Addition Polymerisation
Revise Addition Polymerisation for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) chemistry topic: many alkene monomers join with no other product to form an addition polymer such as poly(ethene).
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Topic overview
Addition polymerisation joins many small unsaturated monomer molecules together to form a very long polymer molecule. This is a Triple-only topic.
The monomers must contain a carbon-carbon double bond. During the reaction that double bond opens, and the monomers join to each other in a long chain. The polymer is the only product — nothing else is formed.
Because the double bond opens rather than breaking completely, the repeating unit has the same atoms as the monomer. Ethene forms poly(ethene), and propene forms poly(propene). The repeating unit is drawn in brackets with the letter n outside.
Revision notes
The reaction
Many small unsaturated monomer molecules join together to form one very large polymer molecule.
The carbon-carbon double bond in each monomer opens, allowing the monomers to bond to each other in a long chain. The polymer is the only product.
Naming and drawing
The polymer is named poly followed by the monomer in brackets: ethene gives poly(ethene).
The repeating unit is drawn with the double bond replaced by a single bond and with extended bonds at each side, inside brackets with n outside.
Same atoms
Because only the double bond opens, the repeating unit contains exactly the same atoms as the monomer.
This distinguishes addition polymerisation from condensation polymerisation, where a small molecule such as water is also produced.
Key points
- Addition polymerisation needs unsaturated monomers.
- The carbon-carbon double bond opens.
- Monomers join in a long chain.
- The polymer is the only product.
- The repeating unit has the same atoms as the monomer.
- Ethene forms poly(ethene).
Worked examples
Example 1
Name the polymer formed from propene. [1 mark]
Model answer
Poly(propene) (1 mark).
Example 2
Explain why the monomers used in addition polymerisation must be unsaturated. [2 marks]
Model answer
The monomers must contain a carbon-carbon double bond (1 mark), which opens during the reaction to allow the monomers to join to each other (1 mark).
Example 3
Explain why the repeating unit of an addition polymer contains the same atoms as the monomer. [2 marks]
Model answer
Only the double bond opens during the reaction (1 mark), and no other molecule is produced, so no atoms are lost or gained (1 mark).
Common mistakes
Saying a small molecule is also produced.
That is condensation polymerisation. Addition produces the polymer only.
Using a saturated monomer.
The monomer must be unsaturated, with a carbon-carbon double bond.
Forgetting the n outside the brackets.
It shows that the unit repeats many times.
Keeping the double bond in the repeating unit.
The double bond opens and becomes a single bond.
Exam tips
- Say the double bond opens, not breaks completely.
- Name polymers as poly followed by the monomer in brackets.
- Emphasise that the polymer is the only product.
- Remember this is a Triple-only topic.
Key terms
- Addition polymerisation
- Joining unsaturated monomers with no other product.
- Monomer
- The small molecule that joins to form a polymer.
- Repeating unit
- The section of polymer that repeats along the chain.
- Unsaturated
- Containing a carbon-carbon double bond.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.