Stabilized polymer microparticles by precipitation with a compressed fluid antisolvent .1. Poly(fluoro acrylates)

Poly(1,1-dihydroperfluorooctyl acrylate) (poly(FOA)) based stabilizers greatly reduce, and in some cases eliminate, flocculation of amorphous poly(methyl methacrylate) (PMMA) and polystyrene (PS) microparticles formed by precipitation into liquid CO2 at 23 degrees C. The microparticle stabilization mechanism is explained in terms of the stabilizer-CO2 phase behavior, the spray characteristics, and the interfacial activity of the stabilizer. Compared with the homopolymer poly(FOA), the diblock copolymer PS-b-poly(FOA) produces smaller and more spherical primary particles (0.1-0.3 mu m) and also prevents flocculation at lower stabilizer concentrations. These differences are due to the greater interfacial activity of PS-b-poly(FOA). Steric stabilization commences in the jet on the order of several tenths of milliseconds and continues for seconds throughout the precipitator. With the use of a coaxial nozzle, precipitation is delayed and the stabilizers become even more effective at preventing flocculation.