Effect of particle size on the mechanical properties of polystyrene and poly(butyl acrylate) core/shell polymers L.A. Pe ´rez-Carrillo a , M. Puca a , M. Rabelero a , K.E. Meza a , J.E. Puig a , E. Mendiza ´bal a, * , F. Lo ´pez-Serrano b , R.G. Lo ´pez c a Departamentos de Quı ´mica e Ingenierı ´a Quı ´mica, Universidad de Guadalajara, M. Garcı ´a Barraga ´n 1451, Guadalajara, Jalisco 44430, Mexico b Facultad de Quı ´mica, Universidad Nacional Auto ´noma de Me ´xico, Me ´xico, D.F. 04510, Mexico c Centro de Investigacio ´n en Quı ´mica Aplicada, Saltillo, Coah. 25253, Mexico Received 6 September 2006; received in revised form 1 January 2007; accepted 2 January 2007 Available online 8 January 2007 Abstract The effects of particle size and polymer location (core or shell) on the mechanical properties of core/shell materials composed of polystyrene (PST) and poly(butyl acrylate) (PBA) made by a two-stage emulsion or microemulsion polymerization process are reported. Low-seed content (LSC) latexes were made by batch polymerization in microemulsions stabilized with DTAB in the presence of an organic salt (dibutyl phos- phite). High-seed content (HSC) latexes were produced by microemulsion or emulsion polymerization in semi-continuous process. These latexes were subsequently used to form core/shell particles of PST/PBA or PBA/PST and their mechanical properties were examined and compared. Our results indicate that core/shell particle size and the location of the polymers have important effects on the mechanical properties. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Core/shell polymer; Particle size; Mechanical properties 1. Introduction Core/shell polymers are attracting scientific and industrial interest because their chemical and mechanical properties can be tailored for applications such as paints, adhesives, paper and textile manufacturing, and impact modifiers [1e7]. Moreover, these materials have better properties than those of the parent polymers [8e10]. Core/shell polymers are usu- ally made by emulsion polymerization in a two-stage process; first one monomer is polymerized to form the core, then the second monomer is added in batch or semi-continuously and polymerized over the seed particles to form the shell [11,12]. One of the polymers has a much lower glass transition temperature (T g ) and the other a higher T g than the tempera- ture at which the material is being used [11e13]. By microemulsion polymerization it is also possible to produce core/shell polymer particles but with smaller sizes than those obtained by emulsion polymerization [14,15]. Aguiar et al. reported that core/shell of polystyrene (PST) and poly(butyl acrylate) (PBA) made by microemulsion polymerization had higher Young’s modulus and tenacity than the core/shell poly- mers with similar composition made by conventional emulsion polymerization because of their smaller particle size [15]. In emulsion polymerization final particle size can be mod- ified by the addition of salts [16e20]. Full et al. reported that smaller polystyrene particles were produced by polymerizing in microemulsions containing electrolytes compared to those obtained in their absence, and that smaller particles were pro- duced as the salt content was increased [21]. In this work we investigated the effects of particle size and polymers’ location and composition on the mechanical properties of core/shell of PST and PBA made by a two-stage emulsion or microemulsion polymerization process in order to contribute to the under- standing of the relationship between morphology and * Corresponding author. Tel.: þ52 3336199920; fax: þ52 3336194028. E-mail address: lalomendizabal@hotmail.com (E. Mendiza ´bal). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.01.001 Polymer 48 (2007) 1212e1218 www.elsevier.com/locate/polymer