Synthesis of Hyperbranched Polypeptide and PEO Block Copolymer by Consecutive Thiol-Yne Chemistry

Hyperbranched poly(epsilon-benzyloxycarbonyl-L-lysine) (HPlys) with multiple alkyne peripheries was synthesized through the click polycondensation of an AB(2) type Plys macromonomer with alpha-thiol and omega-alkyne terminal groups (thiol is the A unit, and each pi bond in alkyne is the B unit), and the resulting HPlys was further conjugated with thiol-termined poly(ethylene oxide) (PEO) to generate HPlys-b-PEO block copolymer by consecutive thiol-yne chemistry. Their molecular structures and physical properties were characterized in detail by FT-IR, H-1 NMR, gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. HPlys and HPlys-b-PEO mainly assumed an alpha-helix conformation similar to the linear precursors, while the liquid crystalline phase transition of Plys segment disappeared within HPlys and HPlys-b-PEO. HPlys-b-PEO self-assembled into nearly spherical micelles in aqueous solution, while it gave a 5-fold lower critical aggregation concentration (8.9 X 10(-3) mg/mL) than a linear counterpart (4.5 X 10(-2) mg/mL), demonstrating a dendritic topology effect. Compared with a linear counterpart, HPlys-b-PEO gave a higher drug-loading capacity and efficiency for the anticancer drug doxorubicin (DOX) and a slower drug-release rate with an improved burst-release profile, enabling them useful for drug delivery systems. Importantly, this work provides a versatile strategy for the synthesis of hyperbranched polypeptides and related block copolymers by utilizing thiol-yne chemistry.