Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well-defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1-cyano-1-methylethyl diethyldithiocarbamate, typically used as chain-transfer agent (CTA) in reversible addition-fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst Cu-I/2,2 '-bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain-end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) with n-butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 376-381