For specific applications in the field of high gradient magnetic separation of biomaterials, magnetic nanoparticle clusters of controlled size and high magnetic moment in an external magnetic field are of particular interest. We report the synthesis and characterization of magnetic microgels designed for magnetic separation purposes, as well as the separation efficiency of the obtained microgel particles. High magnetization magnetic microgels with superparamagnetic behaviour were obtained in a two-step synthesis procedure by a miniemulsion technique using highly stable ferrofluid on a volatile nonpolar carrier. Spherical clusters of closely packed hydrophobic oleic acid-coated magnetite nanoparticles were coated with cross linked polymer shells of polyacrylic acid, poly-N-isopropylacrylamide, and poly-3-acrylamidopropyl trimethylammonium chloride. The morphology, size distribution, chemical surface composition, and magnetic properties of the magnetic microgels were determined using transmission electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. Magnetically induced phase condensation in aqueous suspensions of magnetic microgels was investigated by optical microscopy and static light scattering. The condensed phase consists of elongated oblong structures oriented in the direction of the external magnetic field and may grow up to several microns in thickness and tens or even hundreds of microns in length. The dependence of phase condensation magnetic supersaturation on the magnetic field intensity was determined. The experiments using high gradient magnetic separation show high values of separation efficiency (99.9-99.97%) for the magnetic microgels.

Polydopa amides as new polymers synthesized by oxidative polymerization of dopa amides are used as coatings for magnetite nanoparticles.

3,4‐Dihydroxybenzhydrazide (DHBH) could be considered a structural analogue of dopamine, forming polymers under oxidative conditions in a polydopamine (PDA) fashion. However, the former turns out to be more reluctant to oxidize and thus, more drastic conditions must be applied to achieve polymerization. Heating of DHBH in the presence of ammonium peroxydisulfate in Tris buffer yields a mixture of oligomers (average 9–10 monomer units). Although it looks black like PDA, its structure is very different. The polymer is not built up by CC bond formation but by replacement of hydroxyl groups resulting in acylhydrazine, acylhydrazone, and 1,3,4‐oxadiazoline bridging. Since the catechol moiety of the starting material is destroyed, the polymer lacks the mussel‐like anchoring property found in PDA.

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