Preparation Of Platinum Nanoparticles/polymer Composite Microsphere And Their Catalytic Properties

Poly(N-isopropylacrylamide) (PNIPAAm) macromonomer with a styrol end group was synthesized by free radical polymerization of NIPAAm and end capping reaction. PNIPAAm macromonomer with clear structure was prepared as seen from the spectra of Fourier transform infrared (FTIR) spectroscopy, ultraviolet spectra (UV) and nuclear magnetic resonance (1H-NMR). The result of gel permeation chromatography (GPC) indicated that the molecular weight of PNIPAAm macromonomer can be controlled between 4.6×103 to 1.25×104 through changing the recipe and the molecular weight distribution was narrow.The PNIPAAm grafted poly(acrylonitrile/styrene) (PNIPAAm-g-PAN/PSt) microsphere with unusual morphology can be prepared based on the dispersion copolymerization of PNIPAAm macromonomer with AN/St monomers in ethanol/water mixed solvents. The spectra of FTIR and NMR illustrated that the structure of PNIPAAm-g-PAN/PSt polymer was clear. The morphology and diameter of the microsphere were characterized by scaning electron microscopy (SEM). It showed that the diameter of the resulting microspheres was from about 800nm to 1.2μm with narrow distribution and microsphere had convex on its surface. The convex was uncleared as the decrease of AN monomer. The diameter of the microspheres decreased when more PNIPAAm macromonomer was added. When the volume ratio of ethanol to water is not less than 7 to 3, the morphology of the microsphere is better with narrow distribution.Platinum nanoparticles were stabilized on the surface of the PNIPAAm-g-PAN/PSt microspheres via the in-situ reduction of Pt4+ by ethanol at 90℃when the coordination interaction took place between the platinum ions and amide group of PNIPAAm. It can be seen that the peaks of N-H and amide (I) showed blue shift, the strength of amide (I) decreased simultaneously. The reduction of Pt4+ was characterized by UV spectra. It can be seen that Pt4+ was reduced to Pt2+ as intermediate firstly, and Pt finally. Transmission electron microscopy (TEM) showed that the average diameter of platinum nanoparticles was 6nm and the size distribution was narrow. The weight percent of platinum nanoparticles stabilized onto the microspheres was about 17% based on thermogravimetric analysis (TGA). The nature of the interaction between the amide and Pt nanoparticles was studied in detail by X-ray photoelectron spectroscopy (XPS).Preliminary results indicated that the as-prepared Pt/PNIPAAm-g-PAN/PSt microsphere can catalyzed the electroless polymerization of aniline. The polymerization rate can be controlled by changing the reaction temperature. The as-prepared Pt/PNIPAAm-g-PAN/PSt microsphere also showed sound activity as catalyst in the hydrogenation of citral.