JP7757777B2 - Conductive polymer solution, conductive polymer thin film, and method for producing the same - Google Patents

Description

The present invention relates to a conductive polymer solution, a conductive polymer thin film, and a method for producing the same. More specifically, the present invention relates to a π-conjugated conductive polymer solution, a method for producing a conductive polymer thin film using the same, and a conductive polymer thin film.

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, externally doped conductive polymers have the drawback of being insoluble and infusible, making them difficult to purify and maintaining stable doping.

Meanwhile, 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. Known examples of self-doped conductive 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) (PEDOT-S), which is substituted with linear alkylenesulfonic acid groups, has been reported to exhibit relatively high conductivity (see, for example, Patent Document 1 and Non-Patent Documents 3 and 4). In addition to PEDOT-S, other self-doped conductive polymers have also been reported that combine high conductivity with excellent water solubility (see, for example, Patent Document 2).

Conductive polymers are widely used in a variety of electronics applications, including liquid crystal displays (LCDs) and organic electroluminescence (OLEDs), in televisions, computers, and the various mobile devices that have become popular in recent years. In addition, new applications for conductive polymers, such as transparent electrodes and solid electrolytic capacitors, have been actively explored in recent years. Amid this rapid development in semiconductor technology, the market is demanding conductive polymers and conductive polymer thin films with even higher conductivity.

Patent No. 4974095 International Publication No. 2014/007299

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)

π-conjugated conductive polymers are expected to be used in antistatic materials, solid electrolytes or transparent electrodes for LCDs, organic electroluminescence (EL), and capacitors. If the conductivity of self-doped conductive polymers and their thin films can be increased, it will be possible to further improve the performance of these applications.

The object of the present invention is to provide a technology that can improve the conductivity of conventional π-conjugated conductive polymers.

As a result of extensive research aimed at solving the above-mentioned problems, the inventors discovered that a conductive polymer solution containing a π-conjugated conductive polymer and a dialkylene glycol monoalkyl ether forms a conductive polymer thin film with a high degree of crystal structure regularity not previously observed, and as a result, the conductivity of the conductive polymer thin film formed from the π-conjugated conductive polymer is improved, leading to the completion of the present invention.

That is, the present invention relates to the following conductive polymer solution, a method for producing a conductive polymer film using the same, and a conductive polymer thin film.

[1]
A conductive polymer solution containing a π-conjugated conductive polymer and a dialkylene glycol monoalkyl ether.

[2]
The conductive polymer solution according to [1], wherein the content of the π-conjugated conductive polymer is 0.01 to 10% by weight, and the content of the dialkylene glycol monoalkyl ether is 0.01 to 6% by weight.

[3]
The conductive polymer solution according to [1] or [2], wherein the content ratio of the dialkylene glycol monoalkyl ether relative to 1 part by weight of the π-conjugated conductive polymer is 0.2 to 2 parts by weight.

[4]
The conductive polymer solution according to any one of [1] to [3], wherein the π-conjugated conductive polymer is a polythiophene containing at least two or more structural units of at least one kind selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2):

[In general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In general formulas (1) and (2), ^R1 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom; m independently represents an integer of 1 to 10; and n independently represents 0 or 1.]

[5]
The conductive polymer solution according to [4], wherein R ¹ is a hydrogen atom, a methyl group, or a fluorine atom.

[6]
The conductive polymer solution according to [4] or [5], wherein the M ⁺ is a hydrogen ion.

[7]
The conductive polymer solution according to any one of [4] to [6], wherein the polythiophene has a number average molecular weight, calculated as polystyrene sulfonic acid, of 3,500 or more as measured by gel permeation chromatography.

[8]
The conductive polymer solution according to any one of [1] to [7], wherein the dialkylene glycol monoalkyl ether is at least one selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, and diethylene glycol mono-n-octyl ether.

[9]
A method for producing a conductive polymer thin film, comprising applying the conductive polymer solution according to any one of [1] to [8] to a substrate, and then heating and drying the applied conductive polymer solution.

[10]
A conductive polymer thin film containing a π-conjugated conductive polymer, wherein the half-width of a diffraction peak of a (100) plane detected near 2θ=5° in an X-ray diffraction measurement by out-of-plane measurement is 0.9° or less.

[11]
The conductive polymer thin film according to [10], wherein in X-ray diffraction in out-of-plane measurement, the ratio (B/A) of the peak area (B) of the diffraction peak of the (020) plane detected in the vicinity of 2θ=25° to the peak area (A) of the diffraction peak of the (100) plane detected in the vicinity of 2θ=5° is 0.1 or less.

[12]
The conductive polymer thin film according to [10] or [11], wherein the π-conjugated conductive polymer is a polythiophene containing at least two or more structural units of at least one kind selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2):

[In general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In general formulas (1) and (2), ^R1 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom, m represents an integer of 1 to 10, and n represents 0 or 1.]

[13]
The conductive polymer thin film according to [12], wherein R ¹ is a hydrogen atom, a methyl group, or a fluorine atom.

[14]
The conductive polymer thin film according to [12] or [13], wherein the M ⁺ is a hydrogen ion.

[15]
The conductive polymer thin film according to any one of [12] to [14], wherein the polythiophene has a number average molecular weight, calculated as polystyrene sulfonic acid, of 3,500 or more as measured by gel permeation chromatography.

The present invention provides a technology that can improve the conductivity of conventional π-conjugated conductive polymers.

FIG. 1 shows diffraction patterns obtained by parallel optical system X-ray diffraction out-of-plane measurement of the conductive polymer thin film of Example 1 and the conductive polymer thin film of Comparative Example 1.

The present invention is described in detail below. In this specification, "~" means a numerical range that includes both the upper and lower limits of the numerical value.

The conductive polymer solution according to an embodiment of the present invention contains a π-conjugated conductive polymer and a dialkylene glycol monoalkyl ether.

The π-conjugated conductive polymer is not particularly limited, but examples thereof include π-conjugated conductive polymers having acidic groups. More specifically, examples include π-conjugated conductive polymers that contain at least one acidic group selected from the group consisting of phosphonic acid groups, sulfonic acid groups, and carboxy groups, and that contain at least one repeating unit selected from the group consisting of phenylenevinylene, vinylene, thienylene, pyrrolylene, phenylene, iminophenylene, isothianaphthene, furylene, and carbazolylene.

The thienylene-based π-conjugated conductive polymer is not particularly limited, but examples include polythiophenes containing at least two or more structural units selected from the group consisting of structural units represented by the following general formula (1) and structural units represented by the following general formula (2):

In general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In general formulas (1) and (2), ^R1 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom; m independently represents an integer of 1 to 10; and n independently represents 0 or 1.

The structural unit represented by the general formula (2) above represents the doped state of the structural unit represented by the general formula (1), and this doped state is achieved by the sulfo group or sulfonate group in the structural unit represented by the general formula (1) above acting as a p-type dopant.

The linear or branched alkyl group having 3 to 6 carbon atoms represented by R ¹ in the above general formulas (1) and (2) is not particularly limited, but examples thereof include 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.

^R1 is preferably a hydrogen atom, a methyl group, an ethyl group, or a fluorine atom, more preferably a hydrogen atom, a methyl group, or a fluorine atom, and most preferably a methyl group, in terms of excellent film-forming properties.

In the above formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, a conjugate acid of an amine compound, or a quaternary ammonium cation.

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

The conjugate acid of the amine compound represents a cationic compound in which a proton is added to an amine compound. The amine compound is not particularly limited, but examples thereof include amine compounds having an sp3 hybridized orbital such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, monoethanolamine, diethanolamine, and triethanolamine (all of which are amine compounds represented by the general formula N(R ² )(R ³ )(R ⁴ )), pyridine, 2-methylpyridine, 3-methylpyridine, and 4-methylpyridine (all of which are pyridines), imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-methylimidazole, and 1,2-dimethylimidazole (all of which are imidazoles), and the like.

R ² to R ⁴ each independently represent a hydrogen atom or an alkyl group having a total of 1 to 40 carbon atoms which may have a substituent (among which, alkyl groups having 3 to 40 carbon atoms may be linear, branched, or cyclic). Of these, it is more preferable that R ² to R ⁴ each independently represent a hydrogen atom or an alkyl group having a total of 1 to 20 carbon atoms which may have a substituent (among which, alkyl groups having 3 to 20 carbon atoms may be linear, branched, or cyclic), and it is even more preferable that R 2 to R 4 each independently represent a hydrogen atom or an alkyl group having a total of 1 to 6 carbon atoms which may have a substituent (among which, alkyl groups having 3 to 6 carbon atoms may be linear, branched, or cyclic).

Furthermore, when R ² to R ⁴ are alkyl groups having a substituent, examples of the substituent include an alkoxy group having 1 to 6 carbon atoms, an aryl group having 1 to 20 carbon atoms, a hydroxy group, an amino group, an alkyl ether group, an aryl ether group, a thiol group, an alkyl sulfide group, or a carboxyl group, and more preferably, an alkyl group having a hydroxy group such as a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2-hydroxypropyl group, or a 2,3-dihydroxypropyl group.

Here, the alkyl group having a total of 1 to 40 carbon atoms, which may have a substituent, or the alkyl group having a total of 1 to 20 carbon atoms, which may have a substituent, is not particularly limited, but examples include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-hexyl group, a cyclohexyl group, a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2-hydroxypropyl group, a 2,3-dihydroxypropyl group, a methoxymethyl group, an ethoxymethyl group, a hydroxyethoxyethyl group, a hydroxyethoxyethoxyethyl group, a benzyl group, a phenethyl group, and an aminoethyl group.

The alkyl group having a total of 1 to 6 carbon atoms and optionally having a substituent is not particularly limited, but examples include methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-hexyl, cyclohexyl, 2-hydroxyethyl, 3-hydroxypropyl, 2-hydroxypropyl, 2,3-dihydroxypropyl, methoxymethyl, ethoxymethyl, hydroxyethoxyethyl, and hydroxyethoxyethoxyethyl groups.

Of these, the substituents R ² to R ⁴ are more preferably each independently a hydrogen atom, a methyl group, an ethyl group, or a hydroxyethyl group.

Furthermore, the imidazoles are preferably imidazole compounds having a total of 3 to 20 carbon atoms. Although not particularly limited, more preferred examples include imidazole, 1-methylimidazole, and 1,2-dimethylimidazole.

The pyridines are preferably pyridine compounds having a total of 3 to 20 carbon atoms. While not particularly limited, more preferred examples include pyridine, picoline, and lutidine.

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, from the standpoint of availability, tetramethylammonium cation and tetraethylammonium cation are preferred.

From the viewpoint of the solubility and coatability of the conductive polymer solution, M ⁺ is preferably a conjugate acid of an amine selected from the group consisting of a hydrogen ion, an alkali metal ion (for example, a Li ion, a Na ion, a K ion, etc.), a tetramethylammonium cation, a tetraethylammonium cation, ammonia, trimethylamine, triethylamine, monoethanolamine, N-methylethanolamine, 3-amino-1,2-propanediol, N-methyl-3-amino-1,2-propanediol, diethanolamine, triethanolamine, pyridine, methylpyridine, imidazole, 1-methylimidazole, and 2-methylimidazole, and more preferably a conjugate acid of an amine selected from the group consisting of a hydrogen ion, a Li ion, a Na ion, a K ion, a tetramethylammonium cation, a tetraethylammonium cation, ammonia, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, imidazole, 1-methylimidazole, and 2-methylimidazole. From the above viewpoint, M ⁺ is more preferably a hydrogen ion.

In the above general formulas (1) and (2), m independently represents an integer from 1 to 10, and n independently represents 0 or 1. From the viewpoint of the solubility and coatability of the conductive polymer solution, m is preferably an integer from 2 to 6, more preferably 2, 3, 4, or 5, and even more preferably 2 or 3. Furthermore, from the viewpoint of the solubility and coatability of the conductive polymer solution, n is preferably 1.

For polythiophenes containing at least two or more structural units selected from the group consisting of structural units represented by the general formula (1) and structural units represented by the general formula (2), in order to obtain high conductivity, the number average molecular weight, measured as converted into polystyrene sulfonic acid, is preferably 3,500 or more, more preferably 4,000 or more, and even more preferably 5,000 or more, as determined by gel permeation chromatography. In terms of the operability of the conductive polymer solution, the number average molecular weight, measured as converted into polystyrene sulfonic acid, of the polythiophene in gel permeation chromatography is preferably 30,000 or less, more preferably 20,000 or less, and even more preferably 15,000 or less.

The method and conditions for measuring the molecular weight of the polythiophene by gel permeation chromatography were in accordance with ISO 16014-3:2012 (JIS K 7252-3:2016). In an embodiment of the present invention, the number-average molecular weight of the π-conjugated conductive polymer can be determined, for example, by the method described below in the Examples.

[Other π-conjugated conductive polymers]
The phenylene vinylene-based π-conjugated conductive polymer is not particularly limited, but examples thereof include polyphenylene vinylene containing at least two structural units represented by the following general formula (6).

In the above formula (6), R ¹¹ to R ¹⁴ each independently represent a hydrogen atom, a linear or branched alkyl group having 1 to 24 carbon atoms, a linear or branched alkoxy group having 1 to 24 carbon atoms, an acidic group, a hydroxy group, a nitro group, a halogen atom (-F, -Cl, -Br or I), -N(R ³¹ ) ₂ , -NHCOR ³¹ , -SR ³¹ , -OCOR ³¹ , -COOR ³¹ , -COR ³¹ , -CHO, or -CN. R ³¹ represents an alkyl group having 1 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an aralkyl group having 7 to 24 carbon atoms. However, at least one of R ¹¹ to R ¹⁴ is an acidic group or a salt thereof.

The iminophenylene-based π-conjugated conductive polymer is not particularly limited, but an example thereof is polyaniline containing at least two structural units represented by the following general formula (7):

In the above formula (7), R ²¹ to R ²⁵ each independently represent a hydrogen atom, a linear or branched alkyl group having 1 to 24 carbon atoms, a linear or branched alkoxy group having 1 to 24 carbon atoms, an acidic group, a hydroxy group, a nitro group, a halogen atom (-F, -Cl, -Br or I), -N(R ³¹ ) ₂ , -NHCOR ³¹ , -SR ³¹ , -OCOR ³¹ , -COOR ³¹ , -COR ³¹ , -CHO, or -CN. R ³¹ represents an alkyl group having 1 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an aralkyl group having 7 to 24 carbon atoms. However, at least one of R ²¹ to R ²⁵ is an acidic group or a salt thereof.

The acidic group is not particularly limited, but examples include a phosphonic acid group, a sulfonic acid group (sulfo group), or a carboxylic acid group (carboxy group).

The sulfonic acid group may be in an acid state (-SO ₃ H) or an ionic state (-SO ₃ ^- ). Furthermore, the sulfonic acid group may be a substituent having a sulfonic acid group (-R ³² SO ₃ H).

The carboxylic acid group may be in an acid state (—COOH) or an ionic state (—COO ⁻ ). Furthermore, the carboxylic acid group may be a substituent having a carboxylic acid group (—R ³² COOH).

The R ³² is not particularly limited, but examples thereof include a linear or branched alkylene group having 1 to 24 carbon atoms, a linear or branched arylene group having 6 to 24 carbon atoms, and a linear or branched aralkylene group having 7 to 24 carbon atoms.

The linear or branched alkylene group having 1 to 24 carbon atoms is not particularly limited, but examples include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexadiene group, an octadiene group, and a decanediene group.

The linear or branched arylene group having 6 to 24 carbon atoms is not particularly limited, but examples include a phenylene group, a biphenylylene group, a terphenylylene group, and a tolylene group.

The linear or branched aralkylene group having 7 to 24 carbon atoms is not particularly limited, but examples include a methylene-phenylene group or an ethylene-phenylene group.

Salts of the acidic group mentioned above are not particularly limited, but examples include alkali metal salts, alkaline earth metal salts, ammonium salts, and substituted ammonium salts.

The alkali metal salt is not particularly limited, but examples include lithium salt, sodium salt, potassium salt, and cesium salt.

The alkaline earth metal salts are not particularly limited, but examples include magnesium salts and calcium salts.

The substituted ammonium salt is not particularly limited, but examples include aliphatic ammonium salts, saturated alicyclic ammonium salts, and unsaturated alicyclic ammonium salts.

The aliphatic ammonium salt is not particularly limited, but examples include methylammonium salt, dimethylammonium salt, trimethylammonium salt, ethylammonium salt, diethylammonium salt, triethylammonium salt, methylethylammonium salt, diethylmethylammonium salt, dimethylethylammonium salt, propylammonium salt, dipropylammonium salt, isopropylammonium salt, diisopropylammonium salt, butylammonium salt, dibutylammonium salt, methylpropylammonium salt, ethylpropylammonium salt, methylisopropylammonium salt, ethylisopropylammonium salt, methylbutylammonium salt, ethylbutylammonium salt, tetramethylammonium salt, tetramethylolammonium salt, tetraethylammonium salt, tetra-n-butylammonium salt, tetrasec-butylammonium salt, and tetra-t-butylammonium salt.

The saturated alicyclic ammonium salt is not particularly limited, but examples include piperidinium salts, pyrrolidinium salts, morpholinium salts, and piperazinium salts.

The unsaturated alicyclic ammonium salt is not particularly limited, but examples include pipridinium salts, α-picolinium salts, β-picolinium salts, γ-picolinium salts, quinolinium salts, isoquinolinium salts, and pyrrolinium salts.

All of the above-mentioned π-conjugated conductive polymers can be produced using conventional methods.

The π-conjugated conductive polymer in the conductive polymer solution according to an embodiment of the present invention is preferably a polythiophene containing at least two or more structural units selected from the group consisting of structural units represented by the above general formula (1) and structural units represented by the following general formula (2), in view of its excellent conductivity.

In the conductive polymer solution according to an embodiment of the present invention, the content of the π-conjugated conductive polymer is preferably 0.01 to 10% by weight from the viewpoint of improving film-forming properties, and more preferably 0.01 to 4% by weight from the viewpoint of excellent storage stability.

[Method for producing polythiophene]
A polythiophene containing at least two or more structural units selected from the group consisting of the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2) can be produced by polymerizing a thiophene monomer represented by the following formula (3) in water or an alcohol solvent in the presence of an oxidizing agent such as an iron salt and/or persulfuric acid. If necessary, the resulting product can be subjected to a combination of procedures such as solvent washing, reprecipitation, centrifugal sedimentation, ultrafiltration, dialysis, and ion exchange resin treatment.

In the formula (3), R ¹ , m, and n have the same definitions as R ¹ , m, and n in the general formulae (1) and (2). In the formula, M ⁺ represents an alkali metal ion.

The thiophene monomer represented by the above general formula (3) is not particularly limited, but specific examples include sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propanesulfonate, potassium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, and 3-[( Sodium 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-[(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-butyl-1-propanesulfonate ) 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 ammonium salt, 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, potassium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]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-propanesulfonate, oxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, ammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, triethylammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, sodium 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butanesulfonate, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-butanesulfonate potassium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-butanesulfonate sodium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-butanesulfonate potassium, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-butanesulfonate -fluoro-1-butanesulfonic acid sodium salt, 4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-fluoro-1-butanesulfonic acid potassium salt, 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid sodium salt, 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane Examples include lithium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, potassium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid, sodium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonate, and potassium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonate.

The alkali metal ion represented by M ⁺ is not particularly limited, but examples thereof include a lithium ion, a sodium ion, a potassium ion, and a cesium ion.

The solvent used in the polymerization reaction of the thiophene monomer represented by formula (3) above is preferably water, alcohol, or an aqueous alcohol solution. Examples of water include pure water, but distilled water and ion-exchanged water are also acceptable. Examples of alcohol solvents include alcohols such as methanol, ethanol, propanol, and butanol. These alcohol solvents may be used alone or in combination with water. Of these solvents, water or methanol is preferred, and water is more preferred. The solvent may also be degassed or substituted with an inert gas such as nitrogen.

The amount of solvent used in the polymerization reaction of the thiophene monomer is, for example, an amount that dissolves the thiophene monomer, and is not particularly limited. However, the amount is preferably in the range of 0.1 to 100 times by weight, and more preferably 1 to 20 times by weight, the amount of thiophene monomer used in the embodiment of the present invention.

The oxidizing agent used in the polymerization reaction of the thiophene monomer promotes oxidative polymerization through an oxidative dehydrogenation reaction. The oxidizing agent is not particularly limited, but examples include persulfates, iron salts (II or III), hydrogen peroxide, permanganates, dichromates, cerium (IV) sulfate, and oxygen. These may be used alone or in combination.

Specific examples of persulfates include persulfuric acid, ammonium persulfate, sodium persulfate, and potassium persulfate.

Specific examples of iron salts include trivalent iron salts such as FeCl ₃ , FeBr ₃ , Fe ₂ (SO ₄ ) ₃ , Fe(NO ₃ ) _{3.9H 2} O, iron perchlorate, and iron(III) para-toluenesulfonate, and divalent iron salts such as FeCl ₂ , FeBr ₂ , FeSO _{4.7H 2} O, and iron(II) acetate. These may be used in the form of anhydrous or hydrated.

Specific examples of permanganates include sodium permanganate, potassium permanganate, and magnesium permanganate.

Specific examples of dichromates include ammonium dichromate and potassium dichromate.

Among these oxidizing agents, FeCl ₃ , Fe ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₃ , or a combination of a persulfate and an iron salt (II or III) is particularly preferred.

The amount of oxidizing agent used in the polymerization reaction of the thiophene monomer is not particularly limited, but is preferably 0.5 to 50 times the number of moles of thiophene monomer charged. More preferably, it is 1 to 20 times the number of moles. Even more preferably, it is 1 to 10 times the number of moles.

When the oxidizing agent used in the polymerization reaction of the thiophene monomer is, for example, a system consisting solely of iron salt (III), it is preferable to use iron salt (III) in an amount equal to or greater than the number of moles of thiophene monomer charged as a raw material, and to use it so that the iron concentration in the solvent is 10% by weight or greater. To achieve better conductivity, it is even more preferable that the iron concentration in the solvent is 20% by weight or greater. The iron concentration here is a value expressed as iron salt / (iron salt + water) x 100 (wt%), and the iron salt is calculated as anhydrous.

Furthermore, when the oxidizing agent used in the polymerization reaction of the thiophene monomer is a combination of persulfate and iron salt (II or III), the molar amount of persulfate is preferably in the range of 0.5 to 20 times and the molar amount of iron salt (II or III) is preferably in the range of 0.01 to 10 times, relative to the number of moles of thiophene monomer charged, and more preferably in the range of 1.5 to 10 times and the molar amount of iron salt (II or III) is preferably in the range of 0.05 to 5 times.

The pressure for the polymerization reaction of the above thiophene monomer may be normal pressure, reduced pressure, or increased pressure.

The reaction atmosphere for the polymerization reaction of the thiophene monomer may be air or an inert gas such as nitrogen or argon. An inert gas is more preferred.

The reaction temperature for the polymerization reaction of the above thiophene monomer is not particularly limited, but is preferably in the range of -10 to 100°C, and more preferably in the range of 0 to 50°C.

The reaction time for the polymerization reaction of the above thiophene monomer is the time required for the oxidative polymerization to proceed sufficiently, and is not particularly limited, but is preferably in the range of 0.5 to 200 hours, and more preferably in the range of 0.5 to 80 hours.

The reaction method for the above polymerization reaction is not particularly limited. For example, the thiophene monomer represented by formula (3) above may be dissolved in water in advance, and the oxidizing agent may be added dropwise, either all at once or slowly. Conversely, an aqueous solution of the thiophene monomer represented by formula (3) above may be added dropwise, either all at once or slowly, to a solid or aqueous solution of the oxidizing agent. Furthermore, when two or more oxidizing agents are used, the oxidizing agents may be added sequentially.

In the above polymerization reaction, the viscosity of the liquid tends to increase with the addition of the oxidizing agent, so it is necessary to stir the entire liquid uniformly. Agitator blades that can be used include propeller blades, paddle blades, Maxblend® blades (manufactured by Sumitomo Heavy Industries Process Equipment Co., Ltd.), Fullzone® blades (manufactured by Kobelco Eco-Solutions Co., Ltd.), and disc turbines. Large blades such as Maxblend blades and Fullzone blades are preferred for more uniform mixing within the reaction vessel. Homomixers and homogenizers used for emulsification and dispersion may also be used in combination. When using a stirring method that uses conventional agitator blades, it is preferable to increase the rotation speed of the agitator blades as much as possible, provided that the reaction liquid does not absorb a large amount of gas from the gas phase of the reaction vessel, thereby reducing stirring efficiency.

A typical method for isolating and purifying the above polythiophene is, for example, as follows:

First, the aqueous solution after the polymerization reaction is directly desalted and purified using a membrane separation method such as ultrafiltration or dialysis, and then passed through cation and anion exchange resins to obtain an aqueous solution of acid-type polythiophene in which M ⁺ is a hydrogen ion.

Furthermore, if necessary, the resulting aqueous solution can be roughly concentrated and added to a poor solvent such as acetone to precipitate the polythiophene as a powder.

Furthermore, when forming a salt-type polythiophene, for example, a stock solution of various amine compounds or ammonium salts, or an aqueous solution thereof, or a solution obtained by diluting such a compound with another suitable solvent, is added to the aqueous solution of the acid-type polythiophene. Although not particularly limited, for example, an aqueous solution of ammonium salt-type polythiophene in which M ⁺ is _NH4 ⁺ can be formed by adding ammonia to the aqueous solution of the acid-type polythiophene. If necessary, the obtained aqueous solution can also be added to a poor solvent such as acetone to obtain various ammonium salt-type polythiophenes in powder form.

[Additives]
The conductive polymer solution according to an embodiment of the present invention is characterized by containing a dialkylene glycol monoalkyl ether.

The above dialkylene glycol monoalkyl ethers may be used alone as pure products or as mixtures in any proportion.

The dialkylene glycol monoalkyl ether in the conductive polymer solution according to the embodiment of the present invention is not particularly limited, and examples thereof include diethylene glycol monoalkyl ether, diisopropylene glycol monoalkyl ether, and dipropylene glycol monoalkyl ether. More specifically, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-i-propyl ether, diethylene glycol monocyclopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-i-butyl ether, diethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-pentyl ether, diethylene glycol monocyclopentyl ether, diethylene glycol mono-n-hexyl ether, diethylene glycol monocyclohexyl ether, diethylene glycol mono-n-octyl ether, diisopropylene glycol monoethyl ether, diisopropylene glycol mono-n-propyl ether, diisopropylene glycol mono-i-propyl ether, diisopropylene glycol monocyclopropyl ether, and diisopropylene glycol. Mono-n-butyl ether, diisopropylene glycol mono-i-butyl ether, diisopropylene glycol mono-tert-butyl ether, diisopropylene glycol mono-n-pentyl ether, diisopropylene glycol monocyclopentyl ether, diisopropylene glycol mono-n-hexyl ether, diisopropylene glycol monocyclohexyl ether, diisopropylene glycol mono-n-octyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-i-propyl ether, dipropylene glycol monocyclopropyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-i-butyl ether, dipropylene glycol mono-tert-butyl ether, dipropylene glycol mono-n-pentyl ether, dipropylene glycol monocyclopentyl ether, dipropylene glycol mono-n-hexyl ether, dipropylene glycol Examples include monocyclohexyl ether and dipropylene glycol mono-n-octyl ether.

Of these, the dialkylene glycol monoalkyl ether is preferably at least one selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, and diethylene glycol mono-n-octyl ether, due to its excellent conductivity-enhancing effect, and more preferably at least one selected from the group consisting of diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, and diethylene glycol mono-n-octyl ether.

The concentration of dialkylene glycol monoalkyl ether in the conductive polymer solution according to an embodiment of the present invention is preferably 0.01 to 6% by weight from the viewpoint of improving film-forming properties, and more preferably 0.01 to 4% by weight from the viewpoint of excellent storage stability.

Regarding the content ratio of the π-conjugated conductive polymer to the dialkylene glycol monoalkyl ether, from the viewpoint of improving film-forming properties, the content of the dialkylene glycol monoalkyl ether is preferably 0.1 to 2 parts by weight, more preferably 0.15 to 1.5 parts by weight, and even more preferably 0.2 to 1.2 parts by weight, per 1 part by weight of the π-conjugated conductive polymer.

From the perspective of improving film-forming properties, the conductive polymer solution according to an embodiment of the present invention may further contain a dihydric or trihydric alcohol other than dialkylene glycol monoalkyl ether. The content of the dihydric or trihydric alcohol in the conductive polymer solution is preferably 0.01 to 20% by weight, and more preferably 0.1 to 10% by weight.

In addition, from the perspective of improving film-forming properties, the total content of dihydric or trihydric alcohols other than dialkylene glycol monoalkyl ethers and dialkylene glycol monoalkyl ethers in the conductive polymer solution is preferably 0.5 to 20% by weight, and more preferably 0.5 to 10% by weight.

Dihydric or trihydric alcohols other than dialkylene glycol monoalkyl ethers are not particularly limited, but examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, glycerin, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, glycerin, 1,2,6-hexanetriol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol diisopropyl ether, ethylene glycol dibutyl ether, ethylene glycol dihexyl ether, propylene glycol monomethyl ether, Examples of the ethylene glycol monoester include ethylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, propylene glycol diisopropyl ether, propylene glycol dibutyl ether, propylene glycol dihexyl ether, butylene glycol monomethyl ether, butylene glycol monoethyl ether, butylene glycol monopropyl ether, butylene glycol monoisopropyl ether, butylene glycol monobutyl ether, butylene glycol monohexyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol dipropyl ether, butylene glycol diisopropyl ether, butylene glycol dibutyl ether, butylene glycol dihexyl ether, etc. Among these, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monohexyl ether, and propylene glycol monobutyl ether are more preferred.

The conductive polymer solution of the present invention can be prepared by adding a predetermined amount of the dialkylene glycol monoalkyl ether to a solution containing the π-conjugated conductive polymer at 0 to 60°C, or by adding a mixed solvent of the dialkylene glycol monoalkyl ether and water to a solid π-conjugated conductive polymer.

After adding the dialkylene glycol monoalkyl ether to the solution containing the π-conjugated conductive polymer, it is preferable to stir the mixture to make it uniform. There are no particular restrictions on the stirring method used, as long as it can dissolve and disperse the mixture. For example, conventional stirring using propeller blades, paddle blades, Maxblend® blades (manufactured by Sumitomo Heavy Industries Process Equipment Co., Ltd.), Fullzone® blades (manufactured by Kobelco Eco-Solutions Co., Ltd.), disc turbines, etc., or a combination of forced stirring using a homomixer, ultrasonic homogenizer, high-pressure homogenizer, etc. may be used.

The conductive polymer solution according to the embodiment of the present invention may also contain components other than those described above. These components are not particularly limited, but may include, for example, water, organic solvents, water-soluble resin compounds, surfactants, polysaccharides, etc.

The organic solvent is preferably an organic solvent excluding the dialkylene glycol monoalkyl ethers and dihydric or trihydric alcohols other than the dialkylene glycol monoalkyl ethers. Examples of the organic solvent include, but are not limited to, methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, butoxyethanol, dimethylformamide, and dimethyl sulfoxide.

In the conductive polymer composition according to an embodiment of the present invention, water and the organic solvent may be contained alone or as a mixture. From the viewpoint of improving film-forming properties, the concentration of water, the organic solvent, or the mixture of water and the organic solvent is preferably 70 to 99.98% by weight, more preferably 75 to 99.9% by weight, and even more preferably 80 to 99% by weight.

The conductive polymer composition according to an embodiment of the present invention preferably contains water, the organic solvent, or a mixture of water and the organic solvent, and more preferably contains water.

The water-soluble resin compound is not particularly limited, but specifically, polyvinylpyrrolidone, a polyvinylpyrrolidone copolymer, a water-soluble polyester resin compound, or a water-soluble polyurethane resin compound is preferred, and these compounds may also be used in combination.

The surfactant is not particularly limited, but examples that can be used include anionic surfactants (e.g., sodium lauryl alcohol sulfate, sodium dodecylbenzenesulfonate, etc.), cationic surfactants (e.g., dodecyltrimethylammonium chloride, etc.), nonionic surfactants, amphoteric surfactants, fluorine-based surfactants, and silicone-based surfactants, but more preferably at least one selected from the group consisting of nonionic surfactants and amphoteric surfactants.

The polysaccharides mentioned above are not particularly limited, but examples include monosaccharides and disaccharides such as glucose, sucrose, fructose, galactose, maltose, and lactose, as well as compounds having a lactone ring such as L-ascorbic acid, erythorbic acid, glucuronic acid lactone, and glucaric acid lactone. Of these, glucose, sucrose, L-ascorbic acid, and erythorbic acid are preferred.

When the conductive polymer solution according to an embodiment of the present invention contains the above-mentioned water-soluble resin compound, surfactant, polysaccharide, or other components, the content of each of these components is preferably 0.1% by weight to 60% by weight, and more preferably 1% by weight to 40% by weight, based on 100% by weight of the conductive polymer solution when contained.

The pH of the conductive polymer solution according to the embodiment of the present invention is preferably 10 or less, and more preferably 9 or less. Furthermore, the pH of the conductive polymer solution according to the embodiment of the present invention is preferably in the range of 1.5 to 9.5, more preferably 1.5 to 9, and even more preferably 1.5 to 6. The procedure for adjusting the pH is not particularly limited, but examples include a method in which an amine compound, a basic compound, or an acidic compound is added to the conductive polymer solution in advance. Furthermore, when the conductive polymer solution according to the embodiment of the present invention is used in the acidic region of pH 2 or less, it is not necessarily necessary to add an amine.

[Conductive polymer thin film]
The conductive polymer solution described above can be applied to a substrate and then dried by heating to produce a conductive polymer thin film having the following characteristics.

A conductive polymer thin film according to an embodiment of the present invention contains a π-conjugated conductive polymer, and is characterized in that, in X-ray diffraction using the out-of-plane method, the half-width of the (100) plane diffraction peak detected near 2θ = 5 deg. is 0.9 deg. or less.

These characteristics of the conductive polymer thin film according to the embodiment of the present invention are not particularly limited, but are presumed to be brought about by the presence of the dialkylene glycol monoalkyl ether, which improves the structural regularity in the a-axis direction of the crystal when the π-conjugated conductive polymer forms a polycrystalline thin film. It is presumed that this characteristic structural regularity contributes to the conductive polymer thin film according to the embodiment of the present invention exhibiting high conductivity.

To obtain a conductive polymer thin film that exhibits high conductivity based on the highly regular crystalline structure, the half-width (also called "half-width") of the diffraction peak for the (100) plane near 2θ = 5° in out-of-plane X-ray diffraction of the conductive polymer thin film is preferably 0.9° or less, and more preferably 0.8° or less.

Furthermore, in order to obtain high conductivity, the conductive polymer thin film according to an embodiment of the present invention preferably has an X-ray diffraction ratio (peak area (B) ÷ peak area (A)) of the (020) plane diffraction peak detected at approximately 2θ = 25° relative to the peak area (A) of the (100) plane diffraction peak detected at approximately 2θ = 5° in out-of-plane measurement, and is therefore preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.03 or less.

The conductive polymer thin film preferably contains the above-mentioned π-conjugated conductive polymer, and more preferably contains a π-conjugated conductive polymer represented by polythiophene containing at least two or more structural units selected from the group consisting of structural units represented by general formula (1) and structural units represented by general formula (2).

The conductive polymer thin film according to an embodiment of the present invention is not particularly limited, but can be produced, for example, by applying a conductive polymer solution according to an embodiment of the present invention to a substrate and then drying it.

The substrate is not particularly limited, but examples include glass, plastic, polyester, polyacrylate, polycarbonate, and resist substrates. The coating method is not particularly limited, but examples include casting, dipping, bar coating, roll coating, gravure coating, flexographic printing, spray coating, and inkjet printing.

The drying temperature is not particularly limited as long as it is a temperature at which a uniformly dried conductive thin film is obtained and is equal to or lower than the heat resistance temperature of the substrate. However, a temperature in the range of room temperature (15-25°C) to 300°C is preferred, a temperature in the range of room temperature to 250°C is more preferred, and a temperature in the range of 90-250°C is even more preferred.

The drying atmosphere may be air, an inert gas, a vacuum, or a reduced pressure. From the perspective of preventing deterioration of the conductive film, an inert gas such as nitrogen or argon is preferred.

The thickness of the conductive polymer thin film according to the embodiment of the present invention is not particularly limited, but is preferably in the range of 1×10 ⁻² to 1×10 ² μm.

The π-conjugated conductive polymer thin film according to an embodiment of the present invention has a higher degree of crystalline structure regularity than conventional π-conjugated conductive polymer thin films, which has the effect of improving conductivity. The conductive polymer solution or conductive polymer thin film according to an embodiment of the present invention can be used in applications such as, but not limited to, data storage media, solar cells, rechargeable batteries, electrodes, light-emitting diodes, field-effect transistors, antistatic materials, coatings for copier drums, electric circuit boards, and solid electrolytic capacitors.

In addition, solid electrolytic capacitors can be preferably used in solid-state electrolyte storage batteries based on tantalum, niobium, or aluminum.

The conductive polymer solution according to the embodiment of the present invention can be used for various applications as is, or it can be used after adding conventionally known additives.

This configuration makes it possible to further increase the conductivity of conductive polymer thin films using conventionally known materials. This allows for improved performance of electronic circuits that include such thin films. Therefore, embodiments of the present invention are expected to contribute to the promotion of information transmission technology and the achievement of Sustainable Development Goals (SDGs) related to improved work motivation, industrial development, and environmental conservation, from the perspective of preventing the environmental impact of exhaust and wastewater treatment associated with the use of new materials.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

The following are examples of the conductive polymer solution and conductive polymer thin film of the present invention, but the present invention should not be construed as being limited to these examples. The analytical instruments and measurement methods used in these examples are listed below.

Gel Permeation Chromatography Analysis
2.4 g of a 50 wt % solution of N,N-diisopropylamine (DIPA) in methanol was added to 4.0 g of an aqueous solution containing approximately 0.7 to 1.0 wt % of a π-conjugated conductive polymer, and the mixture was slowly stirred overnight. The solid obtained after drying under reduced pressure was dissolved in 5.5 g of dimethyl sulfoxide (DMSO). The solution was then passed through a PVDF filter (0.45 μm) and analyzed under the following gel permeation chromatography conditions to estimate the number average molecular weight.
Column: TSKgel α-M + guard Column α manufactured by Tosoh Corporation
Eluent: DMSO / 10 mM TBA-Br (tetrabutylammonium bromide) / 10 mM DIPA (N,N-diisopropylamine)
・Flow rate: 0.6mL/min.
Detection: UV (335 nm)
・Temperature: 50℃
・Injection amount: 1000ppm (20μL)
Standard: PSS (polystyrene sulfonic acid)

[Conductivity measurement method]
2.0 mL of the solution containing the π-conjugated conductive polymer was applied to a 50 mm × 50 mm square non-alkali glass plate and dried on a hot plate in a nitrogen atmosphere at 120°C for 40 minutes. The dried coating film was then further dried at 200°C for 1 hour to obtain a conductive polymer thin film. The conductivity was calculated from the film thickness and surface resistivity of the obtained conductive polymer thin film using the following formula.
Electrical conductivity [S/cm] = 10 ⁴ / (Surface resistivity [Ω/□] x Film thickness [μm])

The film thickness of the conductive polymer thin film was measured using a BRUKER stylus profiling system "DEKTAK XT." The surface resistivity of the conductive polymer thin film was measured using a Mitsubishi Chemical Corporation resistivity meter "LORESTA GP MCP-T600."

Synthesis Example 1 Synthesis of Polythiophene (PT) According to a conventionally known production method, an aqueous solution of polythiophene-1 [PT- ¹ , a polymer containing repeating units represented by the following formulas (4) and (5)], which is a π-conjugated conductive polymer, was obtained using a monomer represented by the following formula (3), in which R1 is a methyl group, m = 2, n = 1, and M is a hydrogen atom. As a result of gel permeation chromatography analysis, the number average molecular weight of the polythiophene-1 calculated as polystyrene sulfonic acid was 3,721.

Comparative Example 1
Using the above-mentioned aqueous solution of polythiophene-1 prepared to a concentration of 1.2 wt %, a conductive polymer thin film was prepared according to the above-mentioned conductivity measurement method, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 759 S/cm.

Synthesis Example 2: Synthesis of polythiophene [0049] According to a conventionally known production method, an aqueous solution of polythiophene-2 [PT-2, a polymer containing repeating units represented by the above formulas (4) and (5)], which is a π-conjugated conductive polymer, was obtained using the monomer represented by the above formula (3). As a result of gel permeation chromatography analysis, the number average molecular weight of the polythiophene-2 calculated as polystyrene sulfonic acid was 3,448.

Comparative Example 2
A conductive polymer thin film was prepared using the above-mentioned aqueous solution of polythiophene-2 adjusted to a concentration of 1.2 wt % according to the above-mentioned conductivity measurement method, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 452 S/cm.

Comparative Example 3
To 6.03 g of the 1.2 wt % aqueous solution of polythiophene-1 obtained in Synthesis Example 1, 19.3 mg of diethylene glycol (DEG) (0.32 wt % relative to the total amount of the conductive polymer solution) was added and stirred for 12 hours to obtain a conductive polymer solution. The diethylene glycol content was 0.27 parts by weight relative to 1 part by weight of the π-conjugated conductive polymer. Using the obtained conductive polymer solution, a conductive polymer thin film was produced according to the conductivity measurement method described above, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 696 S/cm.

Comparative Example 4
To 6.02 g of the 1.2 wt % aqueous solution of polythiophene-1 obtained in Synthesis Example 1, 37.6 mg of diethylene glycol (0.62 wt % relative to the total amount of the conductive polymer solution) was added and stirred for 12 hours to obtain a conductive polymer solution. The diethylene glycol content was 0.52 parts by weight relative to 1 part by weight of the π-conjugated conductive polymer. Using the obtained conductive polymer solution, a conductive polymer thin film was produced according to the conductivity measurement method described above, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 693 S/cm.

Example 1
To 6.02 g of the 1.2 wt % aqueous solution of polythiophene-1 obtained in Synthesis Example 1, 17.1 mg of diethylene glycol mono-n-hexyl ether (HxDEG) (0.28 wt % relative to the total amount of the conductive polymer solution) was added and stirred for 12 hours to obtain a conductive polymer solution of the present invention. The content of dialkylene glycol monoalkyl ether was 0.23 parts by weight relative to 1 part by weight of the π-conjugated conductive polymer. Using the obtained conductive polymer solution, a conductive polymer thin film was produced according to the conductivity measurement method described above, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 829 S/cm.

Example 2
To 6.02 g of the 1.2 wt % aqueous solution of polythiophene-1 obtained in Synthesis Example 1, 25.9 mg of diethylene glycol mono-n-hexyl ether (0.43 wt % relative to the total amount of the conductive polymer solution) was added and stirred for 12 hours to obtain a conductive polymer solution of the present invention. The content of dialkylene glycol monoalkyl ether was 0.36 parts by weight relative to 1 part by weight of the π-conjugated conductive polymer. Using the obtained conductive polymer solution, a conductive polymer thin film was produced according to the conductivity measurement method described above, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 772 S/cm.

Example 3
To 6.16 g of the 1.2 wt % aqueous solution of polythiophene-2 obtained in Synthesis Example 2, 24.9 mg of diethylene glycol mono-n-hexyl ether (0.40 wt % relative to the total amount of the conductive polymer solution) was added and stirred for 12 hours to obtain a conductive polymer solution of the present invention. The content of dialkylene glycol monoalkyl ether was 0.33 parts by weight relative to 1 part by weight of the π-conjugated conductive polymer. Using the obtained conductive polymer solution, a conductive polymer thin film was produced according to the conductivity measurement method described above, and the conductivity was measured. The conductivity of the obtained conductive polymer thin film was 465 S/cm.

The compositions of the conductive polymer solutions in the above examples and comparative examples, and the conductivities of the conductive polymer thin films prepared from these solutions, are shown in Table 1. In the table, "PT" stands for polythiophene, "HxDEG" stands for diethylene glycol mono-n-hexyl ether, and "DEG" stands for diethylene glycol.

[Structural regularity of conductive polymer thin films]
X-ray diffraction (out-of-plane measurement) was performed on the conductive polymer thin film obtained in Example 1 under the following conditions. The apparatus used was a multipurpose X-ray diffraction apparatus "SmartLab" (manufactured by Rigaku). The X-ray source used was CuKα radiation, 45 kV, 200 mA (collimated optical system).
<Out-of-plane measurement>
θ/2θ scan Scanning range: 2°≦2θ≦40°
Scanning speed: 1.25 deg./min.
Scanning step: 0.02 deg.

Figure 1 shows the diffraction pattern obtained by out-of-plane parallel optical system X-ray diffraction measurement of the conductive polymer thin film of Example 1.

The scan results were assigned based on a published document (Science Advances, 5(4), eaav9492, 2019). For the thin film of Example 1, a (100) diffraction peak (2θ = 5.43°), a (200) diffraction peak (2θ = 10.66°), and a (020) diffraction peak (2θ = 25.21°) were detected, and the half-width of the (100) diffraction peak was 0.75°.

The ratio of the peak area (B) of the diffraction peak of the (020) plane to the peak area (A) of the diffraction peak of the (100) plane of the conductive polymer thin film obtained in Example 1 (peak area (B) ÷ peak area (A), B/A) was 0.017.

Similarly, X-ray diffraction (out-of-plane measurement) was performed on the conductive polymer thin film obtained in Comparative Example 1 under the same conditions as for the conductive polymer thin film of Example 1.

Figure 1 shows the diffraction pattern obtained by out-of-plane parallel optical system X-ray diffraction measurement of the conductive polymer thin film of Comparative Example 1.

The scan results were assigned according to a published literature reference (Science Advances, 5(4), eaav9492, 2019). A (100) diffraction peak (2θ = 5.45°), a (200) diffraction peak (2θ = 10.67°), and a (020) diffraction peak (2θ = 24.78°) were detected. The half-width of the (100) diffraction peak was 1.17°.

The ratio of the peak area (B) of the diffraction peak of the (020) plane to the peak area (A) of the diffraction peak of the (100) plane of the conductive polymer thin film obtained in Comparative Example 1 (peak area (B) ÷ peak area (A)) was 0.14.

The results of X-ray crystal structure analysis of the above conductive polymer thin film are shown in Table 2.

In Synthesis Examples 1 and 2, π-conjugated conductive polymers with different molecular weights were obtained, and as shown in Comparative Examples 1 and 2, the π-conjugated conductive polymer of Synthesis Example 1, which had a higher molecular weight, had higher conductivity.

Comparing the results of Comparative Example 1 with those of Examples 1 and 2, it was found that adding an appropriate amount of diethylene glycol mono-n-hexyl ether to the aqueous polythiophene solution of Synthesis Example 1 before forming a film improved conductivity compared to when no diethylene glycol mono-n-hexyl ether was added.

Comparing the results of Comparative Example 2 and Example 3, it was found that even in the aqueous polythiophene solution of Synthesis Example 2, which has a different molecular weight than Synthesis Example 1, the addition of an appropriate amount of diethylene glycol mono-n-hexyl ether improved conductivity compared to when no diethylene glycol mono-n-hexyl ether was added. This demonstrates that diethylene glycol mono-n-hexyl ether has the effect of improving the conductivity of conductive polymer thin films, regardless of the molecular weight of the π-conjugated conductive polymer. It was also found that the greater the molecular weight of the π-conjugated conductive polymer, the greater the effect of improving conductivity.

A comparison of the results of Comparative Example 1 with those of Comparative Examples 3 and 4 shows that when diethylene glycol was added to the aqueous polythiophene solution of Synthesis Example 1, the conductivity-enhancing effect observed in Examples 1 and 2 was not observed.

From this, it is speculated that the aforementioned conductivity improvement effect was achieved by changing the additive dialkylene glycol to a monoalkyl ether.

A comparison of the X-ray diffraction results for the conductive polymer thin film of Example 1 and the conductive polymer thin film of Comparative Example 1 revealed that the π-conjugated conductive polymer solution containing diethylene glycol mono-n-hexyl ether had a sharper (100) diffraction peak shape and a significantly reduced half-width compared to the π-conjugated conductive polymer solution not containing diethylene glycol mono-n-hexyl ether. In particular, the half-width for the thin film of Example 1, which exhibited the highest conductivity, was less than 0.8 deg.

Since a decrease in the half-width of the diffraction peak indicates improved regularity in the crystalline structure, it is speculated that adding diethylene glycol mono-n-hexyl ether to an aqueous solution of a π-type conductive polymer improves the regularity of the crystalline structure in the conductive polymer thin film produced from the conductive polymer solution, thereby improving the conductive paths for charge carriers moving through the thin film and improving conductivity.

Since a highly ordered crystal structure has excellent thermodynamic stability, the conductive polymer thin film of the present invention is expected to have high heat resistance.

A known patent document (JP 2021-42266 A) discusses the results of X-ray diffraction analysis of a thin film of conductive polythiophene synthesized by a conventional manufacturing method. The polythiophene thin film in this document had a (100) diffraction peak half-width of 1.0 deg.

The (100) diffraction peak half-width of the conductive polymer thin film of Example 1 of the present invention was less than 0.8 deg., indicating that the conductive polythiophene thin film of the present invention has a significantly higher degree of regularity in its crystalline structure than the conductive polythiophene thin film described in the known patent document (JP 2021-42266 A).

Furthermore, the ratio of the peak area (B) of the diffraction peak of the (020) plane to the peak area (A) of the diffraction peak of the (100) plane in the conductive polymer thin film of Example 1 of the present invention (peak area (B) ÷ peak area (A)) is less than 0.02. Therefore, the polythiophene thin film of the present invention has edge-on orientation comparable to that of the polythiophene thin film described in the publicly known literature (JP 2021-42266 A).

From this, it can be said that the polythiophene thin film of the present invention has edge-on orientation comparable to that of the polythiophene thin film described in a publicly known patent document (JP 2021-42266 A), and also has a high degree of regularity in its crystal structure that significantly exceeds that of the polythiophene thin film described in said patent document. Based on this high degree of regularity in its crystal structure, the polythiophene thin film of the present invention is expected to have superior dimensional stability. In other words, since capacitors equipped with the polythiophene thin film of the present invention exhibit minimal dimensional change due to temperature changes, it is expected that the risk of performance degradation due to repeated use will be reduced.

From the above, it is believed that the dialkylene glycol monoalkyl ether, an essential component of the present invention, has the effect of inducing the formation of a π-conjugated conductive polymer thin film with a highly regular crystalline structure, as shown in the example of diethylene glycol mono-n-hexyl ether. Furthermore, in the formation of a π-conjugated conductive polymer thin film, it is believed to have the effect of improving the conductive paths in the thin film and increasing the conductivity of the thin film.

The conductive polymer thin film of the present invention is expected to contribute to improving the performance of antistatic materials, LCDs, organic EL displays, solid electrolytes or transparent electrodes in capacitors, etc.

Claims (8)

The conductive polymer contains a π-conjugated conductive polymer and a dialkylene glycol monoalkyl ether ,
the content ratio of the dialkylene glycol monoalkyl ether relative to 1 part by weight of the π-conjugated conductive polymer is 0.1 to 2 parts by weight;
Conductive polymer solution. The conductive polymer solution according to claim 1, wherein the content of the π-conjugated conductive polymer is 0.01 to 10% by weight, and the content of the dialkylene glycol monoalkyl ether is 0.01 to 6% by weight. 3. The conductive polymer solution according to claim 1, wherein the π-conjugated conductive polymer is a polythiophene containing at least two or more structural units of at least one type selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2):
[In general formula (1), M ⁺ represents a hydrogen ion, an alkali metal ion, a conjugate acid of an amine compound, or a quaternary ammonium cation. In general formulas (1) and (2), ^R1 represents a hydrogen atom, a methyl group, an ethyl group, a linear or branched alkyl group having 3 to 6 carbon atoms, or a fluorine atom; m independently represents an integer of 1 to 10; and n independently represents 0 or 1.] The conductive polymer solution according to claim 3 , wherein R ¹ is a hydrogen atom, a methyl group, or a fluorine atom. The conductive polymer solution according to claim 3 or 4 , wherein the M ⁺ is a hydrogen ion. The conductive polymer solution according to any one of claims 3 to 5 , wherein the polythiophene has a number average molecular weight of 3,500 or more as calculated on polystyrene sulfonic acid basis, as measured by gel permeation chromatography. 7. The conductive polymer solution according to claim 1, wherein the dialkylene glycol monoalkyl ether is at least one selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono- n -hexyl ether, and diethylene glycol mono-n-octyl ether. A method for producing a conductive polymer thin film, comprising applying the conductive polymer solution according to any one of claims 1 to 7 to a substrate, and then drying the applied conductive polymer solution by heating.