The unique combination of the gas like viscosity and liquid like density of supercritical CO2 (scCO2) is exploited to blend poly(D,L-lactic acid) (PDLLA) and poly(ethylene glycol) (PEG) at near ambient temperatures. This novel process lowers the polymer blend viscosity and also permits incorporation of thermally and solvent labile protein based drugs. A series of blends are prepared with agitation in scCO2. Differential scanning calorimetry (DSC) data shows that miscible blends can be produced at moderate temperatures. A surprising region of miscibility is revealed between 8 and 25%w/w PEG. The properties of this miscible region are probed with high pressure parallel plate rheological studies, showing that the viscosity in scCO2 is directly related to the miscibility. Using the particles from gas saturated solutions (PGSS) method, microparticles of these PDLLA/PEG blends are produced using scCO2 and it is determined that the yields obtained are proportional to the miscibility of the polymers. Thus scCO2 provides a unique route to low temperature, solvent free processing that accesses a window of miscibility that has not previously been observed. Finally, DSC analyses of these sprayed microparticles confirm the presence of the same high miscibility region observed in the bulk samples prepared under supercritical conditions.
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