This topic summary covers Knowledge Organiser: 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 12 of 12 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Polymers
Key Terms
- Polymer: long chain molecule made of many monomers
- Monomer: small molecule with C=C that joins to form polymer
- Addition polymerisation: C=C opens, monomers join, no atoms lost
- Repeat unit: smallest repeating section of polymer chain
- Intermolecular forces: weak forces BETWEEN polymer chains
- Thermosoftening: no cross-links, melts on heating, can be recycled
- Thermosetting: covalent cross-links, cannot melt, decomposes on heating
Must-Know Facts
- Strong covalent bonds WITHIN chains
- Weak intermolecular forces BETWEEN chains
- Low MP — only intermolecular forces between chains broken
- Do NOT conduct — no free electrons or ions
- Ethene (CH₂=CH₂) → poly(ethene)
- Naming: poly(monomer name)
- Thermosoftening: poly(ethene), PVC, polystyrene — can be remoulded
- Thermosetting: Bakelite, melamine, epoxy resin — permanent shape
- Cross-links prevent chain movement → thermosetting stays rigid when heated
Key Equations
- n(CH₂=CH₂) → (−CH₂−CH₂−)ₙ (addition polymerisation of ethene)
- Monomer must contain C=C double bond for addition polymerisation
- Repeat unit = monomer with double bond replaced by single bond and brackets with n
Common Mistakes
- Drawing the repeat unit with a double bond: The C=C opens during polymerisation — the repeat unit has only single bonds
- Saying polymers have high melting points: Thermosoftening polymers have relatively low melting points — only intermolecular forces between chains break
- Confusing thermosoftening and thermosetting: Thermosoftening = no cross-links, can be remelted; thermosetting = covalent cross-links, cannot be remelted
- Forgetting the subscript n: The repeat unit must show n outside the brackets to indicate many repeating units
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.
Quick recall flashcards
What is a monomer?
A small molecule that joins with others to form a polymer
What is a polymer?
A large molecule made of many small repeating units (monomers) joined by covalent bonds