Synthesis, pH- and temperature-induced micellization and gelation of doubly hydrophilic triblock copolymer of poly(N,N-dimethylamino-2-ethylmethacrylate)-b-poly(ethylene glycol)-b-poly(N,N-dimethylamino-2-ethylmethacrylate) in aqueous solutions

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 (1)H 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.