Controlled radical polymerization of 4-vinylpyridine (4VP) was achieved in a 50 vol % 1-methyl-2-pyrrolidone/water solvent mixture using a 2,2'-azobis(2,4-dimethylpentanitrile) initiator and a CUCl2/2,2'-bipyridine catalyst-ligand complex, for an initial monomer concentration of [M](0) = 2.32-3.24 M and a temperature range of 70-80 degrees C. Radical polymerization control was achieved at catalyst to initiator molar ratios in the range of 1.3:1 to 1.6:1. First-order kinetics of the rate of polymerization (with respect to the monomer), linear increase of the number-average degree of polymerization with monomer conversion, and a polydispersity index in the range of 1.29-1.35 were indicative of controlled radical polymerization. The highest number-average degree of polymerization of 247 (number-average molecular weight = 26,000 g/mol) was achieved at a temperature of 70 degrees C, [M](0) = 3.24 M and a catalyst to initiator molar ratio of 1.6:1. Over the temperature range studied (70-80 degrees C), the initiator efficiency increased from 50 to 64% whereas the apparent polymerization rate constant increased by about 60%. (c) 2007 Wiley Periodicals, Inc.