Condensation Polymers and Addition PolymersAQA GCSE Chemistry: Revision notes
Section 1
What Is Addition Polymerisation?
Addition polymerisation happens when many small molecules called monomers join together to form one very large molecule called a polymer, with no other product formed.
Alkenes such as ethene can undergo addition polymerisation because they contain a reactive C=C double bond. During polymerisation, the double bonds open up and the monomers link into a long chain.
In an addition polymer, the repeating unit has exactly the same atoms as the monomer it came from — you can spot the monomer by looking at the repeating unit in the polymer's structure.
Addition polymers only need one type of monomer with a C=C double bond — no by-product is released.
Section 2
What Is Condensation Polymerisation? (Higher Tier)
In condensation polymerisation, monomers with two functional groups join together, and a small molecule — usually water — is lost at each new bond formed.
A classic example is the reaction between ethanediol and hexanedioic acid, which react to form a polyester, releasing water as the by-product at every link in the chain.
Because each monomer has two reactive ends, the chain can keep growing in both directions.
Ethanediol + hexanedioic acid → polyester + water (repeated many times along the chain).
Section 3
Addition vs Condensation Polymerisation
| Feature | Addition polymerisation | Condensation polymerisation |
|---|---|---|
| Monomer | One type, contains C=C | Usually two types, each with two functional groups |
| By-product | None | Small molecule, usually water |
| Example | Poly(ethene) from ethene | Polyester from ethanediol + hexanedioic acid |
Don't assume all polymerisation releases water — only condensation polymerisation does; addition polymerisation does not.
Section 4
How Do Amino Acids Form Proteins? (Higher Tier)
Amino acids are monomers that contain two different functional groups in the same molecule. This allows them to react by condensation polymerisation, joining together to form polypeptides.
Different amino acids can be combined in the same chain, and the specific sequence and combination of amino acids produces different proteins.
Section 5
What Is DNA?
DNA (deoxyribonucleic acid) is a large molecule essential for life, encoding genetic instructions. Most DNA molecules consist of two polymer chains made from four different monomers called nucleotides, arranged in a double helix shape.
DNA is one of several important natural polymers, alongside proteins (made from amino acids), starch and cellulose (made from sugar monomers).
Must Know
- Addition polymerisation: monomers with C=C join with no by-product; the repeating unit matches the monomer
- Condensation polymerisation (HT): monomers with two functional groups join, losing a small molecule (usually water) — e.g. ethanediol + hexanedioic acid → polyester
- Amino acids (HT) have two different functional groups and join by condensation polymerisation to form polypeptides, and ultimately proteins
- DNA is a natural polymer of four different nucleotides, arranged as two chains in a double helix
- Natural polymers include proteins, starch, cellulose and DNA
That's the notes covered.
Carry on to the next subtopic.