Preparation of core–shell latex particles by emulsion co-polymerization of styrene and butyl acrylate, and evaluation of their pigment properties in emulsion paints

A series of core–shell polymeric particles with poly(n-butyl acrylate-co-methacrylic acid-co-ethylene glycol dimethylacrylate) as core and poly(styrene-co-methyl methacrylate) as shell were prepared by seeded emulsion polymerization. The role of ethylene 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 analyses. 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 TiO₂ in the paint formulation.