Polymers and Addition Polymerisation

• newEditor
• Chemistry
• Upper Secondary (Key Stage 4)
• GCSE

Polymers: Structure, Uses and Waste

This GCSE chemistry lesson explores Polymers and Addition Polymerisation. Students explain how monomers form polymers, represent addition polymerisation and evaluate how polymer properties, uses and disposal affect society and the environment. It supports KS4 classroom teaching, independent study and exam revision using clear, subject-specific vocabulary.

Polymers, KS4 Chemistry, GCSE Chemistry, Polymerisation, Addition Polymerisation, Condensation Polymerisation, Monomers, Synthetic Polymers, Polyethene, Polypropene, Thermosoftening Polymers, Thermosetting Polymers, Plastics, Polyesters, Polyamides, Natural Polymers, DNA, Proteins, Starch, Cellulose, Structural Formulas, Repeat Units, MCQs, Open Questions, Polls, Emoji Polls, Exit Tickets

Learning goal

I can understand what polymers are, how monomers join by polymerisation to form long-chain molecules, and how the structure and properties of polymers relate to their uses.

Try and think of as many words as possible that link to polymers

Use this to surface prior ideas such as plastic, chain, strong, rubbish, bottles, flexible, pollution. Pick out misconceptions too, for example if students think polymer just means plastic bag.

What is a polymer?

• A polymer is a very large molecule made from many smaller repeating units

• The small starting molecules are called monomers

• When many monomers join together, they make a long-chain molecule

• Many useful materials, including plastics, are polymers

Students may think all polymers are synthetic plastics. You can note that the key idea is repeating units in a long chain; this lesson focuses on synthetic addition polymers.

Monomers and repeat units

• A monomer is one small molecule that can join to others

• In the polymer chain, the pattern that repeats is the repeat unit

• The repeat unit comes from the monomer, but it is shown as part of the chain

Emphasise that a repeat unit is not a separate molecule floating on its own; it is the section of structure repeated along the polymer chain.

What is polymerisation?

Polymerisation is the reaction in which many monomer molecules join to make a polymer. The product is a much larger molecule with a long chain of repeating units.

Long chains change the material

• Polymer molecules are much larger than the monomers they come from

• Their long chains can tangle together

• This gives polymer materials different properties from small simple molecules

• That is why polymers are useful as solids such as plastics

Keep this at a simple particle-level explanation: larger molecules and tangled chains help explain why polymers are solids with useful strength and flexibility.

Addition polymerisation

• Addition polymerisation happens when many alkene monomers join together

• The monomers add to each other one after another

• No small molecule is removed in this process

• The polymer contains all the atoms from the monomers

What is a repeat unit?

A

a small molecule

B

a section of chain

C

a double bond

D

a whole reaction

Checks the distinction between monomer, repeat unit and polymerisation from slides 2 to 4.

Key ideas so far

A polymer is a very large molecule made from many repeating units. A monomer is a small molecule that joins to others. This joining reaction is called polymerisation, which forms a long-chain molecule.

polymer

monomer

polymerisation

alkene

biodegradable

disposal

All three blanks are load-bearing terms introduced in the first subtopic.

Why alkenes can form polymers

• Alkene monomers contain a C=C double bond

• This double bond can open during the reaction

• That allows each monomer to join to neighbouring monomers and build a chain

Link to prior knowledge: alkenes are unsaturated because they contain a carbon–carbon double bond.

What happens to the double bond?

C=C double bond breaks open → new single bonds form to neighbouring monomers → a long saturated polymer chain forms

Clarify that the polymer is described as saturated because the carbon atoms in the backbone are linked by single bonds only.

From alkene to polymer

• Start with many identical alkene monomers

• Break the C=C bond in each monomer

• Join the monomers into a chain of repeat units

• Name the polymer from the monomer, for example ethene → poly(ethene)

You may mention bracket notation and the use of n if helpful, but it is not essential to place the full symbolic form on the slide.

Poly(ethene)

• Made by addition polymerisation of ethene

• Its chain has only carbon and hydrogen atoms

• The structure gives a material that is light and useful for making everyday plastic items

You can mention common examples such as carrier bags and bottles, depending on the type of poly(ethene). Keep the focus on the link between simple chain structure and practical use.

Why poly(ethene) is used

• It is chemically unreactive because it has strong covalent bonds in long chains

• It is light in mass

• It can be flexible or tough, depending on how it is made

• These properties make it suitable for packaging and containers

Avoid overloading with density details unless needed. The important link is structure to properties to uses.

Why can alkene monomers form addition polymers?

A

They contain oxygen

B

They are very large

C

They have C=C bonds

D

They are biodegradable

Targets the key idea that the carbon-carbon double bond allows the monomers to join.

From alkene to polymer

In addition polymerisation, many alkene monomers join together. The double bond breaks open, and new single bonds form. This produces a long saturated chain such as poly(ethene).

alkene

double bond

saturated

repeat unit

biodegradable

chlorine

Echoes slides 6 to 11 and checks the mechanism language without needing symbolic structures.

Poly(propene)

• Made from propene monomers

• It has a methyl side group on the chain

• This affects how the chains pack together

• It is often used where a tougher plastic is needed

If useful, compare its side group to poly(ethene), which helps explain differences in properties.

Why poly(propene) is used

• Poly(propene) is tough and resistant to chemicals

• It can be made into fibres and moulded shapes

• Typical uses include ropes, crates and food containers

• Its uses depend on the balance of low mass, strength and durability

PVC

• PVC is poly(chloroethene)

• It is made from chloroethene monomers

• Each repeat unit contains chlorine as well as carbon and hydrogen

• This changes the properties of the polymer

Use both names if helpful: PVC and poly(chloroethene). This helps students connect common and systematic naming.

Why PVC is used

• The chlorine-containing structure helps make PVC hard and durable

• It is resistant to water and many chemicals

• Rigid PVC is used for pipes and window frames

• Plasticised PVC can be made more flexible for cable coverings

A useful contrast is that changing formulation can change properties, but the core teaching point remains that structure affects properties and uses.

Structure, properties and uses

Different monomers make polymer chains with different structures. Those structural differences affect how the chains move, pack and interact, which changes properties such as flexibility, toughness and chemical resistance.

This is the key generalisation slide. Draw together the examples: poly(ethene), poly(propene) and PVC each show the same principle.

Examples compared

Structure and property

Typical uses

Poly(ethene) - simple chain, light, flexible or tough

Poly(propene) - side group on chain, tough, durable

PVC - chlorine in repeat unit, hard, chemically resistant

Poly(ethene) - bags, bottles, packaging

Poly(propene) - ropes, crates, containers

PVC - pipes, window frames, cable coverings

Which polymer is commonly used for pipes and window frames?

A

poly(ethene)

B

poly(propene)

C

PVC

D

ethene

Uses a familiar application to check the structure-properties-uses link in the comparison block.

Compare the polymers

Poly(ethene) has a simple chain and is often used for packaging. Poly(propene) has a side group on the chain, which helps make it tough. PVC contains chlorine in each repeat unit, which helps make it hard and durable.

packaging

side group

chlorine

oxygen

monomer

disposal

Draws together examples from slides 12 to 17.

How does structure affect a polymer's use?

Expected elements: structure affects chain packing and movement; this changes properties such as flexibility, toughness or chemical resistance; those properties decide suitable uses. Accept answers using any one of the named examples.

Why polymer waste is a problem

• Many polymers are made to be durable and unreactive

• These useful properties also mean they break down very slowly in the environment

• Large amounts of plastic waste can build up on land and in water

Why many polymers are not biodegradable

• Biodegradable materials can be broken down by microorganisms

• Many addition polymers have strong, stable chains

• Microorganisms cannot easily break these chains apart

You can contrast this with natural materials that enzymes can attack more easily, without going into detailed biochemistry.

Recycling and disposal

• Recycling means collecting and processing polymers so the material can be used again

• Disposal means getting rid of waste, for example by landfill or burning

• Recycling aims to reduce the amount of new raw material needed

• Disposal does not recover the polymer in the same way

Students often use 'recycling' and 'throwing away carefully' as if they mean the same thing. This slide separates them clearly.

Choosing what to do with polymer waste

• Recycling can reduce waste and save resources

• Disposal may still be used when recycling is difficult

• The best choice depends on the type of polymer, contamination and available facilities

• Polymer chemistry affects environmental decisions

Keep the discussion balanced and rooted in chemistry: the properties that make polymers useful also create waste-management challenges.

Why are many addition polymers not biodegradable?

A

They dissolve in water

B

Their chains are unstable

C

Microbes break them fast

D

Their chains are strong

Tests the reason given on slides 18 to 20: durable, stable chains are hard for microorganisms to break down.

Which is the best description of recycling?

1

using again

2

processing waste

3

burying waste

4

burning waste

How confident do you now feel in your understanding of polymers?

Glossary

polymer - a very large molecule made from many repeating units

monomer - a small molecule that can join to other similar molecules

repeat unit - the section of a polymer chain that repeats

polymerisation - the reaction in which monomers join to form a polymer

addition polymerisation - polymerisation in which alkene monomers add together with no other product formed

alkene - an unsaturated hydrocarbon with a carbon–carbon double bond

saturated - containing only single carbon–carbon bonds

Glossary

poly(ethene) - a polymer made from ethene monomers

poly(propene) - a polymer made from propene monomers

PVC - poly(chloroethene), a polymer made from chloroethene monomers

biodegradable - able to be broken down by microorganisms

recycling - processing a material so it can be used again

disposal - getting rid of waste by methods such as landfill or burning