AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
When these types of monomers react they join together, usually losing…
Full specification wording
Condensation polymerisation (HT only): When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions.
In condensation polymerisation, monomers that each carry at least two reactive functional groups link repeatedly to form a polymer.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 4
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In condensation polymerisation, monomers that each carry at least two reactive functional groups link repeatedly to form a polymer. As each new bond forms between monomer units, a small molecule is eliminated, most commonly water. For example, when a carboxylic acid group reacts with an alcohol group, an ester link forms and one water molecule is released per link. The word condensation signals this loss of a small molecule, distinguishing the process from addition polymerisation, where monomers join without losing anything. The small molecule is not a side product of the whole reaction only; it is expelled at every joining step, so the polymer repeat unit contains fewer atoms than the sum of the monomer fragments that formed it.
What earns the marks
- Monomers must have at least two functional groups so that chains can grow in two directions.
- Each linking step forms a new covalent bond between monomer units.
- A small molecule, commonly water, is eliminated at each link formed.
- The reaction is called condensation because of this loss of a small molecule.
- The polymer repeat unit has fewer atoms than the combined monomer fragments because of the eliminated molecules.
- Polyester formation from a diol and a dicarboxylic acid is a valid example of this process.
Common mistakes and how to put them right
Thinking that water is lost only once for the whole polymer.
Put it right by stressing that one small molecule is lost per new link formed.
Confusing condensation with addition polymerisation.
Put it right by noting that addition polymerisation loses no small molecule.
Assuming any monomer can undergo condensation polymerisation.
Put it right by requiring two functional groups per monomer.
Exam tips
- State clearly which small molecule is eliminated and why it is eliminated.
- Use the phrase 'loss of a small molecule' when explaining the name condensation.
- Link the functional groups present to the type of link formed, such as ester links from alcohol and carboxylic acid groups.
Try the lesson
The start of the Condensation polymerisation (HT only): When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions. lesson, made from checked teaching notes for this specification point.
Have a go first
In a condensation polymerisation, two monomer molecules react together and a molecule of water is released. What name is given to the small molecule that is released in this way?
Listen
In condensation polymerisation, monomers that each carry at least two reactive functional groups link repeatedly to form a polymer. As each new bond forms between monomer units, a small molecule is eliminated, most commonly water. For example, when a carboxylic acid group reacts with an alcohol group, an ester link forms and one water molecule is released per link. The word condensation signals this loss of a small molecule, distinguishing the process from addition polymerisation, where monomers join without losing anything. The small molecule is not a side product of the whole reaction only; it is expelled at every joining step, so the polymer repeat unit contains fewer atoms than the sum of the monomer fragments that formed it. A strong answer earns marks for these points. Monomers must have at least two functional groups so that chains can grow in two directions. Each linking step forms a new covalent bond between monomer units. A small molecule, commonly water, is eliminated at each link formed. The reaction is called condensation because of this loss of a small molecule. A common slip: Thinking that water is lost only once for the whole polymer. Instead, stressing that one small molecule is lost per new link formed. Exam tip: State clearly which small molecule is eliminated and why it is eliminated.
Key words
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Condensation reactions
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Elimination of small molecules
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See every definition
- Condensation reactions
- Reactions in which monomers join together, usually losing small molecules such as water.
- Elimination of small molecules
- A small molecule, commonly water, is lost at each link formed as a new covalent bond forms between monomer units.
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