COMPOSITION

The present invention relates to a process for the preparation of a conductive polymer composition. The present invention also relates to conductive polymer compositions, comprising a polyamide, as well as to articles prepared from the conductive polymer compositions.

A process for preparing a conductive polymer composition is known in the art.

US 5,196,144 discloses a method to obtain a solution of conductive polyaniline and polypara (phenylene terephtalamide) (PPTA) in a strong acid. PPTA is added to improve the performance characteristics of the solid polyaniline articles, e.g. improve tear strength.

US 2006/0188718 discloses a method to obtain composite fibers of aromatic polyamide and carbon nanotubes. In these composites carbon nanotubes are used to reinforce the fibers.

Ramesh et at. (J. Phys. Chem. B 2004, 108, 8794-8798) disclose a method to dissolve pristine single walled carbon nanotubes in strong acids.

WO 2009/033933 disclose a process to obtain a conductive polymer composition, comprising the steps of a) providing a latex containing a conductive polymer; b) mixing the latex from a) with an aqueous latex of a polymer; c) removing water from the so obtained mixture; d) heating the product from c) to a temperature at which the polymer added in step b) flows and e) processing and/or solidifying the product from step d) into a desired form. It takes considerable preparations to obtain a well dispersed latex and at least 5 steps are needed to arrive at the desired form.

The above mentioned state of the art does not disclose a simple process for making a conductive polymer composition having a low percolation threshold, while the obtained solid conductive polymer composition has low amounts of a conductive polymer and a conductive filler.

There is a need for a simple process which results in 1) a conductive polymer composition with low amounts of conductive polymer and conductive filler and 2) a process which enables to make different conductive articles having the form of films, fibers, rods, tapes and the like. The present invention relates to a process for the preparation of a conductive polymer composition, comprising a polyamide, a conductive polymer and a conductive filler, wherein the process comprises the following steps:

A) Providing a solution, comprising a strong acid, a polyamide

(compound i), a conductive polymer (compound ii) and a conductive filler (compound iii);

B) Subjecting the conductive polymer composition from step A) to a

shaping step selected from the group of casting, coating, spinning or extrusion;

C) Contacting the conductive polymer composition from step B) with

water, whereby the conductive polymer composition is precipitated and/or quenched;

D) Optionally wash and/or dry the precipitated conductive polymer

composition from step C).

The present invention has the advantage that a solution is obtained of a polyamide, a conductive polymer and a conductive filler. The obtained solid conductive polymer composition has a percolation threshold at low amounts of conductive polymer and conductive filler. The solution can be shaped into film, fibers, rods, tapes and the like.

The steps of the process of the present invention will be separately discussed below.

The weight percentage (wt%) of a component or components is here and hereinafter defined as the wt% of that component or these components relative to the accumulated weight of components i-iii, unless explicitly stated otherwise. When a weight percentage of a component of components is used relative to the conductive polymer composition, the conductive polymer composition is based on a dry sample (containing less than 1 wt% water).

Step A): Various acids have been found to be suitable solvents for the components i-iii used in this invention. Typically, complete dissolution requires strong acids, although fine dispersions have also been found to be effective. Examples of strong acids are chlorosulfonic acid, fluorosulfonic acid, sulfuric acid,

trifluoromethylsulfonic acid, methylsulfonic acid, camphorsulfonic acid or nitric acid. All of the mentioned strong acids might be concentrated or if applicable fuming. The strong acid might be used alone or if applicable in combination. Generally it is preferred to select strong acids such as concentrated sulfuric acid or chlorosulfonic acid that completely dissolve or at least finely disperse the components used, without substantial degradation of the components. It is within the skill of the art based on the present disclosure to screen various strong acids, for their ability to dissolve or finely disperse the components i-iii used. Degradation of the polymeric components used can be judged from infrared spectra and decrease of viscosity of the solution or of the polymer obtained from the solution. Most preferred solvent is chlorosulfonic acid A polyamide is a polymer containing amide moieties. These amide moieties are generally formed from the reaction of a carboxylic acid or acyl halides and an amine. The reaction is a polycondensation reaction, whereby water is formed as the reaction product, which needs to be removed from the mixture to obtain a high degree of polymerization. Polyamides used in the present invention can be an aliphatic polyamide or an aromatic polyamide.

Examples of aliphatic polyamides are the common polyamides such as polyamide 6, polyamide 1 1 , polyamide 12, polyamide 4,6, polyamide 6,6, polyamide 6,9, polyamide 6, 10, polyamide 6,12, but the potential combinations may extend beyond these. Copolymers of polyamides with other monomers or block-copolymers of polyamides can also be mentioned as examples of polyamides that can be used in the process of the present invention.

Aromatic polyamides are also known as aramids. Aramids are generally prepared by the reaction between a molecule containing an aromatic moiety having an amine group and/or a carboxylic acid halide group. The most well-known examples of aramids are Nomex, Kevlar, Twaron, X-fiper and New Star). Nomex, X-Fiper, New Star and Teijinconex contain predominantly the meta-linkage and are po\y-metaphenylene isophtalamides (MPIA). Kevlar and Twaron are both p-phenylene terephtalamides (PPTA). PPTA is a product of p-phenylene diamine (PPD) and terephtaloyl dichloride (TDC or TCI).

The viscosity average molecular weight of the polyamides used in the present invention preferably ranges between 10 ⁴ to about 10 ⁹ g/mol, more preferably between 10 ⁵ and 10 ⁷ . The viscosity average molecular weight of the polyamide is calculated from the Mark-Houwink equation:

[ri]=KMW ^a Wherein: [η] is the intrinsic viscosity; M _w is the viscosity averaged molecular weight; and K and a are constants which can be found in literature, like for example the Polymer Data Handbook, edited by James E. Mark, published by Oxford University Books (1999),

(http://www.qmc.ufsc.br/~minatti/docs/20061/polvmer data handbook.pdf).

For example for the system nylon 6,6/formic acid at 25 °C the value for K is 35.3 ml/g and the value for a = 0.786.

The intrinsic viscosity can be determined from the following equation,

Wherein: [η] is the intrinsic viscosity; C is the polymer concentration; and r _e( is the relative viscosity of the polymer solution (i.e. the viscosity of the polymer relative to the viscosity of the pure solvent)

The relative viscosity, η _Γβ ι, may be determined by viscometric measurements using an Ubbelohde viscometer (Test Methods: ISO 3104, ISO 3105, ASTM D 445, ASTM D 446, IP 71 , BS 188). The viscosimetric measurements are generally conducted at 25°C, and formic acid is used as a solvent. The relative viscosity may be calculated using the following equation: η_ tp_

ηο t _Q o

Wherein: η _Γ = η _Γβ ι; η is the viscosity of the polymer solution; η ₀ = the viscosity of the pure solvent, t is the characteristic flow time of the polymer solution measured with the Ubbelohde viscosimeter, t ₀ is the characteristic flow time of the pure solvent measured with the Ubbelohde viscosimeter; p is the mass density of the polymer solution; and p ₀ is the mass density of the polymer solution. Preferably aromatic polyamides are used in the present invention. More preferable a para-polyaramide is used. Most preferable the polyamide is

polypara(phenylene terephtalamide).

A conductive polymer is an organic polymer that conducts electricity. Examples of organic conductive polymers are polyacetylenes, polypyrroles, polythiophenes, polyanilines, poly(p-phenylene sulfides), and poly(para-phenylene vinylene)s. Other less well known examples are polyindole, polypyrene, polycarbazole, polyazulene, poiyazepine, poly(fluorene)s, and polynaphthalene. Preferably the conductive polymer is selected from polyanilines, polypyrroles, polyacetylenes or polythiophenes. Most preferable the conductive polymer is a polyaniline.

Polyaniline is polymerized from the aniline monomer, and can be found in one of three idealized oxidation states: i) leucoemeraldine - white/clear; ii) emeraldine - green or blue or iii) pernigraniline - blue/violet.

In Figure 1 , x equals half the degree of polymerization (DP). Leucoemeraldine with n = 1 , m = 0 is the fully reduced state. Pernigraniline is the fully oxidized state (n = 0, m = 1) with imine links instead of amine links.

Figure 1. Main polyaniline structures n+m = 1, x = degree of polymerization.

The emeraldine (n = m = 0.5) form of polyaniline, often referred to as emeraldine base (EB), is either neutral or doped, with the imine nitrogen protonated by an acid. In the present invention preferably the EB form of polyaniline is used. Most preferably the EB form of polyaniline is protonated by an acid before dissolving it into the strong acid.

In an embodiment, the polyaniline has a molecular weight (M _w ) of between 200,000 and 1 ,500,000, preferably between 300,000 and 1 ,000,000 and more preferably between 400,000 and 800,000, according to ISO 3104. A conductive filler is a filler that conducts electricity and does not belong to the group of conductive polymers as described above. The conductive filler may be an inorganic or an organic filler. Preferably an organic filler is used. Examples of organic conductive fillers are conductive carbon filler. Examples of conductive carbon fillers are fullerenes in general and more specific carbon nanotubes, graphene and the like.

In a preferred embodiment of the invention conductive carbon fillers are used. More preferable carbon nanotubes are used. Carbon nanotubes (CNTs) are allotropes of carbon. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). A single wall carbon nanotube is a one-atom thick graphene sheet of graphite (called graphene) rolled up into a seamless cylinder with diameters of the order of a nanometer. This results in a nanostructure where the synthesized length-to-diameter ratio may exceed 1000. Multi-walled nanotubes (MWNT) consist of multiple layers of graphite rolled in on themselves to form a tube shape. In the present invention most preferable single-walled carbon nanotubes are used.

The solution or fine dispersion can be obtained by dissolving the components i- iii in the strong acid in arbitrary order. Preferably the conductive polymer and conductive filler are added before adding the polyamide to the strong acid. Most preferably the conductive filler is added first to the strong acid; secondly the conductive polymer and thirdly the polyamide is added. The solutions are preferably during the process of the invention. Preferably the solution is mechanically stirred when adding the components. As viscosity increases considerably, mixing conditions should be chosen in a way a homogeneous solution or fine dispersion is obtained before starting step B. In a preferred embodiment, the conductive filler is exfoliated before adding the conductive polymer. Exfoliation can be done by intensive mixing the filler for example with the aid of an ultrasonication mixing device.

The solution can be prepared between 0 and 100 °C. Preferable the solution is prepared between 10 and 70 °C. Most preferable the solution is prepared at room temperature.

The process of the present invention applies the components i-iii used preferably in an amount between 1 and 90 weight percent (relative to the total of the weight of the solution or fine dispersion), more preferable between 2 and 80 wt%, and most preferable between 5 and 50 wt%.

A preferred embodiment of the present invention is a process in which the following weight percentages are applied; the polyamide between 70 and 99 wt%, the conductive polymer between 1 and 20 wt% and the conductive filler between 0.01 and 10 wt% (relative to components i-iii). In an even more preferred embodiment the following weight percentages are applied; the polyamide between 80 and 98 wt%, the conductive polymer between 2 and 15 wt% and the conductive filler between 0.05 and 5 wt%. In a most preferred embodiment the following weight percentages are applied; the polyamide between 88 and 97 wt%, the conductive polymer between 3 and 10 wt% and the conductive filler between 0.1 and 2 wt%.

Step B): The solution or fine dispersion from step A) can be shaped into different articles. Preferably the shaping step is selected from casting, spincoating, spinning or extrusion. Casting, spin coating, spinning or extrusion from solution or fine dispersion are well known to the man skilled in the art. For example films can be prepared by casting or spin coating the conductive polymer composition / acid solution onto a (glass) substrate. Fibers can be spun using standard spinning equipment. Other shapes, such as rods, can be prepared by standard extrusion techniques.

Step C): The shaped conductive polymer composition from step B) is subsequently contacted with water. Upon contacting with water the conductive polymer composition will be precipitated and/or quenched into its final shape, such as film, fibers, rods, tapes and the like.

Solid compositions of the invention comprising the conductive polymer composition are prepared by precipitating and/or quenching the conductive polymer composition from the above described strong acid solutions. The addition of a liquid in which the conductive polymer composition is not soluble to the acid solution of the present invention will cause the conductive polymer composition to precipitate. Various liquids can be used, such as water or organic solvents miscible in water, such as methanol, ethanol, acetone, aqueous salt solutions, or even acids in which the conductive polymer composition is not soluble. The rate of addition of this liquid or non- solvent, temperature, mixing conditions and the like will have an effect of the degree of crystallinity of the resulting solid article. However, a crystalline structure is achieved over a wide range of these parameters, and the selection of suitable conditions is within the skill of the art in view of the present disclosure.

Though various liquids can be used, most preferably water is being used. Step D): The solid articles, comprising the conductive polymer composition obtained from step C) can optionally be washed and/or dried. Washing typically takes a few minutes, while drying is performed at elevated temperature of typically 60 °C for a few hours, typically 12 hours. The man skilled in the art will be able to choose appropriate conditions to obtain solid articles with desired levels of strong acids and liquid content.

The conductive polymer composition is conductive because the conductive polymer and conductive filler form a long-range connectivity throughout the polyamide matrix. When this long-range connectivity is reached the so called percolation threshold is surpassed and the polyamide polymer composition becomes conductive. At the percolation threshold a sudden increase in conductivity is measured. Typically the difference between conductivity below and above the percolation threshold is a few orders of magnitude as is shown in table 1 in the examples. As mentioned before, a polyamide with a conductive polymer is known in the art. This polymer composition did not show conductivity. Surprisingly in the present invention it has been found that a combination of a polyamide with a conductive polymer and a conductive filler produces a conductive composition having a percolation threshold at a low weight percentage of the conductive polymer and conductive filler.

A preferred embodiment of the present invention yields a conductive polymer composition in which the following weight percentages are applied; the polyamide between 70 and 99 wt%, the conductive polymer between 1 and 20 wt% and the conductive filler between 0.01 and 5 wt%. In an even more preferred embodiment the following weight percentages in the conductive polymer composition are applied; the polyamide between 80 and 98 wt%, the conductive polymer between 2 and 12 wt% and the conductive filler between 0.03 and 1 wt%. In a most preferred embodiment the following weight percentages in the conductive polymer composition are applied; the polyamide between 88 and 97 wt%, the conductive polymer between 3 and 10 wt% and the conductive filler between 0.05 and 0.5 wt%, and wherein the polyamide is polypara (phenylene terephtalamide). The conductive polymer composition and articles thereof of the present invention can be used for several applications. For example conductive fibers can be used in filtration, shielding, anti-static, and military applications. Conductive films can also be used in films as well as in more biomedical applications such as medical electrodes. Conductive tapes can be used in Scanning Electron Microscopy, while conductive rods are for example used in printed circuit boards.

The invention is illustrated by the following non-limiting experimental section, examples and comparative experiments.

Experimental Section

Material and Techniques

Chlorosulfonic acid was obtained as 98% chlorosulfonic acid from Fluka.

Single walled nanotubes are purchased from Carbon Nanotubes International and used without purification.

Polyaniline in emeraldine base (EB) form having a molecular weight (M _w ) of 300,000 was purchased from Sigma-Aldrich.

Polypara(phenylene terephtalamide) (PPTA) is TWARON ^® 1095 and purchased from Teijin Aramid and is used as such.

Conductivity is measured through the so called four probe technique. In this case the four probe co-linear system using a nanovoltmeter (Keithley 2182A) and programmable current source (Keithley 6220) at room temperature. The conductivity calculations are performed using appropriate correction factors based on ratio of sample diameter to probe spacing.

Examples and comparative experiments.

Scheme 1 : Making a solution or fine dispersion of protonated EB form of polyaniline in 98% chlorosulfonic acid.

Before using the purchased polyaniline it is protonated. The EB form of polyaniline was protonated by treating it with 1 M HCI in water by rigorous stirring at 500 rpm for 24 hours. The sample was then washed with excess amounts of 1 M HCI followed by washing with acetone till the filtrate becomes colorless. Afterwards, the sample was dried under vacuum at 60 °C for 24 hours.

Subsequently the required amount of protonated EB form of polyaniline is mixed with 98% chlorosulfonic acid at room temperature. The mixture is gently stirred with a glass rod, yielding a fine dispersion.

Scheme 2: Making a solution or fine dispersion of single walled nanotubes in 98% chlorosulfonic acid.

The required amount of single walled nanotubes is added to the 98% chlorosulfonic acid at room temperature. The mixture is stirred to finely disperse the single walled nanotubes. Stirring should be maintained until a homogeneous solution has been obtained. Scheme 3: Making a solution or fine dispersion of single walled nanotubes and protonated EB form of polyaniline in 98% chlorosulfonic acid.

A required amount of single walled nanotubes is added to the 98% chlorosulfonic acid at room temperature. The mixture is stirred to finely disperse the single walled nanotubes. Stirring should be maintained until a homogeneous solution has been obtained. Subsequently an amount of the protonated EB form of polyaniline is added to the homogeneous solution in order to obtain the preferred ratio as compared to the single walled nanotubes and amount in the final polymer composition. Mixing should be prolonged for at least 30 minutes at room temperature. The mixture obtained is a solution or fine dispersion.

Experiments- Experiments 1-6

In order to determine the percolation threshold of polyaniline in PPTA the following experiments were performed.

Experiment 1

PPTA in the required weight % was dissolved in 98% chlorosulfonic acid at room temperature. The mixture was stirred until a homogenous solution was obtained. The solution was either poured on a petridish or viscous drop is stretched on the glass slide. Next the stretched film is quenched in distilled water. As a result the PPTA film is precipitated. After subsequent washing for approximate 15 minutes with excess amounts of water, the sample is dried under vacuum at 60 °C for 12 hours. The conductivity of the obtained sample containing only PPTA was measured, and can be found in Table 1 as Sample 1.

Experiment 2-6

To the fine dispersion obtained from Scheme 1 , PPTA was added at room

temperatures in amounts the desired weight percentages of polyaniline in the final polymer composition are obtained. Typically the weight percentage (wt%) of PPTA was 1-7 wt% as compared to the total weight of the solution or fine dispersion. It is observed that above 3 wt% of PPTA in the solution or fine dispersion, the viscosity of the solution increased significantly. The solution or fine dispersion was either poured on a petridish or viscous drop is stretched on the glass slide. Next the stretched film is quenched in distilled water. As a result the polymer composition containing PPTA and polyaniline is precipitated. After subsequent washing for approximate 5 minutes, the sample is dried under vacuum at 60 °C for 12 hours.

The amounts of polyaniline and PPTA were chosen in a way the following weight percentage (wt%) of polyaniline (PANI) in the final polymer composition were obtained: 4, 6, 8, 10 and 12 wt%. The conductivity of the obtained samples were measured, and can be found in Table 1 as Sample 2-6.

Experiments 7-9

In order to determine the percolation threshold of single walled nanotubes in PPTA the following experiments were performed.

To the homogenous solution obtained from Scheme 2, PPTA was added at room temperatures in amounts the desired weight percentages of single walled nanotubes in the final polymer composition are obtained. Typically the weight percentage (wt%) of PPTA was 1-7 wt% as compared to the total weight of the solution or fine dispersion. It is observed that above 3 wt% of PPTA in the solution or fine dispersion, the viscosity of the solution increased significantly. The solution or fine dispersion was either poured on a petridish or viscous drop is stretched on the glass slide. Next the stretched film is quenched in distilled water. As a result the polymer composition containing PPTA and single walled nanotubes is precipitated. After subsequent washing for approximate 15 minutes, the sample is dried under vacuum at 60 °C for 12 hours.

The amounts of single walled nanotubes and PPTA were chosen in a way the following weight percentage (wt %) of single walled nanotubes (SWNT) in the final polymer composition were obtained: 0.3, 0.6 and 1.0 wt%. The conductivity of the obtained samples was measured, and can be found in Table 1 as Sample 7-9.

Examples 1 and 2: experiments 10-1 .

Experiments 10-1 1

In order to make conductive polymer compositions with minimal amounts of polyaniline and single walled nanotubes the following experiments were performed.

To the solution or fine dispersion obtained from Scheme 3, PPTA was added at room temperatures in amounts the desired weight percentages of single walled nanotubes and polyaniline in the final conductive polymer composition are obtained. Typically the weight percentage (wt %) of PPTA was 1 -7 wt% as compared to the total weight of the solution or fine dispersion. It is observed that above 3 wt% of PPTA in the solution or fine dispersion, the viscosity of the solution increased significantly. The solution or fine dispersion was either poured on a Petridis or viscous drop is stretched on the glass slide. Next the stretched film is quenched in distilled water. As a result the conductive polymer composition containing PPTA, single walled nanotubes and polyaniline is precipitated. After subsequent washing for approximate 15 minutes, the sample is dried under vacuum at 60 °C for 12 hours.

The amounts of single walled nanotubes, polyaniline and PPTA were chosen in a way the following weight percentage (wt %) of single walled nanotubes (SWNT) and polyaniline (PANI) in the final conductive polymer composition were obtained: 0.3 wt% of SWNT and 8 wt% of PANI; 1.0 wt% of SWNT and 8 wt% of PANI. The conductivity of the obtained samples was measured, and can be found in Table 1 as Sample 10-1 1. Results and Discussion

Results

Table 1 shows the conductivity measurements of Samples 1-11 obtained from the experiments 1-9 and examples 1 and 2 (experiments 10-11). The description mentions the abbreviations of the components present in the polymer composition; PPTA = Polypara (phenylene terephtalamide), PANI = polyaniline and SWNT = single walled nanotubes.

Table 1. Conductivity measurements for Samples 1-1 1. Discussion From the conductivity measurements shown in Table 1 it becomes clear that the percolation threshold of PANI in PPTA is reached at loadings of 12 wt% (Sample 6). The percolation threshold for SWNT in PPTA is reached at loadings of 0.6 wt% (Sample 8). Surprisingly when both PANI and SWNT are added the percolation threshold is found at lower amounts compared to adding PANI or SWNT separately (Sample 10). Now PANI loadings of only 8 wt% are needed (in combination with 0.3 wt% of SWNT) as compared to 12 wt% of PANI when added separately. On the other hand SWNT loadings of only 0.3 wt% are needed (in combination with 8 wt% of PANI) as compared to 0.6 wt% of SWNT when added separately.

Andretta ef al. (Polymer Communications 1991 , 31, 275-278) showed that the use of polyaniline only deteriorates the mechanical properties the mechanical properties of the PPTA-PANI fiber. On the other hand extensive use of SWNT is not beneficial from an economical point of view. Therefore this invention may serve as a new process for making conductive polymer compositions yielding a low percolation threshold, having low amounts of a conductive polymer (PANI) and a conductive filler (SWNT).

The conductivity can be tuned by varying the amount of SWNT as is shown in sample 1 1. Again it can be seen that the combination of PANI and SWNT yields a higher conductivity (Sample 1 1 ) when compared to conductivity levels of SWNT only (Sample 9) at the same loadings of SWNT. The conductivity level is one order of magnitude higher.

Without being bound to any theory, it is believed that the combination of a conductive polymer and conductive filler (preferably of high aspect ratio) yields some kind of synergetic effect, which is beneficial for lowering the percolation threshold when compared to adding a conductive polymer or conductive filler separate to the polyamide.