Nylon-3 polymers contain beta-amino-acid-derive subunits and can be viewed as higher homologues of poly(alpha-amino acids). This structural relationship raises the possibility that nylon-3 polymers offer a platform for development of new materials with a variety of biological activities, a prospect that has recently begun to receive experimental support. Nylon-3 homo- and copolymers can be prepared via anionic ring opening polymerization of beta-lactams, and use of an N-acyl-beta-lactam as coinitiator in the polymerization reaction allows placement of a specific functional group, borne by the N-acyl-beta-lactam, at the N-terminus of each polymer chain. Controlling the unit at the, C-termini of nylon-3 polymer chains, however, has been problematic. Here we describe a strategy for specifying C-terminal functionality that is based on the polymerization mechanism. After the anionic ring opening polymerization is complete, we introduce a new beta-lactam, approximately 1 equiv relative to the expected number of polymer chains. Because the polymer chains bear a reactive imide group at their C-termini, this new beta-lactam should become attached at this position. If the terminating beta-lactam bears a distinctive functional group, that,functionality should be affixed to most or all C-termini in the reaction mixture. We use the new technique to compare the impact of N- and C-terminal placement of a critical hydrophobic fragment on the biological activity profile of nylon-3 copolymers. The synthetic advance described here should prove to be generally useful for tailoring the properties of nylon-3 materials.