Histidine functional block copolymers are thermally selfâassembled into polymer micelles with polyâNâisopropylacrylamide in the core and the histidine functionality in the corona. The thermally induced selfâassemblies are reversible until treated with Cu2+ ions at 50â°C. Upon treatment with 0.5 equivalents of Cu2+ relative to the histidine moieties, metalâion coordination locks the selfâassemblies. The selfâassembly behavior of histidine functional block copolymers is explored at different values of pH using DLS and 1H NMR. Metalâion coordination locking of the histidine functional micelles is also explored at different pH values, with stable micelles forming at pHâ9, observed by DLS and imaged by atomic force microscopy. The thermal selfâassembly of glycine functional block copolymers at pHâ5, 7, and 9 is similar to the histidine functional materials; however, the selfâassemblies do not become stable after the addition of Cu2+, indicating that the imidazole plays a crucial role in metalâion coordination that locks the micelles. The reversibility of the histidineâcopper complex locking mechanism is demonstrated by the addition of acid to protonate the imidazole and destabilize the polymer selfâassemblies. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1964â1973