EP0236367B1 - Method for the preparation of an electrically conductive polymer in the form of a moldable powder - Google Patents

Abstract

Electrically conductive polymers are obtained by chemical oxidation of pyrrole and other aromatic heterocycles by means of a metal oxidant in anhydrous medium. In the presence of a mineral or organic filler, a moldable powder comprised of particles coated with electrically conductive polymer is obtained.

Description

The subject of the present invention is a process for the preparation of an electrically conductive organic polymer in the form of a powder which may contain mineral or organic fillers, this powder being compactable under pressure and moldable in the form of electrically conductive articles. This polymer is obtained by chemical oxidation of one or more pentacyclic hetero-compounds such as thiophene, selenophene, furan, pyrrole, thiazole, oxazole or pyrazole in the presence of a doping agent.

Obtaining an electroconductive organic polymer, which may contain mineral or organic fillers in the form of a pressure moldable powder, by electrolytic or chemical oxidation of aromatic heterocyclic compounds has recently been disclosed in documents EP-A-123,827 and 131,914 (BASF). According to these documents, when chemical oxidation is carried out, a heterocyclic compound chosen from pyrrole and its derivatives, thiophene, furan, is reacted in aqueous media (in water or in an organic solvent containing water). , thiazole with, on the one hand, an oxidizing agent containing oxygen and, on the other hand, a conductive salt such as KHS0 ₄ , Na ₂ S0 ₄ , HCOOH, LiC10 ₄ , HClO ₄ , Et ₄ NC10 ₄ , KBF ₄ , H ₂ S0 ₄ , FeCl ₃ or KAsF ₆ . The powders thus obtained have a conductivity of between 10 ^-2 and 50 S / cm that is to say, a resistivity 100-2x10 ^-2 Ohm. cm.

Document GB-A-2,133,022 describes the production of electroconductive polymers with a negative temperature coefficient by treatment of dimethylpyrroles with oxidizing salts such as perchlorate or ferric chloride in an aqueous medium or with chlorine gas in an acetonitrile medium. The polymers thus obtained however have a low conductivity (resistivity greater than 10 Ohm. Cm).

Furthermore, the production of electroconductive polymers in the form of films or in the form of products for impregnating porous materials has also been disclosed.

Thus, the document DE-A-33 21 281 mentions the impregnation of insulating materials such as cellulose fibers, papers, porcelain or epoxy resins with an aqueous solution of a salt of a metal of varying degree of oxidation, this metal being at a high oxidation level, in particular FeCl ₃ , La (S0 ₄ ) ₂ , K ₃ Fe (CN) ₆ , Cr0 ₃ , preferably in the presence of an acid, then the addition in gaseous or liquid form of a pyrrolic compound in an alkolic solution or in a nitrile. The resistivity of the products obtained is however not less than 65 Ohm. cm (see example 1).

The document "Japanese Journal of Applied Physics" 23 (1984), 899-900, by K. Yoshino et al. describes the formation, on a glass plate, of films resulting from the oxidative cationic polymerization of heterocycles such as thiophene, furan and pyrrole. The process consists in depositing on the surface to be coated a Lewis acid such as FeCl ₃ , MoCl ₅ or RuCI ₃ in solution in chloroform or dioxane and exposing the surface thus treated to heterocyclic compounds in the gas phase. This technique provided films with low conductivity (~ 10 ^-9 S / cm, that is to say p = ₁₀ ⁹ Ohm. Cm) but which, after doping with iodine, exhibited a relatively high conductivity (14 S / cm, i.e. ρ = 1.4x10 ^-1 Ohm. Cm).

Despite the interesting results disclosed in the prior art, it was desirable to have available a simplified technique for preparing an electroconductive powder with further improved properties and making it possible, by molding under moderate pressure and at a low temperature , electrically conductive articles. This objective was achieved starting from the surprising discovery that, according to the process of the present invention summarized in claim 1, electroconductive polymers can be obtained by homogeneous polymerization of aromatic heterocycles, for example in an anhydrous organic solvent , and using, both as an oxidant and as a dopant, Lewis acids with oxidizing capacity.

avec x étant compris entre 2 et 12.As such, there may be mentioned the halides and other salts and complexes of mineral and organic acids of metals having the character of Lewis acids in an oxidation state of a higher level and capable of passing, by reaction with an aromatic heterocycle, at a lower oxidation level by polymerizing oxidation of said heterocycle, and, simultaneously, to form doping anions of the polymer thus obtained. As such Lewis acids, the following bodies may be mentioned: FeCl ₃ , FeBr ₃ , CuCl ₂ , BiCl _s , AsCl _s , SbCl ₅ , SbF _S , MnCI ₃ and others. It should be noted that salts having only a weak character of a Lewis acid, such as, for example, Fe2 (SO ₄ ) ₃ and Fe (NO ₃ ) ₃ may also be suitable. The principle of the reaction according to the invention can be illustrated by the following diagram relating to the reaction of pyrrole (PYR) with FeCl ₃ , it being understood that similar criteria are applicable to the other cases encompassed by the invention:

with x being between 2 and 12.

In the case shown above, the polymer obtained has a charge + for x pyrrole groups; the value of x being between 2 and 12 and preferably 3 and 10. The important factor, underlined by this diagram, is however the fact that the salt or the Lewis acid used functions both as an oxidative polymerization agent pyrrole and as a doping agent which makes it possible to achieve relatively high conductivities without the addition of additional dopant.

As solvents which can be used in the present process, mention may be made of solvents having an ether function, such as ethyl, propyl or butyl ethers, "glymes", in particular monoglyme (ethylene glycol dimethyl ether), dioxane, THF, esters such as ethyl acetate and propionate, nitromethane, nitrobenzene, chlorinated solvents such as CCI ₄ , chlorobenzene, ethyl chloride, methyl chloride , ethylene or methylene chloride. From a practical point of view, the implementation of the method of the invention is very simple. Preferably, on the one hand, a solution of Lewis acid in the chosen organic solvent is prepared and, on the other hand, a solution of pyrrole or another heterocycle in this solvent or another solvent and the procedure is carried out. mixing of the two solutions at ordinary temperature or with cooling to moderate the reaction when it is lively. It is also possible to add the heterocyclic compound when it is liquid undiluted by a solvent.

In general, relative amounts of reagents are preferably used in accordance with the stoichiometry of the reaction; for example, in the reaction schematized above, yields close to the theory will be obtained by using 3 moles of FeCl ₃ per mole of pyrrole; however, there is no need to strictly observe these conditions and a similar polymer will be obtained (albeit with a lower yield) using, for example, 1 mole of FeCl ₃ per mole of pyrrole.

In general, the precipitation of the desired product is rapidly observed, in the form of a pulverulent mass which may be fibrous. This mass can be collected by filtration and spinning and dried by the usual means. The mass is then compacted in an appropriate form and molded according to the shape of the desired object. Among such objects, mention may be made of components useful in electrical engineering, special electrodes, switches and circuit components.

Furthermore, the present electroconductive polymer can be used to obtain, in the presence of an inorganic or organic pulverulent filler, a pulverulent substance making it possible to manufacture, by the usual methods of compacting and pressure molding or by sintering, compact electroactive articles.

By "electroactive" we refer to electroconductive materials capable of being subjected to reversible electro-oxidation-reduction processes involving a variation in the rate of electrical charge (doping) without the participation of metals or metal ions. As an example of such a known material, mention may be made of polyacetylene. This polymer is normally a semiconductor but, by oxidizing or reducing doping, its conductivity can be varied by a factor of the order of 10 ¹² (see Chemical & Engineering News, January 26, 1981, pages 39―40). Such a polymer can be used in particular for the manufacture of accumulators and plastic batteries (see Research, No. 126, October 1981, vol. 12, pages 1132-1134; RL Elsenbaumer et al., Polymer Preprint 25/2, August 1984, pages 132-133; A. Pron et al., J. Chem. Soc. (Chem. Comm.) 1981, pages (783-784).

The electroconductive powder thus obtained from the electroconductive polymer of the invention and a charge lends itself to all the usual applications involving the use of metallic powders such as electroconductive paints, electroconductive articles in the electrical industry, electrodes in the chemical industry.

It is known, in fact, that the manufacture of such articles using metallic powders or carbon black encounters various problems linked, in particular, to the price of metallic powders, to the need to incorporate high rates of such fillers in a polymer matrix to obtain sufficient conductivity, with the frequent lack of compatibility (wettability) between the filler and the matrix which can possibly lead to a loss of its mechanical properties, to the difficulty of distributing the filler in a homogeneous manner the matrix and, finally, to a possible loss of conductivity over time for reasons of corrosion of the metal particles.

As the pulverulent filler, it is preferred to use carbon black or mineral particles. The particle size of the filler is preferably from 0.01 nm to 1 µm, more preferably from 5 to 1000 nm.

As carbon black particles, it is possible to use the various types of carbon black available on the market and whose dimensions are of the order of 0.001 to 1 μm with a specific surface of 1 mg to 100 mg / m ² . Such carbon blacks are described in document EP-A-98,338.

As mineral particles, all mineral materials in fine powder such as, for example, those containing silica, alumina or other metal oxides can be used. Preferably, submicron particles such as precipitated or pyrogenic silica are used, such dimensional requirements however not being critical and can be overridden if desired. A description of such mineral materials can be found in the document. EP-A-69.133. Other silicate particles such as talc, bentonite, vollastonite, montmorillonite, may also be suitable.

To manufacture the present powder, it is preferred to carry out the polymerization of the electroconductive polymer in the presence of the charge dispersed in the reaction medium.

The amount by weight of electroconductive polymer relative to the. particulate matter in the present powder is preferably between about 10 and 100% depending on the desired properties. The thickness of the polymer layer which is deposited on the particles during the polymerization can be of the order of a few Angstroms to several micrometers. The resistivity of the powder (as measured on an article made by compression) generally varies between 10000 and 10- ² ohm. cm depending on the rate of fixation of the electroconductive polymer, and according to the method of preparation.

To obtain the present pulverulent substance, it is possible to proceed in various ways including the simultaneous bringing into contact of the particulate filler, the polymerization reagent and the monomer to be polymerized, or the impregnation of the filler with said reagent and, subsequently, the in the presence of the charge thus treated with said monomer in liquid (solution) or vapor phase. In the case of Si0 ₂ or carbon black to be coated with polypyrrole, the procedure is, for example, in organic solution using one of the aforementioned reagents simultaneously playing the role of polymerization catalyst and dopant, in particular FeCl ₃ . Once the charge is coated with a layer of electroconductive polymer, it is isolated and stored until it is used.

To manufacture, by molding and compacting, articles such as those mentioned above, the present powder is subjected, in a mold, to a pressure sufficient to promote the adhesion between them of the electroconductive particles, this operation being able to take place, according to cases, in the presence or absence of a usual binder.

In the case of incorporation of the conductive filler in a plastic matrix, this filler can be dispersed in a solution of a polymer or in a liquid monomer and then proceed to the polymerization of this monomer. It will be noted that one of the significant advantages of the present powder is its excellent compatibility (good wettability) with most organic polymers, which clearly distinguishes it from the electroconductive powders of the prior art.

The following examples illustrate the invention.

Example 1

24.33 g of anhydrous FeCl ₃ (0.15 mol) are dissolved in 150 ml of absolute ether. 3.354 g of pyrrole (0.05 mole) are introduced into this solution dropwise and with stirring. The reaction is exothermic and a black precipitate forms immediately. After the end of the introduction, the mixture is further stirred for 1 hour at room temperature and the precipitate is separated by filtration. The precipitate is then washed successively with ethanol and ether until the washings are colorless. It is dried under vacuum in a desiccator in the presence of P ₂ O ₅ . 3.45 g of conductive black powder are obtained.

The elemental analysis gives the following values: C: 53.4%, H: 3.40%, N: 15.4% CI: 15.2%, which corresponds to the following composition C _4.045 H _3.066 N ₁ Cl _0.39 . Assuming that the doping anion is FeC1 ₄ , we arrive at the following crude formula: - [(PYRROLE) _10.2 FeCl ₄ ] _n or about 1 group FeC1 ₄ for 10 pyrrole cycles.

The volume electrical conductivity measured on a pellet obtained by compacting under a pressure of 15 t / cm ² is 28 Ohm ^-1 cm ^-1 , that is to say 3.5 × 10 ^-2 Ohm. cm.

Example 2

The procedure is as in Example 1 but by reducing the amount of ferric chloride to 0.1 mole or 16.22 g (molar ratio FeCl ₃ / pyrrole 2: 1 instead of 3: 1 in the previous example). In this case, 2.53 g of powder are obtained, the volume conductivity of which, after compaction, is 24 Ohm ^-1 cm ^-1 (p = ₄ x10- ² Ohm. Cm).

Example 3: Comparative example in an aqueous medium

To demonstrate the advantages of the invention over the prior art, the following test was carried out:

40.55 g of FeCl _{3 are} dissolved. 6H ₂ 0 (0.15 mole) in 200 ml of water and 3.354 g of pyrrole (0.05 mole) are added dropwise. There is an immediate black coloration and a fibrous precipitate is deposited. After the end of the introduction, the mixture is still stirred for 1 hour at room temperature and then the bulky precipitate is separated by filtration. The precipitate is then washed successively with water, ethanol and ether until the washings are colorless. It is dried under vacuum in a desiccator in the presence of P ₂ 0 ₅ . 4.11 g of a very light fibrous precipitate are obtained.

The volume electrical conductivity, measured on a pellet obtained by compacting under a pressure of 15 t / cm ² is 2.10 hm ^-1 cm ^-1 , ie a factor of 10 less than the sample obtained in an anhydrous medium (example 1) .

• C: 53,6%; H: 3,2%; N: 15,3%. Ces chiffres étant pratiquement les mêmes que ceux de l'analyse du produit de l'exemple 1, il n'est pas possible, sur ce plan analytique, d'expliquer la raison pour laquelle le polymère préparé en milieu anhydre est environ 10 fois plus conducteur que le polymère obtenu en milieu aqueux.

The elementary analysis provides the following values:

• C: 53.6%; H: 3.2%; N: 15.3%. These figures being practically the same as those for the analysis of the product of Example 1, it is not possible, from this analytical point of view, to explain the reason why the polymer prepared in an anhydrous medium is approximately 10 times more conductive than the polymer obtained in an aqueous medium.

Example 4 Comparative Example in an Aqueous Medium

The procedure is as in Example 3 but decreasing the amount of FeCl ₃ . 6H ₂ 0 to 0.1 mole or 27.03 g (molar ratio FeCl _3. 6H.0 / pyrrole 2: 1). Is obtained in this case 3.188 g of very light fibrous precipitate whose volume conductivity after compaction is ₀ = _{1, 1} ohm ^-1 cm ^-1 which is about 20 times lower than in the corresponding test in an anhydrous medium (Example 2) . This test therefore confirms the above observations.

Example 5

The procedure is as in Example 1 but using 22.43 g (0.075 mole) of SbCl ₅ in 150 ml of CCI ₄ . The precipitate is washed with CCI ₄ and dried under vacuum. 10.8 g of powder are obtained, the volume conductivity of which after compacting is 3.6 × 10 ⁻³ Ohm ⁻¹ cm ⁻¹ .

Example 6

The procedure is as in Example 1 but using 16.25 g (0.075 mole) of SbF ₅ in 150 ml of CCI ₄ . The precipitate is washed with CCI ₄ and dried under vacuum. 12.6 g of powder are obtained, the volume conductivity of which after compacting is 0.28 Ohm ^-1 cm ^-1.

Example 7

The procedure is as in Example 1 but using 20.17 g (0.15 mole) of anhydrous CuCl ₂ in 150 ml of MeOH. The precipitate is washed with MeOH and dried under vacuum. 1.25 g of powder are obtained, the volume conductivity of which after compacting is 5.47 Ohm ^-1 cm ^-1 . By performing the test in 150 ml water with 0.15 mol of CuCl ₂ .2H ₂ O (25.57 g) gives a similar performance (conductivity o = _2, 79 Ohm ^-1 cm ^-1.

Example 8

A mixture of 3.35 g of Elftex 5 carbon black, 1 g of lauroyl peroxide, 100 g of 2 mm glass beads and 150 ml of butyl acetate was dispersed for 4 hours at reflux with stirring.

After cooling, the carbon black dispersion thus obtained was treated with 16.22 g of anhydrous FeC) ₃ , then with 3.35 g of pyrrole. After a few hours of stirring, the dispersion was filtered off, washed and dried; yield 5.12 g. The volume conductivity of the black powder thus obtained was 13.27 Siemens / cm.

Example 9

9.21 of Si0 ₂ , Aerosil A-380 were dispersed with Rotavapor (obtained by drying 10 g of Si0 ₂ at 150 ° C for 3 h) and 200 ml of an ethermethanol solvent (95: 5). A solution of 1 g of anhydrous FeCl ₃ in 4 ml of the above solvent was then added and the mixture was stirred for 15 minutes at room temperature; then the solvent was evaporated under 79993 Pa (600 Torr) at 50 ° C for 2.5 h. After standing overnight on P ₂ 0 ₅ in a desiccator, 10.53 g of a yellow powder were obtained. 2 g of this powder impregnated with FeCl _{3 were} stirred with 11.6 g of pyrrole at room temperature for 4.5 h and then 20 ml of ether were added to facilitate stirring for another 45 min. There was thus obtained after spinning, washing with ether and drying, 2.52 g of solid, which corresponds to an increase in weight, due to the deposition of polypyrrole, of 25%. The conductivity of the black powder thus obtained being 0.4. 10 ^-3 5 / cm.

Example 10

1.957 g of SiO ₂ impregnated with FeCl ₃ were placed side by side in a desiccator under the conditions of Example 9 and 10 g of pyrrole, each in an independent open container. The pressure in the desiccator was lowered to 79993 Pa (600 Torr) and, after 72 hours, it was found that the increase in weight, due to the deposition of polypyrrole in the vapor phase was 0.3494 g, or 17.7 %. The conductivity of the black powder thus obtained was 0.45 10-2 S / cm.

Example 11

10 g of Si0 ₂ , Aerosil A-380, previously dried at 150 ° C. for 3 h, were dispersed in Rotavapor in 200 ml of an ether-methanol mixture (95: 5). Then a solution of 10 g of anhydrous FeCl ₃ in 30 ml of ether was added and, after a few minutes, the solvent was removed under a pressure of 79993 Pa (600 Torr) at 50 ° C. 19.33 g of a yellow powder were thus obtained, weight measured after grinding and drying at 100 ° C. 2.0109 g of this powder was then treated with pyrrole in the vapor phase under a pressure of 600 Torr in a desiccator as described in Example 5 and its conductivity as a function of time was measured at intervals. that is to say the weight of polypyrrole deposited little by little (this value is expressed as% increase in the initial weight).

Examples 12-16

The procedure was as in Example 11 but using 10 g of silicas of various types and making vary, on the one hand, the amount of FeCl ₃ adsorbed on the silica and, on the other hand, the contact time in vapor phase with the pyrrole.

Examples 17-21

• ΔP=augmentation de poids que au dépôt de polypyrrole
  

The procedure was as in Example 11, but with 10 g of various fillers (aluminum oxide and rutile are Degussa products), variable amounts of FeCl ₃ and different contact times

• ΔP = increase in weight only when polypyrrole is deposited
  

Claims (13)

1. A method for the preparation of an electroconductive polymer in the form of a powder to be compacted and moulded under pressure, obtained by a chemical oxidation of aromatic heterocycles in the presence of a Lewis acid, characterized in that one operates in anhydrous medium, one uses as a Lewis acid a salt or a complex of a polyvalent metal in a higher state of oxidation and capable of going to a lower oxidation state during the reaction, and one operates without adding further dopant or oxidant.

2. Method according to claim 1, characterized in that one uses, as the medium, one or more solvents selected from ether, dioxane, monoglyme (ethylene-glycol dimethyl ether), THF, ethyl acetate, nitromethane, nitrobenzene, CCI₄, ethyl chloride, methylchloride.

3. Method according to claim 1, eharacterized in using, as a Lewis acid, at least one of the following substances: FeC1₃, FeBr₃, AsCl₅, SbCl₅, CuCl₂, BiCl_s, SbF_s.

4. A method for converting the electroconductive polymer obtained according to claim 1, into an electroconductive powdery substance appropriate for the manufacture, by compacting and moulding, of electroactive articles, characterized in that mineral particles or carbon black particles are added to the polymer.

5. Method according to claim 4, characterized in that the electroconductive polymer is selected from polypyrrole, polythiophene and polyfurane.

6. Method according to claim 4, characterized in that the ratio by weight of the electroconductive polymer to that of the particles is 0.1 to 10.

7. Method according to claim 4, characterized in that the conductivity of the substance after being compacted is 10-⁴ to 100 S/cm (p=₁₀ ⁴ to 10^-2 Ω . c_m).

8. Method according to claim 4, characterized in that the size of the particles of the substance vary from 5 nm to 1000 nm.

9. Method according to claim 4, characterized in that one puts an amount of carbon black filler or an amount of a mineral filler in the presence, on one hand, of reagents for the polymerization and doping of heterocyclic monomers and, on the other hand, of one or more of these monomers, the latter undergoing polymerization thereafter, in the form of an electroconductive polymer, at the surface of the particles of said filler.

10. Method according to claim 9, characterized in that one impregnates first the mineral filler with FeCl₃, this reactant acting as a dopant and as a polymerization reagent, then one puts the impregnated mineral filler in the presence of the monomer.

11. Method according to claim 10, characterized in that one operates in an anhydrous medium or in the gas phase.

12. Method according to claim 11, characterized in that one puts the FeC1₃ impregnated filler in the presence of pyrrole vapors under subatmospheric pressure.

13. Method according to claim 11, characterized in operating at room temperature.