Ahelreaktsioonpolümerisatsioon

Ahelreaktsioonpolümerisatsioon, also known as chain-growth polymerization, is a polymerization mechanism where monomers add sequentially to an active center. This active center is typically an ion or a radical. The process begins with an initiation step, where a small number of monomers are converted into an active species. This is followed by a propagation step, where the active center reacts with monomers, causing the polymer chain to grow. Each propagation step adds one monomer unit to the growing chain, maintaining the active center at the end of the chain. The process terminates when the active center is destroyed, for example, by combination or disproportionation of two growing chains, or by reaction with an impurity. The molecular weight of the polymer is determined by the relative rates of propagation and termination. This type of polymerization is responsible for the formation of many common plastics, such as polyethylene, polypropylene, and polystyrene. It is distinct from step-growth polymerization, where polymer chains grow by reaction between functional groups on monomers or oligomers. The specific type of active center, whether anionic, cationic, or radical, dictates the conditions under which the polymerization occurs and the properties of the resulting polymer.