Dynamic Modeling of the Morphology of Latex Particles with In Situ Formation of Graft Copolymer Elena Akhmatskaya, 1 Jos e M. Asua 2 1 Basque Center for Applied Mathematics (BCAM), Building 500, Bizkaia Technology Park, E-48160, Derio, Spain 2 Institute for Polymer Materials, POLYMAT, and Grupo de Ingenierı ´a Quı ´mica, Departamento de Quı´mica Aplicada, Facultad de Ciencias Quı ´micas, University of the Basque Country, UPV/EHU, Joxe Mari Korta zentroa, Tolosa etorbidea 72, Donostia-San Sebasti an 20018, Spain Correspondence to: J. M. Asua (E-mail: jmasua@ehu.es) Received 27 September 2011; accepted 12 December 2011; published online 12 January 2012 DOI: 10.1002/pola.25904 ABSTRACT: Modification of the polymer–polymer interfacial ten- sion is a way to tailor-make particle morphology of waterborne polymer–polymer hybrids. This allows achieving a broader spectrum of application properties and maximizing the synergy of the positive properties of both polymers, avoiding their drawbacks. In situ formation of graft copolymer during poly- merization is an efficient way to modify the polymer–polymer interfacial tension. Currently, no dynamic model is available for polymer–polymer hybrids in which a graft copolymer is generated during polymerization. In this article, a novel model based on stochastic dynamics is developed for predicting the dynamics of the development of particle morphology for com- posite waterborne systems in which a graft copolymer is pro- duced in situ during the process. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 1383–1393, 2012 KEYWORDS: dynamic modeling; development of particle mor- phology; emulsion polymerization; grafting; graft copolymers; miniemulsion polymerization; morphology; polymer–polymer hybrid; seeded emulsion polymerization INTRODUCTION The production of composite latex particles with well-defined morphology is a problem of great technical interest as they have a broader spectrum of properties than particles having uniform composition for applications such as coatings, adhesives, impact modifiers, and many other materials. 1–3 Composite latex particles are commonly pre- pared by seeded semicontinuous emulsion polymerization. A preformed latex (Polymer 1) is swollen with a certain amount of Monomer 2, and polymerization is started by add- ing initiator. Polymerization leads to the formation of chains of Polymer 2 in a matrix of Polymer 1 swollen with Mono- mer 2. Because of the incompatibility between the two poly- mers, phase separation occurs and clusters of Polymer 2 are formed within the matrix of Polymer 1. Polymerization continues in both clusters and matrix, and hence the clusters grow in size and new clusters are formed, which migrate toward the equilibrium morphology. 4–8 Depending on the polymerization conditions, a wide variety of particle mor- phologies can be produced: core shell, 9 ‘‘inverted’’ core shell, 10 hemispheres, 11 ‘‘raspberry-like,’’ 12 and void particles. 13 Particle morphology depends on the interplay between ther- modynamics and kinetics. 4–8,14,15 Thermodynamics deter- mines the particle morphology at equilibrium, according to the minimum surface energy. Kinetic factors control whether the particle reaches the equilibrium morphology or remains at a metastable (kinetically stable) morphology. The polymer–polymer and polymer–aqueous phase interfa- cial tensions play a key role in the development of the parti- cle morphology as they determine the surface energy, and hence the equilibrium morphology. In addition, they strongly affect cluster migration toward the equilibrium morphology, that is, the kinetics. 4–6 Modification of the polymer–polymer interfacial tension is a way to tailor-make particle morphology. 16–19 Thus, Rajatapiti et al. 16 prepared a miniemulsion of butyl acrylate containing a methyl methacrylate macromonomer, which upon polymer- ization led to the formation of the polybutyl acrylate seed with poly(butyl acrylate)–graft–poly(methyl methacrylate) copolymers. Polymerization of methyl methacrylate on this seed led to composite PBA/PMMA particles. The authors showed that morphology was strongly affected by the pres- ence of the graft copolymer, which reduced the poly(butyl acrylate)–poly(methyl methacrylate) interfacial tension. For polystyrene–poly(methyl methacrylate) and polystyrene– poly(butyl acrylate), Herrera et al. 17–19 showed that block copolymers produced in situ by controlled radical polymer- ization (CRP) substantially modified the particle morphology. V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1383–1393 1383 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE