Synthesis and Characterization of Bifunctional Silica Gel Surfaces

Bifunctional silica surfaces consisting of various combinations of the following organofunctional silanes were synthesized and characterized using diffuse reflectance infrared spectroscopy: hexamethyldisilazane, octyldimethylmethoxysilane, phenyldimethylethoxysilane, (3-aminopropyl) -dimethylmethoxysilane, ( 2 - cyanoethyl)triethoxysilane, and trimethylmethoxysilane. The relative amounts of organosilanes loaded on a silica surface were obtained from band area ratios of IR bands. Ratios of organosilanes bonded to the same silica surface were calculated from normalized band areas of the isolated silanol peak. In reactions in which surface coverage was incomplete, the relative amount of inaccessible silanols was determined from the band area ratio of the silanol peak. Comparisons of organosilane loading when reactions were done in one and two steps were also made. It was found that for reactions which are incomplete when the second organosilane is a relatively bulky group, better surface coverage is obtained when silylation reactions are done using a mixture of organosilanes.