Emulsion polymerization in the presence of colloidal silica particles. Application to the reinforcement of poly(ethyl acrylate) films

Emulsion polymerization of ethyl acrylate was carried out in the presence of different kinds of functionalized and non‐functionalized silica particles. 3‐(Trimethoxysilyl)propyl methacrylate, 2‐hydroxyethyl methacrylate and 3‐(triethoxysilyl)‐propanethiol functionalization agents were examined. It is demonstrated that use of the first two coupling agents results latexes able to give films which display remarkable mechanical properties similar to those of vulcanized elastomers reinforced with solid particles. A qualitative model is then set up to give account for these properties. It is proposed that a part of the polymer is covalently bound to silica as tight loops, giving rise to a set of strong entanglements with the non‐grafted polymer during film formation. This model is supported by stress‐strain measurements. Some validation experiments are described using the third grafting agent of the series.