This comparison covers Thermosoftening vs Thermosetting Polymers within Polymers for GCSE Chemistry. Revise Polymers in Bonding & Structure for GCSE Chemistry with 22 exam-style questions and 21 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 5 of 12 in this topic. Use this comparison to connect the idea to the wider topic before moving on to questions and flashcards.
⚖️ Thermosoftening vs Thermosetting Polymers
Not all plastics behave the same way when heated. There are two distinct types of polymer, and they differ because of the structural arrangement of their chains.
| Feature | Thermosoftening Polymers | Thermosetting Polymers |
|---|---|---|
| Cross-links between chains? | No — chains held by weak intermolecular forces only | Yes — strong covalent cross-links between chains |
| What happens on heating? | Softens and melts — can be reshaped repeatedly | Does NOT melt — decomposes or chars on strong heating |
| Can it be remoulded? | Yes — heat, reshape, cool, repeat | No — once set, shape is permanent |
| Examples | Poly(ethene), PVC, polystyrene | Bakelite, melamine, epoxy resin |
| Typical uses | Plastic bags, drinks bottles, food packaging | Electrical fittings, saucepan handles, adhesives |
Why they behave differently — the structural explanation:
In a thermosoftening polymer, the long chains are only held together by weak intermolecular forces. When heated, these weak forces are easily overcome, the chains can move apart, and the polymer softens and flows. On cooling, the forces re-form and the polymer hardens again — this process can be repeated over and over. This is also why thermosoftening polymers can be recycled.
In a thermosetting polymer, the chains are permanently joined to each other by strong covalent cross-links formed during the original setting (curing) process. These cross-links lock the structure rigidly in place. When heated, the cross-links cannot be broken by normal heating — instead, the polymer decomposes or chars. This is why thermosetting plastics are used where heat resistance is essential, such as electrical fittings and saucepan handles.
Test yourself: thermosoftening vs thermosetting polymers
Apply the bonding difference to real material choices, not just definitions.
A kettle handle must withstand high temperatures without melting. Which type of polymer should be used, and why?2 marks
A thermosetting polymer, because the covalent cross-links between its chains are strong and need a lot of energy to break, so the material chars or decomposes instead of melting.
Full marks needs the correct type AND the bonding reason. Naming 'thermosetting' with no explanation caps at 1 of 2.
A drinks bottle is made from a polymer that can be melted down and reshaped for recycling. What type of polymer must this be, and why can it be melted?2 marks
A thermosoftening polymer. It has only weak intermolecular forces between chains and no covalent cross-links, so heating overcomes those forces and the chains slide past each other, allowing it to melt and be remoulded.
Examiners want 'weak intermolecular forces' explicitly. Confusing these with the covalent bonds within a chain is a common lost mark.
Explain, in terms of bonding, why thermosetting polymers do not melt when heated strongly.3 marks
Thermosetting polymers have covalent cross-links between adjacent chains, as well as covalent bonds within each chain. These cross-links are strong and need a large amount of energy to break. Because they are chemical bonds rather than weak intermolecular forces, heating breaks them permanently, decomposing or charring the material instead of letting chains separate and flow.
Top marks require distinguishing the cross-links (covalent, strong, break permanently) from weak intermolecular forces. 'Strong bonds' without naming covalent cross-links loses a mark.
Practice questions for Polymers
In addition polymerisation, what feature of monomer molecules allows them to join together?
Explain why thermosetting polymers are rigid and do not melt when heated.