Preparation of Poly(methylacrylic acid) Monolayer-protected Gold Nanoparticles and Its pH Responsive Catalysis

The pH stimuli-sensitive polymer,poly(methylacrylic acid)(PMAA),was firstly obtained by reversible addition-fragmentation transfer(RAFT) polymerization of tert-butylmethacrylate(PtBMA) and then hydrolysis.The PMAA monolayer-protected gold nanoparticles(PMAA-GNPs) was prepared via the strong binding between the thiol groups on the polymer chain-ends and gold.The dispersion and aggregation of PMAA-GNPs could be tuned by controlling the pH values of the solution,which was investigated by UV-Vis spectra and TEM.It was found that the catalytic activity was responsive to pH when it is applied in the catalytic reduction of the 4-nitrophenol by NaBH4.The responsive mechanism could be interpreted as: the hydrophobic PMAA collapsed onto the surface of the GNPs in the acid solution,which hindered the contaction between reactant and GNPs,and reduced the catalytic activity.On the contrary,in the alkaline system,polymer chains repulsion due to electrostatic effect can improve the catalytic activity.