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 amorphou s poly(methyl methacrylate) (PMMA) and polystyrene (PS) microparticles formed by precipitation into liquid CO2 at 23 degrees C. The micropar ticle stabilization mechanism is explained in terms of the stabilizer- CO2 phase behavior, the spray characteristics, and the interfacial act ivity of the stabilizer. Compared with the homopolymer poly(FOA), the diblock copolymer PS-b-poly(FOA) produces smaller and more spherical p rimary particles (0.1-0.3 mu m) and also prevents flocculation at lowe r 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 continu es 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.