Magneto-Responsive Organogels Prepared Through Surface-Initiated Atom Transfer Radical Polymerization on Iron Nanoparticles

Iron nanoparticles (Fe-np) with average diameter 50 nm have been synthesized by addition of NaBH4 to FeCl3 solution then radical initiator, (11-(2-bromo-2-methyl)propionyloxy)undecyltrichlorosilaile (1) has been immobilized on to Fe-np. Surface-initiated atom transfer radical polymerization (SI-ATRP) of different monomers such as styrene, methyl methacrylate, methacrylonitrile and N-vinylimiclazol have been carried out from initiator-grafted Fe-np and the amount of grafted polymers was determined by thermogravimetric analysis (TGA). Immobilization of PMMA has been monitored by TGA of samples; taken from the reaction mixture after 4, 9 and 21 hours. Activators regenerated by electron transfer (ARGET) ATRP of methyl methacrylate and styrene were conducted from initiator-grafted Fe-np in the presence of phenol and Na-phenoxide respectively and the yields of immobilized polymers were found lower than those we observed in the case of conventional ATRR The concentration of Fe-np (c(m)) in the reaction mixture was found to influence significantly the appearance of products; at higher c(m) values SI-ATRF1 of styrene resulted in the formation of magneto-responsive gels. Transmission electron microscope investigation of bare Fe-np and magnetic gel revealed that the particles are well-dispersed in the gel while non-grafted Fe-np form aggregates. XRID measurements were used to determine the composition of magnetic nanoparticles. It was found that the crystalline phase of Fe-np is mostly reduced iron and the fraction of iron-oxide (hydroxide) species is below the detection limit of XRD. Immobilized polymers have been degrafted by digestion of Fe-np in HCl and trifluoroacetic acid and the residual polymeric material were identified by FTIR and H-1-NMR spectroscopy. A plausible mechanism for the formation of magnetic gel was given in which polymer network is built up through interparticle termination reactions and Fe-np act as functional cross-linkers.