Chem. Mater. 2006, 18, 5137-5143
5137
Covalently Linked Nanocomposites: Poly(methyl methacrylate) Brushes Grafted from Zirconium Phosphonate Sandra L. Burkett,* Narae Ko, Nathan D. Stern, Joseph A. Caissie, and Debanti Sengupta Department of Chemistry, Amherst College, Amherst, Massachusetts 01002 ReceiVed June 22, 2006. ReVised Manuscript ReceiVed August 8, 2006
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(AbPO3)x(EtPO3)2-x, x ≈ 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-AbPO3)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, 13C 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.
Introduction Hybrid materials that combine inorganic and organic components are appealing because of the potential for combining the properties of the different constituents, such as the hardness or electronic properties of inorganic materials and the flexibility or processability of polymers.1 Dispersion of a small amount (
