This definitions covers Key Definitions 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 6 of 12 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Polymer: A large molecule formed by joining together many small repeating units (monomers) — the backbone is held together by covalent bonds.
Monomer: A small molecule that can join together with many other monomers to form a polymer chain (must have a C=C double bond for addition polymerisation).
Addition polymerisation: The process by which many monomer molecules (containing C=C double bonds) join together to form a long chain polymer, with no atoms lost.
Repeat unit: The smallest section of the polymer chain that represents the pattern which repeats throughout — derived from the monomer structure with the double bond converted to a single bond.
Intermolecular forces: The weak attractions between separate polymer chains — these determine the physical properties like flexibility and melting point.
Thermosoftening polymer: A polymer with no cross-links between chains — held only by weak intermolecular forces. Softens and melts on heating; can be remoulded and recycled. Examples: poly(ethene), PVC, polystyrene.
Thermosetting polymer: A polymer with strong covalent cross-links between chains, formed during curing. Cannot be melted or remoulded once set — decomposes on strong heating. Examples: Bakelite, melamine, epoxy resin.
Cross-links: Covalent bonds that join adjacent polymer chains together in a thermosetting polymer, preventing them from sliding apart when heated.
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.