WO2008072858A1 - Method of preparing conductive polyaniline by temperature-controlled self-stabilized dispersion polymerization - Google Patents

Abstract

The present invention provides a method of preparing conductive polyaniline by temperature-controlled self- stabilized dispersion polymerization, the method comprising the steps of : (a) mixing an aqueous solution, in which an aniline monomer and a protonic acid are dissolved in water or in a mixed solvent of water and a water-miscible organic solvent, with a water-immiscible organic solvent in a reactor; (b) lowering the internal temperature of the reactor until reaching a polymerization temperature at a rate of 0.05 to 5 °C/min when the internal temperature of the reactor reaches 0°C by cooling the reactor and, at the same time, adding an initiator thereto; (c) carrying out a polymerization propagation reaction by maintaining the internal temperature of the reactor constant; and (d) carrying out a polymerization termination reaction by increasing the internal temperature of the reactor until reaching a temperature of -5 to 0°C at a rate of 0.05 to 5 °C/min.

Description

[DESCRIPTION]

[invention Title]

METHOD OF PREPARING CONDUCTIVE POLYANILINE BY TEMPERATURE- CONTROLLED SELF-STABILIZED DISPERSION POLYMERIZATION

[Technical Field]

The present invention relates to a method of preparing conductive polymers and, more particularly, to a method of synthesizing conductive polyaniline by temperature- controlled self-stabilized dispersion polymerization.

[Background Art]

Conductive plastics are polymers which have been known to the general public since Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa were awarded the Noble Prize for Chemistry in 2000. They reported the fact that a polymer such as polyacetylene was electrically conductive by passing through a doping process in 1977, and extensive research has continued to progress since then. Conductive polymers are often called a fourth generation plastic having characteristics in which the plastic plays an active role such as an organic semiconductor, not a passive role such as an insulator.

The conductive polymers can be used in various applications according to their electrical conductivity. For example, the conductive polymers with an electrical conductivity of 10^~13 to 10^~7 S/cm have been used as antistatic materials, the conductive polymers with an electrical conductivity of 10^~6 to 10^~2 S/cm have been used as static discharge materials, and the conductive polymers with an electrical conductivity of more than 1 S/cm have been used as electro-magnetic interference (EMI) shielding materials, battery electrodes, semiconductors or solar cells, Accordingly, the conductive polymers may be utilized in more various applications by improving their electrical conductivity.

The important conductive polymers well known at present include polyaniline, polypyrrole, polythiophene, polyphenylenevinylene, polyphenylene sulfide, and polyparaphenylene. Among them, the polyaniline has attracted much attention in the related art, since it is very stable in the air and can be easily synthesized. Moreover, it is expected that the polyaniline plays an essential role in the production of major elements such as organic light emitting diodes (OLED) , field-effect transistors (FET), and the like.

The polyaniline can be classified into leucoemeraldine that is a completely reduced form, emeraldine that is a partially oxidized form, and pernigraniline that is a fully oxidized form according to its oxidation state. Methods of synthesizing polyanilines can be broadly classified into an electrochemical method by an electrically charge transfer reaction and a chemical oxidation method by a protonation through an acid-base or redox reaction. It has been known that the chemical oxidation method is most suitable for producing polyaniline in an industrial scale.

In general, the polymers are synthesized by a polymerization process that repeatedly couples monomers. In the polymerization process, an addition polymerization that emits a great deal of heat may cause an explosion since the reaction occurs repeatedly in a short time and becomes very vigorous. In order to control the reaction heat, water is often used as a reaction medium.

However, most of the polymers are formed from nonpolar monomers and such monomers are hardly dissolved in water. Moreover, since the thus formed polymers are not dissolved in water, various heterogeneous polymerizations are used to effectively carry out the reaction.

Among them, a dispersion polymerization process uses a stabilizer that sterically stabilizes polymer particles in the polymerization process so as to prevent the formed polymer from precipitating and at the same time to obtain stable microparticles as the final product. However, if the stabilizer is used in preparing a conductive polymer such as polyaniline, since it is difficult to remove the stabilizer after the reaction, there occurs a problem that the electrical conductivity is sharply reduced.

For this reason, A. G. MacDiarmid who was awarded the Noble Prize in the middle of past 1980s did not use a steric stabilizer in synthesizing polyaniline but carried out the reaction directly in an aqueous solution phase, and this method has been used widely and regarded as a standardized method for producing polyaniline (A. G. MacDiarmid, J. C. Chiang, A. F. Richter, N. L. D. Somarisi, in L. Alcacer (ed.), Conducting E'olymers, Special Applications, Reidel, Dordercht, 1987, p. 105) .

This method is directed to a method of synthesizing polyaniline by polymerizing an aniline monomer dissolved in hydrochloric acid using an oxidizing agent such as ammonium persulfate in an aqueous solution phase in the temperature range of 1 to 5^°C and separating and washing the precipitates. Since the aniline monomer is dissolved in the hydrochloric acid solution, there is no problem at the initial stage of the polymerization reaction; however, there is a difficulty in increasing the molecular weight or preventing side reactions since a precipitation occurs as the polymer grows .

Among the polyanilines in the form of emeraldine base (EB) synthesized according to the MacDiarmid method (hereinafter referred to as the conventional method) , only the polyaniline having a low molecular weight and an intrinsic viscosity 0.8 to 1.2 dl/g is dissolved in 1- methyl-2-pyrrolidon (NMP) , and the emeraldine salt doped with 10-camphorsulfonic acid (ES-CSA) is dissolved a little in meta-cresol .

Film made from the above solution containing ES-CSA has an electrical conductivity of about 100 S/cm, on the other hand, the film made from emeraldine salt doped with hydrochloric acid (ES-HCl) shows an electrical conductivity of about 5 S/cm. Especially, the conventional method has some drawbacks in that it is necessary to separate the undissolved portion and it is difficult to adjust the structure of the synthesized polyaniline and increase the molecular weight or the electrical conductivity. In order to improve the drawbacks and the inferior processability of the polyaniline synthesized by the conventional method, a lot of methods which use emulsion polymerization have been suggested. For example, U.S. Patent Nos . 5,232,631 and 5,324,453 to Cao et al . , which are incorporated herein by reference, disclose a method of synthesizing polyaniline by dissolving an aniline monomer and a functionalized protonic acid in a polar solvent such as water, mixing the resulting solution with a nonpolar organic solvent to prepare an emulsion, and then adding an oxidizing agent in the emulsion. It is known that the thus prepared emeraldine salt (ES) can be dissolved in a nonpolar organic solvent such as xylene since an emulsifier acts as a dopant and thus the emeraldine salt is reacted with the polyaniline to form a composite. However, it is difficult to control the doping process using the functionalized protonic acid acting as the emulsifier and the process requires a high cost. Furthermore, since the functionalized protonic acid is hardly separated from the synthesized polyaniline, there are limitations in the use the polyaniline and the electrical properties are inferior . For instance, the emeraldine salt doped with dodecylbenzene sulfonate (DBS) has a solubility of less than 0.5% and an electrical conductivity of only about 0.1 S/cm. Dr. Patrick. J. Kinlen of Monsanto Co. produced a polyaniline salt by preparing a reverse emulsion comprising an organic solvent such as 2-butoxyethanol soluble in water and an organic acid, which is not soluble in water but soluble in the organic solvent, as a hydrophobic emulsifier, mixing an aniline monomer and a radical initiator with the emulsion, and polymerizing the mixture to form a polymer solution that has an organic layer, which contains polyaniline salt, separated from an aqueous layer containing the radical initiator and non-reacting compounds. Kinlen reported that the polyaniline salt was soluble in a nonpolar solvent of no less than 1% (w/w) .

However, it is difficult to carry out the polymerization since the radical initiator in the aqueous layer is separated from the monomer in the organic layer, and the thus synthesized polyaniline has a low electrical conductivity since it is difficult to control the doping process. For example, it was reported that the polyaniline salt synthesized in a pellet form with dinonylnaphthalene sulfonic acid as a hydrophobic organic acid had an electrical conductivity of about 10^~5 S/cm.

In addition to the above emulsion polymerization, various methods of synthesizing polyanilines using a dispersion polymerization process, in which monomers such as aniline are fully dissolved in a reacting solvent while synthesized polymers are not dissolved in the same solvent, have been reported. For example, Armes et al. reported a polymerization method, in which the polymer was sterically stabilized using a specific stabilizer and then granulated (Armes et al . , Handbook of Conducting Polymers, Elsenbaumer ed. M. Dekker, New York, 1996, Vol. 1, p. 423).

In this dispersion polymerization method, since most of the stabilizers cover the polyaniline, the polyaniline can be prepared in an aqueous solution phase. However, since the synthesized polyaniline has a particle size of about 60 to 300 nm, which is affected by the stabilizer and has a low electrical conductivity, its application is limited.

Meanwhile, a method of synthesizing polyaniline in an aqueous solution containing an organic solvent was reported. According to Cao et al. (Cao et al . , Polymer, 30, 2305, 1989) , it was reported that polyaniline was synthesized using various oxidizing agents and inorganic acids; however, the yield was not increased. Moreover, it was reported that a hydrophilic organic solvent such as dimethylformamide was added to the reaction system in order to prevent the polymer from precipitating at the initial stage of the reaction; however, it was of no effect.

Geng et al. prepared polyaniline film having an electrical conductivity of about 10 S/cm by polymerizing aniline using an organic solvent such as ethanol, THF, and acetone in an aqueous solution; however, the effect of the organic solvent was not so significant (Geng et al . , Synth. Metals. 96, 1, 1998) .

Angelopoulos et al . disclose a method of fabricating electrically conductive polymers including polyaniline in Korean Patent Publication No. 10-1999-0063696, in which the amount of an oxidant is adjusted or an organic solvent is added in order to control the rate of the polymer precipitation, thus inducing a homogeneous reaction at the initial stage of the reaction and obtaining a molecular weight distribution in which multiple peaks are transformed into a single peak.

Moreover, Huang et al. synthesized polyaniline in the form of nanofibers by preparing a system which comprises an organic layer and an aqueous layer immiscible with the organic layer, dissolving an aniline monomer in the organic layer, and an initiator and an organic acid in the aqueous layer, and polymerizing the monomer in the interface (Huang et al., J. Am. Soc. 125, 314, 2003). In the following study, Huang et al . reported that if the interfacial polymerization was carried out using an organic solvent, the yield of the nanofibers could be increased and further the organic solvent was not necessary, rather, it was possible to obtain the nanofibers due to rapid mixing in an aqueous solution. (Huang et al . , Angew. Chem. Int. Ed. 43, p5817, 2003)

The inventors of the present invention have disclosed a self-stabilized dispersion polymerization method in Korean Patent Application Nos. 10-2005-0032461 and 10-2004-0019312 and reported that the thus prepared polyaniline showed a pure metallicity first in the world (Nature, vol. 441, p. 65, 2006) . However, the inventors of the invention have found that, with an improvement of the above method, it is possible to obtain polyaniline having improved performance, in which the reaction efficiency is increased, the solubility is increased even at a high molecular weight, and the electrical conductivity is increased even at a low molecular weight, and the improved method will be described in the present invention. According to the study by Beadel et al . , in the polyaniline produced by the standardized synthesis method disclosed by MacDiarmid as described above, the higher the molecular weight is, the higher the electrical conductivity, and the reaction temperature should be lowered in order to increase the molecular weight of the polymer (Beadel et al . , Synth. Met. 95, 29, 1998) .

In order to lower the reaction temperature when the polymerization occurs in a homogeneous solution according to the methods attempted by MacDiarmid, Cao, Geng, Huang et al., it is necessary to prevent the system from freezing by adding a metal salt such as LiCl, CaF₂ and the like to the system. However, if such a metal salt is mixed with the solution system, the reaction time is prolonged to more than 48 hours and it is difficult to control the polymerization reaction. Moreover, if the reaction temperature is lowered, the molecular weight as well as the molecular weight distribution is increased (polydispersity more than 2.5).

Moreover, side chains are formed when the aniline monomer is added to a quinonediimine group in the middle of chains. Accordingly, FeCl₃ as an oxidizing agent may be added during the polymerization reaction in order to inhibit the formation of the side chains, or an extraction process with an organic solvent may be carried out in order to remove side products such as oligomers, of which the synthesis reaction is stopped during the polymerization reaction.

Furthermore, in the above-described emulsion polymerization or interfacial polymerization, since it is Likely that the addition reaction may occur on the ortho position as much as the para position of the benzene ring in the polyaniline backbone, the synthesized polyaniline has a large number of side chains, thus lowering the electrical conductivity and solubility of the polyaniline.

However, since the methods of synthesizing polyaniline published until now use a lot of additives such as stabilizers or emulsifiers, it is difficult to obtain pure polyaniline. Moreover, since the synthesized polyaniline has a microstructure in which chains are coupled on the ortho positions and side chains are often attached to the polyaniline backbone due to side reactions, the electrical conductivity of the thus synthesized polyaniline is not so high.

Since the conductive polymers do not have a completely linear structure per se, they cannot form a complete order like a crystalline structure. Accordingly, the real conductivity of the polyaniline is much lower than theoretically calculated electrical conductivity, about 10^5~6 S/cm (Kohlman et al . , Phys . Rev. Lett. 78(20), 3915, 1997).

Since such polymers with lower electrical conductivity cannot be utilized as transparent plastic electrodes or EMI shielding materials, it is necessary to provide a conductive polymer having excellent electrical conductivity and a method of facilitating the polymerization reaction.

[Disclosure] [Technical Problem]

Accordingly, the present invention has been made in an effort to solve the above-described drawbacks, and an object of the present invention is provide conductive polymers, in which a low molecular weight polymer having an intrinsic viscosity of more than 1.3 has a high electrical conductivity of more than 300 S/cm and a high molecular weight polymer having an intrinsic viscosity of more than 2.7 is readily dissolved in an organic solvent.

Another object of the present invention is to provide a method of preparing conductive polyaniline by temperature- controlled self-stabilized dispersion polymerization, in which the temperature is controlled in respective steps of initiation, propagation and termination of a polymerization reaction .

[Technical Solution]

To accomplish the above objects of the present invention, there is provided a method of preparing conductive polyaniline by temperature-controlled self-stabilized dispersion polymerization, the method comprising the steps of: (a) mixing an aqueous solution, in which an aniline monomer and a protonic acid are dissolved in water or in a mixed solvent of water and a water-miscible organic solvent, with a water-immiscible organic solvent in a reactor; (b) Lowering the internal temperature of the reactor until reaching a polymerization temperature at a rate of 0.05 to 5 °C/min when the internal temperature* of the reactor reaches 0°C by cooling the reactor and, at the same time, adding an initiator thereto; (c) carrying out a polymerization propagation reaction by maintaining the internal temperature of the reactor constant; and (d) carrying out a polymerization termination reaction by increasing the internal temperature of the reactor until reaching a temperature of -5 to 0^°C at a rate of- 0.05 to 5 ^°C/min.

[Description of Drawings] FIG. 1 shows a structural formula of an aniline monomer;

FIG. 2 shows a chemical formula showing the repeating unit of polyaniline substituted with tert-butoxycarbonyl (t- BOC) to be dissolved in an organic solvent in order to Identify the molecular structure of the synthesized polyaniline;

FIG. 3 is a schematic diagram illustrating the concept of self-stabilized dispersion polymerization;

FIGS. 4A to 4G are graphs showing Raman scattering spectra of a reaction medium at -25^"C;

FIG. 5 is a graph showing Raman spectrum intensity ratio of 800 cm^"1/1350 cm^"1 and 1160 cirfVl350 cm^"1 of a reaction medium of the FIGS. 4A to 4G according to reaction bime; FIG. 6 is a graph showing the results of ¹³C CPMAS (cross-polarization/magic angle spinning) NMR spectral analysis of the synthesized polyaniline;

FIG. 7 is a graph showing the results of solution state ¹³C CPMAS NMR spectral analysis of the polyaniline substituted with tert-butoxycarbonyl (t-BOC) ;

FIG. 8 is a graph showing DEPT spectra (solvent CDCl₃) of the polyaniline of the present invention, in which (a) is DEPT 135 (top) and (b) is DEPT 90 (bottom) ;

FIG. 9 is a diagram showing an HMBC spectrum at room temperature (solvent CDCl₃) of the polyaniline of the present invention;

FIG. 10 is a diagram showing a peak at around 154 ppm of the polyanilines prepared in Example 1 and Comparative Example (bottom and middle) and that prepared according to a conventional method (top) ;

FIG. 11 is a graph showing thermogravimetric curves of prepared polyaniline particles, in which the dotted line curve represents the conventional polyaniline and the solid Line curve represents the polyaniline of the present invention;

FIG. 12 is a graph showing a GPC chromatogram of the polyaniline substituted with t-BOC prepared in Example 1;

FIG. 13 is a scanning electron microscope (SEM) photograph showing nanoparticles having a size of 30 to 80 nanometers and formed in a tubular shape; and

FIG. 14 is an SEM photograph showing nanoparticles connected to each other to form a porous network.

[Mode for Invention] Hereinafter, preferred embodiments in accordance with the present invention will be described with reference to the accompanying drawings. The preferred embodiments are provided so that those skilled in the art can sufficiently understand the present invention, but can be modified in various forms and the scope of the present invention is not limited to the preferred embodiments.

In this specification, temperature-controlled self- stabilized dispersion polymerization (TSDP) is directed to a polymerization method in which any additives such as stabilizers or emulsifiers are not used and reactants or polymerization products function as the stabilizers.

Polyaniline is a polymer synthesized from an aniline monomer having the following Formula 1 as shown in FIG. 1 and is referred to as one or all of leucoemeraldine, emeraldine base (EB) , emeraldine salt (ES) , pernigraniline and a mixture thereof according to its oxidation state. Conductive polyaniline obtained according to the synthesis method of the present invention will be referred to as "PANi" unless indicated otherwise. [Formula 1]

wherein Ri is hydrogen, C₁-C₂₄ al kyl , or C₁-C₂₄ alkyloxy; and R₂ , R₃ , R₄ , and R₅, are independently hydrogen, C₁-C₂₄ alkyl , C₁-C₂₄ alkenyl , C₁-C₂₄ alkoxy, oligo ( ethylene oxide ) , Ci-C₂₄ alky-thio-Ci-C24 alkyl, C1-C24 alkanoyl, C1-C24 alkylthio, aryl-Ci-C24 alkyl, C1-C24 alkylamino, arαino, C1-C24 alkoxycarbonyl, C₁-C₂4 alkylsulfonyl, C1-C24 alkylsulfinyl, arylthio, sulfonyl, carboxyl, hydroxy!, halogen, nitro, or Ci-C₂₄ alkyl-aryl. Preferably, an aniline monomer in which the Ri, R₂, R₃, R₄, and R₅ are hydrogen may be used.

The present invention provides a method of preparing conductive polyaniline by temperature-controlled self- stabilized dispersion polymerization, the method comprising: (a) mixing an aqueous solution, in which an aniline monomer and a protonic acid are dissolved in water or in a mixed solvent of water and a water-miscible organic solvent, with a water-immiscible organic solvent in a reactor; (b) lowering the internal temperature of the reactor until reaching a polymerization temperature at a rate of 0.05 to 5 "C/min when the internal temperature of the reactor reaches 0^°C by cooling the reactor and, at the same time, adding an initiator so that Raman spectrum intensity ratio of a reaction medium is 800 Cm^-1ZlSSO cm^"1 ≤ 0.01 and 1160 Cm^-1ZlSSO cm^"1 ≤ 0.05; (c) carrying out a polymerization propagation reaction by maintaining the internal temperature of the reactor constant until reaching the Raman spectrum intensity ratio of the reaction medium 800 Cm^-1ZlSSO cm^"1 ≤ 0.26 and 1160 cm^-1Zl350 cm^"1 < 0.28, preferably; and (d) carrying out a polymerization termination reaction by increasing the internal temperature of the reactor until reaching a temperature of -5 to 0^°C at a rate of 0.05 to 5 ^°C/min.

In the synthesis method of the present invention, the reaction of reactants containing the aniline monomer proceeds in a 2-phase reaction system composed of an aqueous solution phase and an organic solution phase, and the reactants and products act to stabilize the system. As shown in FIG. 3, the synthesis method in accordance with the present invention is distinguished from the conventional standardized polymerization method in the aqueous phase, the conventional aqueous solution/organic solvent mixed homogeneous reaction disclosed by Angelopoulos, Huang et al., and the conventional heterogeneous reactions such as emulsion polymerization, suspension polymerization, or dispersion polymerization, in which emulsifiers, polymeric stabilizers, monomeric and/or oligomeric stabilizers, or other templates are principally used. That is, in the two phases constituting the reaction system in accordance with the present invention, if the aqueous solution phase is a continuous phase, the organic solution phase may be a non- continuous phase, and if the organic solution phase is the continuous phase, the aqueous solution phase may be a non- continuous phase, otherwise, the two phase may be all the continuous phase. The synthesis method of the present invention comprises the step (a) of mixing an aqueous solution, in which an aniline monomer and a protonic acid are dissolved in water or in a mixed solvent of water and a water-miscible organic solvent, with a water-immiscible organic solvent in a reactor.

The water-miscible organic solvent used in the mixed solvent water and a water-miscible organic solvent is not particularly limited unless it can be mixed with water. For example, methanol, ethanol, acetonitrile, or 2-methoxy ethanol may be used. Preferably, the aqueous solution of step (a) may be obtained by solely using water as a solvent. That is, the aqueous solution of step (a) may be a solution obtained by dissolving the aniline monomer and the protonic acid in water.

The protonic acid may be an inorganic acid or an organic acid having a pKa of less than 4.0, preferably, less than 3.5. For example, the protonic acid may be one selected from the group consisting of an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid, an organic acid such as Ci-C₂₄ alkylsulfonic acid like methylsulfonic acid, arylsulfonic acid such as dodecylbenzene sulfonic acid, halogenated C₁-C₂₄ alkylsulfonic acid such as chlorosulfonic acid or trifluorosulfonic acid, and a mixture thereof. Preferably, the protonic acid may comprise an inorganic acid such as hydrochloric acid.

The water-immiscible organic solvent is an organic solvent, which is not mixed with the aqueous solution phase, and it may comprise aliphatic or aromatic hydrocarbons capable of containing halogen, hydroxy and the like. Preferably, an organic solvent having a dielectric constant of 4.3 to 65.1 may be used. For example, the organic solvent may comprise one selected from the group consisting of tetrachloroethane, trichloroethane, chloroform, dichloroethane, bis (2-chloroethyl) ether, 1,2,3- brichloropropane, dichloromethane, ethyl chloride, dichloroethyl ether, dichloropropane, neopentyl alcohol, isopropyl alcohol, alkylbutanol, alkylpentanol, butanol, propanol, pentanol, 1, 5-pentanediol, amyl alcohol, cyclopentanone, 4-methyl-2-pentanone, cyclohexanone, diacetone alcohol, 2-ethyl-l, 3-hexanediol, ethyhexanol, cyclohexanol, heptanol, octanol, decanol, dodecanol, propylene carbonate, dimethyl glutarate, benzyl acetate, ethyl aceto acetate, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, tetrahydrofurfuryl alcohol, nitrobenzene, and a mixture thereof. Preferably, the organic solvent may be one selected from the group consisting of chloroform, a mixed solvent of dichloroethane and isopropyl alcohol, and a mixed solvent of propylene carbonate and 4-methyl-2-pentanone. The synthesis method of the present invention comprises the step (b) of lowering the internal temperature of the reactor until reaching a polymerization temperature at a rate of 0.05 to 5 ^°C/min when the internal temperature of the reactor reaches 0^°C by cooling the reactor and, at the same time, adding an initiator so that Raman spectrum intensity ratio of a reaction medium is 800 Cm^-1ZlSSO cm^'1 ≤ 0.01 and 1160 cm^"1/ 1350 cm^"1 < 0.05.

The initiator may be one selected from the group consisting of ammonium peroxysulfate, hydrogen peroxide, manganese dioxide, potassium dichromate, potassium iodate, ferric chloride, potassium permanganate, potassium bromate, potassium chlorate, and a mixture thereof. Preferably, ammonium peroxysulfate may be used. The amount of the initiator, i.e., a radical initiator, is not particularly limited. For example, in the case where the ammonium peroxysulfate is used as the radical initiator, since two electrons per one molecule are related, the amount of the radical initiator may be about 0.1 to 2 molar equivalent per mole of aniline monomer, preferably, about 0.1 to 0.75 molar equivalent, and more preferably, about 0.1 to 0.5 molar equivalent .

The method of synthesizing conductive polyaniline in accordance with the present invention is preferably carried out by controlling the temperature in the respective reaction steps using the Raman spectrum. The reaction time and the adding times of the initiator are varied according to the temperature. For instant, FIGS. 4A to 4G are graphs showing Raman scattering spectra of a reaction medium measured at -25°C by varying the reaction time. Here, the wavelength of the exciting light λ exc = 785 mm was selected so that the reaction medium does not absorb the light, the spectral resolution was 4 cm^"1, and the power of a semiconductor laser was 300 mW. In FIGS. 4A to 4G, since the vicinity of 800 cm^"1 is associated with para- disubstituted benzene, it tends to be increased along with the polymerization. The vicinity of 1160 cm^"1 is a peak associated with radical cations of C-H in plane bending and -C=NH group and indicates the ratio of quinone diimide. In order to quantitatively extract the relative change, the intensity in the vicinity of 1350 cm^"1 in which diffusion intensity was commonly well defined was standardized.

FIG. 5 is a graph showing the Raman spectrum intensity ratio of 800 cm^"Vl350 cm^"1 and 1160 cm^"1/1350 cm^"1 of the reaction medium of the FIGS. 4A to 4G, in which the reaction zones were adjusted by varying the temperature. In particular, the polymerization initiation reaction is carried out by lowering the reaction temperature of the mixture obtained from step (a) until reaching a desired polymerization temperature at a rate of 0. 05 to 5 ^°C/min, if the internal temperature of the reactor reaches 0^°C by cooling the reactor and, at the same time, slowly adding the initiator dropwise so that the Raman spectrum intensity ratio of the reaction medium is 800 Cm^-1ZlSSO cm^"1 ≤ 0.01 and 1160 cm^""1/1350 cm^"1 ≤ 0.05, thus completing the addition of the initiator [step (b) ] . The polymerization propagation reaction is carried out by maintaining the temperature of the reaction mixture obtained from the initiation step constant until reaching the Raman spectrum intensity ratio of the reaction medium 800 cm^"1/1350 cm^"1 ≤ 0.26 and 1160 cm^" Vl350 cm^"1 ≤ 0.28, preferably [step (c) ] . Moreover, the polymerization termination reaction is carried out by increasing the temperature of the reaction mixture from the temperature selected from step (c) until reaching a temperature of -5 to 0^°C at a rate of 0.05 to 5 ^°C/min and, then, the polymerization reaction is terminated [step (d) ] .

Since the polymerization reaction in accordance with the present invention is carried out in the aqueous system mixed with organic solvents having various boiling points or freezing points and is an exothermic reaction, the present invention provides synthesis conditions that can stir the dispersion media effectively and prevent the side reactions in order to maintain the dispersion system stable. Especially, since the amine group and the like of the synthesized polymer may cause side reactions such as chloride substitution, it is preferable to increase the acidity of the reaction system.

The respective temperatures in the initiation, propagation and termination steps of the polymerization reaction may be controlled in the range of -45 to 0^°C, preferably, in the range of -35 to -5^°C. Since the reaction time and the molecular weight of the synthesized polymer sensitively respond to the reaction temperature, it is possible to select an appropriate temperature from the above temperature range and a temperature control rate to reach the same Raman spectrum ratio although the molecular weight of the obtained polyaniline and the desired electrical conductivity level are different. Accordingly, the reaction time in the respective steps may be adjusted according to the above temperature range and the temperature control rate and, if the reaction temperature is lowered, the reaction time is increased.

The reaction heat is closely associated with the amount of the initiator and the addition rate. If the content of the initiator is high or if the addition rate is increased, the yield may be increased; however, the initiation reaction is promoted more than chain propagation and, if the reaction time is prolonged, a hydrolysis occurs and thus it is difficult to obtain a high electrical conductivity. Contrarily, according to the synthesis method of the present invention, it is possible to synthesize polyaniline having a high electrical conductivity by controlling the temperature step by step. That is, since it was observed that the reaction temperature was increased for about 5 to 240 minutes after the reaction initiation, the reaction temperature is gradually lowered in the initiation step. Moreover, in the middle of the reaction where the chain propagation mainly occurs, the reaction temperature is maintained at a low level constant in order to prevent the side reactions and, in the reaction termination step where the reaction has proceeded and thus the shape of the polymer is distorted, the reaction temperature is increased.

Since the reaction medium of the present invention forms a heterogeneous dispersion system with an organic solvent, the selection of the reaction temperature significantly depends on the properties and content of the organic solvent. The reason for this is that the degree that the same organic solvent is mixed with water is different according to the content and the temperature. For example, if isopropyl alcohol that is miscible with water is mixed with water, the freezing point is changed from -3^°C to -35^°C (See the following Table 1) .

[Table 1] Change in freezing point according to content of mixed solvent of water and isopropyl alcohol

However, although chloroform which is not readily mixed with water has a boiling point of 62 ^°C and a freezing point of -64 ^°C, it is dissolved in water about 0.5 wt%, the boiling point is lowered about 3 to 4 "C and the freezing point is increased at room temperature. Accordingly, an appropriate selection of the reaction temperature is necessary for maintaining the dispersion system in view of the characteristics of the reaction system in which the polymer is produced and the concentration of the monomer is reduced. Especially, since the aniline monomer forms a complex with an inorganic or organic acid to function as a surfactant of water and the organic solvent in the synthesis method in accordance with the present invention, the selection of the reaction temperature is important.

Moreover, if the aniline monomer is present in a semi-solid state at a temperature below -9^°C, a predetermined amount of aniline monomer is dissolved to participate in the reaction, and thus it is possible to prevent the side reactions. The properties and content of the organic solvent added to the reaction medium in the present invention is associated with the selection of the reaction temperature.

Accordingly, since the conventional homogeneous solution attempted by MacDiarmid is frozen if the reaction temperature is lowered, it is impossible to decrease the reaction temperature, and thus it has limitations in increasing the mole:cular weight or the electrical conductivity.

With the polyaniline synthesized according to the synthesis method of the present invention, it is possible to separate polymers in various methods according to a desired shape of the final product.

For example, when PANi is washed with water or methyl alcohol and collected, it is possible to obtain conductive emeraldine salts (ES) in various shapes. Moreover, when the conductive emeraldine salt is treated with a base, it is possible to obtain emeraldine base (EB) which is very soluble in an organic solvent. Furthermore, the emeraldine base (EB) may be used in various ways by reprocessing the same via a doping process or re-doping the same after processing. In addition, it is possible to prepare the obtained emeraldine base (EB) in the form of leucoemeraldine or pernigraniline by a redox reaction.

One of the merits of the method of synthesizing conductive polymers in accordance with the present invention is that it is easy to control the molecular weight of the polymers. A polymer material having an intrinsic viscosity of 1.1 to 2.9 can be obtained by varying the reaction conditions in accordance with the present invention. The polymer material synthesized in accordance with the present invention had an intrinsic viscosity of 2.5 measured at about 30^°C after being dissolved in NMP at a concentration of 0.1 g/dl, a weight average molecular weight of 34,000 measured by GPC, and a molecular weight distribution degree of 2.6. According to Table 2, which will be described later, it was found that the polymer material synthesized in accordance with the present invention was a peculiar conductive polymer, which could not be realized by the conventional methods. That is, the conductive polymer in accordance with the present invention had a high electrical conductivity even in the case where it had a low molecular weight, and was easily dissolved in an organic solvent even in the case where it had a high molecular weight, compared with the PANi synthesized according to the conventional method.

Next, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 shows the structural formula of the aniline monomer, FIG. 2 shows a chemical formula schematically showing the repeating unit of polyaniline substituted with tert-butoxycarbonyl (t-BOC) to be dissolved in an organic solvent in order to identify the molecular structure of the polyaniline synthesized in accordance with the present invention, FIG. 3 is a schematic diagram illustrating the concept of self-stabilized dispersion polymerization, FIGS. 4A to 4G are graphs showing Raman scattering spectra of a reaction medium at -25^°C, and FIG. 5 is a graph showing the Raman spectrum intensity ratio of 800 Cm^-1ZlSSO cm^"1 and 1160 cirfVlSδO cm^"1 of the reaction medium of the FIGS. 4A to 4G according to reaction time.

FIG. 6 is a graph showing the results of ¹³C CPMAS (cross-polarization/magic angle spinning) NMR spectral analysis of the synthesized polyaniline, FIG. 7 is a graph showing the results of solution state ¹³C CPMAS NMR spectral analysis of the polyaniline substituted with tert- butoxycarbonyl (t-BOC) , FIG. 8 is a graph showing DEPT spectra (solvent CDCI₃) of the polyaniline of the present invention, in which (a) is DEPT 135 (top) and (b) is DEPT 90 (bottom) , FIG. 9 is a diagram showing an HMBC spectrum at room temperature (solvent CDCI₃) of the polyaniline of the present invention, FIG. 10 is a diagram showing a peak at around 154 ppm of the polyanilines prepared in Example 1 and Comparative Example (bottom and middle) and that prepared according to a conventional method (top) , FIG. 11 is a graph showing thermogravimetric curves of prepared polyaniline particles, in which the dotted line curve represents the conventional polyaniline and the solid line curve represents the polyaniline of the present invention, FIG. 12 is a graph showing a GPC chromatogram of the polyaniline substituted with t-BOC prepared in Example 1, FIG. 13 is a scanning electron microscope (SEM) photograph showing nanoparticles having a size of 30 to 80 nanometers and formed in a tubular shape, and FIG. 14 is an SEM photograph showing nanoparticles connected to each other to form a porous network.

As shown in the figures, the PANi synthesized in accordance with the synthesis method of the present invention shows a peculiar shape in which nanoparticles are connected like bunches of grapes. Moreover, as the results of the ¹³C CPMAS NMR spectral analysis, the PANi synthesized in accordance with the present invention shows only apparent peaks at around of 158, 140 and 128 ppm without any other small peaks.

As the results of solution state ¹³C NMR spectral analysis of the polyaniline substituted with t-BOC to be dissolved, there were shown 4 major peaks between 139.5 ppm and 160 ppm of chemical shift. Accordingly, it was concluded that the PANi synthesized in accordance with the present invention had little defects in carbons formed on the quinoid ring in the repeating unit of the polyaniline and that the monomers were coupled to the para positions without any side reactions.

Moreover, it was confirmed that the molecular weight, bhe reaction temperature and the electrical conductivity of the polymer synthesized in accordance with the present invention were closely correlated with each other (See Table 2).

Next, the present invention will be described in more detail through the illustrative Examples. However, the following Examples are provided only for illustrations and thus the present invention is not limited to the following Examples .

EXAMPLES [Measurement of Electrical Conductivity]

The electrical conductivity was measured with a commonly used four line probe method at room temperature at a relative humidity of about 50%. Carbon paste was used for preventing corrosion when contacting gold wire electrodes. The electrical conductivities of film samples with a thickness of about 0.1 to 100 μm (thickness t, width w) with respect to currents (i) , voltages (V), and distances (1) between two external electrodes and two internal electrodes were measured with a Keithley instrument. The conductivity was calculated using the following formula and expressed as a unit of Siemen/cm or S/cm. - Conductivity = (1 ^• i) / (w ^• t ^• v)

[Measurement of SEM Particle Shapes] Particle shapes of the conductive polymers synthesized in the following Examples were observed using a scanning electron microscope (SEM, Model No. XL-30, Philips Co.). Since the image observation was available in very restricted regions, a great number of photographs were taken and observed in order to obtain representative images.

[NMR Analysis]

¹³C CPMAS-NMR spectra were measured at 100.6 MHz and spinning rate of 7 KHz by a Bruker NMR instrument with the use of tetramethyl silane (TMS) as a standard. Solution state ¹³C NMR spectra were obtained by an ordinary method after dissolving the samples in CDCI₃ using a JEOL Lambda 400 instrument

[Thermogravimetric Analysis]

Thermogravimetric analysis (TGA) was carried out under a nitrogen atmosphere using a TA instrument (Model No. 2050) and measured at a heating ratio of 10 ^°C/min.

[Molecular Weight Analysis] Molecular weight analysis was ceirried out with GPC-717 manufactured by Waters Co. having an automatic sample collector using a solvent THF.

Example 1

PANi in the form of emeraldine base (EB) was synthesized according to the temperature-controlled self- stabilized dispersion polymerization of the present invention. First, 100 mL of distilled and purified aniline was slowly added dropwise to 3 L of 1 M HCL solution and then 8 L of chloroform was mixed with the resulting solution. While lowering the temperature of the mixed solution from 0^°C at a rate of 0.1 ^°C/min, a solution, in which 56 g of ammonium persulfate [ (NH₄) ₂S₂O₈] as an initiator was dissolved in 1 L of 1 M HCL solution, was added dropwise to the mixed solution for 40 minutes while stirring to initiate the polymerization reaction. After the completion of the addition of the initiator, the temperature was maintained constant at -25^°C for 8 hours to carry out the polymerization propagation reaction. Then, the polymerization reaction was terminated by increasing the temperature of the reaction mixture to 0^°C at a rate of 0.2 ^°C/min. Here, the stirring rate was maintained 100 rpm/min. The obtained precipitate was filtered with a filter paper to collect polyaniline in the form of base. A portion of the collected polyaniline was washed with 1 L of 1 M ammonium hydroxide (NH₄OH) solution. The precipitate was transferred into 5 L aqueous solution of 0.1 M ammonium hydroxide, stirred for 20 hours, filtered, and then dried under reduced pressure for 48 hours to yield 1.9 g of PANi emeraldine base (EB) .

The synthesized polymer was analyzed with an infrared spectrometer. As a result, the vibration absorption bands were shown at a peak of about 1590 cm^"1 attributable to a typical quinoid structure, at a peak of about 1495 cm^"1 attributable to a benzenoid structure, and at a peak of about 3010 cm^"1, resulting from the stretching vibration of C-H of aromatic ring. Moreover, as the results of solution state ¹³C NMR spectrum, since the chemical shifts of the aromatic carbons had characteristic peaks at 118 ppm, 137 ppm and 141 ppm, respectively, the synthesis of the PANi was confirmed.

Comparative Example PANi emeraldine base (EB) was prepared by the conventional method by MacDiarmid et al. (MacDiarmid et al . , Conducting Polymers Ed. by Alcacer, Dordrecht, 105, 1987). First, 10 mL of distilled and purified aniline and 600 mL of IM HCl solution were placed in an Erlenmeyer flask. Subsequently, 200 mL of 1 M HCL solution in which 5.6 g of ammonium persulfate [(NHJ₂S₂O₈] was dissolved was added dropwise to the flask for 15 minutes while stirring to initiate the polymerization reaction. Precipitate obtained after 2 hours was filtered with a filter paper and washed with 100 mL of 1 M ammonium hydroxide (NH₄OH) solution. The precipitate was transferred into 500 mL of 0. IM ammonium hydroxide solution, stirred for 20 hours, filtered, and dried with a vacuum pump for 48 hours to yield 1.5 g of PANi emeraldine base (EB) . The synthesis of the PANi in the form of emeraldine base (EB) was confirmed using an ultraviolet spectrometer and by an NMR analysis.

Example 2 During the polymerization reaction in Example 1, the reactant was taken out by 3 mL according to reaction time, and 2 mL of 0.1 M NH₄OH solution was added thereto to stop the reaction. Then, the Raman spectral analysis was carried out to set the reaction zones according to the intensity ratio of 800 cirfVl350 cm^"1 and 1160 crrfVlSSO cm^"1 as shown in FIGS. 4 to 5. The reaction time was adjusted according to the reaction temperature by classifying the polymerization reaction into the steps of completing the addition of the initiator by slowly adding the initiator dropwise so that the Raman spectrum intensity ratio of the reaction medium is 800 cnfV1350 cm^"1 < 0.01 and 1160 cm^~Vl350 cm^"1 < 0.05, carrying out the polymerization propagation reaction by- maintaining the temperature of the reaction mixture constant until reaching the Raman spectrum intensity ratio 800 cm^" 71350 cm^"1 < 0.26 and 1160 cm^"Vl350 cm^"1 < 0.28, and carrying out a polymerization termination reaction by increasing the temperature of the reaction mixture until reaching a temperature of -5 to 0^°C at a rate of 0.05 to 5 ^°C/min. In the case where the reaction temperature was - 25^°C, the detailed reaction conditions were as follows. 100 mL of distilled and purified aniline was slowly added dropwise to 3 L of 1 M HCL solution and then 8 L of chloroform was mixed with the resulting solution. While lowering the temperature of the mixed solution from 0^°C at a rate of 0.5 ^°C/min, a solution, in which 56 g of ammonium persulfate [ (NH₄) ₂S₂θ₈] as an initiator was dissolved in 1 L of 1 M HCL solution, was added dropwise to the above mixed solution for 40 minutes while stirring to initiate polymerization reaction. After the completion of the addition of the initiator, the temperature was maintained constant at -25^°C for 8 hours to carry out the polymerization propagation reaction. Then, the polymerization reaction was terminated by increasing the temperature of the reaction mixture to 0^°C at a rate of 0.5 ^°C/min. The reaction was terminated in accordance with Example 1, and the following procedures were repeated. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base (EB) using an ultraviolet spectrometer and by an NMR analysis.

Example 3

The reaction temperature during the polymerization of the PANi was fixed to -10 ^°C and the reaction was terminated after the total reaction time the same as Example 2. The following procedures were repeated in the same manner as Example 2. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base (EB) using an ultraviolet spectrometer and by an NMR analysis.

Example 4

The reaction temperature during the polymerization of the PANi was fixed to -5^°C and the reaction was terminated after the total reaction time the same as Example 2. The following procedures were repeated in the same manner as Example 2. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base using an ultraviolet spectrometer and by an NMR analysis.

Example 5 PANi was synthesized in the same manner as Example 2, except that 8 L of a mixed solvent of dichloroethane and isopropyl alcohol at a volume ratio of 2:1 was used instead of chloroform as the organic solvent. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base using an ultraviolet spectrometer and by an NMR analysis.

Example 6

PANi was synthesized in the same manner as Example 2, except that a mixed solvent of propylene carbonate and 4- methyl-2-pentanone at a volume ratio of 1:1 was used instead of chloroform as the organic solvent. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base using an ultraviolet spectrometer and by an NMR analysis.

Example 7

PANi was synthesized in the same manner as Example 2, except that 4 L of chloroform and 8 L of hydrochloric acid solution were used at a volume ratio of 1:2. It was confirmed that the synthesize compound was the PANi in the form of emeraldine base using an ultraviolet spectrometer and by an NMR analysis.

Example 8 The procedures were repeated in the same manner as Example 1, except that the polymerization temperature was lowered to -35^°C and the reaction time was increased by 2 times .

Example 9: Measurement of intrinsic viscosity of PANi The emeraldine bases (EB) synthesized in the above Examples and Comparative Example were dissolved in a concentration of 0.1 g/dl in N-methylpyrrolidinone (NMP) or in concentrated sulfuric acid and then the intrinsic viscosities were measured at 30^°C. The intrinsic viscosities for the respective polymer materials are shown in the following Table 2.

It can be seen from Table 2 that, if the temperature is adjusted step by step, the intrinsic viscosity is increased and the electrical conductivity is improved in the same conditions. The intrinsic viscosity that represents the molecular weight of the polymer is closely associated with the reaction temperature, which is similar to the case where the polymerization occurs in an aqueous solution like the convention MacDiarmid method.

•Ϊ

Example 10: Measurement of spectral characteristics of synthesized PANi solid powder 1³C CPMAS MNR spectra of the solid powder PANi EB samples synthesized in Example 1 and Comparative Example were obtained at 100.6 MHz and spinning rate of 7 KHz by a Bruker NMR instrument with the use of tetramethyl silane (TMS) as a standard. The results of ^]3C CPMAS analysis are shown in FIG. 6.

The PANi prepared in accordance with the present invention showed apparently distinguishable peaks at around 158 ppm, 140 ppm and 127 ppm without any other peripheral peaks caused by side reactions, unlike the conventional samples. Especially, the peak observed at around 127 ppm was formed from the carbon atoms of the benzenoid ring, which might be rotated a little bit, in the repeating units of the polyaniline. Accordingly, it could be understood that the PANi prepared in accordance with the present invention had an equivalent; however, the conventional PANi did not have a single peak, but had separate peaks.

Likewise, the conventional PANi had several small peaks at around 138 ppm and their strengths were weaker than those of the peaks at around 143 ppm. Contrarily, the PANi synthesized in accordance with the present invention had at least two apparently distinguished peaks at around 140 ppm. That is, it could be understood that the PANi synthesized in accordance with the present invention had little defects in carbons formed on the quinoid ring in the repeating unit of the polyaniline and that most of the aniline monomers were coupled to the para positions during the polymerization.

Example 11: Measurement of spectral characteristics of solution state of synthesized PANi EB PANi substituted with t-BOC to improve the solubility was synthesized. The PANi was synthesized in the same procedures as Example 1. 1.0 g of the synthesized EB polymer (5.5X1CT³ mol) and 4.8 g (2.2XlO^"2 mol) of di-tert- butyldicarbonate (di-t-BOC) were dissolved in 30 mL of NMP. Subsequently, 20 mL of pyridine was added to the resulting solution, and then the solution was stirred at 90^°C for 6 hours. The reaction product was precipitated in excessive water to be filtered and the filtered precipitate was washed with a solution of water and ethanol at a mixed ratio of 1:1 to yield 0.6 g of pure t-BOC polyaniline.

The NMR spectrum measured after dissolving the thus obtained t-BOC polyaniline in CDCI₃ is shown in FIG. 7. As a result, in the solution state ¹³C NMR spectrum, there were shown 4 major peaks between 139.5 ppm and 160 ppm of chemical shift, no distinguishable peaks were shown at below 110 ppm of chemical shift and/or between 130 ppm and 135 ppm of chemical shift, and no distinguishable peaks were shown between 149 ppm and 152 ppm of chemical shift. However, the polymer synthesized in accordance with Comparative Example had a complicated peak and, in the solution sate spectrum, the peak at around 154 ppm was shown as divided into two peaks .

The results of the solution state NMR spectrum are as follows . It could be seen from the NMR technique such as a distortionless enhancement by polarization transfer (DEPT) as shown in FIG. 8 that the four major peaks between 139.5 ppm and 160 ppm of chemical shift in the solution state ¹³C NMR spectrum resulted from carbon atoms having no hydrogen. Here, the DEPT method is directed to a method that reveals a connection relation between carbon atoms by making the carbon atoms, which are not bonded to hydrogen, not show up by transferring polarization. It could be seen from the spectrum shown at the bottom of FIG. 8 that all peaks disappeared at the above sections.

Accordingly, the NMR peaks at the above sections were carbon atoms corresponding to the carbon atom numbers 7, 8, 9, 10 and 12 in view of the repeating structure of FIG. 2. The reason why the four peaks, not five peaks, were shown was that the carbon atoms corresponding to the carbon atom numbers of 8 and 9 were under substantially the same NMR spectrum.

The reason why the polyaniline of the present invention showed only four major peaks was that the polyaniline was synthesized in the above repeating structure. And it could be understood that a lot of side reactions occurred in the other two conventional samples. Since these four peaks represent a polymer chain structure, they are important in representing the microstructure of the polymer chain rather than the other peaks. If the following oxidation reactions occur during the polymerization reaction, the carbon atoms which are not bonded to hydrogen are increased.

Likewise, if an ortho coupling which has a high possibility of causing side reactions occurs, side peaks are shown at positions lower than the main peak at around 154 ppm due to the fol Lowing hydrogen coupling (See FIG. 10).

The bonding state of the carbon atoms were identified by heteronuclear multiple bonds correlation (HMBC) NMR technique as shown in FIG. 9. It could be seen that the peak at around 154 ppm and, more precisely, 153.8 ppm, resulted from the 12^th carbon atom of FIG. 2 which was not directly bonded to hydrogen.

However, the conventional sample had a considerably high peak observed at around 154.2 ppm lower than the above position, and it could be seen that the ortho coupling was more than 30% by calculating the area ratio (See FIG. 11) . FIG. 11 shows the degrees of the ortho coupling of the samples in accordance with Examples 1 and 4 and Comparative Example in order to identify the relation between the side peaks and the electrical conductivity.

It can be understood from FIG. 11 that the PANi prepared in accordance with the present invention has an ortho coupling less than 7.2%; however, if the self- stabilized dispersion polymerization is carried out at below 5^°C or the conventional method is carried out to synthesize bhe PANi, the ortho content is increased and the electrical conductivity is reduced. The ortho coupling is related to a peak at around 123 ppm since it is known that the benzene ring, α, β carbons are shown in the vicinity of 123 ppm, besides the carbonyl carbon at around 154 ppm (See Ward et al. Macromolecules, Volume 36, p. 4368-4373, 2003). It can be seen from the results that most of the PANi synthesized in accordance with the present invention are coupled to the para positions, and thus the linearity is significantly improved.

Example 12: Thermogravimetric analysis (TGA) The samples prepared in accordance with Example 1 and Comparative Example were treated by the method described in Example 11, and the results of the thermogravimetric analysis (TGA) are shown in FIG. 11. The first reduction in which a mass reduction was completed at 250 ^°C had a significant difference between the product of the present invention and the conventional product. The reason for this was that, since all of the two amine groups of the repeating unit of FIG. 2 were substituted with t-BOC in the polyaniline of the present invention, the mass reduction reached 35%; however, since only one amine group was substituted with t-BOC in the conventional sample, they were separated by heat and thus the mass reduction was reduced 17.2%.

Theoretically, in the case where; one BOC is substituted, there is a mass reduction of 20.5%, which means that the polyaniline of the present invention has chemical properties different from those of the conventional aniline since the t-BOC substitution rate differs in the same reaction. These results coincide with those of the NMR analysis of Example 10. The reason for this is that all of the two amine groups cannot be substituted with t-BOC due to a steric hindrance if there are much ortho couplings like the conventional polyaniline.

Example 13: Measurement of molecular weight Since the synthesized polyaniline was not easily dissolved in a typical organic solvent and, even if it was dissolved, it was turned to gel or aggregate, the t-BOC polyaniline prepared by the method of Example 10 using the polyaniline synthesized by the method of Example 1 was dissolved in tetrahydrofuran in order to inhibit the hydrogen bonding, and the molecular weight of the polyaniline substituted with t-BOC was measured by GPC. As a result, with the use of a polystyrene standard sample, the weight average molecular weight was 34,000, the molecular weight distribution showed a single peak, and the distribution degree was as narrow as about 2.6 (See FIG. 12) Example 14 : Observation of particle shape of synthesized PANi

The structure of the PANi EB powder synthesized in Example 1 was observed using a scanning electron microscope. As shown in FIGS. 13 and 14, the synthesized PANi EB powder had a hollow nanotube structure changed from a structure such as foamed plastic composed of nanoparticles . That is, it was ascertained that the polymer synthesized in accordance with the present invention had a steric structure increasing the surface area compared with the polymer synthesized in accordance with the conventional method.

Example 15: Measurement of surface area of PANi particles

The particle surface areas of the products taken out of the reactor in Examples 1 to 8 were measured by a BET method. The surface areas measured from nitrogen adsorption isotherm curves at an absolute temperature of 77K were 72 to 101 m²/g according to the properties of the solvent and the reaction temperature. While the conventional sample in accordance with Comparative Example showed the surface area of 8 m²/g in the same conditions, the surface areas of the samples in accordance with the present invention were increased by 12.6 times at the maximum. Meanwhile, the surface area of dedoped emeraldine base (EB) was slightly lowered than that of the above emeraldine salt (ES) ; however, the surfaces areas were all more than 51 m²/g.

Example 16: Measurement of electrical conductivity of PANi in CSA solution

The PANi salts synthesized in Examples 1 to 8 were dedoped to form emeraldine bases (EB) and the thus formed emeraldine bases were re-doped to measure the electrical conductivities .

First, the PANi salts synthesized in Examples 1 to 8 were dedoped to obtain PANi emeraldine bases (EB) . Each of 1.23 g of the thus obtained PANi emeraldine bases (EB) was mixed with 1.57 g of camphorsulfonic acid (CSA) in an equivalent ratio of 1:2. Subsequently, the respective mixtures were dissolved in meta-cresol at a concentration of 2% (w/w) , and then solutions were prepared by sonication for 2 hours. Each of 0.5 mL of the thus prepared solutions was cast on a slide glass and dried at 50 ^°C to form films with a thickness of 0.5 to 80 μm. The measurement of the electrical conductivity was carried out on the thus formed films and the electrical conductivity values measured are shown in the following Table 2.

The physical properties of the polyanilines obtained from the above Examples and Comparative Example are summarized in the following Table 2.

[Table 2] Physical properties of synthesized polyanilines

In can be understood from the relation between the reaction temperature, the molecular weight and the electrical conductivity that it is preferable that the self- stabilized dispersion polymerization is carried out by controlling the temperature of the polymerization reaction step by step and the temperature is selected from a temperature of below -5^°C

It will be apparent to those skilled in the art that various modifications and variations can be made in the fabrication and application of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents .

[industrial Applicability]

As described above, the method of synthesizing conductive polyaniline in accordance with the present invention synthesizes conductive polyaniline having a high linearity and a low density of side chains caused by side reactions. Accordingly, even in case of the polyaniline having an intrinsic viscosity of more than 2.7, it is easily dissolved and has an electrical conductivity of more than 1,300 and, even in case of the polyaniline having a pure metallicity and an intrinsic viscosity of 1.3, it has an electrical conductivity of more than 300 S/cm. Moreover, since the obtained conductive polyaniline has a structure with pores such as foam, honeycomb, and hollow capsule, formed of nanoparticles, the surface area is increased (about more than 51 m²/g when measured by the BET method) , and thus the conductive polyaniline has a high chemical reactivity such as polymerization reaction, doping, and dedoping. Accordingly, the polyaniline synthesized in accordance with the present invention may be effectively used as various electrodes, conductive films, conductive fibers, conductive coatings, various sensors, blends with polymers, battery electrodes, or organic semiconductors. Especially, since the polyaniline synthesized in accordance with the present invention has a high electrical conductivity although a small amount is used, it is suitable for specific applications such as corrosion prevention, near-infrared absorption, conductive etch mask layer, and the like.

Claims

[CLAIMS]

[Claim l]

A method of preparing conductive polyaniline by ■ temperature-controlled self-stabilized dispersion polymerization, the method comprising the steps of:

(a) mixing an aqueous solution, in which an aniline monomer and a protonic acid are dissolved in water or in a mixed solvent of water and a water-miscible organic solvent, with a water-immiscible organic solvent in a reactor; (b) lowering the internal temperature of the reactor until reaching a polymerization temperature at a rate of 0.05 to 5 ^°C/min when the internal temperature of the reactor reaches 0^°C by cooling the reactor and, at the same time, adding an initiator thereto; (c) carrying out a polymerization propagation reaction by maintaining the internal temperature of the reactor constant; and

(d) carrying out a polymerization termination reaction by increasing the internal temperature of the reactor until reaching a temperature of -5 to 0^°C at a rate of 0.05 to 5 ^°C/min.

[Claim 2]

The method of claim 1, wherein the water-miscible organic solvent is one selected from the group consisting of methanol, ethanol, acetonitrile, and 2-methoxyenthanol .

[Claim 3]

The method of claim 1, wherein the aqueous solution is a solution obtained by dissolving an aniline monomer and a protonic acid in water.

[Claim 4]

The method of claim 1, wherein the protonic acid is one selected from the group consisting of an inorganic acid, a C₁-C₂₄ alkylsulfonic acid, an arylsulfonic acid, a halogenated C₁-C₂₄ alkylsulfonic acid, and a mixture thereof.

[Claim 5] The method of claim 4, wherein the protonic acid is one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, methylsulfonic acid, dodecylbenzene sulfonic acid, chlorosulfonic acid, trifluorosulfonic acid, and a mixture thereof.

[Claim β]

The method of claim 5, wherein the protonic acid is hydrochloric acid .

[Claim 7] The method of claim 1, wherein the organic solvent has a dielectric constant of 4.3 to 65.1.

[Claim 8] The method of claim 7, wherein the organic solvent is one selected from the group of tetrachloroethane, trichloroethane, chloroform, dichloroethane, bis (2- chloroethyl) ether, 1, 2, 3-trichloropropane, dichloromethane, ethyl chloride, dichloroethyl ether, dichloropropane, neopentyl alcohol, isopropyl alcohol, alkylbutanol, alkylpentanol, butanol, propanol, pentanol, 1, 5-pentanediol, amyl alcohol, cyclopentanone, 4-methyl-2-pentanone, cyclohexanone, diacetone alcohol, 2-ethyl-l, 3-hexanediol, ethyhexanol, cyclohexanol, heptanol, octanol, decanol, dodecanol, propylene carbonate, dimethyl glutarate, benzyl acetate, ethyl aceto acetate, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, tetrahydrofurfuryl alcohol, nitrobenzene, and a mixture thereof.

[Claim 9]

The method of claim 8, wherein the organic solvent is one selected from the group consisting of chloroform, a mixed solvent of dichloroethane and isopropyl alcohol, and a mixed solvent of propylene carbonate and 4-methyl-2- pentanone.

[Claim lθ]

The method of any one of claims 1 to 9, wherein the initiator is one selected from the group consisting of ammonium peroxysulfate, hydrogen peroxide, manganese dioxide, potassium dichromate, potassium iodate, ferric chloride, potassium permanganate, potassium bromate, potassium chlorate, and a mixture thereof.

[Claim 11]

The method of claim 10, wherein the initiator is ammonium peroxysulfate.

[Claim 12]

The method of any one of claims 1 to 9, wherein the addition of the initiator is carried out so that Raman spectrum intensity ratio of a reaction medium is 800 cm^" 71350 cm^"1 < 0.01 and 1160 cm^"7l350 cm^"1 < 0.05.

[Claim 13]

The method of any one of claims 1 to 9, wherein, in step (c) , a polymerization propagation reaction is carried out by maintaining the internal temperature of the reactor constant until reaching the Raman spectrum intensity ratio of the reaction medium 800 cm^~7l350 cm^"1 < 0.26 and 1160 cm^" 71350 cm^"1 < 0.28.