Preparation of Poly(methylmethacrylate) Microcapsules with Liquid Cores.

Particles with liquid cores and solid shells have been prepared by the controlled phase separation of poly(methylmethacrylate) (PMMA) within the droplets of an oil-in-water emulsion. The oil phase of the emulsion contained poly(methylmethacrylate), a good solvent for the polymer (CH2Cl2), a poor solvent (hexadecane, decane, octanol, or tetrachloromethane), and in some cases acetone (a water soluble co-solvent) to aid emulsification. Emulsions were prepared using a Silverson high-speed stirrer, and the droplet size distributions were determined using a Coulter particle counter. Size distributions were found to be dependent on the nature of the emulsifier, the concentration of acetone in the oil phase, and the concentration of polymer in the oil phase. The good solvent was then removed under reduced pressure, causing the poly(methylmethacrylate) to phase separate within the emulsion droplets. The resultant two-phase particles were characterized by optical microscopy and scanning electron microscopy. Particle morphologies depended strongly on the nature of the non-solvent and also the emulsifier employed. Spreading coefficients were calculated from interfacial tension and contact angle measurements, and were used to account for the morphologies observed. Core/shell microcapsules were formed when hexadecane or decane was used as non-solvent, and only when polymeric emulsifiers were employed. All other combinations yielded "acorn"-shaped particles. The thickness of microcapsule walls was found to be a constant fraction of the overall capsule diameter for all microcapsule sizes and depended, as expected, on the concentration of polymer in the oil phase. Copyright 1998 Academic Press.