3.3.6Organic Chemistry
Addition Polymerisation — Edexcel AS Chemistry Revision Notes & Topical Questions
5 min read 5 parts Lesson 29 of 42
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Part 1 of 5How Addition Polymers Form
1
A monomer is an unsaturated molecule, usually an alkene, that contains a C=C double bond.
2
Under the right conditions the π bond in each monomer opens up and joins to the next molecule.
3
Thousands of monomers link in a long chain, all atoms of the monomer ending up in the polymer.
4
The reaction is called addition polymerisation because no small molecule is lost.
5
For ethene, n CH₂=CH₂ → –(CH₂–CH₂)ₙ–, where the part in brackets is the repeat unit.
Part 2 of 5Common Polymers
Common Polymers
Poly(ethene)
- Poly(ethene) Made from ethene, it is used for carrier bags, bottles and packaging film.
Poly(propene)
- Poly(propene) Made from propene, it has repeat unit –CH(CH₃)–CH₂– and is used in ropes, crates and carpets.
Poly(chloroethene)
- Poly(chloroethene) Made from chloroethene, CH₂=CHCl, also called PVC, it is used for pipes and window frames.
Poly(tetrafluoroethene)
- Poly(tetrafluoroethene) Made from CF₂=CF₂, also called PTFE, it is used for non-stick pans because it resists heat and chemicals.
Properties
- Properties The polymers are generally unreactive, because they contain only strong, non-polar C–C and C–H bonds.
| Monomer | Polymer | Repeat unit |
|---|---|---|
| CH₂=CH₂ | Poly(ethene) | –CH₂–CH₂– |
| CH₃CH=CH₂ | Poly(propene) | –CH(CH₃)–CH₂– |
| CH₂=CHCl | Poly(chloroethene) | –CHCl–CH₂– |
Part 3 of 5Drawing the Repeat Unit
Step 1
- Step 1 Draw the monomer with the double bond in the middle and the other groups above and below.
Step 2
- Step 2 Change the double bond into a single bond to show the opened π bond.
Step 3
- Step 3 Add an open bond (a continuation line) at each end of the carbon chain.
Step 4
- Step 4 Enclose the unit in brackets with the subscript n to represent the many units.
Check
- Check The repeat unit contains the same atoms as the monomer, so the molecular formula is the same.
Part 4 of 5Worked Example
Question
- A sample of poly(chloroethene) has an average relative molecular mass of 62 500.
- Calculate the average number of monomer units per chain.
- (Ar: C 12.0, H 1.0, Cl 35.5.)
- The monomer is C₂H₃Cl, so its Mr = 2 × 12.0 + 3 × 1.0 + 35.5 = 62.5.
- The polymer mass equals n times the monomer mass because addition loses nothing.
- n = 62 500 ÷ 62.5 = 1000.
Answer About 1000 monomer units per chain
Part 5 of 5Exam Checklist & Tips
3.3.6 – Key Points for the Exam
- Monomer A small molecule that joins with many others to make a polymer.
- Polymer A long-chain molecule made of many repeat units.
- Repeat unit The smallest section of a polymer chain that repeats along the chain.
- Addition polymerisation A reaction in which unsaturated monomers add to each other to form a polymer.
- Poly(ethene) The polymer formed by the addition polymerisation of ethene.
Common Mistakes
- Including the double bond in the repeat unit: the polymer chain contains only single bonds.
- Leaving out the open bonds at the ends of the repeat unit.
- Putting the CH₃ group into the main chain of poly(propene) instead of showing it as a side group.
- Saying that a small molecule such as water is lost during addition polymerisation.
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