Polymerisation

  • 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 covalent bonds.
  • Polymerisation reactions usually require high pressures and the use of a catalyst.
  • 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.

Polymers - Basic, IGCSE & GCSE Chemistry revision notes

Diagram showing how lots of monomers bond together to form a polymer

Representing Polymers

  • Addition polymers are formed by the joining up of many monomers and only occurs in monomers that contain C=C bonds.
  • One of the bonds in each C=C bond breaks and forms a bond with the adjacent monomer with the polymer being formed containing single bonds only.
  • Many polymers can be made by the addition of alkene monomers.
  • Others are made from alkene monomers with different atoms attached to the monomer such as chlorine or a hydroxyl group.
  • 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.

Addition-Polymerisation-examples, IGCSE & GCSE Chemistry revision notes

Examples of addition polymerisation: polythene and PVC

Deducing the monomer from the polymer

  • Polymer molecules are very large compared with most other molecules.
  • Repeat units are used when displaying the formula.
  • To draw a repeat unit, change the double bond in the monomer to a single bond in the repeat unit.
  • Add a bond to each end of the repeat unit.
  • 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.
  • Add on the rest of the groups in the same order that they surrounded the double bond in the monomer.

Drawing-repeating-units, IGCSE & GSCE Chemistry revision notes

Diagram showing the concept of drawing a repeat unit of a monomer

Deducing the polymer from the monomer

  • Identify the repeating unit in the polymer.
  • Change the single bond in the repeat unit to a double bond in the monomer.
  • Remove the bond from each end of the repeat unit and the subscript n.

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Deducing monomer structure from repeat units, IGCSE & GCSE Chemistry revision notes

Diagram showing how to deduce the structure of a monomer from a repeat unit

Example: Deducing the structure of chloroethene from a repeat unit of Poly(chloroethene)

Deducing chloroethene structure, IGCSE & GCSE Chemistry revision notes

Diagram showing the monomer of the repeat unit of polychloroethene

AQA 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.