Addition polymerisation
- Alkenes can join together to form very large molecules called polymers. This is addition polymerisation.
- The small molecules are monomers. The double bond opens and the monomers join in a long chain.
- Ethene makes poly(ethene); propene makes poly(propene).
- In the repeating unit, the atoms are the same as in the monomer, but the C=C becomes a single bond with bonds extending on either side.
Condensation polymerisation (Higher)
- Condensation polymerisation uses monomers with two functional groups each.
- When they react, they join together and lose small molecules, such as water.
- Example: a diol (two –OH groups) and a dicarboxylic acid (two –COOH groups) make a polyester and water.
Amino acids and proteins (Higher)
- Amino acids have two different functional groups: an amine group (–NH₂) and a carboxylic acid group (–COOH).
- Amino acids react by condensation polymerisation to form polypeptides; one molecule of water is lost for each bond formed.
- Different amino acids can be combined in the same chain to make proteins. Glycine is the simplest amino acid.
Natural polymers
- DNA is made of two polymer chains of nucleotides that form a double helix.
- Proteins are polymers of amino acids.
- Starch and cellulose are polymers of sugars (glucose).
Key terms
- Polymer
- A very large molecule made by joining many small molecules (monomers).
- Monomer
- A small molecule that joins with others to make a polymer.
- Addition polymerisation
- Joining alkene monomers by opening their double bonds.
- Repeating unit
- The part of a polymer that repeats along the chain.
- Condensation polymerisation
- Joining monomers with two functional groups, with a small molecule such as water lost.
- Polyester
- A condensation polymer made from a diol and a dicarboxylic acid.
- Amino acid
- A molecule with an amine group and a carboxylic acid group; the monomer of proteins.
- Polypeptide
- A chain of amino acids.