Predicting & Deducing the Type of Polymerisation (CIE A Level Chemistry)

• When a set of monomers is given in an exam question, the type of polymerisation can be determined
• Firstly, it’s important to identify the key functional groups in the monomers

Addition polymerisation

• If the monomer/s contain a C=C double bond, they will polymerise through addition polymerisation
• The double bond can open up in order to add more monomers on either side of the starting monomer
• This type of polymerisation makes (poly)alkenes

Addition polymerisation using one monomer

During addition polymerisation of one alkene monomer, a (poly)alkene is formed

• (Poly)alkenes can be produced if there are 2 or more alkene monomers as well
• When more than one monomer is used for addition polymerisation, the resulting product is known as a copolymer

Addition polymerisation using more than one monomer  

Addition polymerisation can also use two or more different alkene monomers forming a co-polymer

Condensation polymerisation

• Condensation polymerisation makes polyamides and polyesters
• When looking to identify this type of polymerisation, there are some key functional groups to be aware of

Monomers for condensation polymers table

Polyamide monomers	Polyester monomers	Molecule expelled as a result of condensation polymerisation
Acyl chlorides (–COCl) Amines (–NH2)	Acyl chlorides (–COCl) Alcohols (–OH)	Hydrochloric acid (HCl)
Carboxylic acids (–COOH) Amines (–NH2)	Carboxylic acids (–COOH) Alcohols (–OH)	Water (H2O)
Aminocarboxylic acids (H2N–CHR–COOH)	Hydroxycarboxylic acids (HO–R–COOH)	Water (H2O)

• The type of polymerisation can be determined by considering the structure of the polymer backbone

Identifying addition polymerisation

• The polymer backbone of an addition polymer does not contain functional groups
• The backbone of the polymer is generally a chain of carbon atoms
• There may be sidechains branching off from the backbone
• Some examples of side chains include:
  • Benzene rings
  • Nitrile groups (-CN)
  • Halogen atoms (-F / -Cl / -Br / -I)

Identifying addition polymers

Addition polymers are identified using the plain carbon chain as the polymer backbone

Identifying condensation polymerisation

• A condensation polymer can be identified by functional groups on the polymer backbone
• The backbone of polyesters contains ester links (-COO-)
• The backbone of polyamides contains amide / peptide links (-CONH-)

Identifying condensation polymers

Condensation polymers are identified using functional groups that form part of the polymer backbone, e.g. ester links in polyesters and amide / peptide links in polyamides