ketjupolimerisaatio

Ketjupolimerisaatio, also known as chain-growth polymerization, is a polymerization mechanism where monomers add sequentially to an active site on a growing polymer chain. This process typically proceeds through distinct steps: initiation, propagation, and termination. Initiation involves the formation of an active center, often a radical, anion, or cation, which then reacts with a monomer molecule to start the polymer chain. Propagation is the rapid addition of successive monomer units to the active site, extending the polymer chain. Termination occurs when the active center is deactivated, stopping the chain growth. This can happen through various mechanisms such as combination or disproportionation of radicals, or by reaction with impurities or chain transfer agents.

Ketjupolimerisaatio is characterized by a low concentration of active chain ends and a broad molecular weight distribution. The rate of polymerization is generally fast, and the molecular weight of the polymer is not directly related to the monomer concentration but rather to the ratio of the rate of propagation to the rate of termination. Common examples of polymers formed by ketjupolimerisaatio include polyethylene, polypropylene, polystyrene, and polyvinyl chloride. The type of active center dictates the specific mechanism, leading to free radical polymerization, anionic polymerization, or cationic polymerization. Each of these methods has specific requirements regarding monomers and reaction conditions.