Addition polymerization (also called chain-growth polymerization) is a type of polymerization in which unsaturated monomers (usually with double or triple bonds, like alkenes) add together one by one to form a polymer without the loss of any small molecules (no by-products).
How it works (basic steps):
- Initiation → An initiator (heat, light, catalyst, or a free radical) starts the reaction by attacking the double bond of a monomer.
- Propagation → The active site (radical, cation, or anion) on the growing chain keeps opening the double bonds of new monomers, adding them one by one.
- Termination → The chain growth stops when two active ends combine or the active site is neutralized.
Key Features:
- Monomers must have C=C double bonds or similar reactive groups.
- No by-product is formed.
- The polymer is just a repeating chain of the original monomer units.
Examples:
- Ethene (C₂H₄) → Polyethylene (plastic bags, bottles).
- Propene (C₃H₆) → Polypropylene (ropes, containers).
- Vinyl chloride (CH₂=CHCl) → Polyvinyl chloride (PVC pipes).
- Styrene (C₆H₅–CH=CH₂) → Polystyrene (packaging, insulation).