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研究论文

两亲性聚氨基酸三嵌段共聚物构筑pH/溶剂可控多级纳米结构

李荣烨, Mehul Khiman, 盛力, 孙静   

  1. 青岛科技大学高分子学院 青岛 266042
  • 发布日期:2020-09-04
  • 通讯作者: 孙静 E-mail:jingsun@qust.edu.cn
  • 基金资助:
    本项目感谢国家自然科学基金(Nos 51722302 and 21674054),山东省杰青基金项目(No.ZR2019JQ17)资助.

pH/solvent tunable hierarchical nanostructures assembled from an amphiphilic polypeptide-containing triblock copolymer

Li Rongye, Mehul Khiman, Sheng Li, Sun Jing   

  1. College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042
  • Published:2020-09-04
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Nos 51722302 and 21674054), Natural Science Foundation of Shandong Province (No. ZR2019JQ17).

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THF水溶液中退火7天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. Note that PS is a glassy polymer at room temperature. Thus, the addition of THF that can dissolve PS is desired to reach an equilibrium in aqueous solution. We demonstrated that the nanostructured self-assemblies can be used as the subunits to construct 1D fiber-like supramolecular structure in water-THF mixed solvent.Self-assembly of the polymer was examined in aqua-organic mixed solution 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 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 days 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