Chain termination

Chain termination is the stopping of polymer-chain extension when a required reactive group is absent or blocked, preventing further addition of monomer units.

End-capping: End-capping is the chemical modification of a polymer chain end to prevent further reaction. A terminating group can cap a reactive end and block additional monomer addition.
Polymerization: Polymerization is the chemical process of joining monomers into polymer chains or networks. Chain termination is one outcome within the broader process of polymer formation.
Molecular weight: Molecular weight is the mass of a molecule, commonly used to characterize polymer-chain size. More frequent termination generally limits how many monomer units each chain accumulates.
Initiation: Initiation is the formation of reactive centers that begin polymer-chain growth. It creates growing chains, whereas termination removes their capacity to extend.
Radical termination: Radical termination is the loss of reactive radical centers through combination or disproportionation. In radical polymerization, these reactions remove the active centers that extend chains.
Polymer chain: A polymer chain is a sequence of covalently linked repeating units derived from monomers. Termination changes whether the chain's end can accept another unit.
Number-average molecular weight: Number-average molecular weight is total polymer mass divided by the number of polymer molecules. The number of terminated chains helps determine this average chain-size measure.
Propagation: Propagation is the repeated addition of monomer units to an active polymer chain. It lengthens a chain through the same reactive end that termination disables.
Chain transfer: Chain transfer is the relocation of a growing chain's reactive center to another molecule. It stops one chain from growing but can create a new active chain elsewhere.
Chain end: A chain end is a terminal atom or group at one end of a polymer molecule. Its chemical state determines whether the chain can continue growing.

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