Addition polymerisation — AQA GCSE Chemistry
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Addition polymerisation explained
Addition polymerisation is the process in which many small unsaturated alkene molecules, called monomers, join together to form a large saturated molecule called a polymer.
Read the full explanation
The monomers contain a carbon-carbon double bond, which opens up during the reaction. For example, ethene monomers join to form poly(ethene), and propene monomers join to form poly(propene). The polymer is the only product, so no other small molecule is eliminated. You should be able to recognise the repeat unit in a polymer structure, draw the repeat unit from a given monomer, and identify the monomer from a given polymer. The general equation can be represented as n monomer → polymer, where n is a large number. The double bond becomes a single bond in the polymer chain.
Your focus
- Describe addition polymerisation as the joining of unsaturated monomers to form a polymer.
- Draw the repeat unit of poly(ethene) and poly(propene) from their monomers.
- Identify the monomer from a given addition polymer structure.
Addition polymerisation exam tips
Marking Points
- Define addition polymerisation as the joining of many unsaturated monomer molecules to form a polymer.
- Identify ethene and propene as monomers used to make poly(ethene) and poly(propene).
- Recognise the carbon-carbon double bond in an alkene monomer and explain that it opens during polymerisation.
- Draw or identify the repeat unit of a polymer from a given monomer structure.
- Identify the monomer from a given polymer structure by locating the two-carbon repeat unit and restoring the double bond.
Examiner Tips
- 💡When drawing a repeat unit, show the two carbon atoms of the original double bond with single bonds and extend the bonds through the brackets.
- 💡Check that the polymer repeat unit has the same atoms as the monomer, with no atoms added or removed.
- 💡Use the name of the monomer to derive the polymer name, for example ethene gives poly(ethene).
Common Mistakes
- Drawing the repeat unit with a double bond still present; correct by showing a single bond between the carbon atoms in the polymer backbone.
- Omitting the 'n' or placing it inside the brackets; correct this by placing the repeat unit in brackets with a subscript 'n' outside to show many units join.
- Confusing addition polymerisation with condensation polymerisation; correct by noting that addition polymerisation produces only the polymer, whereas condensation polymerisation produces a small molecule such as water as well.