What is the list of conductive polymers
After the discovery of polymers and their technical applications, it was initially assumed that all plastics are good insulators against electrical current. However, the history of polymers should take a different route. In 1860, the German chemist August Kekulé (1829–1896) had already proposed the theory of the ring-shaped structural formula of benzene and the equivalence of the hydrogen atoms involved. This laid the foundation for the chemistry of aromatics. In the benzene molecule, the electrons can no longer be clearly assigned to an atom; they are delocalized and can move freely in the benzene ring. One could assume that even in the long chains of those polymers that contain alternating single and double bonds, charge transport via the electrons is possible. The first attempt initially failed. Giulio Natta reported in 1958 about the polymerization of acetylene. He received an insoluble and non-meltable black powder that initially received no attention.
In 1967 the Japanese Hideki Shirakawa (born 1936) succeeded in producing polyacetylene (abbreviation PA; actually: polyethine according to IUPAC) in the form of a film. He used a highly effective organometallic titanium-aluminum catalyst as the catalyst. Due to a calculation error, he used a thousand times the amount of the catalyst, which coincidentally resulted in a thin, stable film rather than powder. Depending on the reaction conditions, the film contained proportions of the two isomers of the silvery, shiny one cis-Polyacetylene (cis-PA) or the copper-colored trans-Polyacetylene (trans-PA). An electrical conductivity could be measured for both, but it was not particularly good and only corresponded to that of a semiconductor.
At the same time, Alan Heeger (born 1936) and Alan MacDiarmid (born 1927) experimented in the USA with metallic-looking films made from the inorganic polymer sulfur nitride. In the 1970s, the two scientists met Shirakawa at a seminar in Tokyo and invited him to the University of Pennsylvania where MacDiarmid worked. There the three researchers showed in 1976 that a treatment of the polyacetylene with an oxidizing agent such as chlorine, bromine, iodine or arsenic pentafluoride leads to a strong increase in the conductivity of the polymer. They received improved conductivity by a factor of ten million. As a result, the conductivity of the polyacetylene treated in this way was almost as good as the best conductive metal silver. This improvement could be achieved by incorporating a small amount of foreign atoms into the semiconductor polyacetylene (doping). A doping of the polymer poly (para-phenylene) (PPP) leads to a conductor that does not conduct quite as well as doped polyacetylene. After finding a way to dissolve and process the conductive polymers in the 1980s, nothing stood in the way of the development of conductive plastics. Shirakawa, Heeger and MacDiarmid received the Nobel Prize in Chemistry in 2000 for the development of electrically conductive polymers.
Polyacetylene can be produced by a process developed by Shirakawa. The acetylene gas is blown onto a highly concentrated catalyst solution. A polymer film is formed on the surface of the solution. The polyacetylene is chemically relatively unstable, therefore the doped polymers polypyrrole, polyaniline (PANI), polythiophene or poly (para-phenylene-vinylene) (PPP) are used.
Electrically conductive polymers found their first technical application in batteries or accumulators, which required low weight and very high performance, for example in portable and relatively small MP3 players and in cell phones. Lithium polymer batteries are far superior to other batteries in terms of their performance and safety. In addition, they are largely non-toxic and easy to recycle. As polymers, they predominantly contain polypyrroles. In 1986 the field effect transistor OFET was presented, in which the semiconductor layer consisted of organic polymers. This laid the foundation for the production of electronic circuits based on organic polymers. In 2001, researchers from Siemens presented integrated circuits made entirely of polymers for the first time. These circuits are much cheaper to manufacture than comparable silicon circuits, and they are much smaller.
A further development was in the organic light-emitting diode from 1987 OLED (Organic light emitting diodes). A thin film of an organic polymer is applied to a transparent anode made of indium tin oxide. The cathode, for example aluminum or magnesium, is evaporated onto this layer. When a voltage is applied, the electrically excited polymer emits electromagnetic radiation and lights up. The first products with OLEDs for lighting came onto the market in car radios and cell phones in 2000. In 2003, the first mobile phones from Samsung, digital cameras from Kodak and computer monitors from Kodak and Sanyo with an OLED display appeared. The advantage of this monitor technology can be seen in the particularly large viewing angle and a better contrast compared to conventional LCD monitors.
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