Nylon is a condensation polymer made from two different monomers. Explain how condensation polymerisation differs from addition polymerisation, and describe two features of the monomers required to form a condensation polymer such as nylon.

OCR A-Level Chemistry B: Salters (H433) — 6.2 Nitrogen compounds, polymers and synthesis · Explain · 5 marks · View as Markdown

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

Nylon is a synthetic polymer widely used in clothing and engineering components. It is produced by condensation polymerisation.

Model answer (5 marks)

In condensation polymerisation a small molecule (e.g. H₂O) is released as the monomers join, whereas in addition polymerisation no small molecule is lost and all atoms of the monomers become part of the polymer.

Condensation polymerisation requires each monomer to possess two different functional groups so that they can react with each other. Two distinct monomers are used – for nylon a diamine and a dicarboxylic acid – allowing linkage at both ends and the growth of a long chain.

These features – loss of a small molecule and the need for two functional groups on each monomer – distinguish condensation from addition polymerisation.

Examiner tips

  • State the loss of a small molecule first to secure the key point. Mention the two functional groups and the two monomer types to hit the remaining marks. Use the exact wording ‘condensation polymerisation’ and ‘addition polymerisation’ as in the mark scheme.
  • common_mistakes
  • :
  • Confusing the small molecule with a catalyst or ignoring the requirement for two functional groups. Using the wrong monomer types (e.g. two alkenes) or failing to mention the loss of water.

Mark scheme (5 marks)

  1. In condensation polymerisation, a small molecule (such as water) is lost/released when monomers join together
  2. In addition polymerisation, no small molecule is lost / all atoms from the monomers are incorporated into the polymer
  3. Addition polymerisation uses monomers with a carbon–carbon double bond (alkenes / unsaturated monomers)
  4. Condensation polymerisation requires monomers that each have two functional groups
  5. Two different types of monomer are used (e.g. a diamine and a dicarboxylic acid) so that linking at both ends builds the long chain

Key terms in this question

condensation polymerisation · addition polymerisation · monomers · polymer

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