polümerisatsioonimehhanismid

Polümerisatsioonimehhanismid refer to the step-by-step processes by which monomers link together to form polymers. These mechanisms dictate the structure, properties, and synthesis methods of the resulting macromolecules. The primary categories of polymerization mechanisms are chain-growth and step-growth polymerization.

Chain-growth polymerization, also known as addition polymerization, involves the rapid addition of monomers to an active center. This active center can be a radical, a cation, or an anion. The process typically proceeds in three stages: initiation, propagation, and termination. Initiation involves the formation of the active center, often by a radical initiator. Propagation is the chain lengthening step where monomers add sequentially to the active center. Termination occurs when the active center is deactivated, ending chain growth. Examples include free radical polymerization of ethylene to polyethylene and anionic polymerization of styrene to polystyrene.

Step-growth polymerization, also known as condensation polymerization, involves the reaction between functional groups of monomers, dimers, trimers, and oligomers, releasing a small molecule byproduct such as water or methanol. The molecular weight of the polymer increases gradually throughout the process. Polymerization occurs through the formation of bonds between monomers or growing chains of any size. This mechanism is characteristic of the synthesis of polyesters, polyamides, and polyurethanes. The reaction rate is generally slower compared to chain-growth polymerization, and high molecular weights are achieved only at high conversions. Understanding these mechanisms is crucial for controlling polymer properties and designing efficient synthesis routes.