Editing Polyacetylene (section)

==Properties==
The structure of polyacetylene films have been examined by both [[infrared spectroscopy]]<ref name="Shirikawa IR">{{cite journal |author1=Shirakawa, H. S. |author2=Ito, T. S. |author3=Ikeda, S. |title=Infrared Spectroscopy of Poly(acetylene) |doi=10.1295/polymj.2.231 |journal=Polym. J. |date=1971 |volume=2 |issue=2 |pages=231–244 |doi-access=free}}</ref> and [[Raman spectroscopy]],<ref name="Shirakawa Raman">{{cite journal |author1=Shirakawa, H. S. |author2=Ito, T. S. |author3=Ikeda, S. |title=Raman Scattering and Electronic Spectra of Poly(acetylene) |journal=Polym. J. |date=1973 |volume=4 |issue=4 |pages=460–462 |doi=10.1295/polymj.4.460 |doi-access=free}}</ref> and found that the structure depends on synthetic conditions. When the synthesis is performed below −78&nbsp;°C, the ''cis'' form predominates, while above 150&nbsp;°C the ''[[cis-trans isomerism|trans]]'' form is favored. At room temperature, the polymerization yields a ratio of 60:40 ''cis'':''trans''.<ref name="McDiarmiad synthetic metals"/> Films containing the ''cis'' form appear coppery, while the ''[[cis-trans isomerism|trans]]'' form is silvery.<ref name="McDiarmiad synthetic metals"/> Films of ''cis''-polyacetylene are very flexible and can be readily stretched, while ''[[cis-trans isomerism|trans]]''-polyacetylene is much more brittle.

The synthesis and processing of polyacetylene films affects the properties. Increasing the catalyst ratio creates thicker films with a greater draw ratio, allowing them to be stretched further.<ref name=Saxman/>  Lower catalyst loadings leads to the formation of dark red [[gel]]s, which can be converted to films by cutting and pressing between glass plates.<ref name="McDiarmiad synthetic metals">{{cite journal |last=MacDiarmid |first=A |author2=Heeger, A. |title=Organic Metals and Semiconductors: The Chemistry of Polyacetylene (CH<sub>x</sub>) and its Derivatives |journal=Synthetic Metals |date=1979 |volume=1 |issue=101–118 |pages=101 |doi=10.1016/0379-6779(80)90002-8 |url=https://apps.dtic.mil/sti/pdfs/ADA087102.pdf |url-status=live |archive-url=https://web.archive.org/web/20170924002910/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA087102 |archive-date=September 24, 2017}}</ref> A foam-like material can be obtained from the gel by displacing the [[solvent]] with [[benzene]], then freezing and subliming the benzene.<ref name=Saxman/> Polyacetylene has a bulk density of 0.4&nbsp;g/cm<sup>3</sup>, while density of the foam is significantly lower, at 0.02–0.04&nbsp;g/cm<sup>3</sup>.<ref name=Saxman/> The morphology consists of [[fibril]]s, with an average width of 200&nbsp;Å. These fibrils form an irregular, web-like network, with some [[cross-link]]ing between chains.<ref name=Saxman/> The insolubility of polyacetylene makes it difficult to characterize this material and to determine the extent of cross-linking in the material.

[[File:Oxidation of Polyacetylene.jpg|thumb|right|500px|Products of oxidation of polyacetylene]]

For applications, polyacetylenes suffer from many drawbacks. They are insoluble in solvents, making it essentially impossible to process the material. While both ''cis'' and ''trans''-polyacetylene show high thermal stability,<ref name="McDiarmiad synthetic metals"/> exposure to air causes a large decrease in the flexibility and conductivity.<ref name=Saxman/>  When polyacetylene is exposed to air, oxidation of the backbone by O<sub>2</sub> occurs. [[Infrared spectroscopy]] shows formation of [[carbonyl]] groups, [[epoxide]]s, and [[peroxide]]s.<ref name=Saxman/><ref>{{cite journal |last=Will |first=F.G. |author2=D.W. McKee |title=Thermal Oxidation of Polyacetylene |journal=Journal of Polymer Science |date=1983 |volume=21 |issue=12 |pages=3479–3492 |doi=10.1002/pol.1983.170211210 |bibcode=1983JPoSA..21.3479W}}</ref> Coating with [[polyethylene]] or wax can slow the [[oxidation]] temporarily, while coating with glass increases stability indefinitely.<ref name=Saxman/>