Magnetic poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) microspheres by dispersion polymerization

Crosslinked poly(2-hydroxyethyl methacrylate)-based magnetic microspheres w ere prepared in a simple one-step procedure by dispersion polymerization in the presence of several kinds of iron oxides. Cellulose acetate butyrate a nd dibenzoyl peroxide were used as steric stabilizer and polymerization ini tiator, respectively, and ethylene dimethacrylate was a crosslinking agent. The resulting product was characterized in terms of particle size, particl e size distribution, iron(III) content, and magnetic properties. In the pre sence of needle-like maghemite in the polymerization mixture and under suit able conditions, magnetic microspheres with relatively narrow size distribu tion were formed. An increase in the particle size and, at the same time, a decrease in molecular weight of uncrosslinked polymers resulted, as the co ntinuous phase became richer in 2-methylpropan-1-ol. Coercive force of need le-like maghemite-containing particles was higher than that of cubic magnet ite-loaded microspheres. Coercive force increased with the decreasing iron content in the particles. (C) 2000 John Wiley & Sons, Inc.