initiating species

https://doi.org/10.1351/goldbook.08959
Species to which monomer adds or becomes inserted to start a chain polymerization.
Notes:
  1. An initiating species may be formed from an initiator or be the initiator itself.
  2. In radical polymerization, initiating species formed directly from an initiator are called primary radicals.
Source:
PAC, 2022, 94, 1093. (Terminology for chain polymerization (IUPAC Recommendations 2021)) on page 1122 [Terms] [Paper]