Aqueous solutions of ABA triblock copolymers, composed of a water-soluble central block and stimuli-responsive outer blocks, can undergo reversible transitions between free-flowing liquids and free-standing hydrogels in response to environmental changes. Such stimuli-responsive micellar hydrogels have received a great deal of interest due to their potential applications in many technologies. Considering that diseased tissues often exhibit unusually acidic pH values, we have designed a series of ABA triblock copolymers with the thermosensitive outer blocks containing weak bases, which would allow drugs loaded into the gels to be released at a greater rate at lower pH values. The thermosensitive ABA triblock copolymers were prepared from a difunctional PEO macroinitiator by atom transfer radical polymerization of methoxydi(ethylene glycol) methacrylate and ethoxydi(ethylene glycol) methacrylate with ~ 5 mol % of either N,N-diethylaminoethyl methacrylate (DEAEMA), N,N-diisopropylaminoethyl methacrylate, or N,N-di(n-butyl)aminoethyl methacrylate. Using rheometry, we measured thermally induced sol-gel transition temperatures (Tsol-gel) of 10 wt % aqueous solutions of these copolymers at various pH values. The Tsol-gel increased with decreasing pH as expected, and the Tsol-gel vs. pH curves of all copolymers exhibited a sigmoidal shape. At a specific pH, the Tsol-gel decreased with increasing hydrophobicity of the tertiary amine. We also studied the effect of different tertiary amines on the release behavior of FITC-dextran from micellar gels of these ABA triblock copolymers in an acidic medium. At 27 °C, the release was significantly faster for the DEAEMA-containing copolymer.

pH dependence of thermally induced sol-gel transitions of aqueous solutions of tertiary amine-containing thermosensitive ABA triblock copolymers

251st National Meeting (2016)

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