A convenient synthesis of silylated silica xerogels

Treated silica xerogels with controlled porosity and surface area were prep ared by the in situ treatment of hydrogels with hexamethyldisiloxane or alk ylchlorosilanes in the presence of isopropyl alcohol. The resulting hydroge ls were hydrophobic and readily transferred to nonpolar organic solvents up on contact. The surface area and porosity of the xerogel were controlled by varying the pH, time, and temperature used to polymerize the hydrogel prio r to treatment. In general, the surface area decreased with increases in ag ing time or temperature, whereas the total pore volume and pore size increa sed. Silylation of the hydrogel in the aqueous phase retains the structure of the hydrogel and permits isolation with minimum structure collapse. By u sing this technique, silylated xerogels with surface areas ranging from 200 to >700 m(2)/g and pore volumes of 1.5 to 3.8 cm(3)/g were obtained.