Polyacetylene

Polyacetylene (IUPAC name: polyethyne) usually refers to an organic polymer with the repeating unit . The name refers to its conceptual construction from polymerization of acetylene to give a chain with repeating olefin groups. This compound is conceptually important, as the discovery of polyacetylene and its high conductivity upon doping helped to launch the field of organic conductive polymers. The high electrical conductivity discovered by Hideki Shirakawa, Alan Heeger, and Alan MacDiarmid for this polymer led to intense interest in the use of organic compounds in microelectronics (organic semiconductors). This discovery was recognized by the Nobel Prize in Chemistry in 2000. Early work in the field of polyacetylene research was aimed at using doped polymers as easily processable and lightweight "plastic metals". Despite the promise of this polymer in the field of conductive polymers, many of its properties such as instability to air and difficulty with processing have led to avoidance in commercial applications. Compounds called polyacetylenes also occur in nature, although in this context the term refers to polyynes, compounds containing multiple acetylene groups ("poly" meaning many), rather than to chains of olefin groups ("poly" meaning polymerization of). Polyacetylene consists of a long chain of carbon atoms with alternating single and double bonds between them, each with one hydrogen atom. The double bonds can have either cis or trans geometry. The controlled synthesis of each isomer of the polymer, cis-polyacetylene or trans-polyacetylene, can be achieved by changing the temperature at which the reaction is conducted. The cis form of the polymer is thermodynamically less stable than the trans isomer. Despite the conjugated nature of the polyacetylene backbone, not all of the carbon–carbon bonds in the material are equal: a distinct single/double alternation exists. Each hydrogen atom can be replaced by a functional group. Substituted polyacetylenes tend to be more rigid than saturated polymers.