Key Learning Objectives
- Draw repeating units for addition polymers from alkene monomer structures.
- Deduce the alkene monomer structure from a section of an addition polymer chain.
- Explain the conditions for addition polymerisation (high pressure, catalyst, unsaturated C=C bonds).
Topic Summary & Core Notes
Master addition polymerisation in seconds. Break the alkene double bond, extend horizontal trailing bonds through square brackets, and annotate with 'n' for poly(ethene), poly(propene), and poly(chloroethene).
Key Rules, Formulas & Definitions
Addition Polymer Rule
Open C=C double bond → Draw single C-C bond with horizontal trailing bonds passing through square brackets, with 'n' subscript
2 Step-by-Step Worked Examples
Worked Example 1
Worked Example 1: Drawing Poly(propene) from Propene
Question: Draw the repeat unit for poly(propene) formed from propene (CH2=CH-CH3).
Step-by-Step Solution:
- Step 1: Align alkene backbone: Draw the two double-bonded carbons horizontally: C=C.
- Step 2: Group substituents vertically: Left carbon has two H atoms (top and bottom). Right carbon has one H (top) and one -CH3 methyl group (bottom).
- Step 3: Open bond and add brackets: Change C=C to C-C, draw bonds through square brackets, and write 'n' subscript: -[CH2-CH(CH3)]-n.
Final Answer: A 2-carbon backbone with single C-C bond, trailing bonds through brackets, with one -CH3 and three -H attached, subscript n.
Senior Examiner Insight: Trailing bonds MUST extend through the brackets; failing to pierce the brackets loses the mark.
Worked Example 2
Worked Example 2: Finding Monomer from Polymer Chain
Question: Given the polymer chain segment -[CH2-CHCl]n-, deduce the name and structure of the monomer.
Step-by-Step Solution:
- Step 1: Identify 2-carbon repeating unit: Two carbon atoms in the backbone: one with two H, one with H and Cl.
- Step 2: Reintroduce double bond: Remove trailing bonds and insert C=C double bond: CH2=CHCl.
- Step 3: Name monomer: Chloroethene.
Final Answer: Chloroethene (CH2=CHCl)
Senior Examiner Insight: Ensure the double bond C=C is clearly drawn in the monomer structure.
Common Pitfalls & Examiner Warnings
Common Mistake: Leaving double bonds inside polymer brackets
Addition polymerisation CONSUMES the double bond; the repeat unit contains only single C-C bonds.
Common Mistake: Forgetting the trailing extension bonds
The horizontal bonds must pass through the brackets to show the polymer chain continues.
Interactive Self-Check Quiz (3 Questions)
Question 1 of 3
What happens to the C=C double bond of alkene monomers during addition polymerisation?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) It breaks open to form single covalent bonds between adjacent monomer units
Detailed Explanation: The pi bond in the C=C double bond opens up, forming single sigma bonds linking adjacent monomers into a polymer chain.
Mark Scheme & Scoring Points: 1 mark for opening up to form single covalent bonds.
Question 2 of 3
Which monomer polymerises to form poly(tetrafluoroethene) [PTFE / Teflon]?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) Tetrafluoroethene (CF2=CF2)
Detailed Explanation: Poly(tetrafluoroethene) is formed by addition polymerisation of tetrafluoroethene (CF2=CF2) monomers.
Mark Scheme & Scoring Points: 1 mark for Tetrafluoroethene.
Question 3 of 3
What does the small subscript letter 'n' represent outside the polymer bracket?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) A very large and unspecified number of repeating monomer units
Detailed Explanation: 'n' signifies that thousands of repeating monomer units are joined in the polymer macromolecule.
Mark Scheme & Scoring Points: 1 mark for large unspecified number of repeat units.
Created by Fiaraz Iqbal
Former Headteacher & Senior Science / Maths Examiner
Fiaraz produces structured video walkthroughs, Tier 3 literacy packs, and exam mark scheme breakdowns to help secondary students achieve top grades.
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