Tetrafluoroethene (CF₂=CF₂) undergoes addition polymerisation to form poly(tetrafluoroethene), known as PTFE. Explain how addition polymerisation produces PTFE from tetrafluoroethene monomers, and describe two features of the polymer that are different from the monomer.

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

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

Model answer (5 marks)

During addition polymerisation the C=C double bond in CF₂=CF₂ breaks, allowing the monomer to add to the growing chain. Each new monomer joins the chain through a covalent bond, so many monomers link together to give a long polymer chain.

The resulting PTFE has no C=C double bonds – it is fully saturated – whereas the monomer is unsaturated.

The polymer also has a much larger molecular mass and a longer chain than the individual monomer.

Examiner tips

  • Use the term "breaks the C=C double bond" to show understanding of the mechanism. Mention covalent bonds and chain growth to hit the 3‑point requirement. Highlight the absence of double bonds and the increased mass for the two feature points.
  • common_mistakes
  • :
  • Forgetting to state that the double bond breaks. Describing the polymer as having double bonds. Not mentioning the increased molecular mass or chain length.

Mark scheme (5 marks)

  1. The C=C double bond in tetrafluoroethene breaks / opens during polymerisation
  2. Many monomers join together to form a long chain / large molecule
  3. The monomers are joined by covalent bonds
  4. The polymer contains no C=C double bonds / is saturated (whereas the monomer is unsaturated)
  5. The polymer has a much larger molecular mass / longer chain than the monomer

Key terms in this question

addition polymerisation · monomer · polymer

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