Reagent that reacts reversibly with the
initiating species or
propagating species to form an initiator or a
dormant chain, respectively, and an activator.
Source:
PAC, 2022, 94, 1093. 'Terminology for chain polymerization (IUPAC Recommendations 2021)' on page 1119 (https://doi.org/10.1515/pac-2020-1211)