Propene (C₃H₆) is an alkene. Explain how propene can be used to make poly(propene), including why propene is able to undergo this reaction.

Edexcel A-Level Chemistry (9CH0) — 6.3 Alkenes · Explain · 5 marks · View as Markdown

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

Alkenes are unsaturated hydrocarbons containing a carbon-to-carbon double bond. They can be used as monomers to form addition polymers.

Model answer (5 marks)

Propene (C₃H₆) has a C=C double bond. In addition polymerisation the double bond opens, forming two new single bonds. Many propene molecules join together through these new bonds, creating a long chain of –CH₂–CH(CH₃)– units. The reaction is called addition polymerisation and no small molecules are released; the only products are the polymer chains.

Examiner tips

  • State the presence of the C=C bond first
  • Explain that the double bond opens during polymerisation
  • Mention that many monomers join to form a chain
  • Use the term ‘addition polymerisation’

Common mistakes

  • Forgetting to mention the opening of the double bond
  • Using the term ‘substitution polymerisation’ instead of ‘addition’
  • Claiming that small molecules are released

Mark scheme (5 marks)

  1. Propene contains a carbon-to-carbon double bond (C=C)
  2. The double bond opens / breaks during the reaction (addition polymerisation)
  3. Many monomers (propene molecules) join together
  4. The process is called addition polymerisation
  5. No other product / no small molecule is released during the reaction

Key terms in this question

alkene

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