The formation of poly(methyl-methacrylate) on transition metal-exchanged hectorite

Hectorite clay films exchanged with Cu²⁺ or Fe³⁺ react with methyl-methacrylate monomer in a solventless process to form poly(methyl-methacrylate) (PMMA). Scanning force microscopy (SFM), electron spin resonance (ESR), and X-ray diffraction (XRD) are useful in studying the resulting clay/polymer composite. SFM shows that PMMA forms on the surface of both the Cu²⁺- and Fe³⁺-exchanged films. In addition, XRD shows PMMA formation in the interlayer region of the Fe³⁺-exchanged hectorite but not the interlayer region of Cu²⁺-exchanged hectorite. SFM shows that the morphology of the polymer formed on the film surface depends on: (1) the type of transition metal exchanged into the interlayer region. (2) The mode of delivery (vapor vs. liquid) of methyl-methacrylate monomer to the surface of the clay. PMMA does not form to a significant extent on or within Ca²⁺-exchanged hectorite, and ESR shows no evidence of free radical formation or reduction of the transition metals during any of the polymerization reactions. The results suggest the possibility of an unusual cationic polymerization of methyl-methacrylate to form PMMA with organic cations being stabilized by interaction with the silicate surface. The experimental results have implications for 'solventless synthesis' of PMMA and other polymers.