The invention relates to a process for the preparation of a polymer composition containing an electrically conductive polymer which involves polymerisation of poly erisable monomer units to yield an electrically conductive polymer in a reaction mixture containing a pH buffer.

Such a process is described by S. Rapi et al. in Synthetic Metals, 24_ (1988), pp. 217-221. According to the process described there, pyrrole monomers are polymerised in the presence of a catalyst to yield the electrically conducting polypyrrole polymer. During the polymerisation, the release of protons leads to incorporation of an amount of 2,5-bis-(2-pyrrolyl)pyrrolidine (BPP) in the polypyrrole. This gives rise to a significant reduction of the electrically conducting properties. To largely avoid the undesirable incorporation of the BPP impurity in polypyrrole, polymerisation must, according to Rapi, take place in a reaction mixture that is pH buffered, in such a manner that the pH is higher than 1 and lower than 7. To this end a buffer is added to the reaction mixture. This results in a significant improvement of the electrically conducting properties of the electrically conducting polymer that is obtained.

Although the process described by S. Rapi et al. is suitable for the preparation of an electrically conducting polymer with good electrically conducting properties, use of this process has the following major disadvantage. In the presence of a catalyst the polymerisation reaction of the monomer units is immediately initiated. As a result, an electrically conducting polymer is directly obtained, which is precipitated as a powder in the reaction mixture. The

2532 _ 2 , _-

precipitate thus formed is not suitable for thermoplastic processing and is not or hardly capable of being shaped into a coherent moulding compound.

It is the object of the invention to provide a process for the preparation of a polymer composition containing an electrically conducting polymer in which the above-mentioned disadvantage is eliminated. This is achieved with 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 subsequently polymerised to yield an electrically conducting polymer. 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 a 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), where

X is -N-, -S- or -0-;

I

H Rl is hydrogen, -C(0)OH, -C(0)C(0)0H, -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)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.

Preferably, use is made of pyrrole-2-carboxylic acid. A synthesis of this precursor monomer is described in J. Am.

Pharm. Assoc. 45_, 509 (1956). All combinations of X, Rl, R2, R3 and R4 not excluded above are possible. The groups Rl and R4 can be eliminated thermally or photochemically to yield a pyrrole, thiophene or furan monomer which is optionally substituted in the R2 and/or the R3 positions. Thus, this precursor monomer is deblocked, allowing free polymerisation via the

Rl and R4 positions. The groups R2 and R3 can be identical or different.

Other suitable precursor monomers that can be used to prepare an electrically conducting polymer are precursor monomers having a structure according to formula (II), 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. 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 be activated, for example, by means of a thermal or a photochemical treatment. In the process according to the invention any precursor monomer can be applied.

After the precursor monomers have been activated to yield polymerisable monomers, polymerisation can take place. Polymerisation is usually effected in the presence of a suitable catalyst. Catalysts that can be added to the reaction mixture in the process according to the invention are generally known and can be chosen, for example, from the group of inorganic acids, such as hydrochloric acid, sulphuric acid, chlorosulphonic acid and nitric acid; Lewis acids such as 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, a nitrate, a sulphonate and/or an acetyl acetonate. Examples of other suitable catalysts are ozone, diazoniu salts, organic catalysts, for example benzoquinone, and persulphates, such as sodium persulphate, ammonium persulphate and potassium persulphate. In certain polymerisation reactions the activity of Ziegler-Natta catalysts and K ₂ Cr ₂ 0 ₇ is good. Examples of oxidants with a good activity are FeCl ₃ , FeBr ₃ , FeCl ₃ .6H ₂ 0, Fe(N0 ₃ ) ₃ .9H ₂ 0, CuCl ₂ .2H ₂ 0, K ₃ Fe(CN) ₆ , Fe(C10 ₄ ) ₃ .9H ₂ 0, Fe ₂ (S0 ₄ ) ₃ .5H ₂ 0, CuS0 ₄ , Cu(N0 ₃ ) ₂ and (C _S H ₅ ) ₂ Fe ⁺ FeCl ₄ - . Optionally, a mixture

of various catalysts is used. Catalysts with an exceptionally good activity are iron(III)chloride and copper(IΙ)chloride.

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. More preferably, this ratio is between 2:1 and 3:1. If desired, the polymer composition prepared using the process according to the invention contains a matrix polymer. If the polymer composition contains this matrix polymer it is extremely suitable for the preparation of moulded articles such as fibres, films and articles. 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, such as 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, such as polyethylene, ultrahigh molecular weight polyethylene (UHMWPE) and polypropylene, polyvinyl acetate, polyvinyl alcohol, polyesters, for example polyethylene terephthalate and polybutylene terephthalate, polycarbonates, polytetrafluoroethylene, polyether imides, polyimides, polyamides, polyamide-imides, polyethylene oxide, polybutadiene rubbers, and the like. If desired, a mixture of various polymers can be applied as matrix polymer.

The desired weight ratio between the amount of matrix polymer and the amount of electrically conducting

2532 _- 6 _-

polymer in the polymer composition prepared using the process 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. High concentrations of matrix polymer have an adverse effect on the conductivity in the resulting polymer composition, while low 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 reaction mixture is often present in a suitable dispersing agent. The dispersing agent 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, such as 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 dispersing agents. In the process according to the invention the reaction mixture contains a pH buffer so that the pH of the mixture, which contains precursor monomer, catalyst and pH buffer, is approximately between 1 and 7. A suitable pH buffer is, for example, the conjugated base of a weak acid in the form of a carboxylate, for example a carbonate, a bicarbonate, an oxalate, an acetate, a formate and a phthalate; a phenolate containing an electron-attracting group, for example 3-nitrophenolate, 3-chlorophenolate and

3,5-dinitrophenolate; or a phosphate. It is also possible to use an amide, for example urea, formamide, acetamide and N- acetyl benzamide. Use can also be made of tertiary amides as pH buffer. Examples of such tertiary amines are triethyl amine, l,4-diazabicyclo[2.2.2]octane and aromatic amines, for example pyridine, imidazole, pyrazine and pyrimidine. If desired a mixture of several buffers is used. Preferably, the buffer contains urea. The buffer is added to the reaction mixture in at least such an amount that all protons released during the polymerisation are caught, the pH in the reaction mixture preferably not becoming higher than 7.

In a suitable embodiment of the process according to the invention a solution is, for example, prepared of precursor monomer, catalyst and buffer in a suitable solvent. Subsequently, if desired the matrix polymer is added to the solution obtained. This can for example be done by impregnating a porous article moulded from the matrix polymer with the mixture of precursor monomer, catalyst and buffer. It is also possible for the matrix polymer to be dissolved in the mixture. The polymer composition 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. These are generally known methods.

The electrically conducting properties of the electrically conducting polymer that is obtained 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, the polymer composition prepared using the process according to the invention contains up to 60 weight percent of fillers and/or antioxidants. Examples of fillers are talc, fibres, pigments, kaolin, wollastonite and glass.

Products obtained by the process according to the invention can be applied in widely divergent fields. Exponents of these are the fields of 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 conducting properties have been 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 ].

Example I

At a temperature of 20°C 6.80 g of FeCl ₃ was dissolved in 12 ml of tetrahydrofuran. Then, 2.00 g of pyrrole-2-carboxylic acid and 1.09 g of urea were dissolved in 20 ml of ethanol at a temperature of 20°C. The two solutions were combined and the resulting solution was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds.

532 _- _Q 9 _-

The resulting film was heated for 5 minutes in a oven at a temperature of 110°C. The film colour gradually changed from reddish brown to black.

The black film was extracted with acetone and air- dried. The specific conductivity of the film was measured to be 2.5 S/cm.

Example II

At a temperature of 20°C 500 mg of pyrrole-2- carboxylic acid and 270 mg urea were dissolved in 5 ml of solvent (85 vol.% methanol and 15 vol.% water). In addition, 1.68 g of FeCl ₃ was dissolved in 5 ml of solution (85 vol.% methanol and 15 vol.% water) at a temperature of 20°C. The two solutions were combined and the resulting solution was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds. After having been air-dried the resulting film was placed between two glass plates and heated for 5 minutes in a oven at a temperature of 110°C.

The resulting black film was extracted with acetone and air-dried. The specific conductivity of the film was measured to be 11.2 S/cm.

Example III

At a temperature of 20°C 1.00 g of 3- methylthiophene-2-carboxylic acid and 0.42 g urea were dissolved in 5 ml of diethyl ether. In addition, 2.28 g of FeCl ₃ was dissolved in 5 ml of diethyl ether at a temperature of 20°C. The two solutions were combined and the resulting solution was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds.

The impregnated film was heated for 5 minutes in a oven at a temperature of 120°C. After extraction the deep- red film was doped with NOSbF ₆ (0.50 g in 30 ml of CH ₃ CN) until the film colour (after some 10 seconds) changed into

blue-grey .

The resulting film was extracted with acetone and air-dried. Then, the entire cycle comprising impregnation, heating, doping, extraction and drying was repeated. The specific conductivity of the film was measured to be 20.0 S/cm.

Example IV

At a temperature of 20°C 1.00 g of 3-methyl- thiophene-2-carboxylic acid and 0.42 g urea were dissolved in 5 ml of solvent (6 parts by volume of methanol, 1 part by volume of water and 3 parts by volume of diethyl ether). In addition, 2.28 g of FeCl ₃ was dissolved in 5 ml of this ternary mixture at a temperature of 20°C. After the two solutions had been combined, the resulting solution was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds, and subsequently this film was heated for 10 minutes in a oven at a temperature of 120°C.

The resulting film was extracted with acetone and doped in the same manner as in example III. After the resulting film had been extracted with acetone and air- dried, the specific conductivity of the film was measured to be 28.0 S/cm.

Comparative experiment A

At a temperature of 20°C 0.25 g of pyrrole-2- carboxylic acid was dissolved in 1.5 ml of tetrahydrofuran. Then, 0.70 g of FeCl ₃ was dissolved in 2.5 ml of ethanol at a temperature of 20°C. The two solutions were combined, and the resulting solution was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds.

The resulting film was heated for 5 minutes in a oven at a temperature of 110°C. The film colour gradually changed from reddish brown to black.

The film was extracted with acetone and air-dried.

2532 _ _{l λ} _

The specific conductivity of the film was measured to be 0.5 S/cm.

Comparative experiment B

At a temperature of 20°C 0.50 mg of pyrrole and 0.45 g urea were dissolved in 8 ml of solvent (85 parts by volume of methanol, 15 parts by volume of water). In addition, 2.78 g of FeCl ₃ was dissolved in 5 ml of the same solvent at a temperature of 20°C. The two solutions were combined, and instantaneously a black precipitate was formed. The resulting mixture was used to impregnate a 47 μm thick, porous polyethylene film (5.0 * 6.0 cm ² , porosity 86%), the impregnation period being 60 seconds. The film was then heated in an oven at a temperature of 110°C for 15 minutes.

The grey, inhomogeneous film was subsequently extracted with acetone and air-dried. The specific conductivity of the film was measured to be 1.0 S/cm.