Synthesis And Characterization Of Dextran-based Dual Stimuli-responsive Nanogels

Nanometer-sized hydrogels (nanogels) is a new type of nanoscale materials, which exhibit properties of both nanoparticles and hydrogels. Stimuli-responsive gels have been called"smart"materials because they respond by a change in swelling to subtle changes in the environment. These hydrogels can be made responsive to temperature, pH value, ionic strength, light, electric field, and biomolecules. The responsive behavior of the hydrogels is inherited from the type of the polymer used in making the gel. For nanogels can be applied to more areas,such as in vivo diagnostics, drug delivery, chemical separation, chemical and biological sensors, optical material, we need to synthesize more complex polymers to get high-functional nanoscale materials.In this thesis, we adopted dextran to prepare stimuli-responsive nanogels. The graft polymers were obtained by grafting PNIPAM chains onto dextran by reversible addition-fragmentation chain transfer (RAFT) polymerization. The chemical structure of graft polymers was affirmed by FTIR and 1H NMR; DLS and SEM were used to characterize the self-assembly behavior of the nanogels; UV-Vis,1H NMR was used to study the phase transition behavior of the nanogels; DLS and UV-Vis were used to investigate the dual stimuli-responsive nature of the nanogels.We could get the following results: poly N-isopropylacrylamide polymer grafted based polymers has been successfully prepared, and the length of the grafted chains is controlled by the molar ratio of N-isopropylacrylamide to dextran; nanogels are formed by self-assembly, and when the temperature is higher than the LCST of nanogels, the grafted chains became hydrophobic and the size of nanogels became smaller; the phase transition nature of nanogels was related to the PNIPAM chain length and polymer concentration: the phase transition of nanogels became acute when the chain length or polymer concentration increases and the LCST of nanogels is controlled by the length and polymer concentration; nanogels that respond to both temperature and redox condition can be obtained by aminolysis.