Angewandte Chemie International Edition
Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2003, 42 (6), 658 - 661
Metamorphosis without Changing Shape
Progress toward rolled-up laptops and
mass-produced chips; a new conducting plastic
The words plastic and electric current usually bring to mind thing like wire coatings or computer casings. That plastics are invariably electric insulators goes without saying. It was discovered about thirty years ago that certain polymers are capable of conducting electricity. Although the initial euphoria has worn off a bit, the dream of making foldable or rollable laptops, wallpaper televisions, or inexpensive disposable chips—for such things as "intelligent" labels—remains. Early prototypes of flat foil batteries, organic light-emitting diodes (LEDs), chips, lasers, and solar cells already exist. However, the problems surrounding material properties and production have not nearly all been solved. Researchers working with Fred Wudl at the University of California in Los Angeles have now discovered an unconventional way to produce a very durable plastic with an especially high conductivity. The material in question is a special polythiophene. Polythiophenes are among the most important types of industrially useful conducting polymers.
Current processes for the production of conducting polymers suffer from the fact that it is not possible to obtain precisely defined, highly ordered polymer structures in the presence of the necessary catalysts or polymerization initiators. This is precisely what Wudl's team has managed to do, since their very simple reaction method works without any additives. Moderate heating and a couple of hours of waiting are sufficient to convert the starting material, white crystals, into a blue-black, highly conducting polymer with a metallic sheen. The unusual thing about this "solid-state reaction" is that the shape and structure of the starting material are retained.
And it is this structure that lies behind the secret of this unusual reaction. The starting material consists of two carbon rings, one six-membered, oxygen-containing ring and one five-membered, sulfur-containing ring. A crucial role is played by two bromine atoms attached to each of the five-membered rings. They cause the individual two-ring units to link together to form long chains. The bromine atoms released in this process remain bound within the polymer and become the dopant necessary for the electrical conductivity of plastic.
"We can also use our method to deposit very thin, highly stable, conducting polythiophene films on nonconducting supports very easily," says Wudl. "These could be used for the production of completely organic LEDs."