Synthesis And Characterization Of PH And Temperature Dual Stimuli-response Diblock Polymer Brushes

Stimuli-response nanoparticles have been widely applied in many fileds,including controlled drug release,targeted separation and biosensors,due to their smart characteristics that physicochemical properties change significantly with envirmontal stimuli.Moreover,with the continuous development of the polymerization technology,the structure and function of the stimuli-response nanoparticles can be designed and optimized according to actual application requirements.Spherical polymer brushes have always been excellent carriers for proteases,drugs and nanometals owing to their good stability and dispersibility.Hence,designing and synthesizing spherical polymer brushes with stimuli-responsive properties have promising application prospects.In this paper,temperature-sensitive monomer N-isopropylacrylamide(NIPA)and pH-sensitive monomer acrylic acid(AA)were successively grafted onto the surface of nano polystyrene microspheres by surface-initiated photoiniferter mediated polymerization(SI-PIMP).Two core-shell structural polymer brushes PSV@PNIPA-b-PAA and PSV@PAA-b-PNIPA with different block sequences were successfully prepared,and their structure and stimuli responsiveness were explored.It was found that the different order of blocks had a great influence on their structural conformation,which in turn caused differences in their stimuli responsiveness.In addition,the interactions between block polymer brushes and proteins were researched,and it was found that the adsorption of proteins can be controlled by pH and temperature,which suggests the block polymer brushes expected to become a new carrier of protein adsorption and separation.The main work is as follows:Two kinds of core-shell diblock polymer brushes,i.e.,poly(acrylic acid)-b-poly(N-isopropylacrylamide)and poly(N-isopropylacrylamide)-b-poly(acrylic acid)diblock polymer brushes with polystyrene cores(PSV@PAA-b-PNIPA and PSV@PNIPA-b-PAA),were prepared by SI-PIMP.Fourier transform infrared(FTIR)and element analysis(EA)were used to characterize the composition of PNIPA and PAA blocks.Dynamic light scattering(DLS)and transmission electron microscopy(TEM)were used to characterize the sizes of nanoparticles before and after monomers modification.The pH and temperature stimuli-responses of the two polymer brushes were investigated by DLS,and it was found that there was a difference in the responsiveness of the two polymers.PSV@PNIPA-b-PAA nanoparticles exhibited normal and good pH and temperature stimuli responsiveness.Moreover,the LCST of nanoparticles woule be affected by pH and salt concentrations.While PSV@PAA-b-PNIPA exhibited the same good pH stimuli responsiveness,but "abnormal" temperature responsiveness.Under the condition of low salt and high pH,the temperature sensitivity was not obvious.Under the condition of high salt and low pH,they exhibited a two-stage response of "LCST" and "UCST".The interactions between PSV@PNIPA-b-PAA and PSV@PAA-b-PNIPA and bovine serum albumin(BSA)under different pH and temperature conditions were studied respectively by turbidity change and DLS,and it was found that the interaction between PSV@PNIPA-b-PAA and BSA at room temperature is dominated by the PAA block.The particle size of polymer brushes and protein mixed solution under different pH conditions is studied with temperature changes.Although the overall hydrophobicity of nanoparticles increased,the temperature did not cause a large amount of BSA adsorption.On the contrary,the temperature response of the mixed solution became more obvious.The interaction between PSV@PAA-b-PNIPA and BSA at room temperature is also dominated by PAA blocks.However,due to the different nanoparticle structure and the difference in its own temperature response,the temperature increase under different pH conditions is more complicated.