JP7718150B2 - Method for producing conductive polymer solution - Google Patents

Description

The present invention relates to a method for producing a self-doping conductive polymer solution having a polythiophene skeleton.

Semiconductor technology has undergone rapid development in recent years, leading to the creation of a huge electronics-related industry and an advanced information society. Among these, the application of conductive polymers to electronic products, such as liquid crystal displays (LCDs) and organic electroluminescence (OLEDs), has become widespread in a variety of fields, including televisions, computers, and the various mobile devices that have become popular in recent years, and has achieved remarkable development.

As materials supporting the electronics industry, externally doped conductive polymers have been developed in which π-conjugated polymers, such as polyacetylene, polythiophene, polyaniline, and polypyrrole, are doped with electron-accepting compounds as dopants. However, these polymers have issues such as difficulty in purification due to their low solubility and difficulty in maintaining stable doping. To address these issues, so-called self-doped conductive polymers have been developed, which have substituents (sulfo groups, sulfonate groups, etc.) in the polymer backbone, either directly or via a spacer, that provide both water solubility and doping properties. Examples of such polymers include sulfonated polyaniline and sulfonated polythiophene (see, for example, Non-Patent Documents 1 and 2). Among these, poly(4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-ylmethoxy)-1-butanesulfonic acid) (PEDT-S), which is substituted with linear alkylenesulfonic acid groups, have been reported (see, for example, Patent Document 1 and Non-Patent Documents 3 and 4). The applicant has also previously reported self-doped conductive polymers that combine high conductivity with excellent water solubility (see, for example, Patent Documents 2 and 3).

Patent No. 4974095 International Publication No. 2014/007299 JP 2020-59837 A

Journal of the American Chemical Society, 117, 10055-10062 (1995) Journal of the Chemical Society, Chemical Communications, 23, 1694-1695 (1990) Chemistry of Materials, 21, 1815-1821 (2009) Advanced Materials, 23, 4403-4408 (2011)

In the above-mentioned prior art (Patent Document 3), self-doped conductive polymers are synthesized by oxidative polymerization, but this method tends to leave metal ions, particularly iron ions, derived from the catalyst or oxidant as impurities in the polymerization product. Since these iron ion impurities cause a decrease in device characteristics and durability in applications such as organic electroluminescence (EL) and LCDs, a method of removing iron ions from conductive polymers using cation exchange resins has been proposed. However, removal using cation exchange resins poses challenges, such as increasing the number of manufacturing steps, raising variable costs, and increasing the environmental impact, making reductions preferable.

As a result of extensive research into resolving the above-mentioned problems, the inventors of the present application discovered that the above-mentioned problems could be solved by bringing at least one pair of electrodes into contact with a thiophene monomer solution to which an acid has been added and applying a potential difference between the electrodes to cause an electrochemical oxidation polymerization reaction. This discovery led to the completion of the present invention, which revealed that the above-mentioned problems could be solved by providing a conductive polymer with a low iron ion content without the need for removal treatment using a cation exchange resin.

That is, the present invention relates to a self-doped conductive polymer solution having a polythiophene skeleton, as shown below, obtained by the above-mentioned means, and to a method for producing the same.

[1]
A repeating structure represented by the following general formula (2) and a repeating structure represented by the following general formula (3)

[In the above general formula (2), each M ⁺ independently represents a hydrogen ion, an alkali metal ion, an ammonium ion, an organic ammonium ion, or a quaternary ammonium cation. In the above general formulas (2) and (3), R ² represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a halogen atom. m represents an integer of 1 to 6, and n represents 0 or 1.]
A method for producing a conductive polymer solution containing polythiophene having at least two or more repeating structures selected from the group consisting of repeating structures represented by the following formula:
(i) a polymerization step of bringing at least one pair of electrodes into contact with a solution containing at least a thiophene monomer represented by the following general formula (1), a solvent, and an acid, and applying a potential difference between the electrodes to polymerize the monomer, thereby obtaining a polymer solid or a polymer solution;
(ii) a dissolving step in which, when the polymer obtained in the polymerization step is a polymer solid, the polymer solid is mixed with a solvent to obtain a polymer solution;
A method for producing a conductive polymer solution, comprising:

[In the above general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, an ammonium ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In the above general formula (1), ^R2 represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a halogen atom. m represents an integer of 1 to 6, and n represents 0 or 1.]
[2]
The method according to [1], wherein R ² is a methyl group.

[3]
[3] The method according to [1] or [2], wherein the concentration of the monomer in the polymerization step is 0.1 to 30% by weight.

[4]
[4] The method according to any one of [1] to [3], wherein in the polymerization step, when the charged solution is an aqueous solution, its pH is in the range of 0 to 6.5.

[5]
[5] The method according to any one of [1] to [4], wherein in the polymerization step, a potential applied to the anode is in the range of 0 to +5 V relative to a silver/silver chloride electrode.

[6]
The manufacturing method according to any one of [1] to [5],
(iii) an anion exchange step of contacting the polymer solution obtained in the polymerization step or dissolution step with an anion exchange resin to exchange the anions in the polymer solution with hydroxide ions;
The manufacturing method further comprises:

The present invention makes it possible to produce and provide self-doped conductive polymers with lower amounts of residual metal ions than conventional polymers. The self-doped conductive polymers of the present invention are extremely useful industrially, as they can improve the performance of organic EL, LCDs, capacitors, and other devices.

The present invention is described in detail below.

The present invention relates to a method for producing a conductive polymer solution as described above.

In the above general formulas (1) and (2), each M ⁺ independently represents a hydrogen ion, an alkali metal ion, an ammonium ion (NH ₄ ⁺ ), a conjugate acid of an amine compound, or a quaternary ammonium cation.

The alkali metal ions are not particularly limited, but preferred examples include Li ions, Na ions, and K ions.

The conjugate acid of the amine compound is an amine compound to which a hydron (H ⁺ ) is added to become a cationic species, and may be any amine compound that reacts with a sulfonic acid group to form a conjugate acid.

The amine compound in the conjugate acid of the amine compound is not particularly limited, but examples thereof include amine compounds having an sp3 hybrid orbital represented by the general formula N(R ¹ ) ₃ , and amine compounds having an sp2 hybrid orbital such as pyridines and imidazoles.

The substituents R ¹ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms and having a substituent.

The alkyl group having 1 to 6 carbon atoms is not particularly limited, but examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a cyclopentyl group, an n-hexyl group, a 2-ethylbutyl group, and a cyclohexyl group.

The alkyl group having 1 to 6 carbon atoms and having the aforementioned substituent is not particularly limited, but examples thereof include an alkyl group having 1 to 6 carbon atoms and having a group selected from the group consisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms, an amino group, and a hydroxy group. Specific examples thereof include, but are not particularly limited to, a trifluoromethyl group and a 2-hydroxyethyl group.

Of these, from the viewpoint of availability, the substituents R ¹ are preferably each independently a hydrogen atom, a methyl group, an ethyl group, or a 2-hydroxyethyl group.

The amine compound represented by the general formula N(R ¹ ) ₃ is not particularly limited, but examples thereof include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, normal-propylamine, isopropylamine, normal-butylamine, tertiary-butylamine, hexylamine, aminoethanol, dimethylaminoethanol, methylaminoethanol, diethanolamine, N-methyldiethanolamine, triethanolamine, 3-amino-1,2-propanediol, 3-methylamino-1,2-propanediol, 3-dimethylamino-1,2-propanediol, and 1,4-butanediamine.

Amine compounds having an sp2 hybrid orbital that form the conjugate acid of the amine compound are not particularly limited, but examples include imidazole, N-methylimidazole, 1,2-dimethylimidazole, pyridine, picoline, and lutidine.

Of the amine compounds that form the conjugate acids of these amine compounds, ammonia, ethanolamine compounds, and imidazole compounds are preferred from the standpoint of availability.

The quaternary ammonium cation is not particularly limited, but examples include tetramethylammonium cation, tetraethylammonium cation, tetra-n-propylammonium cation, tetra-n-butylammonium cation, and tetra-n-hexylammonium cation. Of these, tetramethylammonium cation and tetraethylammonium cation are preferred from the standpoint of availability.

As described above, it is preferable that each M ⁺ independently represents a hydrogen ion, a Li ion, a Na ion, a K ion, an ammonium ion, a monoethanolammonium ion, a diethanolammonium ion, a triethanolammonium ion, an imidazolium ion, an N-methylimidazolium ion, or a 1,2-dimethylimidazolium ion.

In the above general formulas (1), (2), and (3), each R ² independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms, or a halogen atom.

The linear or branched alkyl group having 1 to 6 carbon atoms is not particularly limited, but examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, cyclopentyl, n-hexyl, 2-ethylbutyl, cyclohexyl, and n-octyl groups.

Halogen atoms include, but are not limited to, fluorine atoms, chlorine atoms, bromine atoms, etc.

With respect to ^R2 , from the viewpoint of film-forming properties, each R2 is preferably independently a hydrogen atom, a methyl group, an ethyl group, or a fluorine atom, more preferably a methyl group, an ethyl group, or a fluorine atom, and more preferably a methyl group.

Each m independently represents an integer from 1 to 6, preferably an integer from 1 to 4, more preferably 2.

Each n is independently 0 or 1, preferably 1.

The structural unit represented by the general formula (3) above represents the doped state of the structural unit represented by the general formula (2) above. In the conductive polymer of the present invention, during electrolytic oxidation polymerization, some of the structural units represented by the general formula (2) above undergo a self-doping reaction and are converted into structural units represented by the general formula (3). This action causes the resulting polymer to exhibit conductivity.

Dopants that cause an insulator-metal transition through doping can be divided into acceptors and donors. The former enter the vicinity of the polymer chain of a conductive polymer through doping and remove π electrons from the conjugated system of the main chain. As a result, positive charges (holes) are injected into the main chain, and so they are also called p-type dopants. Conversely, the latter donate electrons to the conjugated system of the main chain, and these electrons move through the conjugated system of the main chain, so they are also called n-type dopants.

The dopant in this invention is a sulfo group or sulfonate group covalently bonded within the polymer molecule, and is a p-type dopant. Polymers that exhibit conductivity without the addition of an external dopant are called self-doping polymers.

The thiophene monomer represented by the above general formula (1) is not particularly limited, but examples include sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propanesulfonate, sodium 3-[( Sodium 2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-pentyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-hexyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopropyl -1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isobutyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopentyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-fluoro-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-isopentyl-1-propanesulfonate ]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate potassium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid ammonium, or 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate triethylammonium.

The thiophene monomers exemplified above can be produced using thieno[3,4-b]-1,4-dioxin-2-methanol and a branched sultone compound, which can be synthesized according to known methods (e.g., Journal of Electroanalytical Chemistry, 443, 217-226 (1998)).

[In the general formula (4) above, ^R2 has the same meaning as ^R2 represented by the general formula (1) above, ^{and M2} represents an alkali metal ion (Li ion, K ion, Na ion, Cs ion, or the like).]
Furthermore, the thiophene monomer represented by the following general formula (4) thus produced can be converted into a sulfonic acid in which ^M2 is a hydrogen atom (the thiophene monomer represented by the above general formula (1)) by acid treatment (contact with an acid, an H ion-type cation exchange resin, or the like). Furthermore, the thiophene monomer represented by the above general formula (1) can be obtained by contacting this sulfonic acid in which ^M2 is a hydrogen atom with an alkali metal compound, ammonia, an amine compound, or a quaternary ammonium compound.

In the method for producing a conductive polymer solution containing polythiophene of the present invention, monomers other than the thiophene monomer represented by the general formula (1) above can be used in combination. Examples of such monomers include, but are not limited to, thiophene, 3-hexylthiophene, 3,4-ethylenedioxythiophene, hydroxymethyl-3,4-ethylenedioxythiophene, hydroxy-3,4-propyleneoxythiophene, bromomethyl-3,4-ethylenedioxythiophene, N-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-ylmethyl)-2-aminoethanesulfonic acid, and N-methyl-N-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-ylmethyl)-2-aminoethanesulfonic acid. Examples include thieno[3,4-b][1,4]dioxin-2-ylmethanesulfonic acid, 6-(2,3-dihydrothieno[3,4-][1,4]dioxin-2-yl)-1-hexene, 6-(2,3-dihydrothieno[3,4-][1,4]dioxin-2-yl)-1-hexanesulfonic acid, 6-(2,3-dihydrothieno[3,4-][1,4]dioxin-2-yl)-1-butanesulfonic acid, and O-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-ylmethyl)-4-phenolsulfonic acid.

The method for producing a conductive polymer solution of the present invention is characterized by including the above steps (i) and (ii), and preferably further includes step (iii).

The following describes the polymerization step (i) of the present invention, in which at least one pair of electrodes is brought into contact with a solution containing at least a thiophene monomer represented by the general formula (1), a solvent, and an acid, and a potential difference is applied between the electrodes to polymerize the monomer and obtain a polymer.

In the polymerization step, a monomer containing at least the thiophene monomer represented by the general formula (1) is polymerized. The concentration range of the monomer in the polymerization reaction is not particularly limited, but is preferably 0.1 to 30% by weight, more preferably 0.2 to 20% by weight, even more preferably 0.3 to 10% by weight, and even more preferably 0.5 to 8% by weight.

The "monomer concentration" referred to here is a value expressed as the weight of (monomers containing thiophene monomers represented by the general formula (1) above) / the weight of (monomers containing thiophene monomers represented by the general formula (1) above + solvent + acid) x 100 (% by weight).

The solvent used in the polymerization step is not particularly limited, but is preferably water, a solvent containing water, or a water-soluble solvent, and more preferably water, a water-water-soluble alcohol mixed solvent, or a water-soluble alcohol.

Examples of water include pure water, but distilled water and ion-exchanged water are also acceptable.

Water-soluble alcohols include, but are not limited to, alcohols such as methanol, ethanol, propanol, and butanol.

Of these aqueous solvents, water or methanol is preferred, and water is more preferred. The aqueous solvent may be degassed or purged with an inert gas such as nitrogen.

The acid used in the polymerization step is not particularly limited, but may be, for example, an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and boric acid. Examples of organic acids include methanesulfonic acid, paratoluenesulfonic acid, formic acid, acetic acid, lactic acid, and benzoic acid. Among these, sulfuric acid, methanesulfonic acid, and paratoluenesulfonic acid are preferred, with sulfuric acid being more preferred, due to their superior polymerization reaction rate.

A solution containing at least a monomer containing a thiophene monomer represented by the following general formula (1), a solvent, and an acid can be produced by mixing these components in any order.

The amount of acid added (content) is not particularly limited, but the normality of the acid in the starting solution (= molar concentration of the acid × valence number of the acid) is preferably 0.01 to 10 [N], more preferably 0.01 to 5 [N], and even more preferably 0.01 to 1 [N]. When the starting solution is an aqueous solution, the acid is preferably added (contained) so that the pH of the solution is in the range of 0 to 6.5, more preferably 0 to 5, and even more preferably 0 to 3.

The method for contacting at least one pair of electrodes with the solution is not particularly limited, but for example, the solution is placed in a container, an anode and a cathode are immersed in the solution, and a potential difference is applied. This may be a three-electrode method using standard electrodes, or a two-electrode method. Alternatively, the container itself may be used as an electrode, and the counter electrode may be brought into contact with the solution.

The potential difference applied between the electrodes is a potential difference that can cause electrochemical oxidation polymerization of the thiophene monomer represented by the general formula (1) above. While there are no particular limitations, the anode potential determined by the three-electrode method is preferably in the range of 0 to +5 V relative to the silver/silver chloride electrode, and more preferably in the range of +0.5 to +1.5 V.

The container material is not particularly limited as long as it is sufficiently durable against the solution, but examples of preferred materials include glass, glass-lined containers, Teflon (registered trademark), polyethylene, polypropylene, polyvinyl chloride, and stainless steel.

The container may be of any shape that can hold the solution inside, and may have a structure that separates the anode and cathode with a porous partition or ionic bridge.

The electrodes used in the polymerization process can be those that allow an electrochemical oxidation reaction to occur on their surfaces by applying a potential difference between them. Examples of materials include, but are not limited to, gold, platinum, nickel, titanium, stainless steel, glassy carbon, and ITO, which may be used alone or in combination of two or more.

The reaction pressure in the polymerization process may be atmospheric pressure, reduced pressure, or increased pressure.

The reaction atmosphere in the method for producing polythiophene of the present invention is not particularly limited, but may be air or an inert gas atmosphere such as nitrogen or argon. An inert gas atmosphere is more preferred.

The reaction temperature in the polymerization step is, for example, a temperature at which the thiophene monomer represented by the general formula (1) can be electrochemically oxidatively polymerized. While not particularly limited, a temperature in the range of -10 to 150°C is preferred, and a temperature in the range of 10 to 100°C is even more preferred.

The reaction time for the polymerization step is not particularly limited, but can be, for example, a time required for the oxidative polymerization of the thiophene monomer represented by general formula (1) to proceed sufficiently. Although not particularly limited, a range of 0.5 to 200 hours is preferred, and a range of 0.5 to 80 hours is even more preferred.

The polymerization step can also be carried out in a state that contains a surfactant in addition to the thiophene monomer represented by general formula (1) and the aqueous solvent. Adding the surfactant is preferable in that it improves the solubility and dispersibility in the aqueous solvent of the thiophene monomer used as a raw material and the resulting thiophene polymer.

The surfactant is not particularly limited, but examples include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, and more preferably at least one selected from the group consisting of anionic surfactants and nonionic surfactants.

Anionic surfactants are not particularly limited, but examples include carboxylic acid types, sulfonic acid types, sulfate ester types, and phosphate ester types.

The carboxylic acid type is not particularly limited, but examples include sodium octanoate, sodium decanoate, sodium palmitate, sodium stearate, etc.

The sulfonic acid type is not particularly limited, but examples include sodium hexanesulfonate, sodium decanesulfonate, sodium toluenesulfonate, sodium octylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium naphthalenesulfonate.

The sulfate ester type is not particularly limited, but examples include sodium lauryl sulfate, sodium laureth sulfate, and ammonium lauryl sulfate.

The phosphate ester type is not particularly limited, but examples include sodium lauryl phosphate, potassium lauryl phosphate, etc.

Nonionic surfactants are not particularly limited, but examples include polyethylene glycol surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, and polymeric nonionic surfactants.

The polyethylene glycol surfactant is not particularly limited, but examples include higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, higher alkylamine ethylene oxide adducts, ethylene oxide adducts of fats and oils, and polypropylene glycol ethylene oxide adducts.

The acetylene glycol surfactant is not particularly limited, but examples include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, Surfynol (registered trademark, manufactured by Air Products Co., Ltd.), and Olfine (registered trademark, manufactured by Nissin Chemical Industry Co., Ltd.).

The polyhydric alcohol surfactants are not particularly limited, but examples include fatty acid esters of glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol and sorbitan, fatty acid esters of sucrose, alkyl ethers of higher alcohols, and fatty acid amides of alkanolamines.

The polymeric nonionic surfactant is not particularly limited, but examples thereof include polyvinylpyrrolidone and polyvinylpyrrolidone copolymers. The polyvinylpyrrolidone copolymer is not particularly limited, but is preferably one having both hydrophilic and hydrophobic moieties in the polymer chain. Examples include copolymers in which polyvinylpyrrolidone is grafted onto polyvinyl alcohol, vinylpyrrolidone-vinyl acetate block copolymers, vinylpyrrolidone-methyl methacrylate copolymers, vinylpyrrolidone-normal butyl methacrylate copolymers, and vinylpyrrolidone-acrylamide copolymers.

By carrying out the above-described polymerization reaction, a polymer can be produced, and the polymer can be obtained as a polymer solution or a polymer solid. When the polymer is obtained as a polymer solid, all or part of the solid tends to be obtained as a precipitate on the anode.

If the polymer is obtained as a solid polymer, the dissolution step shown in (ii) below is carried out to obtain a polymer solution.

Next, we will explain (ii) the dissolution step of the present invention, which is carried out when the polymer obtained in the polymerization step is a solid polymer, in which the solid polymer is mixed with a solvent to obtain a polymer solution.

If the polymer solid obtained in the polymerization step is precipitated on the electrode, it is preferable to separate the polymer solid from the electrode beforehand. The separation method is not particularly limited, but examples include impact peeling, ultrasonic peeling, peeling using a spatula, and dissolution peeling using a good solvent. Regardless of whether the polymer solid has precipitated on the electrode, it is preferable to filter the resulting polymer solid. Examples of the filtration method include, but are not limited to, suction filtration, pressure filtration, and natural filtration.

The filter used to filter the polymer solids may be any filter that can obtain the polymer, and examples include, but are not limited to, filter paper, membrane filters, and glass filters.

The polymer solid separated above is then mixed with a solvent to obtain a polymer solution.

The solvent is not particularly limited, but is preferably water, a solvent containing water, or a water-soluble solvent, and more preferably water, a water-water-soluble alcohol mixed solvent, or a water-soluble alcohol.

Examples of water include pure water, but distilled water and ion-exchanged water are also acceptable.

Water-soluble alcohols include, but are not limited to, alcohols such as methanol, ethanol, propanol, and butanol.

Of these aqueous solvents, water, a water-methanol mixed solvent, or methanol is preferred, and water is more preferred. Furthermore, the aqueous solvent may be degassed or purged with an inert gas such as nitrogen.

The polymer concentration in the polymer solution is not particularly limited, but is preferably in the range of 0.01 to 20% by weight. In terms of achieving excellent processing efficiency in the next step (iii), the polymer concentration is preferably 0.1 to 10% by weight, and more preferably 0.2 to 5% by weight.

It is preferable that the viscosity of the polymer solution be in the range of 0.1 to 1000 mPa·s.

The polymer solution produced in step (i) or step (ii) in this manner is a conductive polymer solution characterized by a low iron content, which is the objective of the present invention, and this process makes it possible to produce the conductive polymer solution desired by the present invention.

Next, we will explain step (iii), which is the anion exchange step in which the polymer solution obtained in the polymerization step or dissolution step is brought into contact with an anion exchange resin to exchange the anions in the polymer solution for hydroxide ions.

The anion exchange resin is not particularly limited, but examples include weakly basic anion exchange resins and strongly basic anion exchange resins. However, weakly basic anion exchange resins are preferred because they are superior in that they can efficiently increase the purity of the polymer. Furthermore, the weakly basic anion exchange resin is not particularly limited, but amine-type weakly basic anion exchange resins are preferred. The amine-type weakly basic anion exchange resin may be a commercially available product, and although not particularly limited, suitable products include Diaion (registered trademark) WA20, Diaion (registered trademark) WA21, and Diaion (registered trademark) WA30 (manufactured by Mitsubishi Chemical Corporation), Amberlite (registered trademark) IRA67, Amberlite (registered trademark) IRA96SB, and Amberlite (registered trademark) IRA98 (manufactured by Organo Corporation), Dowex (registered trademark) 66 (manufactured by Dow), Duolite A368MS (manufactured by Rohm and Haas), LEWATIT (registered trademark) MP62WS, and LEWATIT (registered trademark) Monoplus MP64.

The resulting conductive polymer solution can then be further refined, viscosity adjusted, or component adjusted to produce a conductive polymer solution suitable for the intended application.

The above-mentioned alternative purification methods include, but are not limited to, ultrafiltration, for example.

The viscosity adjustment method is not particularly limited, but examples include removing the solvent by ultrafiltration or distillation, or adding a solvent. When a solvent is added, the solvent is not particularly limited, but examples include the same solvents as those used in the polymerization process, and water is more preferred.

The above-mentioned component adjustment is not particularly limited, but may involve adding conventionally known additives commonly used in the field of conductive polymer compositions according to conventionally known methods.

The conductive polymer aqueous solution produced by the above manufacturing method is characterized by containing a polythiophene containing at least two repeating structures selected from the group consisting of the repeating structure represented by general formula (2) above and the repeating structure represented by general formula (3) above, and further characterized by a low iron ion content. Because the iron ion content is low, the manufacturing method of the present invention does not require the purification operation by cation exchange, which was commonly performed in conventional technology, resulting in reduced steps and a lower environmental impact.

It is desirable that the conductive polymer solution have a low iron ion content when used in its intended application, and the iron content is preferably 10 ppm or less, more preferably 5 ppm or less, more preferably 2 ppm or less, even more preferably 0.5 ppm or less, and even more preferably 0.2 ppm or less.

The present invention will now be described in detail using examples, but the present invention should not be construed as being limited to these.

(Method for measuring iron ion content)
The amount of iron ions in the conductive polymer solution was measured by an internal standard method using inductively coupled plasma atomic emission spectrometry (ICP-AES) on an Optima 8300 manufactured by PerkinElmer.

(Conductivity measurement method)
The conductive polymer solution was cast onto a 5 cm square glass substrate that had been treated with UV/O ₃ , and dried at 120°C to form a film containing the conductive polymer. This was then heat-treated at 150°C for 1 hour. The thickness and surface electrical resistance of the resulting film were measured, and the conductivity was calculated using the following formula:

Electrical conductivity [S/cm] = 10 ⁴ / (Surface resistivity [Ω/□] x Film thickness [μm])
(Molecular weight measurement method)
Apparatus: Tosoh GPC8020
Column: TSK Gel α-M + guard column α
Detector: UV-8020 (335 nm)
Eluent: dimethyl sulfoxide/10 mM LiBr
Detection temperature: 50°C
Flow rate: 0.6mL/min
Injection volume: 20μL (approx. 1000ppm)
Standard sample: Pullulan. Sample preparation method: 1.2 g of a 50 wt % diisopropylamine/methanol solution was added to 2 g of a conductive polymer aqueous solution (solid content = 0.7 wt %) and stirred overnight at room temperature. The resulting solution was concentrated to dryness to obtain a deep purple solid. 25 mL of dimethyl sulfoxide, a polar organic solvent, was added to 25 mg of the solid and allowed to stand overnight. The solution was then filtered through a 0.45 μm syringe filter to prepare an analytical sample.

Example 1
(Polymerization Method)
Polymerization was carried out at 25°C using a standard three-electrode cell. The working electrode and counter electrode were platinum plates (2.0 cm x 2.5 cm), and the standard electrode was a silver/silver chloride electrode. 0.50 g of sodium 3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-2-methyl-1-propanesulfonate (a thiophene monomer represented by the following general formula (5)) was placed in the cell, and 30 g of purified water and 8.7 g of 44% sulfuric acid were added, followed by stirring for 5 minutes to dissolve the monomer. The monomer concentration at this time was 1.3 wt %. The pH of the starting solution was 0.5. Next, the electrodes were attached to the cell, and a potential of +1.1 V relative to the standard electrode was applied to the working electrode for 2 hours, resulting in the deposition of a deep ultramarine solid on the working electrode. The precipitate was polythiophene (a polymer containing repeating units represented by the following general formula (6) and the following general formula (7)) formed by polymerizing the thiophene monomer.

(Purification of Polymer)
A polymer containing polythiophene (a polymer containing repeating units represented by the general formula (6) and the general formula (7)) deposited on the anode by electrochemical oxidative polymerization was separated from the anode and recovered by filtration. Next, 16 g of pure water was added to the resulting polymer, and the mixture was stirred and then homogenized for 15 minutes using an ultrasonic homogenizer to obtain a polymer solution. The polymer solution was passed through an anion exchange resin (LEWATIT (registered trademark) MP62WS) to obtain a deep ultramarine aqueous solution (conductive polymer solution) containing 1.3 wt % polythiophene (a polymer containing repeating units represented by the general formula (6) and the general formula (7) and thus a conductive polymer).

(iron ion content)
The amount of iron ions contained in an aqueous solution containing polythiophene (a polymer containing repeating units represented by the following general formula (6) and the following general formula (7)) at a concentration of 1.3 wt % was measured by the above method. As a result, the iron ion content was 0.19 ppm.

(conductivity)
The conductivity of the resulting conductive polymer was measured by the above-mentioned conductivity measuring method and was found to be 150 S/cm.

(molecular weight)
The molecular weight of the resulting conductive polymer was measured by the above-mentioned molecular weight measurement method, and the weight average molecular weight was found to be 4,755.

Example 2
The same polymerization procedure as in Example 1 was carried out, except that the voltage application time was changed from 2 hours to 1 hour, and then the same purification procedure of the polymer as in Example 1 was carried out to obtain a deep ultramarine aqueous solution (conductive polymer solution) containing a concentration of 1.0 wt % of polythiophene (a conductive polymer, a polymer containing repeating units represented by the above general formula (6) and the above general formula (7)). The pH of the charged solution was 0.5.

(iron ion content)
The amount of iron ions contained in an aqueous solution containing polythiophene (a polymer containing repeating units represented by the following general formula (6) and the following general formula (7)) at a concentration of 1.0 wt % was measured by the above method. As a result, the iron ion content was 0.19 ppm.

(conductivity)
The conductivity of the resulting conductive polymer was measured by the above-mentioned conductivity measuring method and was found to be 122 S/cm.

(molecular weight)
The molecular weight of the resulting conductive polymer was measured by the above-mentioned molecular weight measurement method, and the weight average molecular weight was found to be 4,709.

Example 3
In Example 1, the amount of sodium 3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-2-methyl-1-propanesulfonate (a thiophene monomer represented by the following general formula (5)) was changed from 0.50 g to 1.0 g, the amount of pure water was changed from 30 g to 63 g, and 8.7 g of 44% sulfuric acid was changed to 15 g of paratoluenesulfonic acid (the monomer concentration at this time was 1.3 wt %. The pH of the charged solution was 0.34), and the application of a potential of +1.1 V for 2 hours was changed to the application of a potential of +1.1 V for 75 minutes. Except for this, a deep ultramarine aqueous solution (conductive polymer solution) containing polythiophene (a polymer comprising repeating units represented by the above general formulas (6) and (7) is obtained).

Example 4
The same polymerization procedures as in Example 1 were carried out, except that the amount of pure water was changed from 30 g to 35 g, and 8.7 g of 44% sulfuric acid was changed to 4.1 g of 35% hydrochloric acid (the monomer concentration at this time was 1.3 wt %. The pH of the charged solution was 0.47), and the application of a potential of +1.1 V for 10 minutes was changed from 2 hours, to obtain a deep ultramarine aqueous solution (conductive polymer solution) containing polythiophene (a conductive polymer, a polymer containing repeating units represented by the above general formula (6) and the above general formula (7)).

Example 5
The same polymerization procedure as in Example 1 was carried out, except that the amount of pure water was changed from 30 g to 36 g, and that 8.7 g of 44% sulfuric acid was changed to 2.6 g of phosphoric acid (the monomer concentration at this time was 1.3 wt %. The pH of the charged solution was 1.2). This resulted in a deep ultramarine aqueous solution (conductive polymer solution) containing polythiophene (a conductive polymer, a polymer containing repeating units represented by the above general formula (6) and the above general formula (7)).

Example 6
The same polymerization procedures as in Example 1 were carried out, except that in Example 1, 30 g of pure water was changed to 31 g, 8.7 g of 44% sulfuric acid was changed to 7.5 g of methanesulfonic acid (the monomer concentration at this time was 1.3 wt %. The pH of the charged solution was 0.25), and the application of a potential of +1.1 V for 2 hours was changed to the application of a potential of +0.95 V for 10 minutes, thereby obtaining a deep ultramarine aqueous solution (conductive polymer solution) containing polythiophene (a conductive polymer, a polymer comprising repeating units represented by the above general formula (6) and the above general formula (7)).

Example 7
The same polymerization procedures as in Example 1 were carried out, except that in Example 1, the amount of pure water was changed from 30 g to 31 g, 8.7 g of 44% sulfuric acid was changed to 8.2 g of 60% nitric acid (the monomer concentration at this time was 1.3 wt %. The pH of the charged solution was 0.13), and the application of a potential of +1.1 V for 2 hours was changed to the application of a potential of +0.95 V for 10 minutes, thereby obtaining a deep ultramarine aqueous solution (conductive polymer solution) containing polythiophene (a conductive polymer, a polymer containing repeating units represented by the above general formula (6) and the above general formula (7)).

Example 8
The same apparatus as in Example 1 was used. 0.50 g of sodium 3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-2-methyl-1-propanesulfonate (a thiophene monomer represented by the following general formula (5)) was placed in a cell, and 34 g of pure water and 4.7 g of acetic acid were added. The mixture was then stirred for 5 minutes to dissolve the monomer (the monomer concentration at this stage was 1.3 wt %. The pH of the starting solution was 2.3). Next, an electrode was attached to the cell, and a potential of +1.4 V relative to the standard electrode was applied to the working electrode for 2 hours, yielding a deep ultramarine solid precipitated on the working electrode and a deep ultramarine solution. Both the deep ultramarine solid and the deep ultramarine solution contained polythiophene (a polymer containing the repeating units represented by the above general formulas (6) and (7)) formed by polymerization of the thiophene monomer.

Example 9
A 50 mL beaker was charged with 0.50 g of sodium 3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-2-methyl-1-propanesulfonate (a thiophene monomer represented by the following general formula (5)), and 36 g of methanol and 2.0 g of methanesulfonic acid were added. The mixture was then stirred for 5 minutes to dissolve the solution. Next, a pair of platinum plates (2.0 cm x 2.5 cm) were attached to the beaker as electrodes, a DC power supply was connected to the electrodes, and a potential of +1.0 V was applied for 10 minutes to obtain a reddish-purple solution. This solution was stirred overnight in an air atmosphere to obtain a blue solution. The solution contained polythiophene (a polymer containing the repeating units represented by the above general formulas (6) and (7)) polymerized from the thiophene monomer.

Reference example 1
A 500 mL separable flask was charged with 10 g (30 mmol) of sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate (a thiophene monomer represented by the general formula (5) above) and 150 g of water. After dissolution, 2.94 g (18.1 mmol) of anhydrous iron(III) chloride was added at room temperature and stirred for 20 minutes. Thereafter, a mixed solution consisting of 14.5 g (60.4 mmol) of sodium persulfate and 100 g of water was added dropwise while maintaining the reaction solution temperature at 30°C or below. Next, after stirring at room temperature for 3 hours, the reaction solution was added dropwise to 800 g of acetone to precipitate a black Na-type polymer. The polymer was filtered and dried under vacuum to obtain 18.0 g of crude polymer of sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate.

Next, 14.5 g of this crude polymer was added to water to prepare a 2 wt% solids solution. 700 g of this solution was passed through a column packed with 200 mL of Lewatit Mono Plus S100 (H-type) cation exchange resin (space velocity = 1.1), yielding 738 g of an H-type polymer solution. This polymer solution was then purified by crossflow ultrafiltration (Vivaflow 200 filter, molecular weight cutoff = 5,000, permeability = 5), yielding 698 g of a deep ultramarine-colored solution containing polythiophene (a polymer containing repeating units represented by the general formulas (6) and (7)). The polymer content (solids content) of the polythiophene solution was 0.74 wt%. Furthermore, ICP-MS analysis revealed that the polythiophene solution contained 44 ppm of iron ions based on the solids content. That is, the polythiophene aqueous solution (conductive polymer aqueous solution) contained 0.32 ppm of iron ions.

The method for producing a conductive polymer solution of the present invention can produce a conductive polymer solution with a low iron ion content equivalent to conventional solutions, without the need for a cation exchange operation. The conductive polymer solution obtained by the production method of the present invention is also expected to be applicable to organic EL, LCD, capacitors, antistatic agents, etc.

Claims (6)

A repeating structure represented by the following general formula (2) and a repeating structure represented by the following general formula (3)
[In the above general formula (2), each M ⁺ independently represents a hydrogen ion, an alkali metal ion, an ammonium ion, an organic ammonium ion, or a quaternary ammonium cation. In the above general formulas (2) and (3), ^R2 represents a linear or branched alkyl group having 1 to 6 carbon atoms. m represents an integer of 1 to 6, and n represents 0 or 1.]
A method for producing a conductive polymer solution containing polythiophene having at least two or more repeating structures selected from the group consisting of repeating structures represented by the following formula:
(i) a polymerization step of bringing at least one pair of electrodes into contact with a solution containing at least a thiophene monomer represented by the following general formula (1), a solvent, and an acid, and applying a potential difference between the electrodes to polymerize the monomer, thereby obtaining a polymer solid or a polymer solution;
(ii) a dissolving step in which, when the polymer obtained in the polymerization step is a polymer solid, the polymer solid is mixed with a solvent to obtain a polymer solution;
A method for producing a conductive polymer solution, comprising:
[In the above general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, an ammonium ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In the above general formula (1), ^R2 represents a linear or branched alkyl group having 1 to 6 carbon atoms. m represents an integer of 1 to 6, and n represents 0 or 1.] The method according to claim 1, wherein ^R2 is a methyl group. The manufacturing method described in claim 1 or 2, wherein the concentration of the monomer in the polymerization step is 0.1 to 30% by weight. The manufacturing method described in any one of claims 1 to 3, wherein in the polymerization step, when the feed solution is an aqueous solution, its pH is in the range of 0 to 6.5. The manufacturing method described in any one of claims 1 to 4, wherein the potential applied to the anode in the polymerization step is in the range of 0 to +5 V relative to a silver/silver chloride electrode. The manufacturing method according to any one of claims 1 to 5,
(iii) an anion exchange step of contacting the polymer solution obtained in the polymerization step or dissolution step with an anion exchange resin to exchange the anions in the polymer solution with hydroxide ions;
The manufacturing method further comprises: