What are Addition Polymers? Revision Notes | GCSE AQA Higher Chemistry
Polymerisation is the joining of many small molecules, called monomers, into one giant molecule, a polymer. Free notes with key terms and 11 questions answered.
Updated 19 Mar 2026 · Revise Right Team
What are Addition Polymers? is part of Synthetic and naturally occurring polymers (chemistry only) in GCSE AQA Higher Chemistry.
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What this lesson covers
Polymerisation is the joining of many small molecules, called monomers, into one giant molecule, a polymer. Free notes with key terms and 11 questions answered.
Recognise addition polymers and their monomers from diagrams showing C=C functional groups
Explain how alkenes undergo addition polymerisation to form large molecules
Draw the structures of common addition polymers like poly(ethene) and poly(propene)
Compare the properties of monomers and their corresponding polymers
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Use this lesson to stay inside Synthetic and naturally occurring polymers (chemistry only) while connecting the detail back to the wider Topic 7: Organic chemistry topic.
Topic 7: Organic chemistry
Synthetic and naturally occurring polymers (chemistry only)
GCSE AQA Higher Chemistry
Revision notes
Read the core explanations from What are Addition Polymers? before testing yourself from memory.
1. What Makes a Polymer?
Look around you right now. That plastic water bottle, the polyester in your school jumper, the polythene bag your lunch came in — they're all made from the same basic process. Thousands of tiny molecules linking together like a chain to form one giant molecule.
These giant molecules are called polymers. The word literally means 'many parts' — poly (many) + mer (part). But here's what catches students out: not all polymers are made the same way.
The key phrase is 'no other products formed'. When monomers join up, nothing else is made — no water, no hydrogen chloride, nothing. Just one big chain. This is different from condensation polymers where small molecules like water are eliminated.
2. From Alkenes to Polymers
Remember alkenes from earlier in the course? Those hydrocarbons with C=C double bonds that decolourised bromine water? Well, that reactive double bond is exactly what we need for addition polymerisation.
Think of monomers like LEGO bricks with sticky ends. Each monomer has a C=C double bond that acts like those sticky ends. When conditions are right (heat, pressure, catalyst), these sticky ends grab onto each other.
The simplest example is ethene (C₂H₄). Under the right conditions, thousands of ethene molecules join together to make poly(ethene) — what we commonly call polythene or polyethylene.
Worked example: How Addition Polymerisation Works
Show how ethene monomers join to form poly(ethene)
H₂C=CH₂ + H₂C=CH₂ + H₂C=CH₂ + ... — Each ethene molecule has a reactive C=C double bond
The C=C bonds break to form single bonds — This releases energy to drive the reaction forward
—CH₂—CH₂—CH₂—CH₂—CH₂—CH₂— — Forms a long chain with only single bonds
—(CH₂—CH₂)ₙ— or —(C₂H₄)ₙ— — The 'n' shows the repeating unit happens many times
Answer: Poly(ethene): —(CH₂—CH₂)ₙ—
3. Common Addition Polymers
You've seen poly(ethene), but there are many other addition polymers. The pattern is always the same: take an alkene monomer, apply heat and pressure with a catalyst, and watch the chains grow.
Poly(propene) comes from propene (CH₃CH=CH₂). Notice how we write the polymer name — it's always poly(monomer name) in brackets. This tells you exactly which monomer was used.
Here's the key insight: the polymer keeps the same atoms as the monomers, just rearranged. If you start with C₂H₄ (ethene), your polymer repeating unit is still C₂H₄. No atoms are lost or gained.
4. Recognising Polymers from Diagrams
Exam questions love showing you polymer structures and asking you to identify the monomer. Here's the trick: look for the repeating pattern and imagine 'closing' the chain ends to recreate the C=C double bond.
Worked example: Working Backwards from Polymer to Monomer
Given the polymer structure —(CHClCH₂)ₙ—, identify the monomer
—CHCl—CH₂— — This pattern repeats along the chain
CHCl—CH₂ — Remove the bonds to neighbouring units
CHCl=CH₂ — The single bond becomes a double bond in the monomer
Chloroethene (vinyl chloride) — This polymerises to form PVC (polyvinyl chloride)
Answer: Monomer: CHCl=CH₂ (chloroethene)
The reverse process works too. Given a monomer with a C=C bond, you can predict the polymer structure by 'opening up' the double bond and showing how the units link together.
5. Properties and Uses
Addition polymers have very different properties from their monomers. Ethene is a gas at room temperature, but poly(ethene) is a solid plastic. This happens because the long polymer chains get tangled up with each other.
Most addition polymers are unreactive because they only contain C-C and C-H bonds — both very strong and stable. This makes them useful for packaging and containers, but also means they don't biodegrade easily.
6. Exam Technique
Addition polymer questions follow predictable patterns. You'll either be asked to identify monomers from polymer structures, or draw polymer structures from monomers. Both require the same core skill: understanding how C=C bonds open up.
Common exam mistakes include forgetting that no small molecules are eliminated (that's condensation polymerisation), and drawing polymer structures that still contain C=C bonds. Remember: the double bonds open up to form the chain.
When drawing addition polymerisation, focus on the repeating unit structure and the overall transformation from monomer to polymer.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-19.
Polymerisation is the joining of many small molecules, called monomers, into one giant molecule, a polymer. In addition polymerisation, alkene monomers with C=C double bonds join in a chain, and no other products are formed.
What conditions are needed for addition polymerisation?
Addition polymerisation needs the right conditions: heat, pressure and a catalyst. Under these conditions the C=C double bonds in alkene monomers open up and the molecules join into long chains.
How are addition polymers named?
Addition polymers are named poly(monomer name), with the monomer in brackets, such as poly(ethene) from ethene and poly(propene) from propene. The name tells exactly which monomer was used.
What is PVC made from?
PVC (polyvinyl chloride) is made from the monomer chloroethene, CHCl=CH₂, also called vinyl chloride. Its repeating unit is -CHCl-CH₂-, formed when the C=C double bond opens up.
How does addition polymerisation work?
In addition polymerisation, the C=C double bonds in the monomers open up to form single bonds, so the monomers link together into a long chain. For ethene, H₂C=CH₂ molecules join to form poly(ethene), shown as —(CH₂—CH₂)ₙ—.
What is an addition polymer?
An addition polymer is a large molecule formed when many small monomers containing C=C double bonds join together in a chain, with no other products formed. For example, many ethene molecules join to make poly(ethene).
How do you find the monomer from a polymer?
To find the monomer, identify the repeating unit, remove the bonds to neighbouring units, then turn the single bond back into a C=C double bond. For —(CHClCH₂)ₙ—, the repeating unit —CHCl—CH₂— gives the monomer CHCl=CH₂, chloroethene.
Why don't addition polymers biodegrade?
Most addition polymers are unreactive because they only contain strong, stable C-C and C-H bonds. This makes them useful for packaging and containers, but it also means they do not biodegrade easily.
Why is poly(ethene) a solid when ethene is a gas?
Poly(ethene) is a solid plastic while ethene is a gas at room temperature because the long polymer chains get tangled up with each other. The polymer keeps the same atoms as the monomers, with a repeating unit of C₂H₄.
What does poly mean in polymer?
Poly means 'many' and mer means 'part', so polymer literally means 'many parts'. A polymer is a giant molecule made from thousands of small molecules linked together like a chain.
Do addition polymers contain double bonds?
Addition polymers do not contain C=C double bonds, because the double bonds in the monomers open up to form the chain. Drawing a polymer structure that still contains C=C bonds is a common mistake; the chain has only single bonds.