Preparation of polymer particles in nonaqueous direct and inverse miniemulsions

Polymerizable miniemulsions were formulated in nonaqueous media, and it is shown that these systems exhibit characteristics similar to those of aqueous miniemulsions. Depending on the polarity of the continuous medium and the dispersed phase, the formulation of direct and inverse miniemulsions is possible. Direct miniemulsions in nonaqueous media are exemplified by dispersing styrene in formamide or glycol. Inverse miniemulsions were generated with the polar monomer hydroxyethyl methacrylate, acrylamide, or acrylic acid in cyclohexane or hexadecane as the unpolar continuous phase, and the miniemulsions were polymerized to latexes. For both the direct and inverse miniemulsions, it was shown that during high shear dispersion a steady state of droplet size is reached and that addition of a strong lipophobe (for inverse systems) or ultrahydrophobe (for regular systems) is required to stabilize the resulting miniemulsion for sufficient times. With surface tension measurements, the coverage of the particles with surfactant was determined to be incomplete. These facts are typical for the miniemulsion state; i.e., it is proven that organic miniemulsions indeed can be made and polymerized.