Editing Polymer backbone (section)

{{short description|Longest chain of covalently-bonded atoms in a polymer}}

{{Quote box
 |title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''Main chain''' or '''Backbone'''<br />That linear chain to which all other chains, long or short or both,<br />may be regarded as being pendant.

''Note'': Where two or more chains <br /> could equally be considered to be the main chain, that one is <br />selected which leads to the simplest representation of the <br />molecule.<ref>{{GoldBookRef |title=main chain (backbone) ''of a polymer'' |file=M03694 }}</ref>
}}
In [[polymer science]], the '''polymer chain''' or simply '''backbone''' of a [[polymer]] is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer (such as the [[glass transition]] temperature). For example, in [[Silicone|polysiloxanes]] (silicone), the backbone chain is very flexible, which results in a very low [[glass transition]] temperature of {{Cvt|-123|C|F K}}.<ref>{{Cite web |url=http://courses.chem.psu.edu/chem112/materials/polymers.html |title=Polymers |access-date=2015-09-17 |archive-url=https://web.archive.org/web/20151002172625/http://courses.chem.psu.edu/chem112/materials/polymers.html |archive-date=2015-10-02 |url-status=dead }}</ref> The polymers with rigid backbones are prone to [[crystallization]] (e.g. [[polythiophenes]]) in [[thin film]]s and in [[Solution (chemistry)|solution]]. Crystallization in its turn affects the optical properties of the polymers, its optical [[band gap]] and electronic levels.<ref>{{cite journal|last1=Brabec|first1=C.J.|last2=Winder|first2=C.|last3=Scharber|first3=M.C|last4=Sarıçiftçi|first4=S.N.|last5=Hummelen|first5=J.C.|last6=Svensson|first6=M.|last7=Andersson|first7=M.R.|title=Influence of disorder on the photoinduced excitations in phenyl substituted polythiophenes|journal=Journal of Chemical Physics |date=2001|volume=115|issue=15|page=7235|doi=10.1063/1.1404984|bibcode=2001JChPh.115.7235B|url=https://pure.rug.nl/ws/files/6636890/2001BrabecJChemPhys.pdf|author4-link=Niyazi Serdar Sarıçiftçi}}</ref>