Synthesis and pH-Responsive Self-Assembly Behaviors of Asymmetry Dendron-Like Polypeptide-Based Polyampholyte

An asymmetry dendron-like polyampholyte,poly(L-lysine)₄-D2-b-D1-poly(L-glutamic acid)₂ (PLL)₄-D2-b-D1-(PLGA)₂,where D1 and D2 are the first and second generation of poly(amido amine),was synthesized via the combination of divergent synthesis procedure,ring-opening polymerization (ROP) and click chemistry.The molecular structure,molecular weight and molecular weight distribution were characterized by proton nuclear magnetic resonance spectroscopy (¹H-NMR),Fourier transform-infrared spectroscopy (FT-IR) and gel permeation chromatograph (GPC).The pH-responsive self-assembly behaviors were investigated via potentiometric and conductometric titration,¹H-NMR spectroscopy,zeta potential measurement,scanning electron microscopy (SEM),transmission electron microscopy (TEM) and dynamic light scattering (DLS).It was found that (PLL)₄-D2-b-D1-(PLGA)₂ shows pH-responsive "schizophrenic" micellization behaviors.It can self-assemble into aggregates with PLL-corona and PLGA-core at acid pH,and with PLGA-corona and PLL-core at alkaline pH,companied with the coil-to-helix conformational transition of PLGA and PLL segments.The self-assembled aggregates changed their morphology from spherical to rod-like and then to spindle-like micelles.Moreover,novel villus-like fractal structure was formed by hierarchical assembling of spindle-like micelles at high pH value.