A simple two step reaction was developed to prepare octaphenyloctasilsesquioxane ([PhSiO
, OPS) in high yield from phenyltrichlorosilane (PhSiCl
). Octaphenyloctasilsesquioxane is easily modified by a wide number of electrophilic reactions to provide octa and hexadeca functionalized compounds that can be used as three-dimensional building blocks for nanometer-by-nanometer construction of composite materials. In this study, PhSiCl
was reacted with ethanol under reflux to produce two products, one is the liquid phenyltriethoxysilane [PhSi(OEt)
, PTES], the other is an uncharacterized polymeric material likely, EtO[PhSiO(OEt)]
. OPS was synthesized from both products. PTES gave primarily one crystal form of OPS. However, this material was contaminated by another compound not be easily separated because of the insolubility of OPS. In contrast, the polymeric version of PTES, when dissolved and reacted under identical conditions, gave a second phase of OPS analytically pure as formed. This same polymeric starting material, when reacted with catalytic amounts of KOH in ethanol, provided high molecular weight polyphenylsilsesquioxane (PPS) with only small amounts of OPS.