Effect of the synthetic method and support porosity on the structure and performance of silica-supported CuBr/pyridylmethanimine atom transfer radical polymerization catalysts. I. Catalyst preparation and characterization

Silica-supported CuBr/pyridylmethanimine (PMI) complexes that facilitate the atom transfer radical polymerization of methyl methacrylate have been prepared and characterized. Four different synthetic routes, including multistep-grafting (M1), two-step-grafting (M2), one-pot M3), and preassembled-complex (M4) methods, have been evaluated on three different silica supports (mesoporous SBA15 with 48- and 100-Angstrom pores and nonporous Cab-O-Sil EH5). The resulting solids have been characterized by a battery of techniques, including thermogravimetric analysis/differential scanning calorimetry, FT-Raman spectroscopy, C-13 and Si-29 magic-angle-spinning and cross-polarity/magic-angle-spinning spectroscopy, low-temperature nitrogen physisorption, and elemental analysis. The combination of elemental analysis and spectroscopic results has indicated that a variety of different surface species likely exist for most catalysts, including copper species that are both monocoordinated and biscoordinated by PMI ligands, and PMI-free copper bromide species interacting with the silica surface. M4 appears to give a material that has the smallest amount of the uncomplexed ligand (by FT-Raman spectroscopy) and is, therefore, the most homogeneous. After M4, the metallation efficiency decreases in the order M2 greater than or equal to M3 > M1, with M1 giving a material with a highly heterogeneous surface composition. The ligand loading on all the catalysts has been determined to be approximately 1 mmol/g of SiO2, with Cab-O-Sil-supported materials giving much higher ligand densities because of its lower surface area. (C) 2004 Wiley Periodicals, Inc.