不对称树状聚两性电解质的合成及pH响应性自组装行为

通过发散法、开环聚合以及“点击化学”等方法合成了树状聚两性电解质聚（L-赖氨酸）-聚酰胺-胺-聚（L-谷氨酸）（PLL）₄-D2-b-D1-（PLGA）₂],其中,D1和D2分别代表第1代和第2代聚酰胺-胺。通过氢核磁共振波谱（¹H-NMR）、傅里叶变换红外光谱（FT-IR）和凝胶渗透色谱（GPC）对产物的分子结构、相对分子质量及其分布进行了表征;结合电位电导滴定、¹H-NMR、Zeta电位测定、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和动态光散射（DLS）等表征方法研究了（PLL）₄-D2-b-D1-（PLGA）₂溶液的pH响应性自组装行为。研究结果表明,（PLL）₄-D2-b-D1-（PLGA）₂具有pH响应性多重胶束化行为,在酸性条件下形成PLL为壳、PLGA为核的聚集体,而在碱性条件下形成PLGA为壳、PLL为核的聚集体,同时伴随着PLGA和PLL链段从无规线团到α-螺旋构象的转变。随着溶液pH的增加,自组装聚集体由球形胶束向棒状胶束再向纺锤形胶束转变,并在高pH下二次自组装形成松叶状分形结构。

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.