- 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.
Diagram showing how lots of monomers bond together to form a polymer
- 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.
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.
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.
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)
Diagram showing the monomer of the repeat unit of polychloroethene