Two tapered statistical copolymers were prepared by the oxyanionic polymerization of ethylene oxide and propylene oxide and characterized by gel permeation chromatography and C-13 NMR spectroscopy. We denote the copolymers t-E/P38 and t-E/P30, where E = oxyethylene, OCH2CH2, and P = oxypropylene, OCH2CH(CH3), and the number denotes the mole percentage P. In each case the copolymer chain length was ca. 100 oxyalkylene units. The association of the copolymers to form micelles in aqueous solution was checked by dynamic light scattering. The critical micelle temperatures (cmt) of the copolymers at several concentrations were determined by static light scattering and dye solubilization, and values of the apparent standard enthalpy of micellization (Delta(mic)H(app)(0))were obtained. For both copolymers, a low value of Delta(mic)H(app)(0) was found when the copolymer concentration exceeded ca. 150 gdm(-3). (C) 2004 Elsevier Inc. All rights reserved.