Chain transfer agent

Chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule.

Chain transfer reactions reduce the average molecular weight of the final polymer. Chain transfer can be either introduced deliberately into a polymerization (by use of a chain transfer agent) or it may be an unavoidable side-reaction with various components of the polymerization. Chain transfer reactions occur in most forms of addition polymerization including radical polymerization, ring-opening polymerization, coordination polymerization, and cationic as well as anionic addition polymerization.

Chain transfer (in a chain polymerization): Chemical reaction occurring
during a chain polymerization in which an active center is transferred
from a growing macromolecule or oligomer molecule to another molecule
or to another site on the same molecule.

Chain-transfer agent: Substance able to react with a chain carrier by a
reaction in which the original chain carrier is deactivated and a new chain
carrier is generated.

Chain transfer reactions are usually categorized by the nature of the molecule that reacts with the growing chain.

Chain transfer was first proposed by Taylor and Jones in 1930. They were studying the production of polyethylene [(C
2H
4)_n] from ethylene [C
2H
4] and hydrogen [H
2] in the presence of ethyl radicals that had been generated by the thermal decomposition of (Et)₂Hg and (Et)₄Pb. The observed product mixture could be best explained by postulating "transfer" of radical character from one reactant to another.

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