Amphiphilic Poly( l -lysine-b-caprolactone) Block Copolymers: Synthesis, Characterization, and Solution Properties

We report on the synthesis of poly( l -lysine- b -caprolactone) block copolymers via an original and elegant approach whereby Z- l -lysine is first polymerized in the presence of allylamine and the resulting amino-terminated poly(Z- l -lysine) is then used in situ as macroinitiator for the polymerization of ε-caprolactone in the presence of tin(II) octanoate as catalyst. A range of poly(ester- b -peptide)s were obtained by varying the ratio of polypeptide to polycaprolactone units. After removal of the Z group of l -lysine units, the copolymers were soluble in water and their solution behavior was examined. They spontaneously form micelle-like objects in solution with sizes around 10 and 70 nm depending on the block lengths of the hydrophilic and hydrophobic sequences. The smaller size particles would adopt a core−shell morphology while the larger particles would be more in line with a vesicle morphology.