Thermosoftening & Thermosetting PolymersOxford AQA IGCSE Chemistry: Revision notes

Section 1

What are thermosoftening polymers?

Thermosoftening polymers consist of individual, tangled polymer chains with no chemical bonds linking one chain to another.

When heated, the weak forces between the tangled chains are overcome, allowing the chains to slide over each other, so the polymer softens and melts
On cooling, the polymer becomes solid again but can be remelted and reshaped repeatedly
This makes thermosoftening polymers easy to recycle by melting them down

Key termsthermosoftening polymer

Section 2

Why do thermosoftening polymers melt when heated?

The explanation involves intermolecular forces, not covalent bonds:

Each polymer chain is held together internally by strong covalent bonds, which do not break on heating
Between separate chains there are only weak intermolecular forces
Heating provides enough energy to overcome these weak intermolecular forces, letting the tangled chains move past one another - this is what causes melting, not the breaking of covalent bonds

Key termsintermolecular forces

Common mistake

A common error is to say the covalent bonds break when a thermosoftening polymer melts - it is the weak intermolecular forces between chains that are overcome, not the covalent bonds within each chain.

Section 3

What are thermosetting polymers?

Thermosetting polymers consist of polymer chains that have strong covalent cross-links between them, forming a rigid network.

These cross-links hold the chains firmly in place, so the chains cannot slide over each other
As a result, thermosetting polymers do not melt when heated - instead they char or decompose at very high temperatures
Once set (usually by heating during manufacture), thermosetting polymers cannot be reshaped or recycled by melting

Key termsthermosetting polymercross-links

Think of it like this

Think of thermosoftening polymers as a bowl of loose, tangled spaghetti strands (they can slide apart when warmed), and thermosetting polymers as a knitted jumper where the strands are permanently linked together (it cannot be pulled apart into loose strands by heat).

Must Know

Thermosoftening polymers are made of tangled, separate chains with only weak intermolecular forces between them
Thermosoftening polymers melt and can be reshaped repeatedly on heating
Thermosetting polymers have strong covalent cross-links between chains
Thermosetting polymers do not melt when heated because the cross-links hold the chains firmly in place
Melting a thermosoftening polymer overcomes weak intermolecular forces between chains, not the covalent bonds within a chain

That's the notes covered.

Carry on to the next subtopic.