Lisäpolymerointi

Lisäpolymerointi, also known as addition polymerization, is a type of polymerization reaction in which monomer molecules add to one another in such a way that the polymer contains all the atoms of the monomer unit. This process typically involves monomers with double or triple bonds, which open up to form a chain. The simplest and most common example is the formation of polyethylene from ethylene. In this process, many ethylene molecules react sequentially to form a long chain of repeating $-\text{CH}_2-\text{CH}_2-$ units. The overall empirical formula of the repeating unit is the same as that of the monomer.

Lisäpolymerointi proceeds through a chain mechanism, which can be initiated by free radicals, cations, or anions. Free radical polymerization is perhaps the most widely used method. It involves three main stages: initiation, propagation, and termination. Initiation begins with the formation of a free radical, often from a thermal decomposition of an initiator molecule. This radical then attacks the double bond of a monomer, creating a new radical on the monomer unit. Propagation is the process where this new radical adds to successive monomer units, extending the polymer chain. Termination occurs when the growing radical chains are deactivated, for example, by combination of two growing radicals or by disproportionation.

Common polymers formed by lisäpolymerointi include polyethylene, polypropylene, polyvinyl chloride (PVC), polystyrene, and polymethyl methacrylate (PMMA). These polymers are ubiquitous in modern life, finding applications in packaging, textiles, construction materials, and many other products due to their diverse properties like flexibility, strength, and chemical resistance. The control over molecular weight and chain structure can be achieved through careful selection of initiator, temperature, and solvent.