A sportswear manufacturer is researching materials for a new range of lightweight clothing. They are considering using a polyamide produced by condensation polymerisation from two monomers: a diamine and a dicarboxylic acid. Explain how the structure of these monomers allows condensation polymerisation to occur, and describe what happens to the small molecules produced during the reaction.

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).

Polyamides are condensation polymers widely used in performance sportswear. They are formed from monomers that each contain two functional groups.

Model answer (5 marks)

Each monomer contains two reactive groups. The diamine has two –NH₂ groups, one at each end, and the dicarboxylic acid has two –COOH groups, one at each end. When the two monomers react, an –NH₂ group attacks a –COOH group, forming a –CO–NH– linkage and releasing a water molecule. Because each monomer has two groups, the reaction can continue at both ends, producing a long chain. The small molecule that is eliminated each time a bond forms is water, and the bond formed is an amide (peptide) bond, giving a polyamide.

Examiner tips

  • Mention the two functional groups on each monomer and the –CO–NH– bond formed
  • Explain that water is the small molecule eliminated
  • Show that both ends can react, allowing chain growth

Common mistakes

  • Forgetting that both monomers have two groups
  • Saying the small molecule is CO₂ instead of water
  • Not specifying that the bond is an amide (peptide) bond

Mark scheme (5 marks)

  1. Each monomer has two functional groups
  2. The diamine provides two amine (–NH₂) functional groups and the dicarboxylic acid provides two carboxyl (–COOH) functional groups
  3. Having two functional groups on each monomer allows bonds to form at both ends, enabling a long chain polymer to grow
  4. A small molecule (water) is lost / eliminated each time a bond forms between two monomers
  5. The bond formed between the monomers is a peptide / amide bond (–CO–NH–), forming a polyamide

Key terms in this question

condensation polymerisation · monomers · diamine · dicarboxylic acid · polyamide

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