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. Condensation polymerization joins molecules together with the elimination of water or another small molecule.

Addition polymerization uses only a single monomer (basic molecule); condensation polymerization may involve two or more different monomers (co-polymerization).