Synthesis of Novel Temperature- and pH-Sensitive ABA Triblock Copolymers P(DEAEMA-co-MEO(2)MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO(2)MA-co-OEGMA): Micellization, Sol–Gel Transitions, and Sustained BSA Release

Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO(2)MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO(2)MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer radical polymerization (ATRP). The composition and structure of the copolymer were characterized by (1)H NMR and gel permeation chromatography (GPC). The temperature- and pH-sensitivity, micellization, and the sol–gel transitions of the triblock copolymers in aqueous solutions were studied using transmittance measurements, surface tension, viscosity, fluorescence probe technique, dynamic light scattering (DLS), zeta-potential measurements, and transmission electron microscopy (TEM). The lower critical solution temperature (LCST) of the triblock copolymer, which contains a small amount of a weak base group, (N,N-diethylamino) ethyl methacrylate (DEAEMA), can be tuned precisely and reversibly by changing the solution pH. When the copolymer concentration was sufficiently high, increasing temperature resulted in the free-flowing solution transformation into a micellar gel. The sol-to-gel transition temperature (T(sol–gel)) in aqueous solution will continue to decrease as solution concentration increases.