Addition polymers and their disposal

Addition polymerisation

Many alkene monomers join; the C=C opens and the monomers link through new C-C bonds. There is only one product, so atom economy is 100%.

• ethene -> poly(ethene)
• propene -> poly(propene)
• chloroethene -> poly(chloroethene), PVC
• tetrafluoroethene -> PTFE

Repeat units

To draw the repeat unit, take the two C=C carbons, make the bond single, put extension bonds on each side and put square brackets with n. To find the monomer from a polymer, pick out a two-carbon repeat unit from the main chain and put the double bond back. The main chain of an addition polymer is all carbon.

Dealing with waste

Addition polymers are unreactive, so most do not biodegrade and persist in landfill and the sea. Ways to reduce harm:

• recycling: sorting and remelting, or cracking to feedstock
• incineration for energy, with toxic gases such as HCl from PVC removed (for example by reacting with a base in scrubbers)
• biodegradable and compostable polymers, for example from plant starch

Chemists work to make polymers that are easier to recycle or break down.

Worked example

Draw the repeat unit of poly(propene) in words.

1. Propene is CH2=CHCH3.
2. Open the double bond: -CH2-CH(CH3)-
3. Add brackets and n.

Answer: [-CH2-CH(CH3)-]n, with the CH3 as a side group, not in the main chain

Check yourself

1. Which monomer forms PVC?
   • Ethene, CH2=CH2
   • Chloroethene, CH2=CHCl
   • Propene, CH2=CHCH3
   • Tetrafluoroethene, CF2=CF2
   Show answer

   Chloroethene, CH2=CHCl. PVC is poly(chloroethene).

2. What is the repeat unit of poly(ethene)?
   • CH2=CH2
   • -CH=CH-
   • -CH3-CH3-
   • -CH2-CH2-
   Show answer

   -CH2-CH2-. The double bond opens, leaving two CH2 groups joined by single bonds.

3. A polymer has repeat unit -CH2-CH(CN)-. What is the monomer?
   • CH3CH2CN
   • CH2=CHCN
   • CH2=C(CN)2
   • CH≡CCN
   Show answer

   CH2=CHCN. Put the double bond back between the two main-chain carbons.

4. Why do addition polymers persist in the environment?
   • They contain C=C bonds
   • They dissolve in water
   • They are unreactive saturated chains that microorganisms cannot break down
   • They react rapidly with oxygen
   Show answer

   They are unreactive saturated chains that microorganisms cannot break down. Strong C-C and C-H bonds and no reactive groups make them non-biodegradable.

5. Which toxic gas must be removed when PVC is incinerated?
   • Hydrogen chloride
   • Nitrogen
   • Oxygen
   • Water vapour
   Show answer

   Hydrogen chloride. The chlorine in PVC forms HCl on burning.

6. What is the atom economy of an addition polymerisation, in %?
   Show answer

   100 %. Every monomer atom ends up in the polymer.

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Sources

• Pearson Edexcel IAL Chemistry (2018) scheme of work
• Pearson Edexcel International Advanced Level Chemistry (2018) qualification page

Last updated 7 November 2026. Spotted a mistake? Tell us.