Porraspolymerisaatiossa

Porraspolymerisaatiossa, also known as step-growth polymerization, is a polymerization mechanism where monomer units react with each other in a stepwise manner. Unlike chain-growth polymerization where a chain is built by the addition of single monomer units to an active center, in porraspolymerisaatiossa, monomers typically react to form dimers, then trimers, and so on, gradually increasing the molecular weight of the polymer. This process can occur through various types of reactions, including condensation, esterification, or amidation, often involving the release of a small molecule byproduct like water.

The key characteristic of porraspolymerisaatiossa is that the degree of polymerization increases steadily throughout the reaction. At the beginning of the process, low molecular weight oligomers are prevalent. As the reaction progresses, these oligomers combine, leading to a distribution of polymer chain lengths. High molecular weight polymers are only achieved at very high conversions, often exceeding 90%. This means that to obtain a high molecular weight polymer, the reaction must be driven to completion.

Common examples of polymers formed via porraspolymerisaatiossa include polyesters, polyamides (like nylon), polycarbonates, and polyurethanes. The reaction kinetics are generally described by relatively simple rate equations, and the molecular weight distribution is often described by the Carothers equation. Control over the molecular weight is typically achieved by controlling the monomer stoichiometry and the extent of reaction. This polymerization mechanism is widely used in the industrial production of many important synthetic polymers.