polymerizations

Polymerization is a chemical process that links monomer units to form polymers, large molecules with repeating structural units. Polymers are foundational to plastics, fibers, resins, and many biomaterials, and their properties depend on the nature of the monomers and the polymerization mechanism.

There are two broad classes of polymerization: chain-growth (addition) polymerization and step-growth (condensation) polymerization. In chain-growth polymerization, an active center initiates the rapid addition of monomer units one by one, producing long chains. The process comprises initiation, propagation, and termination or transfer steps. Mechanisms include free-radical, anionic, cationic, and coordination polymerizations. Common examples are the production of polyethylene from ethylene, polystyrene from styrene, and polyvinyl chloride from vinyl chloride. Chain-growth polymerizations can yield very high molecular weights and are often fast, with possibilities for controlled or living polymerization that enable precise molecular weights and architectures.

Step-growth polymerization involves reactions between multifunctional monomers, typically forming polymers through the sequential condensation of functional groups with the release of small molecules such as water or methanol. Molecular weight increases gradually with conversion, and high degrees of polymerization often require high conversion and stoichiometric balance. Polymers such as nylons (polyamides), polyesters, and polyurethanes arise from step-growth processes. These reactions can lead to linear or highly crosslinked networks, depending on monomer functionality.

Industrial relevance spans packaging, textiles, automotive components, coatings, and advanced materials. Control over polymerization methods affects material properties, including molecular weight, composition, architecture, and performance.