Fe3O4 magnetic nanoparticles with mean diameter of about 20 nm were first prepared by a precipitation method with ferric chloride as starting material

which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia.Afterwards

C=C end groups were imported to the surface of Fe3O4 magnetic nanoparticles by silane coupling agent treatment

and then polyvinylpyrrolidone (PVP) with hydroxyl end groups was grafted on the surface by addition polymerization of N-vinylpyrrolidone (NVP) with the C=C bonds.The resultant magnetic initiator was further used to polymerize lactide (LA) to generate the designed PVP-b-PLA modified Fe3O4 magnetic nanoparticles.The characterization of the production was analyzed through XRD

GPC

FTIR

SEM

TG

DSC and laser particle size analyzer.The XRD spectra of PVP-b-PLA modified Fe3O4 magnetic nanoparticles were very similar to those of non-modified nanoparticles

suggesting that the crystal lattice did not change after surface polymerization

which was still the face centered cubic (fcc) structure.There appeared a new wide diffraction peek from 10° to 25° belonging to the surface coatings

which exhibited that the surface polymers were noncrystalline.According to the FTIR analyses

there were chemical bonds between Fe3O4 and PVP and between PVP and PLA.DSC studies indicated that PVP and PLA were linked in the form of block copolymer

and there were apparently micro-phase separations between the two blocks.The results of TG analyses indicated that the coating amount of PVP and PLA was about 15% and 20%

respectively.SEM and laser particle size analyses showed that the composite nanoparticles had a relatively uniform diameter of about 45 nm

and the thickness of the coated copolymer layer was about 13 nm.In addition

the specific saturation magnetization of PVP-b-PLA modified magnetic nanoprarticles was 53 emu/g

which declined by 25% compared to that of bare Fe3O4 nanoparticles.The graft of PVP-b-PLA on the surface of Fe3O4 magnetic nanoparticles on the one hand can endow the Fe3O4 nanoparticles with excellent degradation properties

on the other hand it can make the magnetic nanoparticles with good biocompatibility after degradation because of the covering of PVP

and further it can also endow the particles with more chemical selectivity for further surface functionalization due to the hydroxyl end groups

so these PVP-b-PLA modified Fe3O4 magnetic nanoparticles will provide a platform for potential applications in drug controlled release systems

magnetic targeting drug delivery systems and tumor hyperthermia treatments.