Effect of Monomer Water Solubility on Cationic Microemulsion Polymerization of Three Components (Water, Surfactant, and Monomer) JESU ´ S ARELLANO, 1 JORGE FLORES, 2 FABIO ZULUAGA, 3 EDUARDO MENDIZA ´ BAL, 2 ISSA KATIME 4 1 Departamento de Ingenierı´a Quı ´mica, Universidad de Guadalajara, Guadalajara, Jalisco, Me ´ xico 2 Departamento de Quı ´mica, Universidad de Guadalajara, Guadalajara, Jalisco, Me ´ xico, Blvd Marcelino Garcı `a Barragan 1451, Guadalajara Jal, 44430, Me ´ xico 3 Departamento de Quı ´mica, Universidad del Valle, Cali, Colombia 4 Grupo de Nuevos Materiales y Espectroscopia Supramolecular, Facultad de Ciencias, Campus Leioa, Spain Received 23 February 2011; accepted 12 April 2011 DOI: 10.1002/pola.24734 Published online 18 May 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Here, we present the oil/water (O/W) microemulsion polymerization in three-component microemulsions of n-butyl acrylate, ethyl acrylate, and methyl acrylate, monomers with similar chemical structures but different water solubilities using the cationic surfactant dodecyl trimethyl ammonium bromide. The effects of monomer water solubility, initiator type and initial monomer concentration on the polymerization kinetics were studied. Reaction rates were high with final conversions between 70 and 98% depending on the monomer and reaction conditions. The final latexes were bluish, with a particle size ranging between 20 and 50 nm and polymer with molar masses in the order of 10 6 g mol 1 . Increasing monomer water solubility resulted in a slower reaction rate, larger particles and a lower number density of particles. A higher reaction rate, larger average particle size and higher particle number density were obtained by increasing the monomer concentration. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3014–3019, 2011 KEYWORDS: kinetics; microemulsion polymerization; monomers; monomer water solubility; nanoparticles; three-component microemulsions INTRODUCTION Microemulsion polymerization was found as an alternative process for the production of polymeric latexes with the advantage of unique particle size and struc- ture. The synthesis of stable latexes with particle size rang- ing from 10 to 50 nm has been possible using this process, where fast polymerization rates and polymers with high molar mass can be obtained. 1,2 Stoffer and Bone 3,4 were the first to report a microemulsion polymerization. Most of the microemulsion polymerizations reported in the early periods of microemulsion polymerization, were carried out in four- and five-component systems: water, surfactant, monomer, alcohol (cosurfactant), and electrolytes. 2,5–9 More recently, research has focused on polymerization in three-component microemulsions (water, surfactant, and monomer), because they are simpler, and it is easier to understand the mecha- nisms of the reaction. 5,10–28 Moreover, the presence of alco- hol and electrolytes alters monomer partition. 23,24 The first three-component microemulsion polymerization (water, surfactant, and monomer) was reported by Pe ´rez- Luna et al. 10 in 1990. Since then, the microemulsion polymer- ization of different monomers in three-component systems has been reported, where the influence of different parame- ters on the polymerization kinetics and in the obtained latexes has been studied. Some of the parameters studied are the initial monomer concentration, 7,17,19,27,29–31 the tempera- ture, 8,14,15,17 the initiator concentration, 7,14,15,17,29,32 sur- factant type, 16,17,24,29 electrolyte, 24 alcohol addition, 23 and semicontinuous monomer addition. 13,27,33–38 The industrial feasibility of microemulsion polymerization depends on optimizing the semicontinuous process for which it is necessary to perform systematic studies on the impact of monomer feed rate and monomer water solubility. 28 How- ever, there are only a few reports on the effect of monomer water solubility on the kinetics of microemulsion polymer- ization. In the microemulsion polymerization of alkyl metha- crylates and acrylates using the anionic surfactant sodium dodecyl sulfate (SDS), Capek et al. 39,40 found that there is an increase in polymerization rate with increasing chain length (lower water solubility). However, in the microemulsion po- lymerization at a lower temperature (25  C) using the ani- onic surfactant SDS, and initiated by UV light, Capek 41 later reported that the reaction rate followed the order: ethyl ac- rylate (EA) > methyl methacrylate > nonyl methacrylate (lower reaction rate as water solubility decreased). Using a mathematical model, Mendiza ´bal et al. 42 compared their predictions with experimental data for the microemulsion Correspondence to: I. Katime (E-mail: issa.katime@ehu.es) Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3014–3019 (2011) V C 2011 Wiley Periodicals, Inc. 3014 WILEYONLINELIBRARY.COM/JOURNAL/JPOLA