Preparation And Performance Of Stimuli-responsive Miktoarm Star Cmpolymers Via RAFT Polymerization

Miktoarm star polymers are star-shaped polymers where any numbers of various types of polymer arms emanate from a core.Miktoarm star polymers have attracted considerable research interest because of their branched architectures,complicated microstructure and unique properties which can be tailored by varying their linear polymer arms.Thus endows its unique physical and chemical properties,and flexible adjustable functional group that greatly expanded its performance.In addition,star polymers can be seen as well-defined nanoparticles for potential applications in biological nanomedicine,catalyst and in environmental protection etc.However,the synthesis of well-defined star polymers is varied,the focus of which is living free radical polymerization.In this article,the synthesis of well-defined,narrow polydispersity star polymers via Reversible addition fragmentation chain transfer(RAFT)polymerization.And 'arm-first' method was used.The chain transfer agent 3-(benzylsulfanylthiocarbonylsulfanyl)-propionic acid(BSPA)was preparaed.The good biocompatibility and water-soluble oligo(ethylene glycol)methyl ether acrylate(OEGMA)and di(ethylene glycol)ethyl ether acrylate(DEGEEA)were choosed in this thesis.P(OEGMA-co-DEGEEA),which is temperature responsive were prepared in the presence of 2,2'-azobis(isobutyronitrile)(AIBN)and BSPA.P(2-(Dimethylamino)ethyl acrylate)(PDMAEA)were prepare via RAFT polymerization,and BSPA as chain transfer agent,AIBN as initiator.Miktoarm star polymers(MAS)were preparaed by 'arm-first' method using N,N'-double acryloyl cystamine(BAC)as crosslinking agent,AIBN as initiator,with a range of polymers with different molar ratio of OEGMA or DEGEEA.The chemical structure and composition were characterized and analyzed by 1H NMR spectroscopy(1H NMR)and Fourier Transform Infra Red Spectrophotometer(FTIR).The molecular weight and molecular weight distribution of the products were characterized and analyzed by gel permeation chromatograph(GPC).With the help of Transmission Electron Microscopy(TEM),its morphology is studied.Lower critical solution temperature(LCST)of the aqueous solution of miktoarm star polymers was investigated by Dynamic Light Scattering(DLS)and UV-Vis spectrophotometry(UV-Vis).And the effects of the solution pH,salt concentration,types of salt on the LCST were studied in detail.The results exhibit that:(1)the RAFT chain transfer agent,linear polymers and the miktoarm star polymers were successfully obtained.The relative molecular weight was consistent with the theoretical molecular weight,and polydispersity was narrow.And the RAFT polymerization can be used for the preparation of the miktoarm star polymers.(2)The component content of the segments has effect on the LCST of linear copolymer POD,and the LCST increases with increasing OEGMA content.(3)The effects of the pH value of solution,salt concentration and types of salt on the LCST behavior for the miktoarm star polymers in the aqueous solution were investigated.When the temperature is under LCST,the role of pH is not very obvious because the polymers present a good solubility in water.The effect of the solubility appeared a key factor due to the content of POD is larger.While once the temperature above LCST,the phase transition behavior of POD chain segment changed.And the protonation/deprotonation of amino groups of PDMAEA appeared a key role,which is relation with pH.The ionic strength of solution increases after the salt added,which weakened the interactions between the ether linkage and water molecules.That decreases the LCST.And the effect of reinforcement was increase with the increase of salt concentration.The LCST of the solution were also influenced by types of salt,especially the ionic radius and and ionic valence of salts.The results show that the greater the ionic radius,the less influence on the LCST due to the force between the ionic and the water molecules was weaken.In addition LCST reduced significantly when the ionic valence increased.The LCST of the solution increases when PDMAEA was incorporation.And the LCST increases with the increase of PDMAEA.