Preparation And Characterization Of Temperature, PH And Salt Sensitive Composites Gold Nanoparticles Grafted With Polystyrene-B-Poly(N-Isopropylacrylamide)

Poly(styrene-b-N-isopropylacrylamide)(PSt-b-PNIPAM) with a narrow molecular weight distribution is prepared by reversible addition-fragmentation transfer(RAFT) radical polymerization.The dithioester group at the chain end of PSt-b-PNIPAM is converted into thiol terminal group by LiB(C₂H₅)₃H. Gold nanoparticles and the PSt-b-PNIPAM interact via the terminal thiol group(-SH).The size of the gold nanoparticles coated with copolymers can be easily manipulated by adjusting the molar ratio of HAuCl₄/PSt-b-PNIPAM.The products are characterized by FT-IR,¹H NMR spectra and TEM and a core-shell micellar structure with the hydrophobic inner core(PSt) is obtained,in which the gold nanoparticles are grafted in the surface of the PNIPAM shell.The PSt-b-PNIPAM copolymer micelles in aqueous solution presented the lower LCST than the unmodified PNIPAM.The maximum wavelength of the surface plasmon band and the hydrodynamic size of the PSt-b-PNIPAM-Au micelles are sensitive to temperature,pH and salt concentration.A considerable red shift from 524 nm to 534 nm in the plasmon band is observed in 0.9%NaCl aqueous solution but no appreciable change in the pure water when the temperature increases from 25℃to 40℃.With the pH of the solution decreasing,the maximum wavelength of the surface plasmon band appears a red shift.In addition,dynamic light scatting(DLS) reveals that the hydrodynamic sizes of PSt-b-PNIPAM-Au micelles exhibit a small change under alkaline and neutral(pH=7) conditions,but they give a pronounced change in the acidic condition when the temperature increases from 25℃to 40℃.The hydrodynamic diameters of PSt-b-PNIPAM-Au micelles are also affected by Au:PSt-b-PNIPAM ratio,when the ratio increases, the shrinkage of the PSt-b-PNIPAM-Au micelles becomes less prominent as the temperature increases.Furthermore,the UV-vis absorption spectrum clearly shows the red shift of the thermosensitive gold nanoparticles is reversible.