Interaction of poloxamer block copolymers with cosolvents and surfactants

The interactions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Poloxamers) with cosolvents and surfactants are addressed here. Ternary isothermal (25°C) systems of Pluronic F127 (Poloxamer 407) in the presence of water and polar water-miscible solvents (glycerol, propylene glycol or ethanol), a partially water-miscible solvent (glycerol triacetate), a non-ionic surfactant (tetraethylene glycol monooctyl ether, C₈(EO)₄), an anionic surfactant (sodium dodecyl sulfate, SDS), and a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) have been investigated by phase behavior studies and small angle x-ray scattering (SAXS). A number of regions with different lyotropic liquid crystalline structure have been identified in each ternary Poloxamer-water-cosolvent/surfactant system. For a given Poloxamer, the composition range over which a given self-assembled structure is stable varies according to the cosolvent/surfactant type (and properties). The effects that the different cosolvents or surfactants exhibit on the Poloxamer phase behavior are interpreted in terms of the preference of the cosolvent/surfactant molecules to locate in different domains of the PEO-PPO-PEO block copolymer self-assembly. Organic solvents, depending on their relative polarities, locate preferably in the PEO-rich or the PPO-rich domains of the microstructure. Some solvents (e.g. ethanol and glycerol triacetate) may show amphiphilic behavior and act as cosurfactants by preferably locating at the interface between the PEO-rich and the PPO-rich domains. The location of the solvents in the block copolymer assemblies is established by an analysis of the trends in the structure lattice spacing (obtained from SAXS) and the interfacial area per block copolymer molecule.