Describe how addition polymers are formed from alkene monomers and explain why the resulting polymer is chemically unreactive compared to the monomer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Poly(propene) is an addition polymer widely used to make plastic containers and rope fibres. It is formed from propene monomers.
Model answer (5 marks)
Alkene monomers contain a carbon–carbon double bond (C=C). During polymerisation the double bond opens, breaking the C=C bond. The monomers join together to give a repeat unit, forming a long chain polymer. The resulting polymer has only carbon–carbon single bonds (C–C) in its backbone – no C=C double bonds remain. Carbon–carbon single bonds are strong and do not react easily with other reagents, so the polymer is chemically unreactive and does not undergo addition reactions.
Examiner tips
- State the presence of a C=C bond in the monomer
- Explain that the double bond opens during polymerisation
- Mention that the polymer backbone contains only C–C bonds
- Link the lack of C=C bonds to the polymer’s chemical inertness
Common mistakes
- Confusing the polymerisation mechanism with a radical chain reaction without mentioning the opening of the double bond
- Failing to note that the polymer contains only C–C bonds
- Claiming the polymer reacts readily with reagents instead of explaining its inertness
Mark scheme (5 marks)
- Alkene monomers contain a carbon–carbon double bond (C=C)
- The double bond opens / breaks during polymerisation
- Monomers join together in a repeat unit to form a long chain polymer
- The polymer has only carbon–carbon single bonds (C–C) in its backbone / no C=C double bonds remain
- Carbon–carbon single bonds are strong / do not react easily with other reagents, so the polymer is chemically unreactive / does not undergo addition reactions
Key terms in this question
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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