阅读说明：本技术 聚苯并噁唑前体的制造方法和聚苯并噁唑前体 (Method for producing polybenzoxazole precursor and polybenzoxazole precursor ) 是由 福岛智美 秋元真步 于 2020-09-23 设计创作，主要内容包括：本发明涉及聚苯并噁唑前体的制造方法和聚苯并噁唑前体。[课题]提供：能抑制废液的排出、且能够收率良好地得到残留卤素充分降低了的聚苯并噁唑前体的方法。[解决方案]一种聚苯并噁唑前体的制造方法,其包括如下工序：在非质子性极性溶剂中,使二羧酸二卤化物和双(邻氨基苯酚)反应,得到聚苯并噁唑前体的粗产物的工序；将得到的聚苯并噁唑前体的粗产物根据情况利用选自水和甲醇中的1种以上的溶剂进行清洗后,溶解于选自伯醇(其中,除甲醇之外)和仲醇中的1种以上的醇中而得到醇溶液的工序；和,在水或有机酸水溶液中加入得到的醇溶液,使聚苯并噁唑前体沉淀的工序。(The present invention relates to a method for producing a polybenzoxazole precursor and a polybenzoxazole precursor. [ problem ] to provide: a method for producing a polybenzoxazole precursor having sufficiently reduced residual halogen in a good yield while suppressing the discharge of waste liquid. [ solution ] A method for producing a polybenzoxazole precursor, which comprises the steps of: a step of reacting a dicarboxylic acid dihalide with bis (o-aminophenol) in an aprotic polar solvent to obtain a crude polybenzoxazole precursor; a step of washing the obtained crude polybenzoxazole precursor with 1 or more solvents selected from water and methanol, as the case may be, and dissolving the washed crude polybenzoxazole precursor in 1 or more alcohols selected from a primary alcohol (excluding methanol) and a secondary alcohol to obtain an alcohol solution; and a step of adding the obtained alcohol solution to water or an organic acid aqueous solution to precipitate a polybenzoxazole precursor.)

1. A method for producing a polybenzoxazole precursor, comprising the steps of:

a step of reacting a dicarboxylic acid dihalide with bis (o-aminophenol) in an aprotic polar solvent to obtain a crude polybenzoxazole precursor;

a step of washing the obtained crude polybenzoxazole precursor with 1 or more kinds of solvents selected from water and methanol as the case may be, and dissolving the washed crude polybenzoxazole precursor in 1 or more kinds of alcohols selected from a primary alcohol and a secondary alcohol to obtain an alcohol solution, wherein the primary alcohol is other than methanol; and the combination of (a) and (b),

and a step of adding the obtained alcohol solution to water or an aqueous organic acid solution to precipitate a polybenzoxazole precursor.

2. The method for producing a polybenzoxazole precursor according to claim 1, wherein the alcohol is an alcohol having 2 to 10 carbon atoms.

3. The method for producing a polybenzoxazole precursor according to claim 1 or 2, wherein the alcohol is an alcohol having 2 or more oxygen atoms.

4. The method for producing a polybenzoxazole precursor according to claim 3, wherein the alcohol is an alcohol having an ether bond.

5. The method for producing a polybenzoxazole precursor according to any one of claims 1 to 4, wherein an alcohol solution is added to an aqueous solution of 1 or more organic acids selected from acetic acid, formic acid and oxalic acid to precipitate polybenzoxazole.

6. The method for producing a polybenzoxazole precursor according to claim 5, wherein the concentration of the aqueous organic acid solution is 50ppm or more and 500ppm or less.

7. A polybenzoxazole precursor obtained by the production method according to any one of claims 1 to 6, and having a residual halogen content of 30.0ppm or less.

Technical Field

The present invention relates to a method for producing a polybenzoxazole precursor and a polybenzoxazole precursor.

Background

Polybenzoxazole (hereinafter also referred to as "PBO") precursors have attracted attention in the production of electronic components and the like because they provide cured products excellent in heat resistance and electrical insulation properties.

As a method for synthesizing a polybenzoxazole precursor, the following methods are known: an aromatic dicarboxylic acid dihalide is reacted with bis (o-aminophenol) in an aprotic polar solvent. In this synthesis method, a halogen component remains in the obtained polybenzoxazole precursor, but when used for electronic component applications, the residual halogen must be reduced from the viewpoint of long-term reliability such as insulation.

In order to reduce the residual halogen, the following methods are proposed: a crude polybenzoxazole precursor obtained by the reaction is washed with water or an aqueous alkaline solution (patent document 1).

In addition, the following methods are proposed: water and a water-insoluble solvent are added to a crude polybenzoxazole precursor obtained by the reaction, and the mixture is mixed and left to stand, and then an aqueous layer is separated (patent document 2).

Documents of the prior art

Patent document 1: japanese laid-open patent publication No. 2007-106786

Patent document 2: japanese patent laid-open publication No. 2013-64130

Disclosure of Invention

Problems to be solved by the invention

However, in the method of patent document 1, since repeated washing is required to sufficiently reduce the residual halogen, a large amount of water or an alkaline aqueous solution is required, and a large amount of waste liquid is generated. Further, the pH of the liquid at the time of cleaning is lower than 7 immediately after the cleaning of the crude product is started due to the residual halogen contained in the crude product of the polybenzoxazole precursor, but the pH becomes high at the time of repeated cleaning, and the solubility of the alkali-soluble polybenzoxazole precursor is improved, which also causes a problem that the yield is lowered.

On the other hand, in the method of patent document 2, in order to sufficiently reduce the residual halogen, it is necessary to repeat the separation of the aqueous layer, and as the pH of the aqueous layer increases with the repetition, the solubility of the polybenzoxazole precursor in the aqueous layer increases, and there is a problem that the yield decreases.

An object of the present invention is to provide: the polybenzoxazole precursor having sufficiently reduced residual halogen can be obtained in a good yield while suppressing the discharge of waste liquid.

Means for solving the problems

The inventors of the present invention found that: the present inventors have found that the above problems can be solved by a method for producing a polybenzoxazole precursor, which comprises dissolving a crude product in a specific alcohol to obtain an alcohol solution, and then adding the alcohol solution to water or an aqueous organic acid solution to precipitate a polybenzoxazole precursor.

The gist of the present invention is as follows.

[1] A method for producing a polybenzoxazole precursor, comprising the steps of:

a step of reacting a dicarboxylic acid dihalide with bis (o-aminophenol) in an aprotic polar solvent to obtain a crude polybenzoxazole precursor;

a step of washing the obtained crude polybenzoxazole precursor with 1 or more solvents selected from water and methanol, as the case may be, and dissolving the washed crude polybenzoxazole precursor in 1 or more alcohols selected from a primary alcohol (excluding methanol) and a secondary alcohol to obtain an alcohol solution; and the combination of (a) and (b),

and a step of adding the obtained alcohol solution to water or an aqueous organic acid solution to precipitate a polybenzoxazole precursor.

[2] The method for producing a polybenzoxazole precursor according to item [1], wherein the alcohol is an alcohol having 2 to 10 carbon atoms.

[3] The process for producing a polybenzoxazole precursor according to the above item [1] or [2], wherein the alcohol is an alcohol having 2 or more oxygen atoms.

[4] The process for producing a polybenzoxazole precursor according to item [3], wherein the alcohol is an alcohol having an ether bond.

[5] The method for producing a polybenzoxazole precursor according to any one of [1] to [4], wherein an alcohol solution is added to an aqueous solution of 1 or more kinds of organic acids selected from acetic acid, formic acid and oxalic acid to precipitate polybenzoxazole.

[6] The process for producing a polybenzoxazole precursor according to [5], wherein the concentration of the aqueous organic acid solution is 50ppm to 500 ppm.

[7] A polybenzoxazole precursor obtained by the production method according to any one of [1] to [6], and having a residual halogen content of 30.0ppm or less.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a method for producing a polybenzoxazole precursor having sufficiently reduced residual halogen in a good yield while suppressing the discharge of waste liquid.

Detailed Description

< step of obtaining a crude polybenzoxazole precursor >

The manufacturing method of the present invention includes the steps of: the dicarboxylic acid dihalide and bis (o-aminophenol) are reacted in an aprotic polar solvent to give a crude polybenzoxazole precursor.

The dicarboxylic acid dihalide is not particularly limited, and dicarboxylic acid dichloride is preferred in view of low-temperature reactivity.

Examples of the dicarboxylic acid dihalide include isophthalic acid, terephthalic acid, 5-t-butylisophthalic acid, 5-bromoisophthalic acid, 5-fluoroisophthalic acid, 5-chloroisophthalic acid, 2, 6-naphthalenedicarboxylic acid, 4 ' -dicarboxybiphenyl, 4 ' -dicarboxydiphenyl ether, 4 ' -dicarboxyditetraphenylsilane, bis (4-carboxyphenyl) sulfone, 2-bis (p-carboxyphenyl) propane, 2-bis (4-carboxyphenyl) -1,1,1,3,3, 3-hexafluoropropane and other dicarboxylic acids having an aromatic ring, oxalic acid, malonic acid, succinic acid, 1, 2-cyclobutanedicarboxylic acid, 1, 4-cyclohexanedicarboxylic acid, 1, 3-cyclopentanedicarboxylic acid, and the like, Aliphatic dicarboxylic acids such as bis (cyclohexane) -4, 4' -dicarboxylic acid. Among them, 4' -dicarboxydiphenyl ether is preferable. As dicarboxylic acid dihalides, the dichlorides of these dicarboxylic acids are preferred.

The bis (o-aminophenol) is not particularly limited, and examples thereof include 3,3 '-diamino-4, 4' -dihydroxybiphenyl, 4 '-diamino-3, 3' -dihydroxybiphenyl, bis (3-amino-4-hydroxyphenyl) propane, bis (4-amino-3-hydroxyphenyl) propane, bis (3-amino-4-hydroxyphenyl) sulfone, bis (4-amino-3-hydroxyphenyl) sulfone, 2-bis (3-amino-4-hydroxyphenyl) -1,1,1,3,3, 3-hexafluoropropane, 2-bis (4-amino-3-hydroxyphenyl) -1,1,1,3,3, 3-hexafluoropropane and the like. Among them, 2-bis (3-amino-4-hydroxyphenyl) -1,1,1,3,3, 3-hexafluoropropane is preferable.

The aprotic polar solvent is not particularly limited, and examples thereof include amide solvents such as N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), cyclic ester solvents such as γ -butyrolactone, γ -valerolactone, and γ -caprolactone, acetone, acetophenone, and dimethyl sulfoxide (DMSO). Among them, NMP is preferable.

The method for the reaction of the dicarboxylic acid dihalide and bis (o-aminophenol) is not particularly limited, and examples thereof include the following methods: bis (o-aminophenol) is dissolved in an aprotic polar solvent, followed by addition of a dicarboxylic acid dihalide and stirring. The dicarboxylic acid dihalide may be added in the form of a powder or may be dissolved in a solvent or the like and added in the form of a liquid.

After the reaction, a poor solvent such as water or methanol is added to precipitate a crude polybenzoxazole precursor and the precipitate is filtered to recover the crude polybenzoxazole precursor.

The reaction temperature may be set to-15 ℃ or higher and 60 ℃ or lower, for example.

The reaction time may be 1 hour or more and 24 hours or less.

The dicarboxylic acid dihalide and bis (ortho-aminophenol) may be set as the number of moles of the dicarboxylic acid dihalide: the number of moles of bis (o-aminophenol) became 1: 0.5-1: 2, in the presence of a reducing agent.

The concentration of the dicarboxylic acid dihalide and bis (o-aminophenol) in total in the reaction system may be set to 5% by mass or more and 50% by mass or less.

The amount of the poor solvent used for precipitation of the crude polybenzoxazole precursor may be 50 parts by mass or more and 1000 parts by mass or less, and preferably 100 parts by mass or more and 500 parts by mass or less, based on 100 parts by mass of the aprotic polar solvent.

By the reaction, a crude polybenzoxazole precursor having a repeating structure represented by the formula (1) can be obtained,

(in the formula (1),

x is a 4-valent organic group corresponding to a structure in which 2-OH groups and 2 amino groups are removed from bis (o-aminophenol),

y is a 2-valent organic group corresponding to a structure in which 2C (═ O) X (X is a halogen atom) are removed from a dicarboxylic acid dihalide,

n is an integer of 1 or more, preferably an integer of 10 or more and 50 or less, and more preferably an integer of 20 or more and 40 or less. ).

< cleaning step (optional step) with poor solvent >

The manufacturing method of the present invention may include the steps of: the crude polybenzoxazole precursor is washed with a poor solvent such as water or methanol. The amount of the poor solvent used in 1-time washing may be 3 times or more and 100 times or less, preferably 5 times or more and 50 times or less, by mass, of the crude polybenzoxazole precursor. In the case of cleaning, it is preferable to reduce the number of times of cleaning from the viewpoint of suppressing discharge of waste liquid.

< step of obtaining an alcohol solution of a crude polybenzoxazole precursor >

The manufacturing method of the present invention includes the steps of: the crude polybenzoxazole precursor is dissolved in 1 or more alcohols selected from primary alcohols (except methanol) and secondary alcohols to obtain an alcoholic solution. The alcohol is a good solvent for the polybenzoxazole precursor, and is preferably an alcohol which is liquid at room temperature (25 ℃).

Examples of the primary alcohol include ethanol, 1-propanol, 2-methyl-1-propanol, and 1-butanol, and examples of the secondary alcohol include 2-propanol and 2-butanol.

From the viewpoint of solubility of the polybenzoxazole precursor, the alcohol is preferably an alcohol having 2 or more oxygen atoms, and examples thereof include an alcohol having 2 or more hydroxyl groups, an alcohol having an ether bond, and the like. Among these, alcohols having an ether bond are more preferable from the viewpoint of yield. Examples of the alcohol having 2 or more oxygen atoms include ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-sec-butyl ether, ethylene glycol mono-tert-butyl ether, propylene glycol 1-monomethyl ether, propylene glycol 1-monoethyl ether, propylene glycol 1-mono-n-propyl ether, propylene glycol 1-monoisopropyl ether, propylene glycol 1-mono-n-butyl ether, propylene glycol 1-mono-isobutyl ether, propylene glycol 1-sec-butyl ether, propylene glycol 1-mono-tert-butyl ether, etc., and from the viewpoint of yield, ethylene glycol monomethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol 1-monomethyl ether, etc. are preferable. The above alcohols may be used alone or in combination of two or more.

The concentration of the crude polybenzoxazole precursor in the alcohol solution is preferably 1% by mass or more, more preferably 5% by mass or more, from the viewpoint of the removal efficiency of the halide ion (for example, chloride ion). The upper limit of the concentration is not particularly limited as long as the crude product is dissolved therein, and may be, for example, 50 mass% or less.

< Process for adding the obtained alcohol solution to an aqueous solution of water or an organic acid >

The manufacturing method of the present invention includes the steps of: the resulting alcohol solution is added to water or an aqueous organic acid solution to precipitate a polybenzoxazole precursor. Water or an aqueous organic acid solution is a poor solvent for the polybenzoxazole precursor.

From the viewpoint of yield, an aqueous organic acid solution is preferably used. The organic acid is not particularly limited, and examples thereof include formic acid, acetic acid, oxalic acid, hydroxypropionic acid, alanoic acid, lactic acid, butyric acid, citric acid, ascorbic acid, and the like, and among them, formic acid, acetic acid, and oxalic acid are preferable, and oxalic acid is particularly preferable. The organic acid may be used alone or in combination of two or more.

The concentration of the organic acid in the aqueous organic acid solution is preferably 10000ppm or less, more preferably 1000ppm or less, and still more preferably 500ppm or less, from the viewpoint of insulation reliability of the cured film. The concentration of the organic acid in the aqueous organic acid solution may be 1ppm or more, preferably 20ppm or more, and more preferably 50ppm or more, from the viewpoint of sufficiently obtaining the effect of using the organic acid.

From the viewpoint of the yield of the polybenzoxazole precursor, the pH of the aqueous organic acid solution is preferably 7 or less, more preferably 4 or less.

The method of adding the alcohol solution to the water or the aqueous organic acid solution is not particularly limited, and the alcohol solution may be added at once or may be added in portions, but is preferably added dropwise from the viewpoint of the removal efficiency of halide ions (for example, chloride ions). The dropping may be performed for 10 minutes to 600 hours, and preferably 30 minutes to 300 hours.

The amount of the aqueous solution of water or an organic acid may be, for example, 50 parts by mass or more based on 100 parts by mass of the alcohol solution. From the viewpoint of the removal efficiency of halide ions (for example, chloride ions), it is preferably 500 parts by mass or less, more preferably 200 parts by mass or less.

The temperature at the time of addition may be from-10 ℃ to 60 ℃, preferably from 0 ℃ to 30 ℃.

After the addition is completed, the solution is preferably left to stand, preferably for 30 minutes to 24 hours.

After the addition, the pH may be adjusted by adding an organic acid or an aqueous solution of an organic acid before the mixture is allowed to stand.

The precipitated polybenzoxazole precursor can be recovered by filtration.

In the production method of the present invention, the polybenzoxazole precursor recovered by filtration can be repeatedly subjected to the following steps: a step of dissolving the alcohol in 1 or more types of alcohol selected from a primary alcohol (excluding methanol) and a secondary alcohol to obtain an alcohol solution; the step of adding the obtained alcohol solution to water or an aqueous organic acid solution is preferably repeated 2 times or less, more preferably 1 time without repeating each of these steps, from the viewpoint of suppressing discharge of waste liquid.

In the production method of the present invention, the polybenzoxazole precursor can be obtained at a yield of 80% or more. The yield is preferably 90% or more, more preferably 95% or more. The residual halogen in the obtained polybenzoxazole precursor can be controlled to 30.0ppm or less. The amount of residual halogen is preferably 20.0ppm or less, more preferably 7.0ppm or less.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Hereinafter, "part(s)" and "%" are based on mass unless otherwise specified.

[ example 1]

A300 mL flask was charged with 65g of N-methylpyrrolidone (NMP) and heated to 60 ℃. 9.9777g (0.02724mol) of powdered 2, 2-bis (3-amino-4-hydroxyphenyl) -1,1,1,3,3, 3-hexafluoropropane (6-FAP) was added to completely dissolve it. Further, 10g of NMP was added thereto, and the flask was immersed in an ice bath and stirred until the temperature of the liquid became 10 ℃ or lower. Then, while maintaining the temperature of the liquid at 20 ℃ or lower, 4' -diphenyl ether dicarboxylic acid chloride (DEDC) in powder form, a total of 8.80g (0.02982mol) was added in 1g increments. After stirring was continued at room temperature (25 ℃ C.) for 6 hours, 0.32g of ion-exchanged water was added thereto, the temperature was raised to 50 ℃ C., and stirring was continued at 50 ℃ C. for 30 minutes. 141g of methanol was added and stirring was continued until homogeneous.

The resulting solution was added dropwise to a 800mL beaker containing 282g of ion-exchanged water over 2 hours, and the precipitated solid was filtered through a filter cloth.

The recovered solid was added all at once to a 800mL beaker to which 282g of ion-exchanged water was added, stirred at room temperature for 30 minutes, filtered, and the solid was recovered. This operation was repeated 3 times.

The total amount of the obtained solid was added to a 300mL beaker, and 206g of propylene glycol 1-monomethyl ether (1-methoxy-2-propanol, PGM) as a good solvent was further added thereto, followed by stirring until completely dissolved.

The resulting solution was added to a 800mL beaker containing 302g of ion-exchanged water as a poor solvent and 0.0605g of oxalic acid as an organic acid for 2 hours. The pH of the liquid in the beaker before the addition of the solution was 3 or less.

After the addition, 0.183g of oxalic acid was further added to the 800mL beaker, and the mixture was left for 1 day. The filtered and recovered solid was dried under reduced pressure at 80 ℃ to obtain 16.5g of Polybenzoxazole (PBO) precursor. The molecular weights in terms of polystyrene based on GPC were as follows: mn: 12600. mw: 30300. the chlorine concentration based on ion chromatography was 6.4 ppm.

[ example 2]

A PBO precursor was prepared in the same manner as in example 1, except that oxalic acid was changed to acetic acid.

[ example 3]

A PBO precursor was prepared in the same manner as in example 1, except that oxalic acid was not used.

[ example 4]

A PBO precursor was prepared in the same manner as in example 1, except that propylene glycol 1-monomethyl ether was changed to ethanol.

[ example 5]

A PBO precursor was prepared in the same manner as in example 1, except that propylene glycol 1-monomethyl ether was changed to ethylene glycol.

[ comparative example 1]

A PBO precursor was prepared in the same manner as in example 1, except that N-methylpyrrolidone was used as a good solvent and oxalic acid was not used.

[ comparative example 2]

A PBO precursor was prepared in the same manner as in example 1, except that acetone was used as a good solvent and oxalic acid was not used.

For examples and comparative examples, chlorine concentration and yield were evaluated. The results are shown in table 1.

The chlorine concentration was evaluated as follows.

(1) Using a cryo-pulverization apparatus TI500DX (CMT science), 1.5g of the PBO precursor was pulverized at 196 ℃ for 10 minutes with shaking.

(2) 1g of the pulverized PBO precursor was subjected to solid-phase extraction using 10g of ultrapure water (resistance: 18.2 M.OMEGA.) at 121 ℃ for 20 hours in a pressure vessel made of polytetrafluoroethylene.

(3) The aqueous solution obtained in (2) was subjected to ion chromatography, and various ion concentrations were calculated by a 1-point calibration curve method using a standard solution. The conditions for ion chromatography are as follows.

Ion chromatography: aquion (trade mark) System (manufactured by Thermo Scientific Co., Ltd.)

Using a column: dionex IonPac (trademark) AS22-Fast(manufactured by Thermo Scientific Co., Ltd.)

Column temperature: 30 deg.C

Eluent: 4.5mM Na₂CO₃Aqueous solution with 1.4mM NaHCO₃1 part of aqueous solution: 1 (weight ratio) of the mixed solution

Eluent flow rate: 1.2 mL/min

Standard solution for standard curve: anion standard solution for ion chromatography (manufactured by Kanto chemical Co., Ltd.)

The chlorine concentration was evaluated as follows.

Very excellent: 7.0ppm or less

Very good: more than 7.0ppm and 20.0pm or less

O: more than 20.0ppm and not more than 30.0ppm

X: over 30.0ppm

The yield in the examples was evaluated as follows.

The yield was calculated by the following equation.

Yield [% ]

Weight of PBO precursor [ g ]/(DEDC weight [ g ] +6-FAP weight [ g ] -HCl weight [ g ]) x 100 of example

The weight of the PBO precursor is a value of the PBO precursor as a final product of each example measured with an electronic balance.

The weight of DEDC and the weight of 6-FAP were the weight of 4, 4' -diphenyl ether dicarboxylic acid chloride (DEDC) and 2, 2-bis (3-amino-4-hydroxyphenyl) -1,1,1,3,3, 3-hexafluoropropane (6-FAP) used in the examples.

The HCl weight is a value converted from the amount of chlorine contained in the DEDC used.

The yield was evaluated as follows.

Very excellent: more than 95 percent

Very good: more than 90 percent and less than 95 percent

O: more than 80 percent and less than 90 percent

X: less than 80 percent

[ Table 1]

Comparative example 1 using N-methylpyrrolidone as a good solvent had a low yield and insufficient reduction in chlorine concentration. The yield of comparative example 2 using acetone as a good solvent was low.

On the other hand, the results of evaluation of the yield and chlorine concentration in examples 1 to 5 were good. From the results of examples 1 to 3, it is understood that more excellent results are obtained by using an aqueous organic acid solution as a poor solvent. In the examples, it was found that the discharge of the waste liquid was suppressed and the chlorine concentration was sufficiently reduced.

[ reference example ]

For the solvents shown in table 2 below, preliminary experiments concerning solubility and yield were performed.

Solubility was evaluated by visual observation by adding 1g of the PBO precursor obtained in example 1 and 19g of the solvent shown in Table 2 to a 50mL beaker equipped with a 2cm Teflon-coated stirrer, stirring the mixture at 25 ℃ and 200rpm for 2 hours.

The solubility was evaluated as follows.

O: completely dissolve

And (delta): has a part of gel

X: insoluble matter

Regarding the yield, 1g of the PBO precursor obtained in example 1 and 19g of the solvent shown in the following Table 2 were charged into a 50mL beaker equipped with a 2cm Teflon-coated stirrer, and stirred at 25 ℃ and 200rpm for 2 hours. The resulting solution was added dropwise over 3 minutes to a 100mL beaker containing 20mL of ion-exchanged water, and the mixture was further stirred for 10 minutes, followed by purification for 10 minutes. The solution was filtered through a filter paper (circular qualitative filter paper No.5B, manufactured by ADVANTEC) whose weight was measured in advance, and dried in a blast drying oven at 85 ℃ for 2 hours together with the filter paper, and then the weight was measured. The yield was determined according to the following equation.

Yield [% ] (weight [ g ] -filter paper weight [ g ])/[ 1[ g ] × 100 after drying)

The yield was evaluated as follows.

Very good: more than 95 percent

O: over 90 percent

And (delta): over 80 percent

-: it was not performed because of insolubility.

[ Table 2]

Solvent(s)	Solubility in water	Yield of
			Methanol	×	－
Ethanol	△	○
			N-propanol	△	○
Isopropanol (I-propanol)	△	○
			Tert-butyl alcohol	×	－
Ethylene glycol	○	△
			Ethylene glycol monoethyl ether	○	○
Ethylene glycol mono-n-butyl ether	○	○
			Propylene glycol 1-monomethyl ether	○	◎

As can be understood from table 2: the same effects as in the examples can be expected even when the solvents of Nos. 3 and 4, and 7 to 8 are used.

Industrial applicability

According to the method for producing a polybenzoxazole precursor of the present invention, a polybenzoxazole precursor having sufficiently reduced residual halogen can be obtained in a good yield while suppressing discharge of waste liquid, and thus the method is highly useful industrially.