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 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
- Condensation polymers can be formed by:
- dicarboxylic acids and diols
- dicarboxylic acids and diamines
- amino acids
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, 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
- In this example, the polyester is poly(ethylene terephthalate) or PET, which is sometimes known by its brand names of Terylene or Dacron
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
Polyamides
- Polyamides are polymers where repeating units are bonded together by amide links
- The formula of an amide group is -CONH
An amide link - also known as a peptide link - is the key functional group in a polyamide
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 but more expensive than dicarboxylic acid
The monomers for making polyamides
Formation of polyamides
This shows the expulsion of a small molecule as the amide link forms
Amino acids - formation of 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