A student wants to make a polymer from but-1-ene (CH₂=CHCH₂CH₃) using addition polymerisation. Explain what happens during addition polymerisation and describe the structure of the repeat unit that would be produced from this monomer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
But-1-ene is an alkene with the molecular formula C₄H₈. It can be used as a monomer in addition polymerisation.
Model answer (5 marks)
In addition polymerisation many small monomer molecules join to give a large long‑chain polymer.
The double bond of but‑1‑ene opens during the reaction.
The opened double bond allows covalent bonds to form between monomer units, so the monomers link together via C–C single bonds.
No other product is formed – no small molecule is lost or released.
The repeat unit contains four carbon atoms: a chain of four carbons with only single bonds between them and hydrogen atoms attached, with no double bond present.
The double bond of but‑1‑ene opens during the reaction.
The opened double bond allows covalent bonds to form between monomer units, so the monomers link together via C–C single bonds.
No other product is formed – no small molecule is lost or released.
The repeat unit contains four carbon atoms: a chain of four carbons with only single bonds between them and hydrogen atoms attached, with no double bond present.
Examiner tips
- Use the term ‘addition polymerisation’ and emphasise the opening of the double bond.
- Show that the repeat unit is a saturated chain of four carbons – the same as the monomer but with all single bonds.
- Mention that no small molecule is released – this is a key point in the mark scheme.
- Keep the answer concise – 5 marks can be earned with 5 short points.
Common mistakes
- Writing that the polymer contains double bonds – the repeat unit is saturated.
- Saying that a small molecule is released (e.g. H₂) – addition polymerisation does not produce a by‑product.
- Using vague wording such as ‘the monomers join together’ without specifying covalent bonds or the opening of the double bond.
Mark scheme (5 marks)
- Many small molecules (monomers) join together to form a polymer / large long-chain molecule
- The double bond in but-1-ene opens / breaks during the reaction
- The opened double bond allows covalent bonds to form between monomer units / monomers link together via covalent bonds
- No other product / no small molecule is lost / nothing is released
- The repeat unit contains four carbon atoms / a chain of four carbons with only single bonds between them and hydrogen atoms attached, with no double bond present
Key terms in this question
addition polymerisation · monomer · polymer · repeat unit
Related
- All AQA A-Level Chemistry (7405) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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