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Synthesis And Properties Of Cyclic And Linear Block Copolymer Based On N-vinylcaprolactam

Posted on:2018-03-27Degree:MasterType:Thesis
Country:ChinaCandidate:D YouFull Text:PDF
GTID:2321330533965278Subject:Polymer Chemistry and Physics
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Cyclic polymers are promising for many applications,including biomedicines,nanotechnology and material modification due to their closed topology and unique properties compared to their linear counterparts.Currently,the most popular method of synthesizing cyclic polymers by ring-closure techniques is cyclization of ?,?-telechelic linear polymer by the Cu-catalyzed azide/alkyne cyclo addition(CuAAC)reaction.However,in the case of the CuAAC coupling reaction very high levels of copper are required to achieve fast coupling rates,which may cause the contamination of the resultant cyclic polymers and are limited in biomedical application.Poly(N-vinyl caprolactam)(PNVCL)is a thermoresponsive polymer with good biocompatibility and show a lower critical temperature(LCST)in the physiological range.It is promising for biomedical applications.But to the best our knowledge,NVCL-based cyclic block copolymers and biodegradable multi-responsive block copolymers have not been reported.In this thesis,cyclic poly(DL-lactide)-b-poly(N-vinylcaprolactam)(c-PDLLA-bPNVCL)block copolymer was synthesized by reversible addition-fragmentation chain transfer(RAFT)polymerization to be cyclized in one-pot using copper-free thiol-Michael addition reaction.The copolymer was characterized by 1HNMR,IR and gel permeation chromatography-multi-angle laser light scattering(GPC-MALLS).The thermoresponsive and aqueous self-assembly properties of c-PDLLA-bPNVCL and its linear precursor were investigated and compared by UV-vis spectrometer,fluorescent probe technology,sub-micron laser particle size analyzer and transmission electron microscopy.The result showed that c-PDLLA-b-PNVCL possesses higher lower critical solution temperature(LCST)and higher critical micelle concentration in comparison with its linear analogue.c-PDLLA-b-PNVCL can self-assemble to form vesicles while its linear precursor form spherical micelles in aqueous solution.Poly(N-vinylcaprolactam)-b-poly(L-lysine)(PNVCL-b-PLL)block copolymers were synthesized by a combination of RAFT polymerization and ring-opening polymerization.The results of investigation on properties showed that when the pH?10,the LCST of PNVCL-b-PLL decreased and the size increased.The copolymers display temperature and pH responsive properties.Poly(N-vinylcaprolactam)-b-poly(L-lysine hydrochloride)(PNVCL-b-PLKC)and adenosine-5?-triphosphate(ATP)are employed as building blocks to fabricate a polymeric “supra-amphiphile” based on electrostatic interactions.The polymeric “supra-amphiphile” can self-assemble to form spherical aggregates in water.The spherical aggregates would undergo disassembly upon addition of phosphatase.The supra-amphiphile disassembles in response to enzymatic stimulus.Folate-capped polyethylene glycol-b-poly(N-vinylcaprolactam)-b-poly(Lglutamic acid)(FA-PEG-b-PNVCL-b-PLGA)triblock copolymer was prepared by a combination of ring-opening polymerization,RAFT polymerization and thiol-Michael addition reaction.The results of investigation on properties showed that when the pH?6,the LCST of the triblock copolymer decreased and the size increased.The copolymers display temperature and pH responsive properties.
Keywords/Search Tags:poly(N-vinylcaprolactam), poly(DL-lactide), cyclic block copolymer, poly(L-lysine), polyethylene glycol, poly(L-glutamic acid), triblock copolymer, reversible addition-fragmentation chain transfer(RAFT) polymerization, ring-open polymertion(ROP)
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