Covalently linked nanocomposites: Poly(methyl methacrylate) brushes grafted from zirconium phosphonate

Fully covalently connected polymer-clay nanocomposites have been prepared by growing the polymer chains from initiator sites on the lamellae of a zirconium phosphonate clay. The zirconium phosphonate material was synthesized with an approximately 1: 3 ratio of 4-aminobenzylphosphonate and ethylphosphonate groups (Zr(AbPO(3))(x)(EtPO3)(2-x), x approximate to 0.5) in a "solid solution" distribution within the lamellae. After conversion of the amine groups to 2-bromo-2-methylpropionamide moieties, composites of the zirconium phosphonate and tethered poly( methyl methacrylate) ( PMMA) brushes were synthesized by atom transfer radical polymerization (ATRP); the tethered initiator within Zr(Init-AbPO(3))(x)(EtPO3)(2-x) and its soluble analogue are the first examples of aromatic amide-based initiators for ATRP. To facilitate characterization of the composites, the polymerization conditions were intentionally not optimized for high molecular weight polymer, but PMMA was nonetheless formed at the conditions studied, and the weight fraction of polymer was observed to increase with polymerization time. A combination of thermogravimetric analysis, C-13 CP MAS NMR, X-ray diffraction, and scanning electron microscopy confirmed the compositions and structures of the composites, including the covalent connectivity among all of the components.