A monomer ( ; , "one" + , "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.[Young, R. J. (1987) Introduction to Polymers, Chapman & Hall ][ International Union of Pure and Applied Chemistry, et al. (2000) IUPAC Gold Book, Polymerization]
Classification
Chemistry classifies monomers by type, and two broad classes based on the type of
polymer they form.
By type:
By type of polymer they form:
-
those that participate in condensation polymerization
-
those that participate in addition polymerization
Differing stoichiometry
- of two monomers, yielding water]]
The polymerization of one kind of monomer gives a homopolymer. Many polymers are copolymers, meaning that they are derived from two different monomers. In the case of condensation polymerizations, the ratio of is usually 1:1. For example, the formation of many nylons requires equal amounts of a dicarboxylic acid and diamine. In the case of addition polymerizations, the comonomer content is often only a few percent. For example, small amounts of 1-octene monomer are copolymerized with ethylene to give specialized polyethylene.
Synthetic monomers
-
Ethylene gas (H2C=CH2) is the monomer for polyethylene.
-
Other modified ethylene derivatives include:
-
Epoxide monomers may be cross linked with themselves, or with the addition of a co-reactant, to form epoxy
-
Bisphenol A is the monomer precursor for polycarbonate
-
Terephthalic acid is a comonomer that, with ethylene glycol, forms polyethylene terephthalate.
-
Dimethylsilicon dichloride is a monomer that, upon hydrolysis, gives polydimethylsiloxane.
-
Ethyl methacrylate is an acrylic monomer that, when combined with an acrylic polymer, catalyzes and forms an acrylate plastic used to create artificial nail extensions
Biopolymers
The term "monomeric
protein" may also be used to describe one of the proteins making up a multiprotein complex.
[Bruce Alberts, Alexander Johnson, Julian Lewis, Otin Raff, Keith Roberts, and Peter Walter, Molecular Biology of the Cell, 2008, Garland Science, .]
Natural monomers
Some of the main
are listed below:
Amino acids
For
proteins, the monomers are
. Polymerization occurs at
. Usually about 20 types of amino acid monomers are used to produce proteins. Hence proteins are not homopolymers.
Nucleotides
For polynucleic acids (
DNA/
RNA), the monomers are
, each of which is made of a
pentose sugar, a nitrogenous base and a phosphate group. Nucleotide monomers are found in the
cell nucleus. Four types of nucleotide monomers are precursors to DNA and four different nucleotide monomers are precursors to RNA.
Glucose and related sugars
For carbohydrates, the monomers are monosaccharides. The most abundant natural monomer is
glucose, which is linked by
glycosidic bonds into the polymers
cellulose,
starch, and
glycogen.
Isoprene
Isoprene is a natural monomer that polymerizes to form a
natural rubber, most often
cis-1,4-polyisoprene, but also
trans-1,4-polymer.
are often based on
butadiene, which is structurally related to isoprene.
See also
Notes
