Preparation and characterization of PVP-b-PLA modified Fe3O 4 magnetic nanoparticles

Fe3 O4 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 Na 2 SO3 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-6-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 (fee) 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.