Facile Fabrication And Kinetic Analysis Of Polymeric Assemblies And Organic/Inorganic Hybrid System

With the development of polymer science and polymer materials applications,more and more facile chemical/physical methods are employed to construct new polymeric materials with new structures and functions,such as the host-guest recognition,hydrogen bonding,electrostatic interaction,as well as click chemistry and other efficient coupling reactions.Such strategies greatly enrich the structural design of polymeric assemblies and provide solid research foundation and technical support for the area of biology,medicine and chemical engineering,showing strong application potential.In this thesis,a series of supramacromolecular assemblies and an organic/inorganic system were prepared facilely and delicately through the above mentioned host-guest recognition and electrostatic interaction with the combination of click chemistry.On the other hand,kinetic analyses were also made to further understand the self-assembly process of two polyion complex(PIC)micelles.1.Facile construction of pH-and thermo-sensitive three-layer micelle via host-guest recognition.Two kinds of double hydrophilic diblock copolymers(DHBCs)end-capped by ?-cyclodextrin(?-CD)moieties,?-CD-PMEO2MA-b-PDEA and ?-CD-PDEA-b-PMEO2MA,were synthesized through successive Atom Transfer Radical Polymerization(ATRP)followed by click reaction,where PDEA is poly(2-(diethylamino)ethyl methacrylate)and PMEO2MA is poly(di(ethylene glycol)methyl ether methacrylate).Owing to the pH sensitiveness of PDEA blocks and the thermo-responsiveness of the PMEO2MA blocks,the obtained two DHBCs could respectively self-assemble into two-layered micelles decorated with ?-CD moieties by controlling the pH or temperature of the corresponding aqueous solution.Furthermore,polyethylene glycol end-functionalized with adamantane(Ad-PEG)was synthesized and then introduced onto the coronas of the DHBC micelles via the host-guest recognition between ?-CD and adamantane(Ad)moieties,thus affording three-layered micelles.Such strategy for the preparation of three-layered micelles suggested a facile way to construct complex supramolecular self-assemblies instead of complicated and tough synthesis processes.2.Construction of thermo-sensitive and reversibly core crosslinkable micelles.Double hydrophilic diblock copolymer,poly(ethylene glycol)-b-poly(N-isopropylacrylamide-co-N-acryloxysuccinimide)(PEG-b-P(NIPAM-co-NAS)),was synthesized via Reversible Addition-Fragmentation Chain Transfer(RAFT)polymerization in the presence of macromolecular PEG chain transfer.The obtained DHBC can unimolecularly dissolve in aqueous solution at room temperature,while self-assemble into micelles with P(NIPAM-co-NAS)cores and PEG coronas at elevated temperatures due to the thermo-responsiveness of the PNIPAM blocks,which collapsed when being heated above the well-known Lower Critical Solution Temperature(LCST).Then core-crosslinked(CCL)micelles were prepared by addition of bifunctional cystamine as the crosslinker that can react with the N-acryloxysuccinimide(NAS)side groups in the micellar cores.The cross-linked micellar cores of the prepared CCL micelles also exhibit thermos-sensitive swelling/deswelling behavior.On the other hand,the disulfide bonds in the crosslinking linkages can be cleavaged by sulfhydryl compounds such as dithiothreitol(DTT),thus fulfilling the reversible crosslinking in the micellar cores..3.Construction of the thermo-sensitive core-crosslinked(CCL)polyion complex(PIC)micelles based on electrostatic complexation.Two kinds of diblock copolymers,P(tBMA-co-AzPMA)and P(DMA-co-AzPMA),were synthesized through ATRP,in which tBMA,DMA and AzPMA were tert-butyl methacrylate,2-(dimethylamino)ethyl methacrylate and 3-azidopropyl methacrylate,respectively.These two copolymers were then grafted by PNIPAM chains to give amphiphilic P(tBMA-co-AzPMA)-g-PNIPAM and P(DMA-co-AzPMA)-g-PNIPAM via click chemistry between the alkynyl groups at the end of PNIPAM chains and the aizde side groups pendent in the side chains of the two diblock copolymers.After hydrolysis of the tertiary butyl ester groups in P(tBMA-co-AzPMA)-g-PNIPAM,the obtained P(MAA-co-AzPMA)-g-PNIPAM can co-assemble with P(QDMA-co-AzPMA)-g-PNIPAM,which was obtained after quarterized with P(DMA-co-AzPMA)-g-PNIPAM in aqueous solution to form PIC micelles with PNIPAM corona,while the micellar cores were composed from P(MAA-co-AzPMA)and P(DMA-co-AzPMA)blocks via electrostatic complexation interaction.Furthermore,the remaining azide groups after grafting PNIPAM can be used to make the micellar cores crosslinked and fix the micellar structure by addition of propargyl ether as the crosslinker.The structural stability and thermo-induced aggregation of non-cross-linked and cross-linked PIC micelles were thoroughly characterized by laser light scattering(LLS)and temperature-dependent turbidimetry.4.Delicate construction of organic-inorganic hybrid polymer by surface click crosslinking.Core-crosslinked star-type polystyrene(PS),(alkynyl-PS)n-CCL,was synthesized using macromolecular PS initiator with two alkynyl end groups to initiate the ATRP of divinylbenzene(DVB).At the same time,octa(3-azidopropyl)polyhedral oligomeric silsesquioxane bearing azide groups at the surface,POSS-(N3)8,was prepared based on POSS.Then in high dilute solutions,(alkynyl-PS)n-CCL star polymer was surface-crosslinked by octa(3-azidopropyl)-POSS via azide-alkynyl click reaction.FT-IR,1H NMR,GPC and elemental analysis were used to characterize the star polymer and the final hybrid microstructure.The thermal property,including glass transition temperature and thermal stability of the surface-crosslinked product and the core-crosslinked precursor,were compared using DSC and TGA,respectively.The corresponding experiment results will no doubt broaden and boost the researches on new organic-inorganic hybrid materials and new structures.5.Construction and kinetic analysis of the thermo-sensitive PIC micelles from diblock polyions by electrostatic complexation.Oppositely charged polyions,anionic block copolymer poly(ethylene oxide)-b-poly(sodium 4-styrene sulfonate)(PEG-b-PSSNa)and cationic block copolymer poly(N-isopropylacrylamide)-b-poly(2-(dimethyl amino)ethyl methacrylate)(PNIPAM-b-PDMA)were prepared through ATRP and RAFT respectively,followed by the quaternization of the dimethyl amino groups to give poly(N-isopropylacrylamide)-b-poly(quaternized 2-(dimethyl amino)ethyl methacrylate)(PNIPAM-b-PQDMA).Upon directly mixing the aqueous solutions of the two block copolymers,PIC micelles possessing mixed thermo-responsive PEG/PNIPAM coronas were obtained,while the micellar cores were composed from anionic PSSNa and cationic PQDMA blocks via electrostatic complexation interaction.The thermo-responsiveness of the PIC micelles was studied using laser light scattering(LLS)and the formation process of the PIC micelles was kinetically investigated by means of stopped-flow technique.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 structure rearrangements of the formed quasi-equilibrium complex to the final equilibrium ones.Both stages are determined to be second-order reactions and processed through micelle fusion/fission mechanism.6.Construction and kinetic analysis of the thermo-sensitive PIC micelles from polyelectrolyte and lysozyme by electrostatic complexation.Poly(N-isopropylacrylamide)-b-poly(sodium acrylate)(PNIPAM-b-PANa)was synthesized via RAFT polymerization and directly mixed with positively charged lysozyme to fabricate PIC micelles with PNIPAM corona in sodium phosphate buffer solution(pH 7.4).Due to the thermos-responsiveness of PNIPAM blocks,the PIC micelles would aggregate to precipitate upon temperature increasing,thus separating the lysozyme from the solution.The formation and dissociation of the PIC micelles can be modulated by protonation/deprotonation of the carboxyl side groups upon changing the solution pH value,which in return affect the lysozyme activity.Moreover,the kinetic processes of PIC micelles formation were investigated using stopped-flow technique.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 structure rearrangements of the pre-complexes to the final equilibrium state.And the fast relaxation process was proceeded through unimer insertion/expulsion mechanism,while the slow process was through micelle fusion/fission mechanism.