The kinetics of copper electrodeposition from an acidified cupric sulfate electrolyte containing SPS-PEG-Cl were examined. Voltammetric and chronoamperometric experiments reveal a competition between poly(ethylene glycol) (PEG) and Na-2[SO3(CH2)(3)S](2) (SPS) for surface sites. PEG interacts synergistically with Cl- and Cu+ to form a passivating film that inhibits the metal deposition rate by two orders of magnitude. Subsequent adsorption of short chain disulfide or thiol molecules with a sulfonate-end group(s) leads to the disruption and/or displacement of the passivating surface complex and acceleration of the metal deposition rate. The effect of submonolayer quantities of catalytic SPS is sustained even after extensive metal deposition, indicating that the catalyst largely remains segregated on the growth surface. Multicycle voltammetry reveals a significant potential dependence for SPS adsorption as well as its subsequent deactivation. Catalyst deactivation, or consumption, was examined by monitoring the quenching of the metal deposition rate occurring on SPS-derivatized electrodes in a SPS-free electrolyte. Catalyst consumption is a higher order process in terms of its coverage dependence and a maximum deactivation rate is observed near an overpotential of -0.1 V. Derivatization experiments are shown to be particularly effective in revealing the influence of molecular functionality in additive electroplating. Specifically, the charged sulfonate end group is shown to be central to effective catalysis. (C) 2004 The Electrochemical Society.