Composite magnetic beads

Abstract

This invention provides a novel composite magnetic bead and a method for making the composite magnetic bead. The composite magnetic bead is comprised of a matrix formed from vinyl monomers throughout which is distributed primary beads, each primary bead of which is a magnetizable metal oxide encapsulated in a rigid polymeric coating. The matrix structure allows the composite magnetic bead to swell in organic solvents without loss of the intermeshed primary beads. Further, the matrix can be functionalized to allow the covalent bonding of sites useful for organic syntheses. The composite magnetic beads are made utilizing a core-shell polymerization techinque under conditions which preserve the oxidation state of the magnetizable metal oxide in the primary particles. In one embodiment, primary beads, each having a hydrophobic exterior surface, are dispersed in an inert solvent with a vinyl monomer and a crosslinking agent for that monomer to form a dispersed phase. The dispersed phase is mixed into an aqueous solvent-dispersing agent phase and stirred until the desired droplet size is achieved, then polymerization is initiated. After removal of the solvent and unreacted components, the composite magnetic beads are dried and sieved.