AQA A Level Chemistry

Revision Notes

7.6.1 Condensation Polymers

Condensation Polymers

  • 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

Uses of Condensation Polymers

Uses of Condensation Polymers

Nylon 6,6

Amide link

  • Polyamides are also formed using condensation polymerisation

 

An amide link – also known as a peptide link – is the key functional group in a polyamide

Monomers

  • A diamine and a dicarboxylic acid are required to form a polyamide
    • A diamine contains 2 -NH2 groups
    • A dicarboxylic acid contains 2 -COOH groups
  • Dioyl dichlorides can also used to react with the diamine instead of the acid
    • A dioyl chloride contains 2 -COCl groups
  • This is a more reactive monomer than dicarboxylic acid. However, a more expensive alternative

The monomers for making polyamides

Formation of polyamides

This shows the expulsion of a small molecule as the amide link forms

  • Nylon 6,6 is a synthetic polyamide
  • Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid
    • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

 

Nylon 6,6 is a synthetic polyamide made using diamine and dicarboxylic acid monomers

Kevlar

  • Kevlar is another example of a polymer formed through condensation polymerisation
  • The polymer chains are neatly arranged with many hydrogen bonds between them
  • This results in a strong and flexible polymer material with fire resistance properties
  • These properties also lend Kevlar to a vital application in bullet-proof vests
  • The monomers used to make Kevlar
    • 1,4-diaminobenzene
    • Benzene-1,4-dicarboxylic acid
  • As seen with Nylon, a dioyl chloride can be used instead of the acid as well (benzene-1,4-dioyl chloride)

Kevlar is made using a diamine and dicarboxylic acid monomers

Aminocarboxylic acids

  • So far, condensation polymerisation has covered the use of monomers that contain 2 of the same functional group (eg. diamine, Diol etc.)
  • It is possible to carry out a condensation polymerisation where one monomer provides both of the function groups necessary for an amide/peptide link
  • For example 6-aminohexanoic acid has an amino group and a carboxylic acid group on the same molecule
  • Molecules like this are called amino carboxylic acids
  • They are able to polymerise to form a structure similar to Nylon 6,6

6-aminohexanoic acid can be polymerised to make the synthetic polymer Nylon 6,6

Making Proteins

  • Proteins are vital biological molecules with varying functions within the body
  • They are essentially polymers made up of amino acid monomers
  • Amino acids have an aminocarboxylic acid structure
  • Their properties are governed by a branching side group – the R group

 

Amino acids contain an amine group, an acid group and a unique R group

  • Different amino acids are identified by their unique R group
  • The names of each amino acid is given using 3 letters
  • For example Glutamine is known as ‘Gln’
  • Dipeptides can be produced by polymerising 2 amino acids together
    • The amine group (-NH2) and acid group (-COOH) of each amino acid is used to polymerise with another amino acid
  • Polypeptides are made through polymerising more than 2 amino acids together

Dipeptides and polypeptides are formed by polymerising amino acid molecules together

Protein hydrolysis

  • Proteins (polypeptides) can be broken down into its constituent amino acids
  • This process occurs through a hydrolysis reaction

 

Polymerisation - Peptide Hydrolysis, downloadable AS & A Level Chemistry revision notes

Proteins are broken down by hydrolysis

Exam Tip

Become familiar with the structures of the different monomers that can be used to make condensation polymers.

Also, remember that exam questions will require you to identify the key functional groups and also draw small sections of polymers.

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