CA1200614A - Ntc electrical device - Google Patents
Ntc electrical deviceInfo
- Publication number
- CA1200614A CA1200614A CA000444821A CA444821A CA1200614A CA 1200614 A CA1200614 A CA 1200614A CA 000444821 A CA000444821 A CA 000444821A CA 444821 A CA444821 A CA 444821A CA 1200614 A CA1200614 A CA 1200614A
- Authority
- CA
- Canada
- Prior art keywords
- pyrrole
- substituted
- electrically conductive
- lower alkyl
- conductive material
- 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.)
- Expired
Links
Classifications
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Polyoxymethylene Polymers And Polymers With Carbon-To-Carbon Bonds (AREA)
- Thermistors And Varistors (AREA)
Abstract
ABSTRACT
Electrically conductive materials having pro-nounced negative temperature coefficient (NTC) are produced by oxidation and doping of 2 substituted pyrroles, and these materials are useful in making NTC
electrical devices.
Electrically conductive materials having pro-nounced 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
- 2 - RK182 This invention relates to negative temperature coefficient (NTC) electrical devicesr these ~eing devices which become less electrically resistive with increasing temperature. Known NTC devices such as thermistors may be made from the oxides of such mater-ials as iron, chromium! manganese, cobalt and nickel doped by the addition of small quantities of a metal with a different valency.
The invention provides an NTC electrical device having as an NTC element an electrically conductive material produced by oxidative doping of a 2-substit-uted pyrrole.
It is known that electrically conductive materials can be produced by oxidation of pyrrole which results - 15 in the formation of an electrically charged polymer or oligomer inherently capable of conducting 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 of the dopant will be referred to as "oxidative doping", regardless of whether the doping is performed together with, or aEter, the oxidation. Examples o dopants include BF4 , Br , p-toluenesulphonate.
It has now been found that 2-substituted pyrroles when subjected to oxidative doping produce electrically conductive materials of surprisingly high negative temperature coefficient, which are accordingly useful in making NTC electrical devices.
,.~u
The invention provides an NTC electrical device having as an NTC element an electrically conductive material produced by oxidative doping of a 2-substit-uted pyrrole.
It is known that electrically conductive materials can be produced by oxidation of pyrrole which results - 15 in the formation of an electrically charged polymer or oligomer inherently capable of conducting 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 of the dopant will be referred to as "oxidative doping", regardless of whether the doping is performed together with, or aEter, the oxidation. Examples o dopants include BF4 , Br , p-toluenesulphonate.
It has now been found that 2-substituted pyrroles when subjected to oxidative doping produce electrically conductive materials of surprisingly high negative temperature coefficient, which are accordingly useful in making NTC electrical devices.
,.~u
- 3 - RK182 The preferred 2-substituents are electron-releas-ing groups, preferably lower alkyl groups, especially methyl, although other (more expensive) substituents may be useful. Further substitution in the 3-~ 4- or 5- positions of the pyrrole also produces high negative temperature coefficients compared with 3,4-disubstit-ution or unsubstituted pyrrole, the preferred 3-, 4-, or 5-substituents also being electron-donating groups, preferably lower alkyl groups, especially methyl.
Electrically conductive materials produced from pyrroles tend to have advantageous oxidation resistance over other conductive polymers such as polyacetylenes. To obtain a conductive polymer, sufficient positions must be left ~nsubstituted ~o permit polymerisation. Electrically conductive poly-mers are generally believed to operate by way of a conjugated pi-electron system, and it will be under-stood that some substituents or com~inations of sub-stituents may interfere with the conjugated system so as to detract from or destroy the desired electrical conductivity, acceptable substituents being readily determinable by simply testing the conductivity 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 identif-iable as a polymer, but has the strong NTC effect aforementioned. The products of oxidative doping of 2~3-dimethyl pyrrole, 2,4-dimethyl pyrrole and 2-methyl pyrrole have the aforementioned NTC effect are believed to be new materials which are accordingly claimed
Electrically conductive materials produced from pyrroles tend to have advantageous oxidation resistance over other conductive polymers such as polyacetylenes. To obtain a conductive polymer, sufficient positions must be left ~nsubstituted ~o permit polymerisation. Electrically conductive poly-mers are generally believed to operate by way of a conjugated pi-electron system, and it will be under-stood that some substituents or com~inations of sub-stituents may interfere with the conjugated system so as to detract from or destroy the desired electrical conductivity, acceptable substituents being readily determinable by simply testing the conductivity 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 identif-iable as a polymer, but has the strong NTC effect aforementioned. The products of oxidative doping of 2~3-dimethyl pyrrole, 2,4-dimethyl pyrrole and 2-methyl pyrrole have the aforementioned NTC effect are believed to be new materials which are accordingly claimed
- 4 - RK182 ~er se together with their lower alkyl homologues as paxt of the present invention.
Chemical preparative methods are preferred for producing the conductive materials of this 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 polymer-isation 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 or in 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 pyrrole is commercially available~
The remaining methyl pyrroles: 2-methyl; 2,3-dimethyl;
2,4-dimethyl and 3,4 dimethyl were synthesised by known literature methods.
Oxidation of the methyl pyrroles All the methyl pyrroles can be oxidised by metal salt oxidants such as ferric perchlorate to brown or 6~
black conductive powders. With the exception of 2,5-dimethyl pyrrole, chlorine can also be used to oxidise the methyl pyrroles.
Example l S Oxidation of 2,5 dimethyl pyrrole by Ferric chloride 10g of 2,5-dimethylpyrrole was added dropwise with stirring to 300 cm3 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 passinq it through ion-exchange columns. The product was dried under reduced pressure to give a dark brown powder.
Typical analysis: 15-20~ wt. Cl; 0.4-0.9% wt. Fe;
17-21% wt. water.
Example 2 Oxidation of 2,4-dimethyl pyrrole by Chlorine
Chemical preparative methods are preferred for producing the conductive materials of this 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 polymer-isation 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 or in 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 pyrrole is commercially available~
The remaining methyl pyrroles: 2-methyl; 2,3-dimethyl;
2,4-dimethyl and 3,4 dimethyl were synthesised by known literature methods.
Oxidation of the methyl pyrroles All the methyl pyrroles can be oxidised by metal salt oxidants such as ferric perchlorate to brown or 6~
black conductive powders. With the exception of 2,5-dimethyl pyrrole, chlorine can also be used to oxidise the methyl pyrroles.
Example l S Oxidation of 2,5 dimethyl pyrrole by Ferric chloride 10g of 2,5-dimethylpyrrole was added dropwise with stirring to 300 cm3 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 passinq it through ion-exchange columns. The product was dried under reduced pressure to give a dark brown powder.
Typical analysis: 15-20~ wt. Cl; 0.4-0.9% wt. Fe;
17-21% wt. water.
Example 2 Oxidation of 2,4-dimethyl pyrrole by Chlorine
5 cm3 of 2,4-dimethylpyrrole and 150 cm of acetonitrile were placed in a conical flask and chlor-ine 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 dichloromethane and methanol.
The relative proportions of a) and b) could be varied by the amount of 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 for the 2,4 dimethylpyrrole.
10 Example 4 Example 2 was repeated substituting 2,3-dimethyl-pyrrole for the 2,4-dimethylpyrrole.
Electrical Conductivity Measurements The pyrrole samples were compressed into pellets 15 1.3cm diameter using a SPECAC Powder Jig. The powder was preheated in the jig to about 140C then 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 20 locating the pellet between spring-loaded circular copper electrodes in a 2 probe configuration. Conduc-tivity vs. temperature curves were obtained by placing the device in a temperature programmable oven. The results are shown in the accompanying drawing. The Q6~
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 signif-icant NTC effect of oxidatively doped 3,4-dimethyl pyrrole. Unsubstituted pyrrole produces a substan-tially zero temperature coefficient, which could be p]otted as a substantially horizontal line on this graph.
It may be advantageous to use mixtures of the 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 of the 2-substituted pyrrole itself, while consid-erably raising the conductivity (lowering the resis-tivity) of the resulting material.
Example 5 Mixture of Pyrrole and 2,4-dimethylpyrrole 1.41g 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 solution of chlorine in carbon tetrachloride tO.12mol chlorine). An exothermic reaction ensued and a black precipitate was formed. The precipitate was filtered off and dried under recived pressure~ A
compressed pellet of this material had the following electrical characteristic:
Resistivity (ohm cm) 23045 13844 9726 5617
The relative proportions of a) and b) could be varied by the amount of 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 for the 2,4 dimethylpyrrole.
10 Example 4 Example 2 was repeated substituting 2,3-dimethyl-pyrrole for the 2,4-dimethylpyrrole.
Electrical Conductivity Measurements The pyrrole samples were compressed into pellets 15 1.3cm diameter using a SPECAC Powder Jig. The powder was preheated in the jig to about 140C then 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 20 locating the pellet between spring-loaded circular copper electrodes in a 2 probe configuration. Conduc-tivity vs. temperature curves were obtained by placing the device in a temperature programmable oven. The results are shown in the accompanying drawing. The Q6~
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 signif-icant NTC effect of oxidatively doped 3,4-dimethyl pyrrole. Unsubstituted pyrrole produces a substan-tially zero temperature coefficient, which could be p]otted as a substantially horizontal line on this graph.
It may be advantageous to use mixtures of the 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 of the 2-substituted pyrrole itself, while consid-erably raising the conductivity (lowering the resis-tivity) of the resulting material.
Example 5 Mixture of Pyrrole and 2,4-dimethylpyrrole 1.41g 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 solution of chlorine in carbon tetrachloride tO.12mol chlorine). An exothermic reaction ensued and a black precipitate was formed. The precipitate was filtered off and dried under recived pressure~ A
compressed pellet of this material had the following electrical characteristic:
Resistivity (ohm cm) 23045 13844 9726 5617
Claims (28)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. An NTC electrical device having as an NTC
element an electrically conductive material produced by oxidative doping of a 2-substituted pyrrole.
element an electrically conductive material produced by oxidative doping of a 2-substituted pyrrole.
2. A device according to claim 1, wherein the 2-substituent of the pyrrole is an electron-releasing group.
3. A device according to claim 2, wherein the 2-substituent of the pyrrole is a lower alkyl group.
4. A device according to claim 3, wherein the 2-substituent of the pyrrole is a methyl group.
5. A device according to claim 1, 2 or 3, wherein the pyrrole is 2,3-substituted.
6. A device according to claims 1, 2 or 3, wherein the pyrrole is 2,4-substituted.
7. A device according to claim 1, 2 or 3, wherein the pyrrole is 2,5-substituted.
8. A device according to claim 1, wherein the pyrrole is 3-,4- or 5-substituted with an electron-releasing group.
9. A device according to claim 8, wherein the 3-,4-, or 5-substituent is a lower alkyl group.
10. A device according to claim 9, wherein the 3,4 or 5-substituent is a methyl group.
11. A device according to claim 1, 2 or 3, wherein the electrically conductive material is a polymer or oligomer.
12. A device according to claim 1, wherein the electrically conductive material is produced by oxida-tive doping of the 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. An electrically conductive material produced by oxidative doping of 2-(lower alkyl) pyrrole.
15. An electrically conductive material produced by oxidative doping of 2,3-di(lower alkyl) pyrrole.
16. An electrically conductive material produced by oxidative doping of 2,4-di (lower alkyl) pyrrole.
17. An electrically conductive material produced by oxidative doping of 2,5-di(lower alkyl) pyrrole.
18. A material according to claim 14, 15,or 16, wherein the lower alkyl group(s) is or are methyl group(s).
19. An electrically conductive material produced by oxidative doping of a 2-substituted pyrrole.
20. An electrically conductive material produced by doping of a mixture of 2-substituted pyrroles or a mixture of a 2-substituted pyrrole with another pyrrole.
21. A material according to claim 20, wherein a mixture of a 2-substituted pyrrole and unsubstituted pyrrole is used.
22. A material according to claim 19, 20 or 21 wherein the 2-substituent of the pyrrole is an electron-releas-ing group.
23. A material acording to claim 19, 20 or 21, wherein the 2-substituent is lower alkyl group, preferably a methyl group.
24. A material according to claim 19, 20 or 21, wherein the 2-substituted pyrrole is also substituted in the 3-,4-, or 5- position.
25. A material according to claim 19, 20 or 21, wherein the 2-substituted pyrrole is 3-,4-, or 5-substituted with an electron-releasing group.
26. A material according to claim 19, 20 or 21, wherein the 2-substituted pyrrole is 3-,4-, or 5-substituted with a lower alkyl group, preferably a methyl group.
27. A material according to claim 19 to 20 which is a polymer or oligomer.
28. A material according to claim 19 to 20 which displays NTC electrical characteristics.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8300352 | 1983-01-07 | ||
| GB838300352A GB8300352D0 (en) | 1983-01-07 | 1983-01-07 | Ntc electrical device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1200614A true CA1200614A (en) | 1986-02-11 |
Family
ID=10536020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000444821A Expired CA1200614A (en) | 1983-01-07 | 1984-01-06 | Ntc electrical device |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0121289A1 (en) |
| JP (1) | JPS59135704A (en) |
| CA (1) | CA1200614A (en) |
| GB (1) | GB8300352D0 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0618863B2 (en) * | 1986-03-28 | 1994-03-16 | 三菱化成株式会社 | Organic semiconductor |
| WO2003052777A1 (en) | 2001-12-14 | 2003-06-26 | Shin-Etsu Polymer Co., Ltd. | Organic ntc composition, organic ntc element, and process for producing the same |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3574072A (en) * | 1968-04-03 | 1971-04-06 | Universal Oil Prod Co | Polymerization of heterocyclic compounds |
| DE3013924A1 (en) * | 1980-04-11 | 1981-10-22 | Basf Ag, 6700 Ludwigshafen | METHOD FOR THE PRODUCTION OF ELECTRICALLY CONDUCTIVE POLYCONDENSATES AND THEIR USE IN ELECTROTECHNICS AND FOR THE ANTISTATIC EQUIPMENT OF PLASTICS |
| DE3049551A1 (en) * | 1980-12-31 | 1982-07-29 | Basf Ag, 6700 Ludwigshafen | ELECTRICALLY CONDUCTIVE POLY (PYRROL) DERIVATIVES |
-
1983
- 1983-01-07 GB GB838300352A patent/GB8300352D0/en active Pending
-
1984
- 1984-01-06 CA CA000444821A patent/CA1200614A/en not_active Expired
- 1984-01-06 EP EP19840300084 patent/EP0121289A1/en not_active Withdrawn
- 1984-01-07 JP JP123284A patent/JPS59135704A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB8300352D0 (en) | 1983-02-09 |
| JPS59135704A (en) | 1984-08-04 |
| EP0121289A1 (en) | 1984-10-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |