JPH0315943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to carbon-based materials and compositions thereof having high electrical conductivity, and more particularly to highly conductive carbon-based materials and compositions characterized by firing a conjugated polymer.

In recent years, it has been discovered that complex compounds with natural or artificial high-purity graphite electron acceptors or electron donors (hereinafter referred to as dopants) exhibit high conductivity comparable to that of metals, and have attracted attention as highly conductive materials. It's starting to feel like this. As this type of highly conductive carbon material, pyrolytic graphite is known, which is obtained by subjecting a hydrocarbon compound to gas phase pyrolysis at high temperature to produce pyrolytic carbon, which is then heat-treated at an ultra-high temperature.
This carbon material has a highly developed graphite structure, and exhibits even higher conductivity due to the formation of a complex compound with a dopant.

On the other hand, attempts have also been made to obtain carbon-based materials that are carbonized and further graphitized by firing polymers. For example, there is a method of firing organic fibers such as polyacrylonitrile and rayon to make carbon fibers. However, the electrical conductivity of the obtained carbon fibers is low, and even after firing at 3000°C, the electrical conductivity is 10 ³ s/
cm or less, and the effect of improving conductivity due to the formation of a dopant complex compound is only slight, making it impossible to obtain a sufficiently graphitized material.
In this way, carbon materials obtained by firing polymers do not necessarily have a graphite structure when fired at high temperatures. In addition, a special phenolic resin is one of the few examples of polymeric materials that are easily converted into graphite by firing. (Carbon, 1975 (No. 82) p. 102) However, these do not retain their original form because they melt and soften during the firing carbonization process.

Generally, in order to obtain a carbon material having an industrially useful form such as a film or fiber, an insolubilization treatment such as an oxidative crosslinking reaction using air during firing is essential. However, this treatment is not suitable for obtaining a highly conductive material, and it has been extremely difficult to obtain a highly conductive carbon material that can be fired while retaining its shape.

The present inventors extensively studied the firing of conjugated polymers, and as a result, discovered a new fact and arrived at the present invention. In other words, even when p-phenylene vinylene polymer films and fibers are fired in an inert atmosphere at temperatures exceeding 400°C, they not only retain their shape and become carbonized without melting, but also turn into graphite at high temperatures. It has been found that this material can be highly conductive, and that it can be made even more conductive by doping.

That is, the present invention is based on the general formula (-R-CH=CH) _-o (R is p-phenylene group, 2,5-dimethyl-p
-phenylene group or 2,5-dimethoxy-p-
It represents a phenylene group, and n represents an integer of 2 or more. ) in an inert atmosphere at 800
A highly conductive carbon-based fired product obtained by firing at a temperature of ~3500°C, and (2) a highly conductive composition comprising the highly conductive carbon-based fired product and a dopant in an amount of 0.1 to 150% based on the weight of the fired product. Our goal is to provide the following.

There is no particular restriction on the method of synthesizing the conjugated polymer () used in the present invention, and various methods can be used, but preferably J.Amer.Chem.Soc., 82 , 4669
(1960) described the wittig reaction method, Makromol.
Chem. 131 , 105 (1970) and the snium salt decomposition method described in J. Polymer Sci., A-1, 6 , 1058 (1968) are exemplified. The polymer can be formed into a homogeneous film-like or thread-like molded product and can be suitably used.

The R group of the conjugated polymer (1) used in the present invention is a p-phenylene group with good symmetry, 2,5-dimethyl-p-
A phenylene group or a 2,5-dimethoxy p-phenylene group is preferable because it retains its shape well during the firing process.

It is preferable that the conjugated polymer used in the present invention has a sufficiently large molecular weight, and n is 2 or more, preferably 5 or more.
For example, a substance having a molecular weight of 50,000 and which cannot be dialyzed by dialysis treatment with a dialysis membrane with a molecular weight fraction of 3,500 is effectively used.

The form of the conjugated polymer to be subjected to the firing of the present invention may be powder, sheet, film, thread, or other molded products, but it may be a film or thread-like product made by the sulfonium salt decomposition method and stretched and oriented. The product has higher conductivity and is particularly preferable.

In the present invention, the firing temperature is preferably higher than 400°C, and the upper temperature limit is limited by the evaporation temperature of carbon. By firing in a pressurized system, the temperature can be further increased. Not economical. In order to obtain a highly conductive material, the higher the firing temperature, the better. Practically speaking, the temperature is preferably higher than 400°C and lower than 3500°C, and more preferably higher than 800°C and lower than 3300°C.

Furthermore, when firing at a high temperature of 1000°C or higher, temporary firing may be performed at 1000°C or lower, followed by firing at 1000°C or higher.

In the present invention, effective inert atmospheres are nitrogen gas, argon gas, vacuum, etc., and argon gas is more preferable at 2000° C. or higher.

There are no particular restrictions on the heating method during firing, but the heating method differs depending on the firing temperature. That is,
At temperatures below 1500℃, use resistance wire furnaces, siliconite furnaces, etc.
At temperatures above 1500℃, graphite heating element Tammann furnaces and high-frequency induction heating furnaces are effectively used.

The fired product of the conjugated polymer () obtained in this manner often exhibits an electrical conductivity of 10 ² to ^{10 4} s/cm.

More importantly, the conductivity of the fired product is further improved by doping with an electron acceptor or an electron donor, reaching 10 ³ to ^{10 5} s/cm or more. The dopant is not particularly limited, but compounds that have been found to have high conductivity in conjugated polymers such as graphite, polyacetylene, and polypyrrole can be effectively used.

The doping method can be carried out by a known method, ie, a method of direct contact with a dopant in a gas phase or liquid phase, an electrochemical method, an ion implantation method, or the like.

Specifically, electron acceptors include halogen compounds: bromine, etc., Lewis acids: iron trichloride, arsenic pentafluoride, antimony pentafluoride, boron trifluoride, sulfur trioxide, aluminum trichloride, antimony pentachloride, etc. , protonic acids: nitric acid, sulfuric acid, chlorosulfonic acid, etc., electron donors: alkali metals: lithium, potassium, rubidium, cesium, etc., alkaline earth metals: calcium, strontium, barium, etc., other rare earth metals: ( Sm, Eu, Yb),
Metal amides: potassium amide, calcium amide, etc. are exemplified. There is no particular restriction on the amount of doping, but the preferred content is 0.1 per weight of the heat-treated product.
% to 150%, especially 10% to 100%.

The fired product of the conjugated polymer () according to the present invention is characterized in that, unlike conventional graphitized materials, it has high conductivity and can be made into any shaped fired product. It can be used for various purposes.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto.

Example 1 P-xylylene bis(diethylsulfonium bromide) was allowed to react with an aqueous solution of caustic soda to obtain an aqueous solution of a polymeric sulfonium salt having a sulfonium salt in its side chain. Subsequently, after dialysis, it was cast and formed into a film.

This film (length: 5 cm, width: 10 cm) was subjected to static heat treatment at 200° C. for 2 hours in a nitrogen atmosphere using a horizontal tube furnace. This material has a poly-p-phenylene vinylene structure, and its electrical conductivity is
It was less than 10 ^-10 s/cm.

A quartz glass furnace core tube (30 mmφ x 700 mm L) was inserted into a resistance wire heating horizontal tubular electric furnace (450 mm L), and the device was assembled so that inert gas could be introduced. Place the above film (20
x 50 mm) and passed 100 ml of nitrogen gas per minute to raise the temperature inside the electric furnace to 950°C. After firing at 950°C for 2 hours, the fired product was cooled to room temperature and taken out. The fired film showed a high conductivity of 90 s/cm at room temperature. Furthermore, when this film was doped from the gas phase at room temperature using an ordinary method using sulfuric anhydride as an electron acceptor compound, it showed an electrical conductivity of 136 s/cm in 24 hours.

The electrical conductivity was measured using a four-terminal method or a two-terminal method.

Example 2 The fired film obtained in Example 1 was further fired at 3000°C. Firing was performed for 20 minutes in an argon stream using a graphite tube heating element. The fired product maintained its film shape. This film is 8×10 ³ s/at room temperature.
It showed a conductivity of cm. When it was further doped with anhydrous sulfuric acid, it showed an electrical conductivity of 1.1×10 ⁴ s/cm.

Example 3 The cast film obtained in Example 1 was heated to 150°C.
After heating while uniaxially stretching at a stretching speed of mm/min, constant length annealing was performed at 200℃ for 30 minutes.
A film stretched 10.8 times was obtained. This film was fired at 950°C in a nitrogen gas stream. The stretched film maintained its film shape. The obtained film was doped at 120s/cm and with sulfuric anhydride.
It showed an electrical conductivity of 150s/cm.

Example 4 The stock solution obtained in Example 1 was extruded into a 50% caustic soda aqueous solution at 80°C and spun. The produced filament was drawn at 150°C to obtain a thread drawn six times. This thread was heated from room temperature to 3000 in an argon stream.
The temperature was raised to ℃ over 2 hours and baked at 3000℃ for 20 minutes. The fired product retained its filamentous shape.

The fired yarn exhibited an electrical conductivity of 1.2×10 ⁴ s/cm at room temperature or 1.1×10 ⁵ s/cm when doped with anhydrous sulfuric acid.

Example 5 Polymerization and film molding were carried out in the same manner as in Example 1 except that 2,5-dimethyl-p-xylylene bis(diethylsulfonium bromide) was used.

This film was heated to 5 cm in length and 1 cm in width for 2 hours at 200℃ under an argon gas atmosphere to form poly-2,5-dimethyl-p-phenylene vinylene, and then heated to 3000℃ for 2 hours. It was heated and baked at 3000°C for 20 minutes.

The fired product retained its film state. The resulting film exhibited an electrical conductivity of 5.2×10 ³ s/cm at room temperature and 8.6×10 ³ s/cm when doped with nitric acid.

Example 6 Polymerization and film molding were carried out in the same manner as in Example 1 except that 2,5-dimethoxy-p-xylylene bis(diethylsulfonium bromide) was used.

The obtained polymer sulfonium salt film was heat-treated at up to 200°C under nitrogen flow to form poly-2,
After converting into 5-dimethoxy-p-phenylenevinylene, the resulting film was fired at 3000 °C in argon. The fired product maintained a film state. The resulting film exhibited an electrical conductivity of 5.5×10 ³ s/cm at room temperature and 7.2×10 ³ s/cm when doped with nitric acid.

Claims (1)

[Claims] 1 General formula (-R-CH=CH)- _o (R is p-phenylene group, 2,5-dimethyl-
p-phenylene group or 2,5-dimethoxy-p
- represents a phenylene group, and n represents an integer of 2 or more. ) in an inert atmosphere at 800
Highly conductive carbon-based fired product 2 obtained by firing at a temperature of ~3500°C General formula (-R-CH=CH)- _o (R is p-phenylene group, 2,5-dimethyl-
p-phenylene group or 2,5-dimethoxy-p
- represents a phenylene group, and n represents an integer of 2 or more. ) in an inert atmosphere at 800
A highly conductive carbon-based fired product obtained by firing at a temperature of ~3500°C and a highly conductive composition comprising a dopant of 0.1 to 150% based on the fired weight