Chain transfer

Chain transfer is a reaction in chain-growth polymerization that ends one growing chain while creating a reactive species capable of initiating another.

Chain-growth polymerization: Polymerization in which monomers add successively to reactive chain ends. Chain transfer is one reaction pathway within this broader mode of polymerization.
Mayo equation: An equation relating polymer molecular weight to chain-transfer rates and concentrations. It estimates how strongly transfer agents lower the degree of polymerization.
Thiocarbonylthio compound: An organic compound containing a thiocarbonyl group bonded to sulfur, used as a reversible chain-transfer agent. Thiocarbonylthio agents mediate reversible transfer in RAFT polymerization.
Combination (polymer chemistry): A radical termination reaction in which two growing polymer radicals join into one molecule. Combination consumes both radicals, whereas transfer can create a replacement reactive species.
Propagation (chemistry): A step in a chain reaction that consumes a reactive intermediate and produces another reactive intermediate. Transfer competes with propagation for the active chain end.
Degree of polymerization: The number of repeat units in a polymer molecule or average polymer chain. Frequent transfer creates more chains from a given amount of monomer, reducing average chain length.
RAFT polymerization: A controlled radical polymerization using reversible addition–fragmentation chain transfer. It uses chain transfer to regulate radical concentrations and polymer-chain growth.
Disproportionation (polymer chemistry): A radical termination reaction in which hydrogen transfer yields one saturated and one unsaturated polymer chain. Disproportionation ends two radical chains without passing activity to a new molecule.
Initiation (chemistry): The reaction step that first generates reactive species in a chain reaction. The new species formed by transfer can initiate growth of another polymer chain.
Molecular weight distribution: The distribution of polymer-chain molecular weights within a sample. Transfer frequency and selectivity can alter the spread of chain lengths.

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