initializer

in RDP
https://doi.org/10.1351/goldbook.08957
Starting initiator or transfer agent in reversible-deactivation polymerization (RDP).

Examples: A starting alkoxyamine initiator in aminoxyl-mediated radical polymerization (AMRP), a starting alkyl halide initiator in atom-transfer radical polymerization (ATRP) and a starting RAFT agent in RAFT polymerization.

Source:
PAC, 2022, 94, 1093. 'Terminology for chain polymerization (IUPAC Recommendations 2021)' on page 1122 (https://doi.org/10.1515/pac-2020-1211)