monomer

In polymerization, small molecules (monomers) join together to make large molecules (polymers). In the polymerization of ethene to polyethene (polythene), electrons are transferred from the carbon–carbon double bond of the ethene molecule, allowing the molecules to join together as a long chain of carbon–carbon single bonds.

Chemical compound composed of simple molecules from which polymers can be made. Under certain conditions the simple molecules (of the monomer) join together (polymerize) to form a very long chain molecule (macromolecule) called a polymer. For example, the polymerization of ethene (ethylene) monomers produces the polymer polythene (polyethylene):

2nCH₂ CH₂→(CH₂CH₂ CH₂CH₂)_n

Large biomolecules are also assembled from monomers, for example proteins from amino acids, and starch from glucose. On a higher structural level, an entire protein can serve as a monomer for the assembly of complex molecular structures, for example in haemoglobin, where four identical protein subunits form a tetramer.