Polyimide-supported Cu/2,2,6,6-tetramethyl-1-piperidine-N-oxyl catalytic systems: Aromatic donor-acceptor interaction-directed cooperative catalysis

Non-covalent immobilization of multifunctional catalysts onto polymer supports is a promising technique to build highly efficient heterogeneous cooperative catalysts. Here, we present a strategy to build polyimide-supported Cu/2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) catalytic systems based on hydrophobic interactions and aromatic donor-acceptor interactions. Pyrene-containing catalytic species and naphthalene diimide (NDI)-based polyimides were chosen for the preparation of nanoparticle catalysts using the nanoprecipitation technique. The cooperative behaviors of catalytic components were evaluated by the catalytic activities of aerobic oxidation of benzyl alcohol (BnOH) in water. We studied the influence of effective constituent ratio of polymers, chain length of monomer, and the incorporation of a second monomer on catalytic activities. The aggregate structures were investigated by X-ray powder diffraction (XRD) patterns and small angle X-ray scattering (SAXS), and speculated to be random distributions of aromatic stacking clusters within nanoparticle catalysts. This strategy will find applications in the construction of other multifunctional heterogeneous catalysts.