Low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with unimodal polydispersity was synthesized by oxidative polymerization of 2,6-dimethylphenol in the presence of Cu-ethylene diamine tetraacetic acid catalyst in water. A series of low-molecular-weight PPO oligomers with Mn ranged from 360 to 3500 were obtained. It was found that the molecular weight and polydispersity were affected by reaction time, reaction temperature, and catalyst concentration. Based on the detector response-elution volume curve and the molecular weight from gel permeation chromatography, a possible molecular weight growth mechanism was proposed. The structure and properties of low-molecular-weight PPO oligomers were characterized by atomic absorption spectroscopy, differential scanning calorimetry, Ubbelohde viscometer, and nuclear magnetic resonance spectroscopy. Compared to the commercial low-molecular-weight PPO, PPO oligomers synthesized in water had a much lower residual copper content. The relationships between Tg and Mn at relatively low-molecular weight are in good agreement with the equation proposed by Fox and Loshack. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013