AROMATIC POLYESTER, PRODUCTION METHOD THEREFOR, AND COMPOSITION

Abstract

An aromatic polyester having a repeating unit represented by formula (1) shown below and a terminal structural unit represented by formula (1e) shown below, wherein the proportion of the terminal structural unit per unit mass of the aromatic polyester is not more than 50 μmol/g.

—O—Ar.sup.1—CO—  (1)

—O—Ar.sup.1—CO—OH  (1e)

(In the formulas, Ar.sup.1 represents a 1,4-phenylene group, a 2,6-naphthylene group or a 4,4′-biphenylylene group. The hydrogen atoms that exist in the groups represented by Ar.sup.1 may each be independently substituted with a halogen atom, an alkyl group or an aryl group.)

Claims

1. An aromatic polyester having a repeating unit represented by formula (1) shown below and a terminal structural unit represented by formula (1e) shown below, wherein a proportion of the terminal structural unit per unit mass of the aromatic polyester is not more than 50 μmol/g,
—O—Ar.sup.1—CO—  (1)
—O—Ar.sup.1—CO—OH  (1e) wherein Ar.sup.1 represents a 1,4-phenylene group, a 2,6-naphthylene group or a 4,4′-biphenylylene group, and hydrogen atoms that exist in the groups represented by Ar.sup.1 may each be independently substituted with a halogen atom, an alkyl group or an aryl group.

2. The aromatic polyester according to claim 1, wherein Ar.sup.1 in the formula (1) and the formula (1e) is a 1,4-phenylene group.

3. A composition comprising the aromatic polyester according to claim 1, and a polytetrafluoroethylene.

4. A method for producing an aromatic polyester comprising: a step (P1) of obtaining a lump-like material of an aromatic polyester by conducting a melt polymerization of a compound (1a) represented by formula (1a) shown below in presence of a carboxylic acid anhydride, a step (P2) of grinding the lump-like material to obtain a ground material, and a step (P3) of subjecting the ground material to a solid phase polymerization under temperature conditions exceeding 320° C.,
R.sup.0CO—O—Ar.sup.1—CO—OH  (1a) wherein R.sup.0CO represents an acyl group, Ar.sup.1 represents a 1,4-phenylene group, a 2,6-naphthylene group or a 4,4′-biphenylylene group, and hydrogen atoms that exist in the group represented by Ar.sup.1 may each be independently substituted with a halogen atom, an alkyl group or an aryl group.

5. The method for producing an aromatic polyester according to claim 4, having, at a stage prior to the step (P1), a step (P0) of reacting a compound (1h) represented by formula (1h) shown below and a carboxylic acid anhydride to obtain the compound (1a), wherein the compound (1a) obtained in the step (P0) is used in the step (P1),
H—O—Ar.sup.1—CO—OH  (1h) wherein Ar.sup.1 represents a 1,4-phenylene group, a 2,6-naphthylene group or a 4,4′-biphenylylene group, and hydrogen atoms that exist in the group represented by Ar.sup.1 may each be independently substituted with a halogen atom, an alkyl group or an aryl group.

6. The method for producing an aromatic polyester according to claim 5, wherein the reaction between the compound (1h) and the carboxylic acid anhydride in the step (P0) is conducted under conditions in which a molar ratio represented by carboxylic acid anhydride/compound (1h) exceeds 1.

7. The method for producing an aromatic polyester according to claim 6, wherein a reaction liquid obtained following the reaction of the compound (1h) and the carboxylic acid anhydride under conditions in which the molar ratio exceeds 1 is used to conduct the melt polymerization in the step (P1).

8. The method for producing an aromatic polyester according to claim 6, wherein the molar ratio is at least 1.05 but not more than 1.10.

9. A composition comprising the aromatic polyester according to claim 2, and a polytetrafluoroethylene.

10. The method for producing an aromatic polyester according to claim 7, wherein the molar ratio is at least 1.05 but not more than 1.10.

Description

EXAMPLES

[0168] The present invention is described below in further detail using a series of specific examples. However, the present invention is in no way limited by the following examples.

[Quantification of Terminal Carboxyl Groups]

[0169] For the aromatic polyester produced in each example, the proportion of terminal structural units in which the aromatic polyester terminal was a carboxyl group (—CO—OH), per unit mass of the aromatic polyester, was quantified by liquid chromatography by the absolute calibration curve method using an internal standard. The measurement conditions are described below.

Sample Preparation:

[0170] The aromatic polyester powder produced in each example was added to a round-bottom flask containing N-methylpyrrolidone and n-butylamine, a condenser was fitted to the flask, and the sample was dissolved by heating the flask in a 200° C. sand bath, and then decomposed by heating at 200° C. for a further two hours. Subsequently, excess n-butylamine was removed by an evaporator while heating in an 80° C. sand bath, and formic acid was added to neutralize the solution, thus obtaining a sample solution containing added N-methylpyrrolidone and anisic acid as an internal standard.

[0171] When preparing the sample solution, the aromatic polyester formed from the repeating unit (1) described above reacts with the primary amine such as n-butylamine and decomposes. In this case, the ester linkage (—CO—O—) in the main chain of the aromatic polyester is cleaved, selectively forming a chain-derived compound (the —CO— side) in which bonding with the primary amine forms an amide linkage, and a terminal-derived compound (the —O— side) which forms a hydroxyl group. At this time, the primary amine does not react with carboxyl groups that exist at aromatic polyester terminals or on side chains.

[0172] The aromatic carboxylic acid formed by the hydroxyl group (HO—Ar.sup.1—CO—OH) contained within the entire decomposition product of the aromatic polyester contains the terminal structural unit (—O—Ar.sup.1—CO—OH) represented by the above formula (1e).

[0173] The case in which an aromatic polyester composed of a repeating unit (1) in which Ar.sup.1 is a 1,4-phenylene group is decomposed by reaction with a primary amine (R.sup.1—NH.sub.2) is shown below as an example of the above reaction. In this case, the 4-hydroxybenzoic acid in the decomposition product contains the terminal structural unit (—O—C.sub.6H.sub.4—CO—OH) represented by formula (1e).

##STR00003##

Measurement:

[0174] The sample solution prepared in the manner described above was measured by a liquid chromatography method under the measurement conditions described below, and based on the ratio of the peak at a retention time in the vicinity of 4.5 minutes (the peak attributable to the terminal-derived carboxyl groups) relative to the peak at a retention time of 13.55 minutes (the anisic acid peak), and the ratio of the peak at a retention time in the vicinity of 14.4 minutes (the peak attributable to the chain-derived compound) relative to the peak at 13.55 minutes (the anisic acid peak), the component derived from the terminal carboxyl groups was quantified.

[Liquid Chromatography Measurement Conditions]

[0175] Column: product name: sumipax-K ODS (4.6 mmø×15 cm, 5 μm), manufactured by Sumika Chemical Analysis Service, Ltd.

[0176] Guard column: product name: sumipax filter PG-ODS, manufactured by Sumika Chemical Analysis Service, Ltd.

[0177] Mobile phase flow rate: 1.0 mL/min

[0178] Column temperature: 40° C.

[0179] Sample injection volume: 10 μL

[0180] Detector: UV-Vis spectrophotometer (UV)

[0181] Detection wavelength: 240 nm

[0182] Analysis time: 25 min

[0183] Measurement interval: 15 min

[0184] Measurement method: gradient elution method

[0185] Mobile phase (eluent): using an aqueous solution containing 0.1% by volume of added acetic acid and an acetonitrile solution containing 0.1% by volume of added acetic acid, the composition of the eluent was changed using the gradient conditions described below.

[0186] Gradient Conditions:

[0187] An eluent containing 10% by volume of the acetonitrile solution containing 0.1% by volume of added acetic acid and 90% by volume of the aqueous solution containing 0.1% by volume of added acetic acid was prepared.

[0188] First, the proportion of the acetonitrile solution containing 0.1% by volume of added acetic acid, relative to the total volume of the eluent, was changed in a linear manner from 10% by volume to 25% by volume over a period of 15 minutes. Subsequently, the proportion of the acetonitrile solution containing 0.1% by volume of added acetic acid, relative to the total volume of the eluent, was changed in a linear manner from 25% by volume to 100% by volume over a period of 10 minutes.

[Measurement of Particle Size]

[0189] The particle size of the aromatic polyester powder was measured in the manner described below, using a laser diffraction/scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.).

[0190] First, approximately 100 mg of the aromatic polyester powder was dispersed in water to prepare a dispersion.

[0191] Next, a particle size distribution of the aromatic polyester powder in the thus obtained dispersion was obtained using the laser diffraction/scattering particle size distribution analyzer mentioned above. The proportion (% by volume) of particles having a particle size of not more than 90 μm was determined from the obtained particle size distribution for the aromatic polyester powder.

[Measurement of Bulk Specific Gravity]

[0192] The bulk specific gravity of the aromatic polyester powder was measured in accordance with the JIS standard (JIS K6720) using a bulk specific gravity analyzer (manufactured by Tsutsui Scientific Instruments Co., Ltd.).

<Production of Aromatic Polyesters>

Example 1

[0193] Step (P0):

[0194] The inside of a reactor fitted with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser was flushed thoroughly with nitrogen gas, the reactor was then charged with 70 parts by mass of 4-hydroxybenzoic aid and 56.4 parts by mass of acetic anhydride (so that the molar ratio represented by acetic anhydride/4-hydroxybenzoic acid was 1.09), and a reaction (acylation) was conducted by gradually raising the internal temperature to 140° C. and then stirring for 3 hours.

[0195] Step (P1):

[0196] The reaction liquid obtained following the above step (P0) was heated further to 280° C. over a period of about 3.5 hours while stirring was continued. Subsequently, the reaction product was cooled, thus obtaining an aromatic polyester prepolymer (lump-like material of the aromatic polyester).

[0197] Step (P2):

[0198] The prepolymer obtained in the above step (P1) was ground using a pulverizer to obtain a ground material of the aromatic polyester.

[0199] Step (P3):

[0200] The ground material obtained in the above step (P2) was subjected to a solid phase polymerization by heating the material from room temperature to 380° C. over a period of 9 hours in a nitrogen gas atmosphere, and then holding the temperature at 380° C. for a further 5 hours.

[0201] In this description, room temperature means a temperature within a range from 5 to 35° C.

[0202] Subsequently, the product obtained following the above solid phase polymerization was cooled to room temperature to obtain a powdered aromatic polyester. The thus obtained powdered aromatic polyester was then sieved through a dry sieve with a mesh size of 100 μm to obtain the target aromatic polyester powder.

[0203] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.40.

Example 2

[0204] In the step (P3) of Example 1, with the exception of performing an operation in which the temperature was raised from room temperature to 390° C. over a period of 9 hours and then held at 390° C. for a further 5 hours, an aromatic polyester powder was obtained in a similar manner to Example 1.

[0205] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.42.

Example 3

[0206] In the step (P3) of Example 1, with the exception of performing an operation in which the temperature was raised from room temperature to 370° C. over a period of 9 hours and then held at 370° C. for a further 5 hours, an aromatic polyester powder was obtained in a similar manner to Example 1.

[0207] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.39.

Example 4

[0208] In the step (P0) of Example 1, with the exception of altering the amount added of the acetic anhydride to 54.4 parts by mass (a molar ratio represented by acetic anhydride/4-hydroxybenzoic acid of 1.05), an aromatic polyester powder was obtained in a similar manner to Example 1.

[0209] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.39.

Comparative Example 1

[0210] In the step (P03) of Example 1, with the exception of performing an operation in which the temperature was raised from room temperature to 320° C. over a period of 9 hours and then held at 320° C. for a further 5 hours, an aromatic polyester powder was obtained in a similar manner to Example 1.

[0211] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.37.

Comparative Example 2

[0212] In the step (P0) of Example 1, with the exception of altering the amount added of the acetic anhydride to 51.8 parts by mass (a molar ratio represented by acetic anhydride/4-hydroxybenzoic acid of 1.00), an aromatic polyester powder was obtained in a similar manner to Example 1.

[0213] The thus obtained aromatic polyester powder had a proportion of particles with a particle size of not more than 90 μm of 99% by volume, and had a bulk specific gravity of 0.38.

<Evaluations>

[0214] The aromatic polyester powders produced using the production methods of the above examples were each evaluated for thermal stability using the methods described below.

[Thermal Stability Evaluation (1): Weight Loss on Heating]

[0215] Ten grams of the aromatic polyester powder was heated in an air atmosphere in an oven at 370° C. for 5 hours, the change in mass from before to after the heating was measured, and the percentage weight loss was determined. The result is shown in Table 1 as “Weight loss on heating (%)”.

[Thermal Stability Evaluation (2): Black Spot Foreign Matter]

[0216] Ten grams of the aromatic polyester powder was heated in an air atmosphere in an oven at 370° C. for 5 hours. Subsequently, the heated particle groups were spread out thinly, and the surfaces of the various aromatic polyester particles were inspected visually. The number of black spot foreign matter defects having a size of 0.1 mm or greater was counted and evaluated against the following evaluation criteria. The results are shown in Table 1 as “Black spot foreign matter”.

[0217] Evaluation Criteria

[0218] A: number of black spot foreign matter defects was 1 or fewer.

[0219] B: number of black spot foreign matter defects was from 2 to 5.

[0220] C: number of black spot foreign matter defects was 6 or greater.

[0221] The black spot foreign matter observed in this evaluation represents carbides formed by the heating at 370° C. for 5 hours.

TABLE-US-00001 TABLE 11 Example Example Example Example Comparative Comparative 1 2 3 4 Example 1 Example 2 Step (P0) Molar ratio represented 1.09 1.09 1.09 1.05 1.09 1.00 by acetic anhydride/ 4-hydroxybenzoic acid Step (P3) Temperature conditions 380 390 370 380 320 380 for solid phase polymerization (° C.) Quantification Proportion of terminal 29 15 49 38 139 90 of terminal structural units in which carboxyl terminal is —CO—OH groups (μmol/g) Thermal Weight loss on heating 1.30 1.10 1.72 1.50 1.90 1.80 stability (%) evaluations Black spot foreign A A B A C C matter

[0222] From the results shown in Table 1, it can be confirmed that aromatic polyesters of the present invention, for which the proportion of terminal structural units in which the terminal is a carboxyl group (—CO—OH) is not more than 50 μmol/g, have a smaller value for weight loss on heating and enhanced thermal stability compared with aromatic polyesters for which the above proportion exceeds 50 μmol/g.

[0223] In addition, it can also be confirmed that aromatic polyesters for which the proportion of terminal structural units in which the terminal is a carboxyl group is not 40 μmol/g or less exhibit a small number of black spot foreign matter defects which occur when the powder is heated in a high-temperature atmosphere, and have further enhanced thermal stability and external appearance.

<Preparation of Composition>

Example 5

[0224] By mixing the aromatic polyester powder obtained in Example 1 and a PTFE powder in a mass ratio of 80:20, molding the mixture into a circular cylindrical shape using a compression molding die, conducting firing at a temperature of 370° C. or higher, and then cutting the molded product into a sheet-like form, a molded item (composition) for use in oil sealing can be obtained.

INDUSTRIAL APPLICABILITY

[0225] The aromatic polyester of the present invention exhibits enhanced thermal stability compared with conventional products. This aromatic polyester is useful as an organic filler, and is particularly useful as a modifier for polytetrafluoroethylene (PTFE). Use of the aromatic polyester in a variety of applications can be expected, including jet engine sealing materials, oil sealing, and bearings.

[0226] In other words, the present invention is able to provide an aromatic polyester having enhanced thermal stability, a production method therefor, and a composition containing the aromatic polyester, and is therefore extremely useful industrially.