TEMPO-Functionalized Aromatic Polymer as a Highly Active, pH-Responsive Polymeric Interfacial Catalyst for Alcohol Oxidation

We report in this paper the design and synthesis of a pH-responsive polymeric interfacial catalyst (PIC) via one-step grafting of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) onto a polyaryletherketone having pendant benzimidazole groups (SCBI-PAEK-6F). The TEMPO-functionalized polymer has been systematically characterized with 1H nuclear magnetic resonance, Fourier-transform infrared spectroscopy, elemental analysis, contact angle, and transmission electron microscopy. Moreover, this well-designed polymer has been applied in the oxidation of alcohols under Montanari conditions. It is found that the functionalized polymer can aggregate at the water–oil interface and act as an efficient stabilizer to facilitate the formation of a stable Pickering emulsion, which shows outstanding catalytic activity for alcohol oxidation through the microreactor mechanism. Moreover, the PIC is featured with desirable high pH responsiveness due to the valuable benzimidazole groups. De-emulsification of the Pickering emulsion reaction system can be conveniently triggered by simply tuning the system pH value to 3, thus facilitating the facile recovery of the PIC. In addition, the sustainable catalyst can be reused for subsequent cycles of alcohol oxidation without appreciable loss in catalytic activity or selectivity.