Comparative studies of grafting and direct syntheses of inorganic-organic hybrid mesoporous materials

Vinyl-functionalized MCM-41 samples were prepared by either a postsynthesis grafting (PSG) process or a direct, co-condensation synthesis. The structu res, stabilities, and reactivities of products from both methods were compa red. The mesoscopic order of the hexagonal pore structure of vinyl-grafted MCM-41 (v-gr-MCM-41) resembled that of the MCM-41 host. On the basis of pow der X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and b romination kinetics data, the vinyl groups appeared to be nonuniformly dist ributed in v-gr-MCM-41 prepared by the present PSG process, with a large pr oportion of vinyl groups on the external surface of the crystallites or ins ide channels but near the channel openings. The mesoscopic order of product s from the direct synthesis (v-MCM-41) depended on the type of alkoxysilane precursor used and on the ratio of vinylsiloxane to alkoxysilane in the re action mixture. The vinyl groups appeared to be more uniformly distributed in v-MCM-41. Vinyl-grafted MCM-41 exhibited greater hydrothermal stability than unmodified MCM-41 and was capable of absorbing nonpolar solvents from aqueous mixtures or emulsions.