WO1987001504A1

WO1987001504A1 - Method for the preparation of an electrically conductive polymer in the form of a moldable powder

Info

Publication number: WO1987001504A1
Application number: PCT/CH1986/000123
Authority: WO
Inventors: Günter Bellmann; Van-Tao Nguyen
Original assignee: Battelle Memorial Institute
Priority date: 1985-09-06
Filing date: 1986-09-01
Publication date: 1987-03-12
Also published as: EP0236367B1; DE3673155D1; EP0236367A1

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

PROCESS FOR THE PREPARATION OF AN ELECTRICALLY CONDUCTIVE POLYMER IN THE FORM OF A MOLDABLE POWDER

The present invention relates to a process for the preparation of an electroconductive 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 electroconductive articles. This polymer is obtained by chemical oxidation of one or more pentacyclic hetero-compounds such as thiophene, selenophene, furan, pyrrole, thiazole, oxazole, pyrazole, etc. in the presence of a doping agent .

Obtaining an electroconductive organic polymer, which may contain mineral or organic fillers in tonnes of a pressure moldable powder, by electrolytic or chemical oxidation of aromatic heterocyclic compounds has recently been disclosed in documents EP-A123.327 and 131.914 (BASF). According to these documents, when a 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, etc. with, on the one hand, an oxidizing agent containing oxygen and, on the other hand, a conductive salt such as KHSO ₄ , Na ₂ SO ₄ , HCOOH, LiClO ₄ , HClO ₄ . And ₄ MClO ₄ , KBF ₄ , H ₂ SO ₄ , FeCi ₃ , KAsF ₆ , etc. The powders thus obtained have a conductivity varying between 10 ^-2 and 50 S / cm, that is to say a resistivity of 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 dimethylpyrroies with oxidizing salts such as perchlorate or ferric chloride in aqueous medium or with chlorine gas in 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, document DE-A-33 21 281 mentions the impregnation of insulating materials such as cellulose fibers, papers, porcelain, epoxy resins, etc. with an aqueous solution of a salt of a metal of degree variable oxidation, this metal being at a high oxidation level, in particular FeCl ₃ , La (SO ₄ ) ₂ , K ₃ Fe (CN) ₆ , CrO 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 not, however, 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 RuCl 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, i.e. p = 10 ⁹ Ohm.cm) but which, after doping with iodine, exhibited relatively high conductivity (14 S / cm, i.e. p = 1.4 x 10 ^-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 to produce, by molding under moderate pressure and at a low temperature. , electrically conductive articles. This objective was achieved on the basis of the surprising discovery that, according to the process of the present invention summarized in claim 1, it is possible to obtain electroconductive polymers by homogeneous polymerization of aromatic heterocycles, for example in an anhydrous organic solvent. , and by using, both as oxidant and as dopant, Lewis acids with oxidizing capacity.

As such, there may be mentioned the halides and other salts 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, to a level of internal oxidation by polymerizing oxidation of said heterocycle, and, simultaneously, of forming doping anions of the polymer thus obtained. As such Lewis acids, the following bodies may be mentioned: FeCl ₃ , CuCl ₂ , BiCl ₅ , AsCl ₅ , SbCl ₅ , SbF ₅ , MnCl ₃ and others. It should be noted that salts having only a weak character of a Lewis acid, such as, for example, Fe ₂ (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: n [xPYR + (2x + 2) FeCl ₃ ] -> [(PYR) -FeCl ₄ ] + n (2x + 1) FeCl ₂ + 2nxHCl 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, there may be mentioned solvents with an ether function such as ethyl, propyl, butyl ethers, etc., "glymes", dioxane, THF ', esters such as acetate and propionate d ethyl, nitromethane, nitrobenzene, chlorinated solvents such as CCl ₄ , chlorobenzene, ethylene or methylene chloride, etc. From the practical point of view, the implementation of the process 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 pyrross 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 heterocystic 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 pyrross; however, there is no need to strictly observe these conditions and a similar polymer (albeit with a lower yield) will be obtained 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 somewhat fibrous pulverulent mass. 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, there may be mentioned components useful in electrical engineering, special electrodes, switches, circuit components, etc. 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 "electroactit" 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 polyacetyethylene. This polymer is normally a conductive 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 filler 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, etc.

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, a possible loss of conductivity over time for reasons of corrosion of the metal particles.

As a pulverulent filler, it is preferred to use carbon black or mineral particles.

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 micrometer 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 fine powder mineral materials can be used such as, for example, those containing silica, alumina or other metal oxides. 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 document EP-A-69,133. Other silicate particles such as talc, bentonite, vollastonite, montmorillonite, etc. 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 electrically conductive polymer relative to the particulate substance in the present powder is preferably between approximately 10 and 100% depending on the properties desired. 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 (measured on an article obtained by pressing) generally varies between 10,000 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 charge, the polymerization reagent and the monomer to be polymerized, or the impregnation of the charge with said reagent and, subsequently, the setting in the presence of the charge thus treated with said monomer in liquid (solution) or vapor phase. In the case of SiO 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 1 in. iymer 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 still 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 black conductive powder are obtained.

The elementary analysis provides the following values: C: 53.4%, H: 3.40%, N: 15.4%, Cl: 15.2%, which corresponds to the following composition C ₄₀₄₅ H ₃ , ₀₆₆ N ₁ Cl _0.39 . Assuming that the doping anion is FeCl ₄ , we arrive at the following crude formula: - [(PYRROLE) _10.2 FeCl ₄ ] _n or approximately 1 FeCl ₄ group for 10 pyrrole cycles.

The electrical volume 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 x 10 ^-2 Ohm. cm.

Example 2

The procedure is as in Example 1 but by reducing the quantity of ferric chlorine to 0.1 mole, ie 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 compacting, is 24 Ohm ^-1 cm ^-1 (p = 4 x 10 ^-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 .6H ₂ O (0.15 mol) are dissolved in 200 ml of water and introduced 3.354 g of pyrrole (0.05 mol) 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 O 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 2.10hm ^-1 cm-1, ie a factor of 10 less than the sample obtained in an anhydrous medium (example 1) .

Elementary analysis provides the following values: C: 53.6%; K: 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 is aqueous medium.

Example 4 Comparative Example in an Aqueous Medium

The procedure is as in Example 3 but by reducing the amount of FeCl ₃ .6H ₂ O to 0.1 mole, ie 27.03 g (molar ratio FeCl ₃ .6H ₂ O / pyrrole 2: 1). In this case, 3.168 g of very light fibrous precipitate is obtained, the volume conductivity of which after compacting is σ = 1.1 Ohm ^-1 cm ^{-1, which} is approximately 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 compaction 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 carrying out the test in 150 ml of water with 0.15 mole of CuCl ₂ .2H ₂ O (25.57 g), a similar yield is obtained (conductivity σ = 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 FeCl 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 SiO2, Aerosil A-380 (Rotovapor, obtained by drying 10 g of SiO2 at 150 ° C. for 3 h) and 200 ml of an etherhanol solvent (95: 5) were dispersed with Rotavapor. 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 600 Torr at 50 ° C for 2.5 h. After standing overnight on P ₂ O ₅ in a desiccator, 10.53 g of a yellow powder were obtained. 2 g of this FeCi-impregnated powder 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 deposit of polypyrrole, from 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 a separate open container. The pressure in the desiccator was lowered (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 SiO 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 EeCl ₃ in 30 ml of ether was added and, after a few minutes, the solvent was removed under a pressure of 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. i.e. the weight of polypyrrole deposited little by little (this value is expressed as% increase in the initial weight).

weight increase conductivity

44.4% 0.45 S / cm

49.9% 0.76 S / cm

57.2% 0.84 S / cm

87.8% 0.63 S / cm

Examples 12-16

The procedure was as in Example 11 but using 10 g of silica of various types and varying, 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 pyrrole. Example No Silica FeCl ₃ duration Δ P conductivity

12 A-380 bg 648 h 84.3% 0.36 S / cm 13. A-200 2 g 432 h 67.1% 0.02 S / cm 14 A-200 5 g 432 h 63.3% 0, 11 S / cm

15 A-130 2 g 432 h 70.6% 0.08 S / cm 16 A-130 5 g 432 h 52.6% 0.35 S / cm

Examples 17-21

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

Δ P = increase in weight due to the deposition of polypyrrole

Example No Charge FeCl ₃ duration ΔP conductivity

17 Al ₂ O ₃ 2 g 288 h 110.5% 0.50 S / cm

18 "" 5 g 288 h 102.2% 1.1 S / cm

19 "'' 10 g 648 h 25.5% 0.55 S / cm

20 TiO ₂ 10 g 64c8 h 14.4% 0.11 S / cm

21 CB Elflex 5 10 g 648 h 29.3% 2.1 S / cm

Claims

REVE NDI CA TIONS

1. Process for the preparation of an electrically conductive polymer in the form of a compactable and pressure-moldable powder, obtained by chemical oxidation of aromatic heterocycles in the presence of a Lewis acid, characterized in that it operates in a medium anhydrous, which is used as Lewis acid a salt or complex or other compound of a polyvalent metal with a higher degree of oxidation and passing to a lower degree of oxidation during the reaction and which is worked without addition of dopant or additional oxidant, the powdery polymer formed providing, by molding, articles with a volume resistivity of between 1 and 10 ^-2 Ohm. cm.

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

3. Method according to claim 1, characterized in that at least one of the following bodies is used as Lewis acid: FeCl ₃ , FeBr ₃ , AsCl ₅ , SbCl ₅ , CuCl ₂ , BiCl ₅ , SbF ₅ .

4. Method for converting the electroconductive polymer obtained according to claim 1, into an electroconductive pulverulent substance suitable for the manufacture, by compacting and molding, of electroactive articles characterized in that mineral or black particles are added to the polymer of carbon.

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

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

7. Method according to claim 4, characterized in that the conductivity of the substance after compaction is 10 ^-4 to 100 S / cm (σ = 10 ⁺⁴ to 10 ^-2 Ohm. Cm).

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

9. Method according to claim 4, characterized in that a carbon black charge or a mineral charge is placed in the presence, on the one hand, of polymerization reagents and of doping of heterocyclic monomers and, on the other hand, one or more of these monomers, the latter then polymerizing, in the form of an electroconductive polymer, on the surface of the particles of said charge.

10. Method according to claim 9, characterized in that the mineral filler is first impregnated with FeCi-, this reagent acting as a polymerization and doping agent, then the mineral filler is thus impregnated in the presence of the monomer.

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

12. The method of claim 11, characterized in that metila charge impregnated with FeCl ₃ in the presence of pyrrole vapors at pressure, subatmospheric.

13. The method of claim 11, characterized in that one works at room temperature.