Condensation polymerisation (HT only) — AQA GCSE Chemistry
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Condensation polymerisation (HT only) explained
The simplest condensation polymers form when two different monomers each carry two identical functional groups.
Read the full explanation
One monomer might be a diol with two alcohol groups, and the other a dicarboxylic acid with two carboxylic acid groups. Because each monomer has two reactive groups, it can bond at both ends, allowing a long chain to build up. If a monomer had only one functional group, chain growth would stop after one link. Using two different monomers with matching pairs of groups gives a regular alternating pattern in the polymer chain. This is why the simplest polyesters are made from pairs such as a diol and a dicarboxylic acid, reacting to form ester links and water.
Your focus
- Identify monomers with two identical functional groups.
- Explain how two functional groups per monomer enable polymer chain growth.
- Recognise diols and dicarboxylic acids as suitable monomer pairs.
Condensation polymerisation (HT only) exam tips
Marking Points
- Two different monomers are used in the simplest condensation polymers.
- Each monomer has two of the same functional group.
- A diol has two alcohol groups and a dicarboxylic acid has two carboxylic acid groups.
- Two functional groups per monomer allow chain growth in two directions.
- A monomer with only one functional group would terminate chain growth.
- The resulting polymer has an alternating pattern of the two monomer units.
Examiner Tips
- 💡Name the functional groups present on each monomer before predicting the polymer.
- 💡Check that each monomer has two reactive sites before describing chain growth.
- 💡Use 'diol' and 'dicarboxylic acid' accurately when giving examples.
Common Mistakes
- Thinking the two functional groups on a monomer must be different: correct this by noting they are the same on each monomer in the simplest case.
- Believing one functional group per monomer is enough: correct this by explaining that chain growth needs two reactive sites.
- Assuming the two monomers must be identical: correct this by stating that two different monomers are used.