In the presence of excess NaOH, reaction of Cu(OAc)(2)center dot H2O with equimolar ammonium calix[4]arene [H4L]I-4 (1, H4L = [5,11,17,23-tetrakis(trimethylammonium)-25,26,27,28-tetrahydroxycalix[4]arene]) resulted in the formation of a mononuclear cationic Cu(II) complex [Cu(II)L(H2O)]I-2 (2) in 43% yield. Complex 2 was characterized by elemental analysis, infrared (IR), and single crystal X-ray diffraction. The Cu(II) atom in 2 is coordinated by four oxygen atoms of one L-4-ligand and one O atom from one water molecule, forming a square pyramidal geometry. Complex 2 exhibited high catalytic activity in the oxidative polymerization of 2,6-dimethylphenol using O-2 as oxidizing agent in water under mild conditions. The selective polymerization produced poly(2,6-dimethyl-1,4-phenylene oxide) in high yields with almost no diphenoquinone. The influence of the polymerization temperature, the time interval, the molar ratio of 2,6-dimethylphenol/2, the concentrations of sodium hydroxide, and sodium n-dodecyl sulfate were examined. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 4864-4870, 2012