| Owing to the absence of chain ends, the polymers with ring topology structure haveshown fantastic performance in solution or bulk state. With the development in syntheticmethods, macromolecule’s researchers have given more and more attentions to the cyclicpolymers in recent years.At present, the most impressive ones about the research results obtained from thecyclic polymers is from amphiphilic cyclic polymers. The amphiphilic cyclic polymershave displayed many unique properties based on the self-assembled aggregates, becausetheir “endless” topology reduces chain entanglement in contrast to the linear ones.However, the researches of cyclic polymers are limited owing to the complicated anddifficult structure confirmation for a pure polymer. Although there have been someinteresting research reports about cyclic amphiphilic polymers, they have only a smallnumber compared with other amphiphilic polymers. For example, the stimulus-responsecyclic amphiphilic polymer has seldom been seldom researched so far. Azobenzene grouphas a typical characteristic of the reversible transformation between the trans-and cis-isomerization induced by light. Light responsive self-assembly aggregates can be obtainedby introducing azobenzene into the amphiphilic polymer. In addition, polymers containingcarboxyl groups are responsive to the environment where a little changes to pH areproduced. As a result, the solubility of the chain segment is reversibly changed betweenhydrophilic and hydrophobic state.In this thesis, cyclic amphiphilic block copolymers based on stimulus-response to pHand light, containing azobenzene and carboxyl groups in side chains, were designed andsynthesized by combining ATRP with CuAAC chemistry. Then, the topology effects ofring structure on the self-assembly process of copolymers in solution and thestimulus-response of obtained aggregates to pH and light were investigated by comparisonof the corresponsive linear precursors. The detailed researches are summarized as thefollowing: (1)Homopolymer PBHME were obtained by ATRP of novel monomer BHMEbearing a pendent azobenzene using an alkynyl-ended initiator. Then,linear-PBHMEm-b-Pt-BAn-Br were obtained via chain extension using PBHME as ATRPmacroinitiator and t-BA as second monomer, followed by the conversion of terminalbromine group into azide group by NaN3to obtain linear-PBHMEm-b-Pt-BAn-N3. Thesubsequent CuAAC ring closuring reaction of linear-PBHMEm-b-Pt-BAn-N3waseffectively performed under high dilute solution to obtain cyclic-PBHMEm-b-Pt-BAn. Thecyclic structure was evidenced by NMR, GPC, TD-GPC, MALDI-TOF and FT-IRmeasurement. The linear-and cyclic-PBHMEm-b-PAAnwere synthesized throughselectively hydrolyze of t-BA using CF3COOH, and the structure were ascertained byFT-IR,1H NMR and13C NMR.(2)The difference of thermal performance and self-assembling behavior betweenlinear and cyclic polymers were investigated.(A)The results determined by DSC measurement showed that thecyclic-PBHMEm-b-PAAnhas a higher Tgcompared with that of the linear precursor.(B)Photoisomerization behavior of linear-and cyclic-PBHMEm-b-PAAnwasinvestigated in THF and the results showed that the cyclic polymer displayed relatively fastphotoisomerization rate. The self-assembly behavior of amphiphilic block copolymers inH2O/THF solutions as well as their responses to pH and light were investigated. Theobtained self-assembly aggregates and their change at different stimulus-responsecondition were observed and characterized by TEM and DLS. Both linear-and cyclic-copolymers formed large compound micelles in H2O/THF solutions, but the aggregatesobtained from cyclic polymers showed more sensitive response to light and pH, possiblydue to more evacuated aggregates for endless cyclic polymer compared with tighter onescaused by chain entanglement for linear polymer. The study can make up for gaps in theresearch field of cyclic polymers and provide theoretical basis in the application of drugrelease based on the self-assembling of cyclic amphiphilic polymers. |
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