What are Addition Polymers?
Addition polymers form when small unsaturated molecules called monomers link together through addition reactions across their double bonds — no atoms are lost in the process. This is how everyday plastics like polyethylene, polypropylene and PVC are made.
Addition polymers are long-chain molecules formed when many monomer units with C=C double bonds add together in a chain reaction, one after another, without losing atoms.
- 1↓MonomerUnsaturated molecule with C=C double bond (e.g. ethene CH₂=CH₂)
- 2↓InitiationRadical or catalyst breaks double bond and attacks first monomer
- 3↓PropagationGrowing chain attacks next monomer, adding it to the chain
- 4↓TerminationChain ends when two radicals meet or inhibitor stops reaction
- 5PolymerLong chain of thousands of monomer units linked by single bonds
Step-by-step worked examples
Polyethylene (PE) is made from ethene monomers. Write the monomer structure and describe how they link.
Monomer = CH₂=CH₂ (ethene) Double bond breaks: C=C → C-C Thousands of ethene units link via single bonds forming (–CH₂–CH₂–)ₙ This is polyethylene (PE), used in bags and bottles.
Why is addition polymerization called 'addition'?
Because monomers add together via addition reactions. No small molecules (like H₂O) are removed during polymerization. All atoms in the monomers end up in the final polymer chain.
Polypropylene is made from propene (CH₂=CH–CH₃). What is the repeating unit of the polymer?
Propene = CH₂=CH–CH₃ Double bond breaks: C=C → C-C Repeating unit = (–CH₂–CH(CH₃)–)ₙ This creates polypropylene (PP), a tough plastic.
Flashcards
Quick quiz
Q1.What structural feature do all monomers in addition polymerization have?
Q2.Which is an addition polymer?
Q3.In addition polymerization, what happens to the C=C double bond?
Q4.Why is PVC (polyvinyl chloride) an addition polymer?
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Common mistakes
Addition polymers are made by adding polymers together. — Correct: Addition polymers are made by monomers adding to each other, not by joining two existing polymers.
The C=C double bond stays intact in the polymer chain. — Correct: The C=C double bond breaks; each carbon forms a single bond with the next monomer.
Addition polymerization always produces water as a byproduct. — Correct: Addition polymerization produces no byproducts — all monomer atoms end up in the polymer.
Only hydrocarbons can undergo addition polymerization. — Correct: Any monomer with a C=C (or C≡C) double bond can, including chloroethene (vinyl chloride).
FAQ
What is the formula for addition polymers?
Addition polymers follow the pattern (–R₁–R₂–)ₙ where R₁ and R₂ are the groups from the monomer structure after the double bond breaks.
Can unsaturated fats undergo addition polymerization?
Unsaturated fats have C=C bonds, so theoretically yes, but they are not used as polymerization monomers in practice.
Why are addition polymers usually stronger and more durable?
The long chains of covalent single bonds create strong intermolecular forces and a stable 3D structure.
How many times does a monomer need to react for a useful polymer?
Typically 500–10,000 times, creating chains of up to 100,000 atoms or more.