Species to which monomer adds or becomes inserted to start a chain polymerization.
Notes: - An initiating species may be formed from an initiator or be the initiator itself.
- 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 (https://doi.org/10.1515/pac-2020-1211)