- Repeat unit
An essential concept which defines
polymer structure, the repeat unit is the simplest structural unit of apolymer chain . So a polymer consists of repeat units linked together, like the beads of a necklace. One of the simplest repeat units is that ofpolyethylene :- [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 theatomic mass es of theatom s within the repeat unit. The molecular mass of the chain is just the product nMR. Other thanmonodisperse polymers, there is normally amolar mass distribution caused by chains of different length.Vinyl Polymers
More complex repeat units occur in
vinyl polymer s, where one of thehydrogen atom s is substituted by another different atom, or by a larger fragment. SoPVC for example possesses a chain in which the hydrogen atom is substituted by achlorine atom:- [CH2-CHCl] n-
Polystyrene has a chain where the substituent is aphenyl group (C6H5), corresponding to a benzene ring minus one hydrogen:- [CH2-CH(C6H5)] n-
ee also
*
Copolymers
*Polymers References
* [http://openlearn.open.ac.uk/mod/resource/view.php?id=196629 Structure of polymer chains]
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