Fe3O4 magnetic nanoparticles have been widely used in biomedical applications such as magnetic resonance imaging contrast reagent

tissue repair

immunoassay

hyperthermia

drug delivery and cell separation

etc.due to their specific magnetic properties.All these applications require high magnetization values

nanostructure size with overall narrow particle size distribution and special surface coating of the magnetic particles.The latter not only makes Fe3O4 magnetic nanoparticles nontoxic and biocompatible to organism but also provides more chemical selections for molecular device designs.In this paper

Fe3O4 magnetic nanoparticles with mean diameter of about 25 nm were prepared by a precipitation method with ferric chloride as starting material

which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia.XRD analyses showed that the crystal lattice of the magnetic nanoparticles was face centered cubic (fcc) structure.Afterwards

Si—H bonds were imported to the surface of Fe3O4 magnetic nanoparticles by chemical treatment

and then a magnetic-initiator with bromine end groups was prepared from a selective hydrosylation.The resultant initiator was further used to polymerize acrylamide through atom transfer radical polymerization (ATRP).The grafted polyacrylamide on the surface of Fe3O4 magnetic nanoparticles exhibited the characteristics of ATRP-controlled molecular weights and narrow polydispersity.The molecular mass of polyacrylamide could be modulated by controlling the molar ratio of monomer acrylamide to magnetic-initiator.When the molar ratio was 90

the number average molecular weight was 6440

the polydispersity was 1.19

the molar grafting ratio of polyacrylamide was about 5%， and the thickness of the surface polymer coatings was about 10 nm.Becauseit was difficult to directly characterize the surface polyacrylamide of magnetic nanoparticles

so a linear polyacrylamide in the solution was prepared through ATRP to investigate the polymeric structures.Both 1H-NMR and FTIR exhibited the characteristics of polyacrylamide.DSC measurements showed that the decomposition temperature (Td) of the surface polyacrylamide of magnetic nanoparticles was 242℃

and the glass transition temperature (Tg) was 102℃

which apparently decreased as compared to that of linear polyacrylamide (Tg=165℃).This was because the star structure weakened the interaction of polyacrylamide molecules and reduced the cohesive energies of materials and then made the polymeric chains move more easily.The specific saturation magnetization of polyacrylamidemodified Fe3O4 magnetic nanoparticles was 58.5 emu.g-1

which declined 20% compared to that of the non-modified Fe3O4 nanoparticles.The graft of polyacrylamide on the surface of Fe3O4 magnetic nanoparticles can improve the biocompatibility of magnetic nanoparticles

and also endow the particles with more chemical selectivities for the further surface functionalization of magnetic nanoparticles

so these polyacrylamidemodified Fe3O4 magnetic nanoparticles will provide a platform for potential applications in biomedicines.