A polymer is a long chain molecule made up of small, repeating units.
Poly(ethene) is a polymer made from a very large number of ethene molecules bonded together.
The reaction is called a polymerisation reaction:
The number of molecules (n) joining up is variable, but is in the region of 2000 to 20000.
The C=C double bond in ethene is involved in the polymerisation reaction. It allows ethene molecules to join, so it is an example of an addition reaction>. Poly(ethene) is an addition polymer.
The table shows the structure of ethene and its polymer.
Poly(chloroethene) is commonly known by the initials of its old name, PVC (poly vinyl chloride). Poly(chloroethene) is made by polymerising chloroethene.
Equations use repeating units to model addition polymerisation reactions. The letter n stands for a large number.