Chain polymerization in which the active centres are nucleophilic species.
Examples: Non-ionic nucleophilic species are nitrogen and sulfur lone pairs.
Source:
PAC, 2022, 94, 1093. 'Terminology for chain polymerization (IUPAC Recommendations 2021)' on page 1129 (https://doi.org/10.1515/pac-2020-1211)