Synthesis Of Stimuli-Responsive Polymers And Study Of Their Self-Assembly Behaviors In Solution

Based on the composition, morphology and function, this dissertation successfully synthesized a series of stimuli-responsive macromolecules by using atom transfer radical polymerization (ATRP) or click chemistry. In addition, their self-assembly behaviors in solution (water or oil) were studied. By changing the molecular structure or the external conditions (temperature, pH, light, solvent et al.), the ratio of hydrophilic and hydrophobic blocks was changed, and in this way we can control the aggregation form of the molecules. Moreover, a preliminary attempt was made in controllable upload and release of small guest substance.This dissertation mainly studied the effect of the game between the hydrophilic block and the hydrophobic one on the final gather form of the macromolecules, and how to obtain the needed gather form by controlling the external conditions. This might be helpful for the application of polymers and also guided the molecular design. This dissertation mainly included the following four parts: (1) A pH/thermo-responsive tadpole-shaped polymers, polyhedral oligomeric silsesquioxane (POSS) end-capped poly[2-(dimethyl-lamino) ethyl methacrylate](POSS-PDMAEMA), was successfully synthesized via ATRP. Then the self-assembly behaviors of POSS-PDMAEMA in aqueous solution were studied and the results revealed its two self-assembly processes.First the polymer molecules self-assembled into a single micelle with the POSS molecules forming a crystal core and the PDMAEMA chains stretching as a corona. Then the single micelles, as building blocks, were able to reversibly form a complex micelle under external stimuli. Besides, the thermo-responsiveness of POSS-PDMAEMA was influenced by pH; the thermo-and pH-responsiveness together influenced the gathering behaviors of the polymer.(2) A POSS-containing pH/temperature-responsive diblock copolymer (PDMAEMA-b-PMAPOSS) was successfully synthesized via ATRP; the number of the POSS group was about5.Compared with tadpole-shaped polymer, the increase of POSS group enhanced the aggregation ability of the diblock copolymer; this made the polymer tended to form short rod micelles. And the reversible transformation between single micelles and complex micelles of PDMAEMA-b-PMAPOSS under the control of pH was similar to POSS-PDMAEMA. Moreover, we successfully controlled the upload and release of pyrene in water by using PDMAEMA-b-PMAPOSS.(3) A spiropyran-containing photo-responsive Y-shaped molecule SP-TPPE-(C16)2was successfully synthesized by click chemistry. Results reveal that this molecule could reversibly and repeatedly response to light. Under the UV light irradiation, the spiropyran group transformed from nonpolar SP form to polar MC form, and the group with increased polarity induced the aggregation of the molecules. The polarity of solvent could affect the molecular aggregation form, and the main reason was that it changed the proportion of the solvophilic and the solvophobic part of the molecule. A solvent with suitable polarity helped the molecule form into nanoscale aggregates with uniform size and good dispersion. Besides, by extending the time of UV irradiation, the molecule could have enough time to form a well-structured form.(4) A series of POSS end-capped tadpole-shaped poly(spiropyran-containing methacrylate)(POSS-PSPMA), a kind of photo-responsive organic-inorganic hybrid polymers, with different molecular weights were synthesized via ATRP. It has been proved that the molecular weight of POSS-PSPMA was obviously increased by raising the proportion of methanol. The reason is that methanol changed the balance between active and dormant species and in this way accelerated the polymerization;besides, it increased the proportion of MC form, which reduced the steric hindrance of SPMA monomer. The self-assembly behaviors of POSS-PSPMA were studied in toluene; the results show that under the control of UV and visible light, POSS-PSPMA could reversibly self-assembled into compound micelles because the charged MC groups formed stacks. These MC stacks acted as noncovalent cross-linking points, making the polymer chains tightly packed, limiting the transformation of MC form to SP form, and thus preventing the spontaneous dissociation of the aggregates. Moreover, the POSS shell prevented the further large-scaled phase separation of the polymers and guaranteed the stability of the aggregates. In addition, larger polymers were more likely to form denser aggregates which needed long time to dissociate, so the dissociation rate of the aggregates could be controlled by varying the molecular weight. This system has a broad potential use in naonocontainers and nanocarriers, especially for encapsulating and releasing polar substances in the nonpolar organic solvents.