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

Stimuli-responsive polymer micelles were the topic of intense research due to their potential applications in biomedical and nanotechnology fields. Developments of polymerization techniques made it possible to precisely design well-defined stimuli-responsive polymers. The combination of several responsive moieties within one polymer could exhibit multifaceted behaviors and a more pronounced or more detailed response when applying one or more external stimuli.In this dissertation, we have synthesized a series of well-defined stimuli-responsive polymers and investigated their structure and properties, especially the morphology changes of micellar aggregates toward the external stimuli such as pH, temperature and light. In summary, this dissertation included the following five parts:1. Synthesis and self-assembly behavior of thermoresponsive POSS-based polymersA novel amphiphilic polyhedral oligoraeric silsesquioxane (POSS) end-capped poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (POSS-P(ME02MA-co-OEGMA)) was successfully synthesized via ATRP. These thermoresponsive organic-inorganic hybrid polymers exhibited critical phase transition temperature in water, which could be finely tuned by changing the feed ratio of OEGMA and MEO2MA. The lower critical solution temperature (LCST) of POSS-PMO increased from 31℃ to 59℃ with the increasing of OEGMA content. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies showed that these polymers could self-assemble into spherical micelles with the thermosensitive block into the corona and the POSS forming the core, and larger aggregates were formed when the temperature values were above their LCSTs. These thermoresponsive polymers POSS-PMO with self-assembly behavior and tunable tempetature responsive property have the potential applications in material science and biotechnology.2. Synthesis and self-assembly behavior of POSS-based polymers with thermo- and pH-responseWell-defined pH- and thermo-repsonsive amphiphilic block copolymers POSS-poly(2-(2-methoxyethoxy)ethyl methacrylate)-block-poly (dimethylaminoethy methacrylate) (POSS-PMEO2MA-b-PDMAEMA) with different PDMAEMA block lengths were successfully synthesized by ATRP.The obtained polymer displayed LCST behaviors in water, and the temperatures of phase transition and CMC values increased with the increase of PDMAEMA content in the block copolymers. Due to the pH responsivity of PDMAEMA chains, the size of the micelles and phase tranition temperatures decreased with increasing pH.3. Synthesis and self-assembly behavior of o-nitrobenzyl-based amphiphilic hybrid polymer with light and pH dual responseA novel light-responsive polyhedral oligomeric silsesquioxane (POSS) end-capped poly(o-nitrobenzyl methacrylate) (POSS-PNBMA) were synthesized by the combination of atom transfer radical polymerization (ATRP) and click chemistry. After subsequent partial photocleavage of PNBMA yielding poly(methacrylic acid) (PMAA), pH-and light-responsive random copolymer of POSS-P(NBMA-coMAA) was obtained. The o-nitrobenzyl-based amphiphilic hybrid polymer could self-assemble into spherical micelles in aqueous solution. Hydrophobic POSS and PNBMA segments aggregated into the inner core, and the hydrophilic PMAA chains tended to stretch from the core. The micellar morphology could be tuned by pH changes and UV irradiation. Light irradiation led to the transformation of P(NBMA-coMAA) into PMAA and to the reorganization of the assemblies, causing the release of encapsulated guest molecule Nile Red into water. This dual-responsive polymer has a broad potential use in targeted drug delivery.4. Synthesis and self-assembly behavior of o-nitrobenzyl-based multiple stimuli-responsive polymerA novel multi-responsive diblock copolymer composed of a hydrophilic poly(ethylene oxide) (PEO) block and a responsive poly(o-nitrobenzyl methacrylate-co-(dimethylaminoethy methacrylate)) (P(NBMA-co-DMAEMA)) block were synthesized by ATRP. Above the CMT, the block copolymer was amphiphilic and self-assembled into micelles. Adjusting the pH to acidic, the disruption of the micelles could be observed. Furether adjustign the pH to basic, the size of the micelles decreased. After UV irradiation, the CMT of the block copolymers increased, causing the disruption of the micelles and the release of encapsulated Nile Red.5. Stimuli-induced multiple dissociation and micellization transitions of o-nitrobenzyl-based amphiphilic random copolymerNovel thermo- and light-responsive random copolymers poly(o-nitrobenzyl methacrylate)-co-2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol) methacrylate) (P(NBMA-co-ME02MA-co-OEGMA)) was synthesized by ATRP. This random copolymer self-assembled into spherical micelles with a PNBMA core and a PMEO2MA/POEGMA corona in aqueous solution. Upon UV irradiation, the transformation of PNBMA into poly(methacrylic acid) (PMAA) induced the disruption of the initial micelles and the release of encapsulated fluorescent dye Nile Red into water. Further increasing the temperature or decreasing the pH, the resulting P(MAA-co-MEO2MA-co-OEGMA) could form PMEO2MA/POEGMA-core or PMAA-core micelles with the re-encapsulation of Nile Red. These random copolymers have the great potential applications in targeted drug delivery and nanomedicine.