The Synthesis Of Stimuli-responsive Copolymers And Study Of Their Micellization Behaviors

Block copolymers can self-assemble into core-shell structure in the selective solvents,and the insoluble segment is core while the soluble segment is the shell.By introducing the environmental responsive polymer block into the polymer micelle,the micelle will become stimuli-responsive and more suitable for the application of controlled release drug and catalyst carrier,etc.Since the nano hollow sphere has bigger interior space than the conventional micelle,the study on the nano hollow draws much attention in recent years.In this paper,two different kinds of block copolymers were synthesized via atom transfer radical polymerization(ATRP),and then different polymeric micelles were prepared in the selective solvent.The complex micelle was prepared by the non-covalently connecting of micelles,and the strcuture of complex micelles were fixed by cross-linking agent,and then the hollow sphere was prepared by wiping off the core of complex micelle.The main contents are as follows:1.Two different kinds of block copolymers,poly(t-butyl acry late)-b-poly(N-isopropylacry lam ide)(PtBA-b-PNI PAM)and poly(t-butyl acrylate)-b-poly(2-(dimethylamino)ethyl methacrylate)(PtBA-b-PDMAEMA),were synthesized by atom transfer radical polymerization(ATRP).And then PtBA-b-PDMAEMA was hydrolyzed to PAA-b-PDMAEMA copolymers in an acidic medium.By using 1H NMR spectroscopy and gel permeation chromatography(GPC)the structure of the block copolymers were characterized.The ressults showed that actual compositions of the polymers were PtBA32-b-PNIPAM6,and PtBA78-b-PDMAEMA71.And the degree of hydrolysis of PtBA-b-PDMAEMA was 98%which was measured by 1H NMR.2.The effect of external stimuli on the hydrodynamic diameter of different copolymers was investigated by Malvern nano particle sizer.The transmittance of PAA-b-PDMAEMA solution was measured by UV-visible spectrophotometer,the results indicated that the lower critical solution temperature(LCST)of PAA-b-PDMAEMA was approximately 40?.The isoelectric point of PAA-b-PDMAEMA measured by Zetasizer NanoZS Instrument was 4.1.Therefore,the best conditions for preparing the complex micelles was determined to be the temperature lower than 40? and pH value 4.1.3.The complex micelles were prepared by the complexation of hydrogen bond between PAA chain and PNIPAM chain under the optimal conditions determined before.The hydrogen bonding interaction between PAA chain and PNIPAM chain was characterized by Fourier transform infrared spectroscopy(FTIR).And the hydrodynamic diameter of complex micelles was studied by Nano ZS instrument,the results showed that the complex micelles had environmental stimuli-responsive behavior.The morphology of complex micelles were observed by transmission electron microscope(TEM)and the TEM images showed distinct core-shell structure.4.The shell of complex micelles was fixed by reacting with a bifunctional cross-linker,1,2-bis-(2-iodoethoxy)ethane(BIEE).The results of hydrodynamic diameter showed that the cross-link between micelles wasn't occur.The polymer nano hollow spheres were prepared by adding N,N-Dimethylmethanamide(DMF)into cross-linked micelles,and then dialyzing in water to remove the core.The TEM images show the obvious hollow structure.There are two common methods,"template" and "self-assembly method",to prepare hollow sphere.And this paper combine the two common methods' advantages,regard The block copolymer which was narrow molecular weight distributed was regarded as the coreand the complex micelles were prepared through "non-covalently connected”method.The micelles had thermo/pH responsive behavior in solvent.Therefore,it can be predicted that the hollow spheres may have the possibility of applying in the field of drug release and nano carrier.