Composite magnetic beads

A method for making a composite magnetic bead having a plurality of primary beads randomly distributed throughout said composite magnetic bead, said method comprising the steps of:

• (1) preparing a continuous fluid phase comprising a solvent and a dispersing agent;
• (2) preparing a dispersed phase comprising:
• (a) said plurality of primary beads, where each of said primary beads comprises a metal oxide particle having inducible magnetic properties and of a rigid polymeric coating encapsulating said metal oxide particle;
• (b) at least one vinyl monomer selected from the group consisting of styrenes, methacrylates, acrylates, and derivatives thereof;
• and
• (c) an inert diluent;
• (3) mixing said dispersed phase with said continuous fluid phase to form an emulsion having a plurality of droplets, each droplet containing said primary beads, each droplet having a diameter greater than 10 microns;
• (4) adsorbing said vinyl monomer onto said rigid polymeric coating of each of said plurality of primary beads;
• and
• (5) polymerizing said vinyl monomer to provide a microporous polymeric matrix interlinking said primary beads.

A composite magnetic bead comprises a microporous matrix and of a plurality of primary beads, each primary bead having a cross-linked polymeric coating enclosing a metal oxide particle, said metal oxide particle having inducible magnetic properties, said plurality of primary beads randomly distributed throughout said microporous matrix, said composite magnetic bead prepared according to the process of:

• (1) mixing a dispersing agent with an aqueous solvent to form a continuous fluid phase;
• (2) dispersing at least one vinyl monomer, a crosslinking monomer for said vinyl monomer, an emulsion inhibitor, a polymerization initiator and said plurality of primary beads in an inert solvent to form a dispersed phase, wherein said coating on each of said plurality of primary beads is comprises a polymer having a degree of cross-linking of at least about 10 percent;
• (3) mixing said continuous fluid phase and said dispersed phase at a speed to form a plurality of droplets, each droplet containing said plurality of primary beads, said vinyl monomer, and said crosslinking monomer;
• (4) initiating a free radical polymerization to form a polymeric mesh, thereby interlinking in said mesh said plurality of primary beads in each of said droplets;
• and
• (5) removing said inert solvent and said aqueous solvent.