Addition Polymerisation (AQA GCSE Chemistry)

Addition 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

Forming polymers from monomers 

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
• Polyethene is formed by the addition polymerisation of ethene monomers

Formation of poly(ethene) and poly(chloroethene)

Examples of addition polymerisation: polyethene and PVC

Deducing the polymer from the monomer

• Polymer molecules are very large compared with most other molecule
• 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

The monomer & repeat unit

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

Deducing the monomer from the polymer

• 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 (which can be placed in front of the monomer)

The repeat unit & monomer

Diagram showing the monomer of the repeat unit of polymer