Backbone chain

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IUPAC definition

Main chain
That linear chain to which all other chains, long or short or both,
may be regarded as being pendant.

Note: Where two or more chains could equally be considered to be the
main chain, that one is selected which leads to the simplest representation
of the molecule.[1]

In polymer science, the backbone chain or main chain of a polymer is the series of covalently bounded atoms that together create the continuous chain of the molecule.

Character of the backbone

In a way the character of the backbone chain depends on the type of polymerization: in step-growth polymerization the monomer moiety becomes the backbone, and thus the backbone is typically functional, like in polythiophenes or low band gap polymers in organic semiconductors.[2] In chain-growth polymerization, typically applied for alkenes, the backbone is not functional, but is bearing the functional side chains or pendant groups. However, in polypeptides, the backbone is as important for the functionality of the polymer as the side chains. The backbone in polypeptides consists of carbon and nitrogen atoms of the constituent amino acids and does not include the side chains.

The character of the backbone, i.e. its flexibility, determines the thermal properties of the polymer (such as the glass transition temperature), e.g. in polisiloxanes the backbone chain is very flexible, resultin in very low glass transition temperature of -123 °C.[3] The polymers with a rigid backbone are prone to crystallization (e.g. polythiophenes) in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels.[4]

The configuration of a polypeptide relies on the flexibility of the torsion angles of the backbone. [5] The flexibility of the peptide backbone determines its ability to stretch which is important for proteins under mechanical stress.

Types of backbone


  1. "Glossary of basic terms in polymer science (IUPAC Recommendations 1996)" (PDF). Pure and Applied Chemistry. 68 (12): 2287–2311. 1996. doi:10.1351/pac199668122287. 
  2. Budgaard, Eva; Krebs, Frederik (2006). "Low band gap polymers for organic photovoltaics". Solar Energy Materials and Solar Cells. 91 (11): 954-985. 
  3. Polymers
  4. Brabec, C.J.; Winder, C.; Scharber, M.C; Sariciftci, S.N.; Hummelen, J.C.; Svensson, M.; Andersson, M.R. (2001). "Influence of disorder on the photoinduced excitations in phenyl substituted polythiophenes". J. Chem. Phys. 115: 7235. doi:10.1063/1.1404984. 
  5. Voet, Donald; Voet, Judith; Pratt, Charlotte (2013). Fundamentals of Biochemistry: Life at the Molecular Level (4th ed.). United States of America: John Wiley & Sons, Inc. p. 129-130. ISBN 978-0470-54784-7. 
  6. "Biochemistry. 5th edition.Section 3.2 Primary Structure: Amino Acids Are Linked by Peptide Bonds to Form Polypeptide Chains". NCBI Bookshelf. Retrieved 10 September 2015. 
  7. Hirsch, Andreas (1993). "Fullerene polymers". Advanced Materials. 5 (11): 859–861. doi:10.1002/adma.19930051116. 

See also