摘要/Abstract

通过开环聚合（ROP）和原子转移自由基聚合（ATRP）合成了一种pH响应性三嵌段共聚物聚乙二醇-b-聚赖氨酸-b-聚苯乙烯（PEG-b-PLL-b-PS），在水-有机溶剂混合溶液中进行组装，并采用透射电子显微镜（TEM）、原子力显微镜（AFM）和衰减全反射红外光谱法（ATR-IR）表征.该三嵌段共聚物在四氢呋喃（THF）与水的混合溶剂（V：V=1：1）中可组装成疏水性聚苯乙烯为核、亲水性聚赖氨酸和聚乙二醇分别为内壳和外壳的球状胶束.采用TEM和AFM发现该球状胶束在四氢呋喃（THF）水溶液中退火7 d后可进一步转变为纤维状结构.进一步除去THF后，可恢复至粒径略小的冻结球状胶束.另外，球状胶束的粒径随着pH的增加而增加，当pH为13时，聚赖氨酸的二级结构由无规卷曲构象过渡到α-螺旋构象，聚集体由球形结构过渡到空心囊泡.溶液经透析后可使囊泡恢复至球状胶束.
关键词: 三嵌段共聚物, 开环聚合, 原子转移自由基聚合, 自组装, pH响应性, 纳米结构
Similar to natural proteins, polypeptides can form secondary structures depending on their physical properties. Many efforts have been made towards the self-assembly of triblock copolymer containing polypeptide as an important component to construct hierarchical structures by utilizing the pH-responsive conformation transformation. In this work, a pH-responsive poly(ethylene glycol)-b-poly(L-lysine)-b-poly(styrene) (PEG-b-PLL-b-PS) triblock copolymer was prepared via a combination of controlled ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP). In the triblock copolymer, PLL is water-soluble in acidic solution with random coil conformation, but becomes insoluble helix in alkaline solution. PEG has excellent water solubility that can exhibit protein-resistant property. PS serves as hydrophobic part. Self-assembly of the polymer was examined by transmission electron microscopy (TEM), atomic force microscopy (AFM) and attenuated total reflection-infrared spectrometer (ATR-IR). The triblock copolymer forms spherical micelles in 1：1 volume ratio of tetrahydrofuran-water mixed solvent, in which the hydrophobic PS segment forms a core and the two hydrophilic segments PLL and PEG serve as shell and corona, respectively. The spheres as the subunits further transform into hierarchical 1D fiber-like structure in the presence of THF after 7 d of aging, confirmed by both TEM and AFM techniques. Upon removing THF, the spherical shape was re-obtained with slightly smaller diameter, so called “frozen micelles”. Further, the diameter of the spheres increases with pH increasing. A sphere-to-vesicle transition was observed at pH 13 as the secondary conformation of PLL transforms from coil to α-helix. The dialysis of these solutions can convert the vesicles back into spherical morphology with slightly smaller diameter.
Key words: triblock copolymer, ring-opening polymerization, atom transfer radical polymerization, self-assembly, pH responsive, nanostructure


PDF全文下载地址:

点我下载PDF