Study On Synthesis,property And Application Of TEMPO-containing Methacrylate-based Copolymers

Stimuli-responsive self-assembled nanostructures cause great attention as "smart"materials.Among them,bioinspired redox-responsive nanostructures appear as promising materials for their biomedical applications,especially in drug delivery.The presence of redox-responsive groups such as nitroxide radical(or unpaired electron)in nanostructures gives them the capability of reducing reactive oxygen species(ROS)levels and other side effects in targeted therapies.Accordingly,much attention has been focused on redox-responsive materials as nanocarriers of drugs.However,research on nanostructures constructed from copolymers with redox-responsive nitroxide radical functionality is limited in design and synthesis.There are some studies on redoxresponsive nanostructures through self-assembly with nitroxide radical-functionalized copolymers as building materials.In order to explore the nitroxide radical-containing copolymers in the fields of self-assembly and drug delivery application,as well as to overcome the limitations of designing controlled assemblies,the following researches were done in this thesis:1)Four spin-labeled copolymers poly(methyl methacrylate-co-acrylic acid)s(SLp(MMA-co-AA)s)were synthesized and characterized by proton nuclear magnetic resonance(1H NMR),gel permeation chromatography(GPC),Fourier transform infrared(FT-IR),ultraviolet-visible(UV-Vis),thermogravimetric analysis(TGA),differential scanning calorimetry(DSC)and water contact angle(CA)techniques.Transmission electron microscopy(TEM)and dynamic light scattering(DLS)techniques were performed to observe the self-assembled particles’ morphology and size distribution.Electron paramagnetic resonance(EPR)spectroscopy and TEM were employed to elucidate the structural changes in different microenvironments.At pH 5,the copolymers formed polymersomes and the EPR line intensity was found to be the lowest compared with those at pH 2,7 and 9.The micelles were aggregated with the increasing temperature(323 K<T<413 K)where the spin-exchange interaction was greater.The conformational inversion(inverse micelle)was noticed in intrinsic nonpolar environments.Upon the addition of the reducing agent(ascorbic acid),the micelles were rapidly disassembled by losing their hydrophilic-lipophilic balance(HLB),where the reduction of the nitroxide radicals was rate controlled.Overall,the studies on the spin-labeled copolymers offer a novel way to develop multi-stimuliresponsive nanomaterials by changing the microenvironment.2)Three spin-labeled copolymers poly(N-isopropyl methacrylamide-co-acrylic acid)s(SL-p(NIPMAM-co-AA)s)were synthesized and characterized by 1H NMR,GPC,FT-IR,TGA,DSC and CA techniques.Their self-assembled nanoaggregates were confirmed by scanning electron microscopy(SEM)and TEM.EPR spectroscopy and TEM revealed the formation and morphological transitions of supramolecular nanoaggregates in different external parameters(e.g.pH,temperature,reductant,polarity and viscosity).In an acidic medium(≤pH 3),the colloidal nanoparticles disassembled due to the disproportionation of nitroxide radicals.The particles’morphology was observed to be an LCST-type character,where multi-micelle aggregates were formed upon increasing the temperature(303 K<T<373 K).The rate controlled redox-triggered disassembly was noticed upon the addition of different molar equivalents of ascorbic acid as a reducing agent.Interestingly,the morphological transitions were observed on changing the polarity of the medium.The micellar inversion was observed in 1-octanol by forming wormlike micelle.The nanoaggregates were used as anticancer drug(5-FU)nanocarriers where the redox-responsive disassembly accelerated the cumulative release up to 76%at 37℃ within 24 h,which is helpful for the targeted drug delivery.3)Three nitroxide radical-functionalized copolymers poly(2-hydroxypropyl methacrylate-co-2,2,6,6-tetramethylpiperidin-1-oxyl methacrylate)(PHTs)were synthesized and characterized by 1H NMR,GPC,FT-IR,DSC and CA techniques.Their self-assembly structures were studied by SEM,TEM,DLS and energy-dispersive spectroscopy(EDS).TEM,EPR and UV-Vis spectroscopy was applied to disclose the supramolecular nanoparticles(NPs)formation and structural changes.Spherical nanostructures were formed in a neutral pH solution,while in acidic and basic media the morphology of the nanoparticles was found to be partially disassembled and formed necklace-like nanostructures,respectively.The NPs showed rate controlled redoxresponsiveness upon the addition of different molar equivalents of reducing agents.At relatively high temperatures(303 K<T<353 K),the nanoparticles were high in stretching as the global mobility of the polymer chains was increased.The polarity stimulus also had significant effects on the morphology,where inverse nanostructures were constructed by converting the conformation.The NPs showed good biocompatibility as evaluated by hemolysis and MTT assay.The NPs were used to release DOX where the redox environment showed the high release property(61.53%at 37℃ within 48 h).4)Four nitroxide radical-functionalized copolymers poly(hydroxyethyl methacrylate-g-polylactide-co-2,2,6,6-tetramethylpiperidin-1-oxyl methacrylate)s(PHLTs)were synthesized and and characterized by 1H NMR,GPC,TGA,UV-Vis,DSC,CA and CV techniques.TEM and EPR spectroscopy were applied to reveal the supramolecular vesicular structure and local chain dynamics in stimuli-responsive controlled assemblies.At the acidic pH range(<pH 5),phase/morphological transitions were observed where the polymer chain dynamics were increased.The vesicular morphology was transferred to spherical reverse micelle in THF,while the vesicular morphology was sustained in 1-octanol with reverse conformation.The rate controlled reduction-responsive behavior was noticed upon the addition of the different molar equivalent of ascorbic acid.The hemolysis and MTT assay were performed to estimate the biocompatibility.Furthermore,the obtained vesicles were used as anticancer drug(DEX)carriers and showed high drug loading efficiency(63.65%).The reductionresponse prompted disassembly accelerated the drug release(83.2%at 37℃ within 24 h).The DEX-loaded vesicles showed good anticancer activity against HeLa cells.