Condensation polymerisation
Condensation polymerisation
- In condensation polymerisation, monomers join and a small molecule is lost each time.
- Each monomer needs two reactive groups, so the chain grows at both ends.
- The result is a polyester or a polyamide.
Practice
In condensation polymerisation:
Each new link releases a small molecule; the monomers need two reactive groups.
Polyesters and polyamides
- a polyester has many ester links. Make it from a diol + a dicarboxylic acid (or dioyl chloride), or from a single hydroxycarboxylic acid.
- a polyamide has many amide links. Make it from a diamine + a dicarboxylic acid, or from amino acids joining (proteins are natural polyamides).
Practice
A polyester can be made from:
A diol (two –OH) and a dicarboxylic acid (two –COOH) form ester links along the chain.
Practice
Proteins are examples of:
Amino acids join by amide (peptide) links, so proteins are polyamides.
Repeat units and monomers
- The repeat unit contains parts of both monomers, minus the small molecule lost.
- To find the monomers: break the chain at each ester/amide link, then add back –OH and –H (or –Cl).
Practice
To find the monomers of a condensation polymer, you:
Breaking the links and restoring the lost atoms recreates the original monomers.
You've got it
Key idea
- condensation polymerisation: monomers join + a small molecule (e.g. water) is lost; each monomer has two groups
- polyester = ester links (diol + dicarboxylic acid); polyamide = amide links (diamine + dicarboxylic acid)
- proteins are natural polyamides; find monomers by breaking links and adding back –OH/–H