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 SiOx. The reaction of silica with excess POCl3 and treatment with collidine results in both physisorbed and chemisorbed HxPO4(x-3) being present at the SiOx, surface. The P-31 NMR spectrum of zirconium phosphate grown from silica shows no residual Cl-containing species, indicating essentially complete hydrolysis. The phosphate P-31 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.