Lesson 6: Polymers: Addition Polymerisation & Materials
Turn alkene monomers into repeating units, connect polymer structure to material properties, and evaluate synthetic-plastic waste through kaitiakitanga.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Addition polymerisation mechanisms of alkene monomers (e.g., ethene to polyethene, propene to polypropene, chloroethene to PVC), repeating units, and environmental lifecycle impacts.
Draw structural formulas for monomers and polymer repeating units, explain physical property changes from monomer to polymer, and evaluate kaitiakitanga challenges of synthetic plastic waste.
🎥 Media Anchor & Pedagogical Scaffold
Addition Polymerisation & Polymer Structure
Video Clip: GCSE Chemistry — Addition Polymers and Polymerisation (2026/27 exams) | Cognito (Runtime: 7m 11s).
🧠 1. Before Viewing (Activate & Predict)
How do small reactive gas molecules (monomers) link together to form tough, durable solid plastics (polymers)?
👁️ 2. During Viewing (Watch With a Job)
- Definition: in your own words, what is a polymer? What is a monomer, and what must a monomer have to undergo addition polymerisation?
- Draw: sketch the polymerisation of ethene into poly(ethene). Show 3 monomer units combining and draw the repeating unit of the polymer.
- Properties: the video links polymer structure to properties. Explain why poly(ethene) is flexible but NOT suitable for very high-temperature applications.
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Connect synthetic polymer persistence with kaitiakitanga taiao and local NZ microplastic research in marine ecosystems.
Immediate Task: Complete Section 6 of your Organic Portfolio: Monomer-to-Polymer Drawing Sheet & Environmental Impact Analysis.
⚡ Whakaoho | Do Now: Organic Recall Challenge (10 mins)
Same reaction, different plastic. Polyethene, polypropene and PVC are all made by the same kind of reaction from three different alkenes.
Two minutes: draw ethene. Now draw three of them joined in a row with no atoms left over. What had to happen to the double bond to make that possible? Write it in one sentence — that sentence is addition polymerisation.
📖 Activity 1: Core Reaction Mechanism & Structure Analysis (25 mins)
Monomer ↔ repeating unit (15 min). Draw the repeating unit of the polymer made from each of these four monomers, with the bonds shown continuing at both ends: ethene (CH2=CH2), propene (CH2=CHCH3), chloroethene (CH2=CHCl), tetrafluoroethene (CF2=CF2). Then work backwards: name the monomer that made each of these two repeating units — –[CH2–CCl2]– and –[CH2–CH(CH2CH3)]–. Watch the substituents — that is where the marks are.
Kaiako answer key — Monomer ↔ repeating unit. Forwards: ethene → –[CH2–CH2]–; propene → –[CH2–CH(CH3)]–; chloroethene → –[CH2–CHCl]–; tetrafluoroethene → –[CF2–CF2]–. Backwards: –[CH2–CCl2]– came from 1,1-dichloroethene; –[CH2–CH(CH2CH3)]– came from but-1-ene. The two marks students drop: leaving the double bond in the repeating unit (it is gone — that is the whole reaction), and not drawing the bonds continuing out of both ends of the bracket, which is what says "this repeats". A repeating unit has the same atoms as its monomer, never fewer and never more; if the count changed, the drawing is wrong.
Find out, don't guess (10 min). Bring or find three plastic items. Look up the recycling code on each and what polymer it stands for — look it up, do not recall it — then match each to its monomer. Discuss: your local council accepts some of these and not others. Using structure, suggest why some plastics are easier to remelt and reuse than others.
📝 Activity 2: Level 2 Chemistry Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Organic Portfolio — Section 6. Submit: (1) four monomer → repeating-unit conversions; (2) two reverse conversions; (3) a short evidence-based paragraph on one plastic your council does or does not accept, citing where you found the recycling information.
🏫 Kaiako Planning & Pedagogy Notes
Where this sits in the standard. Polymerisation is the final item in the standard's addition-reaction list. Only addition polymerisation is in scope here — condensation polymers belong to Level 3 and cannot be assessed against this standard.
Exit ticket (3 min, on a slip, collected). Draw the repeating unit of the polymer made from CH2=CHCH3, showing the bonds continuing at both ends.
What to watch for while they work. The two things to check on every drawing: is the double bond gone, and do the bonds continue out of both ends of the repeating unit? A repeating unit with a C=C still in it is the commonest error in this topic and it is visible from across the room.
Differentiation. Support: Give students a paper-chain or linked-model demonstration before any drawing. Seeing three ethene units open and join makes the disappearing double bond concrete. Extension: Ask why poly(ethene) and poly(tetrafluoroethene) behave so differently despite being made the same way, and have them answer from the substituents rather than from what they already know about the products.
The error to head off. Students add or lose atoms between monomer and repeating unit. The atom count must be identical — addition polymerisation loses nothing, which is exactly what distinguishes it from the condensation polymers they may have met elsewhere.