CIE A Level Chemistry复习笔记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

7.7-Polymerisation-Making-Terylene-PETExpulsion 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