Synthesis of Polypyrrole Using Benzoyl Peroxide as a Novel Oxidizing Agent Chandrasekaran Saravanan, Rampally Chandra Shekhar, Srinivasan Palaniappan* Organic Coatings & Polymers Division, Indian Institute of Chemical Technology, Hyderabad 500 007, India Fax: þ91 (40) 2719 3991, þ91 (40) 2716 0757; E-mail: palani74@rediffmail.com Received: August 20, 2005; Revised: October 19, 2005; Accepted: December 6, 2005; DOI: 10.1002/macp.200500376 Keywords: benzoyl peroxide (BPO); dopants; emulsion polymerization; polypyrrole Introduction A wide variety of electrically conducting polymers have been studied due to their exclusive physical properties. Of all these polymers, polypyrrole (PPy) is one of the most extensively studied electrically conducting polymers because of its high electrical conductivity and favorable physicochemical properties. Technologically, polypyrrole has a high potential for uses such as the fabrication of molecular electronic device, [1] electrodes for lithium-ion batteries, [2] solid electrolytes for capacitors, [3] and electro- magnetic-interference-shielding materials, as well as in antistatic formulations [4] and ion sensors. [5,6] Polypyrrole can generally be prepared by electrochem- ical [7] and chemical oxidative-polymerization methods. [8] The chemical oxidative polymerization of pyrrole is very important as it is a more feasible route for producing polypyrrole on a large scale. In the last two decades, many efforts have been made to enhance the electrical properties and air stability of PPy using chemical oxidative polymer- ization with oxidizing agents such as ferric chloride, [8a–b,9] Chlorine (used to prepare granular-type PPy), [10] copper (II) perchlorate, [11] ferric tetrafluoroborate, [12] ferric sul- fate, [13] and hexacyanoferrate (used to produce highly conducting PPy), [14] ferric perchlorate [15] and Cu(BF 4 ) 2 (used to produce improved PPy), [16] and colloidal dis- persions of surfactant-stabilized polypyrrole prepared with ammonium persulfate, [17] pyridinium chlorochromate, tetraethylammonium tetrafluoroborate, [18] and ammonium ferric sulfate. [8e] Of the above-mentioned reagents, some have limitations such as toxicity, lower conductivity and higher reaction times, or there may be difficulty in removing the inorganic by-product from the polymer formed, difficult preparation conditions, or the properties of the resultant polymer may be affected by various additives introduced into the reaction mixture. In recent years, emulsion-polymerization and micro- emulsion-polymerization techniques have come to the forefront in the preparation of polypyrrole. [19] The emulsion-polymerization methods have several distinct advantages. For example, the physical state of the emulsion system makes it easier to control the process; thermal Summary: Benzoyl peroxide is used as an oxidizing agent for the first time in the synthesis of conducting polypyrrole. Synthesis of polypyrrole is commonly performed by chem- ical oxidative polymerization using water-soluble oxidizing agents. In this work, polypyrrole was prepared using organic solvent-soluble benzoyl peroxide as an oxidizing agent in the presence of p-toluenesulfonic acid (p-TSA) and sodium lauryl sulfate (SLS) surfactant via the inverted-emulsion- polymerization technique. During polymerization, SLS is converted to dodecyl hydrogensulfate (DHS) and incorpo- rated on to polypyrrole along with p-TSA dopant, indicating SLS is acting as emulsifier as well as dopant. The influence of synthesis conditions such as the duration of the reaction, the temperature, the concentration of the reactants, etc., on the properties of polypyrrole was investigated to determine the optimum conditions for the synthesis of polypyrrole salt. Polypyrrole was obtained in a reaction time of 1 h with high yield (154 wt.-% with respect to pyrrole used) and good conductivity (2 S  cm 1 ). The conductivity of polypyrrole- salt was found to be nearly the same even after seven months of storage at ambient temperature (1.7 S  cm 1 ). Macromol. Chem. Phys. 2006, 207, 342–348 ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 342 DOI: 10.1002/macp.200500376 Full Paper