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. Examples of monomers are hydrocarbons such as the alkene 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. Glucose monomers can also 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. The lower molecular weight compounds built from monomers are also referred to as dimers, trimers, tetramers, quadramers, 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.
