Facts about plastics:
Polythene (polyethene) is made by forming a long chain of ethene molecules. Many other compounds are made in a similar way. A compound made like this is called a polymer.
Polymers are long chains of monomers. A monomer is the building block or in other words the repeating unit that is used to make the polymer. In the above example, ethene is the monomer and polythene the polymer.
Polystyrene (many styrene molecules) is another well-known polymer.
Many polymers can be easily moulded into many shapes - these are called plastics.
Polymerisation is the name given to the reaction that produces polymers.
Remember: alkenes can become polymers but alkanes cannot. This is because alkanes are saturated whereas alkenes are unsaturated which means that they can carry out addition reactions, required for polymerisation.
This type of polymerisation is called addition polymerisation.