Stimuli-responsive polymers for regulated catalytic materials: effect of polymer functionality on the regulation mechanism
There has been an increasing interest in tailored catalysts with stimuli-responsive polymers, to improve the performance of the catalyst. Catalyst performance can be improved through the use of stimulus responsive polymers, as they can expose or hide the metal site depending on the environmental changes, such as temperature, light or pH.
Temperature responsive polymer brushes will be coated on silicon surfaces containing metal nanoparticles and the effect of temperature, and hence brush conformation, on the chemisorption of a probe molecule will be studied. The catalytic activity can be switched on and off by adjusting the temperature below or above lower critical solution temperature (LCST) and as a result, diffusion of the probe molecule into the metal site can be controlled. As long as the polymer brushes are solvated, the reaction proceeds because the active sites are available for adsorption. The isothermal chemisorption of CO will be studied as a function of temperature using in-situ attenuated total reflectance (ATR) infrared spectroscopy in aqueous environments. The surface of the catalyst will be functionalized with APTES (3-aminopropyltriethxysilane), a coupling agent, followed by the controlled radical polymerization. Activators continuously regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) will be used as it is an environmentally friendly and oxygen sensitive controlled polymerization. Another parameter that can be measured is the thickness of the brushes, for that ellipsometry can be used. Also, thermogravimetric analysis (TGA) is another way to study the polymer brushes which the molecular weight is studied with the increase of the temperature.
This project is focused on studying the effect of the responsive polymer functionality on catalyst performance. Temperature responsive polymers with distinct LCST behavior will be synthesized. Poly(N-isoproylacrylamide) (PNIPAM) has a solution LCST of 32 °C, while poly(di(ethyleneglycol) methyl ether methacrylate) (PMEO2MA) has a solution LCST of 28 °C. Optimization of brush growth kinetics will be vital to regulating catalyst performance.
Maria E. Dasilva