3.4.5Physical Chemistry
Addition Polymers — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 5 parts Lesson 80 of 102
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.
Part 1 of 5Forming an Addition Polymer
Forming an Addition Polymer
Monomer
- Monomer A monomer is a small molecule with a C=C bond, such as ethene, propene or chloroethene.
Polymerisation
- Polymerisation In each monomer the pi bond opens, and the carbon atoms link in a long chain of single bonds.
Only one product
- Only one product The polymer is the sole product, so addition polymerisation has an atom economy of 100%.
Polymer
- Polymer A polymer is a very long molecule made of many repeating units joined together.
Part 2 of 5Repeat Units and Monomers
To go from monomer to polymer, or back, follow these steps.
1
Draw the monomer so the C=C bond is in the middle, with other groups above and below it.
2
Change the C=C double bond into a single C–C bond and add a bond sticking out at each end.
3
Place square brackets around this unit with the bonds crossing the brackets, and write n outside.
4
To work backwards, pick out the two-carbon repeat unit in the main chain of the polymer.
5
Replace the single bond between those two carbons with a double bond to recover the monomer.
Part 3 of 5Common Addition Polymers
Poly(ethene)
- Poly(ethene) Made from ethene, CH₂=CH₂, with repeat unit –CH₂–CH₂–, and used for bags and bottles.
Poly(propene)
- Poly(propene) Made from propene, CH₃CH=CH₂, with a methyl group on every second carbon of the chain.
Poly(chloroethene)
- Poly(chloroethene) Made from chloroethene, CH₂=CHCl, commonly called PVC, with a chlorine atom on every second carbon.
Poly(phenylethene)
- Poly(phenylethene) Made from phenylethene (styrene), with a benzene ring as the side group on alternate carbons.
| Monomer | Repeat unit |
|---|---|
| CH₂=CH₂ | –CH₂–CH₂– |
| CH₂=CHCl | –CH₂–CHCl– |
| CH₂=CHCH₃ | –CH₂–CH(CH₃)– |
Part 4 of 5Properties and Plasticisers
Properties and Plasticisers
Unreactive chains
- Unreactive chains Poly(alkenes) are saturated with non-polar C–C and C–H bonds, so they resist attack by acids and bases.
Intermolecular forces
- Intermolecular forces Chains are held together by van der Waals forces, so longer chains give a stronger, more rigid material.
Plasticiser
- Plasticiser A small molecule added to PVC that sits between chains, pushing them apart and weakening the forces between them.
Effect
- Effect With a plasticiser the chains slide more easily, so PVC becomes flexible, as needed for pool liners rather than drainpipes.
Part 5 of 5Exam Checklist & Tips
3.4.5 – Key Points for the Exam
- Monomer A small molecule that joins with many others to form a polymer.
- Polymer A long-chain molecule built from many repeating units.
- Repeat unit The smallest group of atoms which, repeated along the chain, makes up the polymer.
- Plasticiser An additive that weakens the forces between polymer chains and makes the material more flexible.
- Addition polymerisation Joining of many alkene monomers through their C=C bonds to give one polymer product.
Common Mistakes
- Leaving a C=C bond in the repeat unit; it must be a single C–C bond.
- Drawing the repeat unit without the bonds that extend through the brackets at both ends.
- Confusing the repeat unit with the monomer, which still contains the double bond.
- Including more than two carbons in the main chain of the repeat unit of a substituted poly(alkene).
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