Repeat Units & Monomers (Cambridge (CIE) A Level Chemistry): Revision Note

Deducing the Repeat Unit of a Condensation Polymer

Repeat units for condensation polymers

• Remember we can tell the type of polymerisation by identifying the linking between the monomers

  • If a chain of carbon atoms is present, the polymer is an addition polymer

  • If there is an ester link, the polymer is a polyester (formed by condensation polymerisation)

Example polyester structure

Polyesters contain the ester link

• If there is an amide link, the polymer is a polyamide (formed by condensation polymerisation)

Example polyamide structure

Polyamides contain the amide or peptide link

• In condensation polymerisation, the monomers either contain:

  • 2 monomers each with the same functional group, such as a diamine with a dicarboxylic acid or

  • One single monomer that has both of the functional groups needed for polymerisation, such as an aminocarboxylic acid

Identifying Monomers in Condensation Polymers

• When a section of polymer is presented, the monomers can be identified by considering the small molecules expelled from the monomers

• If a water molecule is expelled, the -OH must have been from an acid group

• The hydrogen atom may be from an amine group of a monomer.

• If the molecule was hydrochloric acid (HCl), a dioyl chloride monomer may have been used