Polycondensation to a polyamide (nylon-6,6): mechanism and explanation
Adipic acid and hexamethylenediamine form amide bonds again and again: nylon-6,6 forms. The numbers give the carbons of the diamine and the diacid.
Example
Acid and amine first form a salt (nylon salt); on heating water is eliminated and the amide bonds form. Hydrogen bonds between the N–H and C=O groups of neighbouring chains make nylon so tear-resistant.
Mechanism step by step
- 1
The diacid and diamine form a 1:1 salt (carboxylate and ammonium).
- 2
On heating the amine attacks the carbonyl group and water leaves: an amide bond.
- 3
The chain keeps growing at both ends (step growth) until long polyamide chains are present.
To read
This topic is part of the syllabus but not in the training: polymers consist of repeating units and biomolecules react through enzymes in the cell. There is no clear-cut task with exactly one product for it.
Go to the trainer with 157 reactions to practiseFrequently asked questions
What is the difference between nylon-6,6 and nylon-6?
Nylon-6,6 is made from two monomers (diamine and diacid). Nylon-6 is made from one monomer, caprolactam, which contains the amine and acid in one ring.
How does this relate to proteins?
Proteins are polyamides too: the peptide bond is an amide bond between amino acids.