Cobalt-mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)(2), lauroyl peroxide, citric acid trisodium salt, and VPv at 30 degrees C results in controlled polymerizations that yield homopolymers with M-n = 2.5-27 kg/mol with M-w/M-n = 1.20-1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (M-n = 4-16 kg/mol; M-w/M-n = 1.34-1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small-angle X-ray scattering analyses. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 242-249, 2011