Chloroethene (CH₂=CHCl) is a monomer that undergoes addition polymerisation to form poly(chloroethene), also known as PVC. Describe the process of addition polymerisation and explain what happens to the double bond in chloroethene monomers during this process.

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

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

Poly(chloroethene), commonly known as PVC, is a widely used polymer made from the monomer chloroethene. Chloroethene contains a carbon-carbon double bond.

Model answer (5 marks)

Addition polymerisation involves many small monomer molecules joining to form one very large polymer chain. The monomers are linked by new covalent bonds. In chloroethene the carbon–carbon double bond opens up, breaking the π‑bond. Each carbon then forms a single bond with a carbon of the next monomer, leaving a single C–C bond in the polymer. No other small molecules are produced – the reaction is a simple addition.

Examiner tips

  • Use the word ‘addition’ to show you know the type of polymerisation. Mention that the double bond opens and a single bond is formed. State that no other products are formed.
  • common_mistakes
  • :
  • Confusing addition with condensation and claiming water is produced. Forgetting to say the double bond opens. Using vague terms like ‘reacts’ without describing the bond change.

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. The carbon-carbon double bond in chloroethene breaks open / opens up
  4. A single bond remains / is left between the two carbon atoms (after the double bond opens)
  5. No other products / small molecules are formed (addition polymerisation produces only the polymer)

Key terms in this question

addition polymerisation · monomer · polymer · double bond

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