JPH07304858A - Poly(3-alkylthiophene) and electric conductor consisting of the same polymer - Google Patents

Abstract

PURPOSE:To obtain a poly(3-alkylthiophene) excellent in crystallinity, soluble in organic solvents, having high degree of crystallization, excellent in electric characteristics and useful as an electrically conductive substance. CONSTITUTION:The poly(3-alkylthiophene) of the formula [R is a 1-18C alkyl] is obtained by subjecting a 3-alkylthiophene whose alkyl is a 1-18C alkyl, preferably a >=6C alkyl to chemical oxidation polymerization at <=0 deg.C, preferably -20 deg.C to -40 deg.C. This electric conductor can be obtained by subjecting the polymer to annealing treatment. Furthermore, a polymerization catalyst (e.g. ferric chloride, sulfuric acid or chloroform) is preferably used in the polymerization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to poly (3-alkylthiophene), and further 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) is produced by electropolymerizing or chemically oxidatively polymerizing a corresponding monomer, 3-alkylthiophene. Although poly (3-alkylthiophene) polymerized by these polymerization methods can be formed into a film or the like, the polymerization yield is lower in the electrolytic polymerization method than in the chemical oxidative polymerization method. Thus, a polymer having a side chain alkyl group of hexyl or more polymerized by a chemical oxidative polymerization method is attracting attention as a conductive polymer which is soluble in a solvent such as toluene and partially crystalline. .

However, the conventional polymers prepared by this chemical oxidative polymerization method have a small crystallinity, and when used in various electronic devices, their respective desired characteristics are not sufficient,
It has not been put to practical use. For example, when a diode or a transistor using a conductor as an active component is used, the rectifying characteristics are generally analyzed using a thermoelectron emission model. In that case, the characteristics are good or bad ( It is convenient to judge the stability of the barrier) using an ideal factor. In a silicon diode or the like, the ideal factor is close to 1, and stable rectifying characteristics are in the range of 1 to 2. However, the conductive polymer is as large as 6 to 10, and in many cases a stable barrier is not formed. This results in crystallinity problems. When applied to a transistor, if the crystallinity is low, the electron mobility is low and stable characteristics are not exhibited. Further, regarding the application of the crystalline conductor, various properties such as a thermal fuse can be considered by utilizing the property that the resistance value suddenly changes near the melting point (positive resistance temperature characteristic: PCT characteristic). If the properties are poor, the stability is lacking and the PTC characteristics themselves are small, which makes it difficult to put them into practical use. Therefore, poly (3-alkylthiophene) having excellent crystallinity and high crystallinity is desired.

[0004]

DISCLOSURE OF THE INVENTION The present invention aims to provide poly (3-alkylthiophene) which is excellent in crystallinity and soluble in an organic solvent, and has high crystallinity and excellent electric characteristics. It aims at providing the electric conductor which consists of poly (3-alkyl thiophene) which has.

[0005]

It is known that poly (3-alkylthiophenes) can be polymerized with a corresponding monomer, 3-alkylthiophene, using an oxidizing agent. In this polymerization, since the yield increases as the polymerization temperature rises, the polymerization is conventionally carried out at a temperature of room temperature or higher. The present inventor has conducted a study to obtain a polymer having good crystallinity by polymerizing 3-alkylthiophene by a chemical oxidative polymerization method, and as a result of carrying out this polymerization at a low temperature, poly (3 -Alkylthiophene) was obtained, and the present invention was completed. That is, the present invention is poly (3-alkylthiophene) obtained by polymerizing 3-alkylthiophene at a temperature of 0 ° C or lower.
The poly (3-alkylthiophene) of the present invention is represented by the following general formula.

[0006]

[Chemical 1]

(In the formula, R represents an alkyl group having 1 to 18 carbon atoms.) Poly (3-alkylthiophene) of the present invention
Is a poly (3-alkylthiophene) having an alkyl group having 1 to 18 carbon atoms. 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 halides, protonic acids, etc. are used for the polymerization catalyst,
Specifically, for example, ferric chloride, molybdenum chloride, sulfuric acid and the like. By polymerizing at a temperature of 0 ° C. or less, the regularity of the molecules during the polymerization is improved, and the crystallinity of the obtained polymer is remarkably improved. The improvement in crystallinity of the produced polymer becomes more remarkable as the polymerization temperature is lower. 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 although the temperature is lowered, the effect of improving the crystallinity is not necessarily high. Therefore, for example, when chloroform is used as the polymerization solvent, it is preferable to carry out the polymerization reaction in a temperature range where the solution does not freeze, for example, -20 to -40 ° C.

The crystallinity of the poly (3-alkylthiophene) of the present invention, which is chemically oxidatively polymerized at a temperature of 0 ° C. or lower, is improved by the annealing treatment. When the polymer of the present invention is used as a conductor, it is dissolved in a solvent or melted by heat to be molded into a suitable form such as an electronic device substrate or film. The low-temperature polymerized polymer of the present invention has a reduced crystallinity when formed into a molded article such as a film, but by subjecting the molded article with the reduced crystallinity to an annealing treatment, the crystallinity of the molded article is reduced. It can be greatly increased. The phenomenon of improving the crystallinity by the annealing treatment in the polymer of the present invention is remarkably large as compared with the conventional polymer polymerized at a normal temperature. As the crystallinity is improved, various properties of the molded product as a conductor are significantly improved.

Thus, the present invention is also a conductor obtained by annealing the poly (3-alkylthiophene) chemically oxidized and polymerized at the temperature of 0 ° C. or lower. The annealing treatment in the present invention is performed in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen at a temperature between the melting point temperature of the polymer and a temperature 60 ° C. lower than the melting point. The annealing treatment time is not particularly limited as long as the effect can be obtained. The poly (3-alkylthiophene) of the present invention has an alkyl group having 1 to 18 carbon atoms, and in particular, a polymer having an alkyl group having 6 or more carbon atoms, that is, poly (3-hexylthiophene) or 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 crystallinity by the annealing treatment is good and preferable.

The present invention will be further described with reference to specific examples. Example 1. A. Polymerization of poly (3-hexylthiophene) First, dehydrated and distilled chloroform was deaerated in a vacuum. Ferric chloride (FeCl ₃ ) was dissolved in this chloroform to prepare a ferric chloride solution having a concentration of 0.4M, 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 constant temperature bath for 1 hour so as to reach a predetermined temperature. 182 m of 3-hexylthiophene was added to the temperature-controlled solution (catalyst solution).
g, and the mixture was allowed to react with stirring for a predetermined time in a constant temperature bath. After the reaction, a black powdery polymerization product was put into 500 ml of a precipitant, methanol, together with the catalyst solution, and stirred for 30 minutes. Then, the resulting black precipitate was filtered using a glass filter, washed with a large amount of methanol, and washed with stirring in ethanol twice. Next, cleaning and dedoping of residual iron ions were performed in a solution consisting of 70% ethanol and 30% ammonia water 30%. Then, it was dried under reduced pressure to obtain a dark brown powdery poly (3-hexylthiophene). The produced poly (3-hexylthiophene) was soluble in solvents such as chloroform, toluene and benzonitrile.

B. Effect of polymerization temperature The above polymerization reaction was carried out at temperatures of 40 ° C, 20 ° C, 0 ° C, -20 ° C and -40 ° C. The influence of the polymerization temperature will be described below. (1) The above polymerization reaction reached saturation in 120 minutes, but the yield decreased as the polymerization temperature became lower. That is, in a polymerization reaction of 120 minutes, a yield of 90% at a polymerization temperature of 40 ° C.
At a polymerization temperature of 20 ° C, the yield is 85%, and the polymerization temperature is 0 ° C.
The yield is 80%, and the yield is 70 at a polymerization temperature of -20 ° C.
%, And the yield was 65% at a polymerization temperature of −40 ° C.

(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.
The weight average molecular weight was 100,000 when polymerized at 00 and a polymerization temperature of 0 ° C, and the weight average molecular weight was 120,000 when polymerized at a polymerization temperature of -20 ° C. Thus, the lower the polymerization temperature, the higher the molecular weight of the polymer produced. (3) A small amount of ferric chloride, which is an oxidizing agent, remains in the polymer obtained by the above method, and this acts as an electron-accepting molecule (dopant) to impart conductivity. Poly (3 above
Fe element in the (hexylthiophene) polymer was analyzed by plasma emission spectroscopy. The results are shown in Table 1. Although there is no big difference as a whole, iron having a higher tendency to remain in the case of being polymerized at a lower temperature 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 clear from FIG. 1, when the polymerized at 40 ° C. is used as a reference,
Polymerization at -20 ° C increased the crystallinity 1.2 times.

(5) Poly (3) polymerized at various polymerization temperatures
-Hexylthiophene) was subjected to differential scanning calorimetry (DSC analysis). The results are shown in Fig. 2. 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 polymer produced. That is, the melting point of a polymer polymerized at a polymerization temperature of 20 ° C. is 18
Although it was 0 ° C, the melting point of the polymer polymerized at a polymerization temperature of -20 ° C was 190 ° C, and the melting point was as high as 10 ° C. The lower the polymerization temperature, the smaller the full width at half maximum. Furthermore, the endothermic amount of crystal melting was 8.67 J / g for the former, and 34.81 J / g for the latter, which was a 4-fold increase.

(6) Further, regarding poly (3-hexylthiophene) polymerized by changing the polymerization temperature, each polymer is annealed by the method of Example 2, and how the melting point is changed by this annealing treatment. Examined. FIG. 3 is a DSC profile of the poly (3-hexylthiophene) powder before the annealing treatment, and FIG. 4 is a DSC profile of the poly (3-hexylthiophene) powder after the annealing treatment. is there. As can be seen by comparing the DSC profiles of FIG. 3 and FIG. 4, the melting point of the polymer polymerized at 20 ° C. does not rise even after annealing, while the polymer polymerized at −20 ° C. A melting point of 190 ° C to 220
Rose to ℃. 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 steep. This indicates that the crystallinity has increased.

(7) Further, thermal analysis was conducted on poly (3-octylthiophene) polymerized in the same manner as the above poly (3-hexylthiophene). The results are shown in FIGS. 5 is a DSC profile of poly (3-octylthiophene) before annealing, FIG.
[Fig. 4] is a DSC profile after an annealing treatment of poly (3-octylthiophene) (140 ° C, 60 minutes). Polymerized poly (3-octylthiophene) is
As shown in FIG. 5, a large peak was not seen in the one polymerized at a polymerization temperature of 20 ° C.
A melting point was observed at 4 ° C. However, looking at those obtained by annealing these, as shown in FIG.
The one polymerized at 20 ° C. showed almost no effect even after the annealing treatment, whereas the one polymerized at −20 ° C. showed a clear peak at 170 ° C. by the annealing treatment. And the amount of heat per gram is 1
It was 2.1 J / g. That is, a polymer polymerized at a low temperature has an increased melting point and a sharp peak due to the annealing treatment. 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. 7. That is, FIG. 7 shows the polymerization temperature dependence of the direct current conductivity of poly (3-hexylthiophene) before the annealing treatment. The polymers polymerized at any temperature were semiconductor-like, showing a linear relationship between the reciprocal of temperature and the electric conductivity in the temperature range of room temperature or lower. Further, the lower the polymerization temperature, the higher the conductivity. The one polymerized at a polymerization temperature of -30 ° C showed a conductivity that was an order of magnitude higher than that of the one polymerized at a polymerization temperature of 20 ° C. It is presumed that this is because the one polymerized at a low temperature has a better crystallinity, which increases the conductivity.

(Ii) As shown in FIG. 7, in the temperature range of room temperature or higher, the increase in conductivity is once slowed down to 100 ° C.
At around 150 ° C. (excluding those at a polymerization temperature of 20 ° C.), the electric conductivity sharply increased, and the peak peaked near the melting point. FIG. 8 is a graph showing changes in conductivity-temperature characteristics of 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 increase in conductivity from 100 ° C. to 150 ° C. in FIG.
As can be seen from the electric conductivity-temperature characteristics after the annealing treatment shown in (4), the annealing treatment increased the electric conductivity by the amount that the crystallization was promoted, and was corrected gently. However, this tendency has almost no effect on those polymerized at 20 ° C., and is a characteristic observed for those polymerized at a temperature of 0 ° C. or lower.

(Iii) In the temperature region above the melting point near 190 ° C., the conductivity rapidly decreases, which is considered to be because the conductive circuit is disturbed as the crystal melts.
Such a characteristic is known as a PTC characteristic, but it can be applied to a thermal fuse or the like. This characteristic is also related to crystallinity, and the greater the degree of crystallinity, the sharper the change. Such PTC characteristics are known for barium titanate and carbon black-polymer composite materials, but not for a single organic substance such as the present invention.

Example 2. Poly (3-hexylthiophene) Conductor In Example 1, poly (3-hexylthiophene) obtained by polymerization at a polymerization temperature of −20 ° C. was dissolved in toluene to form a film by a casting method. This film was placed in a nitrogen gas atmosphere at 140 ° C. for 60 minutes.
An annealing treatment of heating for a minute was performed. The annealed film had a 1.4-fold increase in crystallinity as compared to the film before annealing.

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

[0023]

INDUSTRIAL APPLICABILITY The poly (3-alkylthiophene) polymerized at a low temperature of 0 ° C. or lower according to the present invention has a higher poly (3-alkylthiophene) content than the conventional poly (3-alkylthiophene).
Although the polymer yield is poor, the molecular weight of the produced polymer is large, and a large amount of electron-accepting molecules (dopants) necessary for conductivity are stably incorporated. In addition, the crystallinity is also excellent, for example, the one polymerized at −20 ° C.
It has a crystallinity 1.2 times higher than that of a polymerized product at 0 degree. Furthermore, the lower the polymerization temperature, the higher the melting point of the polymer obtained. Further, since this polymer is soluble in an organic solvent, it can be cast-molded and is easy to handle. Further, the poly (3-alkylthiophene) polymerized at a low temperature of 0 ° C. or less according to the present invention cannot be obtained when the poly (3-alkylthiophene) polymerized at a temperature higher than ordinary room temperature is annealed by an annealing treatment. Demonstrate the characteristics. That is, for example, a polymer polymerized at a temperature of room temperature or higher in the related art does not increase the melting point even if an annealing treatment is performed, and the crystallinity is not changed, but the polymer polymerized at a low temperature of the present invention is annealed. This significantly raises 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 reaches its maximum, but by annealing this polymer,
This increase in conductivity can be smoothed. This phenomenon does not occur even if the polymer polymerized at room temperature or higher is annealed. On the other hand, when the temperature exceeds the melting point of the polymer, the conductivity rapidly decreases as the crystal melts.
Utilizing this property, this polymer can be used for thermal fuse applications. As described above, the poly (3-alkylthiophene) polymerized at a low temperature of 0 ° C. or lower according to the present invention has good crystallinity, and the degree of crystallinity is increased by the annealing treatment. It is useful.

[Brief description of drawings]

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

FIG. 2 is a graph showing polymerization temperature dependence of 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 treatment.

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

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

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

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

Claims (2)

[Claims] 1. An alkyl group having 1 to 18 carbon atoms.
Poly (3-alkylthiophene) obtained by chemically oxidatively polymerizing alkylthiophene at a temperature of 0 ° C. or lower. 2. A conductor obtained by annealing the poly (3-alkylthiophene) according to claim 1.