Block copolymer micelles used for drug delivery are normally formed and processed in aqueous solutions. A major challenge in this area is how to increase the concentration of hydrophobic drugs in the nanoparticle core. Other issues are the lengthy dialysis procedure and the inefficient freeze dry procedure. We address these issues by processing the polymeric nanoparticles in highly compressible non-aqueous solvents, such as subcritical and supercritical polar fluids. Toward this end, one needs phase equilibrium data, such as cloud-point and micellization pressures as a function of temperature. These data will be presented for model diblocks, such as polyethylene-block-polycaprolactone, in near critical fluids.