Synthesis of clay-armored poly(vinylidene chloride-co-methyl acrylate) latexes by Pickering emulsion polymerization and their film-forming properties

We report the surfactant-free emulsion copolymerization of styrene (Sty)/methyl acrylate (MA) and vinylidene chloride (VDC)/MA by using clay platelets (LAPONITE (R) or a mixture of LAPONITE (R) and Montmorillonite) as Pickering stabilizers. Several parameters such as the presence of MA, the clay percentage and the monomer composition were shown to play a crucial role in the formation and stability of the resulting clay-armored particles. Optimal batch conditions led to stable latexes with a shelf life of at least one year. The film-forming process of the clay/P(VDC-co-MA) hybrid latexes was then studied. Transmission electron microscopy analysis of ultrathin cross-sections of the nanocomposite films revealed that latexes with high VDC contents (>= 90 wt%) were not film-forming, whereas those of the same polymer composition but without clay led to a continuous film, suggesting that the clay platelets hindered polymer chain interdiffusion. Decreasing the VDC content to 87 wt% enhanced chain mobility, resulting in a uniform film with a honeycomb structure arising from the original clay-armored particle morphology.