polymerization

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 union of two or more (usually small) molecules of the same kind to form a new compound. Addition polymerization produces simple multiples of the same compound. The new bonds are formed at the expense of a double bond in the monomer which is converted to a single bond. Condensation polymerization joins molecules together with the elimination of water or another small molecule.

Addition polymerization typically uses only a single monomer (basic molecule); condensation polymerization may involve two or more different monomers (co-polymerization). Proteins are formed by condensation of amino acids.