CIE A Level Chemistry (9701) exams from 2022

Revision Notes

7.7.1 Formation of Polyesters

Formation of Polyesters

  • Addition polymerisation has been covered in reactions of alkenes
    • They are made using monomers that have C-C double bonds joined together to form polymers such as (poly)ethene
  • Condensation polymerisation is another type of reaction and is used in the making of polyesters
    • A small molecule (eg. a water molecule) is lost when the monomers join together to form a polyester
    • Polyesters contain ester linkages

This polymer structure shows an ester functional group linking monomers together

Formation of polyesters

  • A diol and a dicarboxylic acid are required to form a polyester
    • A diol contains 2 -OH groups
    • A dicarboxylic acid contains 2 COOH groups

 

The position of the functional groups on both of these molecules allows condensation polymerisation to take place effectively

  • When the polyester is formed, one of the -OH groups on the diol and the hydrogen atom of the -COOH are expelled as a water molecule (H2O)
  • The resulting polymer is a polyester

 

Expulsion of a water molecule in this condensation polymerisation forms the polyester called Terylene (PET)

Hydroxycarboxylic acids

  • So far the examples of making polyesters have focused on using 2 separate monomers for the polymerisation
  • There is another route to making polyesters
  • A single monomer containing both of the key functional groups can also be used
  • These monomers are called hydroxycarboxylic acids
    • They contain an alcohol group (-OH) at one end of the molecule while the other end is capped by a carboxylic acid group (-COOH)

Both functional groups are needed to make a polyester are from the same monomer

Exam Tip

  • Polyesters can be made using condensation polymerisation
  • The monomers needed are diols and dicarboxylic acids/dioyl chlorides or a single hydroxycarboxylic acid monomer

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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