Polymers from Alkenes: Addition Polymerisation

Active learning works for addition polymerisation because the process is invisible to the naked eye. Students need to manipulate models, handle real materials, and draw reaction steps to see how monomers link into long chains. These concrete experiences make abstract mechanisms visible and memorable.

• Year 12
• Chemistry
• 4 activities
• 25 min–45 min

Learning Objectives

1. Explain the mechanism of addition polymerization, including the role of the double bond in alkene monomers.
2. Compare and contrast the properties and specific applications of at least three common addition polymers (e.g., polyethene, polypropene, PVC, polystyrene).
3. Analyze the environmental impact of common addition polymers, evaluating methods for waste reduction and recycling.
4. Justify the industrial choice of addition polymerization for large-scale plastic production based on efficiency and monomer availability.

Case Study Analysis

⏱ 30 min·Pairs

Molecular Modeling: Alkene to Polymer Chains

Provide ball-and-stick kits for students to build ethene monomers, then link them by breaking double bonds to form polyethene chains of varying lengths. Pairs compare short versus long chains for flexibility. Conclude with drawings of the repeating unit.

Prepare & details

Justify the transition from monomers to polymers in industrial manufacturing.

Facilitation Tip: During Molecular Modeling, circulate with a set of pre-made monomer pieces and challenge pairs to physically link three units before they can use the whole set.

Setup: Groups at tables with case materials

Materials: Case study packet (3-5 pages), Analysis framework worksheet, Presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Stations Rotation

⏱ 45 min·Small Groups

Stations Rotation: Polymer Property Tests

Set up stations with polythene, PVC, and polystyrene samples. Groups test tensile strength by stretching, heat resistance with hot water, and solubility in solvents. Record data in tables and discuss structure-property links.

Prepare & details

Compare the properties and uses of different addition polymers.

Facilitation Tip: In Station Rotation, assign each group one polymer property to test while another group presents their findings to compare flexibility, strength, and melting point.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Formal Debate

⏱ 40 min·Whole Class

Formal Debate: Polymers in Industry and Environment

Divide class into teams to research and argue for or against expanding polymer use, citing properties, manufacturing, and disposal data. Whole class votes and reflects on key evidence presented.

Prepare & details

Analyze the environmental challenges associated with polymer disposal.

Facilitation Tip: In the Debate, provide a fact sheet with polymer properties and disposal data so students can reference specific evidence during their arguments.

Setup: Two teams facing each other, audience seating for the rest

Materials: Debate proposition card, Research brief for each side, Judging rubric for audience, Timer

• Analyze
• Evaluate
• Create
• Self-Management
• Decision-Making

Case Study Analysis

⏱ 25 min·Individual

Microscale Polymerisation Demo

Demonstrate addition polymerisation using styrene and benzoyl peroxide in test tubes. Students observe viscosity changes over time, draw mechanisms, and predict products individually before class discussion.

Prepare & details

Justify the transition from monomers to polymers in industrial manufacturing.

Facilitation Tip: For the Microscale Demo, use a clear plastic tray to contain the reaction and pause at the propagation step to ask students to predict the next unit addition.

Setup: Groups at tables with case materials

Materials: Case study packet (3-5 pages), Analysis framework worksheet, Presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Teaching This Topic

Teach this topic by starting with molecular models to build intuition, then move to small-scale reactions to observe change over time. Avoid overwhelming students with complex kinetics early; focus first on the visual chain growth. Research shows that drawing mechanisms step-by-step while narrating the process improves retention more than lecturing alone. Use real-world samples to anchor learning, but balance examples of ideal polymers with cases where additives change behavior.

What to Expect

By the end of these activities, students should accurately draw monomer-to-polymer conversions, explain the role of free radicals, and connect polymer structure to real-world properties. They should also discuss trade-offs between industrial use and environmental impact with evidence-based reasoning.

Watch Out for These Misconceptions

Common Misconception

During Molecular Modeling: Alkene to Polymer Chains, watch for students who treat the process as a physical mixing rather than a chemical change.

What to Teach Instead

Have students physically break the double bond in their ethene model and snap monomers together end-to-end, narrating each step aloud to reinforce bond breaking and forming.

Common Misconception

During Station Rotation: Polymer Property Tests, watch for students who assume all polymers with similar names have identical properties.

What to Teach Instead

Provide samples labeled with monomer structure and reaction conditions, then ask groups to check melting points and flexibility before drawing conclusions about their differences.

Common Misconception

During the Microscale Polymerisation Demo, watch for students who expect visible byproducts or gas release.

What to Teach Instead

After the demo, ask students to draw the complete mechanism and compare it to condensation polymerisation, highlighting the absence of small molecule loss.

Assessment Ideas

Quick Check

After Molecular Modeling, collect each pair’s chain drawing and ask them to label the repeating unit and the bond formed during propagation.

Discussion Prompt

During Station Rotation, have each group present one surprising property test result, then facilitate a class vote on which polymer would best serve as reusable food packaging, citing evidence.

Exit Ticket

After the Debate, ask students to write a one-paragraph reflection on one thing they changed their mind about during the discussion, using evidence from the activity.

Extensions & Scaffolding

• Challenge early finishers to predict how a branched alkene monomer would affect the polymer’s density and strength, then sketch the resulting structure.
• Scaffolding: Provide a partially completed mechanism diagram with missing propagation steps for students to fill in during the Microscale Demo.
• Deeper exploration: Ask students to research a biodegradable polymer alternative and compare its formation, properties, and cost to a traditional addition polymer.

Key Vocabulary

Monomer	A small molecule that can be bonded together with other identical or similar molecules to form a larger molecule called a polymer. In addition polymerization, these are typically alkenes.
Polymer	A large molecule composed of many repeating subunits (monomers) linked together. Addition polymers are formed without the loss of any atoms.
Addition Polymerisation	A type of polymerisation reaction where unsaturated monomers (containing double or triple bonds) add to one another without the loss of any small molecules to form a polymer.
Repeating Unit	The structural unit that is repeated throughout the polymer chain, derived from the monomer.
Alkene	An unsaturated hydrocarbon containing at least one carbon-carbon double bond. The double bond is key to initiating addition polymerization.