Formation of Polythene

Specification Point 9.18C:
  • Describe:
    a) how ethene molecules can combine together in a polymerisation reaction
    b) that the addition polymer formed is called poly(ethene) (conditions and mechanisms not required)

Polymerisation

  • Addition polymers are formed by the joining together of many monomers that contain C=C bonds.
  • One of the bonds in each C=C breaks and forms a bond with the adjacent monomer.
  • The polymer formed contains only carbon carbon single bonds.
  • Many polymers can be made by the addition of alkene monomers.

Polythene

  • The name of the polymer is deduced by putting the name of the monomer in brackets and adding poly- as the prefix.
  • For example if propene is the alkene monomer used, then the name is polypropene
  • Polythene is formed by the addition polymerisation of ethene monomers.

Making Polythene, Edexcel GCSE Chemistry

Many ethene monomers are joined together in addition polymerisation to form polythene

Other Polymers

Specification Point 9.19C:
  • Describe how other addition polymers can be made by combining together other monomer molecules containing C=C, to include poly(propene), poly(chloroethene) (PVC) and poly(tetrafluoroethene) (PTFE) (conditions and mechanisms not required)
  • Addition polymers can be made from any alkene molecule.
  • Different monomer molecules produce polymers that have different structures and hence different properties.

Polypropene

  • Made from monomers of propene, C3H6.

Making Polypropene, Edexcel GCSE Chemistry

Polychloroethene (PVC)

  • Made from monomers of chloroethene, C2H3Cl.

Making PVC, Edexcel GCSE Chemistry

Polytetrafluoroethene (PTFE) also known as Teflon

  • Made from monomers of tetrafluoroethene, C2F4.

Making PTFE, Edexcel GCSE Chemistry

Deducing Structures

Specification Point 9.20C:
  • Deduce the structure of a monomer from the structure of an addition polymer and vice versa

Deducing Monomer Structure

  • Identify the repeat units in the polymer.
  • Do this visually by looking for identical units that repeat and then highlight or draw a circle around one.
  • Change the single bond between the carbon atoms in the repeat unit to a double bond.
  • Add on the other atoms or groups that are bonded to each carbon atom, making sure you arrange them in the correct positions.
  • You can then draw the monomer out using shorthand notation.

Diagram showing shorthand notation of a monomer deduced from the polymer

Example

Deduce the structure of chloroethene from polychloroethene.

Diagram showing the monomer from the repeat unit of an addition polymer (polychloroethene)

Deducing Polymer Structure

  • Change the double bond in the monomer to a single bond.
  • Add a bond to each end of the repeat unit.
  • Draw three or more units together with single bonds between the carbons.
  • Add on the other atoms or groups that are connected to each carbon atom, making sure you arrange them in the correct positions.
  • If using shorthand notation, make sure you place the extension bonds on either side of the large brackets, adding a subscript n on the right hand side to indicate a large number.

Diagram showing shorthand notation of a polymer deduced from the monomer

Uses of Polymers

Specification Point 9.21C:
  • Explain how the uses of polymers are related to their properties and vice versa: including poly(ethene), poly(propene), poly(chloroethene) (PVC) and poly(tetrafluoroethene) (PTFE)
  • Addition polymers can be engineered to have distinctive properties depending on their intended use.
  • This is done by the selection of the monomer.
  • Four common polymers are listed with their properties and uses.

Polymer uses table, Edexcel GCSE Chemistry

Need help?

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.