Polymerisation

Polymerisation is the process in which many small molecules (monomers) join together to form a long-chain molecule called a polymer. This commonly occurs with alkenes, such as ethene (C2H4).

For example, when many ethene monomers join up, they form poly(ethene). Poly(ethene) does not contain double bonds ($C=C$); instead, the double bond in each monomer breaks to form single covalent bonds ($C-C$) that link the monomers into a continuous chain.

For addition polymerisation to take place, reaction conditions typically require high pressure, high temperature, or the presence of a catalyst or initiator.