The polymer additives are key factor materials in the Cu electroplating process, essential for controlled acceleration and inhibition of Cu deposition. In this study, the degradation behavior of a polymer additive poly(ethylene glycol) (PEG) during the Cu electroplating was investigated by MALDI-TOF MS technique. The PEG was completely degraded after 4 h at a constant electric current density of 13 mA/cm(2), whereas it showed no degradation without an electric field even at a very low pH (pH < 1). The pathways and energetics of PEG degradation by electrolysis in aqueous chloride medium was investigated using density functional theory calculations at the same time. It demonstrated how facile the decomposition of PEG internal radical is, which is generated via the hydrogen abstraction from PEG by hydroxyl radical formed at the anode in aqueous chloride medium under an electric field. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2083-2089, 2010