Polymerisation

Polymer literally means 'many parts'. Many repeating units called monomers join together to make a long chain polymer molecule.

Ethene is the monomer that is used to make the polymer called polythene (a shortened version of poly-ethene). This process is called addition polymerisation. Ethene belongs to a group of chemicals called alkenes that can be used as monomers because they are unsaturated (they have a double bond).

Plasticisers are chemicals that are used to soften polymers whereas cross-linking agents can strengthen them.