Mercaptopropyl Functionalized Polymethylsilsesquioxane Microspheres Prepared by Co-Condensation Method as Organosilica-Based Chromatographic Packings

Abstract

Mercaptopropyl functionalized polymethylsilsesquioxane microspheres have been prepared by a two-step acid/base catalyzed hydrolysis and co-condensation of methyltrimethoxysilane (MTMS) and mercaptopropyltrimethoxysilane (MpTMS) precursors. The mercaptopropyl loading of the microspheres is controlled by regulating the ratio of MpTMS to MTMS in the reaction feedstock. A pronounced decrease in surface area, pore volume, and pore size with increasing mercaptopropyl loading was observed and a transition in pore structure from mesopores to micropores/nearly nonporous occurred at mole fractions of mercaptopropyl groups greater than 0.23. The resulting particles exhibited low silanol/thiol activity as both the concentrations and dissociation constants of the acidic groups were considerably lower than those reported for inorganic silica-based packings. Chromatographic evaluation using a test mixture containing uracil, toluene, ethylbenzene, quinizarin, and amitriptyline revealed that the new materials possess typical reverse phase chromatographic properties with moderate methylene selectivity and intrinsic inertness to bases. Taken together, the mercaptopropyl functionalized microspheres are a promising alternative to base-deactivated silica-based packings for the separation of the basic compounds which constitute a large proportion of pharmaceuticals.