Anticorrosively Enhanced PMMA−Clay Nanocomposite Materials with Quaternary Alkylphosphonium Salt as an Intercalating Agent

A series of polymer−clay nanocomposite (PCN) materials that consisted of poly(methyl methacrylate) (PMMA) and layered montmorillonite (MMT) clay were prepared by effectively dispersing the inorganic nanolayers of MMT clay in an organic PMMA matrix via in situ thermal polymerization. Organic methyl methacrylate monomers were first intercalated into the interlayer regions of organophilic clay hosts followed by a typical free radical polymerization. The as-synthesized PCN materials were characterized by infrared spectroscopy, wide-angle powder X-ray diffraction, and transmission electron microscopy. PCN coatings with low clay loading (e.g., 1 wt %) on cold-rolled steel were found much superior in anticorrosion over those of bulk PMMA based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current, and impedance spectroscopy in 5 wt % aqueous NaCl electrolyte. The molecular weights of PMMA extracted from PCN materials and bulk PMMA were determined by gel permeation chromatography with tetrahydrofuran as an eluant. Effects of the material composition on the molecular barrier, optical clarity, and thermal stability of PMMA along with PCN materials, in the form of both free-standing film and fine powder, were also studied by molecular permeability analysis, ultraviolet−visible transmission spectra, differential scanning calorimetry, and thermogravimetric analysis, respectively.