Addition polymerization

Addition polymerization joins unsaturated monomers into a polymer without releasing small-molecule byproducts. It commonly proceeds by chain growth across carbon–carbon double bonds.

Chain-growth polymerization: Polymerization in which monomers add successively to reactive chain ends. Addition polymerization commonly follows this growth pattern, extending chains one monomer at a time.
Alkene: A hydrocarbon containing at least one carbon–carbon double bond. Many addition-polymerization monomers are alkenes whose double bonds open during chain growth.
Polyethylene: A thermoplastic polymer made from ethylene repeat units. It is produced by addition polymerization and is one of the most widely used plastics.
Step-growth polymerization: Polymer formation through reactions between functional groups on molecules of many sizes. Unlike typical addition polymerization, it builds chains through repeated reactions between molecular species.
Free-radical polymerization: Chain-growth polymerization initiated and propagated by radical species. It is a widely used route for adding vinyl monomers into polymer chains.
Vinyl monomer: A monomer containing a CH₂=CH– group that can form a carbon-chain polymer. Vinyl monomers are a central feedstock class for addition polymerization.
Polypropylene: A thermoplastic polymer made from propylene repeat units. Its industrial production uses addition polymerization of propylene.
Condensation polymerization: Polymer formation accompanied by elimination of small molecules such as water or methanol. It contrasts with addition polymerization’s defining absence of small-molecule byproducts.
Initiator (chemistry): A substance that generates reactive species to start a chemical reaction or chain process. An initiator creates the active centers that begin many addition polymerizations.
Polymer: A large molecule composed of repeating structural units connected by covalent bonds. Addition polymerization is one way to produce this class of macromolecules.

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