A small, simple compond with low molecular weight, which can be joined with other identical components to form long chains, known as polymers. Two similar monomers joined together in a long chain is known as a copolymer, and 3 similar monomers, makes a terpolymer: for example , acrylonitirile butadiene styrene.
A monomer (from Greek mono "one" and meros "part") is a small molecule that may become chemically bonded to other monomers to form a polymer. The most common natural monomer is glucose, which is linked by glycosidic bonds into polymers such as cellulose and starch, and is over 76% of the weight of all plant matter.
Examples of synthetic monomers are hydrocarbons such as the alkine and arene homologous series. Here hydrocarbon monomers such as phenylethene and ethene form polymers used as plastics like polyphenylethene (commonly known as polystyrene) and polyethene (commonly known as polyethylene or polythene). Other commercially important monomers include acrylic monomers such as acrylic acid, methyl methacrylate, and acrylamide.
Amino acids are natural monomers and polymerize to form proteins. Nucleotides, monomers found in the cell nucleus, polymerize to form nucleic acids - most famously, DNA and RNA. Glucose monomers can polymerize to form starches, amylopectins and glycogen polymers. In this case the polymerization reaction is known as a dehydration or condensation reaction (due to the formation of water (H2O) as one of the products) where a hydrogen atom and a hydroxyl (-OH) group are lost to form H2O and an oxygen molecule bonds between each monomer unit.
Isoprene is a natural monomer and polymerizes to form natural rubber, most often cis-1,4-polyisoprene, but also trans-1,4-polyisoprene.
The lower molecular weight compounds built from monomers are also referred to as dimers, trimers, tetramers, pentamers, octamers, 20-mers, etc. if they have 2, 3, 4, 5, 8, or 20 monomer units, respectively. Any number of these monomer units may be indicated by the appropriate prefix, eg, decamer, being a 10-unit monomer chain or polymer. Larger numbers are often stated in English in lieu of Greek. Polymers with relatively low number of units are called oligomers.