Editing Polyacetylene (section)

==History==
One of the earliest reported acetylene polymers was named cuprene. Its highly cross-linked nature led to no further studies in the field for quite some time.<ref name=Feast>{{cite journal |last=Feast |first=W.J. |author2=Tsibouklis, J. |author3=Pouwer, K.L. |author4=Groenendaal, L. |author5=Meijer, E.W. |title=Synthesis, processing and material properties of conjugated polymers |journal=Polymer |date=1996 |volume=37 |issue=22 |page=5017 |doi=10.1016/0032-3861(96)00439-9|url=https://pure.tue.nl/ws/files/1422993/587897.pdf }}</ref> Linear polyacetylene was first prepared by [[Giulio Natta]] in 1958.<ref name=Saxman>{{cite journal |last=Saxon |first=A.M. |author2=Liepins, F. |author3=Aldissi, M. |title=Polyacetylene: Its Synthesis, Doping, and Structure |journal=Prog. Polym. Sci. |date=1985 |volume=11 |issue=1–2 |page=57 |doi=10.1016/0079-6700(85)90008-5}}</ref> The resulting polyacetylene was linear, of high molecular weight, displayed high crystallinity, and had a regular structure. X-ray diffraction studies demonstrated that the resulting polyacetylene was ''trans''-polyacetylene.<ref name=Saxman/> After this first reported synthesis, few chemists were interested in polyacetylene because the product of Natta's preparation was an insoluble, air sensitive, and infusible black powder.

The next major development of polyacetylene polymerization was made by [[Hideki Shirakawa]]’s group who were able to prepare silvery films of polyacetylene. They discovered that the polymerization of polyacetylene could be achieved at the surface of a concentrated solution of the catalyst system of [[triethylaluminium|Et<sub>3</sub>Al]] and Ti(OBu)<sub>4</sub> in an inert solvent such as toluene.<ref name=Norden>{{cite web |last=Norden |first=B |author2=Krutmeijer, E. |title=The Nobel Prize in Chemistry, 2000: Conductive Polymers |url=https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2000/advanced-chemistryprize2000.pdf}}</ref> In parallel with Shirakawa's studies, [[Alan Heeger]] and [[Alan MacDiarmid]] were studying the metallic properties of [[polythiazyl]] [(SN)<sub>x</sub>], a related but inorganic polymer.<ref name=Hall>{{cite journal |last1=Hall |first1=N |title=Twenty-five years of conducting polymers |journal=Chem. Comm. |date=2003 |doi=10.1039/B210718J |pages=1–4 |last2=McDiarmid |first2=Alan |last3=Heeger |first3=Alan |issue=1 |pmid=12610942 |url=http://teaching.ust.hk/~chem328/ChemComm03-1.pdf |access-date=2014-03-14 |url-status=dead |archive-url=https://web.archive.org/web/20160304023630/http://teaching.ust.hk/~chem328/ChemComm03-1.pdf |archive-date=2016-03-04}}</ref> Polythiazyl caught Heeger's interest as a chain-like metallic material, and he collaborated with [[Alan MacDiarmid]] who had previous experience with this material. By the early 1970s, this polymer was known to be [[superconductive]] at low temperatures.<ref name=Hall/> Shirakawa, Heeger, and MacDiarmid collaborated on further development of polyacetylene.<ref name=Saxman/>

Upon [[doping (semiconductor)|doping]] polyacetylene with I<sub>2</sub>, the conductivity increased seven orders of magnitude.<ref name=Norden/> Similar results were achieved using Cl<sub>2</sub> and Br<sub>2</sub>. These materials exhibited the largest room temperature conductivity observed for a covalent organic polymer, and this seminal report was key in furthering the development of organic [[conductive polymers]].<ref name="Shirakawa">{{cite journal |last=Shirakawa |first=H. |author2=Louis, E.J. |author3=MacDiarmid, A.G. |author4=Chiang, C.K. |author5=Heeger, A.J. |title=Synthesis of Electrically Conducting Organic Polymers: Halogen Derivatives of Polyacetylene, (CH)<sub>x</sub> |journal=Journal of the Chemical Society, Chemical Communications |issue=16 |date=1977 |pages=578–580 |doi=10.1039/C39770000578}}</ref> Further studies led to improved control of the ''cis''/''trans'' isomer ratio and demonstrated that ''cis''-polyacetylene doping led to higher [[Ionic conductivity (solid state)|conductivity]] than doping of ''trans''-polyacetylene.<ref name="Norden" /> Doping ''cis''-polyacetylene with AsF<sub>5</sub> further increased the conductivities, bringing them close to that of copper. Furthermore, it was found that heat treatment of the catalyst used for polymerization led to films with higher conductivities.<ref>{{cite journal |last=Shirakawa |first=Hideki |title=Synthesis and characterization of highly conducting polyacetylene |journal=Synthetic Metals |date=1995 |volume=69 |issue=1–3 |page=3 |doi=10.1016/0379-6779(94)02340-5}}</ref>

To account for such an increase in conductivity in polyacetylene, [[John Robert Schrieffer|J. R. Schrieffer]] and Heeger considered the existence of topologically protected [[Soliton|solitonic]] defects, their model is now known as the [[Su–Schrieffer–Heeger model]], which has served as model in other contexts to understand [[Topological insulator|topological insulators]].<ref>{{Cite journal |last1=Meier |first1=Eric J. |last2=An |first2=Fangzhao Alex |last3=Gadway |first3=Bryce |date=2016 |title=Observation of the topological soliton state in the Su–Schrieffer–Heeger model |journal=Nature Communications |language=en |volume=7 |issue=1 |pages=13986 |doi=10.1038/ncomms13986 |issn=2041-1723 |pmc=5196433 |pmid=28008924|arxiv=1607.02811 |bibcode=2016NatCo...713986M }}</ref>