Transition-metal-mediated living radical polymerizations (atom transfer radical polymerization, ATRP) have many potential applications, but the high concentration of residual catalyst colors their products. Supporting catalyst on insoluble solids has been used to reduce the content of residual catalyst and to reuse the catalyst, but the ability of the supported catalyst to mediate a polymerization is substantially reduced due to heterogeneity. Here we report a soluble but recoverable catalyst support for ATRP. Polg(ethylene)-block-poly(ethylene glycol) (PE-PEG) was soluble in toluene above 70 degreesC but insoluble at room temperature. CuBr supported on PE-PEG via tetraethyldiethylenetriamine thus mediated Living polymerizations of methyl methacrylate, 2-(dimethylamino)ethyl methacrylate, and styrene as homogeneous catalyst at 80 or 100 degreesC, producing polymers with well-controlled molecular weight and very low polydispersity. The catalyst recycled at ambient temperature retained high activity and still mediated living polymerizations as well as the fresh catalyst. Subsequent block copolymerization confirmed its living nature.