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

Abstract

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)undecyltrichlorosilane (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-vinylimidazol 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 ATRP. 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-ATRP 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. XRD 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 1H-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.

Novel Surface-Attachable Multifunctional Initiators: Synthesis, Grafting, and Polymerization in Aprotic and Protic Solvents

“…It should be noted here that SEM investigation of these Sil-PNVP particles revealed the presence of insoluble, most likely cross-linked domains precluding the separation of the hybrid particles from each other and the formation of a fine suspension (Figure S6). Most probably, the relatively high grafting density of 2c , the lack of solvent and the noncontrolled feature of the polymerization resulted in high concentration of propagating radicals that might undergo radical termination reactions giving nonsoluble cross-linked network …”

“…Most probably, the relatively high grafting density of 2c, the lack of solvent and the noncontrolled feature of the polymerization resulted in high concentration of propagating radicals that might undergo radical termination reactions giving nonsoluble cross-linked network. 32 Further characterization of polymer-grafted particles was performed using infrared spectroscopy (Figure 4). The DRIFT spectrum of Sil-PNVP 2c (d) is the superposition of the spectra of the three components: silica gel (a), initiatorgrafted silica (b), and PNVP (c).…”

d-Sorbitol, a structurally simple, low molecular-mass gelator

“…During the last several years, this reversibility has made LMOG gels very attractive materials for a large number of applications [3][4][5] in the cosmetics, 6 food 7,8 and pharmaceutical 9,10 industries. Obviously, for these applications, the LMOGs must be non-toxic.…”

Strategy for preparation of hybrid polymer hydrogels using silicananoparticles as multifunctional crosslinking points

“…The nanocomposite hydrogel (NC gel) was first reported by Haraguchi and Takehisa; this hybrid gel was prepared by in situ free radical polymerization of monomers from the initiator absorbed on the sheet-like nanoclay by ionic interactions. 6 Huang et al 7 and Czaun et al 8 reported that a hybrid hydrogel could be formed by the termination of grafting polymer chains growing from the surfaces of the particles. More recently, Wang et al reported that nanoparticles coated with a specific polymer with a dendritic structure at both its terminals underwent aggregation by electrostatic interactions, thereby inducing gel formation.…”