GB2133022A - NTC electrically conductive materials - Google Patents

NTC electrically conductive materials Download PDF

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Publication number
GB2133022A
GB2133022A GB08400344A GB8400344A GB2133022A GB 2133022 A GB2133022 A GB 2133022A GB 08400344 A GB08400344 A GB 08400344A GB 8400344 A GB8400344 A GB 8400344A GB 2133022 A GB2133022 A GB 2133022A
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United Kingdom
Prior art keywords
pyrrole
substituted
electrically conductive
conductive material
group
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08400344A
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GB8400344D0 (en
Inventor
Stephen Baigrie
Robert Lines
Judith Hardy
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Raychem Ltd
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Raychem Ltd
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Priority claimed from GB838300352A external-priority patent/GB8300352D0/en
Application filed by Raychem Ltd filed Critical Raychem Ltd
Priority to GB08400344A priority Critical patent/GB2133022A/en
Publication of GB8400344D0 publication Critical patent/GB8400344D0/en
Publication of GB2133022A publication Critical patent/GB2133022A/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
    • H01B1/12—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances organic substances
    • H01B1/124—Intrinsically conductive polymers
    • H01B1/128—Intrinsically conductive polymers comprising six-membered aromatic rings in the main chain, e.g. polyanilines, polyphenylenes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G61/00—Macromolecular compounds obtained by reactions forming a carbon-to-carbon link in the main chain of the macromolecule
    • C08G61/12—Macromolecular compounds containing atoms other than carbon in the main chain of the macromolecule
    • C08G61/122—Macromolecular compounds containing atoms other than carbon in the main chain of the macromolecule derived from five- or six-membered heterocyclic compounds, other than imides
    • C08G61/123—Macromolecular compounds containing atoms other than carbon in the main chain of the macromolecule derived from five- or six-membered heterocyclic compounds, other than imides derived from five-membered heterocyclic compounds
    • C08G61/124—Macromolecular compounds containing atoms other than carbon in the main chain of the macromolecule derived from five- or six-membered heterocyclic compounds, other than imides derived from five-membered heterocyclic compounds with a five-membered ring containing one nitrogen atom in the ring
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/04—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient
    • H01C7/049—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having negative temperature coefficient mainly consisting of organic or organo-metal substances

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Electromagnetism (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

Electrically conductive materials having pronounced negative temperature coefficient (NTC) are produced by oxidation and doping of 2-substituted pyrroles, and these materials are useful in making NTC electrical devices.

Description

SPECIFICATION NTC electrical device This invention relates to negative temperature coefficient (NTC) electrical devices, these being devices which become less electrically resistive with increasing temperature. Known NTC devices such as thermistors may be made from the oxides of such materials as iron, chromium, manganese, cobalt and nickel doped by the addition of small quantities of a metal with a differentvalency.
The invention provides an NTC electrical device having as an NTC element an electrically conductive material produced by oxidative doping of a 2substituted pyrrole.
It is known that electrically conductive materials can be produced by oxidation of pyrrolewhich results in the formation of an electrically charged polymer or oligomerinherentlycapableofconducting electricity.
A negative counter-ion is required to balance the positive electrical charge on the oxidised electrically conductive pyrrole material. This counter-ion will be hereinafter referred to as a "dopant", and the process of oxidation and introduction ofthe dopantwill be referred to as "oxidative doping", regardless of whether the doping is performed together with, or after, the oxidation. Examples of dopents include BF4-, Br-, p-toiuenesulphonate.
It has now been found that 2-substituted pyrroles when subjected to oxidative doping produceelectrically conductive materials of surprisingly high nega tivetemperature coefficient, which are accordingly useful in making NTC electrical devices.
The preferred 2-substituents are electron-releasing groups, preferably lower alkyl groups, especially methyl, although other (more expensive) substituents may be useful. Furthersubstitution in the 3-, 4- or 5- positions of thepyrrole also produces high negative temperature coefficients compared with 3,4-disubstitution or unsubstituted pyrrole, the preferred 3-,4-, or 5-substituents also being electrondonating groups, preferably loweralkyl groups, especially methyl.
Electrically conductive materials produced from pyrrolestendto have advantageous oxidation resist anceoverotherconductive polymers such as polyacetylenes. To obtain a conductive polymer, sufficient positions must be left unsubstituted to permit polymerisation. Electrically conductive polymers are generally believed to operate by way of a conjugated pi-electron system, and it will be understood that somesubstituents or combinations of substituents may interfere with the conjugated system so as to detract from or destroy the desired electrical conductivity, acceptable substituents being readily determinable by simplytesting the conductiv- ity of the resulting polymer.It is however not essential that the conductive material be a true polymer or oligomer, provided that it displays the required NTC effect. For example, oxidative doping of 2,5-dimethyl pyrrole can produce a black powder which is not readily identifiable as a polymer, but has the strong NTC effect aforementioned. The products of oxidative doping of 2,3-dimethyl pyrrole, 2,4dimethyl pyrrole and 2-methyl pyrrole have the aforementioned NTC effect are believed to be new materials which are accordingly claimed perse together with their lower alkyl homologues as part of the present invention.
Chemical preparative methods are preferred for producing the conductive materials ofthis invention.
The 2-substituted pyrrole and the dopant are mixed with an oxidising agent in a suitable liquid vehicle.
The oxidising agent can advantageously be carried by the dopant, for example by forming the ferric salt of a dopant such as p-toluenesulphonate or halide ions, thereby bringing about simultaneous oxidative polymerisation and doping with the negatively charged dopant. Some oxidation reactions tend to produce an insoluble product, which is relatively non-conductive, and a soluble product which, alone orin a mixture with the insoluble product, displays the marked NTC behaviour on which the present invention is based.
Some specific examples of the present invention will now be described.
Preparation of methyl pyrroles 2,5-dimethyl pyrroles is commercially available.
The remaining methyl pyrroles: 2-methyl; 2,3dimethyl; 2,4-dimethyl and 3,4-dimethyl were synthesised by known literature methods.
Oxidation ofthe methylpyrroles All the methyl pyrroles can be oxidised by metal saltoxidants such asferric perchlorateto brown or black conductive powders. With the exception of 2,5-dimethyl pyrrole, chlorine can also be used to oxidisethe methyl pyrroles.
Example 1 Oxidation of2,5-dimethyl pyrrole by Ferric chloride 1 0g of 2,5-dimethylpyrrole was added dropwise with stirring to 300cam3 of 60% w/v aqueous ferric chloride solution. After 24 hours the precipitate was filtered off. Residual ferric and ferrous chloride was removed by dissolving the product in water and passing it thorough ion-exchange columns. The product was dried under reduced pressure to give a dark brown powder.
Typical analysis: 15-20% wt. CI; 0.4-0.9% wt, Fe; 17-21% wt. water.
Example 2 Oxidation of2,4-dimethylpyrrole by Chlorine 5 cm3 of 2,4-dimethylpyrrole and 150 cm3 of acetonitrile were placed in a conical flask and chlorine gas was bubbled through for two hours. The solvent was removed by evaporation to give a black powder.
The powder consisted of two fractions: a) insoluble in acetonitrile and b) soluble in acetonitrile and most other common organic solvents such as dichlor omethaneand methanol.
The relative proportions of a) and b) could be varied by the amount chlorine admitted, higher doses favoring the insoluble fraction a).
Typical analysis Total chlorine (%wt) Chloride (%wt) Nitrogen (%wt) Fraction a) 26 5 9.73 Fraction b) 33 10 10.73 Example 3 Example 2 was repeated substituting 2-methyl pyrrole forthe 2,4-dimethylpyrrole.
Example 4 Example 2 was repeated substituting 2,3-dimethyl pyrroleforthe 2,4-dimenthylpyrrole.
Electrical Conductivity Measurements The pyrrole samples were compressed into pellets 1.3cm diameter using a SPECAC Powder Jig. The powderwas preheated in thejig to about 140 Cthen loaded under pressure (ca. 40 kgcm-2)for 5 minutes.
Upon cooling, the compressed sample was removed, checked for quality, and measured on a digital multimeter by locating the pellet between spring loadedcircularcopperelectrodes in a 2 probe configuration. Conductivity vs. temperature curves were obtained by placing the device in a temperature programmable oven. The results are shown in the accompanying drawing. The NTC effect of oxidatively doped 2-methyl pyrrole, 2,4-dimethyl pyrrole and 2,5-dimethyl pyrrole is shown graphically compared with the very much less significant NTC effect of oxidatively doped 3,4-dimethyl pyrrole. Unsubstituted pyrrole produces a substantially zero temperature coefficient, which could be plotted as a substantially horizontal line on this graph.
It may be advantageous to use mixtures ofthe 2-substituted pyrroles with one another or with other pyrroles. For example, oxidative doping of a mixture of a 2-substituted pyrrole with unsubstituted pyrrole has been found to achieve an NTC effect comparable with that ofthe 2-substituted pyrrole itself, while considerably raising the conductivity (lowering the resistivity) ofthe resulting material.
Example 5 Mixture ofPyrrole and2,4-dimethylpyrrole 1 .419 of pyrrole and 0.869 of 2,4-dimethyl pyrrole (7:3 mole ratio) were dissolved in 25ml of carbon tetrachloride. To this mixture was added dropwise 25mls of a solutionofchlorine in carbon tetrachloride (0.12mol chlorine). An exothermic reaction ensued and a black precipitate was formed. The precipitate was filtered off and dried under received pressure. A compressed pelletofthis material had the following electrical characteristic: T"C 30 60 85 110 Resistivity (ohm cm) 23045 13844 9726 5617

Claims (30)

1. An NTC electrical device having as an NTC element an electrically conductive material produced byoxidative doping of a 2-substituted pyrrole.
2. A device according to claim 1, wherein the 2-substituent ofthe pyrrole is an electron-releasing group.
3. A device according to claim 2, wherein the 2-substituentofthe pyrrole is a lower alkyl group.
4. A device according to claim 3, wherein the 2-substituentofthe pyrrole is a methyl group.
5. A device according to any ofthe preceding claims,whereinthe pyrrole is 2,3-substituted.
6. A device according to any of claims 1 to 4 wherein the pyrrole is 2,4-substituted.
7. Adevice according to any of claims 1 to 4 wherein the pyrrole is 2,5-substituted.
8. A device according to claim 5,6 or7, wherein the 3,4 or 5-substituent is an electron-releasing group.
9. A deviceaccording to claim 8, wherein the 3,4, or5-substituentisa loweralkyl group.
10. A device according to claim 9, wherein the 3,4 or 5-substituent isa methyl group.
11. A device according to any of the preceding claims wherein the electrically conductive material is a polymer or oligomer.
12. A device accordingto any ofthe preceding claimswhereinthe electrically conductive material is produced by oxidative doping ofthe 2-substituted pyrrole in a mixture with another pyrrole.
13. A device according to claim 12 wherein a mixture of the 2-substituted pyrrole with unsubstituted pyrrole is used.
14. A device according to claim 1 substantiallyas described with reference to any one of the foregoing Examples.
15. An electrically conductive material produced by oxidative doping of 2-(lower alkyl) pyrrole.
16. An electrically conductive material produced by oxidative doping of 2Bdi(lower alkyl) pyrrole.
17. An electrically conductive material produced by oxidative doping of2,4-di(loweralkyl) pyrrole.
18. An electrically conductive material produced by oxidative doping of 2,5-di(lower alkyl) pyrrole.
19. A material according to claim 15, 16. 17 or18, wherein the loweralkyl group(s) is or are methyl group(s).
20. An electrically conductive material produced by oxidative doping of 2-substituted pyrrole.
21. An electrically conductive material produced by oxidative doping of a mixture of 2-substituted pyrroles or a mixture of a 2-substituted pyrrole with another pyrrole.
22. Amaterial accordingto claim 21 wherein a mixture of a 2-substituted pyrrole and unsubstituted pyrrole is used.
23. A material according to claim 20,21 or 22 wherein the 2-subsstituentofthe pyrrole is an electron-releasing group.
24. A material according to claim 23, wherein the 2-substituentis a lower alkyl group, preferably a methyl group
25. A material according to any of claims 20to 24 whereintheR-substituted pyrrole is also substituted in the3-,4-, orS position.
26. A material according to claim 25, wherein the 3-4-, or 5- substituent is an electron-releasing group
27. Amaterial according to claim 26,whreinthe 3-, 4-, or Fi-substituent is a lower alkyl group, preferably a methyl group.
28. A material according to any of claims 15to 27 which is a polymer or oligomer.
29. A material according to any of claims 1 5to 28 which displays NTC electrical characteristics.
30. A material according to claim 20 or 21 substantially as described in any one of the foregoing Examples 1 to 5.
GB08400344A 1983-01-07 1984-01-06 NTC electrically conductive materials Withdrawn GB2133022A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08400344A GB2133022A (en) 1983-01-07 1984-01-06 NTC electrically conductive materials

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB838300352A GB8300352D0 (en) 1983-01-07 1983-01-07 Ntc electrical device
GB08400344A GB2133022A (en) 1983-01-07 1984-01-06 NTC electrically conductive materials

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GB2133022A true GB2133022A (en) 1984-07-18

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4803096A (en) * 1987-08-03 1989-02-07 Milliken Research Corporation Electrically conductive textile materials and method for making same
US4877646A (en) * 1988-06-27 1989-10-31 Milliken Research Corporation Method for making electrically conductive textile materials

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4803096A (en) * 1987-08-03 1989-02-07 Milliken Research Corporation Electrically conductive textile materials and method for making same
US4877646A (en) * 1988-06-27 1989-10-31 Milliken Research Corporation Method for making electrically conductive textile materials

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Publication number Publication date
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