Siloxane-based high solid acrylic latex by mini-emulsion polymerization for coatings with improved water resistance

Water resistance of a coating is an important parameter in its protective nature. Therefore, developing a viable coating formulation for improved water resistance has significant research interest. In this study, we prepared an acrylic latex composed of poly (methyl methacrylate-co-butyl acrylate-co-acrylic acid) having high solid content (54–57 %) by mini-emulsion polymerization. Herein, we synthesized a methacrylate-terminated tetrafunctional siloxane monomer (MTS) and used it at 0.5–4.0 wt% as a crosslinking comonomer in the acrylic emulsion formulation. The structural elucidation of MTS was performed by FT-IR, 1H & 13C NMR and ESI-MS analysis. The copolymer latexes were characterized in terms of their solid content, particle size and viscosity. All the high solid latexes were stable for months without any coagulum. The analysis of microscopic, optical, thermal and mechanical properties of the air-dried cast films exhibited that the copolymers with MTS had rough surface morphology, high optical transparency (~98 % transmittance), and improved thermal properties and poor mechanical properties. In addition, the films showed improved water resistance as observed from the increased water contact angle from 43.0° (0 % MTS) to 64.2° (1 % MTS) and reduced water absorption from 50 % (0 % MTS) to 18.2 % (1 % MTS). This work focusing on the incorporation of siloxane moieties for improving the water resistance and many other properties of acrylic coatings will make an advancement to develop fluorine-free protective coatings.