Polymerization

Polymerization is a chemical process in which monomers or smaller molecules react to form polymers with repeating structural units.

Chain-growth polymerization: Polymerization in which reactive chain ends add monomers one at a time. This pathway builds chains through initiation, propagation, and termination steps.
Monomer: A small molecule that can react with other molecules to form a polymer. Monomers supply the repeating units incorporated during polymerization.
Polyethylene: A thermoplastic polymer made from ethylene and used widely in packaging and products. Its manufacture illustrates large-scale addition polymerization of a simple alkene.
Addition polymerization: Polymer formation by successive addition of unsaturated monomers, typically without small-molecule byproducts. It contrasts with condensation routes that release small molecules during chain formation.
Step-growth polymerization: Polymerization in which molecules with reactive functional groups combine in successive reactions. This pathway grows polymers through reactions between molecules of many sizes.
Functional group: A group of atoms in a molecule that governs characteristic chemical reactions. Reactive functional groups determine which monomers can link in step-growth reactions.
Nylon: A family of synthetic polyamides used in fibers, films, and molded parts. Nylon illustrates how step-growth reactions produce strong engineering polymers.
Condensation polymerization: Polymer formation through reactions that often release small molecules such as water. Its byproducts distinguish it from addition polymerization, though usage overlaps with step-growth.
Free-radical polymerization: Chain-growth polymerization driven by reactive radicals that add to monomer double bonds. It is a common route for making polymers such as polyethylene and polystyrene.
Degree of polymerization: The number of repeating units in a polymer chain or molecule. It quantifies how far polymerization has extended the chains.

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