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9701 AS Chemistry/ Topic 20 Polymerisation/ 5 interactive simulations/ drag to rotate 3D scenes

Addition polymerisation, made interactive

Five simulations covering Topic 20.1: alkene monomers joining into a poly(alkene) chain in 3D as each pi bond opens, with the substituents landing on alternate carbons; a repeat-unit finder where you bracket a section of chain and recover the monomer, or start from the monomer and write the repeat unit; a counter that works out how many monomers are in a chain from its relative molecular mass; a bond-polarity view that shows why a poly(alkene) has no reactive site while an ester does; and a disposal comparison of landfill, incineration and recycling with the equations for burning poly(ethene) and PVC.

1. Monomer to polymer 3D · 20.1

An alkene has a double bond, and the pi part of it is weak and exposed. Under heat, pressure and a catalyst that pi bond opens, each carbon uses its freed electron to grab a neighbour, and thousands of small molecules join end to end into one long chain. Pick a monomer, set how many units to start with, and join them one at a time.

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Monomer

4
JOINED
MONOMER
REPEAT UNIT
EQUATION
Exam point: in addition polymerisation the monomers simply add together. The only product is the polymer, there is no small molecule lost, and the empirical formula of the polymer is the same as that of the monomer. Conditions for poly(ethene): high pressure, about 200 °C and a trace of oxygen or a peroxide initiator, or a Ziegler-Natta catalyst at lower pressure.

2. Find the repeat unit 2D · 20.1

A repeat unit is the smallest piece of chain that, copied end to end, rebuilds the whole polymer. For an addition polymer it is always two backbone carbons: the two that used to share the double bond. Slide the bracket along a section of chain and set its width, then check. The reverse direction is here too: start from a monomer and write its repeat unit.

Direction

Polymer

2
3
RESULT
set the bracket, then check
MONOMER
Exam point: to get from a section of chain to the monomer, bracket two adjacent backbone carbons, delete the bonds that leave the bracket, and put the double bond back between the two carbons. To get from the monomer to the repeat unit, do the reverse: open the C=C to a single bond and draw a bond leaving each end, with n outside the bracket.

3. Count the monomers 2D · 20.1

Nothing is lost when monomers add together, so the mass of a chain is just the mass of its monomers added up. Divide the relative molecular mass of the chain by the relative molecular mass of one monomer and you have n, the number of monomers that joined. Pick a monomer and slide the chain mass.

Monomer

140 000
Mr OF MONOMER
MONOMERS IN CHAIN, n
BACKBONE CARBONS
CHAIN LENGTH, STRETCHED
WORKING
Exam point: Mr of the repeat unit equals Mr of the monomer, because no atoms are lost. Real samples contain chains of many different lengths, so the Mr you are given is an average and n is an average too. Ar values used: C 12.0, H 1.0, F 19.0, Cl 35.5.

4. Why poly(alkenes) last 3D · 20.1

A reaction needs somewhere to start: a polar bond, a charge, a lone pair, a double bond. A poly(alkene) backbone has none of those. Every bond is C-C or C-H, both strong and both essentially non-polar, so acids, alkalis, water and the enzymes of decomposers find nothing to attack. Compare it with an ester, then send in a nucleophile and watch what happens.

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Molecule

OUTCOME
Exam point: poly(alkenes) are chemically inert because the C-C and C-H bonds are non-polar, so there is no electron-deficient carbon for a nucleophile to attack and no reactive site for enzymes. That is why they are non-biodegradable. Pauling electronegativities: C 2.5, H 2.1, O 3.5, Cl 3.0.

5. Disposal 2D · 20.1

The same inertness that makes poly(alkenes) useful makes them a problem once they are thrown away. Compare the three routes for poly(ethene) and for PVC: bury it, burn it, or melt it down and use it again. Each has a cost, and burning PVC has an extra one.

Polymer

Route

WHAT HAPPENS
EQUATION
FOR
AGAINST
Exam point: incineration of poly(ethene) releases carbon dioxide, a greenhouse gas, and carbon monoxide if the oxygen supply is limited. Incinerating PVC also releases hydrogen chloride, a toxic and acidic gas that must be removed by scrubbing with an alkali. Landfill wastes land and the polymer does not biodegrade. Recycling saves crude oil but needs careful sorting by polymer type.
TheLucidSTEM · Cambridge International AS Chemistry 9701 · Topic 20 Polymerisation. Every scene runs in the browser; drag to rotate 3D scenes, wheel to zoom. Values are standard textbook data rounded for teaching.

About this lab: Addition polymerisation

Five interactive simulations for Cambridge AS Level Chemistry 9701 topic 20 Polymerisation: ethene, propene, chloroethene, phenylethene and tetrafluoroethene monomers joining one by one into a 3D poly(alkene) chain as the pi bond of each C=C opens, a repeat-unit finder that brackets a section of chain and recovers the monomer or builds the repeat unit from the monomer, a monomer counter that divides the relative molecular mass of a chain by that of its monomer, a bond-polarity comparison of a poly(ethene) section with an ester to explain why poly(alkenes) are chemically inert and non-biodegradable, and a disposal comparison of landfill, incineration and recycling with balanced equations for burning poly(ethene) and poly(chloroethene).

Five simulations covering Topic 20.1: alkene monomers joining into a poly(alkene) chain in 3D as each pi bond opens, with the substituents landing on alternate carbons; a repeat-unit finder where you bracket a section of chain and recover the monomer, or start from the monomer and write the repeat unit; a counter that works out how many monomers are in a chain from its relative molecular mass; a bond-polarity view that shows why a poly(alkene) has no reactive site while an ester does; and a disposal comparison of landfill, incineration and recycling with the equations for burning poly(ethene) and PVC.

Addition polymerisation is a free, browser-based simulation for Cambridge International AS & A Level Chemistry 9701 (topic 20 Polymerisation). The course is assessed in Paper 1 (Multiple Choice (AS)), Paper 2 (AS Structured), Paper 3 (Advanced Practical), Paper 4 (A Level Structured), Paper 5 (Planning, Analysis, Evaluation). Syllabus for examination in 2025-2027. There are 5 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.

Syllabus coverage

Full syllabus map: AS Level Chemistry 9701 topic 20.

How to use this simulation

  1. 1. Monomer to polymer. An alkene has a double bond, and the pi part of it is weak and exposed.
  2. 2. Find the repeat unit. A repeat unit is the smallest piece of chain that, copied end to end, rebuilds the whole polymer.
  3. 3. Count the monomers. Nothing is lost when monomers add together, so the mass of a chain is just the mass of its monomers added up.
  4. 4. Why poly(alkenes) last. A reaction needs somewhere to start: a polar bond, a charge, a lone pair, a double bond.
  5. 5. Disposal. The same inertness that makes poly(alkenes) useful makes them a problem once they are thrown away.
  6. The buttons at the end of the tab strip give the scene the whole window (Full screen, Hide controls) and, on a dark stage, a projector-friendly palette (Light scene). Many scenes also have drag handles: drag them to change the set-up directly.

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