Ketjinsiirron

Ketjinsiirron is a Finnish term that translates to "chain transfer" in English. It refers to a process in radical polymerization where a growing polymer chain reacts with a species other than a monomer, resulting in the termination of the growing chain and the initiation of a new one. This species can be a monomer, a solvent molecule, a polymer chain, or even an intentionally added chain transfer agent.

The primary effect of chain transfer is to reduce the average molecular weight of the polymer. This occurs because the chain transfer event breaks the growing polymer chain into smaller fragments, and each fragment then starts a new polymerization. While it limits the molecular weight, chain transfer can also be used to control the molecular weight distribution of the polymer. By carefully selecting the chain transfer agent and its concentration, manufacturers can tailor the properties of the resulting polymer, such as its viscosity and processability.

Chain transfer can occur through various mechanisms, including hydrogen abstraction, atom transfer, or addition to a double bond. The efficiency of chain transfer depends on the specific monomer, initiator, solvent, and the presence of any chain transfer agents. Understanding and controlling chain transfer is crucial in many industrial polymerization processes to achieve desired polymer characteristics.