Polymerisation (Oxford AQA IGCSE Combined Science Double Award)

Polymerisation

• Polymerisation involves small, reactive molecules called monomers reacting together to form very large molecules called polymers

• A monomer is a compound which contains a carbon-carbon double bond / C=C

The process of polymerisation

• The reactivity of a monomer is due to its carbon-carbon double bond / C=C

• One of the bonds in each carbon-carbon double bond / C=C breaks open

  • This allows the molecule to join to another adjacent molecule

  • The end result is a polymer that contains only single bonds 

• Polymerisation of different alkene monomers can form different polymers including:

  • Poly(ethene)

  • Poly(propene)

• To name the polymer the name of the monomer is placed inside brackets and the prefix 'poly' added in front

• The properties of a polymer depend on:

  • The monomer they are made from

  • The conditions under which they are made

• For example, ethene can be used to make either high- density (HD) poly(ethene) or low -density (lD) poly(ethene)

  • Low density poly(ethene) is produced using high pressure and moderate temperature with a catalyst

    • This polymer has a more flexible structure

  • High density poly(ethene) is producing using lower temperatures and pressure, and a different catalyst

    • This polymer has a more rigid, solid structure

Drawing Polymers

• Polymer molecules are very large compared with most other molecule

• Repeat units are used when displaying the formula

• To draw a repeat unit

  1. Change the double bond in the monomer to a single bond in the repeat unit

  2. Add brackets

  3. Add a continuation bonds to each end of the repeat unit

     • The bonds on either side of the polymer must extend outside the brackets

  4. A small subscript n is written on the bottom right hand side to indicate a large number of repeat units

  5. Add on the rest of the groups in the same order that they surrounded the double bond in the monomer

  How to draw repeat units for polymers