Ketjunsiirrot

Ketjunsiirrot, often translated as "chain transfers" in English, is a chemical phenomenon that occurs during certain polymerization processes. It involves the transfer of a growing polymer chain to another molecule, typically a monomer or a solvent. This transfer process terminates the growth of the original polymer chain and initiates the growth of a new one.

In free radical polymerization, chain transfer is a significant factor that influences the molecular weight and molecular weight distribution of the resulting polymer. The rate of chain transfer relative to the rate of propagation determines whether the average chain length is reduced. If chain transfer is frequent, shorter polymer chains will be produced.

Common chain transfer agents include monomers themselves (monomer chain transfer), solvent molecules (solvent chain transfer), and deliberately added chain transfer agents (CTA). CTAs are molecules specifically designed to participate in chain transfer reactions, allowing for better control over the polymerization process and the properties of the final polymer. Examples of CTAs include thiols and certain halogenated compounds.

The mechanism of chain transfer typically involves the abstraction of an atom, most commonly a hydrogen atom, from the transfer agent by the radical end of the growing polymer chain. This results in the formation of a dead polymer chain and a new radical species derived from the transfer agent, which can then initiate a new polymerization. Understanding and controlling chain transfer reactions is crucial for synthesizing polymers with desired characteristics for various applications.