Propene can be used as a monomer to make the polymer poly(propene) by addition polymerisation. Describe the process of addition polymerisation and explain why propene, but not propane, can undergo this reaction.

AQA A-Level Chemistry (7405) — 3.3.12 Polymers (A-Level only) · Describe and Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Many small molecules (monomers) join together to form a very large molecule (polymer)
The monomers are joined by covalent bonds
No other product / no small molecule is lost – it is an addition reaction (nothing is given off)
Propene is unsaturated – it has a carbon–carbon double bond
The double bond in propene opens / breaks to allow monomers to join together; propane has no double bond so cannot react in this way

Examiner tips

  • Use the word ‘addition’ to show no small molecules are lost
  • Mention the double bond opening as the key step
  • Show that covalent bonds form between monomers
  • Explain why propane lacks a double bond

Common mistakes

  • Confusing addition with substitution, claiming a small molecule is lost
  • Forgetting to mention the double bond opening
  • Saying propane reacts because it has a single bond, ignoring lack of unsaturation

Mark scheme (5 marks)

  1. Many small molecules (monomers) join together to form a very large molecule (polymer)
  2. The monomers are joined by covalent bonds
  3. No other product / no small molecule is lost — it is an addition reaction (nothing is given off)
  4. Propene is unsaturated / has a carbon–carbon double bond
  5. The double bond in propene opens / breaks to allow monomers to join together; propane has no double bond so cannot react in this way

Key terms in this question

addition polymerisation · monomer · polymer

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