AQA GCSE Chemistry

Revision Notes

2.2.6 Polymers

Polymers

  • Polymers are large molecules of high relative molecular mass and are made by linking together large numbers of smaller molecules called monomers
  • Each monomer is a repeat unit and is connected to the adjacent units via strong covalent bonds
  • The intermolecular forces acting in between polymer chains are larger than those in between simple molecules so polymers are usually solid at room temperature
    • Examples of polymers include polythene and polychloroethene, commonly known as PVC
  • Many everyday materials such as resins, plastics, polystyrene cups, nylon etc. are polymers
  • These are manufactured and are called synthetic polymers
  • Nature also produces polymers which are called natural or biological polymers
    • Examples include DNA, proteins, silk and wool

 

Polymerisation - Examples of Addition Polymers, downloadable AS & A Level Chemistry revision notes

Polymers are made from very long carbon chains with a repeating unit
This diagram shows a short section of polystyrene, a polymer used widely in packaging materials

Drawing Polymers

  • Polymers are represented using a specific notation which is shown below using polythene as an example
    • You can spell it polythene or polyethene – both are acceptable
  • The bonds on either side of the polymer must extend outside the brackets (these are called extension or continuation bonds)
  • A small subscript n is written on the bottom right hand side to indicate a large number of repeat units

Making Polythene, IGCSE & GCSE Chemistry revision notes

The simplest of all polymers is polyethene

  • The relationship between the monomer, repeating unit and polymer is illustrated in this second example using polychloroethene
  • Notice that the chlorines do not necessarily have to be drawn ‘up’ or ‘down’ from the chain, as long as every carbon has the correct atoms attached

Polymerisation - Polymers From One Alkene Monomer, downloadable AS & A Level Chemistry revision notes

The structure of polychloroethene and its monomer

Exam Tip

The repeat unit only ever contains two carbons in the chain. Students often get this wrong when drawing the repeat unit of polypropene, where CH3CH=CH2 they are tempted to make the repeat unit -[CH2-CH2-CH2]-, which is incorrect. The correct repeating unit for polypropene would be -[CH(CH3)-CH2]-.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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