Nomenclature of
Polymerization Reaction by Addition
A polymer
is a substance composed of macromolecules, molecules that contain a very large
number of atoms and have a high molecular weight. Polymers need not be
homogeneous, and most are not. Even one as simple as polyethylene is a mixture
of macromolecules with different chain lengths and different degrees of
branching.
Although
the IUPAC has set forth rules for naming polymers according to structure, an
alternative IUPAC source-based system that names polymers according to the
monomers from which they are prepared is more widely used.
When the
name of the monomer is a single word, the polymer derived from it is generated
by simply adding the prefix poly-. (Acrylonitrile – Polyacrylonitrile)
When the
name of the monomer consists of two words, both words are enclosed in
parentheses immediately following poly. Thus, polyacrylonitrile and poly (vinyl
chloride) are the polymers of acrylonitrile and vinyl chloride respectively.
The
convention for writing polymer formulas is to enclose the repeating unit within
brackets, followed by the letter “n” to indicate that the number of repeating
units is not specified. It is, however, assumed to be large.
The
structural difference between the two is that the value of “n” is larger for
poly (ethylene oxide) than for poly (ethylene glycol). Therefore, their
physical properties are different and they are known by different source-based
names.
Many
polymers are routinely referred to by their common names or trade names.
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