(604c) Covalent Grafting of Phenylphosphonic Acid On Calcium Niobate Platelets

Inorganic platelets (such as exfoliated montmorillonite) are often treated with alkylammonium cations to improve their compatibility with more hydrophobic polymers.  As an alternate route, we are exploring covalent grafting of organic groups onto the face surfaces of synthetic inorganic platelets.  In this work, we investigate covalent grafting of phenylphosphonic acid (PPA) onto the face surfaces of calcium niobate (CN), a Dion-Jacobsen layered perovskite.  CN can be fully exfoliated in aqueous solutions of tetrabutylammonium hydroxide (TBA), as confirmed by AFM; we denote the product as TBA-CN.  We envisioned that PPA could be easily and fully grafted onto the face surfaces of exfoliated TBA-CN, which has reactive apical oxygen atoms.  This hypothesis has been explored through studies of PPA grafting onto TBA-CN (and unexfoliated CN) in pure water, aqueous TBA solution, and various alcohols.  Characterization results (NMR, FT-IR, XPS, XRD, and TGA) are used to quantify the extent of PPA grafting and different grafting modes (mono-, bi- and tridentate).  The results are rationalized in terms of a more realistic picture of the grafting process, representing the first step towards the synthesis of polymer-grafted platelets (PGPs) prepared by surface-initiated polymerization.