GCSE Chemistry · AQA 8462 · Topic 4.7.3
Synthetic and naturally occurring polymers
Key points
- Addition polymerisation: many small alkene monomers join to form a long chain, and nothing else is made. E.g. many ethene → poly(ethene).
- The repeating unit is drawn in brackets with the C=C replaced by C–C and bonds extending out, followed by 'n'.
- Condensation polymerisation (Higher) involves monomers with two functional groups. When they join, a small molecule such as water is lost.
- The simplest example joins a diol and a dicarboxylic acid to make a polyester.
- Amino acids have an amine group and a carboxylic acid group, so they can join by condensation polymerisation to make polypeptides and proteins.
- Naturally occurring polymers: DNA (two polymer strands of four different nucleotides in a double helix), proteins (amino acids), starch and cellulose (both from sugars).
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Polymers are very long molecules made by joining many small molecules called monomers. Some are made in factories from alkenes; others, such as DNA, proteins, starch and cellulose, are made in living things.
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