Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques These polymers were synthesized with a CuBr/N,N,N',N ",N "-pentamethyldiethylenetriamine catalyst system and had predictable molecular weights based on the degree of polymerization, as calculated from the initial ratio of monomer to initiator, The final polydispersities were low (1.10 < M-w/M-n < 1.3) for all the homopolymers and block copolymers. Polymers of various chain architectures were prepared, ranging from linear AB diblocks to three-armed stars composed of AB diblocks on each arm. The key to controlled synthesis with this catalyst system was the choice of the solvent, temperature, and concentrations of catalyst and deactivator.