 1 equipped with a stirrer, a gas inlet, a distillation head and a condenser. ), 120.12 g (0.42 mol) of 4,4'-diacetoxydiphenyl ether and 0.01 g of sodium acetate as a catalyst were charged. The flask was then evacuated and purged with nitrogen three times, then immersed in a bath maintained at 250 ° C. while flowing dry nitrogen at a rate of about 3 l / h. After the contents of the flask began to melt and turned into a slurry, stirring was started and maintained at the same temperature for 50 minutes. Then, the bath temperature was raised to 280 ° C. over about 10 minutes and maintained at the same temperature for 50 minutes. Then, the bath temperature was raised to 320 ° C. over about 10 minutes, and maintained at the same temperature for 60 minutes. 112ml by this time
Of acetic acid was distilled off. Next, the pressure in the system was gradually reduced to 20 mmHg in 10 minutes. Thereafter, the bath temperature was raised to 340 ° C., and the degree of vacuum was kept at about 0.3 mmHg to continue the polymerization. Forty minutes after the start of the depressurization, the stirring was stopped, nitrogen was introduced, the system was brought to normal pressure, and the flask was cooled. The contents were removed before the contents of the flask had completely solidified. The obtained polymer weighed 290 g. After pulverizing the polymer, it was vacuum dried at 130 ° C. for 10 hours. The resulting polymer was 2.92 d in pentafluorophenol at a temperature of 0.1% w / v at 60 ° C.
It exhibited a logarithmic viscosity of l / g. The logarithmic viscosity ηinh is calculated by the following equation.

to; drop time when pentafluorophenol as a solvent is measured at 60 ° C. with an Ubbelohde viscometer t; fall time of a solution for dissolving a sample c; sample concentration (g / dl) The temperature was increased at a rate of 10 ° C./min in a nitrogen atmosphere in a heating apparatus for microscopes TH-600 manufactured by Linkham Inc.
Observation under a polarizing microscope crossed Nicols revealed that the polymer began to transmit light at 280 ° C. and the amount of transmitted light increased further at around 305 ° C., confirming that the present polymer forms an optically anisotropic molten phase. 2 by DSC (Mettler TH3000)
After a heat treatment at 70 ° C. for 15 minutes, a broad endothermic peak was observed at 280 ° C. at a heating rate of 20 ° C./min.

The polymer was analyzed by ¹ H-NMR (JOEL GX-500) in a pentafluorophenol / trifluoroacetic acid solution, and it was confirmed that the molar ratio of each component in the polymer was the same as the molar ratio of the raw materials. .

When the weight loss of the polymer obtained in an air atmosphere was measured using a thermobalance (Rigaku Denki, differential type differential thermal balance), the weight began to decrease from 415 ° C, and the rate of weight loss until 500 ° C was only 4.6%. % By weight.

Using the obtained polymer, a small injection molding machine (model TK14-1AP) manufactured by Tabata Machine Co., Ltd., using a mold having a cylinder temperature of 320 ° C., an injection pressure of 800 kg / cm ² and a film gate, and a mold temperature of 100 Injection molded articles were prepared at ℃. The gate was devised to obtain a molded product having a size of 75 mm × 15 mm × 2 mm, in which the major axis direction is the direction (TD) orthogonal to the flow direction (MD) of the polymer and the flow direction. The obtained molded product is JISK7203
Flexural strength and flexural modulus according to JISK71
The Izod impact strength with a notch was measured by a method according to 10. The results are shown below.

Glass fiber (Nittobo CS-3J-94 / SP) was added at a ratio of 20 parts by weight to 80 parts by weight of the above polyester, and a plastograph (Plavender) at 300 ° C. for 5 minutes.
After kneading using the same, injection molding was carried out in the same manner, and the physical properties in the flow direction of the obtained molded product were as follows.

Example 2 In Example 1, 4,4'-diphenyldicarboxylic acid 1
Instead of 01.64 g (0.42 mol), 50.82 g (0.21 mol) of 4,4'-diphenyldicarboxylic acid and 34.86 g of terephthalic acid
Example 1 was repeated except that (0.21 mol) was used. The logarithmic viscosity of the obtained polymer was 2.86 dl / g.
As a result of measurement by a polarizing microscope and DSC, it was confirmed that the transition temperature of the present polymer to an optically anisotropic molten phase was 283 ° C.

This polymer was subjected to injection molding in the same manner as in Example 1, and the physical properties of the obtained test pieces were measured. The following results were obtained.

Further, using a film forming apparatus having a T-die having a slit width of 100 mm and a slit interval of 0.2 mm from the obtained polymer, an extruded film was prepared under the conditions of a cylinder temperature of 310 ° C. and an extruding speed of 15 g / min. Is obtained stably. A test piece was prepared from this film, and a tensile test was performed at a tensile speed of 10% / min.
The following results were obtained.

The film was heat-treated at 250 ° C. for 2 hours, 260 ° C. for 5 hours, 270 ° C. for 5 hours, and then at 280 ° C. for 5 hours in a substantially relaxed state under nitrogen flow. The elastic modulus was as follows.

Examples 3 and 4 According to the method of Example 1, 4-acetoxybenzoic acid,
The molar ratio of 4,4'-diphenyldicarboxylic acid and 4,4'-diacetoxydiphenyl ether is 68/16/16, respectively.
(Example 3) and 50/25/25 (Example 4) were charged in proportions to carry out polymerization. The logarithmic viscosity of the obtained polymer is 3.51 and 2.61 dl / g, respectively.As a result of measurement with a polarizing microscope and DSC, the transition temperatures to the optically anisotropic molten phase are 292 ° C and 304 ° C, respectively. Was confirmed.

As a result of subjecting the obtained polymer to injection molding in the same manner as in Example 1, the mechanical performance of the obtained test piece is shown in the following table.

Example 5 According to the method of Example 1, 4-acetoxybenzoic acid,
Polymerization was carried out by charging 2,6-naphthalenedicarboxylic acid and 4,4'-diacetoxydiphenyl ether in a molar ratio of 60/20/20. The logarithmic viscosity of the obtained polymer was 4.39 dl / g, and as a result of measurement with a polarizing microscope and DSC, it was confirmed that the transition temperature to an optically anisotropic molten phase was 283 ° C.

The obtained polymer was subjected to injection molding in the same manner as in Example 1, and as a result, the mechanical performance of the obtained test piece was as follows.

Examples 6 and 7 According to the method of Example 1, 4-acetoxybenzoic acid,
The molar ratios of 4,4'-diphenylcarboxylic, 4,4'-diacetoxydiphenyl ether and 4,4'-diacetoxydiphenyl were 60/20/10/10 (Example 6) and 60/20, respectively.
The polymerization was carried out by charging at a ratio of / 15/5 (Example 7). The logarithmic viscosity of the obtained polymer is 4.44 and
It was 3.56dl / g. As a result of measurement by a polarizing microscope and DSC, it was confirmed that the transition temperatures of the obtained polymer to an optically anisotropic molten phase were 306 ° C. and 298 ° C., respectively.

The obtained polymer was subjected to injection molding in the same manner as in Example 1, and as a result, the physical properties of the obtained test piece in the flow direction were as shown in the following table.

Further, the polymer of Example 6 was used at a temperature of 330 ° C. using a spinneret having a single nozzle having a diameter of 0.2 mm and a hole length of 1.0 mm at a temperature of 0.275.
By spinning at an extrusion speed of g / min, 7.3 denier fiber was obtained. The obtained fiber is circulated for 230
The heat treatment was carried out in a state of relaxation at 1 hour at 260C, 1 hour at 260C, and 6 hours at 290C. The physical properties of the spun yarn and the fiber after the heat treatment were as follows.

Comparative Example 1 According to the method of Example 1, 4-acetoxybenzoic acid, 4,
Polymerization was carried out by charging 4'-diphenyldicarboxylic acid and 4,4'-diacetoxydiphenyl ether at a molar ratio of 30/35/35. In this case, when the pressure was reduced at 320 ° C., the viscosity in the system started to increase remarkably, and even if the bath temperature was raised to 350 ° C. about 20 minutes after the start of the pressure reduction, the system was solidified and could not be stirred. Further, even when the bath temperature was raised to 400 ° C., no melting occurred. The obtained polymer was extremely brittle, and a sharp endothermic peak was observed at 515 ° C. as a result of DSC measurement. This polymer is 4
Molding was not possible below 00 ° C.

Comparative Example 2 According to the method of Example 1, 4-acetoxybenzoic acid,
Polymerization was carried out by charging 4,4'-diphenyldicarboxylic acid and 4,4'-diacetoxydiphenyl in a molar ratio of 60/20/20. In this case, when the pressure was reduced at 320 ° C., the viscosity in the system started to increase remarkably, and even if the bath temperature was raised to 350 ° C. about 20 minutes after the start of the pressure reduction, the system was solidified and could not be stirred. Further, the bath did not dissolve even when the bath temperature was raised to 400 ° C. This polymer could not be molded below 400 ° C.

Claims (3)

(57) [Claims] 1. The following repeating units I, II, III and IV
Consisting of II-OC-A-CO- (wherein A is a 1,4-phenylene group and / or 4,4'-
Represents a diphenylene group and / or a 2,6-naphthalene group, and the proportions of the 1,4-phenylene group, 4,4′-diphenylene group and 2,6-naphthalene group in A are a mol% and b It is assumed that the following relational expression is satisfied when mol% and c mol% are satisfied) a + b + c = 100 0 ≦ a <600 0 ≦ b ≦ 100 0 ≦ c ≦ 100 Unit I is 40-80 mol%, Unit II is 10-30 mol%, Unit II
I is present in an amount within the range of 5 to 30 mol%, unit IV is present in an amount within the range of 0 to 25 mol%, and the sum of the number of moles of unit III and unit IV is equal to the number of moles of unit II; Medium, 0.1% w / v, measured at 60 ° C
A wholly aromatic polyester having an logarithmic viscosity in the range of 0.5 to 10 dl / g and forming an optically anisotropic molten phase at a temperature of 400 ° C. or less. 2. A wholly aromatic polyester according to claim 1, which forms an optically anisotropic molten phase at a temperature of 375 ° C. or lower. 3. A unit I comprising 45 to 70 mol% and a unit II comprising 15 to 27.5 mol%.
Mole%, unit III is 7 to 25 mole%, and unit IV is 0 to 20
%, And the sum of the number of moles of the unit III and the unit IV is equal to the number of moles of the unit II, and forms an optically anisotropic molten phase at a temperature of 375 ° C. or lower. 2. The wholly aromatic polyester according to item 1.