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2.4.5Additional lessons

Addition Polymers — IB Chemistry HL Revision Notes & Topical Questions

5 min read 6 parts Lesson 47 of 172

📚 IB Chemistry HL 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

In addition polymerisation unsaturated monomers add together to form a saturated chain.

Monomers
  • Monomers Alkenes and substituted alkenes that contain a C=C double bond.
Mechanism summary
  • Mechanism summary The double bond opens and each monomer joins to the next through new single bonds.
No by-product
  • No by-product All atoms of the monomers end up in the polymer, so atom economy is 100%.
Equation
  • Equation n CH₂=CH₂ → –(CH₂–CH₂)ₙ–, written with the repeating unit in brackets.

Part 2 of 6Common Polymers

Common Polymers
Poly(ethene)
  • Poly(ethene) Made from ethene, used for bags, bottles and films.
Poly(propene)
  • Poly(propene) Made from propene, used for ropes, crates and car parts.
Poly(chloroethene)
  • Poly(chloroethene) Also called PVC, made from CH₂=CHCl and used for pipes and window frames.
Poly(tetrafluoroethene)
  • Poly(tetrafluoroethene) PTFE, made from CF₂=CF₂, has a non-stick surface and is used in coatings.
MonomerRepeating unit
CH₂=CH₂–CH₂–CH₂–
CH₂=CHCH₃–CH₂–CH(CH₃)–
CH₂=CHCl–CH₂–CHCl–
CF₂=CF₂–CF₂–CF₂–

Part 3 of 6Working With Repeating Units

1
To draw a repeating unit, put the two carbon atoms of the former double bond in the backbone with bonds extending at both ends.
2
Keep all the side groups on the carbon atoms they were attached to in the monomer.
3
To find a monomer, take two carbons of the backbone, replace the link bonds by a double bond, and keep their substituents.
4
Show the continuation bonds at each end of the repeating unit so the chain is clearly open.
5
Check that the backbone contains only carbon–carbon single bonds, since the double bonds have been used.

Part 4 of 6Environmental Issues

Persistence
  • Persistence Addition polymers have strong C–C and C–H bonds, so they are not biodegradable.
Burning
  • Burning Combustion of PVC releases toxic hydrogen chloride and may form other harmful products.
Recycling
  • Recycling Thermoplastics can be melted and reshaped, which reduces waste and saves raw materials.

Part 5 of 6Worked Example

Question Deduce the monomer of the polymer with repeating unit –CH₂–CHCl–.

  1. The backbone has two carbon atomsCH₂ and CHCl.
  2. Replace the two connecting bonds by a C=C double bond between them.
  3. Keep the Cl on the same carbon.

Answer CH₂=CHCl, chloroethene (vinyl chloride).

Part 6 of 6Exam Checklist & Tips

2.4.5 – Key Points for the Exam

  • Addition polymer A polymer formed by the joining of unsaturated monomers without loss of any atoms.
  • Repeating unit The section of the chain that repeats along its length.
  • Thermoplastic A plastic that softens on heating and can be remoulded.
  • Atom economy The proportion of reactant atoms that end up in the desired product.

Common Mistakes

  • Leaving the double bond in the repeating unit.
  • Forgetting the open bonds at the ends of the repeating unit.
  • Writing the monomer with the side groups on the wrong carbon.
  • Saying addition polymers produce water as they form.

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