Ketjunsiirtäjäagenttia

Ketjunsiirtäjäagenttia is a Finnish term that translates to "chain transfer agent" in English. In chemistry, chain transfer agents are substances added to a polymerization reaction that can terminate a growing polymer chain and initiate a new one. This process is crucial for controlling the molecular weight and molecular weight distribution of the resulting polymer.

The mechanism involves a chain transfer agent, often a molecule with a labile atom or group, reacting with the active end of a growing polymer radical. This reaction effectively stops the growth of that particular polymer chain but generates a new radical on the chain transfer agent molecule. This new radical can then initiate the growth of another polymer chain, effectively transferring the "chain" to a new initiator.

By adjusting the concentration of the chain transfer agent, chemists can influence the average length of the polymer chains. Higher concentrations of chain transfer agents lead to shorter polymer chains and thus a lower average molecular weight. Conversely, lower concentrations result in longer chains and higher molecular weights. This control is essential for tailoring polymer properties for specific applications, such as plastics, coatings, and adhesives, where molecular weight significantly impacts viscosity, strength, and other physical characteristics. Common examples of chain transfer agents include thiols and certain halogenated compounds. The efficiency of a chain transfer agent is often quantified by its chain transfer constant.