High purity 4-hydroxystyrene solution, method of producing the same, and method of producing 4-hydroxystyrene polymer

Abstract

To provide a 4-hydroxystyrene solution that is suitable as a raw material for commercial-scale production of 4-hydroxystyrene-based polymers, and has a high purity and good storage stability, and a production method for the 4-hydroxystyrene solution.SOLUTION: A production method for a 4-hydroxystyrene solution according to the present invention comprises the following (i) to (iv): (i) a deprotection step of bringing 4-acetoxystyrene into contact with a base in a solvent to generate 4-hydroxystyrene; (ii) a neutralization step of neutralizing the deprotected solution containing 4-hydroxystyrene by adding an acid to the solution; (iii) a step of washing the neutralized solution containing 4-hydroxystyrene with water; and (iv) a solvent substitution step of adding a solvent capable of dissolving 4-hydroxystyrene to the solution containing 4-hydroxystyrene, and performing distillation at 40°C or lower to remove excess solvent and components other than 4-hydroxystyrene.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a high-purity 4-hydroxystyrene solution having good storage stability and a method for producing the same. The present invention also relates to a method for producing a 4-hydroxystyrene-based polymer by performing polymerization using the 4-hydroxystyrene solution as a raw material.

Background Art

[0002] Polymers having structural units derived from 4-hydroxystyrene (hereinafter referred to as "4-hydroxystyrene-based polymers") are used in many products such as photoresists, printed wiring boards, adhesives, PS printing plates, metal surface treatment agents, and encapsulants. In particular, in the use for photoresists, with the progress of pattern miniaturization, it is required to highly reduce insoluble components and impurities such as metals contained in the polymer. In the future, in order to meet the requirements for further miniaturization of pattern rules such as EUV lithography and electron beam lithography, more stringent property management of the resist polymer is required.

[0003] To produce a 4-hydroxystyrene-based polymer, a method using 4-hydroxystyrene as a starting material and a method using a monomer in which the hydroxyl group of 4-hydroxystyrene is substituted with a protecting group are known.

[0004] A method using a monomer in which the hydroxyl group of 4-hydroxystyrene is substituted with a protecting group is known, for example, a method in which 4-acetoxystyrene or the like is polymerized using it as a raw material, and then the protecting group is removed by the action of an acid or a base to generate a hydroxy group (Patent Document 1, Patent Document 2). Since high-purity acetoxystyrene is easily available, this method can stably produce a polymer commercially. However, since it requires a deprotection reaction with an acid or a base and a subsequent neutralization reaction after polymerization, there is a demerit that the number of manufacturing steps increases and the manufacturing cost increases accordingly. In addition, as the number of steps increases, the risk of impurity contamination also increases. In the case of a polymer for chemically amplified resist applications, since it contains a structural unit having an acid dissociable group that dissociates by the action of an acid in the polymer, a part of the acid dissociable group may be eliminated during the deprotection reaction of the acetoxystyrene unit.

[0005] On the other hand, a method using 4-hydroxystyrene as a starting material (Patent Document 3) has also been studied, but nothing is mentioned about the purity of 4-hydroxystyrene. Also, the production of the polymer is only on a laboratory scale. The reason is that 4-hydroxystyrene is an extremely unstable compound and polymerization proceeds rapidly even at room temperature, so it is difficult to produce and store it in large quantities as a raw material for industrial production of the polymer.

[0006] As a method for producing high-purity 4-hydroxystyrene, a method in which 4-acetoxystyrene is reacted with an alcohol in the presence of a catalytic amount of a suitable base (Patent Document 4) is known.

[0007] In addition, as a method for stably storing unstable 4-hydroxystyrene, a method of adding an alcohol such as methanol in an amount of 3 to 1000% by weight based on 4-hydroxystyrene (Patent Document 5) is known. However, the suppression of polymerization is not sufficient, and it was also essential to mix the alcohol. Further, a polymerization raw material composition (Patent Document 6) in which methanol is added to a 4-hydroxystyrene composition obtained by dehydrogenation of 4-ethylphenol has been disclosed. However, since it contains many impurities such as catalyst residues and residual ethylphenol during the dehydrogenation of 4-ethylphenol, it is not a method suitable for the production of resist resins for state-of-the-art lithography.

[0008] In addition, as a method for producing 4-hydroxystyrene in a high yield and stably storing it, a method of obtaining 4-hydroxystyrene crystals by deprotecting a protecting monomer of 4-hydroxystyrene with a base catalyst in the presence of 1,3,5-trihydroxybenzene and then performing crystallization, and a method of storing 4-hydroxystyrene by containing 0.01% by mass or more and 10% by mass or less of 1,3,5-trihydroxybenzene (Patent Document 7) have been disclosed. However, since 1,3,5-trihydroxybenzene is mixed into the polymer as an impurity, it is not suitable for resist applications for state-of-the-art lithography.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention provides a 4-hydroxystyrene solution having high purity and good storage stability, which is suitable as a raw material for producing a 4-hydroxystyrene-based polymer on a commercial scale, and a method for producing the same. Further, the present invention provides a production method capable of producing a 4-hydroxystyrene-based polymer suitable for a resist for state-of-the-art lithography in a simple process that does not require a deprotection step and on a commercial scale.

Means for Solving the Problems

[0011] As a result of intensive studies to achieve the above object, the present inventors have found that a 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% and a 4-hydroxystyrene polymer content of 0.5% or less with respect to 4-hydroxystyrene can suppress the formation of polymers over a long period of time and can be stably stored. Further, in producing the 4-hydroxystyrene solution, 4-hydroxystyrene is produced by a deprotection reaction using a base catalyst with 4-acetoxystyrene as a starting material, and after neutralization, a solvent capable of dissolving 4-hydroxystyrene is added to the solution containing 4-hydroxystyrene, and the mixture is distilled under reduced pressure at 40° C. or lower to distill off components other than 4-hydroxystyrene and the solvent and excess solvent, thereby performing solvent substitution without crystallizing 4-hydroxystyrene, and it has been found that a 4-hydroxystyrene solution having high purity and good storage stability can be produced on a commercial scale. Further, by polymerizing using the 4-hydroxystyrene solution, a polymer having a structural unit derived from 4-hydroxystyrene in which the incorporation of insoluble components and metal impurities is suppressed at a high level can be produced in a simple process that does not require a deprotection step and on a commercial scale, and the present invention has been completed.

[0012] That is, according to the present invention, the following inventions are provided. [1] The following steps (i) to (iv): (i) A deprotection step of contacting 4-acetoxystyrene with a base in a solvent to produce 4-hydroxystyrene. (ii) A neutralization step of adding an acid to the solution containing 4-hydroxystyrene after deprotection to neutralize it. (iii) A step of washing the solution containing 4-hydroxystyrene after neutralization with water. (iv) A solvent substitution step of adding a solvent capable of dissolving 4-hydroxystyrene to the solution containing 4-hydroxystyrene, distilling at 40 °C or lower, and distilling off components other than 4-hydroxystyrene and the excess solvent. A method for producing a 4-hydroxystyrene solution, comprising the above steps. [2] The method for producing a 4-hydroxystyrene solution according to [1], wherein the base used in the deprotection step is one in which dissolved oxygen has been removed by bubbling with an inert gas before use, and the deprotection step is carried out under a nitrogen atmosphere. [3] The method for producing a 4-hydroxystyrene solution according to [1] or [2], wherein the acid used in the neutralization step is one in which dissolved oxygen has been removed by bubbling with an inert gas before use. [4] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [3], wherein the base used in the deprotection step is a base selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide. [5] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [4], wherein the organic solvent used in the solvent replacement step is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters. [6] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [5], wherein in the solvent replacement step, the 4-hydroxystyrene concentration is adjusted to 10 to 70% by mass. [7] The method for producing a 4-hydroxystyrene solution according to any one of [1] to [6], further comprising a step of passing the 4-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent replacement step. [8] A 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% by mass, wherein in the gel permeation chromatography analysis of the solution, when the total area of the chromatogram of components other than the organic solvent is set to 100, the chromatogram area of 4-hydroxystyrene is 99.5% or more. [9] The 4-hydroxystyrene solution according to [8], wherein in the gel permeation chromatography analysis of the solution, the chromatogram area of the 4-hydroxystyrene polymer relative to the chromatogram area of 4-hydroxystyrene is 0.5% or less.

[10] The 4-hydroxystyrene solution according to [8] or [9], wherein the chromatogram area of the 4-hydroxystyrene is 99.7% or more.

[11] The 4-hydroxystyrene solution according to [8] or [9], wherein the chromatogram area of the 4-hydroxystyrene is 99.9% or more.

[12] The 4-hydroxystyrene solution according to any one of [8] to

[11] , wherein the organic solvent is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters.

[13] The 4-hydroxystyrene solution according to any one of [8] to

[12] , which does not contain a polymerization inhibitor.

[14] A polymerization raw material for a resist polymer, comprising a 4-hydroxystyrene solution according to any one of [8] to

[13] .

[15] A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, wherein the 4-hydroxystyrene solution according to any one of [8] to

[13] is used as a polymerization raw material and polymerized alone or with another monomer copolymerizable therewith.

[16] A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, wherein the 4-hydroxystyrene solution produced by the method according to any one of [1] to [7] is used as a polymerization raw material and polymerized alone or with another monomer copolymerizable therewith.

[17] A step of producing a 4-hydroxystyrene solution by the method according to any one of [1] to [7], A step of polymerizing alone using the 4-hydroxystyrene solution produced in the above step as a polymerization raw material, or polymerizing with another monomer copolymerizable with 4-hydroxystyrene A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, comprising:

[18] The method for producing a polymer according to any one of

[15] to

[17] , wherein the other copolymerizable monomer includes a monomer having an acid dissociable group.

[19] The method for producing a polymer according to

[18] , wherein the monomer having an acid dissociable group is a group having a tertiary carbon atom bonded to an oxygen atom.

[20] The method for producing a polymer according to any one of

[15] to

[19] , which is applied to polymerization using a polymerization tank having a capacity of 30 L or more. [Effect of the Invention]

[0013] According to the present invention, a 4-hydroxystyrene solution with high purity and good storage stability can be easily produced on a commercial scale. Furthermore, a 4-hydroxystyrene-based polymer suitable for state-of-the-art lithography can be produced in a simple process that does not require a deprotection step and on a commercial scale. [Embodiments for Carrying Out the Invention]

[0014] The method for producing a 4-hydroxystyrene solution, the 4-hydroxystyrene solution, and the method for producing a 4-hydroxystyrene-based polymer of the present invention will be described in detail below.

[0015] <Method for Producing 4-Hydroxystyrene Solution> (i) Deprotection step The deprotection step is a step of bringing 4-acetoxystyrene into contact with a base in a solvent to eliminate an acetyl group and produce 4-hydroxystyrene.

[0016] The base used in the deprotection reaction is not particularly limited. Specifically, hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkoxides of alkali metals such as sodium methoxide, potassium methoxide, sodium ethoxide, and potassium tert-butoxide; trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide can be mentioned. Among these, preferably sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide, and more preferably sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, diazabicycloundecene, diazabicyclononene, and tetramethylammonium hydroxide. The above bases may be used alone or in combination of two or more.

[0017] The amount of the base used is preferably 0.1 molar equivalent or more and 10.0 molar equivalents or less, more preferably 0.5 molar equivalent or more and 3.0 molar equivalents or less, relative to 4-acetoxystyrene. When the amount of the base used is within the above range, it is easy to obtain a sufficient reaction rate.

[0018] The base is preferably supplied into the reaction system in a solution state, and further, it is preferable to bubble a solution of the base with an inert gas such as nitrogen gas in advance. Using the degassed base solution has the effect of suppressing the formation of a polymer of hydroxystyrene during the deprotection reaction.

[0019] The deprotection reaction is preferably carried out in an organic solvent. The organic solvent is not particularly limited as long as it can dissolve 4-acetoxystyrene. Specifically, alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-amyl alcohol, isoamyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, n-nonyl alcohol, n-decyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol, benzyl alcohol, triphenylcarbinol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol; ketones such as methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclohexanone; hydrocarbons such as pentane, hexane, heptane, octane, isooctane, decane, cyclopentane, cyclohexane, benzene, toluene or xylene; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetrahydrofuran, diethyl ether, diisopropyl ether or methyl tert-butyl ether; nitrile solvents such as acetonitrile, propionitrile can be exemplified. These organic solvents may be used alone or in combination of two or more. Among them, alcohols are preferred, and particularly, methanol, ethanol, n-propyl alcohol, isopropyl alcohol are preferred. The solution of 4-acetoxystyrene dissolved in the above organic solvent is preferably bubbled with an inert gas such as nitrogen gas in advance. This has the effect of suppressing the formation of polymers of hydroxystyrene during the deprotection reaction.

[0020] The reaction temperature of the deprotection reaction is usually -20 to 50 °C, preferably -10 to 20 °C, more preferably -5 to 10 °C from the viewpoint of suppressing the polymerization reaction.

[0021] The reaction time is not particularly limited as long as it is sufficient for the complete conversion of 4-acetoxystyrene to 4-hydroxystyrene. The completion of the reaction can be confirmed by analyzing the product by methods such as 1 1 1H-NMR, gas chromatography, gel permeation chromatography, etc. In addition, the deprotection reaction of 4-acetoxystyrene is preferably carried out in an inert gas atmosphere such as nitrogen.

[0022] (ii) Neutralization step The neutralization step is a step of adding an acid to the base catalyst remaining in the reaction solution after the deprotection reaction to neutralize it. The type of acid used for neutralization is not particularly limited, and specifically, formic acid, hydrochloric acid, acetic acid, oxalic acid, sulfuric acid, trifluoroacetic acid, methanesulfonic acid, etc. can be mentioned. The acid used for neutralization is preferably diluted with a solvent as needed and bubbled with an inert gas such as nitrogen gas in advance. This has the effect of suppressing the formation of polymers of 4-hydroxystyrene.

[0023] (iii) Water washing step The water washing step is a step of washing the solution containing 4-hydroxystyrene after neutralization. The solution containing 4-hydroxystyrene is preferably extracted with an organic solvent capable of dissolving 4-hydroxystyrene and separable from water, and then washed with deionized water to remove impurities such as by-products and salts.

[0024] The solvent used for extracting 4-hydroxystyrene may be any solvent that can dissolve 4-hydroxystyrene and is separable from water, and more preferably the same as or a solvent having a lower boiling point than the solvent used in the subsequent solvent substitution step described below. Thereby, in the subsequent solvent substitution step, this extraction solvent can be easily distilled off, and the residual of the extraction solvent in the final product can be prevented.

[0025] Specifically, ethers such as diisopropyl ether, ditertiary butyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, diethylene glycol dimethyl ether; ketones such as methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate; hydrocarbons such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, etc. are included. Ethers are preferred, and methyl tert-butyl ether is particularly preferred. These extraction solvents may be used alone or in combination of two or more.

[0026] The temperature during extraction is preferably in the range of -20 or higher and less than 50°C, and more preferably -10 or higher and 30°C or lower from the viewpoint of suppressing the polymerization reaction.

[0027] For the water used for washing the extract of 4-hydroxystyrene, it is preferable to use deionized water in order to avoid contamination with metal ions. There are no particular restrictions on the amount of water used and the number of washing times, but it can be appropriately determined in consideration of operability, extraction efficiency of metal ions, etc., and the amount of waste liquid.

[0028] The temperature during washing is preferably 0°C or higher and 50°C or lower, and more preferably 0°C or higher and 30°C or lower.

[0029] (iv) Solvent replacement step The solvent replacement step is a step of replacing the extract of 4-hydroxystyrene with the target solvent. That is, a replacement solvent capable of dissolving 4-hydroxystyrene is added to the extract of 4-hydroxystyrene, and distilled to distill off components other than 4-hydroxystyrene such as reaction by-products and extraction solvents and the excess replacement solvent. By performing solvent replacement without crystallizing 4-hydroxystyrene to obtain a 4-hydroxystyrene solution, it is possible to suppress the formation of polymers of 4-hydroxystyrene compared to dissolving 4-hydroxystyrene in a solvent after crystallizing it by a conventional crystallization method.

[0030] The addition of a substitution solvent to the 4-hydroxystyrene extract may be carried out before the start of distillation, after the start of distillation, or preferably, it may be appropriately added additionally during distillation. When the concentration of the 4-hydroxystyrene extract is high, it is preferable to add the substitution solvent in advance before distillation in order to suppress the polymerization of 4-hydroxystyrene.

[0031] From the viewpoint of suppressing the polymerization of 4-hydroxystyrene, the temperature during distillation is preferably 40 °C or lower, more preferably 20 to 35 °C, and even more preferably 20 to 30 °C.

[0032] The distillation may be carried out under atmospheric pressure, but it is preferably carried out under reduced pressure. The pressure of the vacuum distillation is not particularly limited and can be appropriately adjusted so that components other than 4-hydroxystyrene such as reaction by-products and extraction solvents and excess substitution solvents can be distilled off. The pressure of the vacuum distillation is, for example, 1 to 100 kPa, preferably 1 to 30 kPa.

[0033] The type of the solvent to be replaced is not particularly limited as long as it can dissolve 4-hydroxystyrene. When the obtained 4-hydroxystyrene solution is directly used as a polymerization raw material in the production of a polymer, it is more preferable if it can be used as a polymerization solvent. Specifically, alcohols such as methanol, ethanol, propanol, butanol, and octanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, and cyclohexanone; ethers such as ethyl tert-butyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; glycol ether esters such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; esters such as ethyl acetate and ethyl lactate; N,N-dimethylformamide, acetonitrile, etc. can be mentioned. Alcohols, ketones, ethers, ether alcohols, ether esters, and esters are preferable, and more preferably, methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate, and particularly preferably, methanol, ethanol, 2-propanol, 2-butanol, n-octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate.

[0034] The amount of the replacement solvent to be used is not particularly limited, but it is determined in consideration of the cost and in an amount sufficient to sufficiently distill off impurities other than 4-hydroxystyrene.

[0035] (v) Filtration through a filter The 4-hydroxystyrene solution is preferably filtered through a fine filter to remove insoluble matters such as polymers slightly generated in the production process. Filtration through a filter may be performed before solvent replacement, after solvent replacement, or before and after solvent replacement.

[0036] As the form of the filter, a membrane filter, a hollow fiber membrane filter, a pleated membrane filter, and a filter filled with a filter medium such as highly purified cellulose or diatomaceous earth can be used. The materials of the membrane filter, the hollow fiber membrane filter, and the pleated membrane filter are preferably made of polyolefins such as polyethylene, ultra-high density polyethylene, and polypropylene, fluororesins such as PTFE, and nylons, and particularly preferably made of nylon. Further, these filters may contain an ion exchange group or a cationic electrification regulator that generates a zeta potential on the filter. The ion exchange group is preferably a weakly acidic or weakly basic group. In the case of a weakly acidic or weakly basic ion exchange group, the polymerization of 4-hydroxystyrene can be suppressed.

[0037] The nominal pore size of the above filter is preferably 1 μm or less, more preferably 0.2 μm or less, and even more preferably 0.05 μm or less. The lower limit value of the nominal pore size of the filter is not particularly limited, but is usually 0.01 μm.

[0038] (vi) Storage of the 4-hydroxystyrene solution When storing the produced 4-hydroxystyrene solution, the temperature is preferably -15°C or higher and 40°C or lower, more preferably -15°C or higher and 20°C or lower, and even more preferably -15°C to 5°C in order to suppress polymerization during storage.

[0039] <4-Hydroxystyrene solution> The 4-hydroxystyrene solution of the present invention is a solution in which 4-hydroxystyrene is dissolved at a specific concentration in a solvent. By adjusting the 4-hydroxystyrene concentration, the storage stability of 4-hydroxystyrene can be improved. The production method of the 4-hydroxystyrene solution is not particularly limited, and those obtained by a production method including the above steps (i) to (iv) can be used. Further, instead of the solvent substitution step (iv), after obtaining crystals of high-purity 4-hydroxystyrene by a conventionally known crystallization method, those obtained by dissolving them in a solvent may also be used. In particular, since the purity of 4-hydroxystyrene can be increased, those obtained by the production method including the above steps (i) to (iv) are preferred.

[0040] The 4-hydroxystyrene concentration in the 4-hydroxystyrene solution is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. If the 4-hydroxystyrene concentration in the 4-hydroxystyrene solution is 10% by mass or more, a decrease in polymerization efficiency can be prevented when used as a polymerization raw material, and if it is 70% by mass or less, precipitation of 4-hydroxystyrene can be prevented, which is preferable. Further, when particular importance is attached to the stability during long-term storage, 50% by mass or less is particularly preferable.

[0041] Further, in a 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% by mass, in the gel permeation chromatography analysis of the solution, when the total area of the chromatogram of components other than the organic solvent is taken as 100, the chromatogram area of 4-hydroxystyrene is preferably 99.5% or more, more preferably 99.7% or more, and even more preferably 99.9% or more.

[0042] The content of the 4-hydroxystyrene polymer in the 4-hydroxystyrene solution with a 4-hydroxystyrene concentration of 10 to 70% by mass is preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.1% or less, based on 4-hydroxystyrene. If the content of the 4-hydroxystyrene polymer is below the above numerical value, it can be said that the progress of the polymerization reaction during storage is sufficiently suppressed.

[0043] The 4-hydroxystyrene solution preferably does not contain a polymerization inhibitor. When producing a polymer for a resist for state-of-the-art lithography using the 4-hydroxystyrene solution, the risk of impurities derived from the polymerization inhibitor being mixed into the polymer for the resist can be avoided. Also, even without adding a polymerization inhibitor, the progress of the polymerization reaction during storage can be suppressed.

[0044] The solvent used for the 4-hydroxystyrene solution is not particularly limited as long as it can dissolve 4-hydroxystyrene. When the obtained 4-hydroxystyrene solution is directly used as a polymerization raw material in the production of a polymer, it is more preferable if it can be used as a polymerization solvent. Specifically, alcohols such as methanol, ethanol, propanol, butanol, and octanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, and cyclohexanone; ethers such as ethyl tert-butyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; glycol ether esters such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; esters such as ethyl acetate and ethyl lactate; N,N-dimethylformamide, acetonitrile, etc. can be mentioned. Alcohols, ketones, ethers, ether alcohols, ether esters, and esters are preferred, and more preferably, methanol, ethanol, propanol, butanol, octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl acetate, and ethyl lactate, and particularly preferably, methanol, ethanol, 2-propanol, 2-butanol, n-octanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate.

[0045] <Method for producing a polymer having a structural unit derived from 4-hydroxystyrene> The method for producing a polymer having a structural unit derived from 4-hydroxystyrene according to the present invention includes a step of polymerizing 4-hydroxystyrene alone or with another monomer copolymerizable therewith using 4-hydroxystyrene as a polymerization raw material. As the polymerization raw material, the 4-hydroxystyrene solution obtained by the production method described in the above <Method for producing a 4-hydroxystyrene solution> and the 4-hydroxystyrene solution described in the above <4-hydroxystyrene solution> can be used as the polymerization raw material as it is. When the 4-hydroxystyrene solution is directly used in the polymerization step, the organic solvent in which 4-hydroxystyrene is dissolved can be directly used as the polymerization solvent.

[0046] (Another monomer copolymerizable) Another monomer copolymerizable is not particularly limited as long as it can polymerize with 4-hydroxystyrene. In the case of resist applications, known monomers used in the production of resist polymers can be used.

[0047] A resist polymer is a polymer whose solubility in a developer changes by the action of an acid, and has at least one repeating unit (A) having a structure in which an alkali-soluble group is protected by an acid-dissociable dissolution-inhibiting group. The acid-dissociable dissolution-inhibiting group refers to a group that inhibits the copolymer from dissolving in an alkali developer and dissociates by the action of an acid to dissolve the copolymer in an alkali developer. Further, in order to improve the substrate adhesion of the polymer, it may contain a repeating unit (B) having a lactone ring structure, a repeating unit (C) having a hydroxy group, etc. Furthermore, if necessary, it can contain other repeating units such as a repeating unit (D) having a structure that inhibits dissolution in an alkali developer and is stable to the action of an acid (hereinafter sometimes referred to as "acid-stable dissolution-inhibiting structure").

[0048] (Repeating unit (A)) The repeating unit (A) is a repeating unit having a structure in which an alkali-soluble group such as a carboxyl group, a phenolic hydroxyl group, or a sulfonic acid group is protected by an acid-dissociable dissolution-inhibiting group that dissociates by the action of an acid. Preferably, it is a repeating unit in which an OH group such as a carboxyl group, a phenolic hydroxyl group, or a sulfonic acid group in a repeating unit derived from (meth)acrylic acid or hydroxystyrene, etc. is protected by an acid-dissociable dissolution-inhibiting group.

[0049] Examples of the acid-dissociable dissolution-inhibiting group include structures represented by formula (a1) or (a2).

Chemical formula

Chemical formula

[0050] Specific examples of the repeating unit (A) are given below, but the present invention is not limited thereto. One type or a plurality of types having different structures can be selected from the repeating units (A) and used.

Chemical formula

Chemical formula

[0051] (Repeating unit (B)) The repeating unit (B) is a repeating unit having a lactone structure or a sultone structure, and has a function of enhancing the adhesion to a substrate or an underlayer film and controlling the solubility in a lithography solvent or an alkali developer. As a preferred example, a structure represented by the formula (B1) can be given.

Chemical formula

Chemical formula

[0052] Specific examples of the above alicyclic rings include a cyclopentane ring, a cyclohexane ring, a norbornane ring, a 7-oxa-norbornane ring, a 7-thia-norbornane ring, a tetracyclo[4.4.0.12,5.17,10]dodecane ring, etc. Preferably, a norbornane ring and a 7-oxa-norbornane ring can be mentioned. Specific examples of the hydrocarbon group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, etc., and specific examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, etc.

[0053] In formula (b), any one of R 301 ~R 308 represents a single bond having a binding site as R 32 and the remaining R 301 ~R 308 represents a hydrogen atom, or a lactone structure particularly preferably represented by a hydrocarbon group or an alkoxy group having 1 to 4 carbon atoms, and examples thereof include a γ-butyrolactone structure and a δ-valerolactone structure. Any one of R 301 ~R 308 has a binding site as R 32 and the other R301 ~R 308 Combined with any one or two of them to form an alicyclic ring having 5 to 15 carbon atoms, which represents a hydrocarbon group having 3 to 14 carbon atoms that may contain an oxygen atom or a sulfur atom, and the remaining R 301 ~R 308 represents a hydrogen atom, or a hydrocarbon group or an alkoxy group having 1 to 4 carbon atoms. Particularly preferred examples of the lactone structure include 1,3 - cyclohexanecarbolactone structure, 2,6 - norbornanecarbolactone structure, 7 - oxa - 2,6 - norbornanecarbolactone structure, and 4 - oxa - tricyclo[5.2.1.02,6]decan - 3 - one structure.

[0054] Specific examples of the repeating unit (B) are given below, but the present invention is not limited thereto. One type or a plurality of types having different structures can be selected and used from among the repeating units (B).

Chemical formula

[0055] (Repeating unit (C)) The repeating unit (C) is a repeating unit having a hydroxy group or a carboxy group in the side chain, which functions to enhance the adhesion of the polymer to a substrate or an underlayer film, control the solubility in a lithography solvent or an alkali developer, and react with a curing agent to form a cross - linked structure.

[0056] As the structure of the repeating unit (C), the structures represented by formulas (C1) to (C3) are particularly preferred.

Chemical formula

Chemical formula

[0057] Specific examples of the repeating unit (C) are given below, but the present invention is not limited thereto. One type or a plurality of types having different structures can be selected and used from among the repeating units (C).

Chemical formula

[0058] (Repeating unit (D)) The repeating unit (D) is a repeating unit having a structure in which an alkali-soluble group such as a carboxyl group or a phenolic hydroxyl group is protected by an acid-stable dissolution-inhibiting group that does not dissociate even under the action of an acid. Preferably, it is a repeating unit in which a carboxyl group or a phenolic hydroxyl group in a repeating unit derived from (meth)acrylic acid or hydroxystyrene, etc. is protected by an acid-stable dissolution-inhibiting group. This repeating unit functions to control properties such as solubility in a lithography solvent and an alkali developer, and optical properties such as the refractive index and light transmittance of a thin film.

[0059] Examples of the acid stability dissolution inhibitor group include an aliphatic hydrocarbon group having 1 to 12 carbon atoms, an aromatic hydrocarbon group, or a structure in which a methyl group and a 1-adamantyl group are bonded, where the carbon atom bonding to an oxygen atom by substituting a hydrogen atom of a carboxyl group or a phenolic hydroxyl group is a primary or secondary carbon atom. Specifically, examples include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a cyclopentyl group, a cyclohexyl group, a 2-norbornyl group, a 2-isobornyl group, an 8-tricyclo[5.2.1.02,6]decanyl group, a 1-adamantyl group, a 2-adamantyl group, a 4-tetracyclo[4.4.0.12,5.17,10]dodecanyl group, a phenyl group, a benzyl group, a naphthyl group, an anthracenyl group, and the like.

[0060] Specific examples of the repeating unit (D) are given below, but the present invention is not limited thereto. One type or a plurality of types having different structures can be selected and used from among the repeating units (D).

Chemical formula

[0061] In addition, examples of the repeating unit having the same effect as the repeating unit (D) include a repeating unit represented by the formula (D’).

Chemical formula

[0062] Specific examples of the repeating unit (D’) are given below. [Chemical formula]

[0063] For the polymerization, conventionally known polymerization methods such as radical polymerization, cationic polymerization, and anionic polymerization can be applied.

[0064] In the case of radical polymerization, it is carried out by heating and stirring in a state where the raw material monomer, radical polymerization initiator, and optionally a chain transfer agent, etc. are dissolved in a solvent, preferably in an inert gas atmosphere such as nitrogen. For example, it can be carried out by the so-called bulk polymerization method in which all raw materials such as monomers, polymerization initiators, and chain transfer agents are dissolved in a solvent and heated to the polymerization temperature, or the so-called dropping polymerization method in which a solution of a monomer or a polymerization initiator dissolved in a solvent is dropped into a solvent heated to the polymerization temperature. Among them, the dropping polymerization method is preferable because of its high reproducibility for each production lot, and particularly the so-called independent dropping method in which the monomer and the polymerization initiator as the radical generation source are dropped separately is preferable. In addition, a part of the monomer, polymerization initiator, chain transfer agent, etc. can be supplied into the polymerization system in advance. In the dropping method, the molecular weight distribution and composition distribution of the copolymer can be controlled by changing the composition and supply rate of each supply solution according to the concentration and composition of the monomer in the polymerization system, the radical concentration, etc.

[0065] As the initiator for radical polymerization, those known in the art can be used. For example, radical polymerization initiators such as azo compounds and peroxides are preferred. Specific examples of azo-based polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 1,1'-azobis(cyclohexane-1-carbonitrile), 4,4'-azobis(4-cyanovaleric acid), and the like. Specific examples of peroxide polymerization initiators include decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide, succinic peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxypivalate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, and the like. These can be used alone or in combination.

[0066] The amount of the polymerization initiator used can be selected according to the target molecular weight, the types of the monomer, polymerization initiator, chain transfer agent, solvent, etc., the repeating unit composition, the polymerization temperature, the dropping rate, and the like.

[0067] As the chain transfer agent, those known as chain transfer agents can be used as needed. Among them, thiol compounds are preferred and can be widely selected from known thiol compounds. The amount of the chain transfer agent used can be selected according to the target molecular weight, the types of the monomer, polymerization initiator, chain transfer agent, and solvent, etc., the repeating unit composition, the polymerization temperature, the dropping rate, and the like.

[0068] The solvent used in the polymerization reaction is not particularly limited as long as it can stably dissolve the monomer, polymerization initiator, chain transfer agent, and polymerization reaction product. Specifically, those exemplified as the solvent of the aforementioned 4-hydroxystyrene solution can be used. These can be used alone or in combination of two or more.

[0069] The amount of the overlapping solvent used is not particularly limited. However, if the amount of the solvent used is too small, the monomer may precipitate or the viscosity may become too high, making it impossible to keep the polymerization system uniform. If it is too large, the conversion rate of the monomer may be insufficient or the molecular weight of the copolymer may not be increased to the desired value. Usually, it is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 1 part by weight of the monomer.

[0070] The amount of the polymerization solvent initially charged into the reaction tank (hereinafter sometimes referred to as the initial charging solvent) only needs to be not less than the minimum amount that allows stirring. However, if it is more than necessary, the amount of the monomer solution that can be supplied will decrease, and the production efficiency will decrease, which is not preferable. Usually, it is selected from the range of, for example, 1 / 30 or more, preferably 1 / 20 to 1 / 2, particularly preferably 1 / 10 to 1 / 3, in terms of volume ratio with respect to the final charging amount (that is, the total amount of the initial charging solvent, the monomer solution to be dropped, and the initiator solution). Note that a part of the monomer and / or the polymerization initiator may be premixed with the initial charging solvent.

[0071] If the dropping time of the monomer solution is short, the molecular weight distribution tends to be broad, and since a large amount of the solution is dropped at once, the temperature of the polymerization solution decreases, which is not preferable. On the contrary, if the dropping time is long, the copolymer is subjected to more heat history than necessary and the productivity decreases, which is not preferable. Therefore, it is usually selected from the range of 0.5 to 24 hours, preferably 1 to 12 hours, particularly preferably 2 to 8 hours.

[0072] Also, after the dropping is completed, it is preferable to carry out aging by maintaining the temperature for a certain period of time or further increasing the temperature to react the remaining unreacted monomer. If the aging time is too long, the production efficiency per unit time decreases and the copolymer is subjected to more heat history than necessary, which is not preferable. Therefore, it is usually selected from the range of within 12 hours, preferably within 6 hours, particularly preferably 1 to 4 hours.

[0073] The polymerization temperature can be appropriately selected according to the boiling points of the solvent, monomer, chain transfer agent, etc., and the half-life temperature of the polymerization initiator, etc. Preferably, it is selected in the range of 40 to 160 °C, particularly preferably 60 to 120 °C. Since the polymerization temperature greatly affects the molecular weight and copolymer composition of the copolymer, it is necessary to precisely control it. On the other hand, since the polymerization reaction is generally an exothermic reaction, it is difficult to control it at a constant temperature. Therefore, it is preferable to contain at least one or more compounds having a boiling point close to the target polymerization temperature as the polymerization solvent, and to set the polymerization temperature above the initial boiling point at the polymerization pressure of the compound. According to this method, the increase in the polymerization temperature can be suppressed by the latent heat of vaporization of the polymerization solvent.

[0074] The polymerization pressure can be set as appropriate. However, when radicals are generated from the initiator, nitrogen gas is generated in the case of azo-based initiators, and oxygen gas is generated in the case of peroxide-based initiators. Therefore, in order to suppress fluctuations in the polymerization pressure, it is preferable to carry out the polymerization system as an open system near atmospheric pressure.

[0075] The polymer after the polymerization reaction contains low molecular weight impurities such as the polymerization solvent, unreacted monomer, oligomer, polymerization initiator, chain transfer agent, and reaction by-products thereof. It is preferable to remove these by a purification process. Specifically, the polymerization reaction solution is diluted by adding a good solvent if necessary, and then contacted with a poor solvent to precipitate the copolymer as a solid, and the impurities are extracted into the poor solvent phase (hereinafter referred to as reprecipitation), or the impurities are extracted into the poor solvent phase as a liquid-liquid two-phase. When reprecipitating, the precipitated solid is separated from the poor solvent by a method such as filtration or decantation, and then the solid can be further purified by a process of redissolving the solid in a good solvent and adding a poor solvent for reprecipitation, or a process of washing the precipitated solid with a poor solvent. Also, when separating into a liquid-liquid two-layer, after separating the poor solvent phase by liquid separation, the obtained copolymer solution can be further purified by adding a poor solvent for reprecipitation or liquid-liquid two-phase separation. These operations may be repeated with the same operation or a combination of different operations.

[0076] Examples of the poor solvent used in this purification step include compounds having a hydroxyl group such as water, methanol, ethanol, isopropanol, ethylene glycol, and ethyl lactate; linear, branched, or cyclic saturated hydrocarbons such as pentane, n - hexane, iso - hexane, n - heptane, cyclopentane, and methylcyclohexane; or aromatic hydrocarbons such as toluene and xylene. These solvents can be used alone or in combination of two or more. Examples of the good solvent include the polymerization solvents described above and the solvents exemplified as the solvent for forming a coating film described later, and a poor solvent can also be mixed with the good solvent for use.

[0077] The type and amount of the poor solvent used in the purification step are not particularly limited as long as the copolymer can be separated from the low - molecular - weight compounds, but can be appropriately selected according to the solubility of the copolymer in the poor solvent, the type and amount of the solvent used in the polymerization, the type and amount of impurities, etc. If the amount of the poor solvent is too small, the separation of impurities such as the polymerization solvent and unreacted monomers will be insufficient. On the contrary, if it is too large, the amount of waste liquid will increase, which is not preferable in terms of workability and cost. Generally, it is 0.5 to 50 times by weight, preferably 1 to 20 times by weight, and more preferably 2 to 10 times by weight based on the total amount of the polymerization reaction solution diluted with the good solvent as required.

[0078] The temperature of the purification step needs to be strictly controlled because it greatly affects the molecular weight, molecular weight distribution of the copolymer, the removal rate of impurities such as residual monomers and initiator residues, and various characteristics in lithography. If the temperature of the purification step is too low, the solubility of impurities in the reprecipitation solvent and washing solvent will be insufficient, and the removal of impurities will not be sufficient, so it is not efficient. On the contrary, if it is too high, the copolymer will elute into the reprecipitation solvent and washing solvent, the composition balance in the low - molecular - weight region of the copolymer will be disrupted, and the yield will decrease, which is not preferable. Therefore, the purification step is preferably carried out in the temperature range of 0 to 40°C, preferably in the range of 0 to 30°C.

[0079] Treatment may be performed to remove metal impurities contained in the polymer. The method may be to wash a solution obtained by dissolving the polymer in an organic solvent with pure water, or to contact it with an ion exchange resin or pass it through a filter having ion exchange ability. These methods may also be combined. As the ion exchange resin or the filter having ion exchange ability, known commercially available products used for removing metals from the resist polymer can be used.

[0080] The purified polymer can be taken out as a dry powder after drying, or can be redissolved by adding a good solvent before or after drying and taken out as a solution. Further, it is also preferable to replace the solvent of the polymer solution with a solvent used for a resist composition or the like by the method shown below to obtain a polymer solution.

[0081] The replacement method is carried out by heating the polymer solution under reduced pressure to distill off low-boiling substances such as the solvent used for purification, and further distilling off the initial solvent and the supplied solvent together while supplying the resist solvent thereto. Low-boiling impurities such as the solvent used during purification can be removed, and the copolymer can be finished into a resist solution.

[0082] The temperature of the heat source during heating under reduced pressure is not particularly limited as long as the copolymer does not deteriorate, but is usually preferably 100 ° C or lower, more preferably 70 ° C or lower, still more preferably 60 ° C or lower, and particularly preferably 50 ° C or lower. In the solvent replacement step, since the low-boiling component and the finishing solvent are evaporated under reduced pressure, the copolymer solution during the step is cooled by the heat of vaporization, and its temperature becomes lower than the temperature of the heat source. By limiting the heat source temperature, deterioration due to overheating of the copolymer can be prevented.

[0083] Further, when replacing the solvent, if the amount of the solvent supplied later is too small, low-boiling compounds cannot be sufficiently removed, and if it is too large, the replacement takes time and gives an excessive heat history to the copolymer, which is not preferable. The supply amount can usually be selected from the range of 1.05 times to 10 times, preferably 1.1 times to 5 times, and particularly preferably 1.2 times to 3 times the amount required as the solvent of the finishing solution.

[0084] The replacement solvent is not particularly limited as long as it can dissolve the copolymer. However, in the case of resist applications, known solvents commonly used in resist compositions can generally be employed. Specifically, solvents such as propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol n-butyl ether, dipropylene glycol n-propyl ether, dipropylene glycol n-butyl ether, ethyl lactate, methyl amyl ketone, γ-butyrolactone, cyclohexanone, 4-methyl-2-pentanol, etc. can be mentioned.

[0085] Furthermore, in order to remove microgels such as undesirable high polymers that may cause pattern defects in the resist, it is preferable to filter the copolymer solution (or the above-mentioned solution for forming a coating film) through a filter. The filtration accuracy of the filter is 0.2 μm or less, preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. Examples of the filter material include polyolefins such as polyethylene and polypropylene, polar group-containing resins such as polyamide, polyester, and polyacrylonitrile, and fluorine-containing resins such as fluorinated polyethylene. Particularly preferred is polyamide. Examples of polyamide-based filters include (hereinafter, trademarks) Ultipleats P-Nylon 66, Ultipore N66 manufactured by Nippon Pall Co., Ltd., Life Assure PSN series, Life Assure EF series manufactured by Kuraray Co., Ltd., etc. Examples of polyolefin-based filters include Microgard Plus HC10, Optimizer D manufactured by Nippon Integris Co., Ltd., etc. These filters can be used individually or in combination of two or more.

[0086] It is preferable that the polymer obtained by the production method of the present invention has a reduced metal contamination at a high level. Specifically, the total metal content based on the polymer mass is preferably 50 ppb or less, more preferably 10 ppb or less, still more preferably 3 ppb or less, and particularly preferably below the detection limit of the analyzer for any metal.

[0087] The metal content is measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0088] The above metal content is typically the sum of the contents in each of Na, K, Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sn, Co, Li, Ti, Ag, W, V, Ba, Pt, Au, As, Cd, Mo, and Zr. Also, the content of each of the above metals is preferably 1 ppb or less.

[0089] [Evaluation Method for Insoluble or Sparingly Soluble Components] The insoluble or sparingly soluble components contained in the polymer solution can be analyzed by the following procedure. Procedure (i): Dilute the polymer solution with a good solvent to prepare a test solution with a polymer concentration of 10.0% by mass. Procedure (ii): Put the above test solution into a flask of a non-contact turbidimeter for rotary shaking culture (ODMonitorA&S manufactured by Taitec Co., Ltd. attached to a shaker NR-2), and while rotary shaking, dropwise add a poor solvent at a constant speed, and record the change in the weight of the test solution and the change in turbidity at a measurement wavelength of 950 nm during that time. Procedure (iii): The addition of the poor solvent is continued until the turbidity reaches 0.20 OD (Optical Density). At that time, record the amount of the poor solvent added until the turbidity reaches 0.10 OD, 0.15 OD, and 0.20 OD. According to the above procedure, the smaller the amount of the poor solvent added until each turbidity is reached, the smaller the amount of insoluble or sparingly soluble components.

[0090] The above evaluation method for insoluble or sparingly soluble components can be applied to the above 4-hydroxystyrene-based polymer solution and other polymer solutions.

Examples

[0091] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples in any way. Unless otherwise specified in the following examples, "parts" are based on mass.

[0092] The analysis in this example was carried out as follows. [Purity of 4-hydroxystyrene solution] and [weight average molecular weight and molecular weight distribution of polymer] The purity, polymer content, weight average molecular weight and molecular weight distribution of the 4-hydroxystyrene solution synthesized below were measured by GPC (gel permeation chromatography) using polystyrene as a standard. As the sample for analysis, a sample prepared to be a tetrahydrofuran solution with a solid content concentration of 2% by mass of the polymer was used. The sample injection volume into the apparatus was 50 μL. Measuring apparatus: HLC-8220GPC manufactured by Tosoh Corporation Detector: Differential refractive index (RI) detector Column: Shodex GPC KF804 × 3 (manufactured by Showa Denko K.K.) Eluent: Tetrahydrofuran Flow rate: 1.0 mL / min Temperature: 40°C Calibration curve: Prepared using a polystyrene standard sample (manufactured by Tosoh Corporation)

[0093] [Water content of 4-hydroxystyrene solution] The water content of the 4-hydroxystyrene solution synthesized below was measured using the following apparatus. Measuring apparatus: Karl Fischer type micro water content measuring apparatus AQ-7 (manufactured by Hiranuma Sangyo Co., Ltd.)

[0094] [Quantification of low molecular weight components in polymer] The quantification of low molecular weight components contained in the polymer synthesized below was analyzed by LC (liquid chromatography). Measuring apparatus: HLC-8320GPC manufactured by Tosoh Corporation Detector: Differential refractive index (RI) detector Column: TOSOH TSKgel superHZ1000x4 Eluent: Tetrahydrofuran Flow rate: 0.35 mL / min Temperature: 40 °C

[0095] [Monomer composition ratio of the polymer] The monomer composition ratio of the polymer synthesized below was analyzed by 13 C-NMR. Apparatus: AV400 manufactured by Bruker Heavy solvent: Acetone-d6 Relaxation reagent: Chromium(III) acetylacetonate Measurement temperature: 40 °C

[0096] [Metal analysis of the polymer solution] The metal content of the polymer synthesized below was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The metals measured were a total of 26 elements: Na, K, Mg, Al, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Pb, Sn, Co, Li, Ti, Ag, W, V, Ba, Pt, Au, As, Cd, Mo, and Zr. The analytical values are based on the mass of the polymer solid content. Apparatus: ICP mass spectrometer (manufactured by Agilent Technologies, Inc., product name: Agilent 7500cs) Sample preparation: Dilute the polymer solution with N-methyl-2-pyrrolidone

[0097] The abbreviations of the compounds used in the following experiments are as follows. PACS: p-acetoxystyrene 4-HS: 4-hydroxystyrene MCpMA: 1-methyl-1-cyclopentyl methacrylate ECpMA: 1-ethyl-1-cyclopentyl methacrylate TBMA: tert-butyl methacrylate GBLMA: γ-butyrolactone-α-methacrylate NLM: 3,5-norbornanelactone-2-yl-methacrylate MEK: Methyl ethyl ketone MTBE: Methyl tertiary butyl ether PGMEA: Propylene Glycol Monomethyl Ether Acetate PGME: Propylene Glycol Monomethyl Ether MeOH: Methanol IPA: 2 - Propanol SBA: 2 - Butanol EtOAc: Ethyl Acetate THF: Tetrahydrofuran

[0098] <Method for Producing 4 - Hydroxystyrene Solution> [Example 1] 7.9 kg of PACS and 23.4 kg of methanol were charged into a 100 L glass - lined reaction vessel equipped with a thermometer, a cooling tube, and a stirring device, and sealed with nitrogen. While stirring the contents, it was cooled to a liquid temperature of - 5°C. Then, the inside of the reaction vessel was depressurized and then repressurized with nitrogen three times. In a separate container from the reaction vessel, an equimolar amount of 3M sodium hydroxide aqueous solution with respect to PACS was prepared, and this aqueous solution was bubbled with nitrogen for 1 hour. The nitrogen - bubbled sodium hydroxide aqueous solution was dropped into the reaction vessel over 100 minutes, and after dropping, stirring was continued for another 30 minutes to carry out the reaction of de - protecting PACS and converting it to 4 - HS.

[0099] Next, 0.97 molar equivalent of 6M hydrochloric acid with respect to the used PACS was dropped into the reaction vessel over 60 minutes. After dropping, stirring was continued for another 30 minutes to neutralize the reaction solution. Note that the 6M hydrochloric acid dropped was pre - bubbled with nitrogen for 1 hour.

[0100] Next, the temperature of the neutralized reaction solution was raised to about 10 - 20°C, and MTBE with a mass three times that of PACS was added thereto. After stirring for 15 minutes and standing for 15 minutes, the aqueous layer was drained. Next, ion - exchanged water with a mass three times that of PACS was added, stirred for 15 minutes and then left standing for 15 minutes, and the aqueous layer was drained. Next, MTBE with a mass two times that of PACS and ion - exchanged water with a mass three times that of PACS were added, stirred for 15 minutes, then left standing for 15 minutes, and the aqueous layer was drained. Finally, the operation of adding ion - exchanged water with a mass three times that of PACS, stirring for 15 minutes, then leaving standing for 15 minutes, and draining the aqueous layer was repeated twice.

[0101] The washed organic layer was transferred to another 100 L reaction vessel, and MEK 13 times the mass of the initial PACS was added. Distillation under reduced pressure was carried out at 5 kPa or less and 25 °C or lower to distill off organic impurities other than 4-HS, such as tert-butyl methyl ether and reaction by-products, and excess MEK, and finally, it was finished into a solution with a 4-HS concentration of 25% by mass. Then, the solution was passed through a polytetrafluoroethylene (PTFE) hollow fiber membrane filter with a pore size of 50 nm to obtain 21 kg of a 25% by mass 4-HS / MEK solution (yield 92%).

[0102] A part of the obtained 4-HS solution was divided into a plurality of containers, and storage tests were carried out at temperatures of -15 °C, -5 °C, and 40 °C, respectively. In the storage test, 4-HS and polymers in the 4-HS solution were analyzed by gel permeation chromatography (GPC) immediately after production, after 20 days, 40 days, 90 days, and 180 days, and the results are shown in Table 1.

[0103]

Table 1

[0104] The 25% by mass 4-HS / MEK solution obtained in Example 1 could be stably stored at -15 °C for 6 months with almost no polymerization. Also, in the accelerated test at 40 °C, the formation of polymers could be suppressed to 0.5% or less until 20 days.

[0105] [Example 2] 53.52 g of PACS and 160.5 g of methanol were charged into a four-necked flask equipped with a thermometer, a condenser, and a stirrer, and sealed with nitrogen. The contents were cooled while stirring to a liquid temperature of -5 °C. Then, the operation of reducing the pressure in the reaction vessel and then repressurizing with nitrogen was repeated 3 times. In a container separate from the reaction vessel, a 3 M aqueous sodium hydroxide solution was prepared to be equimolar to PACS, and this aqueous solution was bubbled with nitrogen for 15 minutes. The nitrogen-bubbled aqueous sodium hydroxide solution was dropped into the reaction vessel over 70 minutes, and after the dropping, stirring was continued for another 30 minutes to carry out the reaction of deprotecting PACS and converting it to 4-HS.

[0106] Next, 0.97 molar equivalent of 6N hydrochloric acid was added dropwise into the reaction vessel to the used PACS over 45 minutes. After the addition, stirring was continued for another 30 minutes to neutralize the reaction solution. Note that the 6N hydrochloric acid used for dropping was pre-bubbled with nitrogen for 1 hour.

[0107] Next, the temperature of the neutralized reaction solution was raised to about 10 - 20 °C, and MTBE with a mass three times that of PACS was added thereto. After stirring for 15 minutes and standing for 15 minutes, the aqueous layer was drained. Next, ion-exchanged water with a mass three times that of PACS was added, stirred for 15 minutes, and then left standing for 15 minutes, after which the aqueous layer was drained. Next, MTBE with a mass two times that of PACS and ion-exchanged water with a mass three times that of PACS were added, stirred for 15 minutes, and then left standing for 15 minutes, after which the aqueous layer was drained. Finally, the operation of adding ion-exchanged water with a mass three times that of PACS, stirring for 15 minutes, and then leaving standing for 15 minutes and draining the aqueous layer was repeated twice.

[0108] The washed organic layer was transferred to another reaction vessel, and MEK with a mass 13 times that of the initial PACS was added. Distillation under reduced pressure was carried out at 25 °C or lower to distill off organic impurities other than 4-HS such as MTBE and reaction by-products, and excess MEK, and finally, a solution with a 4-HS concentration of 50% by mass was obtained. Thereafter, the 4-HS solution was passed through a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 50 nm.

[0109] A part of the obtained 4-HS solution was aliquoted into a container, and a storage test was carried out at -15 °C. In the storage test, 4-hydroxylene and polymers in the 4-HS solution immediately after production and 30 days later were analyzed by GPC, and the results are shown in Table 2.

[0110] [Table 2]

[0111] [Example 3] An experiment was carried out in the same manner as in Example 2 except that propylene glycol methyl ether acetate (hereinafter, PGMEA) was used instead of MEK as the substitution solvent, and finally, a 25% by mass 4-HS / PGMEA solution was obtained.

[0112] A portion of the obtained 4-HS solution was aliquoted into a container, and a storage test was conducted at -15°C. Immediately after production, the 4-HS and polymer in the 4-HS solution after 30 days were analyzed by GPC, and the results are shown in Table 3.

[0113]

Table 3

[0114] [Comparative Example 1] In the same manner as in Example 2, the deprotection reaction, neutralization, and water washing of PACS were carried out to obtain an MTBE solution of 4-HS. This was transferred to a 1-L glass container, and the solvent was distilled off under reduced pressure at 20°C or lower. The obtained polymer was further dried under reduced pressure at 40°C for 4 hours to obtain 32 g of 4-HS crystals. Subsequently, the obtained 4-HS crystals were dissolved in MEK to prepare a 25 mass% 4-HS / MEK solution.

[0115] A portion of the obtained 4-HS solution was aliquoted into a container, and a storage test was conducted at -15°C. Immediately after production, the 4-HS and polymer in the 4-HS solution after 4 days and 7 days were analyzed by GPC, and the results are shown in Table 4.

Table 4

[0116] In Comparative Example 1, without performing a solvent replacement step, the 4-HS crystals obtained by removing the MTBE solvent by distillation under reduced pressure and drying under reduced pressure were dissolved in MEK to obtain a solution. The generation of the polymer of 4-HS could not be suppressed, and the storage stability was also insufficient.

[0117] <Storage Stability Test of 4-Hydroxystyrene Solution> [Example 4] In the same manner as in Example 1, the deprotection reaction of PACS, neutralization of the reaction solution, and water washing were carried out to obtain an MTBE solution of 4-HS.

[0118] This MTBE solution was concentrated with an evaporator until the 4-HS concentration reached 70% by mass, then dropped into n-hexane at 0 °C, and subsequently stirred while cooling the bottom of the container with an ice bath to crystallize 4-HS. The recovered 4-HS crystals were further washed with n-hexane and then dried under reduced pressure at room temperature.

[0119] A part of the obtained 4-HS crystals was dissolved in MEK to prepare a solution with a 4-HS concentration of 25% by mass. This was divided into small portions in a plurality of containers and a storage stability test was conducted. The results are shown in Table 5.

[0120] [Example 5] to [Example 13] 4-HS crystals were synthesized by the same procedure as in Example 4, 4-HS solutions were prepared with the solvents and concentrations shown in Table 5, and the storage temperature was adjusted to -5 °C, 15 °C, or 40 °C to conduct a storage stability test. The results are shown in Table 5.

[0121]

Table 5

[0122] <Method for Producing 4-Hydroxystyrene-Based Polymer> [Example 14] Production of 4-HS / MCpMA Copolymer Into a container, 80.0 g of the 25% by mass 4-HS / MEK solution obtained in Example 1 (the chromatogram area of 4-HS was 99.9% when the total chromatogram area of components other than MEK was set to 100 in GPC analysis), 45.6 g of MCpMA, 8.4 g of 2,2-azobisisobutyric acid dimethyl, and 13.0 g of MEK were added and mixed to prepare a monomer solution.

[0123] 52.7 g of MEK was charged into a 500 mL four-necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer, and after setting it to a nitrogen atmosphere, the temperature was raised to 79 °C. Here, the monomer solution was dropped and supplied at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5 °C, and after the polymerization was completed, it was cooled to room temperature.

[0124] The polymerization solution was mixed with 460 g of n - hexane, stirred to precipitate the polymer, allowed to stand, and then the polymer was separated by decantation. The polymer was redissolved in a mixed solution containing 40 g of acetone and 30 g of 2 - propanol. 460 g of n - hexane was added thereto, stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated 4 times. The recovered polymer was dissolved in 140 g of ethyl acetate. A part of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4 - HS:MCpMA = 41.0:59.0.

[0125] The remaining polymer solution was washed with a 1 mass% aqueous oxalic acid solution using a separating funnel, and then washed 5 times with pure water. The washed polymer solution was distilled while adding PGMEA while distilling off ethyl acetate under reduced pressure at a heat source temperature of 45 °C, and finally a PGMEA solution of a 4 - HS / MCpMA copolymer with a polymer concentration of 15 mass% was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw = 5800, Mw / Mn = 1.40, and the residual low - molecular - weight component with Mw less than 200 was 0.01% (LC area%).

[0126] [Example 15] Production of 4 - HS / MCpMA copolymer The volume of the reaction vessel used for the polymerization reaction was changed to 2 L, and the amounts of the monomers, solvents, reagents, etc. used were changed to 4 times those in Example 14, and the same procedure as in Example 14 was followed.

[0127] The analysis results of the obtained polymer were 4 - HS:MCpMA = 40.3:59.7, Mw = 5810, Mw / Mn = 1.39, and the residual low - molecular - weight component with Mw less than 200 was 0.00% (LC area%).

[0128] [Example 16] Production of 4 - HS / MCpMA copolymer The volume of the reaction vessel used for the polymerization reaction was changed to 10 L, and the amounts of the monomers, solvents, reagents, etc. used were changed to 25 times those in Example 14, and the same procedure as in Example 14 was followed.

[0129] The analysis results of the obtained polymer were as follows: 4-HS:MCpMA = 40.5 / 59.5, Mw = 5,800, Mw / Mn = 1.40, and the residual low molecular weight component with Mw less than 200 was 0.00% (LC area%).

[0130] From the results of Example 15 and Example 16, by this method, even when the production scale was greatly changed, the properties of the polymer could be reproduced well.

[0131] [Example 17] Production of 4-HS / ECpMA copolymer Into a container, 400.0 g of a 25.9 mass% 4-HS / MEK solution (the chromatogram area of 4-HS was 100.0% when the total chromatogram area of components other than MEK in GPC analysis was 100), 280.6 g of ECpMA, 29.6 g of 2,2-azobisisobutyric acid dimethyl, and 86.0 g of MEK were added and mixed to prepare a monomer solution.

[0132] 302 g of MEK was charged into a 2 L four-necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer. After setting the nitrogen atmosphere, the temperature was raised to 79 °C. Here, the monomer solution was dropwise supplied at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5 °C, and after the polymerization was completed, it was cooled to room temperature.

[0133] 1000 g of the polymerization solution was mixed with a mixed solution of 2300 g of n-hexane and 100 g of methanol, stirred to precipitate the polymer, and after standing, the polymer was separated by decantation. The polymer was redissolved in a mixed solution of 200 g of acetone and 100 g of methanol, 2000 g of n-hexane was added thereto and stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated 4 times. The recovered polymer was dissolved in 400 g of acetone. A part of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4-HS:ECpMA = 39.5:60.5.

[0134] The remaining polymer solution was distilled while adding PGMEA while distilling off acetone under a heat source temperature of 45°C under reduced pressure to replace the solvent with PGMEA, and finally a PGMEA solution of a 4-HS / ECpMA copolymer with a polymer concentration of 20% by mass was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw = 7430, Mw / Mn = 1.46, and the residual low molecular weight component with Mw less than 200 was 0.01% (LC area%).

[0135] [Example 18] Production of 4-HS / ECpMA copolymer As a reaction tank used for the polymerization reaction, a 100-liter glass-lined reaction tank equipped with a stirrer, a heat medium circulation jacket, a vacuum line, a nitrogen line, and a cooler was used. The amounts of monomers, solvents, reagents, etc. used were changed to 55 times the amounts in Example 17, and polymerization, purification, and solvent replacement were carried out in the same manner as in Example 17.

[0136] The analysis results of the obtained polymer were 4-HS:ECpMA = 39.8:60.2, Mw = 7450, Mw / Mn = 1.46, and the residual low molecular weight component with Mw less than 200 was 0.01% (LC area%).

[0137] In addition, the metal content of the PGMEA solution of the 4-HS / ECpMA copolymer with a polymer concentration of 20% by mass obtained in Example 18 was, as a result of ICP mass spectrometry, 8 ppb of Na on a polymer weight basis, and all other elements were less than 1.0 ppb.

[0138] From the results of Example 17 and Example 18, even in commercial-scale production by this method, polymers with reproducible polymer properties and extremely low levels of low molecular weight impurities and metal impurities could be produced.

[0139] [Comparative Example 2] Production of 4-HS / MCpMA copolymer The procedure was the same as in Example 15 except that a 25% by mass 4-HS / MEK solution (the chromatogram area of 4-HS was 97.3% when the total chromatogram area of components other than MEK was 100 in GPC analysis) was used.

[0140] The analysis results of the obtained polymer were as follows: 4-HS:MCpMA = 40.4:59.6, Mw = 5860, Mw / Mn = 1.40, and the residual low molecular weight component with Mw less than 200 was 0.00% (LC area%). These physical properties were almost the same as those of the polymer obtained in Example 15.

[0141] [Evaluation of Insoluble or Sparingly Soluble Components] For the PGMEA solutions of the 4-HS / MCpMA copolymers obtained in Example 15 and Comparative Example 2, in order to compare the insoluble or sparingly soluble components contained in each, a test solution was prepared, and the change in turbidity of the test solution when a poor solvent was added thereto was measured in real time. The detailed test method is shown below.

[0142] The test solution was prepared by further diluting the polymer solutions obtained in Example 15 and Comparative Example 2 with PGMEA to adjust the polymer concentration to 10.0% by mass to obtain a test solution.

[0143] The turbidity was measured using a non-contact turbidity meter for rotary shaking culture (OD-Monitor A&S manufactured by Taitec Co., Ltd., attached to a shaker NR-2). 100.0 g of the test solution was placed in a glass Erlenmeyer flask, and the opening of the Erlenmeyer flask was sealed with a stopper equipped with a tube for dropping the poor solvent to prevent evaporation of the solvent. The zero point correction of the turbidity meter was performed while the Erlenmeyer flask containing the test solution was being shaken. While shaking the Erlenmeyer flask, n-hexane, which is a poor solvent, was dropped at a speed of 0.3 g / min, and the change in weight and turbidity of the test solution during that time was measured. The measured value OD (optical density; OD = common logarithm of the transmittance of transmitted light) of the turbidity meter used this time is a value converted and expressed by converting the amount of transmitted light of infrared rays (950 nm) into the OD of Escherichia coli. 600 The dropping of n-hexane was continued until the turbidity reached 0.50 OD. In the test solution with a turbidity of 0.50 OD, a slight turbidity was visually observed in the solution, but no precipitation of the polymer was seen. The measurement was performed three times each, and the average value of the three n-hexane dropping amounts until the turbidity reached 0.10 OD, 0.15 OD, 0.20 OD, 0.30 OD, and 0.50 OD was summarized in Table 1.

[0144]

Table 6

[0145] From the results of the experiments, no difference was observed between the two when the turbidity was 0.30 OD or higher. However, a difference was observed in the level between 0.10 OD and 0.20 OD, that is, the dropping amount of n - hexane required to cause extremely slight turbidity. The dropping amount of n - hexane in Example 15 was larger. The copolymer of Example 15 is almost the same as the copolymer of Comparative Example 2 in terms of physical properties such as monomer composition ratio, Mw, Mw / Mn, and the amount of residual low - molecular - weight components. However, it can be evaluated that the amount of insoluble or hardly soluble components that can be a cause of development defects is less.

[0146] [Example 19] Production of 4 - HS / MCpMA / GBLMA Copolymer Into a container, 48.3 g of a 25% by mass 4 - HS / MEK solution obtained in Example 1 (the chromatogram area of 4 - HS was 99.9% when the total chromatogram area of components other than MEK in GPC analysis was set to 100), 55.5 g of MCpMA, 28.6 g of GBLMA, 6.9 g of 2,2 - azobisisobutyric acid dimethyl, and 61.2 g of MEK were added and mixed to prepare a monomer solution.

[0147] 74.8 g of MEK was charged into a 500 mL four - necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer. After setting the nitrogen atmosphere, the temperature was raised to 79 °C. Here, the monomer solution was drop - fed at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 - 80.5 °C, and after the polymerization was completed, it was cooled to room temperature.

[0148] 275 g of the polymerization solution was mixed with 620 g of n - hexane and 67 g of methanol, stirred to precipitate the polymer, and after standing, the polymer was separated by decantation. The polymer was redissolved in a mixed solution containing 67 g of MEK and 67 g of methanol. 540 g of n - hexane was added thereto and stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated twice.

[0149] The recovered polymer was dissolved in 270 g of ethyl acetate. A portion of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, and subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4-HS:MCpMA:GBLMA = 18.8:51.8:29.4.

[0150] The remaining polymer solution was washed with a 1 mass% aqueous oxalic acid solution using a separatory funnel, and then washed 5 times with pure water. The washed polymer solution was distilled while adding PGMEA while distilling off ethyl acetate under reduced pressure at 45 °C, and finally a PGMEA solution of a 4-HS / MCpMA / GBLMA copolymer with a polymer concentration of 20 mass% was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw = 9720, Mw / Mn = 1.59, and the residual low molecular weight component with Mw less than 200 was 0.01% (LC area%).

[0151] [Example 20] Production of 4-HS / MCpMA / NLM copolymer Into a container, 52.8 g of a 25 mass% 4-HS / MEK solution obtained in Example 1 (the chromatogram area of 4-HS was 99.9% when the total chromatogram area of components other than MEK in GPC analysis was 100), 66.7 g of MCpMA, 24.5 g of NLM, 18.4 g of dimethyl 2,2-azobisisobutyrate, and 61.7 g of MEK were added and mixed to prepare a monomer solution.

[0152] 75.4 g of MEK was charged into a 500 mL four-necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer. After setting the nitrogen atmosphere, the temperature was raised to 79 °C. Here, the monomer solution was dropwise supplied at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5 °C, and after the polymerization was completed, it was cooled to room temperature.

[0153] The polymerization solution was mixed with 690 g of n - hexane, stirred to precipitate the polymer, allowed to stand, and then the polymer was separated by decantation. The polymer was redissolved in a mixed solvent of 120 g of MEK and 45 g of methanol, 690 g of n - hexane was added thereto, stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated 4 times.

[0154] The recovered polymer was dissolved in 450 g of ethyl acetate. A part of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4 - HS:MCpMA:NLM = 20.2:59.4:20.4.

[0155] The remaining polymer solution was washed with a 1 mass% aqueous oxalic acid solution using a separatory funnel and then washed 5 times with pure water. The washed polymer solution was distilled while adding PGMEA while distilling off ethyl acetate under reduced pressure at 45 °C, and finally a PGMEA solution of a 4 - HS / MCpMA / NLM copolymer with a polymer concentration of 15 mass% was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw was 5240, Mw / Mn = 1.39, and the residual low - molecular - weight component with Mw less than 200 was 0.00% (LC area%).

[0156] [Example 21] Production of 4 - HS / TBMA copolymer Into a container, 200.0 g of a 25 mass% 4 - HS / MEK solution obtained in Example 1 (the chromatogram area of 4 - HS was 99.9% when the total chromatogram area of components other than MEK was 100 in GPC analysis), 81.8 g of TBMA, 16.8 g of 2,2 - azobisisobutyronitrile dimethyl, and 17.0 g of MEK were added and mixed to prepare a monomer solution.

[0157] A 1000 mL four-necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer was charged with 105.1 g of MEK. After setting the nitrogen atmosphere, the temperature was raised to 79 °C. Here, the monomer solution was dropwise supplied at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 - 80.5 °C, and after the polymerization was completed, it was cooled to room temperature thereafter.

[0158] The polymerization solution was mixed with 880 g of n-hexane and 20 g of methanol, stirred to precipitate the polymer, and after standing, the polymer was separated by decantation. The polymer was redissolved in a mixed solution containing 176 g of acetone and 12 g of methanol, 800 g of n-hexane was added thereto and stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated 4 times.

[0159] The recovered polymer was dissolved in 180 g of acetone. A part of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4-HS:TBMA = 42.4:57.6.

[0160] The washed polymer solution was distilled while adding PGMEA while distilling off acetone under reduced pressure at 45 °C, and finally a PGMEA solution of a 4-HS / TBMA copolymer with a polymer concentration of 20% by mass was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw = 6,090, Mw / Mn = 1.44, and the residual low molecular weight component with Mw less than 200 was = 0.00% (LC area%).

[0161] [Example 22] Production of 4-HS / TBMA copolymer Into a glass container, 589 g of a 25% by mass 4-HS / MEK solution (the chromatogram area of 4-HS was 99.8% when the total chromatogram area of components other than MEK was 100 in GPC analysis), 267 g of TBMA, 55 g of dimethyl 2,2'-azobis(2-methylpropionate), and 84 g of MEK were supplied and dissolved to prepare a dropping solution.

[0162] Another 2 L glass container was charged with 325 g of MEK and heated to 79°C with stirring. The aforementioned dropping solution was added dropwise thereto over 4 hours, and the reaction was continued for another 2 hours, followed by cooling to room temperature. To the polymerization solution, a hexane mixture containing 2% by mass of methanol was added to precipitate the polymer, and the mixture was stirred. Then, the polymer was separated by decantation. The polymer was redissolved in an acetone mixture containing 7% by mass of methanol, hexane was added thereto to precipitate the polymer, and the mixture was stirred. The operation of separating the polymer by decantation was repeated 4 times.

[0163] The polymer was redissolved in acetone, PGMEA was added, and the mixture was distilled under reduced pressure. Finally, 1580 g of a PGMEA solution containing 20% by mass of the polymer was obtained. Also, 13 As a result of C-NMR analysis, the composition ratio of the obtained copolymer was 4-HS / TBMA = 38.8 / 61.2.

[0164] [Example 23] Production of 4-HS / ECpMA copolymer Into a container, 83.6 g of a 25% by mass 4-HS / PGMEA solution obtained in Example 3 (the chromatogram area of 4-HS was 99.9% when the total chromatogram area of components other than PGMEA was set to 100 in GPC analysis), 46.2 g of ECpMA, 11.4 g of 2,2-azobisisobutyronitrile dimethyl, and 15.4 g of PGMEA were added and mixed to prepare a monomer solution.

[0165] A 500 mL four-necked flask reaction vessel made of glass equipped with a stirrer, a cooler, and a thermometer was charged with 67.1 g of PGMEA. After setting the nitrogen atmosphere, the temperature was raised to 79°C. The monomer solution was dropwise fed thereto at a constant rate over 4 hours, and then the reaction was continued for another 2 hours. The temperature during the polymerization reaction was controlled at 79.0 to 80.5°C, and after completion of the polymerization, it was cooled to room temperature.

[0166] 200 g of the overlapping solution was mixed with a mixed solution of 460 g of n - hexane and 20 g of methanol, stirred to precipitate a polymer, allowed to stand, and then the polymer was separated by decantation. The polymer was redissolved in a mixed solution of 40 g of acetone and 20 g of methanol, 400 g of n - hexane was added thereto and stirred to precipitate the polymer, and the operation of separating the polymer by decantation was repeated 4 times.

[0167] The recovered polymer was dissolved in 80 g of acetone. A part of the polymer solution was sampled, dried under reduced pressure at 40 °C to obtain a polymer powder, which was subjected to NMR analysis. The monomer composition ratio (molar ratio) of the polymer by NMR analysis was 4 - HS:ECpMA = 42.6:57.4.

[0168] The remaining polymer solution was distilled while adding PGMEA while distilling off acetone under reduced pressure at a heat source temperature of 45 °C to replace the solvent with PGMEA, and finally a PGMEA solution of a 4 - HS / ECpMA copolymer with a polymer concentration of 20% by mass was obtained. As a result of analyzing the obtained polymer solution by GPC and LC, Mw = 5810, Mw / Mn = 1.47, and the residual low - molecular - weight component with Mw less than 200 was 0.01% (LC area%).

Industrial Applicability

[0169] The high - purity 4 - hydroxystyrene solution with good storage stability of the present invention can be used as a raw material for a resist polymer for EUV lithography or electron - beam lithography. Furthermore, by using this solution, a 4 - hydroxystyrene - based polymer suitable for a resist for EUV lithography or electron - beam lithography can be produced in a simple process that does not require a deprotection step and on a commercial scale.

Claims

1. The following steps (i) to (iv): (i) A deprotection step of contacting 4-acetoxystyrene with a base in a solvent to produce 4-hydroxystyrene; (ii) A neutralization step of adding an acid to the solution containing 4-hydroxystyrene after deprotection for neutralization; (iii) A step of washing the solution containing 4-hydroxystyrene after neutralization with water; (iv) A solvent substitution step of adding a solvent capable of dissolving 4-hydroxystyrene to the solution containing 4-hydroxystyrene, distilling at 40 °C or lower, and distilling off components other than 4-hydroxystyrene and excess solvent; A method for producing a 4-hydroxystyrene solution, comprising the above steps.

2. The method for producing a 4-hydroxystyrene solution according to claim 1, wherein the base used in the deprotection step is one in which dissolved oxygen has been removed by bubbling with an inert gas before use, and the deprotection step is carried out under a nitrogen atmosphere.

3. The method for producing a 4-hydroxystyrene solution according to claim 1 or 2, wherein the acid used in the neutralization step is one in which dissolved oxygen has been removed by bubbling with an inert gas before use.

4. The base used in the deprotection step is a base selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium ethoxide, potassium tert-butoxide, trimethylamine, triethylamine, ethanolamine, diazabicycloundecene, diazabicyclononene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, and tetramethylammonium hydroxide. The method for producing a 4-hydroxystyrene solution according to any one of claims 1 to 3.

5. The organic solvent used in the solvent substitution step is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters. The method for producing a 4-hydroxystyrene solution according to any one of claims 1 to 4.

6. In the solvent substitution step, the 4-hydroxystyrene concentration is adjusted to 10 to 70% by mass. The method for producing a 4-hydroxystyrene solution according to any one of claims 1 to 5.

7. The method for producing a 4-hydroxystyrene solution according to any one of claims 1 to 6, further comprising a step of passing the 4-hydroxystyrene solution through a filter having a nominal pore size of 1 micron or less before and / or after the solvent replacement step.

8. A 4-hydroxystyrene solution having a 4-hydroxystyrene concentration of 10 to 70% by mass, wherein in the gel permeation chromatography analysis of the solution, when the total area of the chromatogram of components other than the organic solvent is 100, the chromatogram area of 4-hydroxystyrene is 99.5% or more.

9. The 4-hydroxystyrene solution according to claim 8, wherein in the gel permeation chromatography analysis of the solution, the chromatogram area of the 4-hydroxystyrene polymer with respect to the chromatogram area of 4-hydroxystyrene is 0.5% or less.

10. The 4-hydroxystyrene solution according to claim 8 or 9, wherein the chromatogram area of the 4-hydroxystyrene is 99.7% or more.

11. The 4-hydroxystyrene solution according to claim 8 or 9, wherein the chromatogram area of the 4-hydroxystyrene is 99.9% or more.

12. The 4-hydroxystyrene solution according to any one of claims 8 to 11, wherein the organic solvent is any type of organic solvent selected from the group consisting of alcohols, ketones, ethers, glycol ethers, glycol ether esters, and esters.

13. The 4-hydroxystyrene solution according to any one of claims 8 to 12, which does not contain a polymerization inhibitor.

14. A polymerization raw material for a resist polymer comprising the 4-hydroxystyrene solution according to any one of claims 8 to 13.

15. A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, wherein the 4-hydroxystyrene solution according to any one of claims 8 to 13 is used as a polymerization raw material and polymerized alone or with another monomer copolymerizable therewith.

16. A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, wherein the 4-hydroxystyrene solution produced by the method according to any one of claims 1 to 7 is used as a polymerization raw material and polymerized alone or with another monomer copolymerizable therewith.

17. A step of producing a 4-hydroxystyrene solution by the method according to any one of claims 1 to 7; A step of performing polymerization alone using the 4-hydroxystyrene solution produced in the above step as a polymerization raw material, or performing polymerization with another monomer copolymerizable with 4-hydroxystyrene A method for producing a polymer having a structural unit derived from 4-hydroxystyrene, comprising:

18. The method for producing a polymer according to any one of claims 15 to 17, wherein the other copolymerizable monomer includes a monomer having an acid dissociable group.

19. The method for producing a polymer according to claim 18, wherein the monomer having an acid dissociable group is a group having a tertiary carbon atom bonded to an oxygen atom.

20. The method for producing a polymer according to any one of claims 15 to 19, which is applied to polymerization using a polymerization tank having a capacity of 30 L or more.

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