PREPARATION OF POLYSTYRENE-CO-DIVINYLBENZENE MICROSPHERES WITH CONTROLLED SIZES BY POLYMERIZATION OF STABILIZED MICROSUSPENSIONS

The preparation in two steps of polystyrene-co-divinylbenzene microbea ds with controlled sizes in the range 2-20 mum diameter has been studi ed. A stable microsuspension of the monomers is first achieved in wate r at room temperature and under high shear using different steric stab ilizers with or without co-stabilizers. Then, the system is polymerize d using free radical initiators to form microbeads in high yield (85%) . The conditions to control the characteristics of the microsuspension s have been studied. It has been shown that the microsuspensions when properly stabilized can be polymerized without noticeable change of th eir size and size distribution, forming microbeads free of adhering em ulsion particles. However, a study of the evolution of the size and si ze distribution of the particles during polymerization shows that the percentage of particles with higher diameters increases slowly during the polymerization in spite of the rapid gelling process. This suggest s a mechanism in which the small amount of monomers dissolved in the w ater phase is preferably adsorbed by those larger particles probably m ore poorly protected by the steric stabilizer than the finer beads.