CO2-Responsive Polymer Supported Au Used As Easily Reusable Catalyst in Aqueous Media

Gold catalysts have an outstanding catalytic activity when well dispersed in its nanoparticle form (<10nm). In this work, we developed a series of CO₂-responsive star polymer-supported Au as easily-recyclable catalysts in water by simply bubbling CO₂ and N₂. The polymers consisted of a hyperbranched polyethylene(HBPE) core and multiple  poly(2-(dimethylamino)ethyl methacrylate-2-(Diethylamino)ethyl methacrylate) (PDMAEMA-DEAEMA) arms, and were synthesized through a sequential Pd-catalyzed chain walking copolymerization of ethylene and 2-(2-bromoisobutyryloxy)ethyl acrylate, followed by atom-transfer radical polymerization with DMAEMA and DEAEMA. The samples had a molecular weight between 12-40kg/mol with f_{DMAEMA/DEAEMA} making up 41-74 wt%, and could be easily dispersed in water to form micelles of several hundred nanometers. The catalysts were used for the reduction of 4-nitrophenol in water, and were recycled by purging CO₂/N₂. Catalysts with f_{DMAEMA/DEAEMA} making up 45-65wt% performed well, however higher values may have prevented reactant contact with the Au catalyst. The catalysts can be reused several times (up to 15 times) with a concentration of approximately 15ppm and with very little catalysis activity loss. These catalysts demonstrated higher catalytic activity than previously reported supported Au catalysts and good CO₂ switchability.