JPH0555533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a conductive organic polymer. Most organic materials are electrically insulating, however, a group of organic polymers with electrical conductivity known as organic semiconductors have received attention in recent years. Organic materials that are themselves electrically conductive are generally classified into three types. The first is graphite. Although graphite is not strictly considered an organic substance, it can be considered to have the ultimate structure of an organic conjugated system. This graphite already has a fairly high conductivity by itself, but by intercalating it with various compounds, it can be made to have even higher conductivity, eventually becoming a superconductor. However, graphite has strong two-dimensionality and is difficult to mold, which poses an obstacle in its application. The second type is a charge transfer complex, and for example, a crystalline material obtained using tetrathiafulvalene and tetracyanoquinodimethane as an electron donor and an electron acceptor, respectively, has a very high conductivity of 400 to 500 S/cm at room temperature. However, since such charge transfer complexes are not polymers, they have the same difficulty in moldability as graphite for practical application. The third type is a π-electron conjugated organic polymer that becomes highly conductive through doping, as typified by polyacetylene. The conductivity of polyacetylene before doping is that the transformer type
10 ^-5 S/cm, and 10 ^-9 S/cm for the cis type, and has properties close to semiconductors or insulators. However, such polyacetylene contains arsenic pentafluoride, iodine,
By doping with an electron-accepting compound such as sulfur trioxide, ferric chloride, or an electron-donating compound such as an alkali metal, a p-type semiconductor and an n-type semiconductor can be formed, respectively.
Furthermore, it is possible to provide high conductivity at a conductor level of 10 ³ S/cm. The above polyacetylene is an interesting conductive organic polymer in theory, but on the other hand,
Polyacetylene is extremely susceptible to oxidation and is easily oxidized and deteriorated in the air, causing its properties to change significantly.
In the doped state, it is more sensitive to oxidation, and its conductivity decreases rapidly even with the slightest amount of moisture in the air. This tendency is particularly remarkable for n-type semiconductors. Furthermore, poly(p-phenylene) and poly(p-phenylene sulfide) have conductivities of 10 ^-9 S/cm and 10 ^-10 S/cm, respectively, before doping, but By doping with arsenic, the conductivity is 500S/cm and
It can be a conductive organic polymer with a conductivity of 1 S/cm. The electrical properties of these doped organic polymers are also unstable to varying degrees. The fact that the electrical properties of such doped conductive organic polymers are generally very unstable to the environment is a common phenomenon among these types of conductive organic polymers, and it is difficult to use them for practical purposes. This has become an obstacle to practical applications. As described above, various organic conductive substances have been known so far, but from the viewpoint of developing practical applications, polymer forms with excellent moldability are preferred. On the other hand, research on oxidized polymers of aniline as oxidized dyes has been conducted for a long time in connection with aniline black. In particular, as an intermediate for the production of aniline black, the aniline octamer represented by the formula () is emeraldine.
(AGGreen et al., J.
Chem.Soc., 97 , 2388 (1910); 101 , 1117
(1912)), which consists of 80% acetic acid, cold pyridine and N,
Soluble in N-dimethylformamide. It is also known that this emeraldine is oxidized in an ammoniacal medium to produce nigraniline represented by the formula (), which also has similar solubility properties to emeraldine. Furthermore, in recent years, R. Buvet et al. discovered that this sulfate of emeraldine has high conductivity (J. Polymer Sci., C.
16, 2931; 2943 (1967); 22, 1187 (1969)). It is also already known that an organic substance similar to emeraldine can be obtained by electrolytic oxidation of aniline (DMMohilner et al., J.Amer.
Chem.Soc., 84 , 3618 (1962)). That is, according to this, a sulfuric acid aqueous solution of aniline is heated using a platinum electrode,
In order to avoid electrolysis of water, electrolytic oxidation polymerization was performed at an oxidation potential of +0.8 V with respect to a standard calomel electrode (hereinafter referred to as SCE), and the polymer was soluble in 80% acetic acid, pyridine, and N,N-dimethylformamide. A certain substance is obtained. In addition, Diaz et al. (J.Electroanal.Chem.
111, (1980)), Koyama et al. (Proceedings of the Society of Polymer Science, 30 ,
(7), 1524 (1981)) have also attempted to electrolytically impregnate aniline, but both aimed at polymer-coated chemically modified electrodes, and electrolysis was performed at a potential of 1 V or less relative to SCE. There is. In order to obtain stable and highly conductive organic materials, especially conductive organic polymers, the present inventors have conducted intensive research on the electrolytic oxidation polymerization of aniline. Electrolytic oxidation polymerization of aniline is carried out using constant current electrolysis at +1.2V or more for SCE, or +1.2V for SCE.
By oxidatively polymerizing aniline using constant potential electrolysis at 2V or more, it is possible to obtain emeraldine, which has a higher molecular weight than emeraldine and has already been doped during the oxidative polymerization stage, so a new doping operation is required. The present invention was achieved by discovering that it is possible to obtain a stable and highly conductive polymer without the above. That is, according to the present invention, first, an aniline aqueous solution containing aniline and a protonic acid in an amount equivalent to or more than the aniline is heated at an initial electrolytic potential of +1.2 V or more with respect to SCE, and a current density of 0.01 mA/ A conductive organic material which is doped with the above acid and whose conductivity is 10 ^-6 S/cm or more, which undergoes oxidative polymerization by constant current electrolysis in the range of cm ² to 1 A/cm ² . A method of making a polymer is provided. Furthermore, according to the present invention, secondly, an aniline aqueous solution containing aniline and a protonic acid in an amount equivalent to or more than the aniline is electrolyzed at a constant potential of +2 V or more with respect to SCE at a current density of 0.01 mA/cm ² ~1A/
Provided is a method for producing a conductive organic polymer which is doped with the above acid and whose conductivity is 10 ^-6 S/cm or more, which is characterized by oxidative polymerization in the range of cm ² . The protonic acid used in the present invention is preferably a protonic acid whose oxidation potential is higher than the oxidation potential in the present invention, and specifically, hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, perchloric acid, Tetrafluoroboric acid (HBF ₄ ), hexafluorophosphoric acid (HPF ₆ ), and the like are preferably used. In order to obtain a conductive organic polymer having a high electrical conductivity of 10 ^-6 S/cm or more according to the present invention, the above protonic acid is used in an amount equivalent to or more than that of aniline, usually in a range of 1 to 5 times, and When using a method of oxidatively polymerizing an aniline aqueous solution by constant current electrolysis, the initial electrolytic potential can be set to +1.2 V or more with respect to SCE, and the current density can be set in the range of 0.01 mA/cm ² to 1 A/cm ² . is necessary. In addition, when performing oxidative polymerization by constant potential electrolysis, the aniline aqueous solution is subjected to constant potential electrolysis at +2V or more with respect to SCE, and the current density is 0.01 mA/cm ² or more.
It is necessary to carry out oxidative polymerization in the range of 1 A/cm ² . As is well known, constant current electrolysis refers to a method of electrolysis with a constant current, and constant potential electrolysis refers to a method of electrolysis with a constant electrode potential.
In the case of galvanostatic electrolysis, the potential increases over time from the initial electrolysis potential. In electrolytic oxidation polymerization of aniline aqueous solution, in the case of constant current electrolysis, the electrolytic potential is ++ with respect to SCE.
When the electrolytic potential is not set at 1.2 V or higher, or when the electrolytic potential is not set at +2 V or higher relative to SCE in the case of constant potential electrolysis, or when the current density is outside the above range in any method, the The polymer has a low molecular weight and low conductivity. Further, it is desirable that the aniline concentration in the aniline aqueous solution is 1% by weight or more. Even when the aniline concentration is less than 1% by weight, the resulting polymer has a low molecular weight and low conductivity. However, the upper limit of aniline concentration is not particularly limited, but usually
Up to 50% by weight is suitable. In the method of the present invention, water is used as the solvent. The decomposition potential of water is 1.23V, and in some cases, the electrolytic potential in the method of the present invention is higher than the decomposition potential of water, but this is because the oxidation of aniline occurs preferentially than the decomposition of water. According to the present invention, a high molecular weight and highly conductive aniline oxidized polymer can be obtained by employing a high electrolytic potential while using water as a solvent. The oxidation potential of aniline can be determined by a so-called cyclic voltammogram in which the potential is scanned at a constant speed and the current value at each potential is plotted.As shown in Figure 4, the oxidation potential with respect to SCE is around 1V, Approx. 2V and 3V.
These oxidation potentials correspond to the oxidizing power of chemical oxidants; at each oxidation potential, polymers at that oxidation potential are preferentially produced, and in the middle of each oxidation potential, polymers at each oxidation potential are competitively produced. to be generated. As explained earlier, Mohilner et al. performed electrolytic oxidation of aniline at an oxidation potential of +0.8 V relative to SCE in order to avoid electrolysis of water.
According to the method of the present invention, an electrolytic potential of +1.2 V or more (when using constant current electrolysis, the initial electrolytic potential is SCE
electrolytic potential of +1.2 V or more), preferably 2
By performing electrolytic oxidation at an electrolytic potential of ~10 V, it is possible to obtain an alinine polymer with a much higher molecular weight and higher conductivity than emeraldine. In the method of the present invention, the current density in electrolytic oxidation is also important. Current density is 0.01m
When it is smaller than A/cm ² , the obtained polymer is dissolved in concentrated sulfuric acid, so it is considered to be a low molecular weight polymer, and the conductivity of such a polymer is also low. In the present invention, the aniline aqueous solution may contain supporting electrolytes other than the above-mentioned protonic acid. Specific examples include perchlorate metal salts such as lithium perchlorate and sodium perchlorate, and organic salts such as tetrabutylammonium perchlorate. In addition to the above, for example, nitrates, sulfates, hydrochlorides, tetrafluoroborates,
Salts such as hexafluorophosphate and the like can also be used as supporting electrolytes. The conductive organic polymer obtained by the method of the present invention usually exhibits a green to dark green color in a dry powder state, and generally, the higher the conductivity, the brighter the green color. However, the molded product made by pressure molding is
Usually exhibits a shiny blue color. Furthermore, the polymer obtained by the method of the present invention has already been doped with the protonic acid used in the electrolytic oxidative polymerization stage, and its electrical conductivity is usually 10 ^-6 S/cm.
In most cases, it is in the range of 10 ^-3 to 10 ^-1 S/cm. The conductive organic polymer obtained by the method of the present invention includes those that are soluble in concentrated sulfuric acid as long as the conductivity is within the above range.
Polymers with high electrical conductivity of 10 ^-3 S/cm or higher are insoluble in water and most organic solvents, and in particular are substantially insoluble in concentrated sulfuric acid and N,N-dimethylformamide. Such a polymer is in marked contrast to emeraldine, which is soluble in 80% acetic acid, cold pyridine, and N,N-dimethylformamide, as described above, indicating that it is a high molecular weight polymer. Furthermore, the polymer insoluble in concentrated sulfuric acid is shown to be a high molecular weight polymer also from the results of differential thermal analysis. Although the structure of the polymer obtained by the method of the present invention has not yet been determined, its infrared absorption spectrum is similar to that of emeraldine, and since it has a high molecular weight and high conductivity, aniline is present in the head-to-tail bond. It appears to be a substantially linear π-electron conjugated polymer as shown in the following formula, which continuously forms a polymer chain. The polymer obtained by the method of the present invention has high electrical conductivity, but the electrical conductivity is significantly reduced by compensation with ammonia, and by doping again with hydrochloric acid, almost the original high electrical conductivity is lost. This recovery confirms that the protonic acid has already been doped during the oxidative polymerization stage.
Furthermore, the infrared absorption spectrum of a polymer obtained by doping the polymer again with hydrochloric acid after compensating it with ammonia is substantially the same as that of the polymer before compensation with ammonia. It is confirmed that the polymer is doped with protic acid. Furthermore, due to the fact that such a polymer is compensated with ammonia and the sign of the thermoelectromotive force, this polymer is p-type. As described above, the conductive organic polymer obtained by oxidative polymerization of aniline according to the present invention is already doped with protonic acid during the polymerization stage, and thus requires a new doping treatment. It has high conductivity without changing its conductivity, and its conductivity does not change at all even when left in the air for a long period of time, compared to conventionally known doped conductive organic polymers. It has a uniquely high stability. The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 (Experiment No. 1) (1) Production of polymer An anode and a cathode made of platinum were inserted into an aqueous solution with an aniline concentration of 10% by weight and an equivalent amount of hydrochloric acid to aniline, and initial electrolysis for SCE was performed. Electrolytic oxidation polymerization was carried out by applying current for 8 hours at a potential of +1.8 V and a constant current density of 5 mA/cm ² . It is well known that when electrolytic polymerization is carried out at a constant current density, the electrolytic potential gradually increases. Therefore, the electrolytic potential is usually expressed as the initial potential as shown above. be. The aniline polymer produced on the anode in the above reaction was peeled off and pulverized, washed with stirring in distilled water, filtered, and then the filtered polymer was washed with acetone. The filtered polymer was vacuum dried over phosphorus pentoxide at room temperature for 10 hours to obtain a conductive organic polymer according to the present invention as a green powder. (2) Evaluation of physical properties The polymer obtained above was insoluble not only in concentrated sulfuric acid but also in N-methyl-2-pyrrolidone. Next, FIG. 1 shows the infrared absorption spectrum of the polymer obtained above. For comparison, the infrared absorption spectra of emeraldine and commercially available diamond black are shown in FIGS. 2 and 3, respectively. In addition, emeraldine was prepared by the method of DMMohilner et al.
al., J.Am.Chem.Soc., 84 , 3618 (1962). It should be noted that the logarithmic viscosities of emeraldine and diamond black in concentrated sulfuric acid solutions with a concentration of 0.5 g/dl at 30° C. are 0.02 and 0.005, respectively, and it is understood that these have low molecular weights. Furthermore, FIG. 4 shows a cyclic voltammogram in electrolytic oxidation of aniline. Furthermore, the results of thermogravimetric analysis in air of the above polymer according to the present invention and emeraldine are shown in FIG. The temperature increase rate is 10°C/min. Next, about 120 mg of the polymer powder obtained above was crushed in an agate mortar, and then pressure-molded into a disk with a diameter of 13 mm at a pressure of 6000 Kg/cm ² using a tablet molding machine for an infrared spectrophotometer. Four pieces of copper foil with a width of about 1 mm were adhered to the four corners of the disk using silver paste or graphite paste, and the conductivity was measured in air according to the Van der Pauw method, and the conductivity was 4.1 S/cm. Also, even when measured in a vacuum of 10 ^-2 Torr,
They showed almost the same conductivity. The disk was left in air for 4 months with virtually no change in conductivity. In addition, the above polymer according to the present invention (conductivity
6.6S/cm) with ammonia compensation (conductivity
3.3×10 ^-9 S/cm) is shown in FIG. 6, and FIG. 7 shows the infrared absorption spectrum after doping again with 5N hydrochloric acid (conductivity 0.15 S/cm). The spectrum after this redoping is found to be substantially the same as the original shown in FIG. 1, and furthermore, the conductivity is also approximately the same as before ammonia compensation. It is therefore shown that the polymer according to the invention is already doped by the protic acid used in its oxidative polymerization step. Example 2 (Experiment numbers 2 to 7) Aniline was electrolytically oxidized in the same manner as in Example 1, except that the acid shown in the table was used in an equivalent amount to aniline instead of hydrochloric acid as the protonic acid. . The electrical conductivity of these polymers is shown in the table. In addition, both polymers were prepared using concentrated sulfuric acid and N-methyl-2
- It was insoluble in both pyrrolidone. Example 3 (Experiment Nos. 8 and 9) Experiments according to the present invention were carried out in the same manner as in Example 1, except that the aniline concentration in the aniline solution was changed and, accordingly, hydrochloric acid was used in an equivalent amount to aniline. A conductive organic polymer was obtained. The electrical conductivity of the polymer is shown in the table. These polymers were also insoluble in concentrated sulfuric acid and N-methyl-2-pyrrolidone. Example 4 (Experiment No. 10) The aniline concentration in the aniline solution was 6% by weight.
A conductive organic polymer was obtained in the same manner as in Example 1, except that an aqueous solution of sulfuric acid at a concentration of 1 mol/molar was used as the protonic acid. The electrical conductivity of the polymer is shown in the table. This polymer also contains concentrated acids and N-methyl-2-
It was insoluble in pyrrolidone. Comparative Example 1 (Experiment Numbers 11 and 12) For comparison, Example 1 except that the aniline concentration in the aniline solution was 0.1% by weight, and an aqueous solution containing hydrochloric acid or sulfuric acid at a concentration of 1 mol/each as the acid was used. Electrolytic oxidation was carried out in the same manner. The electrical conductivity of the obtained polymer is shown in the table. Further, these polymers were dissolved in concentrated sulfuric acid and partially dissolved in N-methyl-2-pyrrolidone. Example 5 (Experiment No. 13 to 15) Regarding the aniline aqueous solution having the composition of Example 1 Experiment No. 1, the initial electrolytic potential was set to the value shown in the table,
Electrolytic oxidation was performed. The resulting polymer was insoluble in concentrated sulfuric acid and N-methyl-2-pyrrolidone. Furthermore, the electrical conductivity of the polymer is shown in the table. Comparative Example 2 (Experiment No. 16) Similarly to Example 3, for the aniline aqueous solution having the composition of Example 1, the initial electrolytic potential was set to + with respect to SCE.
Electrolytic oxidation was performed at 1V. The results are shown in the table.
In addition, the obtained polymer was mixed with concentrated sulfuric acid and N-methyl-
It was soluble in both 2-pyrrolidone. Example 6 (Experiment No. 17) The aniline concentration was 10% by weight, hydrochloric acid was contained in an equivalent amount to aniline, and 0.5% of tetrabutylammonium perchlorate was additionally used as a supporting electrolyte.
aniline aqueous solution containing % by weight at an initial electrolytic potential of +1.7 V with respect to SCE and a constant current density of 11.1 mA/cm ²
Electrolytic oxidation polymerization was carried out by applying electricity for 30 hours. The aniline polymer formed on the anode was peeled off and treated in the same manner as in Example 1 to obtain a conductive polymer. This polymer had an electrical conductivity of 4.4 S/cm and was insoluble in both concentrated sulfuric acid and N-methyl-2-pyrrolidone. Example 7 (Experiment Nos. 18 to 21) An aqueous aniline solution having an aniline concentration of 25% by weight and containing an equivalent amount of hydrochloric acid to aniline was electrolytically oxidized by passing current at the constant current density shown in the table. The electrical conductivity of the obtained polymer is shown in the table. In addition, both polymers were prepared using concentrated sulfuric acid and N-methyl-2
- It was insoluble in both pyrrolidone. [Table] [Table]

[Brief explanation of the drawing]

FIG. 1 is an infrared absorption spectrum of a conductive organic polymer according to the present invention, FIGS. 2 and 3 are infrared absorption spectra of emeraldine and aniline black, respectively, and FIG. 4 is a cyclic voltammogram of electrolytic oxidation of aniline. FIG. 5 is a graph showing the weight residual rate of the polymer according to the present invention and emeraldine upon heating, FIG. 6 is an infrared absorption spectrum of a polymer obtained by ammonia compensation of the polymer according to the present invention, and FIG. This is an infrared absorption spectrum of a polymer obtained by redoping the polymer shown in Figure 6 with hydrochloric acid.

Claims (1)

[Claims] 1. An aniline aqueous solution containing aniline and a protonic acid in an amount equivalent to or more than the aniline, with an initial electrolytic potential of +1.2 V or more with respect to a standard calomel electrode,
It is doped with the above acid characterized by oxidative polymerization by constant current electrolysis with a current density in the range of 0.01 mA/cm ² to 1 A/cm ² , and its conductivity is 10 ^-6 S/cm The above method for producing a conductive organic polymer. 2 Oxidize aniline and an aqueous aniline solution containing protonic acid in an amount equivalent to or more than aniline using constant potential electrolysis at +2 V or more with respect to a standard calomel electrode at a current density in the range of 0.01 mA/cm ² to 1 A/cm ² A method for producing a conductive organic polymer which is doped with the above acid and has an electrical conductivity of 10 ^-6 S/cm or more.