Effect of polymer architecture on micelle formation, ordering, and gelation in aqueous block polymer blends

Poloxamer 407 (P407) is a commercially available ABA triblock polymer that is widely studied for biomedical applications. In aqueous solutions at low temperatures, the solubility of both the poly(propylene oxide) (PPO) midblock (B) and poly(ethylene oxide) (PEO) endblocks (A) is relatively high. With increasing temperature, the PPO midblock dehydrates to form spherical micelles. When a critical volume fraction of micelles is achieved, the micelles order onto a cubic lattice. This ordering corresponds to a many-order-of-magnitude increase in the dynamic moduli. While this transition is promising for applications such as injectable therapeutics, P407 solutions suffer from limited tunability and often poor rheological stability. Substituting P407 with a BAB triblock polymer with the same composition allows for the formation of intermicellar bridges, leading to physical gel formation. We combine rheology with differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) to show differences in the kinetics and thermodynamics of micellization. Blending these two triblock polymers allows for fine-tuning of the gelation temperature, and expands the accessible ordered morphologies, such as close-packed structures that are not observed in the single-polymer solutions.