Addition polymerisation: monomers joining into a polymer chain (PE, PP, PVC, PTFE, PS)
ChemistryBiomolecules & PolymersAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Biomolecules & Polymers
Monomer molecules with a C=C double bond (ethylene, propylene, vinyl chloride, tetrafluoroethylene, styrene) move freely; as polymerisation runs, the π bond opens and each monomer joins the growing end of the chain. Students count the number of repeat units n, see the equation n CH₂=CHX → (–CH₂–CHX–)n and the polymer's molar mass M = n × M(monomer). A Radical mechanism tab shows initiation by a peroxide, propagation and termination with fish-hook arrows, and lets students change the initiator concentration to see the average chain length change.
Lesson: Polymer concept and structure; addition polymerisation; polymer materials (plastics)
What it shows
Addition polymerisation joins many small monomer molecules into one very long chain. Each monomer must contain a C=C double bond: the π bond breaks and a new σ bond forms to the next monomer, with no small molecule given off, so the molar mass of the polymer is n times that of the monomer. Many addition polymers are made by a free-radical chain reaction: a peroxide initiator splits into radicals (initiation), a radical adds monomer after monomer (propagation), and two radicals combine (termination). More initiator means more radicals at once, so each chain is stopped sooner and the average chain is shorter.
How to use
On Chain growth, choose a Monomer and press Polymerise to watch the units join while the equation and molar mass update. On Radical mechanism, set the Initiator concentration and press Run: the panel shows each step with fish-hook arrows, and the histogram collects the lengths of the finished chains. Each finished run is added to the table, so compare runs at different concentrations.
Parameters you can change
- Monomer Ethylene CH₂=CH₂ → PE, Propylene CH₂=CH–CH₃ → PP, Vinyl chloride CH₂=CHCl → PVC, Tetrafluoroethylene CF₂=CF₂ → PTFE, Styrene CH₂=CH–C₆H₅ → PS
- Number of units n to join 3–30
- Joining speed 0.5–4 units/s
- Label substituent groups
- View Chain growth, Radical mechanism
- Initiator concentration 1–16 mmol/L
Questions to explore
- What structural feature must a monomer have to take part in addition polymerisation?
- A polyethylene sample has a molar mass of 28 000 g/mol. What is its degree of polymerisation n?
- What is the repeat unit of PVC, and how is it related to the structure of vinyl chloride?
- What happens in the initiation, propagation and termination steps of radical polymerisation?
- Why does a higher initiator concentration give shorter polymer chains?
