Forming Polyesters (Edexcel International A Level Chemistry)

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Forming 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 polyethene

  • Condensation polymerisation is another type of reaction whereby a polymer is produced by repeated condensation reactions between monomers
  • Natural condensation polymers are all formed by elimination of water
    • Although the process of condensation polymerisation involves the elimination of a small molecule

  • Condensation polymers can be identified because the monomers are linked by ester or amide bonds

Polyester

  • Is formed by the reaction between dicarboxylic acid monomers and diol monomers
  • Polyester is produced by linking these monomers with ester bonds / links

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, the H atom on the diol and the -OH group of the -COOH are expelled as a water molecule (H2O)
  • The resulting polymer is a polyester
    • In this example, the polyester is poly(ethylene terephthalate) or PET, which is sometimes known by its brand names of Terylene or Dacron

 

Formation of PET, downloadable AS & A Level Chemistry revision notes

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

Formation of polyesters - 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 that are needed to make the polyester come from the same monomer

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Richard

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Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.