DE102015117207A1 - Process for the preparation of polythiophene-containing fluids - Google Patents

Abstract

The present invention is a process for the preparation of polythiophenhaltigen fluids, comprising the following step: reaction of at least one thiophene oligomer with an oxidant selected from metal salts in a predominantly organic reaction medium, wherein the solvent content of the reaction medium to at least 40% by weight of one or more low molecular weight compounds having a number average molecular weight (Mn) of up to 2,000 selected from the group of alkylene glycols, polyalkylene glycols, monoether derivatives, diether derivatives, monoester derivatives, diester derivatives and ether ester derivatives the alkylene glycols or polyalkylene glycols. Further objects of the present invention are a polythiophene-containing fluid and the use of a polythiophene-containing fluid for coating substrates, coated substrates and thermoelectric generators (TEGs) comprising the coated substrates.

Description

The invention relates to a process for the production of polythiophene-containing fluids, a polythiophene-containing fluid, and the use of a polythiophene-containing fluid for coating substrates. The invention further relates to coated substrates and thermoelectric generators (TEGs) comprising the coated substrates.

Much of the energy used by humans is released into the environment in the form of heat. One promising approach for generating electricity is thermoelectric systems operating in a low temperature range. Such systems, which can also be used in the reverse direction as Peltier elements, include thermoelectric generators (TEGs).

A TEG with two different, a thermocouple forming thermoelectrically active materials, which are electrically connected in series and thermally connected in parallel, is for example from DE 102012105086 known. In this case, the thermoelectrically active materials are applied in layers of 1 to 100 micrometers thickness to a flexible and electrically insulating film which is wound and folded such that n- and p-semiconductive layers are arranged as thermo legs.

Particularly suitable as thermoelectrically active materials are electrically conductive polymers, since these combine both the typical properties of a polymer, such as a low weight, high elasticity and corrosion resistance, with an intrinsic electrical conductivity. Prerequisite for the conductivity of the polymers is a doping of the polymers. In addition to polyacetylene, polyaniline, polypyrrole, polycarbazole and the like, polythiophenes are particularly suitable because of their very high electrical conductivity and stability to ambient air in the doped form. A large number of different monomers having a thiophene backbone which can be converted to conductive polythiophenes is known from the relevant literature ( Elschner, Andreas et al. ; PEDOT: Principles and Applications of an Intrinsically Conductive Polymer, pages 33 to 46 ; ISBN 9781420069112 ). Particular attention is given to the 3,4-ethylenedioxy-substituted thiophene EDOT and its derivatives, since these are used for a wide variety of applications.

For the simultaneous polymerization and doping of thiophenes, a chemical oxidative polymerization can be carried out. The resulting conductive polythiophenes are present as cations whose charge is compensated by anions. A common method is to simultaneously react monomeric thiophenes with oxidizing agents such as inorganic iron (III) salts or iron (III) salts of organic acids in organic solvents in heat to form a polythiophene and to dope. The disadvantage here is that only insoluble coatings of polythiophenes can be generated in situ on substrates which have a too small layer thickness for TEGs. Another disadvantage is that the coatings still contain all the residues of the reaction. The residues consist predominantly of water-soluble excess iron (III) salts and / or reduced iron (II) salts and / or of acids formed during the reaction from the oxidizing agents. Further residues consist of unreacted monomers. These residues reduce the electrical conductivity and must be removed by aftertreatment of the coatings with a correspondingly high expenditure of time, which makes the in situ polymerization for coatings on an industrial scale, as required for the production of TEGs, unsuitable.

Experiments by the inventor have shown that oxidative polymerization can be used to produce a dispersion or solution which contains doped polythiophenes in a liquid medium when starting oligomeric starting compounds which consist of at least two repeat units. To carry out the process, thiophene oligomers dissolved in organic solvents are oxidatively reacted at room temperature with a molar excess of an oxidizing agent. In the presence of high molecular weight polymeric additives such as long-chain polyethylene glycols having a molecular weight of about 100,000, highly viscous polythiophene-containing fluids are formed within seconds or minutes, which can then be applied to a substrate and subsequently dried. A summary of the method and the results obtained with the method can be found in Comparative Example 1 of the description. From this it can also be seen that the method has considerable advantages over the usual in-situ polymerization. Above all, the process for TEGs can produce suitable coatings with a layer thickness of more than one micrometer. In addition, the fluids can be applied in a controlled manner, for example, by printing processes on the substrates to be coated. It is also possible to purify the polythiophene-containing fluids prior to generating a coating of reaction residues by extracting the residues from the fluid. The extraction step can now advantageously be carried out with stirring or shaking, which promotes extraction of the residues.

One difficulty in purifying the polythiophene-containing fluids is that large quantities of aqueous solutions must be used to separate the predominantly water-soluble residues. A disadvantage of this is that the resulting solution in the washing step can only be freed of residues by a very time-consuming filtration. A further disadvantage is that undesirably large amounts of solvent and residues soluble in organic solvents, such as excess starting compounds of the polymerization, remain in the purified fluid. Also, the high molecular weight polymeric additives of the reaction are a problem because they also can not be dissolved out of the fluid and adversely affect the electrical conductivity of the polythiophene.

So far it has been possible with the purified polythiophene-containing fluid to produce coatings which have a suitable conductivity for TEGs. As the thermoelectric efficiency of TEGs increases with increasing electrical conductivity of the coatings, it has been desired to increase them.

It was therefore an object of the invention to provide, based on the results of the inventor, an improved process with which polythiophene-containing fluids can be obtained by oxidative polymerization, which can be freed of residues of the reaction as far as possible before they are applied as a coating on substrates.

The object is achieved by a method according to claim 1. Preferred embodiments are provided in subclaims under protection.

The process according to the invention for the production of polythiophene-containing fluids comprises the following step:

Reacting at least one thiophene oligomer with an oxidizing agent selected from metal salts in a predominantly organic reaction medium, wherein the solvent content of the reaction medium to at least 40% by weight of one or more low molecular weight compounds having a number average molecular weight (M _n ) of up to 2,000, selected from the group of the alkylene glycols, the polyalkylene glycols, the monoether derivatives, the diether derivatives, the monoester derivatives, the diester derivatives and the ether-ester derivatives of the alkylene glycols or polyalkylene glycols.

It has surprisingly been found that low molecular weight compounds having a molecular weight (M _n ) of up to 2,000, selected from the group of alkylene glycols and polyalkylene glycols and their mono- and diether derivatives, mono- and diester derivatives and ether-ester derivatives , which are referred to as "low molecular weight compounds" for the purposes of the present invention, are outstandingly suitable as a reaction medium for the reaction step.

It has been found that both thiophene oligomers and the oxidants selected from the metal salts are readily soluble in the low molecular weight compounds.

Surprisingly, without the addition of high molecular weight polymeric additives within a few seconds to a few minutes in the reaction step, a polythiophene-containing fluid of homogeneous nature is obtained. The term "homogeneous texture" in the present invention means the freedom or substantial freedom of the fluid from polymer agglomerates and aggregates. The polythiophenes are dissolved or dispersed in the fluid obtainable by the reaction and are stabilized by the low molecular weight compounds. The transition between the dissolved and the dispersed form is in this case flowing, so that no distinction is to be made in this regard in the present invention.

The use of the low molecular weight compounds affords the distinct advantage that the polythiophene-containing fluid obtained in the reaction can now be freed from residues of the reaction very well by treatment with aqueous and / or organic extractants. Another great advantage is that the polythiophene-containing fluid can also be treated with efficient purification methods involving sedimentation steps by means of centrifugation. As a result, it is now possible for the first time to efficiently remove the residues of the reaction from a polythiophene-containing fluid in a cleaning preceding the coating. In turn, coatings of higher conductivity can be obtained, which are also suitable for the production of TEGs on an industrial scale.

In principle, any low molecular weight compounds or mixtures of low molecular weight compounds having a number average molecular weight (M _n ) of up to 2,000, selected from the group of alkylene glycols and polyalkylene glycols and their mono- and diether derivatives, mono- and diester derivatives and ether esters -Derivate suitable for carrying out the method according to the invention. The molecular weight (M _n ) can be determined, for example, by gel permeation chromatography. Preferably, the one or more low molecular weight compounds have a molecular weight (M _n ) of up to 1,000, more preferably of up to 800, more preferably between 70 and 800, most preferably between 70 and 300, most preferably between 100 and 300. If the reaction medium comprises several low molecular weight compounds, these may be of the same or different molecular weight. It is likewise possible to use any mixtures of alkylene glycols and / or polyalkylene glycols and / or their monoether derivatives and / or their diether derivatives and / or their monoester derivatives and / or their diester derivatives and / or their ether-ester derivatives use.

Alkylene glycols and polyalkylene glycols and derivatives thereof are known in principle to the person skilled in the art and can be prepared by known standard methods or are commercially available. By "alkylene glycols" in the present invention are meant low molecular weight compounds having up to 5 alkylene units and free terminal hydroxyl groups. The term "polyalkylene glycol" in the present invention refers to low molecular weight compounds having more than 5 alkylene units and free terminal hydroxyl groups. In particular, the alkylene units are ethylene and propylene units. But also alkylene glycols or polyalkylene glycols, such as based on methylene, butylene, pentylene, hexylene, etc. are useful. Also included are random copolymers and block copolymers, in particular based on ethylene and propylene glycols. Examples of alkylene glycols are ethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol and tripropylene glycol. Particularly suitable alkylene glycols are triethylene glycol and tetraethylene glycol.

Other suitable low molecular weight compounds include derivatives of the alkylene glycols or polyalkylene glycols. The term "derivative" in the present invention comprises all derivatives of the alkylene glycols or polyalkylene glycols in which at least one hydroxyl end group is etherified or esterified. Included here are mono- and diether derivatives, mono- and diester derivatives and ether-ester derivatives of alkylene glycols and polyalkylene glycols.

Suitable ether groups include linear and branched C ₁ -C ₁₀ alkyl ethers. As examples of monoether derivatives, there may be mentioned ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, triethylene glycol monomethyl ether and triethylene glycol monobutyl ether. Particularly suitable is triethylene glycol monomethyl ether. As a suitable example of a diether derivative, ethylene glycol dimethyl ether may be listed.

Suitable ester groups include esters derived from carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid and the like. In this case, one or both hydroxyl end groups of the alkylene glycols or polyalkylene glycols may be esterified with a carboxylic acid.

Ether-ester derivatives include alkylene glycols and polyalkylene glycols in which one terminal hydroxyl group is etherified and one terminal hydroxyl group is esterified. As examples of ether-ester derivatives, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate or ethylene glycol monobutyl ether acetate can be listed.

The one or more low molecular weight compounds are preferably selected from the group of the alkylene glycols, the polyalkylene glycols and monoether derivatives of the alkylene glycols or polyalkylene glycols, particularly preferably the one or more low molecular weight compounds selected from the group of alkylene glycols and polyalkylene glycols.

Any thiophene oligomers are suitable for carrying out the process according to the invention. The term "thiophene oligomer" in the present invention means thiophenes having at least two repeating units. The repeating units may be identical or different. The synthesis of thiophene oligomers is known from the relevant literature, such as from GA Sotzing, JR Reynolds, PJ Steel Advanced Materials 1997, 9, pages 795-79 8 or off GA Sotzing, JR Reynolds in Advanced Materials 1996, 8, pages 882-889 , Particularly suitable thiophene oligomers may contain between 2 and 4 repeating units. Ter-thiophenes having 3 repeat units are considered to be very useful, especially ter- (ethylene-3,4-dioxythiophene) (TerEDOT). This is preferred Thiophene oligomer is a bi-thiophene with 2 repeating units, particularly preferred is the thiophene oligomer bi- (ethylene-3,4-dioxythiophene) (BiEDOT).

The thiophene oligomer can be converted as such or in admixture with one or more other thiophene oligomers to polymers. When the thiophene oligomer is reacted in admixture with one or more other thiophene oligomers, thiophene oligomers having the same number of repeat units or having a different number of repeat units in any mixing ratio can be oxidatively oxidized to polythiophenes having identical or different repeat units. In the present invention, the term "polythiophene", irrespective of the chain length, comprises the polymerization products obtained by the reaction step of the process according to the invention.

The polythiophene poly (ethylene-3,4-dioxythiophene) (PEDOT) is preferably obtained with the reaction.

For the purposes of the present invention, the at least one thiophene oligomer can also be reacted together with monomeric thiophenes to give polythiophenes having identical or different repeating units. The thiophene oligomer may be reacted as such or in admixture with one or more other thiophene oligomers together with a thiophene monomer or mixtures of two or more different thiophene monomers. The proportion of thiophene monomer with which a fluid is obtained can be determined by one skilled in the art. In this variant of the present invention, it may be advantageous if the molar ratio of thiophene oligomer to thiophene monomer is ≥0.05: 1. Particularly advantageous may be a molar ratio of ≥0.1: 1 of thiophene oligomer to thiophene monomer, particularly advantageously of ≥0.5: 1, most preferably of ≥1: 1. This is advantageous because in these conditions fluids can be obtained which have a homogeneous nature. Advantageously, bi-thiophenes can be reacted together with thiophene monomers. It may sometimes be particularly advantageous to implement BiEDOT together with EDOT.

The thiophene oligomer is usually provided in a reaction mixture for the reaction. The reaction mixture contains, in addition to the thiophene oligomer, at least the reaction medium and an oxidizing agent. In addition, at least one thiophene monomer and additives may be included. The amount of thiophene oligomer can be varied within a wide range and is not limited to the following examples. Highly suitable reaction mixtures can be from 0.05% to 10% by weight of thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer. Particularly suitable reaction mixtures may be from 0.1% to 5% by weight of thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer. Even more suitable reaction mixtures may be from 0.5% to 2.5% by weight of thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer. Very particularly suitable reaction mixtures may be from 0.7% to 1.5% by weight of thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer.

The preparation of the reaction mixture can be carried out in any manner which results in the solution or most complete dissolution of the thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer and the oxidizing agent in the reaction medium. Corresponding methods are known to the person skilled in the art and can be used depending on the thiophene oligomer chosen for the reaction or a mixture of thiophene oligomer and thiophene monomer and oxidizing agent. Advantageously, the thiophene oligomer, optionally the thiophene monomer, the oxidizing agent and optionally additional additives in dissolved form are fed to the reaction mixture. Advantageously, the thiophene oligomer and / or the oxidizing agent are dissolved in the reaction medium. The order of feeding is not critical. Advantageously, the solution containing the oxidizing agent is introduced and the solution containing the thiophene oligomer is added. It is advantageous if the addition of the solution containing the thiophene oligomer takes place over a period of a few seconds to a few minutes.

Advantageously, the reaction mixture is prepared with stirring or shaking. This ensures good mixing of the solutions.

The reaction is initiated by the contact of thiophene oligomer and / or thiophene monomer with the oxidizing agents. The reaction can be carried out continuously or in several stages, optionally with further addition of thiophene oligomer and / or thiophene monomer and / or oxidant. Advantageously, the reaction is carried out with stirring or shaking. As a result, a uniform implementation is promoted. The duration of the reaction can vary widely and depends in particular on the thiophene oligomer used and / or thiophene monomer, the oxidizing agent and optionally other additives.

The oxidizing agents useful in carrying out the process have the task of oxidizing and polymerizing the thiophene oligomer or the mixture of thiphene oligomer and thiophene monomer. The polymerization is based on a cationic-radical reaction mechanism in which the oxidizing agent is consumed. Any metal salts are suitable for this purpose. The metal salts may in particular be inorganic metal salts which contain the electron acceptors Fe ³⁺ , Ce ⁴⁺ , Cu ²⁺ , Au ³⁺ , or Mn ⁴⁺ as well as chloride, chlorate, nitrate or sulfate as the anionic component. Also suitable are metal salts of organic acids, for example with benzenesulfonate, 4-ethylbenzenesulfonate or tosylate as anion. Any combination of electron acceptor and anion may be useful. Preferred oxidizing agents include ferric chloride and ferric tosylate. Particularly preferred is the iron (III) tosylate.

The oxidizing agent is added in an amount suitable for the oxidative polymerization. If desired, several of the oxidizing agents can be used for a reaction. In oxidative polymerization, cationic polythiophenes are formed which are capable of accepting anions. The term "conductive polythiophene" in the present invention refers to cationic polythiophenes doped with anions, the charge of which is compensated or at least largely compensated for by anions incorporated in the polythiophenes. It is advantageous if the cationic polythiophenes are doped by the anions of the oxidizing agent. This is advantageous because no additional anions need to be added. Advantageously, the cationic polythiophenes are doped by tosylate anions. It is particularly advantageous if cationic PEDOT is doped with tosylate, since the reaction gives rise to the very highly conductive polythiophene PE-DOT: tosylate (PEDOT: Tos).

Ideally, the oxidizing agent is used in a ratio to thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer in which the highest possible electrical conductivity of the polythiophene can be achieved. Depending on the oxidation potential of the oxidizing agent, different amounts of oxidizing agent may be suitable to obtain conductive polythiophenes. Particularly suitable ratios include the reaction of thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer with the oxidizing agents iron (III) tosylate or iron (III) chloride in a molar ratio of oxidant to thiophene oligomer or a Mixture of thiophene oligomer and thiophene monomer of ≥1: 1. Particularly suitable is a molar ratio between 2: 1 and 2.7: 1, particularly suitable is a molar ratio of about 2.25: 1 of oxidizing agent to thiophene oligomer or a mixture of thiophene oligomer and thiophene monomer.

Any liquid, organic reaction media are suitable for carrying out the present invention in which the thiophene oligomer, optionally the thiophene monomer, the oxidizing agent selected from metal salts and optionally further additives can be dissolved or largely dissolved and in which the oxidative polymerization with the oxidizing agents can expire. For the purposes of the invention, a "predominantly organic reaction medium" means all reaction media which contain a proportion of more than 80% by weight of organic solvent or mixtures of organic solvents, wherein the solvents do not participate chemically or substantially in the reaction with the oxidizing agent are. In addition to the low molecular weight compounds, a wide variety of solvents or solvent mixtures can provide the solvent content of the reaction medium. Suitable solvents or solvent mixtures are miscible with the low molecular weight compounds and the thiophene oligomer, optionally the thiophene monomer, as well as the oxidizing agent have good solubility in them. As exemplary examples, dimethylformamide, anisole, toluene or alcohols such as 2-propanol and mixtures of these solvents can be listed. However, the invention is not limited to these examples. Advantageously, however, in the implementation of the method on the use of harmful solvents such as anisole can be omitted and the solvent content of the reaction medium can be free of aromatics. In particular, suitable reaction media contain a proportion of between 90 wt .-% and 100 wt .-% of organic solvent or mixtures of organic solvents, particularly advantageously, a proportion of between 90 wt .-% and 99 wt .-%, in particular advantageous can Be proportion of between 95 wt .-% and 98 wt .-%. The reaction medium may in appropriate amounts of water or aqueous solutions, as far as miscible with the solvents.

In preferred reaction media, the solvent content is at least 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight or 70% by weight, particularly preferably at least 75% by weight .- %, 80 wt .-% or 85 wt .-%, particularly preferably at least 90 wt .-%, most preferably at least 95 wt .-% of one or more of the low molecular weight compounds. Most preferably according to the invention, the solvent portion of the reaction medium consists exclusively of one or more low molecular weight compounds. It is advantageous that in the reaction step, a polythiophene-containing fluid is available, which has a very homogeneous nature and which is very well suited for coating substrates. In addition, it is advantageous that it is also possible to dispense completely with other organic solvents which may be harmful to health.

The process of the invention can be carried out in a wide temperature range. Advantageously, the reaction is carried out at room temperature. However, it may also be useful to carry out the reaction at lower or higher temperatures, for example between -30 ° C and 150 ° C, in particular between 20 ° C and 35 ° C. The inventive method is not limited to the temperature ranges mentioned.

Further advantageous embodiments of the method provide for carrying out the reaction in the presence of additives. Suitable additives are, for example, bases or detergents.

The reaction is preferably carried out in the presence of a base. This is particularly advantageous when the reaction medium contains acids that can interfere with the cationic radical polymerization reaction. If oxidizing agents are used from which acids, such as, for example, HCl or p-toluenesulfonic acid in the case of metal chlorides or metal tosylates, are formed as by-products of the polymerization, addition of bases is particularly advantageous. For neutralization of the acids, for example, simple nitrogen-containing bases such as alkylamines, but also inorganic carbonates are suitable. However, preference is given to sterically demanding nitrogen-containing bases, also known as proton scavengers, since in the presence of these bases it is possible to produce fluids whose coatings on substrates have particularly high electrical conductivities. More preferably, the nitrogen-containing base is selected from the following group, since these bases least disturb the oxidation potential of the oxidants:

Most preferably, the nitrogenous base is 2,6-lutidine.

According to a further preferred embodiment of the process, a treatment for removing residues of the reaction follows directly or indirectly to the reaction. This is advantageous because it allows polythiophene-containing fluids of high purity to be obtained. The term "high purity" in the present invention means a freedom or most freedom of the polythiophene-containing fluid from residues of the reaction. The purity manifests itself in particular in a higher conductivity of coatings which can be obtained by means of the treated polythiophene-containing fluids.

Preferably, the residue removal treatment is carried out by contacting the fluid with an extractant to dissolve the residues in the extractant, and separating the residues dissolved in the extractant from the fluid.

In principle, all extractants that are miscible with the reaction medium and that are capable of dissolving the residues of the reaction are useful for the extraction. However, particularly suitable is an extractant containing one or more low molecular weight compounds. Here, the low molecular weight compounds used for the extraction may be identical or different from those of the reaction medium. In addition, it may be advantageous to choose the concentrations of low molecular weight compounds in the extractant different from those of the reaction medium. Particularly suitable extractants consist of at least 30 wt .-%, 35 wt .-%, 40 wt .-%, 45 wt .-%, 50 wt .-%, 55 wt .-%, 60 wt .-%, 70 Wt .-%, 80 wt .-% or 90 wt .-% of one or more of the low molecular weight compounds. Further constituents may be solvents or solvent mixtures and / or water. As examples of solvents, dimethylformamide (DMF) and dimethylsulfoxide (DMSO) can be listed. Also particularly suitable is an extractant which consists of 100 wt .-% of one or more low molecular weight compounds. The advantage of an extractant consisting exclusively of one or more low molecular weight compounds is that it becomes possible to obtain purified, anhydrous polythiophene-containing fluids. However, particularly suitable extractants include water and consist of 30 wt .-% to 70 wt .-%, to 40 wt .-% to 60 wt .-% or to 50 wt .-% to 60 wt .-%, of one or several low molecular weight compounds. An advantage of these extractants is that the residues of the reaction dissolve unexpectedly well in the extractants and the low molecular weight compounds contained in the extractants are both good with other organic solvents and good with water miscible. As a result, a very far-reaching separation of the residues is possible. Another advantage is that, at the same time, the content of organic solvents in the fluid can be reduced. A particularly suitable extractant comprises an ethylene glycol-water mixture.

The extractant may be contacted with the polythiophene-containing fluid for a period of between several minutes to several hours. Particularly advantageous is a contact time of between 30 minutes and 1.5 hours, particularly advantageous is a contact time of about one hour. During the contact time, the solution may be agitated or shaken to help ensure good mixing of extractant and residue.

In principle, all physical and chemical methods with which the residues can be removed from the fluid or removed as far as possible with the aid of the extractant are suitable for the separation of the residues from the fluid dissolved in the extractant. The separation from the impurities dissolved in the extractant is preferably carried out mechanically. The term "mechanically separated" is intended to refer to any physical separation method known to those skilled in the art with which the residues dissolved in the extractant can be removed due to different physical properties such as molecular weight, size, charge, boiling point or density. Preferably, a mechanical separation of the residues is carried out in conjunction with centrifuging. This allows residues to be removed very efficiently and quickly. Particularly preferably, the separation is carried out by decantation or filtration in conjunction with centrifugation. Separation by decantation in conjunction with centrifugation is particularly advantageous because it can be very efficiently removed residues of the reaction. It may be advantageous to repeat the treatment step or parts of the treatment step one or more times and / or to combine it with further purification steps.

Another object of the invention is a polythiophene-containing fluid, which is prepared by the process according to the invention.

Preferably, the polythiophene-containing fluid comprises the conductive polythiophene PEDOT. Particularly preferably, the PEDOT is doped with tosylate. This is advantageous since coatings having a high conductivity are obtained with a fluid comprising PEDOT: Tos.

Another object of the invention is the use of a polythiophene-containing fluid produced by the process according to the invention for coating substrates.

To obtain the coating, the polythiophene-containing fluid is applied to a substrate. To apply the polythiophene-containing fluid, any printing, dipping or coating methods are suitable. Examples of printing methods are a screen printing method, a gravure printing method, a flexographic printing method, an offset printing method, an inkjet printing method or an aerosoljet printing method. Other suitable methods of application include a thin film method such as a slot casting method, a curtain coating method, a doctor blade method, a spraying method, a sputtering method, a sputtering method, a vapor deposition method, a dip coating method, a roll coating method, a plating method, a powder coating method.

Depending on the desired application technique, the person skilled in the art may influence the properties of the polythiophene-containing fluid before application of the coating. For example, the viscosity can be adjusted by known means. It is also possible to concentrate and, if desired, to dry the polythiophene-containing fluid by suitable methods such as decanting or filtering, optionally assisted by centrifuging, and / or by exposure to heat. Even in the dry state can still be spoken of a fluid, since the term "fluid" in the present invention, both compounds and mixtures of compounds are understood to be present in at least one temperature range in a liquid state, as well as solids such as polythiophenes which behave like a liquid under mechanical stress. It is also possible to grind the completely dried fluid to a powder. If desired, emulsifiers, auxiliaries and other additives can be added to the fluid. The polythiophene-containing fluid, a powder based on a dried fluid, or a liquid, dispersion or paste containing the polythiophene-containing fluid or powder are suitable for applying a coating. Furthermore, it is possible to accelerate a drying of the coating, which may be subsequent to the application, by means of a heat treatment.

In principle, any materials are suitable as substrates for the coating. However, in particular electrically insulating substrates are preferred, since these substrates can be used for the production of thermoelectric systems such as TEGs. Particularly preferred are flexible, electrically insulating substrates, since these are suitable for the production of thermoelectric systems by winding and folding. Suitable flexible and electrically insulating substrates are plastic films, in particular films of thermoplastic materials such as polyethylene or polypropylene, fabrics of natural and / or synthetic fibers and / or paints, for example based on synthetic resin, for example, on a smooth surface of plastic, metal, ceramic , Glass or the like are applied. The polythiophene-containing fluids are particularly suitable for the coating of plastic films, since the coating and the substrate then have very similar or identical elasticities.

Another object is the use of a polythiophenhaltigen fluid for the coating of flexible, electrically insulating substrates.

Another object of the invention is a coated substrate, obtainable by the use of a polythiophenhaltigen fluid according to the invention.

A further subject matter is a TEG comprising a coated substrate obtainable by the use of a polythiophene-containing fluid according to the invention for coating.

Further details of the present invention will be described by way of the following examples, which are not intended to limit the invention in any way.

Examples:

Comparative Example 1

This example illustrates the process performed by the inventor in the presence of a high molecular weight polymeric additive.

Iron (III) tosylate solution

A mixture of anisole (92.0 ml) and isopropanol (118 ml) was added to anhydrous iron (III) tosylate (41.4 g, 72.7 mmol), polyethylene monomethyl ether (2.3 g, M _n ca. 2,000 ) and polyethylene glycol (2.3 g, M _v ca. 100,000) were added. The mixture was refluxed for 15 minutes and cooled to room temperature.

BiEDOT solution

A mixture of anisole (158 ml) and isopropanol (26 ml) was added to BiEDOT (9.2 g, 32.9 mmol), polyethylene glycol monomethyl ether (2.3 g, M _n ca. 2,000) and polyethylene glycol (2.3 g, M _v approx. 100,000) was added. The mixture was refluxed for 15 minutes and cooled to room temperature.

Binder solution

Polyethylene glycol (500 mg, M _v ca. 100,000) was added to isopropanol (40 ml). The mixture was refluxed for 15 minutes. The warm mixture was used immediately.

To the ferric tosylate solution at room temperature with stirring was added the BiEDOT solution, resulting in a dark blue colored slurry. The viscous blue mixture was stirred for 5 minutes and 1 liter of a mixture of ethylene glycol and water (1: 1) was added. The resulting solution was stirred for 1 hour and then filtered. The viscous blue filter residue was transferred to a sealable vessel and the binder solution added. The resulting mixture was stirred for 5 minutes to yield 238 g of printable fluid. On a glass slide, a coating was applied using a squeegee template (0.13 mm). The conductivity of the dry coating was 125 S / cm.

Example 2:

Preparation of a reaction mixture and conversion of BiE-DOT to conductive PEDOT with a connected treatment step to remove residues from the reaction of the PEDOT fluid

Solution A

7.2 ml of tetraethylene glycol was added to 669 mg of Fe (III) tosylate .6H ₂ O (1.06 mmol) and the mixture heated to 200 ° C. until a clear orange-red solution formed. The solution was then cooled to room temperature.

Solution B

3 ml of tetraethylene glycol was added to 120 mg of BiEDOT (425 μmol) and the mixture heated to 200 ° C until a clear green solution formed. The solution was then cooled to room temperature.

To solution A, solution B was added at room temperature with stirring to immediately obtain a dark blue colored, highly viscous fluid containing the conductive PEDOT. The PEDOT fluid was stirred for an additional 60 minutes.

The reaction is illustrated by the following reaction scheme, where n is usually a number between 2 and 50:

The representation of the charges of the doped PEDOT is omitted in the reaction scheme.

To remove residues from the reaction, 10 ml of a 1: 1 ethylene glycol / water mixture as extractant was added to the PEDOT fluid, and the batch was shaken at 1300 rpm for one hour. The separation of the extractant was achieved by decanting the PEDOT fluid after a centrifugation step (10 minutes at 4200 rpm). The extraction step was repeated twice more, each centrifuged for 5 minutes at 4200 rpm. This gave a purified PEDOT fluid.

Tetraethylene glycol was added to the purified PEDOT fluid until a suitable viscosity for subsequent application was obtained.

Coatings with the purified PEDOT fluid had a conductivity of 280 S / cm.

Example 3:

According to the method described in Example 2, a PEDOT fluid was prepared. Instead of tetraethylene glycol, triethylene glycol monomethyl ether was used.

Coatings with the purified PEDOT fluid had a conductivity of 160 S / cm.

Example 4:

According to the method described in Example 2, a PEDOT fluid was prepared. Instead of tetraethylene glycol, triethylene glycol was used.

Coatings with the purified PEDOT fluid had a conductivity of 230 S / cm.

Example 5:

Preparation of a reaction mixture and conversion of BiE-DOT to conductive PEDOT in the presence of 2,6-lutidine with a connected treatment step to remove residues from the reaction of the PEDOT fluid

A solution A and a solution B with tetraethylene glycol were prepared. Solution A was prepared as described in Example 2. To prepare Solution B, 98.5 μl of 2,6-lutidine (850 μmol) were added to the solution B approach described in Example 2 after cooling to room temperature.

To solution A, solution B was added at room temperature with stirring, resulting in a dark blue colored mixture. After 20 minutes, a high viscosity fluid containing conductive PEDOT was obtained. The PEDOT fluid was stirred for an additional 40 minutes.

The reaction is illustrated by the following reaction scheme, where n is usually a number between 2 and 50:

The representation of the charges of the doped PEDOT is omitted in the reaction scheme.

To remove residues from the reaction, 10 ml of a 1: 1 ethylene glycol / water mixture as extractant was added to the PEDOT fluid and the batch was set at 1300 rpm for one hour shaken. The separation of the extractant was achieved by decanting the PEDOT fluid after a centrifugation step (10 minutes at 4200 rpm). The extraction step was repeated twice more, each centrifuged for 5 minutes at 4200 rpm. This gave a purified PEDOT fluid.

Tetraethylene glycol was added to the purified PEDOT fluid until a suitable viscosity for subsequent application was obtained.

Coatings with the purified PEDOT fluid had a conductivity of 292 S / cm.

Example 6:

Preparation of a reaction mixture and reaction of BiE-DOT with EDOT to conductive PEDOT with connected treatment step to remove residues of the reaction

Solution A

10 ml of tetraethylene glycol was added to 1.1 g of Fe (III) tosylate x 6 H ₂ O (1.76 mmol) and the mixture heated to 200 ° C until a clear orange-red solution formed. The solution was then cooled to room temperature.

Solution B

3 ml of tetraethylene glycol was added to 99.3 mg of BiEDOT (352 μmol) and the mixture heated to 200 ° C until a clear green solution formed. The solution was then cooled to room temperature and 163 μl of 2,6-lutidine (1.41 mmol) was added to the solution.

To solution A was added 37.5 μl of EDOT (352 μmol, neat) and stirred for 30 seconds. Subsequently, at room temperature, solution B was added with stirring, resulting in a dark blue colored mixture. After 20 minutes, a high viscosity fluid containing the conductive PEDOT was obtained. The PEDOT fluid was stirred for an additional 40 minutes.

The reaction is illustrated by the following reaction scheme, where n is usually a number between 2 and 100:

The representation of the charges of the doped PEDOT is omitted in the reaction scheme.

To remove residues from the reaction, 10 ml of a 1: 1 ethylene glycol / water mixture as extractant was added to the PEDOT fluid, and the batch was shaken at 1300 rpm for one hour. The separation of the extractant was achieved by decanting the PEDOT fluid after a centrifugation step (10 minutes at 4200 rpm). The extraction step was repeated twice more, each centrifuged for 5 minutes at 4200 rpm. This gave a purified PEDOT fluid.

Tetraethylene glycol was added to the purified PEDOT fluid until a suitable viscosity for subsequent application was obtained.

Coatings with the purified PEDOT fluid had a conductivity of 250 S / cm.

The purified PDOT fluids used to prepare the coatings described in Examples 2 to 6 had the following composition:

Solid:

• PEDOT approx. 1.3-3.8% by weight

Liquid:

• Tetraethylene glycol, triethylene glycol or triethylene glycol monomethyl ether: approx. 1-10%
• Ethylene glycol: water (1: 1): about 90-99%

The coatings were produced by the method shown below:

The fluids were manually applied to glass slides using a squeegee template. Subsequently, the coatings were dried by means of a heat gun at about 220 ° C for 10 to 60 seconds. The coatings obtained in Examples 2 to 6 were between 1 and 4 μm thick, depending on the doctor blade used.

The determination of the conductivity of the coatings took place according to the following method:

For the determination of the conductivity, coatings of the purified PEDOT fluids were applied to glass slides. Subsequently, two silver electrodes were applied to the coating with the aid of silver-conducting lacquer. With the aid of a multimeter, the sheet resistance (ohms / square) of the dry coatings was determined. The layer thickness of the coatings was measured on a DektakXT profilometer at any two points between the electrodes and the average value calculated. The electrical conductivity was determined according to the formula 1 / (sheet resistance · layer thickness) from the values obtained.

• • Methode nach G. A. Sotzing, J. R. Reynolds, P.J. Steel, Adv. Mater. 1997, 9, 795.
• • Methode nach Swager, R. Kingsborough, S. S. Zhu in US 6323309 B1 .

The synthesis of BiEDOT optionally took place according to the following methods:

• Method by GA Sotzing, JR Reynolds, PJ Steel, Adv. Mater. 1997, 9, 795.
• • Method according to Swager, R. Kingsborough, SS Zhu in US 6,323,309 B1 ,

The choice of method did not affect the conductivity of the PEDOT obtained by the oxidative polymerization.

All features of the invention may be essential to the invention both individually and in any combination with each other.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012105086 [0003]
• US 6,323,309 B1 [0094]

Cited non-patent literature

• Elschner, Andreas et al. [0004]
• PEDOT: Principles and Applications of an Intrinsically Conductive Polymer, pages 33 to 46 [0004]
• ISBN 9781420069112 [0004]
• GA Sotzing, JR Reynolds, PJ Steel Advanced Materials 1997, 9, pages 795-79 [0024]
• GA Sotzing, JR Reynolds in Advanced Materials 1996, 8, pp. 882-889 [0024]

Claims (19)

A process for preparing polythiophene-containing fluids, comprising the following step: reacting at least one thiophene oligomer with an oxidant selected from metal salts in a predominantly organic reaction medium, wherein the solvent content of the reaction medium is at least 40% by weight of one or more low molecular weight compounds having a number average molecular weight (M _n ) of up to 2,000 selected from the group of alkylene glycols, polyalkylene glycols, monoether derivatives, diether derivatives, monoester derivatives, diester derivatives and ether-ester derivatives of alkylene glycols consists. A method according to claim 1, characterized in that the one or more low molecular weight compounds have a molecular weight (M _n ) of up to 1,000, more preferably of up to 800, more preferably between 70 and 800, most preferably between 70 and 300, most preferably between 100 and 300. A method according to claim 1 or 2, characterized in that the one or more low molecular weight compounds are selected from the group of alkylene glycols, the polyalkylene glycols and monoether derivatives of alkylene or polyalkylene glycols, more preferably selected from the group of alkylene glycols and polyalkylene glycols. Method according to one of the preceding claims, characterized in that the thiophene oligomer is a bi-thiophene. A method according to claim 4, characterized in that the bi-thiophene is bi (ethylene-3,4-dioxythiophene) (BiEDOT). Method according to one of the preceding claims, characterized in that the reaction, the polythiophene poly (ethylene-3,4-dioxythiophene) (PEDOT) is obtained. Method according to one of the preceding claims, characterized in that the oxidizing agent selected from metal salts is iron (III) tosylate. Method according to one of the preceding claims, characterized in that the solvent content of the reaction medium to at least 45 wt .-%, 50 wt .-%, 55 wt .-%, 60 wt .-%, 65 wt .-% or 70 wt. %, more preferably at least 75%, 80% or 85%, more preferably at least 90%, most preferably at least 95%, most preferably exclusively consists of one or more of the low molecular weight compounds. Method according to one of the preceding claims, characterized in that the reaction is carried out in the presence of a base. A method according to claim 9, characterized in that the base is 2,6-lutidine. Method according to one of the preceding claims, characterized in that directly or indirectly to the reaction followed by a treatment for the removal of residues of the reaction. A method according to claim 11, characterized in that the treatment for removing residues by contacting the fluid with an extractant to dissolve the residues in the extractant and separation of the dissolved in the extractant residues from the fluid is performed. A method according to claim 12, characterized in that the separation of the residues is carried out mechanically and in conjunction with centrifuging. Polythiophene-containing fluid prepared according to one of claims 1 to 13. Polythiophenhaltiges fluid according to claim 14, characterized in that the fluid comprises a tosylate doped PEDOT (PEDOT: Tos). Use of a polythiophene-containing fluid according to claim 14 or 15 for coating substrates. Use of a polythiophene-containing fluid according to claim 14 or 15 for coating flexible, electrically insulating substrates. A coated substrate obtainable by the use of a polythiophene-containing fluid according to claim 16 or 17. TEG comprising a coated substrate according to claim 18.