polymerization

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.