astmelispolümerisatsiooni

Astmelispolümerisatsioon refers to a type of polymerization reaction where monomers with two or more reactive functional groups combine to form larger molecules. This process occurs in distinct steps, building the polymer chain incrementally. Unlike chain-growth polymerization, where a chain reaction is initiated and propagates rapidly, step-growth polymerization involves the reaction between functional groups of monomers, dimers, trimers, and so on, regardless of the molecular weight of the species.

The reaction typically proceeds by the condensation of two functional groups, often with the elimination of a small molecule such as water, methanol, or hydrogen chloride. For example, the formation of polyesters involves the reaction between a diol and a dicarboxylic acid. Similarly, polyamides are formed from diamines and dicarboxylic acids. The rate of polymerization is generally slower than chain-growth polymerization, and the molecular weight of the polymer increases gradually throughout the reaction. High molecular weights are typically achieved only when the conversion of monomers is very high.

Key characteristics of step-growth polymerization include the fact that all monomer molecules react with each other at any stage of the reaction, and the initial stages involve the formation of dimers, trimers, and other low molecular weight oligomers. The molecular weight distribution in step-growth polymers is usually broader than in chain-growth polymers. This polymerization mechanism is crucial for the synthesis of many important polymers, including nylons, polyesters, polycarbonates, and polyurethanes, which find widespread applications in textiles, packaging, automotive parts, and construction materials.