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
Examiner Tips and Tricks
Remember: in condensation polymerisation, a small molecule is expelled as a result of the 2 monomers joining together.
When a dioic acid and diamine polymerise, a water molecule is expelled
OH from acid and H from the amine
When a dioyl chloride and diamine are polymerised, a hydrochloric acid molecule is expelled
Cl from the chloride and H from the amine
Worked Example
Draw the repeating unit and identify the monomers used to make the following polymers

Answer:

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
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