Chemistry · Year 11 · Organic Chemistry and Analysis · Summer Term

Polymers and Polymerisation

Understanding the formation of addition polymers from monomers and their uses and disposal.

• National Curriculum Attainment Targets
• GCSE: Chemistry - Organic Chemistry

About This Topic

Addition polymerisation involves unsaturated monomers, such as alkenes with carbon-carbon double bonds, linking together to form long-chain polymers. The double bond breaks open, allowing monomers to join repeatedly and create a repeat unit that defines the polymer's structure. Year 11 students represent this process by drawing monomer structures like propene and its corresponding polymer, polypropene, while noting that no other products form during addition reactions.

This topic fits within GCSE Organic Chemistry, linking monomer properties to polymer uses in everyday items like plastic bags, bottles, and synthetic fibres. Students also examine disposal challenges: polymers do not biodegrade easily, persist in landfills, and fragment into microplastics that harm ecosystems. Evaluating recycling methods versus incineration develops critical thinking about sustainable chemistry practices.

Active learning suits this topic well. When students construct physical models of monomers snapping into chains or test polymer properties through stretching and heating samples, they grasp abstract bonding visually and tactilely. Group analysis of local plastic waste connects theory to real impacts, making concepts stick through inquiry and collaboration.

Key Questions

1. Explain the process of addition polymerisation.
2. Differentiate between different types of polymers based on their monomers.
3. Evaluate the environmental challenges associated with polymer disposal.

Learning Objectives

• Explain the mechanism of addition polymerisation, illustrating the breaking of carbon-carbon double bonds and the formation of a polymer chain.
• Compare and contrast the structures of different addition polymers based on their corresponding alkene monomers.
• Analyze the environmental impact of common addition polymers, identifying specific challenges related to their persistence and fragmentation.
• Evaluate the effectiveness of different disposal methods for addition polymers, such as recycling and incineration, in mitigating environmental harm.
• Identify the repeat unit in a given addition polymer structure and deduce the structure of its monomer.

Before You Start

Alkanes and Alkenes

Why: Students need to understand the structure and bonding of hydrocarbons, particularly the presence and reactivity of the carbon-carbon double bond in alkenes, which is essential for addition polymerisation.

Basic Chemical Bonding

Why: Understanding covalent bonding is fundamental to comprehending how monomers link together to form polymer chains and how double bonds break to form single bonds.

Key Vocabulary

Monomer	A small molecule that can react with other identical or similar molecules to form a larger polymer molecule. In addition polymerisation, monomers typically contain a carbon-carbon double bond.
Polymer	A large molecule made up of many repeating smaller units called monomers, linked together by covalent bonds. Addition polymers are formed by the direct joining of monomers.
Addition Polymerisation	A type of polymerisation reaction where unsaturated monomers (containing double or triple bonds) add to one another in such a way that the polymer contains all the atoms of the monomer unit. No byproducts are formed.
Repeat Unit	The specific arrangement of atoms that repeats itself throughout the polymer chain. It is derived from the monomer structure after the double bond has opened.
Alkene	An unsaturated hydrocarbon containing at least one carbon-carbon double bond. Alkenes like ethene and propene are common monomers for addition polymers.

Watch Out for These Misconceptions

Common Misconception

Polymers form from any molecules gluing together randomly.

What to Teach Instead

Addition polymers form specifically from monomers with C=C bonds, creating identical repeat units. Hands-on chain-building activities let students see the precise linking process, correcting vague ideas through visual construction and peer explanation.

Common Misconception

All polymers break down quickly in the environment like natural materials.

What to Teach Instead

Synthetic addition polymers resist biodegradation due to strong C-C bonds. Testing plastic samples for degradation over time in group experiments reveals persistence, prompting discussions on microplastics and sustainable disposal.

Common Misconception

The repeat unit is identical to the monomer structure.

What to Teach Instead

The repeat unit shows the monomer minus the double bond. Drawing sessions with molecular model kits help students actively modify structures, reinforcing the bond-breaking step through manipulation.

Active Learning Ideas

Modelling: Monomer Chain Building

Provide paper cutouts of monomers with Velcro on double bond sites. Students link them to form polymer chains, label repeat units, and compare chains from different alkenes like ethene and chloroethene. Discuss how chain length affects properties. Wrap up with drawings for portfolios.

30 min·Pairs

Progettazione (Reggio Investigation): Polymer Properties Testing

Supply samples of polythene, polypropene, and polystyrene. Groups test tensile strength by stretching, response to heat with Bunsen burners, and solubility in solvents. Record data in tables and link properties to monomer structure and uses.

45 min·Small Groups

Formal Debate: Disposal Solutions

Divide class into teams to research and argue for or against methods like recycling, biodegradable alternatives, or chemical breakdown. Each team presents evidence on environmental impact, then votes on best solution with justifications.

40 min·Whole Class

Demo Follow-Up: Slime Synthesis

Demonstrate cross-linked polymer formation using PVA glue and borax. Students in pairs make their own slime, vary ratios, and test elasticity. Connect to addition polymerisation by discussing monomer links and real-world applications like adhesives.

25 min·Pairs

Real-World Connections

• Chemical engineers at petrochemical plants design and operate continuous reactors to produce large volumes of polymers like polyethylene, used in plastic films and bottles, from alkene monomers.
• Environmental scientists study the long-term effects of plastic waste in marine environments, investigating how polymers like polypropylene fragment into microplastics that are ingested by marine life.
• Materials scientists at recycling facilities develop new processes to sort and reprocess waste polymers, aiming to create circular economy models for materials like PVC, used in pipes and window frames.

Assessment Ideas

Quick Check

Provide students with the structures of ethene and propene. Ask them to draw the structure of the corresponding addition polymer and label the repeat unit. Check that they have shown the carbon-carbon single bond within the polymer backbone.

Discussion Prompt

Pose the question: 'Given that most addition polymers do not biodegrade, what are the most responsible ways for society to manage plastic waste?' Facilitate a class discussion where students compare the pros and cons of landfill, incineration, and various recycling methods.

Exit Ticket

On an index card, ask students to write the name of one common addition polymer, its monomer, and one significant environmental problem associated with its disposal. Collect these to gauge understanding of the link between polymer type and its impact.

Frequently Asked Questions

How do you explain addition polymerisation to Year 11 students?

Start with alkenes' double bonds as 'reactive sites' using diagrams of ethene forming polyethene. Show repeat unit formation without by-products. Follow with molecular models for students to assemble chains, solidifying the step-by-step addition process. Link to exam questions on drawing polymers from given monomers.

What activities demonstrate polymer uses and disposal issues?

Use property tests on common plastics like stretching polythene bags or burying samples to simulate landfill persistence. Group debates on recycling versus landfilling build evaluation skills. Connect findings to GCSE questions on environmental impacts, making abstract issues concrete.

How can active learning improve understanding of polymers?

Active approaches like building monomer chains with manipulatives or synthesizing slime give tactile experience of polymer formation and properties. Collaborative testing of plastic samples reveals structure-function links that lectures miss. These methods boost retention by 30-50% through doing, as students explain processes to peers.

How to differentiate polymers by their monomers?

Compare alkenes like ethene (symmetric, non-polar polythene) and propene (branched, tougher polypropene). Students draw structures side-by-side, predict properties, and test samples. This scaffolded comparison clarifies how monomer differences dictate uses, preparing for exam-style differentiation questions.