Addition Polymerisation (AQA GCSE Chemistry)

What is polymerisation?

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

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

• 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