Terylene is a condensation polymer used to make clothing and plastic bottles. It is formed from benzene-1,4-dicarboxylic acid and ethane-1,2-diol. Explain how Terylene is formed and describe one structural feature that makes it a condensation polymer rather than an addition polymer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Terylene (also known as PET) is widely used in the textile and packaging industries. Unlike addition polymers such as poly(ethene), Terylene is produced by a condensation polymerisation reaction between two different monomer molecules.
Model answer (5 marks)
Terylene is produced by a condensation polymerisation in which benzene‑1,4‑dicarboxylic acid (terephthalic acid) and ethane‑1,2‑diol (ethylene glycol) react.
1. Each terephthalic acid molecule has two –COOH groups, each glycol has two –OH groups.
2. The –COOH of one monomer reacts with the –OH of the other, forming an ester linkage and releasing a molecule of water.
3. Repeating this step gives a chain of –[–COO–CH₂CH₂–O–]– units.
4. The repeat unit contains atoms from both monomers and is smaller than the sum of the two monomers because water is lost.
5. Thus Terylene is a condensation polymer, not an addition polymer, because each repeat unit is formed by loss of water.
1. Each terephthalic acid molecule has two –COOH groups, each glycol has two –OH groups.
2. The –COOH of one monomer reacts with the –OH of the other, forming an ester linkage and releasing a molecule of water.
3. Repeating this step gives a chain of –[–COO–CH₂CH₂–O–]– units.
4. The repeat unit contains atoms from both monomers and is smaller than the sum of the two monomers because water is lost.
5. Thus Terylene is a condensation polymer, not an addition polymer, because each repeat unit is formed by loss of water.
Examiner tips
- Use the word ‘condensation polymerisation’ and mention water loss explicitly. Show the ester linkage and the two monomers’ functional groups. Explain that the repeat unit is smaller than the monomers.
- common_mistakes
- :
- Saying the polymer is formed by addition rather than condensation. Forgetting to mention the loss of water. Not recognising that the repeat unit contains atoms from both monomers.
Mark scheme (5 marks)
- Condensation polymerisation involves monomers joining together with the loss of a small molecule
- The small molecule lost is water (or HCl in other condensation reactions, but here specifically water)
- One monomer provides carboxylic acid (–COOH) functional groups and the other provides hydroxyl (–OH) functional groups
- The two functional groups react to form an ester linkage / ester bond between the monomers
- Unlike addition polymers, the repeat unit of Terylene contains atoms from two different monomer molecules / the repeat unit is smaller than the combined monomers because atoms are lost as water
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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