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Magnetic polymer particles prepared by treating compact or porous polymer particles with a solution of iron salts and, if desired, salts of other metals which are capable of forming magnetic ferrites, in which the solution swells or penetrates into the particles. Iron hydroxide and possible other me

Magnetic polymer particles prepared by treating compact or porous polymer particles with a solution of iron salts and, if desired, salts of other metals which are capable of forming magnetic ferrites, in which the solution swells or penetrates into the particles. Iron hydroxide and possible other metal hydroxides are precipitated, for instance by raising the pH value, and the particles are optionally heated. In the iron salts used the ratio between di- and trivalent iron is suitably such that magnetic iron oxide is formed directly. It is also possible to use oxidizing or reducing groups or additives to obtain such a ratio. When other metal salts are used in addition to iron salts, the operation is carried out in the same manner. For instance, when Mn++, Co++or Ni++salts are used in addition to Fe++salts, the divalent iron is oxidized to trivalent so that magnetic ferrite is obtained. The polymer particles which are treated with metal salts preferably contain metal-binding groups. Such groups are incorporated for instance by using monomers which contain said groups for the preparation of the polymer particles, or the groups are incorporated in the polymer particles prepared. The magnetic polymer particles are spherical and have a uniform concentration of magnetic material. They may be used for medical, diagnostic or other purposes.

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A process for the preparation of magnetic polymer particles which comprises: mixing: (i) a solution of iron salts alone or in combination with salts of other metals which are capable of forming magnetic oxides, (ii) an aqueous dispersion of filterable polymer particles having a particle size above a

A process for the preparation of magnetic polymer particles which comprises: mixing: (i) a solution of iron salts alone or in combination with salts of other metals which are capable of forming magnetic oxides, (ii) an aqueous dispersion of filterable polymer particles having a particle size above about 0.2mcontaining groups which are capable of binding with the iron and metal salts so that a substantial portion of the iron or metal salts are retained on and in the particles which are porous and/or capable of being swollen by water, and then adding (iii) a base to increase the pH, to precipitate hydroxides of iron and said other metals, if present, thereby forming magnetic particles having said magnetic oxides on the surface as well as within the body thereof.