A doubly hydrophilic triblock copolymer of poly(N,N-dimethylamino-2-ethyl methacrylate)-b-Poly(ethylene glycol)-b-poly(N,N-dimethylamino-2-ethylmethacrylate) (PDMAEMA-b-PEG-b-PDMAEMA) with well-defined structure and narrow molecular weight distribution (M-w/M-n = 1.21) was synthesized in aqueous medium via atom transfer radical polymerization (ATRP) of N,N-dimethylarnino-2-ethylmethacrylate (DMAEMA) initiated by the PEG macroinitiator. The macroinitiator and triblock copolymer were characterized with H-1 NMR and gel permeation chromatography (GPC). Fluorescence spectroscopy, dynamic light scattering (DSL), transmittance measurement, and rheological characterization were applied to investigate pH- and ternperature-induced micellization in the dilute solution of 1 mg/mL when pH > 13 and gelation in the concentrated solution of 25 wt % at pH = 14 and temperatures beyond 80 degrees C. The unimer of R-h = 3.7 +/- 0.8 nm coexisted with micelle of R-h = 45.6 +/- 6.5 nm at pH 14. Phase separation occurred in dilute aqueous solution of the triblock copolymer of 1 mg/mL at about 50 degrees C. Large aggregates with R-h = 300-450 nm were formed after phase separation, which became even larger as R-h = 750-1000 nm with increasing temperature. The gelation temperature determined by rheology measurement was about 80 degrees C at pH 14 for the 25 wt % aqueous solution of the triblock copolymer. (c) 2008 Wiley Periodicals, Inc.