Modification of SiO2 Surfaces by Reaction with Acetals, Ketals, Orthoesters, and Orthocarbonates

SiO2 was treated with compounds of the type C(OR)4 (orthocarbonates), R'C(OR)3 (orthoesters), and R'R"C(OR)2 (acetals and ketals) in CCl4 under reflux. The resulting modified surfaces were analyzed with IR, 1 H NMR, and 13 C NMR spectroscopy, and TGA. The initial compounds decompose, leaving on the surface only OR groups that are tightly bound. The reaction with orthocarbonates and orthoesters is more effective than that with acetals or ketals, and the SiO2 surface can be covered with OR groups to a high degree. The adsorption of polymers is restricted by the bound organic species. The modified surfaces are similar in many respects to those of alcohol-treated silicas, but the reaction proceeds at lower temperatures than those typically used for silica modification with alcohols.