Electrically Conducting Polymers: Science and Technology

For the past 50 years, conventional insulating-polymer systems have increasingly been used as substitutes for structural materials such as wood, ceramics, and metals because of their high strength, light weight, ease of chemical modification/customization, and processability at low temperatures. In 1977 the first intrinsic electrically conducting organic polymer—doped polyacetylene—was reported, spurring interest in “conducting polymers.” Intrinsically conducting polymers are completely different from conducting polymers that are merely a physical mixture of a nonconductive polymer with a conducting material such as metal or carbon powder. Although initially these intrinsically conducting polymers were neither processable nor air-stable, new generations of these materials now are processable into powders, films, and fibers from a wide variety of solvents, and also are airstable. Some forms of these intrinsically conducting polymers can be blended into traditional polymers to form electrically conductive blends. The electrical conductivities of the intrinsically conductingpolymer systems now range from those typical of insulators ( −10 S/cm (10 −10 Ω −1 cm 1 )) to those typical of semiconductors such as silicon (~10 5 S/cm) to those greater than 10 +4 S/cm (nearly that of a good metal such as copper, 5 × 10 5 S/cm). Applications of these polymers, especially polyanilines, have begun to emerge. These include coatings and blends for electrostatic dissipation and electromagnetic-interference (EMI) shielding, electromagnetic-radiation absorbers for welding (joining) of plastics, conductive layers for light-emitting polymer devices, and anticorrosion coatings for iron and steel. The common electronic feature of pris tine (undoped) conducting polymers is the π-conjugated system, which is formed by the overlap of carbon p z orbitals and alternating carbon-carbon bond lengths.