Synthesis and Characterization of Novel Core-Shell Magnetic Nanogels Based on 2-Acrylamido-2- Methylpropane Sulfonic Acid in Aqueous Media Ayman M. Atta Petroleum Application Department, Egyptian Petroleum Research Institute, Nasr City 11727, Cairo, Egypt Received 24 November 2010; accepted 20 June 2011 DOI 10.1002/app.35135 Published online 21 November 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Ultrafine well-dispersed Fe 3 O 4 magnetic nanoparticles were directly prepared in aqueous solution using controlled coprecipitation method. The synthesis of Fe 3 O 4 /poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), Fe 3 O 4 /poly (acrylamide-co-2-acrylamido-2-meth- ylpropane sulfonic acid) poly(AM-co-AMPS) and Fe 3 O 4 / poly (acrylic acid-co-2-acrylamido-2-methylpropane sul- fonic acid) poly(AA-co-AMPS) -core/shell nanogels are reported. The nanogels were prepared via crosslinking copolymerization of 2-acrylamido-2-methylpropane sul- fonic acid, acrylamide and acrylic acid monomers in the presence of Fe 3 O 4 nanoparticles, N,N 0 -methylenebisacryla- mide (MBA) as a crosslinker, N,N,N 0 ,N 0 -tetramethylethyle- nediamine (TEMED) and potassium peroxydisulfate (KPS) as redox initiator system. The results of FTIR and 1 H- NMR spectra indicated that the compositions of the pre- pared nanogels are consistent with the designed structure. X-ray powder diffraction (XRD) and transmission electron microscope (TEM) measurements were used to determine the size of both magnetite and stabilized polymer coated magnetite nanoparticles. The data showed that the mean particle size of synthesized magnetite (Fe 3 O 4 ) nanopar- ticles was about 10 nm. The diameter of the stabilized polymer coated Fe 3 O 4 nanogels ranged from 50 to 250 nm based on polymer type. TEM micrographs proved that nanogels possess the spherical morphology before and after swelling. These nanogels exhibited pH-induced phase transition due to protonation of AMPS copolymer chains. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124: 3276–3285, 2012 Key words: core-shell magnetic nanogels; 2-acrylamido-2- methylpropane sulfonic acid; acrylamide copolymers; polymerization; aqueous solution INTRODUCTION Magnetite Fe 3 O 4 powders, which are nontoxic at cer- tain concentrations and could be easily synthesized, have been intensively investigated. Magnetic nano- particles possess some extraordinary physical and chemical properties and find applications in many industrial and biological fields. 1–4 Magnetic nanopar- ticles also find applications in making membranes, generating electricity, and fabricating memorizer for electronic and quantum computers. 1 The preparation methods of magnetite powders mainly include coprecipitation, 1,2 microwave thermal-hydrolysis, 3 oxidation of Fe(OH) 2 by H 2 O 2 , 4 ultrasonic irradia- tion, 5 micron-scale capsule, 6 and thermal decomposi- tion of Fe(CO) 5 . 7 Because of the high ratio of surface to volume and magnetization, Fe 3 O 4 nanoparticles are prone to aggregate. To enhance the compatibility between the magnetic Fe 3 O 4 nanoparticles and water, and to control and/or tailor of the surface properties of the nanoparticles, the surface modifica- tion for magnetic Fe 3 O 4 nanoparticles is a necessity. However, it is reported that the saturation magnet- ization of nanoparticles was much lower than that of correspondent bulk sample and decreased along with the reduction of the particle size. 8 The superparamagnetic Fe3O4 nanoparticles coated with polymers are usually composed of the magnetic cores to ensure a strong magnetic response and a polymeric shell to provide favorable func- tional groups and features. 9 Polymeric coating mate- rials can be classified into synthetic and natural. Polymers based on poly(ethylene-co-vinyl acetate), poly(vinylpyrrolidone) (PVP), poly(lactic-co-glycolic acid) (PLGA), poly(ethylene glycol) (PEG), poly (vinyl alcohol) (PVA), etc. are typical examples of synthetic polymeric systems. 10 Natural polymer sys- tems include use of gelatin, dextran, chitosan, pullu- lan, etc. 11 The natural polymers modification offers significant advantages in biomedicine application due to their good biocompatibility and degradabil- ity. 10 Several methods have been developed to syn- thesize magnetic nanoparticles, such as microemul- sion polymerization, 12,13 reverse microemulsion, 14 in situ polymerization 15 and suspension crosslinking method, 16 etc. However, these processes were Correspondence to: A. M. Atta (khaled_00atta@yahoo. com). Journal of Applied Polymer Science, Vol. 124, 3276–3285 (2012) V C 2011 Wiley Periodicals, Inc.