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2.4.5Additional lessons

Addition Polymers — IB Chemistry SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 37 of 98

📚 IB Chemistry SL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 6Addition Polymerisation

Addition polymers are formed from unsaturated monomers.

1
The monomer must contain a C=C double bond, as in alkenes.
2
Under suitable conditions one bond of the double bond breaks in each monomer.
3
The freed bonding electrons form single bonds to neighbouring monomers.
4
A long chain of carbon atoms joined by single bonds is formed, with the substituents hanging off.
5
No atoms are lost, so the polymer has the same empirical formula as the monomer.

Part 2 of 6Writing the Equation

General form
  • General form n CH₂=CH₂ → (–CH₂–CH₂–)ₙ shows n ethene molecules forming poly(ethene).
Square brackets
  • Square brackets The bracket shows the repeat unit, with open bonds at both ends to show the chain continues.
Substituted alkenes
  • Substituted alkenes For CH₂=CHX the repeat unit is (–CH₂–CHX–)ₙ, where X can be H, Cl, CH₃ or other groups.
Always carbon only
  • Always carbon only The backbone of an addition polymer contains only carbon atoms.

Part 3 of 6Common Examples

Common Examples
Poly(ethene)
  • Poly(ethene) Made from ethene, it is used for bags, bottles and film.
Poly(propene)
  • Poly(propene) Made from propene, CH₂=CHCH₃, it is used for ropes, crates and food containers.
PVC
  • PVC Made from chloroethene, CH₂=CHCl, it is used for pipes and window frames.
PTFE
  • PTFE Made from tetrafluoroethene, CF₂=CF₂, it gives non-stick coatings.
MonomerPolymerRepeat unit
ethenepoly(ethene)–CH₂–CH₂–
propenepoly(propene)–CH₂–CH(CH₃)–
chloroethenepoly(chloroethene) PVC–CH₂–CHCl–
tetrafluoroethenePTFE–CF₂–CF₂–

Part 4 of 6Working Backwards

Find the repeat unit
  • Find the repeat unit Identify a section of two backbone carbon atoms that repeats along the chain.
Restore the double bond
  • Restore the double bond Draw the two carbon atoms with a C=C between them and keep their side groups.
Check the carbons
  • Check the carbons Each carbon should have four bonds once the double bond is counted.
Name the monomer
  • Name the monomer Name the alkene formed and check that it gives the polymer you started with.

Part 5 of 6Worked Example

Question Calculate the relative molecular mass of a poly(chloroethene) chain with 800 repeat units (Ar: C 12.01, H 1.01, Cl 35.45).

  1. The repeat unit is C₂H₃Cl.
  2. Mr of the repeat unit = 2 × 12.01 + 3 × 1.01 + 35.45 = 62.50.
  3. Mr of chain = 800 × 62.50 = 50 000 (approximately).

Answer About 5.0 × 10⁴

Part 6 of 6Exam Checklist & Tips

2.4.5 – Key Points for the Exam

  • Addition polymer A polymer formed when unsaturated monomers join without losing any atoms.
  • Repeat unit The section of a polymer chain that repeats along its length.
  • Unsaturated Containing at least one carbon-carbon double bond.
  • Poly(ethene) The addition polymer of ethene.

Common Mistakes

  • Leaving the double bond in the repeat unit.
  • Drawing the repeat unit without the open bonds at its ends.
  • Placing the substituent in the chain instead of hanging off it.
  • Writing that a small molecule is released in addition polymerisation.

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