PROCESS FOR THE PREPARATION OF AN ELECTRICALLY CONDUCTING POLYMER

Abstract: The invention relates to a process for the preparation of an electrically conducting polymer, in which polymerisable monomer units in a reaction mixture polymerise to yield and electrically conducting polymer in the presence of a catalyst containing a strongly oxidising cation and a stability promotion anion. The process according to the invention is characterised in that polymerisable monomer units are obtained by in situ activation of precursor monomers. With the process according to the invention it is possible to use simple processing steps to shape moulding compounds and prepare products that contain electrically conducting polymers. Instantaneous, premature polymerisation is prevented; polymerisation takes place at a point of time on one's own choice. In the process according to the invention the precursor monomers are given the desired shape, after which they can at any given moment be subjected to in situ activation to yield polymerisable monomeric units. The activated polymerisable monomeric units subsequently polymerise to give an electrically conducting polymer.

Description: PROCESS FOR THE PREPARATION OF AN ELECTRICALLY CONDUCTING POLYMER The invention relates to a process for the preparation of an electrically conductive polymer in which polymerisable monomer units in a reaction mixture polymerise to yield an electrically conducting polymer in the presence of a catalyst, comprising an oxidising cation and a stability promoting anion. Such a process is known from US-A-4,697,001. According to the process disclosed there, an electrically conducting polypyrrole is prepared by solution polymerisation of pyrrole monomers in the presence of a catalyst. The catalyst contains a strongly oxidising cation, e.g. Fe 3+ and a relatively large anion, especially alkyl or arylsulphonate. The relatively large anion has a stabilising effect on the electrically conducting properties of the electrically conducting polymer formed and also serves as dopant, improving the electrically conducting properties of the electrically conducting polymer. The electrically conducting polymer prepared is obtained in the form of a powder by means of a precipitation step. Application of the process disclosed in US-A- 4,697,001 for the preparation of an electrically conducting polymer with good electrically conducting properties has one major drawback. In the presence of the catalyst the polymerisation reaction of the monomer units is immediately initiated. This results in direct formation of an electrically conducting polymer, which is precipitated as a powder in the reaction mixture. The powder thus formed cannot or hardly be shaped into a coherent moulding mass. It is the object of the invention to provide a process in which the above-mentioned drawback is eliminated. This goal is achieved by the process according to the invention in that the polymerisable monomer units are obtained through in-situ activation of precursor monomers. With the process according to the invention it is possible to use simple processing steps to shape moulding compounds and manufacture products that contain electrically conducting polymers. Premature polymerisation is prevented, polymerisation taking place at a point of time of one's own choice. In the process according to the invention the precursor monomers are given the desired shape, after which they can at any given moment be subjected to in situ activation to yield polymerisable monomeric units. The activated polymerisable monomeric units are subseguently polymerised to yield an electrically conducting polymer The process according to the invention can be used to prepare moulding compounds in which relatively small amounts of electrically conducting polymer are sufficient for obtaining good electrically conducting properties. According to the invention a precursor monomer is understood to be a molecule which as such cannot polymerise under the prevailing process conditions, not even when a catalyst is present. After a simple conversion step, however, this molecule is converted into a polymerisable monomer unit. This conversion step may comprise removal of a blocking group that screens off one or more reactive sites. It is also possible to remove an electron-attracting group which raises the oxidation potential of the molecule and which thus prevents polymerisation. In another embodiment an intramolecular reaction takes place, for example a retro- Diels-Alder reaction, to convert precursor monomer into a polymerisable monomeric unit. Any precursor monomer which after activation becomes a polymerisable monomeric unit from which an electrically conducting polymer can be formed is suitable for use in the process according to the invention. Examples of suitable precursor monomers are molecules having a structure according to formula (I) of the formula sheet, where X is -N-, -S- or -0-; I H Rl is hydrogen, -C(0)OH, -C(0)C(0)OH, -C(0)H, -S0 3 H, -I or -Br; R2 is hydrogen, an alkyl group (with 1-10 carbon atoms), -C(0)OH, or a halogen; R3 is hydrogen, an alkyl group (with 1-10 carbon atoms), -C(0)OH, or a halogen; R4 is hydrogen, -C(0)0H, -C(0)C(0)0H, -C(0)H, -S0 3 H, -I or -Br; it being understood that Rl and R4 are not simultaneously hydrogen, and that R2 and R3 can both form part of a closed ring structure. For formula (I), the formula sheet is referred to. In the precursor monomer according to formula I all combinations of X, Rl, R2, R3 and R4 are possible. The groups Rl and R4 can be eliminated thermally or photochemically, yielding a pyrrole, thiophene or furane monomer which is optionally substituted in the R2 and/or the R3 position. The monomer formed is polymerisable, polymerisation being possible via the Rl and R4 positions. The groups R2 and R3 can be identical or different. Also, the groups R2 and R3 can both form part of a closed ring structure. A suitable example of such a precursor monomer is 3,4-(alkylene-vic-dioxy-) thiophene-2,5-dicarboxylic acid (see Tetrahedron 1967, vol. 23, p. 2137 ff.). Preferably, the precursor monomer is pyrrole-2-carboxylic acid. A synthesis of this precursor monomer is described in J. Am. Pharm. Assoc. 4_5_, 509 (1956). Other suitable precursor monomers that can be used to prepare an electrically conducting polymer are precursor monomers having a structure according to formula (II) of the formula sheet, where XI and X2 are identical or different and are -N-, -S- or -0-; I R4 Rl and R2 are identical or different and are hydrogen or an alkyl group with 1-10 carbon atoms; R4 is hydrogen or an alkyl, aryl or alkoxy group. For formula (II), see the formula sheet. The precursor monomers according to formula (II) can, for example, be synthesised as described in J. Chem. Soc. Perkin Trans. I (1985), pp. 1277-1284. Another suitable precursor monomer is 4-amino benzoic acid (see P. Ruelle, J. Chem. Soc. Perkin trans II, 1953 (1986). The process according to the invention is not restricted to the simultaneous use of precursor monomers of one type. Combinations of all types of precursor monomer are possible. Optionally, also precursor oligomers can be applied. The precursor monomers can, for example, be activated by means of a thermal or a photochemical treatment. In the process according to the invention any precursor monomer can be applied. The precursor monomers are usually present in a suitable solvent. The solvent is often chosen from the group consisting of water; aromatic compounds, for example benzene, toluene and xylene; alcohols, for example methanol and ethanol; hydrocarbons, for example pentane and hexane; ethers, for example dioxane, diethyl ether, ethyl methyl ether and tetrahydrofuran; ketones, for example acetone, diethyl ketone and methyl ethyl ketone; halogenated compounds, for example CHC1 3 , CH 2 C1 2 and carbon tetrachloride; esters, for example ethyl formate and ethyl acetate; and compounds for example acetonitrile, nitromethane, dimethyl sulphoxide, dimethyl formamide, triethyl phosphate, dimethyl acetamide and pyridine. It is also possible to use a mixture of various solvents. The reaction mixture contains a catalyst that contains a strongly oxidising cation and a stability promoting anion. The strongly oxidising cation is chosen. for example, from the group formed by Fe 3+ , Os 4+ , Mn + , Cr 3+ , K + , Cu 2+ , Ce 4+ and (C 6 H 5 ) 3 C + . Preferably, the strongly oxidising cation is Fe 3+ . The stability promoting anion is usually a conjugated base of a strong acid. Stability promoting anion in the framework of this invention is understood to be the anion of a relatively large organic compound, for example an aryl sulphonate compound, an alkyl sulphonate compound, a carboxylate compound, an acetate compound, or an acetonate compound. Preferably, the stability promoting anion is an aryl sulphonate compound or an alkyl sulphonate compound, substituted or not. Examples of such compounds are dodecyl benzene sulphonate, perfluorooctyl sulphonate, benzene sulphonate, ethyl benzene sulphonate, 2-naphthalene sulphonate, trifluoro acetate, perfluoro butyrate, methyl sulphonate, p-toluene sulphonate, 2,7-naphthalene disulphonate, trifluoro methyl sulphonate, 2,6-naphthalene disulphonate, 1,5-naphthalene disulphonate, dinonyl naphthalene sulphonate, 1,3-benzene disulphonate and 2,4,5-trichlorobenzene sulphonate. If desired a mixture of several of these compounds is used. Preferably, p-toluene sulphonate is used as stability promoting anion. The catalyst is usually added in a molar ratio to the precursor monomer that is between 1:10 and 10:1. Preferably, this ratio is between 1:3 and 3:1. To improve the electrically conducting properties of the electrically conducting polymer, the reaction mixture can also contain a second catalyst. The second catalyst is chosen, for example, from the group of inorganic acids, for example hydrochloric acid, sulphuric acid, chlorosulphonic acid and nitric acid; Lewis acids, for example compounds containing positive ions of iron, aluminium, tin, titanium, zirconium, chromium, manganese, cobalt, copper, molybdenum, tungsten, ruthenium, nickel, palladium and/or platinum; and a halogen, a sulphate and/or a nitrate. Examples of other suitable catalysts are ozone, diazonium salts, organic oxidants for example benzoguinone, and persulphates, for example ammonium persulphate, sodium persulphate and potassium persulphate. In certain polymerisation reactions Ziegler-Natta catalysts and K 2 Cr 2 0 7 have a good activity. Examples of catalysts with a good activity are FeCl 3 , K 3 Fe(CN) 6 , FeBr 3 , FeCl 3 .6H 2 0, Fe(N0 3 ) 3 .9H 2 0, Cu(N0 3 ) 2 , Fe(C10 4 ) 3 .9H 2 0, CuCl 2 .2H 2 0, CuS0 4 , Fe 2 (S0 4 ) 3 .5H 2 0 and (C 5 H 5 ) 2 Fe + FeCl 4 " . If desired, a mixture of several catalysts can be applied. In view of the extremely high level of the electrically conducting properties of the resulting electrically conducting polymer, the second catalyst preferably contains iron(III)chloride. The second catalyst is usually added to the precursor monomer in a molar ratio that is between 1:10 and 10:1. Preferably, this ratio is between 1:3 and 3:1. In a special embodiment of the process according to the invention the reaction mixture contains both a catalyst, which contains a strongly oxidising cation and a stability promoting anion, and a second catalyst, the molar ratio between the two catalysts being between 10:1 and 1:10. Preferably, the ratio between the catalyst containing a strongly oxidising cation and a stability promoting anion and the second catalyst is between 10:1 and 1:2, more preferably between 2:1 and 1:2. If desired the electrically conducting polymer can be formed within a polymer matrix. To this end the reaction mixture has to be present in a finely divided form in the polymer matrix and activated and polymerised in that position. This form and the amount of precursor monomer present must be chosen so as to yield in the product after polymerisation continuous paths of conducting polymer. The amount required ranges from 1-50 wt%, preferably from 5-30 wt%. Examples of suitable forms will be given below. A person skilled in the art will appreciate also other methods to obtain the required finely divided form. The required form can for instance be obtained by dispersing or dissolving the matrix polymer in the reaction mixture. The dispersion or solution then can be shaped by the usual techniques and after shaping the conducting polymer can be formed by deblocking the precursor monomer. Another possible embodiment is to impregnate a porous object of the matrix polymer with the reaction mixture and subsequently conducting the steps required for the forming of the conductive polymer described hereinbefore. The polymer composition containing the reaction mixture and the matrix polymer can at a moment of one's own choice be heated or irradiated with a radiation source, so that the precursor monomers are deblocked. Deblocking can for example take place immediately after shaping of the polymer composition, but it is also possible to wait till a later point of time. Generally, this point of time will be chosen after the final form has been obtained. After the polymerisation reaction any catalyst residues and other low- molecular components can be removed by means of extraction and/or evaporation. This makes the polymer composition finally prepared extremely suitable for the preparation of moulding compounds for example granules, fibres or films. The matrix polymer can be chosen within very broad limits. Depending on the requirements to be met by the polymer composition, for example as regards the mechanical properties, in principle any polymer may be chosen. Because of their processing properties thermoplastic polymers are preferred, but thermosetting polymers, for example resins and binders, are also extremely suitable as matrix polymer for certain applications. Examples of suitable matrix polymers are polyvinyl chloride or copolymers of vinyl chloride and other vinyl monomers, polyvinylidene fluoride or copolymers of vinylidene fluoride and other vinyl monomers, polystyrene or copolymers of styrene and other monomers, for example maleic anhydride and maleimide, polyacrylates or copolymers of an acrylate with other monomers, polyvinyl carbazole, polyolefins, for example polyethylene, ultrahigh molecular polyethylene (UHMWPE) and polypropylene, polyvinyl acetate, polyvinyl alcohol, polyesters, for example polyethylene terephthalate and polybutylene terephthalate, polycarbonates, polyether imides, polyimides, polytetrafluoroethylene, polyamides, polyamide-imides, polyethylene oxide, polybutadiene rubbers, alkyd resins, polyurethanes, acrylate resins, and the like. If desired, a mixture of several polymers can be applied as matrix polymer. The desired weight ratio between the amount of matrix polymer and the amount of electrically conducting polymer in the polymer composition according to the invention is a consequence of the optimisation between the various desired properties, for example the electrically conducting properties on the one hand and the desired mechanical properties on the other. Higher concentrations of matrix polymer have an adverse effect on the conductivity in the resulting polymer composition, while lower concentrations of matrix polymer may have an adverse effect on the desired mechanical properties. The weight ratio between the amount of matrix polymer and the amount of electrically conducting polymer in the polymer composition according to the invention may vary within broad limits. As a rule this ratio is between 1:99 and 99:1, preferably between 1:15 and 15:1. The optimum concentration of the matrix polymer is determined to an important extent by the molecular weight and the degree of branching of the matrix polymer. Depending on the electrically conducting polymer obtained, the electrically conducting properties can be improved by means of an (oxidative or reducing) doping step, in which use can be made of the known doping techniques and reagents. These are mentioned, for example, in 'Handbook of conducting polymers' (T.A. Skotheim, Marcel Dekker Inc., New York, USA (1986)). Optionally, up to 60 weight percent of fillers and/or antioxidants can be added to the polymer composition prepared using the process according to the invention. Examples of fillers to be added are talc, fibres, pigments, kaolin, wollastonite and glass. After shaping of the polymer composition any catalyst residues and other low-molecular components can be removed by means of extraction and/or evaporation. These are generally known methods. Products obtained by the process according to the invention can be applied in widely divergent fields. Exponents of these are coatings and EMI-shielding devices. Examples of other suitable applications are conducting films. The invention will be elucidated by means of the following examples, without being restricted thereto. The specific conductivity is measured according to the so-called four point method. A concise description of this method is given in EP-A-314311, while a more detailed description can be found in H.H. Wieder, Laboratory Notes on Electrical and Galvanomagnetic Measurements, Elsevier, New York, 1979. This method is used to measure the specific conductivity: σ - (L/A) * (1/R), where σ = specific conductivity [S/cm] L = distance between the two innermost electrodes [cm] R = resistance [Ohm] A = transverse surface area [cm 2 ]. Examples and comparative experiments Preparation method for iron(III) (p-toluene sulphonate) 3 14.6 g of FeCl 3 .6H 2 0 (Merck) was dissolved in 204 ml of demineralised water. A clear solution with a dark yellow - orange colour was obtained. A solution of 6.5 g of NaOH (Merck, pure) in 44 ml of demineralised water was subsequently added to this solution, which was meanwhile being stirred vigorously. The resulting iron hydroxide was decanted, washed three times with demineralised water, and filtered using a glass filter (20-40 μ , D3). The iron hydroxide was dissolved in 102 ml of methanol. A solution of 29 g of p-toluene sulphonic acid monohydrate (Merck) in 44 ml of methanol was added to this solution. A black suspension was formed. This suspension was heated for 2 hours at a temperature of 45°C while being stirred, and this caused the precipitate to dissolve almost entirely. The resulting solution was subsequently filtered using filter paper. Under reduced pressure the solvent was largely removed with a rotating film evaporator at a temperature of 50°C. The resulting product was then dried for 196 hours in a vacuum stove at a temperature of 50°C. The remaining orange-yellow powder was finally ground using pestle and mortar and stored in a desiccator with P 2 0 5 (N 2 atmosphere). The iron(III) (p-toluene sulphonate) 3 yield was 29 g. Example I A solution was prepared of 0.25 g of pyrrole-2- carboxylic acid in 1.5 ml of tetrahydrofuran (solution A). A second solution was prepared of 1.48 g of iron(III)(p- toluene sulphonate) 3 and 0.42 g of iron(III)chloride in 2.5 ml of tetrahydrofuran (solution B). The two solutions.were poured together, yielding a dark solution. Subsequently, a porous PE film (2*4 cm 2 , thickness 47 μm, porosity 85%) was impregnated with this solution by immersing the film for 30 seconds. The impregnated film was air-dried for 15 minutes and then kept in an oven at a temperature of 110°C (nitrogen atmosphere) for 5 minutes. Polymerisation yielding polypyrrole occurred. Finally the film was extracted with acetone until the acetone remained colourless, and then another time with methanol. The specific conductivity measured, σO, was 0.2 S/cm. Example II Example I was repeated, but this time a film with a thickness of 47 μm and an oven temperature of 136°C were used. Polymerisation yielding polypyrrole took place. The specific conductivity measured, σ0, was 0.3 S/cm. Example III A solution was prepared of 0.25 g of pyrrole-2- carboxylic acid in 1.5 ml of tetrahydrofuran (solution A). A second solution was prepared of 0.74 g of iron(III)(p- toluene sulphonate) 3 and 0.63 g of iron(III)chloride in 2.5 ml of tetrahydrofuran (solution B). The two solutions were poured together at a temperature of 20°C, yielding a dark solution. Subsequently, a porous PE film (2*4 cm 2 , thickness 47 μm) was impregnated with this solution by immersing the film for 30 seconds. The impregnated film was air-dried for 15 minutes and then kept in an oven for 5 minutes at a temperature of 136°C (nitrogen atmosphere). Polymerisation yielding polypyrrole occurred. Finally the film was extracted with acetone until the acetone remained colourless, and then another time with methanol. The specific conductivity measured, σ0, was 0.2 S/cm. Example IV A solution was prepared of 0.25 g of pyrrole-2- carboxylic acid in 1.5 ml of tetrahydrofuran (solution A). A second solution was prepared of 2.21 g of iron(III)(p- toluene sulphonate) 3 and 0.21 g of iron(III)chloride in 2.5 ml of tetrahydrofuran (solution B). The two solutions were poured together at a temperature of 20°C, yielding a dark solution. Subsequently, a porous PE film (2*4 cm 2 , thickness 47 μm) was impregnated with this solution by immersing the film for 30 seconds. The impregnated film was air-dried for 15 minutes and then kept in an oven for 5 minutes at a temperature of 136°C (nitrogen atmosphere). Polymerisation to polypyrrole occurred. Finally the film was extracted with acetone until the acetone remained colourless, and then another time with methanol. The specific conductivity measured, σ0, was 0.07 S/cm. Example V Of the films obtained in examples I, II, III and IV the stability of the conducting properties was measured by placing the films for 24 hours in an oven through which air was passed, the temperature being 120°C. After this tempera- ture treatment the specific conductivity, σl, was measured again. The properties measured are listed in Table 1: film specific conductivity [S/cm] retention σp σl σl/σO I 0.10 II 0.08 III 0.04 IV 0.11 Comparative experiment A In 7 ml of tetrahydrofuran 2.46 g of iron(III)-(p- toluene sulphonate) 3 was dissolved at a temperature of 20°C. Subsequently, 250 mg of pyrrole was added, which immediately resulted in formation of a black precipitate. The examples prove that both the electrically conducting properties and the stability of the electrically conducting properties are good when the electrically conducting polymer is prepared by the process according to the invention. In comparative experiment A a black precipitate is immediately formed, which can only be processed as a powder.

Claims: C L A I M S 1. Process for the preparation of an electrically conducting polymer in which polymerisable monomer units in a reaction mixture polymerise to yield an electrically conducting polymer in the presence of a catalyst containing a strongly oxidising cation and a stability promoting anion, characterised in that the polymerisable monomer units are obtained by in situ activation of precursor monomers. 2. Process according to claim 1, characterised in that the precursor monomer has a structure according to formula I, where X is -N-, -S- or -0-; I H Rl is hydrogen, -C(0)OH, -C(0)C(0)OH, -C(0)H, -S0 3 H, -I or -Br; R2 is hydrogen, an alkyl group (with 1-10 carbon atoms), -C(0)OH, or a halogen; R3 is hydrogen, an alkyl group (with 1-10 carbon atoms), -C(0)OH, or a halogen; R4 is hydrogen, -C(0)OH, -C(0)C(0)OH, -C(0)H, -S0 3 H, -I or -Br; it being understood that Rl and R4 are not simultaneously hydrogen, and that R2 aid R3 can both form part of a closed ring structure. 3. Process according to claim 1 or 2, characterised in that the precursor monomer is pyrrole-2-carboxylic acid. 4. Process according to any one of claims 1-3, characterised in that the oxidising cation is Fe 3+ . 5. Process according to any one of claims 1-4, characterised in that the stability promoting anion is a substituted or unsubstituted aryl or alkyl sulphonate compound. 6. Process according to any one of claims 1-5, characterised in that the stability promoting anion is p-toluene sulphonate. 7. Process according to any one of claims 1-6, characterised in that the molar ratio between catalyst and precursor monomer is between 1:3 and 3:1. 8. Process according to any one of claims 1-7, characterised in that the reaction mixture also contains a second catalyst. 9. Process according to claim 8, characterised in that the second catalyst contains iron(III)chloride. 10. Process according to claim 8 or 9, characterised in that the molar ratio between the second catalyst and the precursor monomer is between 1:3 and 3:1. 11. Process according to any one of claims 8-10, characterised in that the molar ratio between the catalyst containing a oxidising cation and a stability promoting anion and the second catalyst is between 10:1 and 1:2. 12. Process according to any one of claims 8-11, characterised in that the molar ratio between the catalyst containing a oxidising cation and a stability promoting anion and the second catalyst is between 2:1 and 1:2. 13. Process according to any one of claims 1-12, characterised in that the reaction mixture also contains a matrix polymer. 14. Process as substantially described and elucidated on the basis of the examples.

Inventors: BROUNS MATTHIAS JOZEF GERTRUDA, SCHELLEKENS RONALD MICHAEL ALE, BROUNS, MATTHIAS, JOZEF, GERTRUDA, SCHELLEKENS, RONALD, MICHAEL, ALEXANDER, MARIA
Applicants: DSM NV, DSM N.V.
Application year: 1993
Main classification: C08G61
IPC codes: C08G61, H01B1