Fabrication Of Stimuli-Responsive Supramolecular Aggregates And Self-Assembling Kinetic Processes

Supramolecular assemblies have attracted much interest in the past century due to their promising applications in diverse fields such as catalysis,material preparation and biomedicine.In this dissertation,a series of supramolecular assemblies were fabricated via different non-covalent interactions from specific functionalized surfactants and block copolymers with varying chemical architectures.The block copolymers were prepared in the combination of widely-noted controlled radical polymerizations and click chemistry.Besides the construction of the aggregates,new approaches in the fixation of nanostructures from supramolecular assemblies were investigated and the relaxation kinetics of the formation of the assemblies was also studied.The dissertation includes the following four parts:1.Supramolecular assemblies were built based on varies of non-covalent interactions such as electrostatic interaction,inclusion complexation,Ï€-Ï€interactions, hydrogen bond and cation-Ï€interactions.First,ABA triblock copolymer, poly(4-vinyl-pyridine)-b-poly(ethylene oxide)-b-poly(4-vinylpyridine)(P4VP-b-PEO -b-P4VP) was prepared via Atom Transfer Radical Polymerization(ATRP). In the presence of cross-linker,sodium 2,6-naphthalene disulfonate(NDSNa), thermo-sensitive "flower-like" spherical micelles with a "UCST" behavior would form at low polymer concentrations while physical hydrogel can be obtained at high polymer concentrations in acid aqueous solutions.Second,azobenzene groups were introduced to the side chain of poly(2-(dimethylamino) ethyl methacrylate-co-azidopropyl methacrylate),P(DMA-co-AzPMA),by using the click chemistry technology.By mixing aqueous solutions of azobenzene polymer and oligo-β-cyclodextrin,multi-responsive physical hydrogel can form due to the inclusion complexation.The obtained hydrogel would translate to fluid solutions upon heating,UV-irradiation and adding competitive guest molecule.Third, narrow-dispersed PNIPAM-functionalized hyperbranched oligo(mono-N₃-CD), oligo(CD-PNIPAM),and adamantane-terminated PDEA were synthesized via a combination of ATRP and click chemistry.The inclusion complexation betweenβ-CD and Ad moieties was employed as the driving force in constructing supramolecular double hydrophilic miktoarm star copolymer,which consisting of PNIPAM chains as thermo-responsive arms and PDEA chains as pH-responsive arms.The supramolecular star copolymer showed "schizophrenic" micellization behavior in aqueous solution upon dually playing with solution pH and temperature.Forth,amphiphilic ABA triblock copolymers and multi-block copolymers consisting with a rigid azobenzene repeat unit in the main chain were successfully synthesized."Leaf-like" supramolecular aggregates were obtained in aqueous solutions while short "rod-like" aggregates were observed upon UV-irradiation.Last,spontaneous vesicles can form in the aqueous solution of anionic surfactant,sodium dodecyl sulfate(SDS),when hydrotropic salt, p-toluidine hydrochloride(PTHC),was added at certain concentrations.When these vesicles were heated above a critical temperature or diluted with certain water,they would transform into flexible wormlike micelles.2.On the basis of the works concerning the aggregation behavior of block copolymers mentioned above,we further devoted to the fixation the supramolecular assembly nanostructures.First,alkynyl group functionalized anionic polyelectrolyte,poly(ethylene oxide)-b-poly(methacrylic acid-co-propargyl methacrylamide)(PEO-b-P(MAA-co-PgAM)),and azide group functionalized cationic polyelectrolyte,poly(ethylene oxide)-b-poly(quaternized 2-(dimethylamino) ethyl methacrylate-co-azidopropyl methacrylate)(PEO₁₁₃-b-P(QDMA-co-AzPMA)) were synthesized.Polyion complex(PIC) micelles formed by mixing aqueous solution of the two oppositely charged polyelectrolytes. Upon adding Cu(â… ) catalysis,the PIC micelles were facilely cross-linkd via "click" reaction which was processed in the PIC micellar core.Second,surfactant vesicles were observed to form in mixed aqueous solutions of sodium dodecyl benzenesulfonate(SDBS) and p-octyl aniline hydrochloride(POAHC).Both the cationic and anionic surfactants possess a phenyl group connected to the polar head.TheÏ€-Ï€interaction between phenyl groups greatly enhanced the stability of the formed vesicles.3.In the third part,the kinetics processes of supramolecular assembly formation were detailedly investigated using stopped-flow technique.First,Poly(glycerol monomethacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate)-b-poly(2-(di-ethylamino)ethyl methacrylate)(PGMA-PDMA-PDEA) triblock copolymer was synthesized via ATRP.The pH-induced micellization kinetics of the triblock copolymer was investigated by employing the stopped-flow light scattering and fluorescence.Upon pH-jump from 4 to 12,all relaxation curves recorded by stopped-flow light scattering can be well fitted with a double-exponential function, leading to a fast relaxation time constant(Ï„₁) and a slow relaxation time constant (Ï„₂).The fast process(Ï„₁) is associated with the formation of quasi-equilibrium micelles,while the slow process(Ï„₂) is associated with micelle formation-breakup, approaching the final equilibrium state.Both processes occur much more slowly on initial addition of NaCl,and then level off at higher salt concentrations(＞0.5 M NaCl).The concentration dependence ofÏ„₂ revealed that the mechanism of micelle formation/breakup process transforms from unimer insertion/expulsion in the absence of salt to micelle fusion/fission in the presence of high NaCl concentrations.Relaxation curves obtained with stopped-flow fluorescence using pyrene as a probe can be well-fitted with a single-exponential function,and the relaxation time(Ï„_py) was in agreement withÏ„_f,the relaxation time of the overall micellization process as detected by stopped-flow light scattering.Second, oppositely charged polyions,anionic block copolymer poly(ethylene oxide)-b-poly(sodium 4-styrene sulfonate)(PEO-b-PSSNa) and cationic block copolymer poly(ethylene oxide)-b-poly(quaternized 2-(dimethyl amino)ethyl methacrylate)(PEO-b-PQDMA) were prepared via ATRP.Upon directly mixing aqueous solutions of the two block copolymers,colloidally stabilized PIC micelles were obtained.The relaxation curves can be well fitted by a double-exponential function,leading to a fast relaxation process related to the initial quasi-equilibrium complex formation and a slow process related to the pre-complex structure rearrangements to the final equilibrium complexes.Both the two stages are determined to be acted as second-order reactions and processed through micelle fusion/fission mechanism.Fluorescence kinetics studies revealed that the neutralization of oppositely charged polyion was too fast to be detected and should be completed within the stopped-flow dead-time.Thermodynamics studies revealed that the spontaneously complexation is entropy driven.Upon increasing the ionic strength of the solutions,the complexation processes become slower by the reason of the decrease of entropy driven force.Last,the formation process of thermo-degradable micelles obtained by mixing acid aqueous solutions of PEO-b-P4VP diblock copolymer and 8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt(ANTS) were studied both by directly mixing the two solutions and temperature jump from 50℃to 20℃.The relaxation process can be divided into two parts.In the first fast process,small complex micelles with low aggregates number formed via the electrostatic interaction and then transform to the quasi-equilibrium complexes.The quasi-complex structure rearrangements to the final equilibrium complex micelles accrued in the second slow stage.4.In the last section,the block copolymer micelles were employed as the template to assemble the gold nanoparticles.First,cleavable ABA triblock copolymer poly (methyl methacrylate)-(s-s)-poly(tri(ethylene glycol) methyl ether methacrylate)-(s-s)-poly(methyl methacrylate)(PMMA-(s-s)-PMEO₃MA-(s-s)-PMMA) was synthesized.In aqueous solutions,the block copolymer micelles were consisted with a PMMA core,PMEO₃MA outer shell and disulfide bonds in the core-shell interface.Tetrahydroxymethyl phosphate chloride(THPC) stabilized gold nanoparticles were added to the micellar solution.The gold nanoparticles were diffused into inner shell and then reacted with the disulfide bonds to form a compact gold nanoparticle inner shell.Second,pyridine disulfide ether end-functionalized AB diblock copolymer PyDS-PMEO₂MA-b-PDEA was synthesized,pH-jump from 4 to 10 lead to the formation of PDEA-core micelles with PyDS groups at the micellar outer shell.Compact gold nanoparticles outer shell was then obtained by adding the THPC-stabilized gold nanoparticles to the micellar solutions.The gold nanoparticle surface coated micelles can be dispersed in acid aqueous and the re-aggregate to spherical supramolecular assemblies at pH 10.