A reversible catalyst immobilization system via self-assembly of hydrogen bonding between thymine anchored on silica gel support and 2,6-diaminopyridine functionalized with a catalyst (copper bromide-N,N,N',N'-tetraethyldiethylenetriamine (TEDETA) complex) was developed for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). At elevated temperatures, the hydrogen bonding disassociated and released the catalyst as free small molecules for catalysis, which effectively mediated a living polymerization of MMA, producing PMMA with controlled molecular weight and narrow molecular weight distribution (<1.3). At room temperature, the catalyst assembled on the silica gel support by hydrogen bonding, and thus could be recovered and reused for a second run of ATRP. The recovered catalyst still mediated a living polymerization of MMA with reduced activity (54-64%), but had much improved control of the polymerization. The resulting PMMA had molecular weights very close to theoretical vales. (C) 2003 Wiley Periodicals, Inc.