Surface Modification of Iron Oxide (Fe 3 O 4 ) Micro- and Nano-particles with Stimuli Responsive Polymers Erick S. Vasquez, W. Brad Nicholson and Keisha B. Walters* * Dave C. Swalm School of Chemical Engineering Mississippi State University 323 President's Circle, Box 9595 Mississippi State, MS 39762, kwalters@che.msstate.edu ABSTRACT The synthesis of stimuli responsive polymer brushes was carried out using surface-initiated atom transfer radical polymerization (ATRP) on iron oxide (Fe 3 O 4 ) micro- and nano-particles. Commercially available SAM-modified Fe 3 O 4 micro- and nano-particles (1 micron and 200 nm nom. d(H)) were obtained, and a bromine-based initiator was attached onto the particle surface. After addition of the initiator, either poly(methacrylic acid) (PMAA), poly(N- isopropylacrylamide) (PNIPAM), or PMAA-b-PNIPAM was grown from the surface of the micro- and nano- particles. DRIFTS results confirmed the presence of PMAA with peaks for CH 2 and CH 3 (2900-3000 cm -1 ) and a broad O-H stretch (3300 cm -1 ) observed as the ATRP reaction was carried out. TEM measurements demonstrated nanomaterials with the magnetic nanoparticle core and silicate shell surrounded by amorphous material. DLS measurements on 200 nm Fe 3 O 4 grafted with PMAA-b- PNIPAM revealed a decrease in the radius of gyration of the nanoparticles as temperature was increased. Therefore, DLS results demonstrate the thermo-responsive size change of these metal-polymer composite nanoparticles. Keywords: ATRP, magnetic nanoparticles, thermo- responsive, pH-responsive 1 - INTRODUCTION Nanoparticles are materials that are well known to have a high surface area to volume ratio and are considered as an emerging tool for biomedical applications, electronics, enviromental treatments and many other areas of study [1- 3]. Recently, magnetic nanoparticles (MNPs) have gained more interest due to their inherent magnetic properties which allow manipulation and hyperthermic applications of these particles under the presence of a magnetic field. The ease of manipulation of magnetic nanoparticles is widely studied in electronically devices, sensors, catalysts and drug delivery applications [4]. Stimuli-responsive polymers (SRP) are materials used for a wide range of applications and are recognized as “smart materials” [5]. Stimuli for SRPs can be pH, temperature, ionic strength, UV-radiation and many other conditions [6]. One of the most widely SRP polymers studied to-date is poly (N-isopropylacrylamide) (PNIPAM). PNIPAM is well known to have a lower critical solution temperature (LCST) at 32 o C [7]. Weak polyacids are often studied as pH-responsive polymer brushes. Poly(methacrylic acid) (PMAA) has been previously studied and is known to be a pH-sensitive polymer. A hybrid inorganic-organic composite system can then be produced using magnetic nanoparticles and stimuli- responsive polymers. This hybrid composite system will combine the capabilities of easy nanoparticle manipulation and responsive behavior in a single material. Stimuli responsive polymer-magnetic nanoparticle (SRP-MNP) hybrid materials have been previously synthesized using different techniques such as ultraviolet heat treatments, living radical polymerizations, and emulsion processes [8-9]. In this study, a living radical polymerization is undertaken as this process allows for controlled grown of the polymer layer attached to a surface. Atom transfer radical polymerization (ATRP) is used as a “grafting from” approach to produce a polymer brush from the surface of the magnetic nanoparticles [10]. Homo- and co-polymers of PNIPAM/MAA grafted to MNPs have been obtained using this living radical polymerization technique. In this work, the synthesis of PNIPAM-Fe 3 O 4 , PMAA- Fe 3 O 4 and PMAA-PNIPAM-b-Fe 3 O 4 copolymer structures is reported. First, a self-assembled monolayer (SAM) is deposited on the surface of the nanoparticles. Then, a bromine-functional initiator is reacted to finally proceed with the polymerization on the surface of the nanoparticles. Morphology and characterization of the MNPs was analyzed using TEM, DLS, and FTIR techniques as the polymerization was carried out. 2 - EXPERIMENTAL 2.1 Materials Fe 3 O 4 nanoparticles (MTI), Fe 3 O 4 -NH 2 (Chemicell), copper (I) chloride (Aldrich, 97%), triethylamine (Aldrich, 99.5%), Me 6 TREN (Aldrich, 96%), methacrylic acid (Aldrich, 99%), N-(isopropylacrylamide) (NIPAM; TCI, 98%), ethanol (Fisher Sci., 99.9%), water (Aldrich, HPLC grade), 2-bromoisobutyril bromide (Aldrich, 98%), toluene (Acros, 99.8%), tetrahydrofuran (THF; Fisher Sci., 99.9%), NSTI-Nanotech 2011, www.nsti.org, ISBN 978-1-4398-7142-3 Vol. 1, 2011 612