Controlling the Morphology of Methylsilsesquioxane Monoliths Using a Two-Step Processing Method

A new method for fabricating methylsilsesquioxane (MSQ) materials with similar chemical composition yet easily tailored pore morphology is described. MSQ materials were formed using an acid/base two-step processing method (B2). By varying the duration of the initial acidic step, it is possible to control the size and distribution of the clusters resulting from the polymerization of methtrimethoxysilane, which affect the gelation and phase separation time in the second basic step. As a result, the microstructure of the resultant MSQ monoliths, including pore volume, pore size, and distribution of meso- and macropores, can be varied over a wide range. The origin of this phenomenon is discussed based on the sol−gel polymerization kinetics and growth models for MSQ materials. Macroporous materials show minimal shrinkage, allowing for the fabrication of monolithic columns in a 100 μm fused silica capillary with no pullaway, and indicating the potential of this highly stable material as a new chromatographic stationary phase.