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4.8.1Electrochemistry

Addition Polymers — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 15 of 20 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Polymer Basics

4.8.1 Addition Polymers
Polymer
  • Polymers are large molecules of high relative molecular mass, made by linking many small monomer units together.
Addition polymerisation
  • Addition polymers form when alkene monomers join together, with each C=C double bond opening to form single bonds.
Conditions
  • Addition polymerisation usually needs high pressure and a catalyst.
Synthetic polymers
  • Synthetic polymers such as poly(ethene), poly(propene) and PVC are manufactured from monomers obtained from crude oil.
Naming
  • A polymer is named by putting poly- before the name of the monomer in brackets, such as poly(ethene).

Part 2 of 5Drawing Repeat Units

1
Change the C=C double bond in the monomer into a single bond in the repeat unit.
2
Add a bond at each end of the repeat unit, extending outside the brackets as continuation bonds.
3
Write a small n at the bottom right of the brackets to show that there are many repeat units.
4
To deduce the monomer from a polymer, reverse these steps and change the single bond in the repeat unit back to a double bond.

Part 3 of 5Common Addition Polymers

Common Addition Polymers
Poly(ethene)
  • Used for plastic bags and bottles, and made from ethene monomers.
Poly(propene)
  • Tough and used for ropes and containers, and made from propene.
PVC
  • Contains chlorine atoms, and is used for pipes and window frames.
PTFE
  • Non-stick and used as a coating for pans.
MonomerPolymerRepeat unit
Ethene, CH₂=CH₂Poly(ethene)–(CH₂–CH₂)ₙ–
Propene, CH₂=CHCH₃Poly(propene)–(CH₂–CH(CH₃))ₙ–
Chloroethene, CH₂=CHClPoly(chloroethene), PVC–(CH₂–CHCl)ₙ–
Tetrafluoroethene, CF₂=CF₂Poly(tetrafluoroethene), PTFE–(CF₂–CF₂)ₙ–

Part 4 of 5Worked Example

Question Deduce the monomer of the polymer –(CH₂–CHCl)ₙ–.

  1. The repeat unit is –CH₂–CHCl–
  2. Change the single bond in the repeat unit back to a double bond: CH₂=CHCl
  3. The monomer is chloroethene, which polymerises to form PVC

Answer CH₂=CHCl (chloroethene).

Part 5 of 5Exam Checklist & Tips

4.8.1 – Key Points for the Exam

  • Monomer A small molecule that joins with others to form a polymer.
  • Polymer A large molecule made from many repeating units.
  • Addition polymerisation Polymer formation in which alkene monomers join without losing any atoms.
  • Repeat unit The smallest unit that is repeated along the polymer chain.
  • Continuation bond A bond that extends outside the brackets of a repeat unit to show that the chain continues.

Common Mistakes

  • Leaving a double bond in the repeat unit; the repeat unit contains only single bonds.
  • Forgetting the continuation bonds on either side of the brackets.
  • Using the wrong monomer for a polymer, such as ethene for poly(propene).
  • Naming the polymer from the wrong monomer, such as calling PVC poly(ethene).

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