Preparation of core–shell latex particles by emulsion co-polymerization of styrene and butyl acrylate, and evaluation of their pigment properties in emulsion paints Lakhya J. Borthakur, Tirthankar Jana, S. K. Dolui Ó FSCT and OCCA 2010 Abstract A series of core–shell polymeric particles with poly(n-butyl acrylate-co-methacrylic acid-co- ethylene glycol dimethylacrylate) as core and poly(sty- rene-co-methyl methacrylate) as shell were prepared by seeded emulsion polymerization. The role of ethyl- ene glycol dimethylacrylate (EGDMA) is to crosslink the core so as to avoid any probability of gel formation and to bind both the core and the shell phase together. The spherical morphology of the core–shell structure was achieved at 60:40 core to shell ratio. The core–shell morphology was confirmed by SEM and TEM analy- ses. GPC analysis of the particles reveals that the polymer shows a bimodal mode. The first peak has M w = 382700 and M n = 245200 with polydispersity index of 1.6, and the second peak has M w = 21200 and M n = 14800 with polydispersity index of 1.4. These core–shell latexes were applied as a pigment/binder in emulsion paint and the paint properties like gloss, rock hardness, washability, opacity, etc. were compared with the standard. The results show that these core– shell latexes can provide similar hiding power with 17% reduction of TiO 2 in the paint formulation. Keywords Core–shell, Pigments, Emulsion Introduction The core–shell morphology has gained considerable interest in recent years due to its special type of structure and versatility in applications. 1–5 Such kind of latex particles are usually prepared by a series of consecutive emulsion polymerization sequences with different monomer types, where the second stage monomer is polymerized in the presence of seed latex particles. 6,7 The resulting latexes are commonly known as ‘‘core–shell’’ latex, implying a particle structure with the initially polymerized polymers located at the center of the particle, and the later- formed polymers being incorporated into the outer shell layer. The synthesis of such multiple phase composite particles provides an opportunity to tailor properties for a range of desired applications such as paints, coatings, and additives. 8,9 These latexes may be used to create latex films with properties that cannot be achieved by a physical blend of two or more different polymer components. For example, binders used in coatings need to fulfill contradictory demands such as excellent film formation and appearance and good blocking resistance and hard- ness. 10 By using core–shell particles which have hard domains (formed from a high glass transition tem- perature (T g ) polymer) and soft domains (formed from a low T g polymer), it is possible to produce binders with a high block resistance and low mini- mum film-forming temperature (MFFT). 10 In the paint industry, TiO 2 is used as pigment in emulsion paints. Since TiO 2 has comparatively higher refrac- tive index than the polymer phase, its use imparts hiding power in coatings. In core–shell morphology two polymer phases having different refractive indexes are entangled together. Therefore, they may potentially replace TiO 2 as pigment in emulsion paints. Many techniques are available for the prep- aration of core–shell polymer particles. Two-stage emulsion polymerization is a common route for the preparation of core–shell polymer particles. 11–13 Using this method, Okubo and Mori 14 prepared dif- ferent kinds of core–shell polymer particles. Moreover, L. J. Borthakur Department of Chemistry, Nowgong College, Nagaon, Assam, India T. Jana, S. K. Dolui (&) Department of Chemical Sciences, Tezpur University, Napaam, Assam, India e-mail: dolui@tezu.ernet.in J. Coat. Technol. Res., 7 (6) 765–772, 2010 DOI 10.1007/s11998-010-9265-2 765