Polyacetylene

Polyacetylene (IUPAC name: polyethyne) is an organic polymer with the repeat unit (C₂H₂)_n. The high electrical conductivity discovered for these polymers in the 1970’s accelerated interest in the use of organic compounds in microelectronics. Polyacetylenes are also known where the H atoms are replaced with alkyl groups.

tructure of polyacetylene

The polymer consists of a long chain of carbon atoms with alternating single and double bonds between them, each with one hydrogen atom. Schematically the structure of polyacetylene is shown below..

Preparation

Acetylene polymerizes in a similar fashion to ethylene: the polymerization can be effected with anionic, cationic, and radical initiators. Polyacetylene is generally not prepared by polymerizing acetylene, which is a highly flammable gas that uncontrollably oligomerizes at high concentrations. The most common syntheses use ring-opening polymerization ("ROMP") of molecules like cyclooctatetraene and substituted derivatives thereof. [Jozefiak, T. H.; Ginsburg, E. J.; Gorman, C. B.; Grubbs, R. H.; Lewis, N. S."Voltammetric Characterization of Soluble Polyacetylene Derivatives Obtained from the Ring-Opening Metathesis Polymerization (ROMP) of Substituted Cyclooctatetraenes" Journal of the American Chemical Society 1993; volume 115, pages 4705-4713. DOI|10.1021/ja00064a035] [Gorman, C. B. Ginsburg, E. J.; Grubbs, R. H. "Soluble, Highly Conjugated Derivatives of Polyacetylene from the Ring-Opening Metathesis Polymerization of Monosubstituted Cyclooctatetraenes: Synthesis and the Relationship Between Polymer Structure and Physical Properties" Journal of the American Chemical Society 1993, volume 115, pages 1397-1409. DOI|10.1021/ja00057a024] [Langsdorf, Brandi, L.; Zhou, Xin; Lonergan, Mark C., "Kinetic Study of the Ring-Opening Metathesis Polymerization ofIonically Functionalized Cyclooctatetraenes" Macromolecules, 2001, volume 34, pages 2450-2458. DOI|10.1021/ma0020685]

Conductivity and the Nobel Prize

As prepared with a Ziegler-Natta catalyst, with high levels of catalyst, the polyacetylene is a silver, non-conductive film. It was shown in 1976 that oxidation of this material with iodine results in a 10⁸-fold increase in conductivity. The conductivity of this doped material approaches the conductivity of the best available conductor, silver. This was one of the first known examples of a conductive organic polymer. [Chiang, C. K.; Druy, M. A.; Gau, S. C.; Heeger, A. J.; Louis, E. J.; MacDiarmid, A. G.; Park, Y. W.; Shirakawa, H., "Synthesis of Highly Conducting Films of Derivatives of Polyacetylene, (CH)x," J. Am. Chem. Soc. 1978, 100, 1013-15. DOI|10.1021/ja00471a081] The Nobel Prize in Chemistry in 2000 was awarded to Alan J. Heeger, Alan G MacDiarmid, and Hideki Shirakawa for this work.

References

External links

* [http://romano.physics.wisc.edu/winokur/handbook/node5.html Polyacetylene]
* [http://nobelprize.org/chemistry/laureates/2000/presentation-speech.html The Nobel Prize in Chemistry 2000 presentation speech]