Ketjinsiirrolla

Ketjinsiirrolla is a Finnish term that translates to "with a chain transfer" in English. It is a concept primarily encountered in the field of polymer chemistry, specifically in relation to free radical polymerization processes. Chain transfer is a reaction that terminates a growing polymer chain and initiates a new one. This phenomenon affects the molecular weight and molecular weight distribution of the resulting polymer.

When chain transfer occurs, the kinetic chain length, which is the average number of monomer units added to a growing radical before termination, is reduced. This is because the growing radical reacts with a chain transfer agent, abstracting an atom (often hydrogen) and becoming a stable molecule. Simultaneously, the chain transfer agent is converted into a radical species, which can then initiate the polymerization of a new monomer molecule, thus starting a new polymer chain.

The presence of chain transfer agents, often referred to as chain transfer reagents or simply chain transferors, can be intentionally used to control the molecular weight of polymers. By increasing the concentration of a chain transfer agent, more frequent chain transfer events occur, leading to shorter polymer chains and a lower average molecular weight. Conversely, a lower concentration of chain transfer agent results in longer polymer chains and a higher molecular weight. The effectiveness of a chain transfer agent is quantified by its chain transfer constant, which indicates its relative efficiency in causing chain transfer compared to monomer addition. Understanding and controlling ketjinsiirrolla is therefore crucial for tailoring the properties of polymers for specific applications.