Poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)-propylmethacrylate] Coated Aqueous Dispersed Thermosensitive Fe3O4 Nanoparticles

This paper reports a facile synthesis of thermosensitive Fe3O4 nanoparticles coated with poly(N-isopropylacrylamide)-related copolymer in aqueous solution. A functional monomer, namely 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) with methoxysilyl group (-SiOCH3) was copolymerized with N-isopropylacrylamide (NIPAm) to yield a thermo-sensitive copolymer, poly[N-isopropylacrylamide-co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm-co-TMSPMA)]. Such copolymer hence possesses the capability for the silanization of the Fe3O4 nanoparticles. Thermo-sensitive P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles were then easily obtained by in situ synthesis of Fe3O4 nanoparticles in the presence of the copolymer in aqueous solution. The Fe3O4 nanoparticles have mean diameters around 12 nm. The P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles show thermo-sensitive properties. With thick grafted P(NIPAm-co-TMSPMA) layer, the thermo-sensitive behavior of the composite Fe3O4 nanoparticles is reversible. For thinner grafted copolymer layer, it is irreversible. The P(NIPAm-co-TMSPMA) capped Fe3O4 nanoparticles also exhibit superparamagnetic behavior. A linear relation between the saturation magnetization M-s of copolymer-coated Fe3O4 nanoparticles and the weight percent of grafted copolymer layer is first experimentally observed. With increasing the amount of grafted copolymer, M-s of the Fe3O4 nanoparticles decreases linearly.