Condensation Polymerisation (Triple Only)
Lajoy Tucker
Teacher
Contents
What Condensation Polymers Are
Condensation polymers are long-chain molecules made when monomers with two reactive functional groups join together.
Each time a link forms, a small molecule is released (often water, sometimes hydrogen chloride or methanol).
This loss of a small molecule gives the process its name: condensation polymerisation.
Key idea: Every monomer must be able to bond twice so the chain can continue growing.
How Condensation Polymerisation Works
Monomers involved
A condensation polymer can be made from:
1. Two different monomers, each with two identical functional groups
(e.g., a molecule with two groups reacts with a molecule with two –OH groups), or
2. One monomer with two different functional groups
(e.g. an amino acid which contains both and groups).
Step-by-step process
1. Functional groups on neighbouring monomers react.
2. A covalent link forms between the monomers.
3. A small molecule is expelled (commonly water).
4. The product still contains a reactive group at each end, so it can react again.
5. This repeats thousands of times → a polymer chain.
Polyester Formation
Polyesters
Polyesters are one of the most important families of condensation polymers.
Functional groups needed
To make a polyester, you need:
A dicarboxylic acid (contains two groups), and
A diol (contains two groups)
When these react, they form an ester linkage each time the group reacts with an group.
Example 1:
Figure 1: The formation of an ester link.
Figure 2: Formation of a polyester.
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Example 2: Terylene (polyethylene terephthalate (PET)) used in textiles and plastic drinks bottles
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How Condensation Polymerisation Differs from Addition Polymerisation
Both processes create polymers - but the similarities end there.
Types of monomers
Addition polymerisation
Requires alkenes (monomers with double bonds).
Uses one monomer type.
Condensation polymerisation
A single molecule contains two different types of functional groups.
E.g. amino acids with and . Because the two groups can react with each other between molecules, one type of monomer is enough to form a chain.
You use two different molecules, and each one has a single type of functional group — but it has two copies of that group. E.g. a dicarboxylic acid and a diol
Products formed
Addition polymerisation
Only the polymer is produced (no by-products).
Condensation polymerisation
Produces the polymer AND a small molecule (water, , etc.).
Functional groups involved
Addition
Only the bond is reactive.
Condensation
Uses functional groups such as:
These determine the type of polymer (polyester, polyamide, etc.).