{{short description|Molecule which reacts with other monomers to form a polymer}}

A '''monomer''' ({{IPAc-en|ˈ|m|ɒ|n|ə|m|ər}} {{respell|MON|ə|mər}}; ''mono-'', "one" + ''-mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization.<ref>Young, R. J. (1987) ''Introduction to Polymers'', Chapman & Hall {{ISBN|0-412-22170-5}}</ref><ref>[http://goldbook.iupac.org/P04740.html International Union of Pure and Applied Chemistry, ''et al.'' (2000) ''IUPAC Gold Book'', '''Polymerization''']</ref><ref name="clayden_organic">{{Clayden|pages=1450–1466}}</ref>{{Quote box | title = IUPAC definition | quote = '''Monomer molecule''': A molecule which can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule.<ref>{{cite journal|title=Glossary of basic terms in polymer science (IUPAC Recommendations 1996)|journal=Pure and Applied Chemistry|year=1996|volume=68|issue=12|pages=2287–2311|doi=10.1351/pac199668122287|url=http://pac.iupac.org/publications/pac/pdf/1996/pdf/6812x2287.html|doi-access=free|last1=Jenkins|first1=A. D.|last2=Kratochvíl|first2=P.|last3=Stepto|first3=R. F. T.|last4=Suter|first4=U. W.}}</ref> | align = right | width = 30% }}

==Classification== Chemistry classifies monomers by type, and two broad classes based on the type of polymer they form.

By type: * natural vs synthetic, e.g. glycine vs caprolactam, respectively * polar vs nonpolar, e.g. vinyl acetate vs ethylene, respectively * cyclic vs linear, e.g. ethylene oxide vs ethylene glycol, respectively

By type of polymer they form: * those that participate in condensation polymerization * those that participate in addition polymerization

Differing stoichiometry<ref>{{cite book|title=An Introduction to Polymer Chemistry|publisher=Pergamon Press|year= 1967|author=D. Margerison |author2=G. C. East |author3=J. E. Spice |isbn=978-0-08-011891-8}}</ref> causes each class to create its respective form of polymer.

:[[Image:Condensation polymerization diacid diamine.svg|thumb|centre|600px|This nylon is formed by condensation polymerization 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 comonomers 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 (H<sub>2</sub>C=CH<sub>2</sub>) is the monomer for polyethylene. * Other modified ethylene derivatives include: **tetrafluoroethylene (F<sub>2</sub>C=CF<sub>2</sub>) which leads to Teflon **vinyl chloride (H<sub>2</sub>C=CHCl) which leads to PVC **styrene (C<sub>6</sub>H<sub>5</sub>CH=CH<sub>2</sub>) which leads to polystyrene * Epoxide monomers may be cross linked with themselves, or with the addition of a co-reactant, to form epoxy * BPA 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.<ref>Bruce Alberts, Alexander Johnson, Julian Lewis, Otin Raff, Keith Roberts, and Peter Walter, ''Molecular Biology of the Cell,'' 2008, Garland Science, {{ISBN|978-0-8153-4105-5}}.</ref>

==Natural monomers== Some of the main biopolymers are listed below:

===Amino acids=== For ''proteins'', the monomers are amino acids. Polymerization occurs at ribosomes. 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 nucleotides, 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.<ref>{{Cite journal|url = https://www.academia.edu/5082714|title = Biomolecules: Classification and structural properties of carbohydrates|website = Academia.edu|last = Ebuengan|first = Kaye}}</ref>

===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. Synthetic rubbers are often based on butadiene, which is structurally related to isoprene.

==See also== * Protein subunit * List of publications in polymer chemistry * Prepolymer

==Notes== {{Reflist}}

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Category:Monomers