Evolution in structural polymorphism of pluronic F127 poly(ethylene oxide)-poly(propylene oxide) block copolymer in ternary systems with water and pharmaceutically acceptable organic solvents: From "glycols" to "oils"

The evolution in the self-assembly of an amphiphilic poly(ethylene oxide)-p oly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer in ternary systems with water and organic solvents of varying relative polarit y is examined. The phase behavior and microstructure of two ternary systems consisting of Pluronic F127 (Poloxamer 407), water, and the pharmaceutical ly acceptable solvents propylene carbonate (4-methyl-1,3-dioxolan-2-one) or triacetin (glycerol triacetate) are presented. The microstructure of the l yotropic liquid crystalline phases formed and their characteristic length s cales are determined from small-angle X-ray scattering (SAXS). The trends i n the SAXS lattice spacing and the interfacial area per block copolymer mol ecule help establish the location of the solvents in the microstructure. Th e phase behavior of the two systems studied here is discussed in the contex t of ternary systems of Pluronic F127 with water and polar solvents ("glyco ls", e.g., propylene glycol) or apolar organic solvents ("oils", e.g., xyle ne). Propylene carbonate and triacetin are shown to have intermediate behav ior between that of glycols and oils. The block copolymer structural polymo rphism is modulated by the solvent preference to locate in different domain s of the block copolymer microstructure.