School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China.
Macromol Rapid Commun. 2011 Jul 15;32(14):1101-7. doi: 10.1002/marc.201100112. Epub 2011 Jun 3.
Poly(N-isopropylacrylamide) (PNIPAAm) grafted dextran nanogels with dodecyl and thiol end groups have been synthesized by RAFT process. Dodecyl-terminated polymers (DexPNI) can be readily dissolved in water and further self assemble into ordered stable nanostructures through direct noncovalent interactions at room temperature. SEM, AFM and DLS measurements confirm the formation of spherical nanogels at hundred-nanometer scales. The elevation of environment temperature will indirectly result in the formation of collapsed nanostructures due to the LCST phase transition of PNIPAAm side chains. Turbidimetry results show that the phase transition behaviors of DexPNI are greatly dependent on PNIPAAm chain length and polymer concentration: increasing PNIPAAm chain length and polymer concentration both lead to lower LCSTs and sharper phase transitions. Moreover, the dodecyl-terminated polymers can transform into thiol-terminated versions by aminolysis of trithiocarbonate groups, and further into chemical (disulfide) cross-linked versions (SS-DexPNI) by oxidation. SS-DexPNI nanogels have "doubled" chain length of PNIPAAm, and hence sharper phase transitions. In situ DLS measurements of the evolution of hydrodynamic radius attest that the self assembly of SS-DexPNI nanogels can be selectively directed by the change in either external temperature or redox potential. These nanogels thus are promising candidates for triggered intracellular delivery of encapsulated cargo. We can also expect that the polymer can be noncovalently (by dodecyl end groups) or covalently (by thiol end groups) coated on a series of nanomaterials (e.g., carbon nanotubes, graphene, gold nanomaterials) to build a variety of novel smart, and robust nanomaterials.
通过 RAFT 过程合成了具有十二烷基和巯基端基的聚（N-异丙基丙烯酰胺）（PNIPAAm）接枝葡聚糖纳米凝胶。十二烷基封端聚合物（DexPNI）可轻易溶解于水中，并在室温下通过直接非共价相互作用进一步自组装成有序的稳定纳米结构。SEM、AFM 和 DLS 测量证实了在百纳米尺度上形成了球形纳米凝胶。环境温度的升高会由于 PNIPAAm 侧链的 LCST 相转变而间接导致纳米结构的塌陷。浊度法结果表明，DexPNI 的相转变行为极大地依赖于 PNIPAAm 链长和聚合物浓度：增加 PNIPAAm 链长和聚合物浓度都会导致较低的 LCST 和更陡峭的相转变。此外，通过三硫代碳酸酯基团的氨解，十二烷基封端聚合物可以转化为巯基封端的聚合物，然后通过氧化进一步转化为化学（二硫键）交联的聚合物（SS-DexPNI）。SS-DexPNI 纳米凝胶的 PNIPAAm 链长“加倍”，因此相转变更陡峭。动态光散射（DLS）原位测量证明了 SS-DexPNI 纳米凝胶的自组装可以通过外部温度或氧化还原电势的变化来选择性地定向。这些纳米凝胶因此有望成为用于触发包裹货物的细胞内递送的候选物。我们还可以预期，该聚合物可以通过非共价（通过十二烷基端基）或共价（通过巯基端基）与一系列纳米材料（例如，碳纳米管、石墨烯、金纳米材料）结合，构建各种新型智能且坚固的纳米材料。
