Site on a macromolecule or region in a polymer material that takes part in the formation of chemical or physical crosslinks.
Source:
PAC, 2007, 79, 1801. 'Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials (IUPAC Recommendations 2007)' on page 1819 (https://doi.org/10.1351/pac200779101801)