ABSTRACTA series of ternary graft copolymers with poly(3‐azido‐2‐hydroxypropyl methacrylate) (P(GMA‐N3)) as the main chain, end‐functionalized poly(ethylene glycol) methyl ether (MPEG), poly(t‐butyl acrylate) (PtBA), and poly(2‐cinnamoyloxyethyl methacrylate) (PCEMA) as the side‐chains, was synthesized via the combination of atom transfer radical polymerization (ATRP) and click chemistry. The formation of well‐defined ternary graft copolymers was confirmed by both size exclusion chromatography (SEC) and 1H NMR spectroscopy The loose and worm‐like morphology of the ternary graft copolymer in a common solvent (N,N‐dimethylformamide) for both the backbone and the grafts was directly visualized via atomic force microscopy (AFM). The average height, width, and length of these solvated macromolecules were about 1.5, 17, and 45 nm, respectively. The ternary graft copolymers underwent self‐assembly in different selective solvents (dichloromethane, methanol, and water) and thus yielded unimolecular micelles (UMs) with different morphologies. The morphological transitions in response to variations in the selective solvents was investigated by AFM as well as/or transmission electron microscopy (TEM). Experimental results showed that the micellar morphology of the ternary graft copolymer changed from a pearl‐necklace to a worm‐like structure and then to a spherical structure when the selective solvent was respectively changed from CH2Cl2 to CH3OH and then to H2O. SEC characterization revealed that the compact globules formed in H2O with PCEMA/PtBA as the hydrophobic core arose due to intramolecular folding. Thus, multicompartment UMs were generated. The volume ratio of the multicompartment UMs formed in H2O was in close agreement with their molecular weight ratio. The hydrodynamic diameters (Dh) of the acquired multicompartment UMs and their polydispersity indices were characterized by dynamic light scattering. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1021–1030