Addition polymerisation

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.

Ethene molecules make long polyethene molecules.Forming poly(ethene) from ethene

The reaction is called a polymerisation reaction:

  • ethene is the monomer
  • poly(ethene) is the polymer

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.

Structures of a monomer and polymer including covalent bonds.

Poly(chloroethene) is commonly known by the initials of its old name, PVC (poly vinyl chloride). Poly(chloroethene) is made by polymerising chloroethene.

Modelling addition polymerisation - Higher tier

Equations use repeating units to model addition polymerisation reactions. The letter n stands for a large number.

Structure shift from ethene to poly(ethene) and choloroethene to poly(chloroethene).