Effect of the synthetic method and support porosity on the structure and performance of silica-supported CuBr/pyridylmethanimine atom transfer radical polymerization catalysts. II. Polymerization of methyl methacrylate

A systematic study of the effect of the synthesis method and catalyst structure on the atom transfer radical polymerization (ATRP) performance of copper(l) bromide/pyridylmethanimine complexes supported on silica is described. 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 used for ATRP of methyl methacrylate. The catalysts allow for moderate to poor control of the polymerization, with polydispersity indices (PDIs) ranging from 1.46 to greater than 2. The materials made with the preassembled-complex (M4) and one-pot (M3) approaches are generally more effective than those prepared with a grafting method (M1 and M2) on porous silica, whereas all the methods provide similarly performing catalysts on the nonporous support. Nonporous Cab-O-Sil EH5 is the most effective support because of its small particle size, lack of porosity, and relative compatibility in the reaction media. All the catalysts leach copper into solutions in small amounts. In addition, the catalysts can be effectively recycled, with improved controlled character in recycle runs (PD1 similar to 1.2). Control experiments have shown that this improved performance of the used catalysts is likely due to the presence of a soluble Cu(II) complex in the materials that effectively deactivates the growing polymer chain, leading to narrow PDIs and controlled molecular weights. (C) 2004 Wiley Periodicals, Inc.