Repeat unit

Repeat unit

An essential concept which defines polymer structure, the repeat unit is the simplest structural unit of a polymer chain. So a polymer consists of repeat units linked together, like the beads of a necklace. One of the simplest repeat units is that of polyethylene:

- [CH2-CH2-] n-

while polypropylene has the repeat unit

- [CH2-CH(CH3)] n-

The subscript "n" denotes the degree of polymerisation, that is, the number of units linked together. The molecular mass of the repeat unit, MR, is simply the sum of the atomic masses of the atoms within the repeat unit. The molecular mass of the chain is just the product nMR. Other than monodisperse polymers, there is normally a molar mass distribution caused by chains of different length.

Vinyl Polymers

More complex repeat units occur in vinyl polymers, where one of the hydrogen atoms is substituted by another different atom, or by a larger fragment. So PVC for example possesses a chain in which the hydrogen atom is substituted by a chlorine atom:

- [CH2-CHCl] n-

Polystyrene has a chain where the substituent is a phenyl group(C6H5), corresponding to a benzene ring minus one hydrogen:

- [CH2-CH(C6H5)] n-

ee also



* [ Structure of polymer chains]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • repeat unit — noun a specific arrangement of atoms that repeats within a macromolecule …   Wiktionary

  • repeat unit — A sequence of nucleotides that occurs repeatedly, often in a head to tail arrangement (tandemly) …   Glossary of Biotechnology

  • Structural unit — In polymer chemistry, a structural unit is a building block of a polymer chain, and related to the repeat unit. It is the result of a monomer which has been polymerized into a long chain. When different monomer are polymerized, a copolymer is… …   Wikipedia

  • Leucine-rich repeat — Pfam box Symbol = LRR 1 Name = width = caption = An example of a leucine rich repeat protein, a porcine ribonuclease inhibitor Pfam= PF00560 InterPro= IPR001611 SMART= Prosite = SCOP = 1bnh TCDB = OPM family= OPM protein= 1xwd PDB=PDB3|1ogqA:155… …   Wikipedia

  • inter-simple sequence repeat — Abbreviation: ISSR A PCR based molecular marker assay of genomic sequence lying between adjacent microsatellites. Primers carrying, at their 3 end, sequence complementary to the repeat unit of the microsatellite will amplify this genomic DNA …   Glossary of Biotechnology

  • Pleasure Unit — Our Man Flint= Pleasure Unit is the name of several fictional characters in the 1966 sci fi action film Our Man Flint .The trio of mad scientists who lead Galaxy, Dr. Schneider (played by Benson Fong), Dr. Krupov (played by Rhys Williams), and Dr …   Wikipedia

  • Ankyrin repeat — The ankyrin repeat is a 33 residue motif in proteins consisting of two alpha helices separated by loops, first discovered in signaling proteins in yeast Cdc10 and Drosophila Notch. Ankyrin repeats mediate protein protein interactions and are… …   Wikipedia

  • Selective Repeat ARQ — is a specific instance of the Automatic Repeat reQuest (ARQ) Protocol. It may be utilized as a protocol for the delivery and acknowledgement of message units, or it may be utilized as a protocol for the delivery of subdivided message sub… …   Wikipedia

  • Systeme unit (orgue) — Système unit (orgue) Système appliqué aux orgues à tuyaux qui consiste à utiliser non pas strictement 61 tuyaux pour un jeu (c’est à dire un tuyau par note), mais à multiplier les jeux à partir d une même série de tuyaux. C est le cas des Baby… …   Wikipédia en Français

  • Système unit (orgue) — Le Système unit est un système appliqué aux orgues à tuyaux, qui consiste à utiliser non pas strictement 61 tuyaux pour un jeu (c’est à dire un tuyau par note), mais à multiplier les jeux à partir d une même série de tuyaux[1]. C est le cas des… …   Wikipédia en Français

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”