Towards the synthesis of high solids content waterborne poly(methyl methacrylate-co-butyl acrylate)/montmorillonite nanocomposites

Small angle X-ray scattering of Na-montmorillonite (Na-MMT) aqueous dispersions showed that at concentrations below 1.5 wt%, clay platelets were fully dispersed with an average distance between platelets higher than 16 nm. At higher concentrations (3 wt%) platelet–platelet interaction was not negligible and SAXS measurements detected ordered stack structures composed of 2–3 platelets with an average distance of around 14–16 nm. Thus, initiating an emulsion polymerization of methyl methacrylate and butyl acrylate in an aqueous phase containing Na-MMT at concentrations below 1.5 wt% allowed the production of stable and coagulum free waterborne nanocomposites having 30 wt% solids content, with exfoliated structure. The in situ produced poly(methyl methacrylate-co-butyl acrylate)/Na-MMT nanocomposite latexes provided better mechanical, thermal and permeability properties than composites prepared by blending pristine latex with Na-MMT or the pristine copolymer synthesized in the same conditions. Furthermore, for the first time nanocomposite latexes with 45 wt% solids content and intercalated morphologies having enhanced mechanical properties were also produced by seeded semibatch emulsion polymerization. The intercalated structure was likely due to the higher clay concentration in the aqueous phase that favoured platelet–platelet interaction, increased the viscosity of the polymeric dispersion and prevented a complete exfoliation.