HYDROLYSIS OF SURFACE-BOUND PHOSPHONATE ESTERS FOR THE SELF-ASSEMBLY OF MULTILAYER FILMS - USE OF SOLID-STATE MAGIC-ANGLE-SPINNING P-31 NMRAS A PROBE OF REACTIONS ON SURFACES

Solid state static and magic angle spinning (MAS) P-31 NMR have been u sed to assess the efficiency of hydrolysis of surface-bound phosphonat e ester moieties using variations of two hydrolysis reactions. Ineffic ient phosphonate ester hydrolysis has limited the quality of polar haf nium alpha,omega-bis(phosphonate) multilayer films with nonlinear opti cal properties prepared in our laboratory. To incorporate second-order nonlinear optical (NLO) activity into self-assembled films, oriented monolayers are prepared using NLO chromophores with a phosphonic acid moiety on one end of the molecule and a phosphonate ester group on the other. After the phosphonic acid end is bound to a surface metal laye r, the terminal ester must be converted to a phosphonic acid group via hydrolysis in order to bind additional metal and bis(phosphonate) lay ers. Such hydrolysis reactions are well-known in solution but are not necessarily efficient when one of the reactants is confined to a surfa ce. To determine the best method of hydrolysis for surface-bound phosp honate esters, 10-(diethylphosphonate)decylphosphonic acid was self-as sembled onto Hf-functionalized Cab-O-Sil to give a high-surface-area s ilica with surface phosphonate ester groups. Samples were hydrolyzed v ia two different chemical methods under varying conditions. Phosphonic acid and phosphonate ester surface groups have distinct signatures in their solid state static and MAS P-31 NMR spectra, and the latter tec hnique provides an unambiguous assessment of the efficiency of differe nt hydrolysis procedures. This type of study is of general utility for evaluating a wide variety of surface reactions.