Micellization of Poly(ethylene glycol)-block-Poly(caprolactone) in Compressible Near Critical Solvents

Micelles of hydrophilic-hydrophobic block copolymers, such as poly(ethylene glycol)-block-poly(caprolactone) (PEG-b-PCL), are useful for delivery of hydrophobic drugs. Such micelles can be formed by liquid solvent displacement or dialysis. A more recent approach is to use supercritical fluids as solvents, but the selection criteria for solvents are not well understood. The compressible solvents studied in this work can induce pressure-tunable micellization of PEG-b-PCL. Their capacity and selectivity, and hence their ability to form micelles, depends on their density, polarity, and hydrogen bonding potential. By mixing two solvent components, such as dimethyl ether (good solvent) and trifluoromethane (selective antisolvent), one can control not only the micellization temperature and pressure, but also the bulk separation pressure (cloud pressure), crystallization temperature, and melting temperature. This can be utilized to develop efficient ways to prepare micellar precursors for drug-loaded nanoparticles.