Probing Interfaces and Surface Reactions of Zirconium Phosphate/Phosphonate Multilayers Using ³¹P NMR Spectrometry

We report our 31 P magic angle spinning (MAS) NMR characterization of zirconium phosphate/phosphonate (ZP) multilayer assemblies grown on SiO x . The reaction of silica with excess POCl 3 and treatment with collidine results in both physisorbed and chemisorbed H x PO 4 ( x - 3) being present at the SiO x surface. The 31 P NMR spectrum of zirconium phosphate grown from silica shows no residual Cl-containing species, indicating essentially complete hydrolysis. The phosphate 31 P resonances are broadened substantially upon complexation with Zr 4+, and T 1 data demonstrate the broadening to be inhomogeneous in nature. Data on maleimide−vinyl ether copolymer layers we reported recently [ Langmuir 1999, 15, 1418] confirm that hydrolysis/deprotection by bromotrimethylsilane is efficient in converting phosphoesters to the corresponding phosphorus oxyacid in the synthesis of multilayers. Comparison of polymer multilayers with the relatively more ordered bisphosphonic acid-based multilayers indicates that essentially the same interlayer bonding chemistry is seen for both systems, with subtle differences arising as a consequence of the greater available free volume and more extensive disorder within the polymer.