Additsioonipolümerisatsiooni

Additsioonipolümerisatsioon is a chemical reaction where monomers, typically unsaturated organic compounds, join together to form a long polymer chain without the loss of any atoms. This process occurs through the sequential addition of monomer units to an active center, which can be initiated by radicals, ions, or coordinating agents.

The most common type of additsioonipolümerisatsiooni is free-radical polymerization. This process begins with an initiator that decomposes to form free radicals. These radicals then attack the double bond of a monomer, creating a new radical on the monomer. This process repeats, propagating the polymer chain. Finally, the chain terminates when two growing radicals combine or disproportionate.

Ionic polymerization, either cationic or anionic, is another significant pathway. Cationic polymerization is initiated by strong acids or Lewis acids, while anionic polymerization is initiated by strong bases or nucleophiles. These methods are often used to produce polymers with specific stereochemical properties. Coordination polymerization, often catalyzed by transition metal complexes like Ziegler-Natta catalysts, allows for precise control over the polymer structure, particularly in the case of polyolefins.

The key characteristic of additsioonipolümerisatsiooni is that the empirical formula of the repeating unit in the polymer is the same as that of the monomer. This is in contrast to condensation polymerization, where a small molecule, such as water, is eliminated during the reaction. Common polymers formed by additsioonipolümerisatsiooni include polyethylene, polypropylene, polystyrene, and polyvinyl chloride. The choice of monomer and polymerization conditions significantly influences the molecular weight, branching, and overall properties of the resulting polymer.