EP1268608A1

EP1268608A1 - Method of production of polyanilines

Info

Publication number: EP1268608A1
Application number: EP01900818A
Authority: EP
Inventors: Joseph D. Jakowski; Gregory M. Kaplan
Original assignee: Donaldson Co Inc
Current assignee: Donaldson Co Inc
Priority date: 2000-01-04
Filing date: 2001-01-02
Publication date: 2003-01-02
Also published as: WO2001049773A1; JP2004500456A; CA2396374A1; AU2623601A

Abstract

A method of producing polyaniline which comprises reacting a seed oligomer of an aniline with a salt of an aniline monomer and an oxidizing agent at an acidic pH; and further, a method for oxidatively coupling aniline monomer which comprises reacting a salt of said monomer with an electron acceptor in the presence of an enzyme while adding a base to the reaction to maintain the pH in a range in which the enzymes retains its activity.

Description

METHOD OF PRODUCTION OF POLYANILINES

BACKGROUND OF THE INVENTION

This invention relates to a method for producing polyanilines (PA) and, more particularly, to a method for producing conductive polyanilines of a controlled molecular weight.

Traditionally, conductive polyanilines are produced by the chemical oxidation of aniline by ammonium persulfate in the presence of a strong acid. The reaction is highly exothermic. To control the exothermic nature of the reaction, ammonium persulfate is added in several portions. A critical drawback of this process is that it produces a very high molecular weight PA. For example, the molecular weight of the product generally is greater than 100,000. This is problematic for processing for a number of reasons: its poor solubility in organic solvents, its high inherent viscosity, and its very short shelf life in solution. In addition, the high molecular weight PA must be ground (e.g., air-milled) and dispersed before it can be introduced into the desired plastics, fibers or coatings. Fig. 1 illustrates a typical UV spectra for a non-conductive PA in the Emeraldine Base form. It shows two well defined peaks— one at about 640 nm corresponding to conjugated quinoid diimino groups and another at about 320 nm corresponding to the benzoid diamino groups. The spectra shows minimal absorption at 430 nm where non-conjugated imino groups would be expected to absorb.

Methods for generating lower molecular weight polyanilines are known. One such method involves rapidly adding the oxidizing agent to the reaction system. This method results in serious problems due to the highly exothermic nature of polymerization reactions.

An enzymatic reaction for producing polyanilines which involves the use of peroxidase enzyme and hydrogen peroxide is also known and described in U.S. Patent 5,112,752 to Pokora and U.S. Patent 5,420,237 to Zemel of Allied Signal. The latter discloses the use of horseradish peroxidase (HRP) to oxidize aniline in the presence of p- toluenesulfonic acid (PTSA). The process exemplified in the Zemel patent consumes large quantities of enzyme making it unsuitable for large scale production. The enzyme is believed to be consumed because the pH of the reaction falls below 3.5. One theory is that the acid is solubilizing the heme group which the enzyme contains within its structure. Attempts have been made to produce PA using a weak acid aniline salt such as the acetic acid salt. The acetic acid liberated does not reduce the pH to levels below 3 and the enzyme remains active. Unfortunately, acetic acid is not strong enough to protonate all the aniline and deactivate the ortho position. As a result a nonconductive PA having an irregular structure with ortho- substitution is produced. The UV spectra of the dedoped material is shown in Fig. 2 and includes absorption at 350-390 nm and little absorption at 490-500 nm which indicates that little of the head-to-tail linkage is achieved.

SUMMARY OF THE INVENTION

The present invention provides a novel method for producing PA with a controlled molecular weight by reacting a low molecular weight PA oligomer ("seed oligomer") with an aniline monomer in the presence of an oxidizing agent under acidic conditions and also for controlling the molecular weight of said seed oligomers. The method is particularly useful because it provides conductive PA having number average molecular weight less than 70,000, more particularly less than 50,000 and still more particularly less than 20,000. These low molecular weight PA are more readily soluble and have longer shelf life as compared to higher molecular weight PA made by conventional processes. Controlling the amount of the added oligomer chains yields a polymer of a controlled low molecular weight. PA can be obtained which are soluble in common organic solvents like THF (tetrahydrofuran), DMF, DMAC and DMSO (dimethyl sulfoxide). However, under proper conditions this process can also be used to produce higher molecular weight PA, for example, those molecular weight PA achieved in conventional processes. In addition, the use of the oligomers is advantageous because it reduces the induction period for the reaction. In a traditional production of PA by chemical oxidation of strong acid aniline salts, the induction period can be several hours. Depending on the reactants employed, the addition of the oligomer can reduce the induction period to as little as a few seconds. While it has not been confirmed, the oligomer may be forming a template for polymerization and thereby reduce the induction time. Furthermore, a method of this invention employs the use of high frequency vibrations such as ultra sound etc. to additionally reduce any induction period of the polymerization and to improve the physical properties of the final polymer. High frequency e.g. (ultrasound) vibrations my also be used to improve conventional polymerization processes that produce polyanilines. The seed oligomers used in the process of the present invention can be obtained by any process. However, in accordance with a preferred embodiment of the invention, the oligomer is obtained by a enzymatic process wherein acid aniline salt is reacted with a peroxidase or oxidase enzyme in the presence of an electron acceptor. To prevent the liberated acid from inactivating the enzyme, the reaction system is titrated with a base and preferably aniline base. Accordingly, another manifestation of the invention is an improved enzymatic process for producing polyanilines wherein a base, which is preferably an aniline, is added during the course of the reaction to maintain the pH at a level at which the enzyme retains its activity.

A particular manifestation of the present invention is a two step polymerization reaction where in the first stage aniline oligomer is formed by enzymatic reaction most preferably while adding aniline to react with liberated acid and maintain an enzymatically effective pH and in the second stage, the oligomer is reacted with aniline in the presence of an oxidizing agent such as ammonium persulfate. The first stage reaction product has an unresolved peak at about 320 nm corresponding to the benzoid diamino groups and the absorption of the quinoid diimino groups is delocalized from 400 nm to about 570 nm. This spectra indicates the presence of low molecular weight oligomers of different molecular weights. Upon further reaction of the oligomers obtained in the first stage with additional aniline salt, the spectra shown in Fig. 4 is obtained in which the 420 nm absorbency has disappeared indicating the oligomers have been reacted into the final conductive PA.

While the invention is particularly useful in preparing conductive PA, those skilled in the art will recognize that the method of the invention can also be used in conjunction with the preparation of non-conductive PA in the Emeraldine Base form. One of the advantages of the invention is that it provides a safe and controllable (not runaway) reaction. While the disclosure focuses principally on the preparation of PA having a molecular weight less than 70,000, the process can be used to produce higher molecular weight PA, e.g., 200,000 molecular weight if desired.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1-4 are UV absorption spectra for products in the dedoped form. Figs. 5-8 are mass spectra of oligomers prepared in accordance with the present invention after conversion of 5%, 10%, 15% and 20% of aniline monomer, respectively.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention a seed oligomer is used in the preparation of PA. The oligomer can contain about 2 to 20 and more typically about 2 to 12 aniline units. The amount of seed oligomer used in preparing the polymer can be as little as 0.5% but is more typically about 0.5 to 20% and still more typically about 1 to 10%. These percentages are based on total polymerizable material, i.e., the combined amount of aniline and oligomer is 100%.

The seed oligomer can, in accordance with the broadest manifestation of the invention be obtained by any available process including the processes described in U.S. Patent 5,420,237 to Zemel, U.S. Patent 5,112,752 to Pokora, U.S. Patent 3,963,498 and 4,025,463. But, in a preferred embodiment, the oligomer is obtained using a modification of the process described in the Zemel patent wherein the pH of the reaction system is maintained above 3.5 and preferably at about 4.0 to 5.0 by adding to the reaction mixture a base and more particularly aniline. In the Zemel process an acidifying agent is used which has a pKa less than the pKa of the aniline. Typically, the acidifying agent is a strong acid like HC1. Reaction of the aniline under these conditions results in the release of a strong acid. In the Zemel reaction, for every two moles aniline reacted to form polymer, one mole of acid is released. Consequently, the pH of the reaction mixture falls rapidly as the polymerization proceeds. The pH of the Zemel reaction mixture can be as low as 1.0 - 2.5. While this pH ensures head- to-tail coupling of the aniline monomers, it also deactivates the enzyme.

In accordance with the invention, a strong acid aniline salt like the hydrochloride is used, and the pH is controlled by reacting the liberated acid with a base to maintain the pH in the range 3.5 to 4.5. Those skilled in the art should appreciate that small diversions from this range are acceptable although the reaction efficiency of the enzyme is less. Bases such as calcium, sodium or ammonium hydroxide can be used for this purpose, but these introduce impurities or contaminants into the reaction product that would ordinarily need to be removed. Accordingly, the preferred base is the same aniline that is reacted to form the PA. The aniline can be added to the reaction in solution or neat. The aniline can be added at reaction intervals that are coordinated with the addition of the electron donor or titrated into the system while monitoring the pH.

In most cases the polymerization reaction can be conducted in water. However, mixed reaction systems may be useful in preparing the prepolymer as disclosed in U.S. Pat. No. 5,420,237 to Zemel and U.S. Pat. No. 5,112,752 to Pokora. Where a monomer is not sufficiently soluble in water a mixed solvent may be effective. For example, ethanol/water may be useful. Organic solvents which may be suitable for use in solvent/water mixtures include acetone; alcohols, such as methanol, ethanol, propanol and butanol; pyrrolidinones, for example N-methyl-2-pyrrolidinone; acetonitrile and tetrahydrofuran. The organic solvent/water mixtures comprise at least about 0.5% water to about 50%water. In the most preferred embodiment, the solvent medium is 100% water.

The aniline may be substituted or unsubstituted. Useful anilines are known in the art. See for example the Zemel patent. Combinations of differently substituted anilines could be used to make copolymers if this were desired. Examples of substituted anilines useful in the polymers of the invention include the anilines which have previously been proposed as being useful in forming conductive polymers. Examples of these anilines are described in U.S. Pat. Nos. 5,378,403; 5,422,423 and 5,420,237. As disclosed in U.S. Patent 5,420,237, the aniline component is selected from one or more substituted or unsubstituted aniline monomers of Formula I:

Formula I wherein n is an integer from 0 to 4, m is an integer from 1 to 5 with the proviso that the sum of n and m is equal to 5 and that at least one position on the aniline ring is a moiety which allows oxidative coupling at that position. Rl is hydrogen or an R2 substituent, R2 is selected from hydrogen, hydroxy, halogen, cyano, nitro, mercapto, sulfonyl acid, carboxyl; and a hydrocarbon-containing substituent selected from alkyl, alkanoyl, alkoxy, alkenyl, cyclo-alkenyl, aryl, aryloxy, aryloyl, alkylaryl or alkylsubstituted with one or more of halogen, cyano, nitro, mercapto, sulfonic acid and carboxylic acid; said hydrocarbon substituent having 1 to 20 carbons. More particularly preferred embodiments are directed to aniline monomers of Formula I wherein Rl is hydrogen or an alkyl having 1 to 4 carbons and R2 is selected from a hydrogen, hydroxy, halogen, cyano, mercapto, carboxylic acid, sulfonic acid and an alkyl, alkoxy, alkanoyl; said alkyl having 1 to 6 carbons. In the most preferred embodiments the aniline monomer is unsubstituted aniline. The following listing of substituted and unsubstituted anilines are illustrative of those described in the aforesaid patent which can be used in the practice of this invention for preparing polymers and copolymers: aniline, 2-acetylaniline, 2-cyclohexylaniline, 2,5-dimethylaniline, toluidine, 2,3-dimethylaniline, m-toluidine, 2,5-dibutylaniline, o-ethoxyaniline, o-cyanoaniline,m- butylaniline, 2-thiomethylaniline, m-hexylaniline, 2,5-dichloroaniline, m-octylaniline, 3-(n-butanesulfonic acid)aniline, 2-bromoaniline, 3-propoxymethylaniline, 3-bromoaniline, 3-acetamidoaniline, 5-chloro-2-methoxyaniline, 3 -phenoxy aniline, N-methylaniline, 2-(dimethylamino)aniline, 2-ethylthioaniline, N-carbonylaniline, 2-methylthiomethylaniline.

The enzyme is selected based on its ability to oxidize acid salts of aniline to a form which readily polymerizes. Generally, the enzyme must retain its activity in an acidic environment for time sufficient to oxidize the monomer. Some enzymes are characterized by the presence of a heme group. The enzyme is preferably a peroxidase and still more preferably soybean peroxidase but other peroxidases such as horseradish peroxidase, tobacco peroxidase, tomato peroxidase, legume peroxidases, bacterial peroxidases, and chloroperoxidase may be used. Additionally, oxidase enzymes are also believed to be useful in polymerizing the monomers.

The amount of the enzyme used will depend on its reactivity. The example illustrates a suitable amount of soybean peroxidase. The amount of enzyme in the reaction should be sufficient to couple enough of the aniline monomer to form an oligomer of a desired chain length. The concentration of enzyme in the reactor is at least about 0.1 units/ml. The concentration of the enzyme is measured in activity units per milliliter of reaction medium. In the case of peroxidase, one unit of activity (ppu) will form 1.0 milligram of purpurogallin from pyrogallol in twenty seconds at pH =6.0 at 20 °C. The concentration of enzyme per milliliter of reaction medium typically ranges from about 0.1 units/ml to about 10,000 units/ml.

Any peroxide known to be useful as an electron acceptor with a peroxidase can be employed in the practice of the invention. Illustrative of such peroxides are hydrogen peroxide, alkyl hydroperoxides such as methyl hydroperoxide and ethyl hydroperoxide, aromatic peroxides, for example cumenyl hydroperoxide, and peroxy acids. It simplifies manufacture if when the electron acceptor oxidizes the enzyme, the electron acceptor's reduced form is a component of the solvent. For example, hydrogen peroxide is converted to water upon oxidizing the enzyme. Oxidase enzymes would be used with oxygen or an oxygen containing gas instead of a peroxide. Preferably, the molar ratio of electron acceptor to monomer is at least about 1:1 to about 1.5:1.

The molecular weight of the seed oligomer can be controlled by limiting the amount of electron acceptor that is reacted with the monomer. For example, if oligomer having 8 units or less is desired, a molar ratio of delivered electron acceptor to monomer should be about 0.1: 1 to about 0.15:1. (See Figs. 5 and 6.) If oligomer having about 8 to 15 units is desired, a molar ratio of delivered electron acceptor to monomer should be about 0.15:1 to about 0.225:1. (See Fig. 7.) If oligomer having up to 25 units is desired, a molar ratio of delivered electron acceptor to monomer should be about 0.2: 1 to about 0.3 : 1. (See Fig. 8.) Higher molecular weight oligomers can be formed using correspondingly higher amounts of electron acceptor.

The conversion of the oligomer to the higher molecular weight polymer by reaction of the oligomer and the aniline, monomer can be conducted in a manner that is otherwise used in the preparation of PA by reacting aniline monomers. The most widely used oxidizer is ammonium persulfate but other oxidizing agents which are lαiown in the art and which are capable of polymerizing the aniline may be used such as potassium permanganate, potassium dichromate, ferric chloride, etc. Milder oxidizing agents would provide lower yields. Generally, the pH of the reaction mixtures in the second reaction is sufficiently acidic to cause the protonation of the aniline monomer. Generally, the pH of the reaction mixture is less than the pKa of the aniline monomer in the reaction mixture but not so low as to deactivate the enzyme. Preferably, an effective pH creates an environment wherein at least 70% of the aniline monomer is in its protonated form when it is a monomer dispersed in the reaction mixture. In particularly preferred embodiments, the pH is selected such that at least about 95% of the aniline is protonated. Preferably, the pH is greater than about 1 and less than about 4.5. The reaction temperature can range from about -5 to 100°C but is typically in the range of 0 to 30 °C. The temperature generally does not need to be as low as it is for conventional processes, e.g., -5°C, because it is not necessary to prevent runaway exothermic reaction. The second stage reaction with the chemical oxidizer can be carried out in the same reaction vessel as the first stage without recovering the oligomer.

The reaction conditions and reactant concentration illustrated in the examples are illustrative of those used in accordance with the mvention. The aniline will typically be added to an aqueous solution containing the acid. Illustrative acids are HC1, CH₃COOH, HNO₃, H₂SO₄, HBF₄, C_I2H₂₅C₆H₄SO₃H, CH₃C₆H₅SO₃H, C₆H₅SO₃H, CH₃SO₃H, CF₃SO₃H, CF₃COOH and CCI₃COOH. Inorganic and organic phosphoric acids, phosphoric acids, sulfinic acids and the like can also be used. Vigorous agitation is required. About 0.1 to 5 moles of aniline can be added to 1000 ml of water. Addition of the aniline forms the salt and raises the pH to a level acceptable for the enzyme. With the aniline addition complete, the enzyme solution can be added. The amount will vary depending upon the activity of the enzyme. In the case of soybean peroxidase and horseradish peroxidase, the enzyme is used in an amount of about 50 to 3000 ppu per gram of aniline reacted. A solution of the electron acceptor is preferably added to the reaction gradually so as to prevent the oxidizer from inhibiting the enzyme. U.S. Patent 5,278,055 to Pokora discloses a ramped addition in which the rate of addition of the peroxide is gradually reduced. In accordance with the preferred embodiment of the invention, as the reaction proceeds and the acid is liberated, aniline or another base is added in the course of the enzymatic reaction to maintain the pH above 3.0 and preferably in the range of 4.0 to 5.0.

The reaction of the oligomer and monomer to form the low molecular weight polymer is typically performed in the same reaction vessel used in the oligomer preparation when the enzyme process is used to form the oligomers. As explained above, the enzyme reaction can be adjusted to generate about 0.5 to 60% oligomer with the balance being unreacted aniline salt. When the desired oligomer concentration is achieved, the persulfate or other strong oxidizer can be added to complete the polymerization reaction. Since the reaction is exothermic, the reaction is preferably cooled to maintain a temperature below 30 °C. The persulfate can be added in increments and the reaction vessel cooled between the incremental additions to keep the temperature below 30°C. The second stage reaction is usually conducted at 0 to 45 °C. In the second stage reaction, the polymer is grown to higher molecular weights.

The molecular weight of the first stage reaction product (based on mass- spectra) is generally in the range of 300 to 3,000 and more typically it is about 500 to 1,500. The molecular weight of the second stage polymer product generally ranges from about 3,000 to 70,000 and typically it is about 15,000 to 25,000. The polymer product is advantageous not only because it exhibits high conductivity but also because it exhibits good solubility in solvents and has a much longer shelf-life of solutions than other polyanilines. This enables solutions of the polymer to be prepared and incorporated into various polymer systems.

The polymer is doped to render it conductive in a conventional manner. The preferred dopant is an organic protonic acid such as p-toluenesulfonic acid (PTSA), but other dopants that have been described in the literature for use in polyanilines could also be used. If PTSA is used as the acid for the aniline polymerization, it can also function as the dopant. Examples of other dopants are provided in U.S. Patent 5,378,403. The amount of the dopant can vary and is not critical as long as the conductivity limits discussed earlier are achieved. A dopant is any species which provides electrical conductivity to the polymer product. As a dopant, the acidifying agent generally protonates the backbone of conjugated polymers and creates charge carriers along the polymer backbone, resulting in an electrically conductive material. The polymers have a conductivity greater than 10^"4 S/cm and more preferably greater than 10^"3 S/cm and conductivity of 10^"1 S/cm and higher have been achieved. Acids such as hydrochloric acid can be used and are more cost effective where the undoped form of the polymer is desired. If the emeraldine base form is desired the salt can be reacted with ammonium hydroxide.

The polymer of this invention can be blended with the thermoplastic or thermosetting polymers to impart antistatic properties to the blend. The amount of the polymer used in the blend will vary depending upon the final properties desired. The polymers of this invention are potentially useful for any of the purposes for which conductive polymers are useful. Some respective applications are listed in the patents that have already been referenced herein.

In preparing the polymers, it will be noted that it is not essential to isolate the prepolymer. Aniline, the oxidizer and the acid can be added directly to the prepolymer reaction system to form the polymer product. The second stage reaction involves a strong oxidizing agent and an acid. The aniline is reacted in the second stage in an amount which can be widely varied and tailored to the properties desired in the final product. Typically an amount equal to about 25% to 100% of the aniline used in the first stage will be added in the second stage. This amount will also vary depending upon how much unreacted aniline is present after the first stage. If the first stage product includes quantities of unreacted aniline, it may not be necessary to add aniline in the second stage.

The invention is illustrated in more detail by the following non-limiting examples.

Reference Example 1 Chemical Oxidation.

In a reactor 55 gm (0.56 mole) of H₂SO₄ was dissolved in 800 ml of water @ 10°C. 94 gm (1.0 mole) of aniline was added slowly with vigorous stirring to avoid solidifying the reaction mixture. 285 gm (1.25 Mol) of (NH₄)₂S₂O₈ was dissolved in 300 ml of water and added to reaction mixture in four portions: First portion 12.5% of solution of ammonia persulfate added at 12.5 °C. Induction period was 3 min. The exothermic process raised the temperature up to 25 °C. The reaction was cooled to 17 °C and then the remaining ammonium persulfate solution was added in three portions. After each portion reacted, the reaction was cooled to 20 °C before the next portion was added. Total time of ammonium persulfate addition was about 40 min. Filtered, washed with water and dried. Collected 115.5 gm of polyaniline. The UV Spectra is of the dedoped polymer shown in Fig. 1. Reference Example 2 Allied Signal Procedure.

0.95 gm of aniline in 45 ml of water was titrated with para-toluenesulfonic acid to pH 3. The reaction mixture was cooled to 0°C and 5 ml of solution containing 14,000 ppu of HRP and 1.53 ml of 30% solution of hydrogen peroxide were added. The reaction was stirred for 60 hours at 0°C. The product was filtered and dried in vacuum for 12 hours. Collected 0.8 gm of emeraldine salt. The UV Spectra is essentially the same as that shown in Fig. 1.

Reference Example 3

Enzymatic coupling of aniline in acetic acid.

In a reactor 70 gm (1.15 mole) of acetic acid was dissolved in 200 ml of water at 10°C. 94.0 gm (1.0 mole) of aniline was added slowly with vigorous stirring. 550 ml of 300 ppu/ml of soybean peroxidase was added. Solution of H₂O₂ (17.5%) was delivered at a rate of 0.2 ml/min for two hours. The reaction mixture was neutralized with NH₄OH and the products were isolated on the centrifuge, washed with water and dried. Collected 20 g of product. The UV Spectra of the dedoped polymer is shown in Fig 2.

Example 1

Enzymatic preparation of oligomers.

In a reactor 114 gm (0.6 mole) of PTSA was dissolved in 800 ml of water @ 10 °C. 55.8 gm (0.6 mole) of aniline was added slowly with vigorous stirring to avoid solidifying the reaction mixture. 250 ml of 475 ppu/ml of soybean peroxidase solution was added. Solution of H₂O₂ (17.5%) was delivered at a rate of 0.4 ml/min and after delivering 2 ml of H₂O₂, delivery was paused for 1 min and 0.5 gm of fresh aniline was added. 80 ml (0.41 mole) of H₂O₂ was added and 20 g (0.21 mole) of aniline was added for 4 hours. The product was filtered and dried. Collected 55.4 g of polyaniline. The UV Spectra is shown in Fig. 3 for the dedoped polymer. Example 2

Preparation of polyaniline by combination of enzymatic and chemical oxidation.

In a reactor 460 ml (5.37 mole) of 37% solution of HC1 mixed with 1300 ml of water @ 10°C. 500 gm (5.37 mole) of aniline was added. 666 ml of 3000 ppu/ml of soybean peroxidase was added. A solution of H₂O₂ (17.5%) was delivered at a rate of 0.5 ml/min and after delivering 2.0 ml of H₂O₂, delivery was paused for 1 min and 0.5 gm of fresh aniline was added. After 2 hours 62 ml (0.32 Mol) of H₂O₂ and 13.0 gm of aniline were added. Total aniline = 513.0 gm (5.51 Mol). The conversion of initial and added aniline was 5.8%.

1,436 gm (5.38 Mol) of (NH₄)₂S₂O₈ was added to the reaction mixture in 8 portions 179.5 gm each at 10°C initially. No induction period. The process was exothermic and produced an increase in temperature of about 8-10°C per portion. The reaction was allowed to reach 30 °C and then after each portion reacted, cooled to 20 °C before the next portion was added. Total time of ammonium persulfate addition was about 40 min. The reaction mixture was neutralized with NH₄OH, filtered, washed with water and dried. Collected 508 gm (99.0%) of emeraldine base.

Example 3

Enzymatic preparation of oligomers with controlled molecular weight.

In the reactor 520 ml (5.48 mole) of 37% solution of HC1 were mixed with 500 ml of water @ 10°C. 510 gm (5.48 mole) of aniline was added. 2500 ml of 300 ppu/ml of soybean peroxidase was added. A solution of H₂O₂ (17.5%) was delivered at the rate of 1.2 ml/min and after delivering 4.0 ml of H₂O₂, delivery was paused for 1 min and 1.0 gm of fresh aniline was added. After delivery of 54 ml of 11.5% solution of hydrogen peroxide, 5% conversion of initial monomer was achieved. 400 ml of reaction mixture was filtered, oligomers isolated (see Fig. 5) and filtrate returned into the reactor. After delivery of 108 ml of 17.5% solution of hydrogen peroxide, 10% conversion of initial monomer was achieved. 400 ml of reaction mixture was filtered, oligomers isolated (see Fig. 6) and filtrate returned into the reactor. After delivery of 162 ml of 17.5% solution of hydrogen peroxide, 15% conversion of initial monomer was achieved. 400 ml of reaction mixture was filtered, oligomers isolated (see Fig. 7) and filtrate returned into the reactor. After delivery of 216 ml of 17.5% hydrogen peroxide, 20% conversion of initial monomer was achieved. 400 ml of reaction mixture was filtered, oligomers isolated (see Fig. 8) and filtrate returned into the reactor.

Having described the invention in detail and with reference to preferred embodiments thereof it will be apparent that numerous variations and modifications are possible without departing from the spirit and scope of the invention as defined by the following claims.

Claims

1. ■ A method for producing polyaniline which comprises reacting a seed oligomer of an aniline with a salt of an aniline monomer and an oxidizing agent at an acidic pH.

2. The method of claim 1 wherein said seed oligomer contains about 2 to 20 aniline units.

3. The method of claim 2 wherein said acidic pH is less than the pKa of said aniline monomer.

4. The method of claim 3 wherein said seed oligomer contains 2 to 12 aniline units.

5. The method of claim 4 wherein said method includes the additional step of reacting a salt of an aniline monomer with an oxidase enzyme or a peroxidase enzyme in the presence of oxygen or a peroxide to form said seed oligomer.

6. The method of claim 5 wherein during said reaction in the presence of said enzyme, acid is released and a base is added to the reaction to neutralize the acid released.

7. The method of claim 6 wherein the base is an aniline.

8. The method of claim 1 wherein said oligomer is present in an amount of about 0.5 to 20% based on the total oligomer and monomers.

9. The method of claim 1 wherein said pH is about 1.0 to 4.5.

10. The method of claim 5 wherein the enzyme is soybean peroxidase or horseradish peroxidase and the electron acceptor is hydrogen peroxide.

11. A method for oxidatively coupling aniline monomer which comprises reacting a salt of said monomer with an electron acceptor in the presence of an enzyme while adding a base to the reaction to maintain the pH in a range in which the enzyme retains its activity.

12. The method of claim 11 wherein said enzyme is a peroxidase, said electron acceptor is a peroxide and said pH is about 3.5 to 4.5.

13. The method of claim 1 where said method uses high frequency vibrations during polymerization and processing.