Porosity in Polysilsesquioxane Xerogels

Abstract

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR′)3, with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.

Structure of Arylene-Bridged Polysilsesquioxane Xerogels and Aerogels

“…Gas adsorption has been used extensively to assess the “texture” or surface morphology of bridged hybrids. These results show extreme sensitivity of the texture to synthetic variables such as bridging group, ,,, catalyst, , temperature, solvent 11 and drying protocol , and aging . Cerveau et al legitimately associated this sensitivity to the fact that these materials are synthesized far-from-equilibrium. , Kinetically controlled systems often display fractal morphologies, , which we also observe for the aryl-bridged systems studied here.…”