A constitutional unit that is an extremity of a macromolecule or oligomer molecule. An end-group is attached to only one constitutional unit of a macromolecule or oligomer molecule.
Source:
PAC, 1996, 68, 2287. 'Glossary of basic terms in polymer science (IUPAC Recommendations 1996)' on page 2294 (https://doi.org/10.1351/pac199668122287)