Hydrophobic domains in thermogelling solutions of polyether-modified poly(acrylic acid)

The temperature-dependent aggregation in aqueous solutions of self-assembling graft copolymers of Pluronic (PEO-PPO-PEO triblock copolymers) and poly(acrylic acid) (Pluronic-PAA) has been studied using fluorescence techniques (steady-state intensity and depolarization and fluorescence lifetimes). Aggregates that form above the critical micellization temperatures (CMT) are micelle-like, with substantially dehydrated PPO core and hydrated PEO-PAA corona, and provide the physical cross-linking required for gelation. Unexpected hydrophobic domains have been observed below the CMT which provide an environment more hydrophobic than the micelles to pyrene and 1,6-diphenyl-1,3,5-hexatriene (DPH) and are related to the grafting density of the PAA onto the Pluronic copolymers.