A process for the preparation of coated polymer particles containing superparamagnetic crystals, said process comprising reacting porous, surface-functionalized, superparamagnetic crystal-containing polymer particles of diameter 0.5 to 1.8 .mu.m with at least one polyisocyanate and at least one diol or at least one epoxide.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a division of U.S. patent application, Ser. No. 10/834,391, filed on Apr. 28, 2004, which claims priority of U.S. Provisional Patent Application No. 60/488,020, filed on Jul. 17, 2003.
