JPH03109430A - Production of uniaxially oriented polyacetylene film - Google Patents

Abstract

PURPOSE:To obtain the subject polyacetylene film, having a high electric conductivity and useful as an organic electrically conductive material and photosensor by treating a polyacetylene film with a smectic liquid crystal substance as a polymerization medium for acetylene. CONSTITUTION:A uniaxially oriented polyacetylene film is produced by treating a polyacetylene film with an electron accepting substance. In the process, a smectic liquid crystal substance is used as a polymerization medium for acetylene. Furthermore, a phenylcyclohexane derivative is preferably used as the aforementioned liquid crystal substance and a nematic liquid crystal phase is preferably provided between an isotropic liquid phase and the smectic liquid crystal phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a conventional organic conductive material, and particularly to a method for producing a polyacetylene film having high electrical conductivity.

[Conventional technology]

In a method of polymerizing acetylene using a Ziegler-Natsuta catalyst consisting of a transition metal compound and an organometallic compound,
When a polymerization reaction is carried out at the interface between acetylene and a polymerization catalyst solution near the free surface, polyacetylene can be directly obtained as a film sample (Japanese Patent Publication No. 32581/1983).
(No.), this film has a structure in which fibrils (fibrous microcrystals) with a diameter of several tens of nanometers are assembled in a disordered manner.

This polyacetylene film is known as an organic semiconductor, and it is also known that it can be made into a material with high electrical conductivity by treating it with an electron-donating dopant or an electron-accepting dopant (Japanese Patent Laid-Open No. 55-129426).
, specifically when the dopant is arsenic pentafluoride, up to 5
60S (!1''''5 high conductivity materials have been reported to be obtained)
hys, Rev, Latt, ) 39.

1098 (1977), 160Sex for iodine
The Journal on American Chemical Society (J, Am, Chem, 5oc.
).

Kushiryo 0 1013 (1978).

[Problem to be solved by the invention]

Generally, in polymeric materials, it is known that when the -dimensionality is reflected in the visual configuration of the material, that is, when the material has -axis orientation, the material properties are improved. The above polyacetylene film does not melt even when heated, and no solvent has been found that dissolves this polymer. Therefore, the method for obtaining a -axis oriented polyacetylene film is to stretch it by mechanical operation under heating. method is known. (Japanese Unexamined Patent Publication No. 55-14213), the electrical conductivity of the polyacetylene film obtained by this method is significantly improved due to the orientation, and the electrical conductivity in the orientation direction is about 3000 Sam-'.

As can be seen from these facts, differences in the structure of polymers have a large effect on their properties.

On the other hand, the present inventors have previously developed a new synthetic method using a liquid crystal substance as a polymerization solvent for acetylene.

A polyacetylene film is obtained in which the fibrils are partially oriented (Japanese Patent Laid-Open No. 60-23402). It was found that the polyacetylene film obtained by this method had a structure in which not only the fibril chains were partially oriented but also long and thick. When this film-like sample was subjected to the above-mentioned doping operation, it showed a significantly higher electrical conductivity than a polyacetylene film obtained using a normal organic solvent. It was found that the conductivity values are comparable.

In addition, the present inventors have discovered that oriented polyacetylene can also be obtained by a method of polymerizing acetylene under the alignment of nematic liquid crystal in which a Ziegler-Natsuta catalyst is dissolved.
They also discovered that a sample with a large area could be obtained (Japanese Patent Application Laid-open No. 6O-255806). Furthermore, when this alignment film sample was treated with an electron-accepting dopant, its electrical conductivity was significantly improved.

It was found that the value was larger than that of a mechanically oriented polyacetylene film (Japanese Patent Application Laid-Open No. 61-118454).

However, in the polymerization under the orientation of the nematic liquid crystal, the degree of orientation of the resulting polyacetylene film reflects the degree of orientation (about 0.6) of the nematic liquid crystal, and is not perfectly oriented. Here, the degree of orientation in a non-oriented state is defined as O1, and the degree of orientation in a completely uniaxially oriented state is defined as 1.0. Therefore, if a polyacetylene film with a higher degree of orientation is obtained, it is expected that the electrical conductivity of the oriented film will further increase.

An object of the present invention is to synthesize a highly oriented polyacetylene film using a smectic liquid crystal material as an acetylene polymerization medium, and to provide a polyacetylene film having high electrical conductivity.

[Means to solve the problem]

In order to achieve the above object, we investigated smectic liquid crystals that have a higher degree of orientation than nematic liquid crystals. This smectic liquid crystal has a higher viscosity than a nematic liquid crystal, and it was thought that acetylene would not diffuse and monopolymerization would not occur. However, when a chemically stable smectic liquid crystal was prepared as a polymerization catalyst and polymerized, the inventors discovered that a polyacetylene film could be obtained by increasing the polymerization time, leading to the present invention.

The present invention is characterized in that a uniaxially oriented film is obtained by using a smectic liquid crystal substance as a polymerization medium in a method for synthesizing a polyacetylene film, and the oriented film thus obtained is treated with an electron-accepting substance to form a highly conductive polyacetylene film. The goal is to provide a membrane.

The procedure for synthesizing a polyacetylene film is to dissolve a Ziegler-Natsuta catalyst in a smectic liquid crystal material, align the catalyst-containing liquid crystal, and then polymerize acetylene on the surface of the liquid crystal.

Ziegler-Natsuta catalysts consist of transition metal compounds and organometallic compounds, and many catalysts can be obtained by combining them.

However, in order to obtain a high-quality polyacetylene film, the catalyst must be uniformly dissolved in the smectic liquid crystal, and the usable catalysts are limited. Ti(OBu)a and AflEt are highly soluble Ziegler-Natsuta catalysts.
a, VO(acac)z and A 2 E t Jl, T
Combinations such as i (acac)z and A Q E t 3 are known. In order to obtain a polyacetylene film of higher quality as a conductive material, it is desirable that the catalyst has high activity for acetylene polymerization. Considering this point,
It has been found that a catalyst consisting of Ti(OBu)4 and AQEta can provide the most suitable polyacetylene membrane for the present invention.

The composition ratio of Ti(OBu)a and AQEta is not particularly limited as long as the former is 1 and the latter is 3 or more,
It is preferable that the temperature is not too large for the following reasons. Namely, when impurities such as Ziegler-Natsuta catalyst are added to nematic liquid crystal, the nematic liquid crystal-isotropic liquid transition temperature decreases, and when there are many impurities, the nematic liquid crystal phase disappears. For this reason, it is desirable to fix the composition ratio to 3 and not add a high concentration of catalyst.

The liquid crystal material used in the present invention must be chemically stable against the Ziegler-Natsuta catalyst.

From this point of view, various liquid crystal substances were investigated, and a phenylcyclohexane derivative having the following molecular structural formula was found to be the most suitable liquid crystal.

Synthetic metal (Synth, Metalg)
, 1 Sat.

(1986) 199° These substances are hereinafter abbreviated by carbon number. That is, P
It is represented as CH-, mon. In the above formula, when m and n are ■, it is represented as PCH-IOI.

Not all cyclohexane derivatives with carbon numbers exhibit smectic liquid crystals.Those exhibiting smectic liquid crystals include PCH-405, PCH-406, and PCH-50.
5, PCH-506, etc. are known, but are not particularly limited to these.

In the present invention, it is necessary to align the smectic liquid crystal, but the smectic liquid crystal has a high viscosity and cannot be aligned by ordinary alignment treatment unlike the nematic liquid crystal. Therefore, a smectic liquid crystal material having a nematic liquid crystal phase on the high-temperature side of the smectic liquid crystal phase is used, an alignment treatment is performed while the material is in the nematic liquid crystal phase, and then the temperature is lowered to achieve the smectic liquid crystal alignment state. As described above, PCH-406, PCH-505,
PCH-506 and the like are known, but the substance is not particularly limited to these substances.

Although the smectic liquid crystal substance may be used as a single component, it is preferable to use it as a multi-component system of two or more components. This broadens the temperature range of the smectic liquid crystal phase and facilitates experiments. Table 1 shows some combinations of smectic liquid crystal materials and the temperature range of the liquid crystal phase.

Table 1. Smectic liquid crystal mixture for polyacetylene synthesis In the present invention, the electron-accepting substances doped into the polyacetylene film include halogens (e.g. chlorine, bromine, iodine, etc.), Lewis acids (e.g. phosphorus pentafluoride, arsenic pentafluoride, pentafluoride). antimony, boron trifluoride, boron trichloride, ferric chloride, etc.), protic acids (e.g., hydrofluoric acid,
(hydrochloric acid, hydrogen bromide, perchloric acid, sulfuric acid, nitric acid, etc.).

The method for treating a polyacetylene film with an electron-accepting dopant is as follows: (1) When the dopant is a gas, the polyacetylene film is exposed to the gas.

(2) When the dopant is liquid or solid, there are methods such as exposing the polyacetylene film to its vapor or immersing it in a solution in which the dopant is dissolved. Although any of the above doping methods may be used, sufficient doping is required to achieve high electrical conductivity. Sufficiently performing doping treatment means performing doping until the electrical conductivity is saturated. This can be determined by weighing the amount of dopant incorporated into the polyacetylene film during the doping process.
Normally, the dopant per carbon of polyacetylene is 0.1
If the temperature exceeds that level, the electrical conduction tends to be almost saturated. It can also be determined by tracking changes in electrical conductivity over time due to doping. When doping a dopant in a gas phase, if the vapor pressure of the dopant is low, the electrical conductivity may not be saturated even if the doping treatment is performed for a long time, so it is necessary to appropriately control the vapor pressure of the dopant.

[Operation] In order to obtain an oriented polyacetylene film, the nematic liquid crystal serving as the polymerization medium itself must be macroscopically oriented. The methods for aligning liquid crystals can be roughly divided into (1) using a surface-treated substrate; (2) It can be divided into two types of methods using external field application. Method (1) involves polymer coating and rubbing.

Includes oblique deposition and grating surface treatment.

The method (2) includes applying an external field such as an electric field, a magnetic field, and a flow. To obtain an oriented polyacetylene film (1), (2)
) Any method may be used, but except for the method of applying a magnetic field or flowing down, it is necessary to sandwich the nematic liquid crystal material between two substrates. These methods do not cause sufficient diffusion of acetylene gas, making it impossible to obtain a polyacetylene film with excellent film-forming properties useful as a conductive material. Therefore, the liquid crystal orientation method using magnetic field application and flowing drop can provide an oriented polyacetylene film suitable for the present invention.

[Example] The present invention will be specifically explained below using an example, but the present invention is not limited to these examples.

[Example 1] PCH-306 and PCH-506 of lot Nα3 shown in Table 1 in a 300 m Q glass container under nitrogen atmosphere
10 mQ of the smectic liquid crystal mixture was added. This mixture was heated to 45°C, brought to an isotropic liquid state, and 102μQ of tetrabutoxytitanium and 11μQ of triethylaluminum were added.
The polymerization catalyst was aged by adding 62 μQ and stirring for 30 minutes.

This reaction vessel is attached to the polymerization/vacuum line, the nitrogen in the reaction vessel is evacuated, and one reaction vessel is held in a 10,000 Gauss electromagnet, and the temperature of the reaction vessel is set to 30°C to bring the polymerization medium into a nematic state. 0 Gradually lower the temperature of the reaction vessel 10
It was kept at ℃. After confirming that the liquid crystal substance was in a smectic liquid crystal state, the reaction vessel was removed from the electromagnet, and then acetylene gas was introduced. After 1 hour, unreacted acetylene gas was removed and the reaction vessel was removed from the polymerization vacuum line. When about 100 mQ of toluene is added to the reaction vessel under a nitrogen atmosphere, the polyacetylene film peels off from the liquid crystal surface. This polyacetylene membrane was washed several times with toluene to remove the liquid crystal material and polymerization catalyst. After drying the polyacetylene film in vacuum, a film-like sample with a film thickness of 8 μm was obtained. This membrane sample was examined under an electron microscope [? ! ! ! As a result, a shape in which fibrils were aligned in one direction was observed.

This -axis-oriented polyacetylene film was placed in a vacuum container without air leakage, exposed to iodine vapor at Q, Q3 Torr, and electrical conductivity in the orientation direction was measured by a DC four-terminal method. One hour after the start of measurement, the electrical conductivity was saturated and its value was 18,
0OO8/C! It was l.

[Comparative Example 1] In the synthesis of the polyacetylene film shown in Example 1, a film thickness of 9 μm was obtained using the same method except for placing it in an electromagnet.
A polyacetylene film of m was obtained.

When this film-like sample was observed under an electron microscope, no fibril orientation was observed.

This polyacetylene film was placed in a vacuum container without air leakage, exposed to iodine vapor at 0.03 Torr, and the electrical conductivity of this film sample was measured by a DC four-terminal method. One hour after the start of measurement, the electrical conductivity was saturated and its value was 3.20.
It was 05/am.

[Comparative Example 2] In Example 1, PCH was used as the smectic liquid crystal material.
PCH-4 instead of a mixture of -306 and PCB-506
The same method was used except that a single component of 05 was used, and a film thickness of 8
A μm polyacetylene film was obtained. This PCH-405 is a smectic liquid crystal material that does not have a nematic liquid crystal phase on the high temperature side of the smectic liquid crystal phase.

When this film-like sample was observed under an electron microscope, no fibril orientation was observed.

This polyacetylene film was placed in a vacuum container with no air leakage, exposed to iodine vapor at Q, Q3 Torr, and the electrical conductivity of this film sample was measured by a DC four-terminal method. One hour after the start of measurement, the electrical conductivity was saturated and its value was 2.50.
It was 0S/(!l.

〔Effect of the invention〕

According to the present invention, there is an effect that a material having higher electrical conductivity than a conventional polyacetylene film synthesized in an organic solvent can be obtained.

The polyacetylene film obtained in this way can not only be used directly as a conductive material useful as an electric/electronic device, but also a p/n junction device can be made, so it is also useful as a material for optical sensors, solar cells, etc.

Claims (1)

[Claims] 1. A uniaxially oriented polyacetylene film characterized in that a smectic liquid crystal substance is used as an acetylene polymerization medium in the production of a uniaxially oriented polyacetylene film obtained by treating a polyacetylene film with an electron-accepting substance. Production method. 2. The method for producing a uniaxially oriented polyacetylene film according to claim 1, characterized in that a phenylcyclohexane derivative is used as the smectic liquid crystal substance, and a nematic liquid crystal phase is present between the isotropic liquid phase and the smectic liquid crystal phase. 3. The method for producing a uniaxially oriented polyacetylene film according to claim 2, characterized in that the alignment treatment is performed in a state where the smectic liquid crystal substance exhibits a nematic liquid crystal phase to orient the smectic liquid crystal phase.