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.

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Structure 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.^[1][2][3] Depending on the method of preparation, some polyacetylenes are also called acetylene black or polyacetylene black.^{[citation needed]}

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.^[4] The Nobel Prize in Chemistry in 2000 was awarded to Alan J. Heeger, Alan G MacDiarmid, and Hideki Shirakawa for this work.

References

1. ^ 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
2. ^ 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
3. ^ Langsdorf, Brandi, L.; Zhou, Xin; Lonergan, Mark C., "Kinetic Study of the Ring-Opening Metathesis Polymerization of Ionically Functionalized Cyclooctatetraenes" Macromolecules, 2001, volume 34, pages 2450-2458. doi:10.1021/ma0020685
4. ^ 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