Pickering Emulsions Stabilized by Linear Amphiphilic Polymers for Enhancing the Selective Oxidation of Cinnamyl Alcohol

Liquid–liquid biphasic reactions are widely used in academic research and industrial production; however, they have always suffered from low reactivity. In this work, a variety of linear polymeric catalysts were prepared by reversible addition–fragmentation chain transfer polymerization and postoxidation steps. The amphiphilicity of polymeric catalysts was imparted by varying the addition ratios of hydrophilic 1,1,3,3-tetramethyl-2-(4-vinylbenzyl) guanidine, hydrophobic styrene, and catalyst precursor 2,2,6,6-tetramethyl-4-piperidyl methacrylate, thus forming stable Pickering emulsions. Such Pickering emulsion systems with an abundant interfacial area and a unique interfacial environment can promote the selective oxidation reaction. As exemplified by 2,2,6,6-tetramethylpiperidinooxy-mediated oxidation of cinnamyl alcohol, the selectivity of cinnamaldehyde in Pickering emulsions was 97.2% with a turnover frequency of 5.0 mol·mol–1·min–1, which is higher than reported results. The carbon dioxide responsiveness of the guanidine group on the polymers allowed for fast demulsification after the reaction, and the recycled polymer maintained high activity after 10 runs. This polymer-stabilized Pickering emulsion provides a valuable pathway for efficient green catalytic oxidation reactions.