Knowledge Organiser: Polymers
Key Terms
- Monomer — small repeating unit
- Polymer — large molecule of monomers
- Addition polymerisation — alkenes, no by-product
- Condensation polymerisation — two functional groups, water released
Drawing Polymers
- Double bond → single bond
- Add continuation lines at ends
- Put in square brackets
- Add subscript n
Addition vs Condensation
- Addition: one product only (polymer)
- Condensation: polymer + H₂O
- Addition uses alkenes (C=C)
- Natural polymers = condensation
Exam Checklist
- Continuation lines = essential
- n subscript = must include
- Addition ≠ water released
- Not all polymers are plastics
Key Equations
- n(CH₂=CH₂) → (−CH₂−CH₂−)ₙ (addition polymerisation of ethene)
- Condensation: diol + dicarboxylic acid → polyester + nH₂O
- Repeat unit: monomer structure with C=C replaced by C−C and brackets
Common Mistakes
- Drawing the repeat unit with a double bond still in it: In addition polymerisation the C=C opens — the repeat unit must show only single bonds with continuation lines through the brackets
- Forgetting the subscript n: The n outside the bracket indicates many repeating units — omitting it is an error that loses marks
- Saying addition polymerisation produces water: Addition polymerisation produces ONLY the polymer — condensation polymerisation releases water as a by-product
- Confusing natural and synthetic polymers: Proteins and DNA are natural condensation polymers; poly(ethene) and PVC are synthetic addition polymers
Memory Aid
- Addition — alkene opens double bond, chains add together, nothing else produced. Think: ADD = ADD monomer, NOTHING leaves.
- Condensation — two functional groups react, chains join, a small molecule (water) condenses out. Think: CONDENSE = water drops condense out (like water droplets on a cold glass).
- Start with the monomer
- Change C=C to C-C (double → single)
- Add continuation lines from each end carbon
- Add brackets with subscript n