Synthesis And Properties Of Functional Cyclic Polymers Based On Cholesterol And Galactose

There is a continuing quest to construct novel functional polymeric materials based on topological macromolecular structures.As one of the typical topological architectures,cyclic polymers have represented unqiue physical properties in both solution and solid states due to their“endless”feature,which have attracted great interests.Early,the study on cyclic polymers was mainly focused on some basic physical properties and the construction of theoretical models.In recent years,many efficient and convenient synthetic methods,especially controlled radical polymerization and“click”chemistry,were developed to prepare cyclic polymers with specific functions.Cyclic polymers with unique or improved performances have inspired researchers to conduct more extensive and in-depth researches in this area.Exploring the topological effects on the properties of polymers can not only facilitate the general understanding of the structure-property relationships,but also provide theoretical supports for the development of novel functional materials.In this thesis,we designed and synthesized a series of functional cyclic polymers based on bioactive cholesterol and galactose via the combination of reversible addition-fragmentation chain transfer?RAFT?polymerization or atom transfer radical polymerization?ATRP?with Cu?I?-catalyzed azide-alkyne cycloaddition?CuAAC?“click”chemistry.Then,the topological effects of cyclic architectures on the liquid crystalline properties,self-assembly behaviors and lectin-binding abilities were systematically investigated.The detailed researches were summarized as the following:?1?We designed and synthesized an alkyne-bearing RAFT agent and the initiator that has the same alkynyl structure as the R group in the RAFT agent.Then,we prepared the linear liquid crystalline polymers bearing cholesteryl groups with three length methylene spacers?m=2,6,11?by RAFT polymerization.Subsequently,aminolysis/Michael addition sequence in a one-pot fashion was performed to obtain the?-alkyne-?-azide linear precursors.Finally,the intrachain CuAAC cyclization of the linear precursors under high dilute conditions gave rise to the desirable cyclic liquid crystalline polymers.The successful cyclization was confirmed by comprehensive characterization including GPC,¹H NMR,TD-GPC and FT-IR spectra.On the basis of the POM,DSC and SAXS results,both linear and cyclic liquid crystalline polymers form the smectic phase in the liquid crystalline region with the same layer periodicity.Moreover,cyclic polymers exhibit a slightly lower mesophase transition temperature,enthalpy,entropy and smaller texture microstructures than the linear counterparts.Interestingly,the SmC packing structure is preferable in cyclic PChUMA compared with that in the linear one.?2?A series of amphiphilic brush-like liquid crystalline block copolymers linear PChEMA-b-POEGMAbearingcholesterylmesogenswithdifferent hydrophobic/hydrophilic block ratios were synthesized by RAFT polymerization.The block copolymers exhibited different self-assembly behaviors in THF/H₂O,1,4-dioxane/H₂O and DMF,respectively.The morphology transition from micelles to vesicles occurred when THF was used as co-solvent.And the transition point occurred forward with increasing the hydrophobic block ratio.However,using 1,4-dioxane as co-solvent,spherical micelles,short cylindrical micelles,fringed platelets and ellipsoidal vesicles could be obtained respectively,when the hydrophobic block ratio is increased.Meanwhile,apart from the spherical micelles,other self-assembled aggregates displayed a smectic micellar core.Moreover,we obtained cylindrical micelles when DMF was used as self-assembled solvent.Overall,this unique supramolecular system established a general design principle to prepare micellar aggregates with desirable morphologies and functions.On the basis of the above results,we synthesized another two block copolymers with hydrophobic/hydrophilic block ratios among the copolymer composition window where cylindrical micelles would be formed.Subsequently,the corresponding cyclic polymers,cyclic PChEMA₁₃-b-POEGMA₁₅ and cyclic PChEMA₁₈-b-POEGMA₁₄ were obtained by CuAAC“click”reaction,and then their self-assembly behaviors in 1,4-dioxane/H₂O were investigated.The cyclic architecture of amphiphilic side-chain liquid crystalline block copolymers could weaken the order of cholesteryl mesogens,which finally results in the formation of vesicles and other aggregates in solution,while their linear counterparts prefer to self-organize into short cylinders and nanofibers within a smectic micellar core,respectively.This study might be able to provide a new insight into the structure-property relationship of topological amphiphilic liquid crystalline polymers in general.?3?Three cyclic galactosylated glycopolymers with different molecular weights were synthesized via the combination of RAFT polymerization with CuAAC“click”chemistry followed by a deprotection reaction.The successful cyclization was confirmed by comprehensive characterization including GPC,¹H NMR,FT-IR and MALDI-TOF MS spectra.The turbidity assay revealed that the cyclic glycopolymers binding to Ricinus communis?castor bean?agglutinin RCA₁₂₀ were not superior in comparison with their linear precursors due to the inherent topological constraint.Moreover,in order to further elucidate the topological effect on the ability of lectin-binding,quartz crystal microbalance-dissipation?QCM-D?were used for evaluation the binding constants of the RCA₁₂₀ and cyclic glycopolymers.?4?Based on the above studies,we prepared amphiphilic cyclic block glycopolymer via the combination of RAFT polymerization with CuAAC“click”chemistry followed by a deprotection reaction.The successful cyclization was strictly confirmed by comprehensive characterization.It was found that the micellar size of the cyclic glycopolymer was larger than that of the linear one.Meanwhile,the cyclic polymeric micelles exhibited higher loading content for Nile Red?a hydrophobic drug model molecule?than the corresponding linear polymeric micelles.In addition,we also investigated the lectin-binding abilities of the cyclic glycopolymer micelles via the turbidity assay.Considering the biocompatibility and bioactivity of cholesterol and galactose,the self-assembled nanoparticles of cyclic glycopolymer could be used as targeted drug carriers,so that they have the potential applications in the field of biomedicine.