Addition Polymerisation | Chemistry

📖 In-Depth Theory

What Is Addition Polymerisation?

ADDITION POLYMERISATION: many small alkene monomers join together to form a very large polymer molecule.

KEY FEATURES:

Monomer must have a C=C double bond (unsaturated).

Double bonds open up and join — one long chain forms.

ONLY ONE PRODUCT — the polymer itself. No by-products.

Atom economy = 100%.

GENERAL EQUATION:

nCH₂=CHR → (—CH₂—CHR—)ₙ

The brackets with subscript n show the REPEAT UNIT — the smallest repeating section of the polymer.

EXAMPLES:

Ethene → poly(ethene): n(CH₂=CH₂) → (—CH₂—CH₂—)ₙ

Propene → poly(propene): n(CH₂=CHCH₃) → (—CH₂—CHCH₃—)ₙ

Chloroethene → PVC: n(CH₂=CHCl) → (—CH₂—CHCl—)ₙ

Tetrafluoroethene → PTFE: n(CF₂=CF₂) → (—CF₂—CF₂—)ₙ

Drawing and Interpreting Polymer Diagrams

MONOMER → POLYMER:

Identify the monomer: contains C=C double bond.

The repeat unit in the polymer = the monomer minus the double bond (both carbons now have single bonds).

DRAWING A REPEAT UNIT:

Draw the repeat unit inside square brackets.

Add lines through both ends of the bracket (showing the chain continues).

Write subscript n outside the bracket.

FINDING THE MONOMER FROM THE POLYMER:

Look at the repeat unit inside the brackets.

Add a C=C double bond between the two carbon atoms in the backbone.

This gives you the monomer.

PROPERTIES OF ADDITION POLYMERS:

Macromolecules — very large molecular mass.

Thermoplastics — soften when heated, can be reshaped.

Non-biodegradable — cause environmental problems.

Different properties depending on the monomer and branching.

Uses and Environmental Issues

COMMON ADDITION POLYMERS AND USES:

Poly(ethene) [LDPE/HDPE]: bags, bottles, packaging, pipes.

Poly(propene): ropes, carpets, food containers, car bumpers.

PVC (poly(chloroethene)): window frames, pipes, flooring, cables.

PTFE: non-stick coatings (Teflon), bearings, medical implants.

Poly(styrene): insulation, disposable cups, packaging foam.

ENVIRONMENTAL PROBLEMS:

Most addition polymers are NON-BIODEGRADABLE — persist for hundreds of years.

Plastic pollution in oceans, soils and food chains.

SOLUTIONS:

Recycling — melted down and remoulded (thermoplastics).

Incineration — recovers energy but produces CO₂ and toxic gases.

Biodegradable polymers — starch-based or PLA can decompose.

Reducing use — replacing single-use plastics.

⚠️ Common Mistake

The repeat unit of an addition polymer is NOT the same as the monomer — it's the monomer structure but with the double bond replaced by two single bonds (continuing the chain). To find the monomer from the polymer: take the repeat unit and ADD a C=C double bond between the backbone carbons.

📐 Key Equations

n(CH₂=CH₂) → (—CH₂—CH₂—)ₙ (ethene → poly(ethene))

📌 Key Note

Addition polymerisation: alkene monomers + C=C → polymer. One product only, 100% atom economy. Repeat unit in brackets with n subscript. Monomers: ethene → poly(ethene), propene → poly(propene), chloroethene → PVC. Non-biodegradable — environmental problem. Thermoplastics: can be recycled by melting.

🎯 Matching Activity — Addition Polymers

Match each monomer to its polymer and a key use. — drag the symbols on the right to match the component names on the left.

Ethene (CH₂=CH₂)

Drop here

Propene (CH₂=CHCH₃)

Drop here

Chloroethene (CH₂=CHCl)

Drop here

Tetrafluoroethene (CF₂=CF₂)

Drop here

Poly(ethene) — bags, bottles, packaging

PVC — window frames, pipes, cables

PTFE (Teflon) — non-stick coatings

Poly(propene) — ropes, carpets, food containers

⭐ Higher Tier Only

Derive polymer structure from monomer or vice versa. Explain LDPE vs HDPE properties in terms of branching and chain packing. Evaluate environmental impact of non-biodegradable polymers and compare disposal options.

🔬 Triple Science Only

Addition polymerisation (4.7.3.1) is chemistry-only — not in Combined Science.

🎯 Test Yourself

Question 1 of 2

1. How do you determine the monomer from the displayed formula of an addition polymer?

2. Why does addition polymerisation have 100% atom economy?

⭐ How Well Do You Understand This Topic?

Be honest with yourself — this helps you know what to revise!

Don't get it Getting there Nailed it!

🤖 Ask MrBadmus

Stuck? Just ask! 💬

I'll use CFIFA for calculations and flag Higher/Triple content clearly.