Ketjunpäättymisreaktioiden

Ketjunpäättymä, often translated as chain termination, is a crucial concept in polymer chemistry that describes the process by which a growing polymer chain stops extending. This event can occur through several mechanisms, each leading to the deactivation of the active center responsible for monomer addition.

One common mechanism is disproportionation. In this process, a hydrogen atom is transferred from one growing radical chain to another. This results in the formation of two stable, non-radical polymer chains, one with a double bond at its end and the other with a saturated end.

Another significant termination pathway is recombination, also known as combination. Here, two growing radical chains merge, forming a single, longer polymer molecule. This process effectively combines the active centers, leading to a stable, high molecular weight polymer.

In ionic polymerization, termination can also occur through reaction with impurities. Trace amounts of water, oxygen, or other electrophilic or nucleophilic species can quench the active ionic center, effectively stopping chain growth. The specific termination mechanism depends on the type of polymerization (e.g., free radical, anionic, cationic) and the reaction conditions employed. Understanding these termination processes is vital for controlling molecular weight, molecular weight distribution, and the overall properties of the resulting polymers.