In-situ Generation of Paramagnetism during Polymerization K. Mallick * , M. Coyanis * , M. Witcomb ** , R. Erasmus *** and A. Strydom **** * Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, South Africa, kaushikm@mintek.co.za; mabelc@mintek.co.za ** Microscopy and Microanalysis Unit, University of the Witwatersrand, Private Bag 3, South Africa. michael.witcomb@wits.ac.za *** School of Physics, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa. rudolph.erasmus@wits.ac.za **** Physics Department, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa, amstrydom@uj.ac.za ABSTRACT Polyaniline and its derivatives have gained significant interest because of their unique electronic property, simple synthesis process and their environmental stability. We report on the cerium (IV) ammonium nitrate mediated synthesis of poly (amino-acetanilide), PAA, using an interfacial polymerization technique in which PAA serves as a guest of the cerium (III) ion, a paramagnetic species produced during the synthesis condition. Cerium (III) ionic species bonded with the chain nitrogen of the PAA and the supramolecular system show the paramagnetic behavior throughout the experimental temperature range 400-1.9 K. Keywords: cerium ammonium nitrate, composite, paramagnetism, SEM, optical characterization 1 INTRODUCTION Among the known conducting polymers, polyaniline is unique due to its doping adjustable electrical conductivity and metal-like transport property at both room and low temperatures [1]. The electrical conductivity of the polyaniline can be varied over the full range from insulator to metal by doping. Through doping, the chemical potential (Fermi level) can be moved into the region of energy of the high density of electronic states either by a redox reaction or by an acid-base reaction. Doped polyaniline and its derivatives are good conductors due to the fact that doping introduces charge carriers into the electronic structure and the attraction of an electron in one repeat unit to the nuclei in the neighboring unit leads to carrier delocalization along the polymer chain and to charge carrier mobility, which is extended into three dimensions through inter-chain electron transfer [2]. Paramagnetic behaviour in highly protonic acid doped polyaniline has also been reported at low temperatures [3]. EPR study of the camphor-sulphonic acid doped conducting polyaniline showed temperature independent Pauli susceptibility within the temperature range 300 to 50K. The Curie contribution to the electronic paramagnetic susceptibility of the heavily doped polyaniline arises from a disordered metallic state close to the metal-insulator transition. This has been observed only below 50K [3]. Paramagnetism in polyaniline has been reported by introducing paramagnetic metal nanoparticles into the polyaniline matrix [4, 5]. In the present communication we report on an in situ synthesis technique for the preparation of a paramagnetic PAA-cerium (III) supramolecular composite material by applying an ‘in situ polymerization and composite formation’ (IPCF) technique [6] using cerium (IV) ammonium nitrate (CAN) as an oxidizing agent for polymerizing para-amino-acetanilide. CAN is most extensively used in synthetic organic chemistry as an oxidant (reduction potential value of +1.61V vs. NHE) [7]. During the polymerization process each step is associated with a release of electron and that electron reduces the Ce +4 ion to form a Ce +3 ion. The Ce +3 ion binds with the chain nitrogen of the polyaniline which causes the emergence of paramagnetism in polyaniline. 2 EXPERIMENTAL 2.1 Materials Cerium ammonium nitrate and para-amino acetanilide were purchased from Sigma-Aldrich and BDH respectively. Ultra-pure water (specific resistivity >17MΩcm) was used to prepare the solution of cerium ammonium nitrate (10 −2 mol dm −3 ). Toluene was purchased from Merck. 2.2 Characterization Techniques Scanning electron microscopy (SEM) studies were undertaken in a FEI FEG Nova 600 Nanolab at 5 kV. For UV-vis spectra analysis, a small portion of the solid sample was dissolved in methanol and scanned within the range 300-800 nm using a Varian, CARY, 1E, digital spectrophotometer. Raman spectra were acquired using the green (514.5nm) line of an argon ion laser as the excitation NSTI-Nanotech 2010, www.nsti.org, ISBN 978-1-4398-3401-5 Vol. 1, 2010 811