Predicting & Deducing the Type of Polymerisation (Cambridge International A-Level Chemistry)

Predicting Type of Polymerisation

• 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 polymerization 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

Exam Hint

• As well as the functional groups to be aware of, know that a small molecule is expelled when the polymer is formed

• Identify 2 functional groups that can react together to produce either a polyamide or a polyester

• There are instances where both of the functional groups are on the same monomer molecule

  • For example, amino acid molecules contain an amine group (-NH₂) and a carboxylic acid group (-COOH) which means that they can polymerise to produce a polyamide

Deducing Type of Polymerisation

• 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

Exam Hint

• Different sections of polymer chains may be formed using various types of polymerisation

• In an exam, you may be given a section of a polymer and asked to determine the type of polymerisation used to form that section

• Firstly, look at the polymer backbone

  • If there are functional groups along the backbone, that section was made using condensation polymerisation
  • If there are no functional groups along the backbone, addition polymerisation was used