Synthesis and characterization of an iron oxide poly(styrene- co-carboxybutylmaleimide) ferrimagnetic composite Selene Sepu ´lveda-Guzma ´n a, * , Lucia Lara a , Odilia Pe ´rez-Camacho a , Oliverio Rodrı ´guez-Ferna ´ndez a , Amelia Olivas b , Roberto Escudero c a Centro de Investigacio ´n en Quı ´mica Aplicada, # 460 Blvd. Ing. Enrique Reyna H., CP 25252, Saltillo, Coah, Mexico b Centro de Ciencias de la Materia Condensada, Universidad Nacional Auto ´noma de Me ´xico, A. Postal 2681, CP 22800. Ensenada, BC, Mexico c Instituto de Investigacio ´n en Materiales, Universidad Nacional Auto ´noma de Me ´xico, A. Postal 70-360, CP 04510, Me ´xico DF, Mexico Received 9 August 2006; received in revised form 25 October 2006; accepted 3 November 2006 Available online 8 January 2007 Abstract In situ precipitation of iron oxide nanoparticles within the cross-linked styrene-(N-4-carboxybutylmaleimide) copolymer was carried out by an ion-exchange method. The resulting composite was studied by X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectros- copies. FTIR analysis showed the evolution of iron oxide deposition and the formation of sodium carboxylate due to the deposition treatment. In addition, XPS analysis indicated the complete oxidation of iron(II) to iron(III) by the presence of the representative peaks of iron oxide and iron oxyhydroxide. X-ray diffraction analysis was used to identify the inorganic phases. The results showed the formation of maghemite (g-Fe 2 O 3 ), and after several deposition cycles, goethite (a-FeOOH). The morphology and spatial distribution of iron oxide particles within the copolymer matrix were determined by transmission electron microscopy. The mean particle size of the iron oxide was of 14 nm as determined from wide- angle X-ray diffraction using the Scherrer equation. The evolution of magnetic properties with the number of deposition cycles was investigated by magnetometry at room temperature. The poly(styrene-co-N-4-carboxybutylmaleimide)/g-Fe 2 O 3 /a-FeOOH/composite showed a soft ferri- magnetic behavior and, after the third deposition cycle, showed a saturation magnetization of 8.04 emu/g at 12 kOe and coercivity field of 51 Oe. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Magnetic polymers; Composites; Maleimide copolymers 1. Introduction In recent years, there has been marked interest in the devel- opment of hybrid materials that combine the organic function- ality and processability of polymers with the magnetic properties of iron oxide nanoparticles. The polymer/magnetic particle composites have been used in a wide variety of applica- tions such as biological separation systems [1], drug delivery [2], waste water purification adsorbents [3], magnetic resonance markers [4] and different magnetic reprographic methods [5,6]. There are two main methods to prepare polymer/magnetic particle composites. The ex situ method consists of the precip- itation of magnetic particles followed by their incorporation into the polymer matrix. Several approaches such as the encapsulation of magnetic particles by the polymer [7], and melt or solution mixture of the polymer, and magnetic parti- cles to form films or fibers [8,9] belong to the ex situ method. On the other hand, in the in situ method the magnetic particles are grown within the polymer matrix. The metal-bonding abil- ity of chelating groups of the matrix is often used to promote the precipitation of the magnetic particles from a metal salt. This method provides an efficient way to control the shape and size distribution of nanoparticles and, unlike inorganic syn- thetic methods, does not require heating at high temperatures. Several polymers including natural polymers and their deriva- tives, such as cellulose and carboxymethyl cellulose, have already been used to prepare hybrid materials with magnetic properties by the in situ method [10e12]. Sourty et al. [13] synthesized iron oxide particles using a bacterial cellulose * Corresponding author. Tel.: þ52 844 438 9830; fax: þ52 844 438 9463. E-mail address: ssepulveda@ciqa.mx (S. Sepu ´lveda-Guzma ´n). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.11.004 Polymer 48 (2007) 720e727 www.elsevier.com/locate/polymer