Addition polymerisation is the most common way small molecules join to make polymers. It works like this:
• The monomer molecule must contain a C=C double bond
• Under heat and pressure with a catalyst, the double bond "opens up"
• One of the two bonds in the double bond breaks
• This creates two "dangling" bonds that can attach to other monomers
• Each monomer uses its broken double bond to connect to the next
• The chain grows: monomer + monomer + monomer + ... = polymer
• Thousands of monomers join to make one giant chain
• No atoms are lost — "addition" means everything is added in
• Monomer: CH₂=CH₂ (ethene — has a double bond)
• Polymer: -[CH₂-CH₂]ₙ- (poly(ethene) — n means repeated many times)
• Used in: plastic bags, bottles, containers
• The double bond becomes a single bond in the polymer chain
• Poly(propene): from propene (CH₃CH=CH₂) — car bumpers, ropes
• PVC (polyvinylchloride): from chloroethene — pipes, window frames
• Poly(tetrafluoroethene) (PTFE): from CF₂=CF₂ — non-stick coatings (Teflon)
Naming rule: The polymer is named from its monomer — just add "poly" in front and put the monomer name in brackets: ethene → poly(ethene), propene → poly(propene).
This deep dive covers How Polymers Are Made: Addition Polymerisation within Polymers for GCSE Chemistry. Revise Polymers in Bonding & Structure for GCSE Chemistry with 22 exam-style questions and 21 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 2 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Polymers
In addition polymerisation, what feature of monomer molecules allows them to join together?
Explain why thermosetting polymers are rigid and do not melt when heated.