Explain how condensation polymerisation produces a polyester, including the type of monomers required and the small molecule that is lost during the reaction.

AQA GCSE Chemistry (8462) — 4.7.3 Synthetic and naturally occurring polymers (Chem only) · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Monomers used in condensation polymerisation must each contain two reactive functional groups – a dicarboxylic acid and a diol (or two different groups such as –COOH and –OH). During the reaction the –COOH of the acid reacts with the –OH of the diol, forming an ester linkage and joining the monomers into a long chain. Each step releases a small molecule – water – which is removed from the reaction mixture. The resulting polymer chain therefore contains ester bonds in its main chain, making it a polyester.

Examiner tips

  • State the two functional groups on the monomers; link them to the formation of ester bonds.
  • Explain that water is the small molecule lost and why it is removed.
  • Show the chain‑forming step – monomers join to give a long polymer.
  • Use the term ‘polyester’ to describe the final product.

Common mistakes

  • Failing to mention that both monomers must have two reactive groups.
  • Confusing the small molecule lost with CO₂ or other gases.
  • Not identifying the ester linkage as the key feature of a polyester.

Mark scheme (4 marks)

  1. Monomers must have two functional groups (dicarboxylic acid and a diol / two different functional groups)
  2. Monomers join together / react to form a long polymer chain
  3. A small molecule — water — is lost / released during the reaction
  4. The polymer contains the ester functional group / ester linkages in its main chain, making it a polyester

Key terms in this question

condensation polymerisation · polyester · monomers

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