Graphene oxide grafted with polyoxazoline as thermoresponsive support for facile catalyst recycling by reversible thermal switching between dispersion and sedimentation

Grafting polyoxazolines exhibiting a cloud point temperature (TCP) in the reaction medium onto graphene oxide (TRGO) prepared by thermal reduction of graphite oxide affords thermoresponsive catalyst supports and enables catalyst recycling by thermal switching between dispersion and sedimentation. In a facile grafting-to process the functional groups of the TRGO react with the cationic oxazolinium end groups, obtained by living cationic ring-opening polymerization of 2-ethyl-2-oxazoline, and covalently attach PEtOx having an average molar mass >10 000 g∙mol−1 and a TCP of 65 °C in polar solvents like water. Below the TCP at 25–30 °C stable dispersions of palladium supported on TRGO-g-PEtOx (Pd@TRGO-g-PEtOx) are obtained. As compared to the Pd@TRGO benchmark in the absence of PEtOx, Pd@TRGO-g-PEtOx exhibits higher catalyst activity in Suzuki-Miyaura-coupling reactions. Opposite to Pd@TRGO, Pd@TRGO-g-PEtOx readily agglomerates above TCP at 65 °C and enables easy and complete recovery of the catalyst by filtration and repeated catalyst reuse without encountering neither filtration problems nor drastic losses of catalyst activity. Grafting of thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) onto graphene oxide (TRGO) pepared by thermal reduction of graphite oxide enables switching between TRGO dispersion and sedimentation behavior as a function of temperature. Palladium catalysts supported on TRGO-g-PEtOx (Pd@TRGO-g-PEtOx) are highly active in Suzuki-Miyaura-coupling reactions below its TCP and are recycled by thermal switching from dispersion to sedimentation above its TCP. [Display omitted] •Grafting of thermoresponsive poly(2-ethyl-2-oxazoline) onto graphene oxide.•Switching between TRGO dispersion and sedimentation behavior.•Catalyst support for organic coupling reaction.•Facile catalyst recycling by controlling dispersion stability.