Thermo-responsive polymer-based catalytic nanoreactors for controllable catalysis of selective oxidation of alcohols in water

Abstract

Controllable catalytic systems mimicking the controllability of enzymes in nature represent a promising research direction in bionanotechnology. The development of “smart” biomimetic catalysts for controllable catalysis still remains a challenge. Here, we report a kind of thermo-responsive polymer-based catalytic nanoreactor containing a 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) catalyst and investigate its catalytic activities in the selective oxidation of alcohols in aqueous media, as well as the controllable catalytic performance under external temperature stimuli. The catalytic nanoreactor CL-[PDMA₅₇-b-P(MEO₂MA₆₇-co-AMA₁₁)-b-PBMA₁₈]-TEMPO with a thermo-responsive intermediate cross-linking layer was fabricated following the strategies of reversible addition–fragmentation chain transfer (RAFT) polymerization, micelle self-assembly, thiol–ene click addition reaction, and post-polymerization modification. In the catalytic tests, the catalytic nanoreactor accomplished efficient selective oxidation of alcohols to aldehydes with a low catalyst loading. Importantly, the regulation of the catalytic reaction rate was achieved by changing the temperature above and below the lower critical solution temperature (LCST) of the polymer. The “opening” and “closing” of the transport channel of water-soluble reactants such as sodium hypochlorite (NaClO) from the aqueous phase to the hydrophobic core were ascribed to the change in the hydrophilicity and hydrophobicity of the intermediate cross-linking layer, playing a crucial role in reaction rate regulation. This study showcases a thermo-responsive polymer-based catalytic nanoreactor for controllable catalysis, providing a new method for the construction of catalytic materials with adjustable reaction rates.