Process for producing magnetically responsive polymer particles and application thereof

The process to make a magnetically responsive polymer particle covered by a metal oxide/crosslinked polymer coating inert to common solvents comprising

• producing a magnetic oxide particle with an average size of about 1 micron or less by heating an aqueous solution containing admixture of divalent and trivalent transition metal salts in a molar ratio of divalent to trivalent metal salt of 0.5 to 2.0 under alkaline conditions to precipitate a metal oxide, washing said precipitate, breaking down the aggregate of said metal oxide crystals contained in said precipitate, and collecting the smaller sized metal oxide crystals of average size less than 1.0 micron,
• mixing said suspended metal oxide particle with a monomer in a weight ratio of 0.1 to 12, said monomer containing 8 to 10 percent of a cross-linking agent, to produce an admixture, and
• coating a polymeric core particle with said admixture in the presence of a polymerization initiator capable of initiating polymerization of said monomer.