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

Liquid–liquid\nbiphasic reactions are widely used in academic\nresearch and industrial production; however, they have always suffered\nfrom low reactivity. In this work, a variety of linear polymeric catalysts\nwere prepared by reversible addition–fragmentation chain transfer\npolymerization and postoxidation steps. The amphiphilicity of polymeric\ncatalysts was imparted by varying the addition ratios of hydrophilic\n1,1,3,3-tetramethyl-2-(4-vinylbenzyl) guanidine, hydrophobic styrene,\nand catalyst precursor 2,2,6,6-tetramethyl-4-piperidyl methacrylate,\nthus forming stable Pickering emulsions. Such Pickering emulsion systems\nwith an abundant interfacial area and a unique interfacial environment\ncan promote the selective oxidation reaction. As exemplified by 2,2,6,6-tetramethylpiperidinooxy-mediated\noxidation of cinnamyl alcohol, the selectivity of cinnamaldehyde in\nPickering emulsions was 97.2% with a turnover frequency of 5.0 mol·mol<sup>–1</sup>·min<sup>–1</sup>, which is higher than\nreported results. The carbon dioxide responsiveness of the guanidine\ngroup on the polymers allowed for fast demulsification after the reaction,\nand the recycled polymer maintained high activity after 10 runs. This\npolymer-stabilized Pickering emulsion provides a valuable pathway\nfor efficient green catalytic oxidation reactions.