PREPARATION OF MACROPOROUS MICROSPHERES WITH A NUTSHELL STRUCTURE BY INVERSE POLYMERIZATION OF MICROSUSPENSIONS OF POLY(ETHYLENE OXIDE) METHACRYLATE MACROMERS

The preparation of macroporous microspheres of the polymethacrylate of poly(ethylene oxides) (PEOs) with controlled sizes in the range 2-20 mu m is described. A two-step process is proposed. A stable microsuspe nsion in cyclohexane of PEO macromers and of a crosslinking agent, bot h dissolved in water, is first prepared under high shear. The system i s then polymerized under gentle stirring. Observations of the beads by scanning electron microscopy show a nutshell structure with the prese nce of a dense and resistant skin at the bead surface. This formation is explained by considering the relatively high solubility of the macr omers in the cyclohexane phase. While the droplets polymerized and gel led, the part of the macromer dissolved in the cyclohexane phase polym erized at the bead interface.