Astmelpolümerisatsioonis

Astmelpolümerisatsioon is a polymerization process where monomers react stepwise to form larger polymer chains. This is in contrast to chain-growth polymerization where monomers add rapidly to an active center. In step-growth polymerization, monomers, dimers, trimers, and oligomers of increasing molecular weight are formed gradually throughout the reaction. The reaction typically involves functional groups on the monomers reacting with each other, such as hydroxyl and carboxyl groups to form polyesters, or amine and carboxyl groups to form polyamides. The molecular weight of the polymer increases slowly and is dependent on the conversion of the monomers. High molecular weight polymers are only achieved at very high conversions. This type of polymerization can be catalyzed by acids or bases. Common examples of polymers produced by step-growth polymerization include nylon, polyethylene terephthalate (PET), and polycarbonates. The kinetics of step-growth polymerization are generally described by second-order reaction rate equations. The process is often reversible, meaning that the polymerization reaction can be driven backwards by the presence of water or other small molecules, which is why high conversions are necessary for high molecular weight formation.