JP3270958B2 - Conductor made of poly (3-alkylthiophene) - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a poly (3-alkylthiophene), and more particularly to a conductor made of poly (3-alkylthiophene).

[0002]

2. Description of the Related Art Poly (3-alkylthiophene) is known as a conductive polymer. Conventionally, poly (3-alkylthiophene) has been produced by electrolytically polymerizing the corresponding monomer, 3-alkylthiophene, or by chemical oxidative polymerization. Poly (3-alkylthiophene) polymerized by these polymerization methods can be formed into a film or the like, but the polymerization yield is lower in the case of electrolytic polymerization than in the case of chemical oxidation polymerization. Thus, polymers polymerized by a chemical oxidative polymerization method and having a side chain alkyl group of hexyl or more are attracting attention as conductive polymers that are soluble in solvents such as toluene and partially crystalline. .

However, conventional polymers produced by this chemical oxidation polymerization method have low crystallinity and, when used in various electronic devices, do not have the desired properties.
It has not been put to practical use. For example, when a diode or a transistor having a conductor as an active component is employed, the rectification characteristic is generally analyzed using a thermionic emission model. It is convenient to determine the stability of the barrier) using an ideal factor. In a silicon diode or the like, the ideal factor is near 1, and the range of 1 to 2 shows stable rectification characteristics. However, conductive polymers are as large as 6 to 10, and there are many cases where a stable barrier is not formed. This results in crystallinity problems. In addition, in the case of application to a transistor, if the crystallinity is low, the mobility of electrons is small and stable characteristics are not exhibited. Further, as for the application of the crystalline conductor, various applications such as a thermal fuse can be considered by utilizing the property that the resistance value changes abruptly near the melting point (positive resistance temperature characteristic: PCT characteristic). Poor properties lack stability, and the PTC characteristics themselves are small, making it difficult to put them to practical use. Therefore, poly (3-alkylthiophene) having excellent crystallinity and high crystallinity has been demanded.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide poly (3-alkylthiophene) which is excellent in crystallinity and is soluble in an organic solvent, and has high crystallinity and excellent electrical properties. It is an object of the present invention to provide a conductor made of poly (3-alkylthiophene) having

[0005]

It is known that poly (3-alkylthiophene) can polymerize the corresponding monomer, 3-alkylthiophene, using an oxidizing agent. In this polymerization, if the polymerization temperature rises, the yield increases, so that the polymerization is conventionally carried out at room temperature or higher. The present inventors have studied to obtain a polymer having good crystallinity by polymerizing 3-alkylthiophene by a chemical oxidative polymerization method. As a result of conducting this polymerization at a low temperature, poly (3 -Alkylthiophene), which can be annealed to give excellent conductivity.
The present inventor has found that it is an electric conductor, and has completed the present invention. That is, the present invention relates to poly (3-alkylthiophene) obtained by polymerizing 3-alkylthiophene at a temperature of 0 ° C. or less , to annealy.
It is a conductor that has been subjected to a rolling process . The poly (3-alkylthiophene) of the present invention is represented by the following general formula.

[0006]

Embedded image

Wherein R is an alkyl group having 1 to 18 carbon atoms. Poly (3-alkylthiophene) of the present invention
Is a poly (3-alkylthiophene) having 1 to 18 carbon atoms in the alkyl group. This poly (3-alkylthiophene) is a polymer obtained by polymerizing a corresponding monomer, 3-alkylthiophene, at a temperature of 0 ° C. or lower. Transition metal halide, protonic acid, etc. are used for the polymerization catalyst,
Specifically, examples thereof include ferric chloride, molybdenum chloride, and sulfuric acid. By performing the polymerization at a temperature of 0 ° C. or lower, the regularity of the molecules during the polymerization is improved, and the obtained polymer is remarkably improved in crystallinity. The improvement in the crystallinity of the produced polymer becomes more remarkable as the polymerization temperature is lower. The polymerization temperature is 0-
Although the temperature is 100 ° C., the polymerization reaction is easier if the polymerization solution is not frozen. When the polymerization solution freezes, the polymerization reaction time becomes extremely long, and the effect of improving the crystallinity is not always high even though the temperature is lowered. Therefore, for example, when chloroform is used as the polymerization solvent, it is preferable to carry out the polymerization reaction in a temperature range in which the solution does not freeze, for example, -20 to -40 ° C.

The poly (3-alkylthiophene) of the present invention which has been chemically oxidized and polymerized at a temperature of 0 ° C. or lower has an improved crystallinity by annealing. When the polymer of the present invention is used as an electric conductor, the polymer is dissolved in a solvent or melted by heat to be formed into a suitable shape such as an electronic device base or a film. The low-temperature polymerized polymer of the present invention has a reduced crystallinity when molded into a molded product such as a film.By annealing the molded product with the reduced crystallinity, the crystallinity of the molded product is reduced. Can be greatly increased. The phenomenon of the improvement in crystallinity by the annealing treatment in the polymer of the present invention is significantly larger than that of the conventional polymer polymerized at a normal temperature. Then, with the improvement of the crystallinity, various characteristics of the molded product as a conductor are remarkably improved.

Thus, the present invention is also a conductor obtained by annealing poly (3-alkylthiophene) chemically oxidized and polymerized at a temperature of 0 ° C. or lower. The annealing treatment in the present invention is performed at a temperature between the melting point of the polymer and a temperature 60 ° C. lower than the melting point, in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen. The annealing time is not particularly limited as long as the effect can be obtained. The poly (3-alkylthiophene) of the present invention has 1 to 18 carbon atoms in the alkyl group. In particular, a polymer having 6 or more carbon atoms in the alkyl group, that is, poly (3-hexylthiophene), poly (3 -Heptylthiophene), poly (3-octylthiophene), poly (3-nonylthiophene), poly (3-decylthiophene), poly (3-undecylthiophene),
Poly (3-dodecylthiophene), poly (3-tridecylthiophene), poly (3-tetradecylthiophene), poly (3-pentadecylthiophene), poly (3
-Hexadecylthiophene), poly (3-heptadecylthiophene), poly (3-octadecylthiophene)
However, the effect of improving the crystallinity and the degree of crystallinity by the annealing treatment is favorable and preferable.

Hereinafter, the present invention will be further described with reference to specific examples. Embodiment 1 FIG. A. Polymerization of poly (3-hexylthiophene) First, chloroform that had been dehydrated and distilled was degassed in vacuum. Ferric chloride (FeCl ₃ ) was dissolved in this chloroform to prepare a 0.4 M ferric chloride solution, and the mixture was sufficiently stirred. This solution was allowed to stand for 15 minutes, 100 ml of the supernatant solution was taken, placed in a closed container, and kept in a thermostat at a predetermined temperature for 1 hour. 182 m of 3-hexylthiophene was added to the temperature-adjusted solution (catalyst solution).
g of the mixture and reacted while stirring in a thermostat for a predetermined time. After the reaction, the black powdery polymerization product was put together with the catalyst solution into 500 ml of methanol as a precipitant and stirred for 30 minutes. Thereafter, the resulting black precipitate was filtered using a glass filter, washed with a large amount of methanol, and stirred and washed twice in ethanol. Next, washing and dedoping of residual iron ions were performed in a solution containing 70% of ethanol and 30% of 30% aqueous ammonia. Thereafter, the resultant was dried under reduced pressure to obtain brownish powdery poly (3-hexylthiophene). The resulting poly (3-hexylthiophene) was soluble in solvents such as chloroform, toluene, and benzonitrile.

B. Influence of polymerization temperature The above polymerization reaction was carried out at each temperature of 40 ° C, 20 ° C, 0 ° C, -20 ° C and -40 ° C. The effect of the polymerization temperature will be described below. (1) The above polymerization reaction reached saturation in 120 minutes, but the lower the polymerization temperature, the lower the yield. That is, in a polymerization reaction for 120 minutes, at a polymerization temperature of 40 ° C., the yield is 90%.
At a polymerization temperature of 20 ° C., a yield of 85% and a polymerization temperature of 0 ° C.
At a polymerization temperature of −20 ° C., the yield is 80%.
% At a polymerization temperature of -40 ° C, and the yield was 65%.

(2) When the molecular weight was determined by GPC, the one polymerized at a polymerization temperature of 40 ° C. had a weight average molecular weight of 65,0
Those polymerized at a polymerization temperature of 0 ° C. had a weight average molecular weight of 100,000, and those polymerized at a polymerization temperature of −20 ° C. had a weight average molecular weight of 120,000. Thus, a polymer having a higher molecular weight was produced as the polymerization temperature was lower. (3) A small amount of ferric chloride as an oxidizing agent remains in the polymer polymerized by the above method, and this acts as an electron accepting molecule (dopant) to impart conductivity. The above poly (3
-Hexylthiophene) The Fe element in the polymer was analyzed by plasma emission spectroscopy. Table 1 shows the results. Although there is not much difference as a whole, as the polymer is polymerized at a lower temperature, iron tends to remain, which indicates that the dopant is more likely to enter stably.

[0013]

[Table 1]

(4) The crystallinity of the polymer varies depending on the polymerization temperature. That is, the crystallinity of poly (3-hexylthiophene) polymerized at each polymerization temperature was determined by X-ray diffraction using a peak at 23.4 degrees. FIG. 1 is a graph showing the polymerization temperature dependence of the crystallinity of poly (3-hexylthiophene). As is evident from FIG. 1, when polymerized at 40 ° C. as a reference,
Crystallization at -20 ° C increased 1.2-fold.

(5) Poly (3) polymerized at various polymerization temperatures
-Hexylthiophene) was subjected to differential scanning calorimetry (DSC analysis). The result is shown in FIG. FIG. 2 is a graph showing the polymerization temperature dependence of the thermal characteristics of poly (3-hexylthiophene). The lower the polymerization temperature, the higher the melting point of the produced polymer. That is, the melting point of the polymer polymerized at a polymerization temperature of 20 ° C. is 18
Although it was 0 ° C, the melting point of the polymer polymerized at the polymerization temperature of -20 ° C was 190 ° C, and the melting point was as high as 10 ° C. Also, the lower the polymerization temperature, the smaller the half width. Further, the endothermic amount of the crystal melting was 8.67 J / g in the former case, and 34.81 J / g in the latter case, which was a four-fold increase.

(6) With respect to poly (3-hexylthiophene) polymerized by changing the polymerization temperature, each polymer is subjected to an annealing treatment according to the method of Example 2 to determine how the melting point changes. Examined. FIG. 3 shows a DSC profile of the poly (3-hexylthiophene) powder before the annealing treatment, and FIG. 4 shows a DSC profile of the poly (3-hexylthiophene) powder after the annealing treatment. is there. As is clear from the comparison between the DSC profiles of FIGS. 3 and 4, the melting point of the polymer polymerized at 20 ° C. does not rise even after annealing, whereas the polymer polymerized at −20 ° C. Melting point from 190 ° C to 220
° C. That is, the melting point of the polymer polymerized at a low temperature was increased by the annealing treatment. Also, D
The peak of the SC profile became sharp. This indicates that the crystallinity has increased.

(7) Further, the poly (3-octylthiophene) polymerized in the same manner as the above-mentioned poly (3-hexylthiophene) was subjected to a thermal analysis. The results are shown in FIGS. FIG. 5 is a DSC profile of poly (3-octylthiophene) before annealing, FIG.
Is a DSC profile after annealing of poly (3-octylthiophene) (140 ° C., 60 minutes). The polymerized poly (3-octylthiophene) is
As shown in FIG. 5, no large peak was observed in the case of polymerization at a polymerization temperature of 20 ° C.
A melting point was observed at 4 ° C. However, looking at the results obtained by annealing them, as shown in FIG.
Those polymerized at 20 ° C. showed little effect even after annealing, whereas those polymerized at −20 ° C. showed a clear peak at 170 ° C. due to the annealing. And the calorie per gram is 1
2.1 J / g. That is, the melting point of a polymer polymerized at a low temperature is increased by annealing treatment, and the peak is sharpened. This indicates that the crystallinity has increased.

(8) The difference in electrical characteristics due to the difference in polymerization temperature will be described. (I) Poly (3-hexylthiophene) was polymerized at polymerization temperatures of 20 ° C, 10 ° C, -20 ° C and -30 ° C. For each of the produced polymers, from -150 ° C to 200
The conductivity at a temperature of ° C. was measured. The result is shown in FIG. That is, FIG. 7 shows the polymerization temperature dependence of the DC conductivity of poly (3-hexylthiophene) before the annealing treatment. The polymer polymerized at any temperature showed a semiconductor-like relationship between the reciprocal of the temperature and the electrical conductivity in a temperature range of room temperature or lower. Also, the lower the polymerization temperature, the higher the conductivity. Those polymerized at a polymerization temperature of −30 ° C. showed an order of magnitude higher conductivity than those polymerized at a polymerization temperature of 20 ° C. It is presumed that the higher the temperature, the better the crystallinity, and the higher the conductivity, the higher the conductivity.

(Ii) As shown in FIG. 7, in the temperature region above room temperature, the conductivity once rises gradually and reaches 100 ° C.
From 150 ° C. to around 150 ° C. (except for those having a polymerization temperature of 20 ° C.), the conductivity sharply increased, and the peak reached a peak near the melting point. FIG. 8 is a graph showing the change in the electrical conductivity-temperature characteristics of the poly (3-hexylthiophene) polymerized at a polymerization temperature of −20 ° C. before the annealing treatment and after the annealing treatment (according to Example 2). The sharp rise in conductivity between 100 ° C. and 150 ° C. in FIG.
As can be seen from the conductivity-temperature characteristics after the annealing treatment shown in Fig. 7, the annealing treatment increased the conductivity by the amount promoted by the crystallization, and was corrected gently. However, this tendency had almost no effect when polymerized at 20 ° C., and was a characteristic observed when polymerized at a temperature of 0 ° C. or less.

(Iii) In a temperature range exceeding the melting point around 190 ° C., the conductivity rapidly decreases, which is considered to be because the conductive circuit is disturbed by melting of the crystal.
Such characteristics are known as PTC characteristics, but can be applied to thermal fuses and the like. This property is also related to the crystallinity, and the change is sharper as the degree of crystallinity increases. Such PTC properties are known for barium titanate and carbon black-polymer composites, but not for a single organic substance as in the present invention.

Embodiment 2 FIG. Conductor of poly (3-hexylthiophene) In Example 1, poly (3-hexylthiophene) obtained by polymerization at a polymerization temperature of −20 ° C. was dissolved in toluene, and a film was formed by a casting method. This film is heated at 140 ° C. for 60 hours in a nitrogen gas atmosphere.
Annealing treatment for heating for minutes was performed. The annealed film had a 1.4-fold increase in crystallinity compared to the film before the annealing treatment.

Example 3.3 According to Example 1, 3-octylthiophene was polymerized at -20 ° C for 120 minutes to obtain poly (3-octylthiophene) at a yield of 65%. The yield when polymerized at a polymerization temperature of 20 ° C. was 80%. Similarly, poly (3-dodecylthiophene) was obtained by polymerizing 3-dodecylthiophene.

[0023]

According to the present invention, poly (3-alkylthiophene) polymerized at a low temperature of 0 ° C. or lower is lower than the conventional poly (3-alkylthiophene) polymerized at a temperature higher than ordinary temperature.
Although the polymer yield is inferior, the produced polymer has a large molecular weight and incorporates a large amount and stably of electron accepting molecules (dopants) necessary for conductivity. Further, the degree of crystallinity is excellent.
It has 1.2 times the crystallinity of the one polymerized at 0 degree. Further, as the polymerization temperature is lowered, a polymer having a higher melting point can be obtained. Further, since this polymer is soluble in an organic solvent, it is easy to handle, for example, it can be cast molded. Further, the poly (3-alkylthiophene) of the present invention polymerized at a low temperature of 0 ° C. or less cannot be obtained by annealing the conventional poly (3-alkylthiophene) polymerized at a temperature of normal temperature or higher by annealing. Demonstrate the characteristics. That is, for example, a conventional polymer polymerized at a normal temperature or higher does not increase its melting point even after annealing, and does not show any change in crystallinity, but the polymer polymerized at a low temperature of the present invention has an annealing treatment. This significantly increases the melting point and increases the crystallinity.

Furthermore, the lower the polymerization temperature of poly (3-alkylthiophene), the higher the conductivity. Also,
The conductivity of the polymer rises sharply near the melting point and peaks, but by annealing this polymer,
This increase in conductivity can be made gentle. This phenomenon does not occur even if annealing is performed on a polymer polymerized at a temperature higher than ordinary temperature. In addition, when the temperature exceeds the vicinity of the melting point of the polymer, the conductivity rapidly decreases with melting of the crystal.
By utilizing this property, this polymer can be used for thermal fuse applications. As described above, the poly (3-alkylthiophene) of the present invention, which has been polymerized at a low temperature of 0 ° C. or lower, has good crystallinity and has a high degree of crystallinity by annealing, so that it is extremely useful as a conductive polymer in various electronic devices. Useful.

[Brief description of the drawings]

FIG. 1 is a graph showing the polymerization temperature dependence of the crystallinity of poly (3-hexylthiophene).

FIG. 2 is a graph showing the polymerization temperature dependence of the thermal properties of poly (3-hexylthiophene).

FIG. 3. DSC profile of poly (3-hexylthiophene) powder before annealing

FIG. 4. DSC profile of poly (3-hexylthiophene) powder after annealing

FIG. 5 DSC profile of poly (3-octylthiophene) powder before annealing treatment

FIG. 6: DSC profile after annealing of poly (3-octylthiophene) powder

FIG. 7 is a graph showing the polymerization temperature dependence of the DC conductivity of poly (3-hexylthiophene) before the annealing treatment.

FIG. 8 is a graph showing the polymerization temperature dependence of the DC conductivity of poly (3-hexylthiophene) after annealing.

Claims (1)

(57) [Claims] An alkyl group having 1 to 18 carbon atoms.
Poly (3-alkylthiophene) obtained by chemically oxidizing and polymerizing alkylthiophene at a temperature of 0 ° C. or lower is subjected to an annealing treatment.
Electrical conductors.